Effects of exogenous melatonin on the postweaning immune response and growth performance of crossbred beef calves

Objective

Our objective was to evaluate the effects of exogenous melatonin on the immune response and growth performance of beef calves during a vaccination series at weaning.

Materials and Methods

Crossbred beef calves (n = 48, initial BW = 176 ± 21.7 kg) were enrolled in a completely randomized design with a 2 × 2 factorial arrangement of treatments: vaccinated with 0.5 mg of ovalbumin (d 0 and 21) or not, and a 24-mg injection of melatonin (d 0 and 21) or not. Treatments were placebo injections only (CON), vaccination only (VAC), melatonin only (MEL), and both melatonin and vaccination (MVAC). Calves were weaned on d 0 and fed for 63 d. Calf BW and blood samples were collected on d 0, 2, 4, 8, 21, 42, and 63.

Results and Discussion

On d 8, MEL-treated calves had a greater percentage of cells performing oxidative burst and a greater percentage of cells performing phagocytosis, and these were at a greater intensity. On d 21, MEL-treated calves also had greater burst intensity than other treatments. Melatonin alone may bolster the innate immune response. Anti-ovalbumin IgG response was different on d 63, where MVAC calves had greater circulating anti-ovalbumin IgG compared with VAC calves. Calves who received VAC treatment had greater DMI than calves who received MVAC, and MVAC-treated calves tended to have a greater G:F than VAC calves. The administration of melatonin at the time of vaccination resulted in greater feed conversion and greater IgG than VAC alone.

Implications and Applications

Melatonin may bolster the immune response of calves at weaning and improve feed conversion, incentivizing its adoption as a management protocol.