Journal of Animal Science and Technology
Korean Society of Animal Sciences and Technology
RESEARCH ARTICLE

Marine derived Ca-Mg complex supplementation basal diet during four subsequent parities improved longevity and performance of sows and their litters

Santi Devi Upadhaya1https://orcid.org/0000-0002-3801-4964, Woo Jeong Seok1https://orcid.org/0000-0002-1758-7579, Shanmugam Suresh Kumar1https://orcid.org/0000-0002-3632-3114, Rudolf H. van der Veen2https://orcid.org/0000-0003-1092-7961, In Ho Kim1,*https://orcid.org/0000-0001-6652-2504
1Department of Animal Resource and Science, Dankook University, Cheonan 31116, Korea
2Celtic Sea Minerals, Cork P43 NN62, Ireland
*Corresponding author: In Ho Kim, Department of Animal Resource and Science, Dankook University, Cheonan 31116, Korea. Tel: +82-41-550-3652, E-mail: inhokim@dankook.ac.kr

© Copyright 2023 Korean Society of Animal Science and Technology. This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Received: Sep 27, 2022; Revised: Dec 03, 2022; Accepted: Dec 15, 2022

Published Online: May 31, 2023

Abstract

The aim of the present study was to evaluate the effects of dietary supplementation of Ca-Mg complex on the longevity and reproductive performance of sows. In total, seventy-two gilts ([Yorkshire × Landrace] × Duroc, average body weight 181 kg) were randomly allocated to 1 of 3 treatments during 4 successive parity in a 4 × 3 factorial arrangement. Treatments consisted of CON (basal diet), CM1 (basal diet -MgO - 0.3% limestone + 0.4% Ca-Mg complex), and CM2 (basal diet - MgO - 0.7% limestone + 0.4% Ca-Mg complex). A higher (p < 0.05) number of totals born and live piglets, and sows increased feed intake during gestation and lactation, increased backfat thickness, and increased estrus interval were observed (p < 0.05) during their third and fourth parity than during their first and second parity. Ca-Mg complex supplementation improved (p < 0.05) the number of total piglets during the first and second parity as well as live-born piglets during the first to third parity, reduction (p < 0.05) in backfat thickness during the third and fourth parity, a higher (p < 0.05) initial and final number of suckling piglets as well as higher weaning weight compared with sows fed CON diet during the first, second, and third parity. The average daily gain (ADG) was higher (p < 0.05) in piglets born to CM1 and CM2 sows regardless of parity. The treatment diets fed to sows lowered (p < 0.05) the duration of first to last piglet birth and placenta expulsion time compared with CON sows. A significant interactive effect (p = 0.042) between parities and treatment diets was observed for the first to last piglet birth. Thus, Ca-Mg complex supplementation by partially replacing limestone in the basal diet enhanced sow performance, specifically during their third and fourth parity, thereby improving sow longevity.

Keywords: Ca- Mg complex; Longevity; Parity; Sow and suckling piglet performance

INTRODUCTION

Among a wide variety of factors, nutritional management plays an influential role in improving the longevity of breeding animals throughout their productive lives. Moreover, a critical driver of sow lifetime productivity is good management of the gilt [1]. Sows that remain in a breeding herd for a longer period can produce more offspring in their lifetime than those who remain in a breeding herd for a shorter period [2,3], consequently resulting in improved economic returns to the pork producers [4]. Thus, it becomes imperative to improve pork producers’ profitability by improving the sow longevity and reducing the expenses that may incur for the replacement of gilts as well as other associated costs.

In general, the reproductive performance of a sow is supposed to increase with increasing parity, reaching the highest level from parity 3 to 5 [5,6]. Many sows, however, show an equal or lower litter size in the second parity than in the first parity [7,8], which negatively influences the reproductive efficiency of second parity sows and farm productivity [9]. Being physically immature at first farrowing and having limited body reserves, the first parity sows are prone to negative effects of body reserve losses during conception and lactation. In addition, first parity sows still need energy for growth and further development. Thus, it is necessary to develop a sound feeding program that focuses on a nutritional strategy that is beneficial to sows throughout the whole lifespan of the female.

Among several nutrients, minerals constitute a small percentage of swine diets, but their impact on the pig’s growth, health, and productivity is significant. The adequacy of dietary mineral recommendations needs to be re-evaluated due to the improvements in sow productivity resulting from genetic improvements. It has been reported that low levels or a low utilization rate of Ca in the diet fed to gestating sows can reduce litter size, prolong delivery time, increase the number of stillbirths, and result in a higher occurrence of skeletal problems in piglets [10]. Sows that had completed the third parity have shown a decline in mineral (Ca, P, Mg, Na, Zn, and K) composition compared to first parity gilts [10]. Mahan and Newton [11], suggest that proper nutrition management is needed throughout the lifespan of the breeding herd. Therefore, for the enhanced performance of sows, it is necessary to improve the efficient utilization of Ca and other mineral elements. Macro-minerals such as Ca, P, and Mg are indigenous in most feed grains but are available at low concentrations in feedstuffs. Furthermore, the efficiency of mineral absorption is influenced by the concentration of these minerals in the diet, the mineral source and its bioavailability, mineral-to-mineral interactions in the diet, and the mineral status of the animal [12]. The demand for Ca and Mg during gestation and lactation is high therefore, the bioavailability of these minerals in the diet has a significant influence on improving sow longevity.

Previously, several studies indicated that commercial sows leave the breeding herd at approximately parity 4, predominantly due to reduced reproductive performance and an increase in the incidence of feet and leg problems [13,14]. Both Ca, and Mg have been shown to play a role in aiding farrowing ease by increasing the strength and frequency of myometrium contractions, improving milk production, minimizing type II stillbirths and weaning to estrus interval, and improving the number of piglets born alive and their weaning weights [15-18].

Marine-derived Ca and Mg complex is a marine multi-mineral food/feed raw material derived from the calcified skeletal remains of the red marine algae species Lithothamnion and has been reported to be highly bioavailable in Ca and Mg [19]. Lithothamnion is a naturally replenishing alga that grows in the Atlantic waters off the southwest of Ireland and the northwest coast of Iceland. Minerals from seawater are accumulated in the alga frond, which breaks off and falls to the ocean floor from where they are harvested. The mineralized fronds are separated from extraneous materials, sterilized, dried, and milled, making it available as a commercial marine-derived Ca-Mg complex [20] in a number of forms for the feed and food industries. In addition to Ca and Mg, this mineral complex comprises 72 trace minerals associated with bone health, including, strontium, manganese, selenium, copper, and zinc. Unlike the presence of calcite as the main component in calcium carbonate which is derived from limestone or rock, the marine-derived Ca-Mg complex is plant-based and has a porous honeycombed vegetative cell structure containing aragonite, vaterite, and calcite calcium salts. This structural and chemical makeup of marine-derived Ca-Mg complex offers several significant benefits in its chemical behaviour and absorption [21].

