Effect of Low Protein Diets with or without Supplemented Synthetic Amino Acids on Growth Performance of Nursery Pigs

Feeding low protein diets supplemented with crystalline (CAA) and branched chain amino acids (BCAA) may be an economical and easily integrated solution to improve growth performance in nursery pigs. The objective for the first experiment was to determine what level of dietary crude protein (CP) elicits unfavorable physiological and behavioral responses in nursery pigs. A total of 37 weaned pigs (35 days old) were weight matched (8.41 ± 0.14kg), housed individually and randomly assigned into three diets with different levels of CP: 24% (control; n=12), 18% (n=12) and 12% (n=13). Pigs were fed ad libitum and the control diet met all nutrient requirements (NRC ,1998). Throughout the 4-week period, feed intake (FI) was recorded daily and body weight (BW) was measured weekly. Data was analyzed using MIXED model in SPSS^® v.23 with diet, time and the interaction of diet and time as fixed effects and animal as a random effect. The BW was not significant between the control and 18% diets, but 12% diet significantly decreased in BW after week 3 (P < 0.03). Compared to the control, pigs fed 12% decreased FI after day 17 continuing throughout the trial. The second experiments objective was to determine if supplementing CAA and BCAA to a low protein diet (12% CP) would combat the negative effects of low protein diets on energy balance, thus improving performance. A total of 24 nursery pigs (28 days old) were weight matched (8.36 ± 0.34kg), housed individually and allotted into either the 24% CP (control), 12% CP plus the CAA (12+C) and 12% CP plus CAA and BCAA (12+B&C) diets (n=8/ group). FI and BW data were recorded and analyzed consistent with the first experiment. Blood samples were collected on the 4-week of the trial via the jugular vein. Interestingly, compared to the control, 12+B&C showed no significant decrease in BW and FI, until 2-week of the trial. Whereas 12+CAA, which decreased in FI after day 8 and BW after day 11 of the study. After the 2-week point, both 12+C and 12+B&C, exhibited a significantly lower BW and FI, when compared to the control (P < 0.004). Interleukin 12 concentration, a pro-inflammatory cytokine, significantly increased in 12+CAA, while 12+B&C did not significantly differ between control and 12+CAA. In conclusion, 12+B&C diet delayed the onset of negative physiological and behavioral responses compared to 12+CAA, but the supplementation for each treatment did not completely reverse these unwanted responses.