Introduction
With the continuous development of animal husbandry, the world pig production in the past few decades have risen to about 1.2 billion heads. Due to increased demand for corn, and changes in the price of corn on the international market, alternative low cost feed ingredient such as wheat is being researched as a source of energy as well as other nutrients to replace certain amount of corn in the diet.
Wheat is one of the most important agricultural products in the world and produced in many parts of the world (Carré et al., 2007). Due to wheat, generally lower cost per megajoule of digestible energy and its relatively high protein content in comparison to other grains, more attentions have been paid to the wheat. It has a feeding value of approximately 92% of corn for pigs (Hancock et al., 1993). Like most other vegetable feed ingredients, it is not a good source of P because most of its P is bound to phytic acid (PA), which is poorly digested by pigs (Bedford, 2000). Moreover, the higher content of non-starch polysaccharides (NSP) in wheat affects the digestion and absorption of wheat nutrients (Woyengo and Nyachoti, 2011). There have been some studies investigating enzyme supplementation and particle size of wheat in diets of pigs (Mavromichalis et al., 2000). As genetically modified (GM) crops pose a potential environmental, ecological, and human risk, many countries that use wheat as their main staple have opposed to the promotion of GM wheat (Quist and Chapela, 2001; Hanson et al., 2005).
The objective of the experiments reported herein was to investigate the effect of non-GMO wheat-based diet on growth performance, nutrient digestibility, blood profile, and meat quality in grower-finisher pigs.
Materials and Methods
The experimental protocols describing the management and care of animals was reviewed and approved by the Animal Care and Use Committee of Dankook University, South Korea.
Experimental design, animals, and diets
A total of 70 growing pigs [(Landrace × Yorkshire) × Duroc; 26.15 ± 1.57 kg] were used in a 112 days trial to evaluate the growth performance, nutrient digestibility, fecal score, blood profile and meat quality. Dietary treatments included: CD, corn-based diet; non-GMO WD, non-genetically modified organism wheat-based diet. Each treatment consisted of 7 replicate pens with 5 pigs per pen. The diets were formulated to meet or exceed NRC (2012) recommendations for all nutrients (Table 1). Pigs were housed in an environmentally controlled facility with slatted plastic flooring and a mechanical ventilation system. Each pen was equipped with a single face self-feeder and a nipple drinker to allow the pigs ad libitum access to feed and water throughout the experimental period.
Sampling and measurements
The live body weight (BW) of each individual pig was measured at the beginning and end (112 days) of the experimental period. Feed consumption was also recorded and gain/feed ratio was calculated on a pen basis.
Individual pig’s BW was checked at the d 21, 42, 77, and 112, and the feed consumption was recorded per pen during the experiment to calculate the average daily gain (ADG), average daily feed intake (ADFI), and gain/feed (F/G) ratio.
During d 21 to 27, d 42 to 48 and d 112 to 118, chromium oxide (Cr2O3) was added to the diets as an indigestible marker at 0.20% of the diet to measure digestibility. Fresh fecal grab samples were obtained from at least two pigs in each pen at d 27, 48, and 118 to determine the apparent total tract digestibility (ATTD) of dry matter (DM), nitrogen (N) and gross energy (GE). All fecal and feed samples were stored at - 20℃ until analysis. Prior to chemical analysis, the fecal samples were thawed and dried for 72 h at 60℃, after which they were ground to pass through a 1 mm screen. The feed and fecal samples were analyzed for DM, N, and GE according to AOAC (2000). Chromium was analyzed by UV absorption spectrophotometry (Shimadzu, UV-1201, Kyoto, Japan) following the method described by Yin and Kim (2019).
Two pigs were selected randomly from each pen (one barrow and one gilt) and blood samples were collected by anterior vena cava puncture on d 21, 42, 77, and 112. Blood samples were collected in 5 mL vacuum tube (Becton Dickinson Vacutainer System, Franklin Lakes, USA) and then centrifuged (3000 × g, 15 min, 4℃) within one hour after the collection of the sample to separate the serum. The protein, blood urea nitrogen (BUN), creatinine, and glucose in the serum samples were analyzed with an automatic biochemical analyzer (HITACHI 747, Japan) using colorimetric methods.
At the end of the experiment, two pigs (1 barrow and 1 gilt) per replicate pen per treatment were randomly selected and slaughtered at local commercial slaughter house. Carcasses were placed in a conventional chiller at 4℃. After chilling at 4℃ for at least 24 h, piece of the right loin sample was removed between the 10th and 11th ribs. The meat samples were thawed at room temperature before evaluation. Sensory evaluation was conducted by six trained panelists to evaluate the colour darkness, firmness and marbling of fresh loin samples using a five-point assessment scheme according to the procedures established by the NPPC (2000). Immediately after the subjective tests were conducted, meat colour of the longissimus muscle (LM) as lightness (L*), redness (a*), and yellowness (b*), was determined using a Minolta chromameter (Model CR-410, Minolta Co., Japan) to evaluate the freshly cut surface after 30 min of blooming at 4℃. At the same time, duplicate pH values of each sample were directly measured using a pH meter (Model 77p, Istek, Seoul, Korea). Water-holding capacity (WHC) was measured using methods of Kauffman et al. (1986). The areas of pressed sample and expressed moisture were delineated and determined with a digitizing area-line sensor (MT-10S; M. T. Precision Co., Ltd., 123 Tokyo, Japan). A ratio of water area: meat area was calculated to give a measure of WHC, with smaller ratio indicating higher WHC and is termed as ‘expressed juice percentage’. LM area was measured by tracing the LM surface at 10th rib, which also used the above-mentioned digitizing area-line sensor.
