The effects of immuno- and surgical-castration on the behaviour and consequently growth of group-housed, male finisher pigs

Abstract

An experiment was conducted to compare behaviour, in particular social and feeding behaviour, and consequently growth performance of group-housed entire and castrated male pigs during the finisher stage of production. Three treatments: (1) entire males, (2) immuno-castrated males, treated with Improvac^® at 14 and 18 weeks of age, and (3) surgically-castrated males, castrated at 14-days old, were compared to assess whether castration affected feeding and social behaviours. Twelve groups of 15 male pigs were formed at 14 weeks of age (47.1±5.50 kg). Pigs had ad libitum access to pelleted, commercial feed from two single space feeders per pen. Pig behaviour and feeder utilisation were compared during 24-h periods at 17 and 21 weeks of age, using time-lapse video recording. At 17 weeks, entire males and immuno-castrated males were more active (P<0.05) than surgical-castrated males (21.9, 19.8 and 16.1% of 24 h), but at 21 weeks there were no differences among the treatments (pooled mean 16.4% of 24 h). As expected, social behaviour at 17 weeks was greater (P<0.01) for entire males and immuno-castrated than surgical-castrated males (3.8, 1.8 and 0.1% of 24 h), but not at 21 weeks, when it was greater (P<0.01) for entire males than immuno- and surgical-castrated males (1.8, 0.5 and 0.4% of 24 h). While the mean time pigs spent in the feeders at 17 weeks did not differ among the treatments (100 min/pig/24 h), at 21 weeks entire males spent less time (P<0.05) in the feeders (76 min/pig/24 h) than immuno- and surgical-castrated males (110 and 107 min, respectively). On both the observation occasions, the “sexually-active” treatments (entire males and immuno-castrated males at 17 weeks and entire males at 21 weeks of age) on average allocated about one-third of active time to feeding, whereas castrated males spent almost one-half of active time in the feeder, assumed to represent feeding behaviour (P<0.05). At 23 weeks, there was a trend for entire males to be lighter (P=0.061) than immuno-castrated males, with surgical-castrated males in between (102.3, 108.9 and 103.9 kg). Thus, castration reduced social behaviour and increased feeding behaviour in group-housed finisher pigs. The results of the experiment also suggest that the social and feeding behaviours of immuno-castrated males at 21 weeks were similar to surgically-castrated males.

Introduction

Until recently, Australia was one of only a few pork-producing countries that did not routinely castrate male grower or finisher pigs (Moore, 2001). Indeed, the Australian Model Code of Practice for the Welfare of Pigs reflects this situation and currently recommends that (surgical) castration should be avoided wherever possible (Anon., 1998). However, with the increase in exports of Australian pork to the Asian region, to markets that have a strong preference for meat from gilts and barrows (surgically-castrated male pigs), some Australian farmers have reverted to surgical castration of male pigs (Higgins and Cutler, 1999). Surgical castration of male pigs typically occurs when pigs are about 14-days old. A consequence of the procedure is increased body fat content and reduced growth performance (Campbell and Taverner, 1988, Dunshea et al., 1993). A relatively new technology, immuno-castration, has been developed and involves using a vaccine (Improvac^®, CSL Ltd., Parkville, Vic., Australia) against gonadotrophin-releasing hormone (GnRH) to chemically “castrate” male pigs in the latter stage of the finisher phase of production, thereby eliminating the need for surgical removal of the testes (Dunshea et al., 2001). Blocking GnRH release from the hypothalamus with a vaccine inhibits production of luteinising hormone (LH) and follicle stimulating hormone (FSH) by the pituitary gland and prevents testicular development; this effectively castrates the pigs at around 18 weeks of age, after they have had the benefit of growing as entire males to that point.

The nutritional requirements for efficient growth, and the characteristics of feeding behaviour, of individually-housed surgical castrates and entire males are quite well understood (see Campbell and Taverner, 1988, Quiniou et al., 1999). Commercial growing pigs, however, are housed in groups and do not grow as fast and, or as efficiently as expected, compared to their individually-housed counterparts. Clearly, group housing introduces additional variables including stocking density/space allowance, group size and social behaviour. Further, towards the end of the finisher phase of growth, entire males in groups often grow slower than castrates (Patterson, 1985, De Haer and Merks, 1992, De Haer and de Vries, 1993), possibly due to increased sexual activity (courting behaviour and mounting events) and aggression between males; these behaviours are controlled by endocrine factors (Gray, 1971). Thus, the use of a non-surgical method for castration of males late in the growth phase of production may improve the efficiency of growth by reducing undesirable male characteristics that limit growth.

The objectives of this experiment were to record the behaviour of group-housed, male pigs over 24-h periods towards the end of the growth phase of production to examine whether castration per se affected: (1) the animal’s time budget in relation to feeding behaviour and activity, and (2) social behaviour. The hypothesis tested was that castration decreases the time group-housed, male pigs allocate to social behaviour and increases the time allocated to feeding behaviour. Two alternative methods of castration were compared: traditional surgical castration and the new technology of immuno-castration.