Optimizing the ratios of standardized ileal digestible (SID) methionine plus SID cystine and SID threonine to SID lysine in low-protein diets for working boars

This study aimed to optimize the ratios of standardized ileal digestible (SID) methionine (Met) plus cystine (Cys), and threonine (Thr) to SID lysine (Lys) in low-protein diets for working boars. Forty-eight working Duroc boars were randomly allocated to one of 12 dietary treatments in a 3x4 factorial experimental design in which factor 1 was the ratios of SID Met plus Cys to SID Lys (50, 60, 70%), factor 2 was the ratios of SID Thr to SID Lys (40, 50, 60, 70%). Semen was collected at a 4 days interval for 6 weeks for 10 ejaculates. Semen volume (V), percentage of sperm with progressive motility (A), sperm concentration (C), and the total number of motile sperm per ejaculate (VAC) were measured. The results of the study revealed that the ratios of SID Met plus Cys to SID Lys in the diets affected the C and VAC. Values of C and VAC were highest at the ratios of SID Met plus Cys to SID Lys of 70% and lowest at 50% (P<0.05). Similarly, the ratios of SID Thr to SID Lys affected the C and VAC. Further, the values of C and VAC were highest at the ratio of SID Thr to SID Lys of 60% and lowest at 40% (P<0.05). There was no interaction effect between the two factors. In conclusion, the ratios of SID Met plus Cys to SID Lys of 70% and SID Thr to SID Lys of 60% in a 13.5% CP diet are optimal for working boars.