It was hypothesized that the application of this marine-derived Ca-Mg complex in the diet with higher solubility and bioavailability may increase the availability of these minerals to the animals which may eventually contribute to improving longevity, reproductive performance, and the bone health of the sows. Therefore, the present study aimed to evaluate the partial replacement of limestone (that serves mainly as a Ca source) in the basal diet with marine-derived Ca-Mg complex for four successive parities on the performance of sows and their litters.

MATERIALS AND METHODS

Animal care

The experimental protocol (DK-2-1927) for this study got the consent from Animal Care and Use Committee of Dankook University, Cheonan, Republic of Korea.

Ca-Mg complex

The Ca-Mg complex, which is a marine-derived mineral complex containing 27% Ca and 10% Mg is a product of Celtic Sea Minerals (Cork, Ireland). In addition to Ca and Mg, this mineral complex comprises 72 trace minerals that are associated with bone health, including strontium, manganese, selenium, copper, and zinc.

Experimental design, animals, housing, and diets

The experimental trial commenced in June 2019 and ended in March 2021 at Dankook University swine research facility, Cheonan, Republic of Korea. A total of 72 cross-bred gilts ([Yorkshire × Landrace] × Duroc, average body weight [BW] 181 kg) in their first pregnancy were randomly allocated to 1 of 3 treatments with 24 gilts per treatment diet. Each treatment group of 24 gilts was divided into three groups of 8 gilts. The gilts remained in their allocated treatments and groups for subsequent parities up to 4th parity. Thus, each treatment was replicated 24 times for four subsequent parities.

Treatments consisted of CON (basal diet), CM1 (basal diet - MgO - 0.3% limestone + 0.4% marine-derived Ca-Mg complex), and CM2 (basal diet - MgO - 0.7% limestone + 0.4% marine-derived Ca-Mg complex).

Experimental diets were fed from the day of conception to the end of lactation (total of 135 days) during each successive parity. At day 1 of gestation, all sows’ individual BW and backfat thickness were recorded. Sows were moved in fully slatted individual farrowing crates, each with 2.10 × 1.80 m and equipped with a feed trough and water nipple, and were fed either CON or CM1, or CM2 gestation diets in two equal meals. During gestation gilts/sows were fed their respective diets twice a day with a standard concentrated gestation diet (2.5 kg of a diet with 3,200 kcal metabolizable energy and 13% crude protein, half of the allocated daily amount in the morning and the other half of the allocated daily amount 12 h later. The gestation (Table 1) and lactation (Table 2) basal diets of sows were formulated to meet or exceed the nutrient requirements of pigs as recommended by National Research Council [22]. The feed leftovers were recorded weekly to calculate the average daily feed intake (ADFI) during the gestation period. Water was freely available from a drinker within the feed trough. Sows were not offered the feed on the day of parturition. The temperature in the farrowing house was maintained at a minimum of 20°C. Supplemental heat was provided for piglets using heat lamps. After day 1 of farrowing, the lactation diet was offered, and the feed allowance was gradually increased through day 4, and then sows were allowed ad libitum intake until weaning (day 21).

Table 1. Ingredient composition of experimental gestation diets (%, as-fed basis)
Items Gestation
CON1) CM1 CM2
Ingredients
 Corn 49.02 48.93 49.33
 Soybean meal (48%) 4.22 4.25 4.06
 Soybean oil 2.06 2.10 1.89
 Dehulled soybean meal 5.94 5.94 5.94
 Palm kernel meal 2.00 1.94 2.30
 Wheat 24.41 24.41 24.41
 Wheat bran 3.30 3.30 3.33
 Soybean hull 2.20 2.20 2.20
 Molasses 3.25 3.25 3.25
 Mono calcium phosphate 0.80 0.80 0.80
 Limestone 1.39 1.09 0.69
 Magnesium oxide 0.02 - -
 Salt 0.50 0.50 0.50
 Methionine (99%) 0.01 0.01 0.01
 Threonine (100%) 0.09 0.09 0.09
 L-Lysine (78%) 0.23 0.23 0.24
 Vitamin/mineral premix2) 0.40 0.40 0.40
 Choline (25%) 0.15 0.15 0.15
 Phytase 0.01 0.01 0.01
 Ca-Mg complex - 0.40 0.40
Calculated composition
 Metabolizable energy (kcal/kg) 3,200 3,200 3,200
Analyzed composition
 Dry matter 88.5 89.1 88.6
 Gross energy 3,45 3,45 3,46
 Crude protein 12.8 13.0 12.9
 Fat 4.40 4.44 4.24
 Calcium 0.78 0.77 0.62
 Phosphorous 0.51 0.49 0.50
 Magnesium 0.19 0.19 0.19
 Lysine 0.71 0.72 0.70
 Methionine 0.21 0.20 0.22

CON, basal diet; CM1, Basal diet – MgO - 0.3% limestone+ 0.40% marine derived Ca-Mg complex; CM2, basal diet - MgO - 0.7% limestone +0.40% marine derived Ca-Mg complex.

Provided per kg of complete diet: 16,800 IU vitamin A; 2,400 IU vitamin D3; 108 mg vitamin E; 7.2 mg vitamin K; 18 mg riboflavin; 80.4 mg niacin; 2.64 mg thiamine; 45.6 mg D-pantothenic; 0.06 mg cobalamine; 12 mg Cu (as CuSO4); 60 mg Zn (as ZnSO4); 24 mg Mn (as MnSO4); 0.6 mg I (as Ca (IO3)2; 0.36 mg Se (as Na2SeO3).

Download Excel Table
Table 2. Ingredient composition of experimental lactation diets (as-fed basis, %)
Items Lactation
 CON1) CM1 CM2
Ingredients
 Corn 41.08 40.94 41.19
 Soybean meal (48%) 4.02 4.03 3.96
 Soybean oil 3.21 3.26 3.08
 Dehulled soybean meal 12.96 12.96 12.96
 Wheat 23.00 23.00 23.00
 Wheat bran 8.31 8.31 8.31
 Rice bran 2.00 2.00 2.00
 Molasses 2.00 2.00 2.40
 Mono calcium phosphate 0.59 0.59 0.59
 Limestone 1.43 1.13 0.73
 Magnesium oxide 0.02 - -
 Salt 0.50 0.50 0.50
 Threonine (100%) 0.05 0.05 0.05
 L-Lysine (78%) 0.30 0.3 0.3
 Vitamin / mineral premix2) 0.40 0.40 0.40
 Choline (25%) 0.12 0.12 0.12
 Phytase 0.01 0.01 0.01
 Ca-Mg complex - 0.40 0.40
Calculated composition
 Metabolizable energy (kcal/kg) 3,300 3,300 3,300
Analyzed composition
 DM 88.80 88.1 89.00
 Dry matter 3,60 3,59 3,61
 Gross energy 16.30 16.50 16.40
 Crude protein 5.76 5.81 5.64
 Calcium 0.74 0.75 0.60
 Phosphorous 0.51 0.53 0.56
 Magnesium 0.25 0.25 0.25
 Lysine 0.92 0.90 0.89
 Methionine 0.20 0.23 0.21

CON, basal diet; CM1, basal diet – MgO - 0.3% limestone + 0.40% marine derived Ca-Mg complex; CM2, basal diet - MgO - 0.7% limestone + 0.40% marine derived Ca-Mg complex.

