Adjustment of branched-chain amino acid balance fails to prevent feed intake decline in lactating sows fed high soybean meal diets.

A total of 352 sows were used to investigate the effect of soybean meal (SBM) level and adjusted branched-chain amino acid (BCAA) balance on lactating sow and piglet performance. On day 112 ± 1.5 of gestation, sows were randomly assigned, within parity, to one of four dietary treatments: low SBM (LSBM), high SBM (HSBM), LSBM with adjusted BCAA (LSBM+BCAA), or HSBM with adjusted BCAA (HSBM+BCAA). The BCAA balance was adjusted to achieve equal standardized ileal digestible (SID) Ile:Leu:Val in the LSBM and HSBM+BCAA diets (SID Ile:Leu:Val 0.49:1.00:0.73) and in the HSBM and LSBM+BCAA diets (SID Ile:Leu:Val 0.54:1.00:0.58). All diets were formulated to be equal in SID Lys, isocaloric, and meet or exceed NRC (2012) recommendations for all other essential amino acids, vitamins, and minerals. Sow body weight (BW) and backfat thickness (BF) were measured at the time of entry into the farrowing room and at weaning. Litter weights were captured after cross-fostering and at weaning to calculate litter growth rate. Data were analyzed using generalized linear mixed models in R (v4.4.1; R Core Team, 2024) with fixed effects of dietary treatment, parity group, and their interaction and a random effect of lactation group. The sow and her litter were the experimental unit, and results were considered significant if P ≤ 0.05. There was an effect of the dietary treatments on sow average daily feed intake (ADFI; P < 0.001). Sows consuming the LSBM diet exhibited greater ADFI compared to HSBM (7.43 vs. 7.05 kg/d; P = 0.024) or HSBM+BCAA (7.43 vs. 6.87; P < 0.001), while sows fed LSBM+BCAA showed greater ADFI than HSBM+BCAA (7.24 vs. 6.87; P = 0.025), but similar ADFI to LSBM- (P = 0.515) and HSBM-fed (P = 0.466) fed sows. Despite differences in ADFI, sows gained an average of 7.1 kg of BW (P = 0.682) and lost 1.3 mm of BF (P = 0.928) through the lactation period. Sows started the trial with an average of 14.0 piglets/sow (P = 0.787) and weaned 12.6 piglets/sow (P = 0.875) with a piglet average daily gain of 0.22 kg/d (P = 0.646). Increasing SBM inclusion by 14% reduced sow ADFI in lactation by approximately 5%, but did not alter sow BW or BF loss or piglet growth rate. While adjusting BCAA in the LSBM diet slightly reduced sow feed intake, adjusting BCAA in the HSBM diet did not alleviate the reduction in ADFI caused by elevated SBM, suggesting the balance of BCAA does not contribute to the feed intake response observed with elevated SBM inclusion in lactation diets.