The Impact of Dietary SID Trp:Lys on Growth Performance of Nursery Pigs.

The current NRC recommended SID tryptophan-to-lysine ratio (Trp:Lys) for nursery pigs is 0.17 (NRC, 2012). However, studies in both high-health and health-challenged pigs have reported performance advantages with Trp:Lys from 0.20 to 0.26. Therefore, the objective of this experiment was to evaluate the impact of varying SID Trp:Lys on growth performance of nursery pigs. There were 5 dietary treatments with 9 pens (90 pigs) per treatment. Pigs were fed a common diet from d 0 to 7. The five dietary treatments with titrated SID Trp:Lys (0.150, 0.175, 0.200, 0.225, and 0.250) were fed from d 7 to 35 in 2 two-week dietary phases. Pigs were individually weighed, and feed remaining in feeders was weighed on d 0, 7, 14, 21, 28 and 35. Data were analyzed using PROC MIXED of SAS with block as a random effect. Pen was the experimental unit. Incremental body weight and the corresponding rate of gain and feed efficiency were analyzed as repeated measures. For each variable, normal distribution of residuals was tested using PROC UNIVARIATE. Determination of the optimal SID Trp:Lys of the 5 dietary treatment least squared means were analyzed using PROC REG for linear, quadratic, and broken line models. PROC NILN was utilized for exponential regression analysis. Over the entire experiment increasing Trp:Lys resulted in increased ADG (P = 0.002), decreased ADFI (P = 0.023), improved gain to feed ratio (P = 0.008), and increased BW exiting the nursery (d 35; P = 0.007). The relationship between Trp:Lys and overall G/F tended to be significant when fitted to an exponential curve (Figure 3; P = 0.061), but not a linear, quadratic, or broken line curve (P ≥ 0.244). These data indicate that there is no advantage in growth performance and feed efficiency to having a diet containing a SID Trp:Lys greater than 0.175 for nursery pigs. These data are supportive of the 0.17 Trp:Lys ratio specified by the NRC.

Least square means for SID Trp:Lys in nursery pigs

Item	SID Trp:Lys					Pooled SEM		P value
	0.150	0.175	0.200	0.225	0.250
ADG, kg	0.338	0.372	0.356	0.332	0.364	0.013	0.002
ADFI, kg	0.510	0.539	0.531	0.491	0.529	0.021	0.023
Gain/Feed	0.661	0.691	0.680	0.676	0.688	0.006	0.008