Provided per kg of complete diet: 16,800 IU vitamin A; 2,400 IU vitamin D3; 108 mg vitamin E; 7.2 mg vitamin K; 18 mg riboflavin; 80.4 mg niacin; 2.64 mg thiamine; 45.6 mg D-pantothenic; 0.06 mg cobalamine; 12 mg Cu (as CuSO4); 60 mg Zn (as ZnSO4); 24 mg Mn (as MnSO4); 0.6 mg I (as Ca (IO3)2); 0.36 mg Se (as Na2SeO3).

Download Excel Table
Experimental procedures, sampling, and analysis
Performance of sows and their litter

Approximately 7–8 days before farrowing (day 107 of gestation), the BW and backfat thickness were recorded for all sows. One day after farrowing, BW, and backfat were recorded again. The backfat of sows was measured 6 cm off the midline at the 10th rib using a real-time ultrasound instrument (Piglot 105; SFK Technology, Herlev, Denmark) at different periods (initial, before, and after farrowing and at weaning).

Sows’ ADFI was determined from the recording of orts on days 7, 14, and 21 during the lactation period. After farrowing, the numbers of total born piglets, piglets born alive, mummified fetuses, survival rate, and BW of piglets at birth and weaning were recorded. The average daily gain (ADG) of piglets was calculated at the end of weaning. Piglets were weighed collectively in their litters in a portable box scale. Additional heat to newborn piglets for 72 h after farrowing was provided using heat lamps. The morbidity of piglets was measured overall and calculated as a percentage of each pen occurrence for pneumonia, diarrhea, and hernia. Piglets were not offered creep feed; the only feed available during lactation was sow milk. The piglets born to sows from CON and treatment groups were weaned at day 21 of lactation, and sows were returned to their gestation housing systems. The periods to return to estrus were recorded after weaning. After weaning, the detection of estrus in sows was conducted twice per day, at 08:00 h and 16:00 h every day. When the sow exhibited a standing response induced by a back-pressure test when in the presence of a boar, it was considered that the sow was in estrus.

Fecal score

Fresh fecal samples from all sows (n = 24 per treatment) were collected by a rectal massage before and after farrowing. The incidence of constipation was determined by using a 5-grade score system [23], with grade 1 standing for hard, dry pellets in a small, hard mass, grade 2 indicating hard-formed stool that remains firm and soft, grade 3 for the soft-formed and moist stool that retains its shape, grade 4 for a soft unformed stool that assumes the shape of the container, and grade 5 for a watery liquid stool that can be poured.

Duration traits

The duration of farrowing was measured from the first birth piglet to the last birth piglet, and the duration of placenta expulsion from the birth of the last piglet was recorded via visual observation.

Health issues

The shoulder sore of all sows was measured before farrowing and after farrowing, according to the shoulder sore scoring system described by Meyer et al. [24] as follows: Score 0 indicated no sores caused by other factors such as fighting and physical injury, score 1 indicated sores in the top layer of the skin, score 2 for sores in the top layer of the skin, with crust formation and scar tissues, score 3 for sores in the deeper layer of the skin with crust formation and severe scar tissue, and score 4 for deep sores into the muscles, sometimes with visible shoulder bone.

Sows were monitored daily through visual observation for their condition legs to see if they stand normally or limp and other general health problems that may lead to the culling of sows.

Chemical analysis, sampling, and measurements
Feed and fecal samples

Feed samples were analyzed in duplicates for dry matter (DM; method 930.15), crude protein (N×6.25; method 988.05), crude fat (method 954.02), Ca (method 984.01), P (method 965.17), Mg (method 968.08) and amino acids (method 982.30E) following the procedure established by Association of Official Analytical Chemists [25]. Gross energy was determined by measuring the heat of combustion in the samples using a Parr 6100 oxygen bomb calorimeter (Parr Instrument, Moline, IL, USA).

Fresh fecal samples from all sows (n = 24) per treatment at the end of the trial (i.e., from sows in their 4th parity) were collected by rectal massage to determine the apparent total tract digestibility (ATTD) of DM, Ca, P, Mg, and nitrogen (N). Chromium oxide (Cr2O3, 0.2%) was added to the sows’ diets as an indigestible marker for a period of 7 days before feces collection. All fecal samples were stored immediately at −20°C until analysis. Fecal samples were dried at 72°C for 72 h and finely ground to pass through a 1-mm screen and were analyzed for N (method 988.05), Ca (method 984.01), P (method 965.17), and Mg (method 968.08) following the procedures established by the Association of Official Analytical Chemists International [25]. A UV/VIS spectrophotometer (Optizen POP, Daejeon, Korea) was used to analyze chromium oxide. For calculating the ATTD, the following formula was applied:

Digestibility ( % ) = 1 [ ( Nf × Cd ) / ( Nd × Cf ) ] × 100 ,

where Nf = nutrient content in feces (% DM), Nd = nutrient content in the diet, Cd = chromium content in the diet and Cf = of chromium content in the feces.

Statistical analyses

The data were analyzed as a 4 × 3 factorial arrangement using the MIXED procedure of Statistical Analysis Systems [26]. The model included the overall parity effect (4 successive parity) and dietary treatment effects (with/without supplemental marine-derived Ca-Mg complex) from gestation to lactation. Differences among the means for treatments were determined by using Duncan’s multiple-range test. Fecal scores recorded before and after farrowing were analyzed using Chi- square test during four successive parities. Variability in the data was expressed as the standard error of means (SEM), and a probability level of p < 0.05 was considered significant and p < 0.01 or < 0.0001 highly significant.

RESULTS

Reproductive performance of sows

The effect of marine-derived Ca-Mg complex and parity on the performance of sows is presented in Table 3. A significant overall parity and treatment effects (p < 0.0001) on total born and live piglets were observed. The third and fourth parity sows had a higher (p < 0.05) number of total born and live piglets compared to sows from the first and second parity. The feed intake during gestation and lactation, estrus interval, BW, and the backfat thickness change before and after farrowing and at weaning were significantly affected by parity (p < 0.0001). Among the parity, the ADFI during gestation and lactation was higher (p < 0.05) during the third and fourth parity compared to the first and second parity. The backfat thickness before and after farrowing and at weaning were also higher (p < 0.05) for sows in the third and fourth parity compared to those on the first and second parity. The overall parity effect (p < 0.0001) in the decline of backfat thickness after farrowing to lactation was also observed. The estrus interval was the highest in the fourth parity followed by the third (p < 0.05) among the parities investigated. The supplementation of marine-derived Ca-Mg complex to the basal diet (CM1 and CM2) led to a significant improvement (p < 0.05) in total piglets born during the first and second parity as well as live born piglets during the first to third parity. A significant overall treatment effect was observed for the pre-weaning survival rate (p = 0.013) as well as a reduction (p < 0.01) in backfat thickness change in CM1 and CM2 sow groups compared to the CON sow group during the third and fourth parity. There were no interactive effects between parities and treatment diets on the reproductive performance parameters in sows.

