Effects of castration and eucalyptus oil supplementation on growth performance, nutrient digestibility, and blood immunity indicators of male Holstein calves

The purpose of this study was to investigate the effects of early castration and eucalyptus oil (EUC) supplementation on dry matter intake (DMI), growth performance and immune response of Holstein calves. Fifty-six Holstein male calves at the age of 52 d (initial body weight [BW], 63.5 ± 5.27 kg) were used. The animals were blocked by BW and randomly assigned into 1 of the 4 treatments in a randomized complete block design with a 2 (no castration vs. castration) × 2 (without vs. with EUC) factorial arrangement of treatments. The treatments were: uncastrated calves fed without EUC (CON), and with 0.5 g/d EUC (EUC), or castrated steers fed without EUC (Castrated), and with 0.5 g/d EUC (Castrated + EUC). The experiment was 8 weeks long including pre-weaning and post-weaning (weaned at the age of d 72). The EUC × Castration interactions were not significant for DMI, growth performance, nutrient digestibility and immune response. The castration did not affect the DMI, final BW, average daily gain (ADG) or feed efficiency, except that the ADG was greater for uncastrated than castrated steers at post-weaning. Supplementation of EUC increased DMI pre-weaning and post-weaning, and increased ADG of weaned calves. Digestibility in the total digestive tract was not affected by castration (except for organic matter digestibility), whereas adding EUC improved the digestibility of DM, acid detergent fiber and crude protein. Blood concentration of interleukin-6 at d 94 was decreased by feeding EUC. These results indicate that the EUC could be fed to either intact or castrated dairy calves to promote growth and health post-weaning; the castration before weaning may reduce ADG and cause inflammatory stress without affecting feed intake or feed efficiency.