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The effects of immunocastration on the carcass quality and nutrient 
responses of growing pigs (Sus scrofa domesticus)

Tersia Needham MSc Agric
Increased consumer awareness is placing pressure on various aspects of pork production, especially with regards to animal welfare. Therefore pig producers are facing new challenges in terms of management practices, one of which is controlling the prevalence of boar taint without the use of surgical castration in response to the banning of surgical castration without anaesthesia in numerous countries. Boar taint is an offensive smell and taste in pork, caused by the male pheromone androstenone as well as skatole and indole which accumulate in the adipose tissue and decrease the eating quality of the pork.Although the production of intact male pigs is favourable in terms of feed efficiency and lean growth, the production of heavy male carcasses increases the risk of boar taint and thus heavy entire male carcasses are currently penalised. This resulted in the slaughtering of male pigs before puberty and sexual maturity and thus small carcasses with narrow profit margins. In order to produce larger male carcasses while controlling boar taint without the use of surgical castration, immunological castration can be used and has thus received increased attention in the pig industry and pig research. Immunocastration involves immunising the animal against its own gonadotrophin releasing hormone, using products such an Improvac® (ZoetisTM Animal Health), in order to arrest testicular development and functioning.

Currently, there is a substantial body of literature on the effects of immunocastration which include behaviour, hormone levels, growth, and vaccination schedule amongst others. However, few studies have addressed the issue of how immunocastration affects the nutrient responses of immunocastrates, especially in terms of balanced protein. Since feed (dietary protein in particular) contributes to a large proportion of pig production expenses, the provision of correct nutrition for favourable growth and carcass characteristics is of utmost importance. In order to fully exploit the nutrients provided, feed additives such as ractopamine hydrochloride (RAC) have been shown to improve growth performance parameters, carcass.

traits and carcass cutting yields. Thus the need to determine the nutrient requirements of immunocastrated male pigs with and without feed additives such as RAC was identified.
The main objective of the study was thus to establish optimal balanced protein levels for immunocastrates, with and without RAC, in terms of their growth performance and carcass characteristics and yields using a feeding and slaughter trial. The secondary objective was to measure the effect of RAC on the growth, fatness and meat quality of immunocastrates and lastly, to further investigate the influence of immunocastration on the reproductive functioning of the testicles using size measurements and histology. The study involved 120 male pigs and 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 (~ 100 kg hot carcass weight) 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. The loin (Longissimus thoracis) muscle was analysed for its chemical composition as well as standard instrumental meat quality tests. The loin fat was analysed for boar taint compounds (androstenone, skatole and indole) and the testicles of each boar were analysed for various size measurements, cut surface colour and histology.

The results indicated that immunocastrates perform as entire males until their second vaccination and thus should be fed as such, after which the weight gain (ADG) and feed intake (ADFI) increases while the feed efficiency decreases as a result of the castration. The vaccination schedule used in the study was favourable with regards to the fact that there were no differences seen in backfat thickness at slaughter when using the Hennessey Grading Probe (HGP). Both immunocastration and RAC supplementation improved the ADG, thus increasing live slaughter weight. The effect of RAC on feed efficiency depends on the level of dietary balanced protein such that the medium and high diets provided the best results.

Supplementing RAC improved the carcass cutting yields of all the commercial cuts measured and improved the lean yield of these cuts either by increasing the muscle or decreasing the fat and thus the increase in fat deposition in various cuts due to immunocastration could be altered by RAC supplementation. Immunocastration, RAC and dietary protein level had little effect on the chemical composition of the loin muscle as well as the post mortem loin pH and temperature. Although small differences were seen for the cut surface colour values (CIE L*a*b* measurement) and tenderness (Warner Bratzler shear force), results from previous studies indicate that it is unlikely that the consumer will be able to pick these differences up subjectively.

The absence of androstenone in the fat tissue of the immunocastrates supports the use of immunocastration as a means of controlling boar taint in heavy entire male carcasses. Therefore, the vaccination schedule used was successful in eliminating androstenone while providing minimal delay between the second vaccination and slaughter so as to minimise the negative effects of immunocastration on fat deposition. This is in agreement with current literature that the period between the second vaccination and slaughter not be extended past four weeks when using a modern, lean and fast-growing genotype such as the current genotype (PIC®). Although the effects of immunocastration on the testicular function could not be seen using size measurements, the cut surface colour measurements of the testicles and testicle histology provided an indication of decreased activity and functioning. The current results are thus in agreement that testicular size should not be used as an indication of vaccination efficacy or boar taint, but the testicle surface colour measurements could prove more useful in achieving this and thus further research is needed into the correlation between these measurements and the endocrinological activity of the testes.

It was concluded that immunocastration was effective in eliminating androstenone from the adipose tissue while providing a carcass similar in quality to that of entire males. Although feed efficiency is sacrificed when immunocastration is practised, this can be rectified and improved by the supplementation of 10 mg/kg RAC for the last 28 days of growth along with the correct provision of dietary balanced protein. This indicates that the dietary requirements for immunocastrates differ with regards to dietary balanced protein, with and without RAC supplementation. By supplementing RAC at 10 mg/kg 28 days prior to slaughter, producers can improve the cutting yield and lean yield of carcasses which increases the value of expensive cuts, thus increasing the return per carcass. Therefore, with the use of immunocastration, RAC and correct dietary balanced protein, pig producers have the option to produce heavier male carcasses efficiently without sacrificing the meat quality or the lean meat yield, while providing a product which consumers will be acceptable of in terms of both the sensory meat quality traits and animal welfare.

General conclusions

A summary of general conclusions include:
Immunocastration effectively eliminated androstenone while providing a carcass similar in quality to that of entire males.
The dietary protein requirements differed for the sexes, both when fed with or without RAC.
Supplementing RAC (10 ppm; 28 days) improved the FCR along with the correct provision of dietary balanced protein (medium/high), improved carcass cutting yields and lean yields as well as increased the value of cuts and thus the return per carcass.
The combination of immunocastration, RAC and the correct dietary protein level could enable pig producers to produce heavier male carcasses efficiently without sacrificing meat quality or lean meat yield.
This could provide a product which consumers likely to be acceptable of in terms of both the sensory meat quality traits and animal welfare.
However, the movement towards the production of heavier immunocastrated male carcasses could rely on a change in the current classification system.

Recommendations

A summary of the recommendations from my thesis include:
An economic comparison to determine whether the improvements justify the cost input of both the RAC as well as the higher protein diet
To further investigate the effect of a wider range of balanced protein levels on the carcass traits and growth performance of immunocastrates using a larger sample size as well as group housing.
Further research is needed into the mechanism of action of RAC with regards to lipogenesis, since the effects are unclear and contradictory in this and previous research.
Possible re-evaluation of current classification system used for carcasses

Acknowledgements

I would like to thank the South African Pork Producers’ Organisation (SAPPO) for the financial support provided throughout this project so that it could be a success; as well as for allowing me the opportunity to present it at the AGM in 2014.
For more information on this project and other research projects being conducted at Stellenbosch University visit [www0.sun.ac.za/sarchi]www0.sun.ac.za/sarchi or email Prof Louw Hoffman at lch@sun.ac.za

 

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