INTRODUCTION
Generally, not only corn and soybean meal (SBM) but also lactose and whey powder are also main feed ingredients in weaning pigs diet in Korea. It is well known that lactose and whey powder are used as the main raw materials in weaning pig diets and that supplementation of milk by-products helps maintain an enhanced intestinal environment [1]. Moreover, lactose effects growth and enhances feed intake in weaning pig diets [2–4]. However, according to U.S. Department of Agriculture, international price trends for dairy products are very unstable, and their price is expensive compared to grains. Therefore weaning pig diets which contain high levels of milk by-products are expensive and cause an increase in the cost of pork production. Recent studies indicated that growth performance of weaning pigs was increased by increasing dietary lactose in early weaning period [3–6].
Recently, Jin [7] reported an evaluation of supplementation with barley instead of milk by-products in weaning pig’s diet. This demonstrated that barley replacing milk by-product caused low growth performance during the weaning period. However, growth of growing and finishing pigs in the barley treatment caught up with pigs in the milk by-product treatment, resulting in similar days to market weight. For this reason, current study was conducted to understand the effects of various levels of milk by-product in weaning pig diet on growth performance and blood profiles, thereafter growth, carcass characteristics and economics analysis in growing-finishing pigs.
MATERIALS AND METHODS
Experimental design and diet
All experimental procedures involving animals were conducted in accordance with the Animal Experimental Guidelines provided by the Seoul National University Institutional Animal Use and Care Committee (SNUIAUCC; SNU-160513–1).
A total of 160 weaning pigs ([Yorkshire×Landrace]×Duroc), 7.01±1.32 kg initial body weight (BW), were used in a 19 week feeding trial. Pigs were allotted to four treatments based on BW and sex in 10 replications with 4 pigs per pen in a randomized complete block design.
Dietary treatments were: i) Non: corn-SBM based diet+milk by-product 0% (Phases 1 and 2: whey powder and lactose 0%), ii) Low: basal diet+milk by-product 10% to 5% (Phase 1: whey powder 4% and lactose 6%, Phase 2: whey powder 2% and lactose 3%), iii) Medium: basal diet+milk by-product 20% to 10% (Phase 1: whey powder 8% and lactose 12%, Phase 2: whey powder 4% and lactose 6%), iv) High: basal diet+milk by-product 30% to 15% (Phase 1: whey powder 12% and lactose 18%, Phase 2: whey powder 6% and lactose 9%). Those experimental diets were fed during the weaning period (0 to 5 week). All nutrients met or exceeded the requirement estimates of NRC [8]. The formula and chemical compositions of weaning pigs’ diets are presented in Tables 1 and 2. After weaning period (5 weeks), all pigs were fed a common commercial feed during the entire growing-finishing period (14 weeks). Early- growing diet had metabolizable energy (ME) 3,277 kcal/kg, crude protein (CP) 16.4%, total lysine 0.98%, late-growing diet had ME 3,274 kcal/kg, CP 15.24%, total lysine 0.93%, early- finishing diet had ME 3,279 kcal/kg, CP 14.11%, total lysine 0.86%, late-finishing diet had ME 3,280 kcal/kg, CP 12.53%, total lysine 0.74%. The chemical composition of commercial diets during growing-finishing period are presented in Table 3.
Feeding trial
All pigs were housed in an environmentally controlled building with half-slotted concrete floors and each pen equipped with a feeder and a nipple drinker to provide ad-libitum access. The BW and feed intake were recorded at 0, 2, 5, 9, 13, 17, and 19 week to calculate the average daily gain (ADG), average daily feed intake (ADFI), and gain:feed (G:F) ratio.
Blood urea nitrogen
Blood samples were collected from anterior vena cava of 6 pigs per treatment for measuring blood urea nitrogen (BUN) after 3 hours of fasting at 0, 2, 5, 9, 13, 17, and 19 weeks. Collected blood samples were centrifuged for 15 min by 1,700 g at 4°C (Eppendorf centrifuge 5810R, Hamburg, Germany). Then, sera samples were aspirated by pipette and stored at −20°C until analysis. The BUN concentration was analyzed using analyzer (Ciba-Corning model, Express Plus, Ciba Corning Diagnostics Co., Basel, Switzerland).