Table 3. The effect of dietary supplementation of marine derived Ca-Mg complex on reproduction performance in gilts/sows in four successive parities1)
Items Parity 1 Parity 2 Parity 3 Parity 4 SEM p-value
 CON2) CM1 CM2 CON CM1 CM2 CON CM1 CM2 CON CM1 CM2 Parity Treatment P × T
Litter size
 Total birth piglet (head) 14.2bB 15.1a 14.9a 14.4bB 15.2a 15.1a 15.2a 15.8 15.5 15.4a 15.8 15.7 0.212 *** *** NS
 Live piglet (head) 13.7bB 14.8a 14.6a 13.8bB 14.8a 14.7a 14.7bA 15.4a 14.9a 14.8a 15.3 15.3 0.242 *** *** NS
 Stillbirth (head) 0.5 0.3 0.3 0.4 0.3 0.3 0.5 0.4 0.6 0.5 0.4 0.4 0.099 NS NS NS
Mummification (head) 0.04 0.00 0.00 0.04 0 0 0 0 0 0.04 0 0 0.021 NS NS NS
 Dead after 3 days of birth (head) 0.04 0.00 0.08 0.1 0.1 0.1 0 0 0 0.1 0 0 0.050 NS NS NS
 Disorder (head) - - - - - - - - - - - - - - - -
Survival rate (%) 96.1 98.4 97.7 96.0 97.5 97.1 96.7 97.6 96.1 95.9 97.1 97.0 0.702 NS ** NS
Sow body weight (kg)
 Initial 181.4C 181.6 181.3 182.9C 179.8 181.2 198.8B 198.3 199.6 218a 219 219.6 1.28 *** NS NS
 Before farrowing 222.2D 220.7 221.3 238.3C 237.7 239.5 257.9B 258.9 259.8 278.2a 280.6 280.7 1.401 *** NS NS
After farrowing 196.7D 194.1 194.7 213.20C 211.30 212.60 231.70B 232.3 233.4 252.1a 254.4 254.1 1.429 *** NS NS
 Weaning 182.9D 179.8 181.2 198.8C 198.3 199.6 218B 219 219.6 237.6a 240.9 240.6 1.468 *** NS NS
Back fat thickness (mm)
 Initial 15.37C 15.41 15.37 15.41bC 16.12a 15.75a 16.33B 16.95 16.95 18.62bA 19.25a 19.70a 0.242 *** ** NS
 Before farrowing 17.95D 18.16 18.0 18.5C 18.66 18.83 21.04B 21.37 21.54 22.70bA 23.45a 23.50a 0.23 *** * NS
 After farrowing 17.41D 17.75 17.41 17.95C 18.29 18.41 20.25B 20.45 20.87 21.83bA 22.66a 22.62a 0.219 *** ** NS
 Weaning 15.41bD 16.12a 15.79ab 16.33C 16.95 16.95 18.62bB 19.25ab 19.70a 19.95bA 21.08a 21.20a 0.236 *** *** NS
Backfat thickness difference 13) 2.58C 2.75 2.62 3.08C 2.54 3.08 4.70a 4.41 4.58 4.08B 4.20 3.79 0.204 *** NS NS
Backfat thickness difference 2 0.54 0.41 0.58 0.54 0.37 0.41 0.79 0.91 0.66 0.87 0.79 0.87 0.112 *** NS NS
Backfat thickness difference 3 2.05 1.62 1.62 1.62 1.33 1.45 1.62a 1.20B 1.16B 1.87a 1.58ab 1.41B 0.130 *** *** NS
Average daily feed intake (kg)
 Gestation 2.02C 2.02 2.02 2.06B 2.07 2.06 2.16a 2.17 2.16 2.16a 2.17 2.16 0.005 *** NS NS
 Lactation 6.14B 6.17 6.18 6.12B 6.15 6.15 6.38a 6.40 6.40 6.38a 6.41 6.40 0.024 *** NS NS
Estrus interval (day) 3.8C 3.4 3.3 3.6bC 3.3 3.3 4.3ab 3.9 4.3 4.6a 4.5 4.5 0.226 *** NS NS

Values represent the means of 24 sows per treatment.

CON, basal diet; CM1, basal diet – MgO - 0.3% limestone + 0.40% marine derived Ca-Mg complex; CM2, basal diet - MgO - 0.7% limestone + 0.40% marine derived Ca-Mg complex.

Backfat thickness difference: 1, initial to before farrowing; 2, before farrowing to after farrowing; 3, after farrowing to weaning.

Different superscripts within a row indicate a significant difference (p < 0.05) in response to treatment diets CM1 and CM2.

Different superscripts within a row indicate a significant difference (p < 0.05) among parity.

p < 0.05,

p < 0.01,

p < 0.0001.

P × T, interactive effects between parity and dietary treatments; NS, non-significant.

Download Excel Table
Suckling piglet performance

The performance of suckling piglets born to sows fed gestation and lactation diets with marine-derived Ca-Mg complex in four successive parities is presented in Table 4. The initial and final number of suckling piglets was higher (p < 0.05) for the third and fourth parity sows compared to the first and second parity sows. The overall parity effect (p < 0.0001) was observed for the survival rate of suckling piglets, although no significant effects were seen among the parity for the survival rate of the suckling piglets. The supplementation of CM1 and CM2 to the basal diet of the sows resulted in a higher (p < 0.05) initial and final number of suckling piglets as well as higher weaning weight compared to the piglets born to sows fed CON diet during the first, second and third parity. The ADG was higher in piglets born to sow receiving CM1 and CM2 diets (p < 0.05) regardless of parity. However, there were no significant overall parity effects on the weaning weight and ADG of piglets. No morbidity due to pneumonia, hernia, and scouring was observed in piglets born to the sows fed with either CON or CM1, or CM2 diets through four parities (data not shown).

Table 4. The effect of dietary marine derived Ca-Mg complex supplementation to gestating and lactating sows in four successive parities on the performance of their litters
Items Parity 1 Parity 2 Parity 3 Parity 4 SEM p-value
CON1) CM1 CM2 CON CM1 CM2 CON CM1 CM2 CON CM1 CM2 Parity Treatment P × T
Initial number 13.66bB 14.83a 14.58a 13.79bB 14.80a 14.66a 14.70bA 15.40a 14.90ab 14.79a 15.30 15.25 0.242 *** *** NS
Final number 13.40bB 14.83a 14.58a 13.50bB 14.60a 14.54a 14.30a 15 14.58 14.41a 15.08 15.04 0.258 ** *** NS
Survival rate (%) 98.20b 100a 100a 97.90 98.50 99.04 97.20 97.30 97.78 97.47 98.30 98.65 0.614 ** * NS
Birth weight (kg) 1.69 1.67 1.69 1.68 1.70 1.70 1.73 1.70 1.69 1.71 1.67 1.70 0.02 NS NS NS
Weaning weight (kg) 6.40b 6.75a 6.67a 6.45b 6.82a 6.80a 6.40b 6.80a 6.70a 6.46 6.74 6.72 0.05 NS *** NS
Average daily gain (g) 225b 242a 237a 227b 244a 241a 225b 243a 240a 227b 241a 240a 2.12 NS *** NS

CON, basal diet; CM1, basal diet – MgO - 0.3% limestone + 0.40% marine derived Ca-Mg complex; CM2, basal diet - MgO - 0.7% limestone + 0.40% marine derived Ca-Mg complex.

