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.

Two studies were conducted to determine the impact of an absorption enhancer containing a combination of lysophospholipids, monoglycerides and synthetic emulsifiers (LEX) on apparent ileal digestibility, metabolizable energy (ME), and growth performance of growing pigs. In the digestibility study, 12 male crossbred [Duroc x (Large White x Landrace)] pigs with an initial body weight (BW) of 30 kg were randomly allocated to two dietary treatments: (1) a positive control (PC) receiving standard diets formulated to 3100 kcal ME/kg, and (2) a negative control formulated with −100 kcal ME/kg and −2.5% AA content vs. PC and supplemented with LEX at 500 g/t. Apparent ileal digestibility of essential AA was significantly increased for lysine, methionine, threonine, histidine, isoleucine and phenylalanine in the LEX treatment (p < 0.05). Average uplift in AA digestibility as a percent of the PC was +1.88%; with greatest improvement for histidine (+4.22%). LEX supplementation effectively compensated energy deficiency of low-density diet and provided additional ME improvement compared to the PC diet (p < 0.05). A second study was conducted to evaluate LEX dose response on the growth performance of pigs fed a low nutrient density diet. Total 450 cross-bred pigs (240 males (castrated) and 210 females) [Duroc x (Large White x Landrace)] with an average initial BW of 7.19 kg were randomly allocated into 4 dietary treatments: (1) a positive control (PC) formulated with standard specifications, (2) a negative control formulated with −100 kcal ME/kg and −2.5% AA content vs. the PC (NC), (3) NC + LEX at 250 g/t (NC + 250) and (4) NC + LEX at 500 g/t (NC + 500). Results showed significant improvement with LEX supplementation on the final BW, average daily gain (ADG) and feed conversion ratio (FCR) of pigs of >50 kg body weight. Across the study, NC + 500 significantly increased ADG vs. PC and NC, and significantly reduced FCR compared to all other treatments. FCR of negative control diets improved by 9 and 15 points with the supplementation of 250 g/t and 500 g/t of LEX, respectively (p < 0.05). FCR in the NC + 250 diet was statistically similar vs. PC, which was significantly reduced compared to the NC. Taken together, these studies demonstrate that the addition of an absorption enhancer containing a combination of lysophospholipids, monoglycerides and synthetic emulsifiers can improve growth performance in growing pigs, driven by increased nutrient digestibility and retention.