Both genetics and dietary improvements have contributed significantly to increased growth performance of pigs over the last 25 years. Genetic selection has increased the amount and efficiency of lean growth, which allows more nutrients to be deposited in tissue and fewer nutrients excreted in manure. Many changes have taken place in the design of diets for pigs compared to 25 years ago. These include the use of enzymes, crystalline amino acid, improved nutrient balance, improved feed processing (e.g., pelleting) and more sophisticated phase feeding programs.
The objectives of our study were to compare the effects of genotype and diet on nutrient digestion and retention, ammonia emission and odor in manure of growing-finishing pigs.
Materials and Methods
First parity white line females were obtained from an unselected commercial population formed in 1980 that has been maintained at NCSU since 1989. These sows were mated using frozen semen of Hampshire or Duroc boars that were typical of those used in 1980. Pigs representative of 2005 genotype of similar age were obtained from a NC swine production company.
All pigs were reared at the North Carolina Swine Evaluation Station in Clayton, NC. After farrowing, 28 piglets (14 pigs of the 1980 genotype and 14 pigs of the 2005 genotype) were selected and allotted to a 2 × 2 factorial randomized complete block design. Factors included: 1) genotype representative of 1980 and 2005; and 2) feeding program representative of 1980 and 2005. The characteristics of the feeding programs are shown in Table 1.
The nutrient levels for the 4-phase 1980 feeding program (e.g., lysine from 1.05 to 0.62% and ME from 3262 to 3317 Kcal/kg) were based on formula¬tions from the 1978 Pork Industry Handbook (PIH). The 2005 feeding program consisted of a 7-phase program using pelleted diets similar to diets used by NC pork producers (e.g., lysine from 1.51 to 0.73% and ME from 3428 to 3651 Kcal/kg).
Pigs (n=28) were transferred to metabolism crates once they reached a body weight of ap-proximately 65 kg. The 1980 diet (corn-soybean meal, meal form) and the 2005 diet (pelleted, supplemented with amino acids and phytase) fed during the metabolism period contained, respectively 13.3 vs. 14.7% CP, 3317 vs. 3655 kcal/kg ME, 0.67 vs. 0.43% Ca, 0.56 vs. 0.41% P, and 0.62 vs. 0.94% total lysine. After an adaptation period of 7 d, feces and urine were collected quantitatively for 3 days. A portion of the feces and urine was then mixed together and homogenized within respective animal at the rates they were produced to form fresh manure. Half of this fresh manure was aged anaerobically for 21 days to create aged manure.
Both fresh and aged manure were sampled for odor evaluation by a professional odor panel. The panelists were asked to smell each sample individually and assign a designation of degree of pleasantness or unpleasantness according to a -10 to +10 hedonic tone scale, with 0 being neutral. They also were asked to assign a score for strength of odor by smelling the sample and comparing it to standards of n-butanol at increasing concentrations to generate a 1 to 5 scale (very faint, faint, moderate, strong, and very strong).
Ammonia emission of the manure samples was determined by placing 400 ml of the manure mixture in a rectangular container. Air was drawn through the container with manure, and then through a gas dispersion tube placed in a 500 ml Erlenmeyer flask containing dilute sulfuric acid in order to trap the ammonia released from the manure. This sulfuric acid solution was sampled at 12, 24, 36, 48, 72, and 96 h and ana¬lyzed for ammonia.
Results
Pig average daily gain was greater for the modern genetics and feeding program, resulting in heavier body weight when the metabolism study was initiated (69.9 vs. 63.5 kg, P = 0.04 and 73.1 vs. 60.3 kg, P < 0.001, respectively). To account for the differences in body weight, all other data were expressed per unit of metabolic body weight, which eliminates bias due to weight difference of pigs. Intake of N tended (P = 0.07) to be greater (1.15 vs. 1.02 g•BW-0.75•d-1) and intake of P was lower (P < 0.001; 0.20 vs. 0.26 g•BW-0.75•d-1) for the 2005 diet compared to the 1980 diet (Table 2). Feces (15.1 vs. 20.0 g•BW-0.75•d-1) and urine (37.7 vs. 48.3 g•BW-0.75•d-1) production were lower (P < 0.01), fecal N excretion (0.168 vs. 0.196 g•BW-0.75•d-1) tended to be lower (P = 0.08) and fecal P excretion was lower (P < 0.001; 0.117 vs. 0.162 g•BW-0.75•d-1) for the 2005 diet when compared to the 1980 diet. Digestibility of N (85.3 vs. 80.3%) and GE (88.9 vs. 85.3%) was greater (P < 0.05) for the 2005 diet compared to the 1980 diet (Table 2). Urinary N excretion was greater in 1980 pigs when fed 2005 diets compared to 1980 diets (0.35 vs. 0.16 g•BW-0.75•d-1), but no differences between diets were observed in 2005 genetic pigs. Cumulative ammonia emission in fresh manure was greater (P = 0.05) for 2005 pigs at 24 h, but not at any of the other time points. In aged manure (Figure 1), ammonia emission was 86, 52, 29, 18, and 12% greater (P < 0.05) for the 2005 diet at 12, 24, 36, 48, and 96 h, respectively. No differences in manure odor were observed.
Conclusion
Consistent with improvements in growth rate in the present study, we have previously demonstrated a 15% reduction in days to slaughter and a 30% improvement in feed efficiency due to improvements in genetics and nutrition programs. These positive impacts on pork production can be calculated to result in a reduction in nutrient excretion of approximately 23%. In addition, we observed improved nutrient utilization for the 2005 diet, which will further reduce manure output and nutrient excretion; however, we also demonstrated that modern feeding programs may increase ammonia emission when measured in vitro at one point in time.
Submitted by: Eric van Heugten Source : North Carolina State University