Effects of immunocastration on the nutrient responses, carcass traits and meat quality of growing pigs (Sus crofa domesticus)

[摘要] ENGLISH ABSTRACT: Increased consumer awareness has motivated the industry to find alternative methods to surgical castration for controlling boar taint and aggression in male pigs. Immunocastration has been identified as a solution, however; little research has been done into the nutritional requirements of immunocastrated pigs. Thus the objective of this study was to determine the optimal protein levels for immunocastrated pigs with regards to growth performance, carcass traits and yields as well as meat quality when supplemented with or without ractopamine hydrochloride (RAC).The study involved 120 male pigs following a 2 x 2 x 3 factorial design. The main effects evaluated were sex (immunocastrated versus entire), RAC supplementation (0 versus 10 mg/kg and dietary balanced protein level (7.50 {low}, 9.79 {medium} and 12.07 {high} g lysine/kg). Vaccination occurred at 16 and 20 weeks of age and from 20 weeks each pig was allocated to one of the balanced protein diets with RAC supplementation at either 0 or 10 mg/kg for the last 28 days of growth. Slaughtering occurred at 24 weeks at which time carcass traits were measured and carcasses were processed, commercial cuts were weighed, deboned and trimmed into muscle, bone and fat portions which were then weighed individually.Immunocastration increased the average daily gain, average daily feed intake, feed conversion ratio (FCR) and backfat deposition after the second vaccination. The FCR was improved by RAC supplementation, with the best FCRs seen at the medium and high balanced protein diets. Immunocastration and RAC increased live weight at slaughter and calliper backfat thickness but no differences were seen for the dressed hot carcass weight or Hennessey Grading Probe backfat thickness. Supplementation of RAC increased the percentage of the hot carcass weight, comprising of the shoulder, hindquarter, loin and belly, as well as the shoulder muscle, hindquarter muscle and loin muscle percentages, while decreasing the fat percentage of the belly and hindquarter.Chemical composition analysis of the Longissimus thoracis (LT) muscle indicated differences (p ≤ 0.05) for crude protein content but they were considered biologically negligible. The cooking loss of the LT was decreased by immunocastration and feeding medium protein. Feeding RAC decreased the a* and b* colour values and increased the Warner Bratzler shear force (WBSF) values, resulting in less red and less tender meat. Entire males fed low dietary protein had the lowest L* values, while entire males fed medium protein diets had the highest L* values. Immunocastrates fed the low protein diet had the most tender meat, whereas immunocastrates fed the high protein diet had the least tender meat. Immunocastration decreased the androstenone levels to below 0.5 μg/g fat and although it did not significantly affect the testicle size, it influenced the morphology and increased the lightness (L*), yellowness (b*) and decreased the redness (a*) of the testicle's cut surface colour.The results from this study indicated that the balanced dietary protein requirements for immunocastrates differ both with and without RAC supplementation and thus the correct dietary protein level needs to be provided so that growth performance and leanness is not compromised. The return per carcass can also be improved by supplementing RAC, owing to improved cutting yields and lean yields of carcasses. Together, immunocastration, RAC supplementation and the correct balanced protein diet may allow pig producers to efficiently produce heavier male carcasses without boar taint while conforming to the animal welfare expectations of the consumer. However, an incentive for producers in terms of immunocastration needs to be provided by the possible modification of the current carcass classification system so that heavier immunocastrated male carcasses are not penalised.

[发布机构] Stellenbosch University