Diarrhea incidence
Incidence of diarrhea was measured every 9:00 am for 35 days post weaning. Data were recorded by each pen and divided into 2 phases to assess the general pattern (Phase 1 and Phase 2). A score of diarrhea incidence from 0 to 4 score (0 = no evidence of watery diarrhea, 1 = 1 pig showed evidence of watery diarrhea, 2 = 2 pigs, 3 = 3 pigs, and 4 = all pigs (n = 4) showed evidence of watery diarrhea in the pen) was determined by counting pigs with evidence of watery diarrhea [9]. After recording data, evidence of watery diarrhea was cleaned away.
Carcass characteristics
Five pigs from each treatment were slaughtered at an average 113 kg for the carcass analysis at the end of experiment. Longissimus muscle (LM) samples were collected from nearby 10th rib on the right side of carcass. Because of chilling procedure, 30 minutes after slaughter was regarded as initial time (0 h). Longissimus muscle pH and color were measured at initial, 3, 6, 12, and 24 h. The pH of LM was measured using a pH meter (Φ 500 Series, Bechman Coulter, S. Kraember Blvd Brea, CA, USA) and pork color was measured by Commission Internationale de l’Eclairage (CIE) color L*, a*, and b* value using a CR300 spectrophotometer (Minolta Camera Co., Tokyo, Japan). Proximate analysis of LM samples was conducted by the method of AOAC [10].
Water holding capacity (WHC) of pork was measured by centrifuge method. Longissimus muscles were ground and sampled in filter tube, then heated in water bath at 80°C for 20 min and centrifuged for 10 min at 252 g and 10°C (Eppendorf centrifuge 5810R, Hamburg, Germany). For cooking loss analysis, LM samples were packed in a polyethylene bag and weighted then heated in water bath until core temperature reached 72°C and weighed again. After heated, samples were cored (0.75 cm3) parallel to muscle fiber and the cores were used to measure the shear force (Warner Bratzler Shear, Chichago, IL, USA). Cooking loss, shear force, and WHC of LM samples were analyzed by National Institute of Animal Science.
Economic analysis
Economic efficiency was calculated by feed intake, feed cost, and feed efficiency. The total feed cost (won) per weight gain (kg) was calculated using G:F ratio and feed cost. In addition, calculation of estimated feed cost to 110 kg as follows;
The days to market weight (110 kg) was estimated from 19th week as the end of feeding trial and added the estimated days by ADG of 17 to 19 weeks.
Chemical analysis
Diets were ground by a Cyclotec 1093 Sample Mill (Foss Tecator, Hillerod, Denmark) and then the contents analyzed; dry matter (procedure 967.03; AOAC [10]), crude ash (procedure 923.03; AOAC [10]) and crude fat (procedure 920.39; AOAC [10]). The nitrogen content was analyzed by using the Kjeldahl procedure with Kjeltec (KjeltecTM 2200, Foss Tecator, Höganäs, Sweden) and calculating the CP content (Nitrogen×6.25; procedure 981.10; AOAC [10]).
Statistical analysis
Statistical analysis was carried out by general linear model procedure of SAS [11] and orthogonal polynomial contrasts were used to determine linear and quadratic effects by increasing dietary milk by-products levels in weaning pig diet. For data on growth performance, diarrhea incidence, and economic analysis, each pen was considered as experimental unit, while individual pig was used as experimental unit for data on blood profile and carcass characteristics. The differences were declared significant at p<0.05 or highly significant at p<0.01 and the determination of tendency for all analysis was 0.05<p<0.10.