Cook loss was determined as described previously by Sullivan et al. (2007). Drip loss was measured using approximately 2 g of meat sample at d 1, 3, 5 and 7 after slaughter according to the plastic bag method described by Honikel et al. (1986).
Statistical analysis
All data were subjected to the statistical analysis as a randomized complete block design using the general linear model procedures of SAS (SAS Inst., Inc., Cary, USA), and the pen was used as the experimental unit. The initial BW was used as a covariate for the ADFI and ADG. Differences among all treatments were separated by using the Tukey’s test. A probability level of p < 0.05 was considered to be statistically significant.
Results
Growth performance and nutrient digestibility
The growth performance and nutrient digestibility are shown in Tables 2 and 3. In the current study, CD had higher body weight than pigs fed non-GMO WD in d 21 and 77 (p <0.05). There was a significant difference in average daily gain (ADG) at 0 - 21 days (p < 0.05). However, the ADFI and feed conversion ratio (FCR) in the pigs fed non-GMO wheat-based diet were comparable with those fed control diets. In addition, there were no differences in overall ADG, ADFI, and FCR in non GMO group compared with control (Table 2). Non-GMO wheat-based diet showed comparable (p > 0.05) nutrient digestibility compared with corn-based diet (Table 3).
Blood lipid profile
Blood profiles was shown in Table 4. Non-GMO WD had no effects on protein, BUN, creatinine, and glucose except what BUN at d 21 on blood profile; however, the difference was not statistically significant. Thus, overall total blood profiles with WD and non-GMO WD treatments were found to be statistically insignificant.
Meat quality
The effects of dietary treatments on the meat quality are presented in Table 5, the meat quality parameters did not significantly differ among groups (p > 0.05). Thus, overall total meat quality with CD and non-GMO WD treatment were found to be statistically insignificant (p > 0.05).
Discussion
The main factor affecting the digestion and absorption of nutrients may be the content of non-starch polysaccharides (NSP) significantly higher than corn. Relevant studies have shown that the NSP and phytate are major anti-nutritional components in plant feed stuffs for non-ruminant animals (Woyengo and Nyachoti, 2011). On the other hand, others have reported that growing-finishing swine fed wheat tend to gain slower and have a lower average daily feed intake, but are more efficient than pigs fed a corn diet (Luce et al., 1996). The inconsistent results may be due to several factors such as stage of growth, diet complexity, type of wheat, health status of pig and other environmental or management factors. Moreover, introductions of wheat in broiler diets were shown to result in great variations in digestibilities (Maisonnier et al., 2001). It may be the difference in the digestive system between pigs and broilers. However, further investigation is warranted.
If protein intake is insufficient in an animal, the plasma protein concentration will be reduced (Min et al., 2009). In our study, no differences were observed in the concentration of protein in the blood of animals evaluated. This may have been because all of the pigs were provided with sufficient amounts of protein, regardless of the experimental diets they received. Plasma or blood urea N (BUN) concentration may be useful as an indicator of protein status within a group of animals as well as nitrogen utilization, and could help to fine-tune diets or identify problems with a feeding program (Whang et al., 2003). For example, milk urea N concentration is used to predict N excretion in dairy cows (Kohn et al., 2002). The difference in significance of BUN on d 21 may be due to the differences in the contents and types of corn and wheat proteins, and the values are within the normal range. Creatinine index also showed no significant difference. Non-GMO wheat-based diet showed comparable blood profile compared with corn-based diet.
Meat quality is one of the key indicators affecting the profitability of pig production, in addition to feed costs. Based on the results observed in our study, no significant difference was observed in meat quality parameters throughout the whole experiment. Owing to its low protein and high starch levels, wheat is mainly used as an energy source in the same way as corn (Carré et al., 2007). Currently, all research reports on wheat-based diets are concentrated on the addition and digestibility of enzymes; however, there were few reports about the effect of wheat diet on the quality of pork, and our findings warrant further investigation.
Conclusion
In conclusion, Non-GMO wheat-based diet did not have any adverse effect in growth performance, nutrient digestibility, blood profile and meat quality in Grower-Finisher pigs. Therefore, non-GMO wheat-based diet appears to be a viable possible alternative to corn-based diet in grower-finisher pigs.
