Threonine:Lysine Ratio Requirement in Lactating Sows

Camborough PIC sows (n=291) were fed one of five dietary treatments to evaluate the SID Thr:Lys requirement during lactation. Sows were blocked by parity (1, 2 and 3+) and randomly allotted to one of five SID Thr:Lys ratios (52, 60, 68, 76, and 84). SID Lys was formulated to 1.03% and SID M+C:Lys was 55%. Sows were allowed 5.45 kg/day starting on the day of farrowing. All other nutrients met or exceeded the NRC requirements. Sows were allowed ad-libitum access to water and piglets were cross-fostered within treatment. Data collected during the study included: sow pre-farrow body weight, sow wean weight, starting litter weight, weaning litter weight, mortality, wean to estrus interval and subsequent total born. Data were analyzed as a randomized complete block design using PROC MIXED with sow as the experimental unit and treatment and parity as fixed effects. Competing requirement estimation models were: quadratic polynomial (QP), broken-line linear (BLL), and broken-line quadratic (BLQ) using PROC NLMIXED. Models that differed in their bayesian information criterion values by at least 2 points were considered to have meaningful differences in their data fit. The best-fit model was based on the best BIC value. As the SID Thr:Lys ratio increased, there was a quadratic response on ADFI (4.73, 4.57, 4.67, 4.55, and 4.60 kg/d; P = 0.001) and percent of sow body weight loss (-6.44, -7.89, -7.35, -6.19, and -5.81; P = 0.004). In addition, there was a trend for wean to estrus interval to be affected by the ratio (5.42, 4.42, 4.55, 4.46, and 4.84; P = 0.07). Daily litter gain was also quadratically improved as the SID Thr:Lys ratio increased (2.67, 2.67, 2.78, 2.77, and 2.68 kg/d; P value = 0.001). For daily litter gain, the BLQ model was determined to be the best fit with an estimated SID Thr:Lys requirement of 65%. In conclusion, the optimal SID Thr:Lys ratio for litter growth is 65.