Influence of immunisation against GnRF on agonistic and mounting behaviour, serum testosterone concentration and body weight in male pigs compared with boars and barrows

Abstract

The aim of the present study was to assess the effects of vaccination against boar taint on testosterone levels, body weight and behaviour in male fattening pigs when compared with boars and barrows. The study was carried out in two replicates over time. Pigs were allocated to fattening pens according to treatment group (immunised males (IM), castrated males (CM), entire males (EM)) with 10 and 13 pigs per pen in batches one and two, respectively. IM pigs were vaccinated twice with Improvac™ according to manufacturer's instructions (first injection was given on the day of entry to the fattening unit, second injection was performed when pigs had an average weight of 76.6kg and 80.4kg in the two replicates over time, respectively). During fattening, pigs were videotaped twice (test periods one and two) for a consecutive period of 96h during each test period and blood samples were taken. Live weight measurements were conducted on a weekly basis. Before second vaccination was given (test period one), IM pigs had serum testosterone levels comparable to those of entire boars. Two weeks after second Improvac™-injection (test period two) testosterone levels of IM pigs decreased significantly (p<0.05). Agonistic as well as mounting behaviour of IM pigs was comparable to the behaviour of EM pigs during test period one. Two weeks after second Improvac™-injection fight time as well as fight duration decreased significantly (p<0.05) in the Improvac™-treated group to levels comparable to those of CM pigs, whereas both parameters remained on high levels in EM pigs. The number of fights, however, appeared not to be affected by vaccination with Improvac™, as IM and EM pigs revealed higher numbers than CM pigs during both test periods. IM and EM pigs showed comparable numbers of mountings as well as mounting time and mounting duration during test period one. Second Improvac™-injection was followed by a significant decrease in all three parameters in IM pigs (p<0.05). When compared with the other treatment groups CM pigs performed least agonistic and mounting behaviour during both test periods. IM and EM pigs performed significantly more manipulatory behaviour than CM pigs before second Improvac™-injection is given. During test period two EM showed more manipulatory behaviour than CM pigs with IM pigs in between. From our results we conclude that immunisation against 49 GnRH has the potential to reduce agonistic as well as mounting behaviour in male fattening pigs to very low levels which may result in improved animal welfare when compared with fattening of entire boars.