RESULTS AND DISCUSSION
Growth performance
The influence of various levels of milk by-products in weaning pig diet on growth performance during weaning to finishing pig period are presented in Table 4 and 5. During weaning period, BW, ADG, and ADFI increased linearly with increasing milk by-product levels in the weaner diets (linear, p<0.05). The BW increased linearly at 5 and 13 weeks (linear, p<0.01, p = 0.01), ADG increased linearly with tendency during 10–13 weeks (linear, p = 0.09) but decreased during 14–17 weeks (linear, p = 0.08), ADFI increased linearly with tendency during 5–9 weeks (linear, p = 0.08) and G:F ratio decreased quadratically during 14–17 weeks (quadratic, p = 0.03). The trend of weaning phase was continued until the end of 13 week, thereafter there was no significant difference in growth performance among treatments. However, G:F ratios both in weaning and growing-finishing period were not affected by dietary milk by-products treatment.
In the current study, pigs fed the diets containing high level of milk products had greater BW, ADG, and ADFI during weaning period, because the gastrointestinal tract of the newly weaned pig is easily adapted to a milk based diet as a result of high lactase activity [12,13]. Numerous researches reported that the beneficial effects of high dietary lactose improved growth performance of pigs in early weaning phase [3,5,14–16]. In addition, high dietary lactose improved initial stimulation of appetite and feed intake [4,6]. The growth response in BW to dietary treatment continued until late growing period (13 week). However, differences in growth performance during the weaning period disappeared and significant difference was not observed among treatments at the end of experiment (19 week). Shearer and Dunkin [17] demonstrated that growth of pigs could be improved by high levels of dietary lactose (30% or 45% but subsequent growing-finishing pigs grew slower than those fed low lactose diet (0% or 15%). Tokach et al [18] also reported that different levels of milk by-product (0% or 40%) in weaning pig diets produced significant differences in growth performance only during the weaning period and any significant difference was not observed in growth performance during the growing-finishing. Also, growth retardation due to nutrient limitation in weaning pigs induced compensated growth of growing-finishing pigs resulting in similar BW at the end of finishing period [19,20]. Weaning pigs with low growth rate due to limited nutrient intake recovered the normal growth rate compared with other pigs on the same nutritional supply [21]. Ishida et al [20] reported that compensatory growth of pigs induced by lysine sufficiency was partly attributed to greater N retention which increased protein synthesis in skeletal muscle. In this way, pigs fed low milk by-product diet had growth retardation compared with pigs fed high milk by-product diet, however, compensated growth occurred in growing-finishing period. In the present study, BW, ADG, and ADFI decreased in non or low level of milk by-product in the weaning diet, but this trend changed dramatically in the finishing period resulting in no significant difference of BW, ADG, ADFI, and G:F ratio at the end of late finishing period.
Blood urea nitrogen
The concentration of BUN has been used as a good indicator of maximal amino acid utilization [22]. It has been found that BUN is related directly to protein intake and inversely to protein quality [23,24]. In the current study, the concentration of BUN had no significant difference among treatments during whole experimental period except at 19 week where BUN concentrations tended to decrease with increasing milk by-product levels (linear, p = 0.07; Table 6). Dried milk or milk by-products were used as a protein source for young pigs were considered useful feed ingredients due to their nutrient composition, high digestibility, similarity to a sow’s milk [12], and high lactase activity in weaning pig [12,13]. However, the current study demonstrated that protein utilization in pigs fed no or low levels of milk by-product did not differ from high milk by-products treatment.
Diarrhea incidence
The influence of various levels of milk by-products in weaning pig diet on diarrhea incidence is shown in Table 7. In weaning period, there was not any significant difference in the diarrhea incidence due to reduction of milk by-products in weaning pig’s diet. Zinc oxide at pharmacological concentrations (2,000 to 3,000 mg/kg) has been reported to reduce diarrhea during weaning period [25]. In current study, usage of zinc oxide in phase1 diet was 800 ppm and in phase2 diet was 0 ppm. Also, barley has relatively high fiber source which reduced diarrhea occurrence and is helpful in preventing diarrhea [26]. Also, Jin [7] demonstrated that supplement of barley in weaning pig diet reduced the incidence of diarrhea. Due to the effect of ZnO and barley, weaning pigs fed no or low milk by-product had no significant difference in diarrhea incidence compared with pigs fed high milk by-product content.