Different superscripts within a row indicate a significant difference (p < 0.05) in response to treatment diets CM1 and CM2.

Different superscripts within a row indicate a significant difference (p < 0.05) among parity.

p < 0.05;

p < 0.01,

p <0.0001.

P × T, interactive effects between parity and dietary treatments; NS, non-significant.

Download Excel Table
Incidence of constipation and shoulder sores in sows

The effect of marine-derived Ca-Mg complex and parity on the incidence of constipation based on fecal scores before and after farrowing is presented in Table 5. There were no significant dietary treatment, time and parity effects on fecal scores. The shoulder sores (data not shown) were also not affected (p > 0.05) by treatment and parity.

Table 5. The effect of dietary marine derived Ca-Mg complex supplementation to gestating and lactating sows in four successive parities on fecal score before and after farrowing1)
Items Parity 1 Parity 2 Parity 3 Parity 4 SEM p-value
CON2) CM1 CM2 CON CM1 CM2 CON CM1 CM2 CON CM1 CM2 Parity Treatment P × T
Before farrowing 2.27 2.25 2.25 2.27 2.24 2.25 2.24 2.25 2.24 2.21 2.21 2.24 0.020 NS NS NS
After farrowing 2.31 2.29 2.29 2.32 2.29 2.29 2.28 2.31 2.30 2.28 2.30 2.30 0.021 NS NS NS

Values represent the means of 24 sows per treatment.

Fecal score data before and after farrowing were also analyzed using chi-square test. The fecal score before and after farrowing were found to be non-significant during all four subsequent parities.

Fecal score: 1, hard, dry pellet in a small, hard mass; 2, hard, formed stool that remains firm and soft; 3, soft, formed, and moist stool that retains its shape; 4, soft, unformed stool that assumes shape of the container; 5, watery, liquid stool that can be poured.

CON, basal diet; CM1, Basal diet – MgO - 0.3% limestone + 0.40% marine derived Ca-Mg complex; CM2, basal diet - MgO - 0.7% limestone + 0.40% marine derived Ca-Mg complex.

P × T, interactive effects between parity and dietary treatments; NS, non-significant.

Download Excel Table
Duration traits

The effect of marine-derived Ca-Mg complex and parity on the duration of parturition from the first to last piglet birth and the duration of placenta expulsion after the last piglet birth is presented in Table 6. A trend (p = 0.080) in the overall parity effect and a significant treatment effect (p < 0.0001) in the duration of the first to last piglet birth were observed. The treatment diets (CM1 and CM2) fed to the sows lowered (p < 0.05) the duration of the first to last piglet birth compared to those from sows fed the CON diet. Significant interactive effects (p = 0.042) between parities and treatment diets were observed for the duration of the first to last piglet birth. A significant overall parity effect (p = 0.01) and treatment effect (p < 0.0001) were observed for the reduction in the duration of placenta expulsion, and a significant overall treatment effect (p < 0.0001) on the duration between the first and last piglet birth were observed although there were no significant differences among the parity for the placental expulsion duration. The sows fed treatment diets exhibited a reduction (p < 0.05) in placenta expulsion time compared with sows fed CON diet regardless of parities and a significant reduction (p < 0.05) in duration between the first and last piglet birth from sows receiving CM1 and CM2 versus CON diets was observed during parity 1 and 2.

Table 6. The effect of dietary marine derived Ca-Mg complex supplementation to gestating and lactating sows in four successive parities on farrowing and placenta expulsion time duration1)
Items (min) Parity 1 Parity 2 Parity 3 Parity 4 SEM p-value
CON2) CM1 CM2 CON CM1 CM2 CON CM1 CM2 CON CM1 CM2 Parity Treatment P × T
Duration between first to last piglet birth 245a 215b 217b 236a 217b 216b 230 221 238 245.6 223.6 231 5.442 NS *** *
Placenta expulsion time after last piglet birth 83a 62b 61b 84a 72b 70b 85a 75b 72b 85.3a 74.1b 68.3b 3.372 ** *** NS

Values represent the means of 24 sows per treatment.

CON, basal diet; CM1, basal diet – MgO - 0.3% limestone + 0.40% marine derived Ca-Mg complex; CM2, basal diet - MgO - 0.7% limestone + 0.40% marine derived Ca-Mg complex.

Different superscripts within a row indicate a significant difference (p < 0.05) in response to treatment diets CM1 and CM2.

p < 0.05,

p < 0.01,

p <0.0001.

P × T, interactive effects between parity and dietary treatments; NS, non-significant.

Download Excel Table
Apparent total tract digestibility

The ATTD of N, Ca, P and Mg measured at the end of the experimental trial were unaffected (p > 0.05) by the partial replacement of limestone with Ca-Mg complex (Table 7).

Table 7. The effect of dietary marine derived Ca-Mg complex supplementation on apparent total tract digestibility of P, Ca, Mg, and N at the end of trial1)
Items (%) CON2) CM1 CM2 SEM p-value
Phosphorus 32.00 36.08 34.35 1.63 0.2183
Calcium 33.77 36.77 35.88 1.60 0.4024
Magnesium 23.98 25.68 25.05 0.65 0.1839
Nitrogen 66.52 68.21 69.35 1.03 0.1614

Values represent the means of 24 sows per treatment.

CON, basal diet; CM1, basal diet – MgO - 0.3% limestone + 0.40% marine derived Ca-Mg complex; CM2, basal diet - MgO - 0.7% limestone + 0.40% marine derived Ca-Mg complex.

Download Excel Table

DISCUSSION

Sows longevity is a complex trait wherein multiple factors are involved in contributing to a long and productive life in a commercial breeding herd. The predominant reason for sows being removed from the breeding herd due to reproductive failure [27-29]. In modern swine production, sows with lean genotype and improved breed led to high prolificacy of sows, thereby leading to the improvement in their productivity levels, maximization of the number of piglets/litters, lactation yield, optimization of piglet birth weight, and longevity [30]. All these improvements with a sow and her litter warrant proper nutritional support that is bioavailable for animals. The nutritional status of a sow at an earlier stage of the reproductive cycle will affect productivity during subsequent stages. Thus, an integrated feeding intervention, starting with the gilt and continuing throughout each successive parity may maintain productivity and prolong the reproductive life of the sow. Among several nutrients, minerals equally play an important role in the reproductive life of sows. Therefore, the present study was undertaken to assess the parity effects (four successive parities) as well as treatment effects by supplementing the basal diet with marine-derived Ca-Mg complex with better bioavailability as a partial replacement to limestone during four successive parities on the longevity and reproductive performance of sows.

