GROWTH-RESPONSE, SEXUAL DEVELOPMENT, CARCASS AND MEAT QUALITY OF ZINCTANNATE TREATED BULLS

Effects of intratesticularly administered zinc tannate (ZT) on growth performance, sexual development, slaughter, carcass and meat quality c haracteristics of young bull calves (approximately 225 kg, 7 months ol d) were investigated. Comparisons were made across a three (treatments : ZT animals, intact bulls and burdizzo-castrated steers) by two (slau ghter masses: 350 and 440 kg) factorial arrangement. In a separate tri al, sexual male behaviour Of ZT animals was compared to that of bulls, surgically- and burdizzo-castrated animals. Bulls (B) and ZT animals gained mass faster (P < 0.05) and more efficiently (P < 0.05) and prod uced carcasses with less total fat (P < 0.05) and more muscle (P < 0.0 5) than steers (S). These differences coincided with higher plasma tes tosterone levels (P < 0.05) in the B and ZT animals in comparison with that of steers. However, higher relative mass and meat distribution i n the forequarters, lower meat quality (tenderness) and persistent bul l-like behaviour of ZT animals were detrimental. These characteristics could also be ascribed to retained testosterone production. ZT admini stration caused excessive swelling of the testes and necrosis of the t estis parenchyma, especially in the direct vicinity of application. No live sperm could be detected 30 days after application of ZT. Suffici ent Leydig cells were left intact, however, to maintain plasma testost erone levels comparable to that of bulls (P > 0.05). Signs of pain and discomfort were observed directly after treatment with ZT. The study of the behaviour of ZT animals in a feedlot, indicated that they persi sted with bulling and mounting behaviour normally associated with inta ct animals. Although ZT offers positive growth response and therefore seems to be a promising alternative to surgical or burdizzo castration , the negative side-effects hamper its further development.