Effect of antimicrobial peptides on the productive performance and serum antioxidant capacity of Holstein bulls

We aimed to investigate the effect of adding antimicrobial peptides to the diet of Holstein bulls on their production performance and serum antioxidant properties during the fattening period. We selected 12 healthy Holstein bulls for the experiment and randomly divided them into two groups. The bulls were 10 months old and weighed (345.19 ± 3.89) kg. The control group (CK group) was fed a basal diet, and the antimicrobial peptide group (AP group) was supplemented with 8 g·d⁻¹ antimicrobial peptide in the basal diet of each bull. The test period was 270 d, and weighing was performed every 30 d. Blood was collected intravenously at the end of the experimental period to determine blood physiological and antioxidant indices. Carcass traits and muscle nutrient content were evaluated after slaughter to determine slaughter performance. The results showed that: 1) The final body weight was significantly higher, and the gain-to-feed ratio was significantly lower in the AP group compared to the CK group. 2) The percentage of monocytes, mean corpuscular hemoglobin concentration, superoxide dismutase, catalase, glutathione peroxidase, glutathione transferase, and total antioxidant capacity increased significantly in the AP group compared to the CK group. Conversely, malondialdehyde and reactive oxygen species decreased significantly. 3) Pre-slaughter live weight, meat weight, bone weight, hot carcass weight, 72 h cold carcass weight and subcutaneous fat coverage, high-grade and high-quality meat weight, crude fat, and crude protein contents in the AP group were significantly higher than those in the CK group, whereas moisture and crude ash were significantly lower. In conclusion, adding antimicrobial peptides to the diet could improve the growth performance, slaughter performance, and carcass traits of Holstein bulls, enhance antioxidant function, increase the content of muscle nutrients, and improve muscle quality.