Pork quality
The pork quality was measured in order to investigate how the reduction in milk by-product in weaner diets affects the pork quality after slaughter. In the present study, moisture and crude fat of LM had no significant differences among dietary treatments (Table 8). However, crude protein of LM had a quadratic response (quadratic, p = 0.05) and crude ash of LM had a linear response (linear, p 0.05). Frape et al [27] found that early growth rate of weaning pigs was influenced by dietary nutrients but it did not affect the chemical compositions of the carcass in finishing pigs. Although there were no significant differences in moisture and crude fat, high milk by-product treatment had low crude protein and crude ash content in LM. As the dietary milk by-product supplementation increased in weaning period, cooking loss was increased linearly (linear, p<0.01) and WHC was decreased linearly (linear, p = 0.05). Also, shear force of LM tended to increase linearly with dietary milk by-product content increased in weaning pig’s diet (linear, p = 0.07). Beilken et al [28] demonstrated that shear force was increased when WHC decreased. Cooking loss is an indirect index of WHC because it decreases when WHC increases [29]. In addition, WHC is an important factor of pork quality [30,31] and high WHC improves pork quality [32,33]. Consequently these results demonstrated that pork quality of finishing pigs was improved when low milk by-products was provided in weaning pigs’ diet.
In general, the pH change of pork is a critical factor that determines the quality of pork and it has an effect on freshness, WHC, tenderness, binding ability, meat color and texture [34]. Maganhini et al [35] reported that initial pH was regarded as an indication of PSE (pale, soft and exudative) pork and the final pH was acknowledged as an estimation of DFD (dark, firm and dry). The measured pH (0 hour to 24 hour) was not significantly different among treatments (Table 9) and pH of LM was in the normal range (pH 5.5 to pH 6.0).
The result of pork color (CIE value) of LM is presented in Table 10. There were no significantly difference in a value, L*, a*, and b* value at 0, 3, 6, 12, 24 h after slaughter. In pork color, decreasing in redness and increasing in yellowness had a negative influence on the freshness of pork [36]. However, there were no change in redness or yellowness by milk by-products levels in weaning pig diets. Therefore, these results demonstrated that low levels of milk by-products in weaning pig diet had no negative influence on pH and color of pork after slaughter.
Economic analysis
The influence of various level of milk by-product in weaning pig diet on feed cost per weight gain, days to market weight (reached 110 kg BW) and estimated feed cost to 110 kg are presented in Table 11. There were linear increases in feed cost per weight gain during 0 to 2 week, 3 to 5 week, 0 to 5 week, and 0 to 19 week (linear, p<0.01; p<0.01; p<0.01; p<0.01) as the dietary milk by-product supplementation was increased in weaning pigs’ diet. Increasing feed cost of high milk by-products treatment was mainly caused by milk by-products supplementation, since high price of milk by-products caused increasing feed cost of weaning pig diet. In addition, there was no significant difference in days to market weight because growth performance of late-finishing period (18 to 19 week) was not affected by dietary treatments. In estimated feed cost to 110 kg, no significant difference was observed. However, estimated feed cost was reduced numerically as supplement of milk by-product in weaning pig diet decreased. Thus pigs fed lower milk by-products supplemented in weaning pig diet had greater economic profits.
IMPLICATIONS
Feeding of milk by-product in weaning pigs’ diet increased growth performance during weaning period but its carry-over effect disappeared by the end of late finishing period. Also feeding high levels of milk by-products during the weaning period did not show a positive response in the marketing weight of pigs and no beneficial effects were observed in pork quality. Feed cost during whole experimental period could be reduced by about 11% when weaning pigs were fed no milk by-products treatment diet during weaning period. Consequently, supplementation of 10% to 5% milk by-products in weaning pigs’ diet had results equivalent to the high milk treatment. Supplementation with non-milk by-products in the diet had no negative effects on growth performance of finishing pigs and was the most economically efficient.
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