Amino Acid Case Study - (Growth In Pigs)SUMMARY Effect of genotype and dietary lysine content during the grower phase on growth performance, serum urea N, and carcass and meat quality. Fabian, J., L. I. Chiba, D. L. Kuhlers, L. T. Frobish, C. R. Kerth, K. Nadarajah, W. H. McElhenny, and B. L. Anderson. A total of 32 select line (SL) and 32 control line (CL) Duroc pigs were used in two trials to determine the effect of selection for lean growth efficiency and dietary lysine content during the grower phase on pig performance. In each trial, pigs weighing 20 kg were assigned to 16 pens with two gilts or two barrows per pen, and pens were randomly assigned within genetic lines to one of the four grower (G) diets (0.5, 0.7, 0.9, or 1.1 g lysine/kg diet). After 50 kg, all pigs were fed finisher 1 (50-80 kg) and finisher 2 (80-105 kg) diets formulated to meet the NRC nutrient requirements. Pigs were allowed ad libitum access to feed and water. Blood samples were taken from each pig at 20, 50, and 105 kg. Pigs were subjected to ultrasound backfat (UBF) measurement at 50 and 105 kg. The initial statistical analyses revealed that variances between the two trials were homogeneous, thus the data were combined. During the G phase, pigs fed the high-lysine diets consumed less feed [linear (Ln), P < 0.001] and grew faster (Ln, P < 0.05) and more efficiently (Ln, P < 0.001) as the dietary lysine level increased. With the increasing dietary lysine content, pigs had lower ultrasound backfat (Ln, P < 0.001)and higher serum urea N (Ln, P < 0.001) at the end of the G phase. However, during the F1 and F2 phases, pigs grew faster (Ln, P < 0.01 and P = 0.07, respectively) and more efficiently (Ln, P < 0.05) as the lysine content of the G diets decreased, resulting in no differences in overall growth performance or carcass and meat characteristics. The SL pigs grew faster (P < 0.01), and had lower 10th rib backfat ( P < 0.001) and larger longissimus muscle area (P = 0.08) than the CL pigs, which were reflected in higher estimated daily lean gain (P < 0.001). The SL pigs had lower meat color ( P < 0.05) and firmness (P = 0.07) scores. These results indicate that pigs exhibited compensatory growth after dietary lysine restrictions during the G phase, and were able to compensate fully. Although the SL pigs had superior growth rate and body composition, both genetic lines responded similarly to the restrictions. |
