Combined effects of supplementation of amino acids and immunocastration in first antler growth of farmed fallow deer (Dama dama)

Context. Amino acid supplementation and immunocastration are two husbandry practices with an increasing interest in the worldwide growing industry of deer farming. Amino acids (AAs) optimise nutrition and feed costs and improve the quality of products such as venison, velvet or antlers. Immunocastration (IC) reduces agonistic behaviours, which produce carcass damage and reduced growth. Thus, both treatments have positive effects on body growth, but may interfere with hormonal regulation, subsequently affecting antler growth. Aims. This study aimed to evaluate the combined use of both practices and their impact on body and antler growth. Methods. Forty-four yearling male fallow deer, approximate 10 months old, were subjected to the following four combinations based on both treatments: control-control, AA-control, IC-control, and AA-IC. Immunocastration treatment started in March 2020 and was repeated after 50 and 130 days. All groups received 250 g per animal and day of grains, and those under AA supplementation received ruminally protected lysine 6.3 g and ruminally protected methionine 2.1 g per animal and day. Biometric data, antlers and metatarsus were collected at slaughter in November. Antlers and metatarsus were analysed through computer-tomography scanning and mineral spectrometry. Key results. Supplementation of AAs scarcely affected antler growth, although an indirect effect through improved body condition cannot be rejected. Immunocastration showed significant but not dramatic effects: IC animals had lighter antlers, with a lower amount of cortical bone and less mineralisation (density and calcium and phosphorus concentrations) in the base of the antler than did control animals. In contrast, the effects were scarce at the top of the antler and the metatarsus. Conclusions. The results suggest a reduction but not total suppression of testosterone, with almost negligible effects on body growth and internal bones, thus not raising animal welfare issues. Implications. Both techniques can be used simultaneously in deer farming, especially in farms with venison-production goals. Future research should focus on optimising the vaccination schedule for the main farmed deer species to ensure that the welfare benefits are well balanced with productivity.