Marine-derived Ca-Mg complex effects

The predominant reasons for the culling of sows having three parities or less are due to reproductive failure and leg and foot problems [31-33]. Results from the present study demonstrated that during the four successive parities, sows were not culled since there were no problems in the overall health of sows including lameness, shoulder sores, or incidence of constipation regardless of the diets offered to sows, and their parities.

The inclusion of Ca-Mg complex in the basal diet or the partial replacement of limestone in the basal diet of sows with marine-derived Ca-Mg complex significantly improved total and live born piglets, piglet survival rate, number of piglets pre-weaning, number of weaned piglets, and weaning weight. However, there was no effect observed on the piglet birth weight and weaning to oestrus interval compared with the sow-fed CON diet regardless of parity although first and second-parity sows had better results. Different inclusion levels of Ca in the diet of sows did not significantly affect the number of born alive, birth weight, weaning weight, and ADG of piglets [34]. Earlier studies revealed that Mg supplementation to the diet of gilts had no influence on the number of total and live piglets at birth [16,35]. In contrast, the supplementation of 0.015 and 0.03% Mg to parity 3 sows significantly increased the total number of piglets born, live-born piglets, and weaned reduced the weaning to oestrus interval in gilts as well [16] which agreed with the findings of Gaal et al. [36] who indicated that Mg supplementation improved litter size and reduced wean to estrus interval. The disparities in the findings among different studies might be due to the bioavailability of mineral supplements as well as the dose and feeding duration of these minerals from gestation to lactation.

To increase sow longevity, it is important for breeding and farrowing managers to focus on the maintenance of sow body tissue reserves throughout their lifetime. Improper nutrition may cause direct or indirect adverse effects resulting in premature culling. To maximize the lifetime number of live piglet birth, some minimum level of backfat is needed [14]. Females that are too lean may experience low litter weaning weights, smaller subsequent litter size, physical weakness, and poor return to estrus [37]. An earlier study reported that in Duroc females at an off-test weight of 96.2 kg, the optimum backfat thickness is 16 mm [38]. A study by Challinor [39], reported that gilts at an average weight of 150 kg that had 18 to 22 mm of backfat had an average of 7.2 more piglets over five parities than the gilts having a backfat thickness of 14 to 16 mm. In agreement with this, Tummaruk et al. [40] noted that gilts with higher backfat adjusted to 100 kg had a higher number of live-born piglets in their second parity than the gilts with low backfat. In the present study, the backfat thickness of sows (before and after farrowing as well as at weaning) was improved by supplementing the diet with marine-derived Ca-Mg complex but gestation and lactation feed intake and the ATTD of Ca, Mg, P, and N were not affected by the inclusion of marine-derived Ca-Mg complex in the sow basal gestation and lactation diets. The improvement in sow backfat thickness in treatment groups might have resulted in an increased number of piglets born alive and weaned piglets in this study which affirms the report of Čechová and Tvrdoň [41] which suggested that the number of live born and weaned piglet is correlated with backfat thickness. The reduction in backfat thickness loss in sows receiving treatment diets during lactation may suggest that this marine-derived Ca-Mg complex had a positive effect in meeting the energy needs of the body. A recent study by Gao et al. [42] noted that ADFI and backfat thickness on day 85 of gestation was not affected by feeding extra Ca during different feeding time. The probable reason for the improvement in the reproductive performance in the present study could be due to the higher bioavailability of these minerals especially Mg because it is an important co-factor of different enzymes that are involved in energy and protein metabolism as well as other biochemical processes [36]. Calcium was found to play a role in lipogenesis and lipolysis, where a high Ca level in the plasma suppresses calcitriol. When combined with an energy-dense diet, this effect of Ca on calcitriol aided to prevent excessive fat accumulation and helped to maintain weight and fat content [43,44]. Likewise, increased availability of Ca reduced the sows reliance on bone deposits to satisfy lactational demands thus preserving bone stores and consequently improving bone health and sow longevity [13,21].

The risk of stillbirth has been reported to increase significantly when the birth interval is more than 90 min, whereas the duration of farrowing increased the risk cumulatively with every 2 h that elapsed [45]. Thus, the duration of birth from the first to the last piglet of a litter and the duration of placenta expulsion play an important role in determining the number of stillbirths. These duration traits seem to be partially affected by the availability of minerals such as Ca. In a recent study by Gao et al. [42], it has been reported that feeding an extra 9 g of Ca to sows led to a reduction in the number of stillbirths, the duration of farrowing, and placenta expulsion, and increased the ADG of piglets compared to the sows fed extra 4.5 g of Ca. In the present study, the supplementation of marine-derived Ca-Mg complex showed a decline in the duration of birth of piglets from the first to the last. A reduction in the duration of placenta expulsion from the time after the birth of the last piglet was also observed. The reduction in the duration of placenta expulsion and farrowing may be associated with the role of Ca ion in enhancing the contraction ability of smooth muscle in the uterine system [15,46].

Parity effects

Parity order is linked with the development of the reproductive system of animals. Pluym et al. [32] showed that it is economically viable to keep sows at least until parity 5. An important foundation of production is to lengthen the production life of sows because the economic returns to the producer begin from the third parity [47].

Therefore, in the present study, we evaluated the performance of gilt/sows during four successive parities and observed that the first parity gilts and second parity sows had significantly lesser numbers of litter and live born piglets, lower sow BW and backfat thickness size, lower lactation feed intake compared to third and fourth parity sows, but the birth weight, weaning weight, and ADG of piglets were not affected by parity. However, the results are inconsistent. For instance, Takai and Koketsu [48] observed that a higher number of piglets were born only in the first and second parity, but not in subsequent ones whereas Hoving et al. [49] reported that sows exhibited the best reproductive parameters between parity 3 and 5. Previous studies reported a lower birth weight for pigs born to primiparous sows versus multiparous sows [50,51], indicating that this difference could be due to fetal growth retardation and fewer skeletal muscle fibers [52], even though no differences in BW were detected at birth [53]. The possible reason for the increase in BW and backfat thickness of sows at the third and fourth parity as compared with the first parity gilts could be due to the higher maintenance requirement and feed intake. Sows with a 17 to 21 mm backfat thickness have been reported to be more efficient than those with a backfat thickness beyond this interval [54] suggesting the sow in first to third parity had a backfat thickness of reasonable range. The decline in backfat thickness after farrowing to weaning was slightly higher for the first parity sows compared with the other parities suggesting that with the increase in parity, sows were able to meet the energy demands via feed. The mechanisms behind these parity effects of young and old sows are different. In the case of primiparous sows, their reproductive cycle and hormonal system are naive and show lower feed intake capacity and lower fat and protein stores [55] despite their higher nutrient requirement for reproduction and muscle development as compared with multiparous sows which have well-established reproductive cycle [56] consequently, affecting the performance of sows. Interestingly, the duration of placenta expulsion after the birth of the last piglet was higher in the third and fourth parity sows compared with the first parity gilts and the second parity sows which could possibly be due to lower oxytocin levels in older sows [57,58]. Interactive effects were observed between treatment diets and parity in the duration of the first to last piglet birth indicating the synergistic effects of both parity and marine-derived Ca-Mg Complex treatment on the given parameter.

