Soybean meal is one of major ingredients for pigs as a protein source, but it contains several anti-nutritional factors (ANF), such as lectins, oligosaccharides, haemagglutinin, goitrogenic factors, trypsin inhibitors, and antigenic proteins, that cause reduction of protein utilization of pigs by inhibiting the secretion of pancreatic digestive enzymes and increasing the loss of endogenous secretions of pigs [1–4]. These ANFs can be reduced by heat treatment, fermentation process, addition of enzymes, or etc., resulting in improvement of protein utilization of pigs [4,5]. Futhermore, there are two issues in the swine production, such as the increase of feed cost and environmental pollution from undigested protein by pigs. The protein sources including soybean meal in pig diets are relatively expensive compared with other ingredients and thus the unavailable protein by pigs cause the increase of feed cost. The undigested protein by pigs is also related to the environmental pollution by nitrogen emission from pigs [6,7]. Therefore, the swine industry has been looking for the ways to solve these issues.
Addition of dietary protease in pig diets may be one of strategies to improve nutrient availability and reduce the feed cost in the swine industry. Dietary protease is generally used to reduce the undigested protein and contribute to improvement of nutrient utilization of pigs . However, dietary protease in pig diets has been commonly used as one of enzyme sources for commercially available multi-enzyme products [9–13]. Recently, several studies showed beneficial effects on growth performance, nutrient digestibility, or etc. of pigs fed diets containg dietary protease alone, not multi-enzyme types [14–16], but there was limited evidence for its effects and modes of action. Therefore, the objective of this study was to investigate the effects of dietary protease in on the growth performance, blood constituents, and carcass characteristics of growing-finishing pigs.
Materials and Methods
The experimental protocol for this research was reviewed and approved by the Institutional Animal Care and Use committee at the National Institute of Animal Science. This experiment was conducted at the facility of National Institute of Animal Science Farm.
A total of 48 growing pigs [(Landrace × Yorkshire) × Duroc; 34.8 ± 0.62 kg of initial body weight (BW); all barrows] were randomly assigned to 2 dietary treatments (6 pigs/pen; 4 replicates/treatment) in a completely randomized design. The treatments were a diet based on corn and soybean meal (CON) and CON supplemented with 0.01% of protease (PRO). The protease used in this study was a commercial product (Ronozyme® ProAct, DSM nutrition products, Kaiseraugst, Switzerland) containing 75,000 protease units/g derived from Bacillus licheniformis. The diets were formulated to meet or exceed the nutrient requirements of growing and finishing pigs, estimated by the NRC (2012) (Table 1). The pigs were fed respective dietary treatments with a 2-phase feeding program for 12 weeks. Pigs were housed in conventional facilities with an all-slatted concrete floor (3.2 × 3.6 m2) and allowed access to diets and water during the overall experimental period.
1) The vitamin-mineral premix provided the following quantities of vitamins and minerals per kilogram of diets: vitamin A, 10,000 IU; vitamin D3, 2,000 IU; vitamin E, 250 IU; vitamin K3, 0.5 mg; vitamin B1, 0.49 mg as mononitrate; thiamin, 0.49 mg as thiamin mononitrate; riboflavin, 1.50 mg; pyridoxine, 1 mg as pyridoxine hydrochloride; vitamin B12, 0.01 mg; niacin, 10 mg as nicotinic acid; pantothenic acid, 5 mg as calcium pantothenate; folic acid, 1 mg; biotin as d-biotin, 0.1 mg; choline, 125 mg as choline-chloride; Mn, 60 mg as manganese sulfate; Zn, 75 mg as zinc sulfate; Fe, 20 mg as ferrous sulfate; Cu, 3 mg as cupric sulfate; I, 1.25 mg as calcium iodate; Co, 0.5 mg as cobaltous carbonate; and Mg, 10 mg as magnesium oxide.
The pig BW and feed intake were recorded at the starting day and end of each phase. Average daily gain (ADG), average daily feed intake (ADFI) and gain to feed ratio (G:F) were calculated. Blood samples were collected from the jugular vein of 8 pigs per treatment using 8 mL EDTA tubes. The blood samples were analyzed to measure number of white blood cells and proportions of their differentiation using a multi-parameter automated hematology analyzer calibrated for porcine blood (Hemavet 950FS, Drew Scientific, UK).
After completion of the finishing period, pigs fed experimental diets until slaughtered. Approximately four hours before transport, feed was withdrawn. The live BW of finishing pigs used in the experiments was recorded before slaughter. To reduce stress, the pigs were showered with water, and water was freely available for drinking during lairage. The pigs were rested for about eight hours. Pigs were slaughtered according to industry accepted procedures (Korea Institute for Animal Products Quality Evaluation). The final live BW of pigs was recorded, and then they were slaughtered through electrical stunning and scalding-singeing. The hot carcass weight (HCW) was recorded, and dressing percentage was calculated by comparing final live BW and HCW. After splitting, the back fat depth at the 11th and 12th thoracic vertebra and between the last thoracic vertebra and the 1st lumbar vertebra was measured.
Data were analyzed with the PROC GLM procedure of SAS (SAS Inst. Inc., Cary, NC, USA) in the completely randomized design. The experimental unit was the pen. The statistical model for growth performance, blood constituents, and carcass characteristics included dietary treatments as the fixed effect and initial BW as the covariate. Results are presented as a mean ± SEM. Statistical significance and tendency were considered at p < 0.05 and 0.05 ≤ p < 0.10, respectively.
Results and Discussion
Pigs fed PRO had higher ADG (p < 0.05) during phase I and overall experimental period and gain to feed ratio (p < 0.05) during phase I than those fed CON, but there was no difference on ADFI of pigs between CON and PRO (Table 2). Most previous studies also showed that pigs fed diets with dietary protease had higher growth rate of pigs than those fed diets without dietary protease [14–17]. However, other research reported that addition of dietary protease in pig diets did not improved growth rate [18–20]. The reason for the positive effect of dietary protease on growth rate may be related to the improvement of nutrient digestibility and utilization from more hydrolysis of protein by addition of dietary protease in pig diets [21–24].
Addition of dietary protease in the pig diet did not modulate blood constituents of pigs (Table 3). These results were similar to the results reported by Tactacan et al. . The blood constituents measured in this experiment were the total number of white blood cell and its differentiation, such as neutrophils, lymphocytes, monocytes, eosinophils, and basophils, that can be used as indicators for inflammation or immunity [25–27]. The modification of indicators for immunity by some changes of pig diet formula may not be easy in normal conditions of pigs and environment. During the whole experimental period of this experiment, pigs and environmental conditions were normal and thus the blood constituents of pigs may not be changed by addition of dietary protease in pig diets in this experiment. In addition, there were no differences on carcass characteristics among dietary treatments (Table 4). These results were similar to the results of previous studies [16,28,29], but Wang et al.  showed addition of dietary protease in the pig diet changed carcass characteristics of pigs. However, further investigation is needed to clarify the effects of dietary protease on the blood constituents and carcass characteristics of growing-finishing pigs.
|Live weight (kg)||117.05||117.42||1.84||0.890|
|Hot carcass weight (kg)||84.85||84.82||1.50||0.990|
|Dressing percentage (%)||72.49||72.21||0.33||0.556|
|Backfat thickness (mm)||27.00||25.55||1.47||0.491|