Shortening the immunocastration-to-slaughter interval from 3 to 2 weeks reduced carcass backfat and weight, increased sexual behaviour and carcass skin blemishes in group-housed male pigs sold at fixed age

Abstract

Context Pig producers require strategies to temporarily slow growth rate, particularly when markets impose penalties on over-weight and fat carcasses. Immunocastrated pigs usually have higher feed intakes (e.g. during the 3–5-week immunocastration-to-slaughter interval, which is commonly used in Australian pig industry), resulting in higher carcass weight and backfat thickness. Shortening the immunocastration-to-slaughter interval by delaying the second vaccination by a week may be a fine-tuned strategy to reduce carcass backfat and weight of male pigs. However, postponing the age receiving immunocastration as a method to achieve a shorter immunocastration-to-slaughter interval may increase aggressive and sexual behaviours of pigs. Aims The experiment aimed to quantify the effects of shortening the interval between the second dose of immunocastration and slaughter from 3 weeks to 2 weeks on growth performance, carcass traits, aggressive and sexual behaviours, and carcass skin blemishes in group-housed male finisher pigs slaughtered at a fixed age. Methods Pigs (n = 58 pens; 45 pigs per pen) were selected into the experiment at 16 weeks of age. Half of the pens received the second anti-GnRH vaccine (V2) as a means of immunocastration at 19 weeks (a common immunocastration age used in Australian pig industry; control group), and the remaining half of the pens received V2 at 20 weeks of age. All the pigs were slaughtered at 22 weeks of age. Growth performance was recorded between 16 and 22 weeks of age. Behavioural observation was conducted at 20 and 21 weeks of age. Carcass weight, backfat thickness and severity of skin blemishes on carcasses were recorded in the abattoir. Key results Results showed that shortening the immunocastration-to-slaughter interval from 3 to 2 weeks reduced average daily feed intake by 9%, growth rate by 8%, carcass weight by 3%, and backfat thickness by 7% (all P < 0.05), but the percentage of pigs that displayed sexual behaviour and carcasses with >25 lesions both increased (both P < 0.05). Conclusions Shortening the immunocastration-to-slaughter interval from 3 to 2 weeks by delaying V2 is an effective strategy to reduce feed intake, growth rate, carcass weight and backfat in group-housed male pigs, but at a risk of increasing carcass skin blemishes. Implications The increased sexual behaviour and carcass skin blemishes will need to be managed when using a shortened immunocastration-to-slaughter interval to temporarily reduce carcass weight and backfat.