Diet complexity and L-threonine supplementation: effects on nutrient digestibility, nitrogen and energy balance, and body composition in nursery pigs

Bonjin Koo, Jinyoung Lee, Charles Martin Nyachoti

This study was conducted to investigate the effects of dietary complexity and L-Thr supplementation on energy and nutrient utilization in nursery pigs. Thirty-two nursery pigs (7.23 ± 0.48 kg) were randomly assigned to a 2 × 2 factorial treatment arrangement based on diet complexity (complex vs. simple) with different levels of L-Thr supplementation. The complex diet contained animal protein sources (e.g., fish meal and plasma) and a dairy product (e.g., dried whey) to mimic a conventional nursery diet. The simple diet was formulated with corn, wheat, and soybean meal. Both diets were supplemented with L-Thr to contain either 100% or 115% (SUP Thr) of the estimated standardized ileal digestible Thr requirement for 9 kg body weight pigs (NRC, 2012). The pigs were individually housed in metabolism crates and fed an experimental diet ad libitum for a 7-d adaptation period and 5 d of total but separate urine and fecal collection. On day 14, all pigs were euthanized to determine body composition. The diet complexity, L-Thr supplementation, and their interactions were considered main effects. Pigs fed the complex diet tended to exhibit greater (P < 0.10) apparent total tract digestibility (ATTD) of ash and urinary energy output than those fed the simple diet. The complex diet had greater (P < 0.05) digestible energy and net energy contents than the simple diet. Furthermore, the complex diet-fed pigs had lower (P < 0.05) plasma urea nitrogen concentration on day 14 than simple diet-fed pigs. The SUP Thr decreased (P < 0.05) ATTD of acid detergent fiber but trended (P < 0.10) toward a decrease in urinary nitrogen (N) output and an increase in N retention and body N mass. In conclusion, the simple diet for nursery pigs had lower digestible and net energy contents than a complex diet. The SUP Thr can improve N utilization and body protein deposition, irrespective of diet complexity.