IMMUNIZATION OF GOAT BUCKS AGAINST GNRH TO PREVENT SEASONAL REPRODUCTIVE AND AGONISTIC BEHAVIOR

The study was designed to test the efficacy of a commercially availabl e vaccine, Vaxstrate(R) (Arthur Webster Pty Ltd, Castle Hill, N.S.W.), to immunise adult male goats against GnRH. The general hypothesis tes ted was that immunisation of goats against GnRH using Vaxstrate(R) wou ld suppress gonadotrophin secretion, steroidogenesis and gametogenesis in the testis, production of male odour and agonistic behaviour betwe en males. We also compared intervals of 2 and 4 weeks between primary and booster immunisations and monitored recovery from immunisation for approximately 1 year. Twenty bucks of feral origin obtained from a co mmercial feedlotter were allocated to one of four treatment groups (n = 5): entire control (intact non-immunised bucks); Vaxstrate 2 (immuni sed with 1 mi of Vaxstrate(R) on Days 0 and 14); Vaxstrate 4 (immunise d with 1 mi of Vaxstrate(R) on Days 0 and 28); and castrate control (s urgical castration on Day 0). The level of immunity against GnRH was s ignificantly elevated (P < 0.01) 14 days following the booster immunis ation compared with pre-treatment levels in both Vaxstrate 2 and Vaxst rate 4 treatments. Immunisation prevented the seasonal increase in LH and testosterone concentration seen in entire bucks, and resulted in l ower concentrations of these hormones and FSH in vaccinated bucks from Day 28 (P < 0.001). Scrotal circumference of immunised bucks was smal ler than entire bucks from Day 56(P < 0.05). Bucks in the Vaxstrate 2 and Vaxtrate 4 treatments had lower(P < 0.01) odour scores than entire controls from Day 42 and 56 respectively. Numbers of spermatozoa ml(- 1) were lower in immunised than entire bucks at Days 175 and 329 (P < 0.05 and P < 0.01 respectively). Agonist confrontations recorded at Da y 64 in vaccinated bucks appeared to be intermediate between that of s urgically castrate animals and entire bucks. The results have shown im munisation against GnRH in goats is effective in suppressing the incre ase in testes size, male odour and agonistic behaviour that is associa ted with the seasonal breeding season. Immunisation against GnRH was s uccessful in all goats and in 90% of goats the testes remained small f or more than a year following primary immunisation. In this experiment , a 2 week interval was as effective as a 4 week interval between prim ary and booster immunisations.