Abstract A total of 450 newly weaned pigs (PIC 800 x 1050, PIC, Hendersonville, TN) were used to evaluate the dietary SID Phe:Lys requirement in nursery pigs. Pigs were sorted into pens (5 barrows and 5 gilts each (10 pigs/pen)). Seven days after arrival pigs were blocked by body weight (5.73 ± 0.03 kg) and randomly assigned to one of six diets (0.330, 0.394, 0.458, 0.522, 0.586, 0.650 SID Phe:Lys). All pigs received a common medicated starter diet from day 0-7. Experimental diets were fed in two phases: 7-21 days and 21-28 days. Diets were isonitrogenous, isocaloric, and deficient in lysine (SID Lys 1.25 and 1.14%, respectively) with balanced dietary electrolytes. All other nutrients met or exceeded NRC (2012) dietary recommendations. Pen and feeder weights were recorded on day 7, 21, and 28 to calculate average daily gain (ADG), average daily feed intake (ADFI), and gain to feed (GF). Data were analyzed using polynomial contrasts based on equally spaced treatments in R (v4.4.1) with significance at P ≤ 0.05. Pen was the experimental unit, and block was treated as a fixed effect. Feeding SID Phe:Lys ratio of 0.65 maximized the ADG and GF during the trial period, while the SID Phe:Lys level of 0.586 maximized the overall ADFI. Similarly, on day 28 BW of pigs increased quadratically (P 0.001) as SID Phe:Lys increased and the pigs with the greatest BW were fed a SID Phe:Lys ratio of 0.65. Breakpoint analysis was done with multiple model types; however, the broken line quadratic (BLQ) was used to estimate the requirement as it had the best fit based on the BIC value. The breakpoint for overall ADG was estimated to be 0.516 (95% CI 0.488, 0.544). The overall ADFI breakpoint was estimated to be 0.534 (95% CI 0.496, 0.571). The overall G:F breakpoint was estimated at 0.497 (95% CI 0.467, 0.528). Based upon these data, the Phe:Lys requirement for nursery pigs is 0.516 for ADG, 0.534 for ADFI and 0.497 for G:F.
Craig et al. (Wed,) studied this question.