Effects of Standardized Ileal Digestible Histidine:Lysine Ratio on Growth Performance of 7 to 11 Kg Pigs

An experiment was conducted to determine the standardized ileal digestible (SID) His:Lys ratio requirement for 7 to 11 kg pigs. A total of 360 pigs (DNA 600×241, initially 7.1±0.31 kg BW) were fed experimental diets for 10 d with 12 replicates and 5 pigs per pen. Pens were blocked by weight and assigned in a randomized complete block design to 1 of 6 dietary treatments containing 24, 28, 32, 36, 40, or 44% SID His:Lys. Dietary SID Lys was 1.25% and all other AA met or exceeded the NRC (2012) requirement estimates. Diets were corn, spray-dried whey, and whey protein concentrate-based and treatments were formed by adding crystalline L-His at the expense of corn. Response variables ADG, ADFI, and G:F were fitted using general linear and nonlinear mixed models with heterogeneous variances and pen as the experimental unit. Competing models included quadratic polynomial, broken-line linear, and broken-line quadratic. For each response variable, the best fitting model was selected based on Bayesian Information Criterion. Increasing the His:Lys resulted in quadratic increases (P < 0.01) in ADG, ADFI, and G:F. The best fitting model for the three response variables was the broken-line linear. For ADG, the requirement was estimated at 29.7% SID His:Lys (95% CI: 27.8 to 31.6). For ADFI, the breakpoint occurred at 29.1% SID His:Lys (95% CI: 27.6 to 30.6). The maximum G:F was obtained at 29.8% SID His:Lys (95% CI: 27.6 to 32.1). In conclusion, the estimated SID His:Lys requirement for 7 to 11 kg pigs ranged from 29.1% to 29.8%.

	SID His:Lys, %
	24	28	32	36	40	44	SEM
BW d 0	7.1	7.1	7.1	7.1	7.1	7.1	0.306
BW d 101	10.3	11.3	11.8	11.8	11.5	11.7	0.415
ADG, g1	327	423	469	474	448	462	15.16
ADFI, g1	463	541	570	572	567	566	19.59
G:F1	0.709	0.782	0.826	0.829	0.791	0.818	0.013
1 Quadratic, P < 0.01