CONCLUSIONS

The supplementation of marine-derived Ca-Mg complex exerted positive effects on the reproductive performance of sows regardless of parities. The number of weaned piglets, weaning weight, and the ADG of suckling piglets born to sows in treatment groups were higher compared to those born from control group sows, indicating that marine-derived Ca-Mg complex supplementation is effective in improving the longevity and performance of sows and their litters. Among the parties, the third and fourth parity sows had better performance ability than the first and second parity sows. Thus, the findings of this study indicate that partial replacement of limestone with marine-derived Ca-Mg complex to the basal diets of sows is beneficial for improving sows’ reproductive performance and longevity.

Competing interests

No potential conflict of interest relevant to this article was reported.

Funding sources

This work was supported by Celtic Sea Minerals, Strand Farm, Currabinny, Carrigaline, Co.Cork, Ireland and the Department of Animal Resource and Science was supported through the Research - Focused Department Promotion & Interdisciplinary Convergence Research Project as a part of the University Innovation Support Program for Dankook University in 2022.

Acknowledgements

Not applicable.

Availability of data and material

Upon reasonable request, the datasets of this study can be available from the corresponding author.

Authors’ contributions

Conceptualization: Upadhaya SD, van der Veen RH, Kim IH.

Data curation: Seok WJ, Suresh Kumar S.

Formal analysis: Upadhaya SD, Seok WJ, van der Veen RH.

Investigation: Kim IH.

Writing - original draft: Upadhaya SD, Suresh Kumar S.

Writing - review & editing: Upadhaya SD, Seok WJ, Suresh Kumar S, van der Veen RH, Kim IH.

Ethics approval and consent to participate

The experimental protocol (DK-2-1927) for this study got the consent from Animal Care and Use Committee of Dankook University, Cheonan, Korea.

REFERENCES

1.

Tubbs J. Sow longevity: it begins with the gilt [Internet]. Ohio Swine Health Symposium. 2015[cited 2022 Aug 7]http://www.ohiopork.org/media/sow

2.

Stalder K. Non-genetic factors influencing sow longevity. Ames, IA: U.S. Pork Center of Excellence. 2006Fact Sheets No.: PIG 08-04-02

3.

Joab M. Determining the optimal age of breeding gilts and its impact on lifetime performance, literature review. Acta Agrar Debr. 2019; 1:15-20

4.

Stalder K, D’Allaire S, Drolet R, Abell C. Longevity in breeding animals.In In: Zimmermann JJ, Karriker LA, Ramirez A, Schwartz KJ, Stevenson GW, editors.editors Diseases of swine. 10th ed Ames: Wiley-Blackwell. 2012; p p. 50-9

5.

Koketsu Y, Takahashi H, Akachi K. Longevity, lifetime pig production and productivity, and age at first conception in a cohort of gilts observed over six years on commercial farms. J Vet Med Sci. 1999; 61:1001-5

6.

Hughes P, Varley MA. Lifetime performance of the sow.In In: Wiseman J, Varley MA, Kemp B, editors.editors Perspectives in pig science. Notthingham: Nottingham University Press. 2003; p p. 333-55

7.

Morrow WEM, Leman AD, Williamson NB, Morrison RB, Ashley Robinson R. An epidemiological investigation of reduced second-litter size in swine. Prev Vet Med. 1992; 12:15-26

8.

Saito H, Sasaki Y, Hoshino Y, Koketsu Y. The occurrence of decreased numbers of pigs born alive in parity 2 sows does not negatively affect herd productivity in Japan. Livest Sci. 2010; 128:189-92

9.

Willis HJ, Zak LJ, Foxcroft GR. Duration of lactation, endocrine and metabolic state, and fertility of primiparous sows. J Anim Sci. 2003; 81:2088-102

10.

Mahan DC. Mineral nutrition of the sow: a review. J Anim Sci. 1990; 68:573-82

11.

Mahan DC, Newton EA. Effect of initial breeding weight on macro- and micromineral composition over a three-parity period using a high-producing sow genotype. J Anim Sci. 1995; 73:151-8

12.

Richert BT. Macro minerals for swine diets [Internet]. National swine nutrition guide 2010.[cited 2021 May 6]https://porkgateway.org/resource/macro-minerals-for-swine-diets/.

13.

Koketsu Y, Tani S, Iida R. Factors for improving reproductive performance of sows and herd productivity in commercial breeding herds. Porc Health Manag. 2017; 3:1

14.

Stalder KJ, Knauer M, Baas TJ, Rothschild MF, Mabry JW. Sow longevity. Pig News Inf. 2004; 25:53N-74N

15.

Elrod ND, Harp RM, Bryan KG. Effect of calcium ion supplementation on swine parturition. Tex J Agric Nat Resour. 2015; 28:12-7

16.

Zang J, Chen J, Tian J, Wang A, Liu H, Hu S, et al. Effects of magnesium on the performance of sows and their piglets. J Anim Sci Biotechnol. 2014; 5:39

17.

Hou WX, Cheng SY, Liu ST, Shi BM, Shan AS. Dietary supplementation of magnesium sulfate during late gestation and lactation affects the milk composition and immunoglobulin levels in sows. Asian-Australas J Anim Sci. 2014; 27:1469-77

18.

Trawńska B, Polonis A, Lechowski J, Tymczyna L, Borowski R, Gizińska K. Effect of the addition of magnesium salt to a feed mixture on intestinal microflora, health, and production of sows. Bull Vet Inst Pulawy. 2013; 57:69-72

19.

Zenk JL, Frestedt JL, Kuskowski MA. Effect of calcium derived from Lithothamnion sp. on markers of calcium metabolism in premenopausal women. J Med Food. 2018; 21:154-8

20.

O’Driscoll K, O’Gorman DM, Taylor S, Boyle LA. The influence of a magnesium-rich marine extract on behaviour, salivary cortisol levels and skin lesions in growing pigs. Animal. 2013; 7:1017-27

21.

Brennan O, Sweeney J, O’Meara B, Widaa A, Bonnier F, Byrne HJ, et al. A natural, calcium-rich marine multi-mineral complex preserves bone structure, composition and strength in an ovariectomised rat model of osteoporosis. Calcif Tissue Int. 2017; 101:445-55

22.

National Research Council. Nutrient requirements of swine. 11th rev. ed Washington, DC: National Academies Press. 2012

23.

Hu CH, Gu LY, Luan ZS, Song J, Zhu K. Effects of montmorillonite–zinc oxide hybrid on performance, diarrhea, intestinal permeability and morphology of weanling pigs. Anim Feed Sci Technol. 2012; 177:108-15

24.

Meyer D, Hewicker-Trautwein M, Hartmann M, Kreienbrock L, grosse Beilage E. Scoring shoulder ulcers in breeding sows – is a distinction between substantial and insubstantial animal welfare-related lesions possible on clinical examination?. Porcine Health Manag. 2019; 5:3

25.

AOAC [Association of Official Analytical Chemists] International. Official methods of analysis of the AOAC International. 17th ed Arlington, VA: AOAC International. 2000

26.

SAS Institute. SAS system for Windows computer program. Version 9.0 Cary, NC: SAS Institute. 2002

27.

Friendship RM, Wilson MR, Almond GW, McMillan I, Hacker RR, Pieper R, et al. Sow wastage: reasons for and effect on productivity. Can J Vet Res. 1986; 50:205-8

28.

Pedersen PN. Longevity and culling rates in the Danish sow production and the consequences of a different strategy for culling.In In: Danielsen V, editor.editor Proceedings of the Nordiska Jordbruksforskares Forening Seminar 265-Longevity of Sows. Tjele: Research Centre Foulum. 1996; p p. 28-33

29.

Lucia T, Dial GD, Marsh WE. Lifetime reproductive performance in female pigs having distinct reasons for removal. Livest Prod Sci. 2000; 63:213-22

30.

Kim SW, Weaver AC, Shen YB, Zhao Y. Improving efficiency of sow productivity: nutrition and health. J Anim Sci Biotechnol. 2013; 4:26

31.

Lucia T, Dial GD, Marsh WE. Patterns of female removal. I. Lifetime productivity for reproduction and performance-related culls.In Proceedings of the International Pig Veterinary Society 14th Congress. 1996; Bologna, Italy. p p. 540

32.

Pluym LM, Van Nuffel A, Van Weyenberg S, Maes D. Prevalence of lameness and claw lesions during different stages in the reproductive cycle of sows and the impact on reproduction results. Animal. 2013; 7:1174-81

33.

Kraeling RR, Webel SK. Current strategies for reproductive management of gilts and sows in North America. J Anim Sci Biotechnol. 2015; 6:3

34.

Tan F, Beaulieu AD. Impact of calcium and phosphorus on sow lameness and sow longevity [Internet]. Swine innovation porcine 2012.[cited 2021 Aug 16]https://www.prairieswine.com/wp-content/uploads/2020/11/Impact-of-Calcium-and-Phosphorus-on-Sow-Lameness-and-Sow-Longevity.pdf.

35.

Harmon BG, Liu CT, Jensen AH, Baker DH. Dietary magnesium levels for sows during gestation and lactation. J Anim Sci. 1976; 42:860-5

36.

Gaál KK, Sáfár O, Gulyás L, Stadler P. Magnesium in animal nutrition. J Am Coll Nutr. 2004; 23:754S-7S

37.

Rozeboom DW, Johnston LJ. Nutritional aspects of sow longevity [Internet]. U.S. Pork Center of Excellence 2015.[cited 2021 Jun 11]https://porkgateway.org/wp-content/uploads/2015/07/nutritional-aspects-of-sow-longevity4.pdf.

38.

Tarrés J, Tibau J, Piedrafita J, Fàbrega E, Reixach J. Factors affecting longevity in maternal Duroc swine lines. Livest Sci. 2006; 100:121-31

39.

Challinor CM. The effect of body composition of gilts at first mating on long-term sow productivity. Anim Sci. 1996; 62:660

40.

Tummaruk P, Lundeheim N, Einarsson S, Dalin AM. Effect of birth litter size, birth parity number, growth rate, backfat thickness and age at first mating of gilts on their reproductive performance as sows. Anim Reprod Sci. 2001; 66:225-37

41.

Čechová M, Tvrdoň Z. Relationships between backfat thickness and parameters of reproduction in the Czech Large White sows (short communication). Arch Tierz. 2006; 49:363-9

42.

Gao L, Lin X, Xie C, Zhang T, Wu X, Yin Y. The time of calcium feeding affects the productive performance of sows. Animals. 2019; 9:337

43.

Zemel MB, Sun X. Calcitriol and energy metabolism. Nutr Rev. 2008; 66:S139-46

44.

Zemel MB, Shi H, Greer B, Dirienzo D, Zemel PC. Regulation of adiposity by dietary calcium. FASEB J. 2000; 14:1132-8

45.

Langendijk P, Fleuren M, van Kempen TA. Birth interval or duration of parturition: which is relevant to risk of stillbirth and intervention?.In Book of Abstracts of the 69th Annual Meeting of the European Federation of Animal Science. 2018; Dubrovnik, Croatia. p p. 112

46.

Parkington HC, Tonta MA, Brennecke SP, Coleman HA. Contractile activity, membrane potential, and cytoplasmic calcium in human uterine smooth muscle in the third trimester of pregnancy and during labor. Am J Obstet Gynecol. 1999; 181:1445-51

47.

Engblom L, Lundeheim N, Dalin AM, Andersson K. Sow removal in Swedish commercial herds. Livest Sci. 2007; 106:76-86

48.

Takai Y, Koketsu Y. Number of services and the reservice intervals in relation to suboptimal reproductive performance in female pigs on commercial farms. Livest Sci. 2008; 114:42-7

49.

Hoving LL, Soede NM, Graat EAM, Feitsma H, Kemp B. Reproductive performance of second parity sows: relations with subsequent reproduction. Livest Sci. 2011; 140:124-30

50.

Averette LA, Odle J, Monaco MH, Donovan SM. Dietary fat during pregnancy and lactation increases milk fat and insulin-like growth factor I concentrations and improves neonatal growth rates in swine. J Nutr. 1999; 129:2123-9

51.

Moore C. Segregated production: how far could we go?.In Proceedings of the 2001 Allen D. Leman Swine Conference. 2001; Minneapolis, MN. p p. 203-6

52.

Rehfeldt C, Kuhn G. Consequences of birth weight for postnatal growth performance and carcass quality in pigs as related to myogenesis. J Anim Sci. 2006; 84:E113-23

53.

Moore VM, Davies MJ. Diet during pregnancy, neonatal outcomes and later health. Reprod Fertil Dev. 2005; 17:341-8

54.

Block T. Sow productivity improvements can boost profits. West Des Moines: Farm Bureau Spokesman. 2003

55.

Kemp B, Soede NM. Reproductive problems in primiparous sows.In Proceedings of the 18th International Pig Veterinary Society Congress. 2004; Hoya, Germany. p p. 843-8

56.

Whittemore CT. Nutrition reproduction interactions in primiparous sows. Livest Prod Sci. 1996; 46:65-83

57.

Oliviero C, Heinonen M, Valros A, Peltoniemi O. Environmental and sow-related factors affecting the duration of farrowing. Anim Reprod Sci. 2010; 119:85-91

58.

Björkman S, Oliviero C, Rajala-Schultz PJ, Soede NM, Peltoniemi OAT. The effect of litter size, parity and farrowing duration on placenta expulsion and retention in sows. Theriogenology. 2017; 92:36-44