Effects of feeding ractopamine (Paylean®) to immunologically castrated (Improvest®) pigs on growth performance, carcass yields, and further processing characteristics

The objective of this dissertation was to evaluate the effects of feeding ractopamine hydrochloride (RAC; Paylean, Elanco Animal Health, Greenfield, IN) on growth performance, carcass characteristics, fresh meat quality, and further processing characteristics of immunologically castrated (IC; Improvest, Zoetis, Kalamazoo, MI) pigs. With costs of production rising in the swine industry, producers are constantly seeking methods to improve growth performance while keeping production costs minimal. Two technologies that have been beneficial in helping producers improve feed efficiency and save on feed costs is the use of RAC and immunological castration. Ractopamine hydrochloride is an orally active β-agonist that repartitions nutrients away from fat deposition and towards lean deposition. Animals become less efficient over the course of production, especially during the finishing phase when the body has decreased the rate at which it is accumulating muscle and increased the rate at which it is accumulating fat. These changes often result in increasing average daily gains (ADG), improving feed conversion (G:F), increasing slaughter weights and carcass weights, improving carcass muscling, and improving carcass cutability. Similarly, immunological castration through the use of Improvest allows producers to take advantage of the increased efficiency of young intact pigs by delaying castration until later in production. Boars are the most efficient of all sexes of swine mainly due to increased testosterone levels and the effects they have on appetite and lean accretion. However, as boars age and reach market weights, the meat from these pigs often has an unpleasant odor referred to as ‘boar taint’ due to the affects that testosterone has on the body’s ability to clear androstenone and skatole from the system. Androstenone is a testicular steroid that has no hormonal activity but functions merely as a sex pheromone. Contrary to androstenone which is only produced in males, skatole is produced by both males and females via bacterial digestion of the amino acid tryptophan in the hind gut of pigs from where it is absorbed and, if not cleared by the liver, accumulates in fatty tissues. Improvest works through a two dose program that inhibits production of both luteinizing hormone and follicle stimulating hormone which ultimately inhibits testicular activity. This inhibition in testicular activity decreases testosterone production and allows the body to metabolize and clear away androstenone and skatole. Using Improvest in swine operations allows producers to take advantage of the increased efficiency and carcass leanness commonly associated with raising boars without having any boar taint issues with meat from those pigs. While the reports of feeding RAC, as well as immunological castration, are extensive and numerous, there is very limited data evaluating the use of these technologies together. Therefore, the objectives of these studies were to evaluate the effects of feeding RAC (5 mg/kg for up to 33 d) on growth performance, carcass characteristics, fresh meat quality, and further processing characteristics of IC pigs managed in a commercial setting. Feeding RAC during the last 33 d of finishing increased ADG by 17% and increased G:F by 18%. Carcasses from RAC-fed pigs were 2.3 kg heavier, had 2.2 mm deeper loins, and were estimated to be 0.4 percentage units leaner than control-fed carcasses. In terms of carcass cutability, feeding RAC increased boneless lean, bone-in lean, and total carcass cutting yields by 0.70, 0.76, and 0.70 percentage units, respectively. There was very little impact of feeding RAC on fresh meat quality parameters including loin color, marbling, and firmness scores, pH, and tenderness; however, feeding RAC increased loin moisture and decreased loin fat in physically castrated (PC) carcasses while having no effects in IC carcasses. This was also seen when evaluating further processing characteristics where RAC increased leanness of cured hams and bellies from PC carcasses while having no impact on hams and bellies from IC carcasses. Over the entire growth study (120 d), IC pigs gained 2.6% faster, consumed 4.6% less feed, and were ultimately 7.3% more feed efficient than PC pigs. While carcass weights of PC and IC pigs were similar, IC carcasses had 1.3 mm less fat which is indicative of IC carcasses having greater amounts of lean than PC carcasses. This was made apparent when evaluating carcass cutting yields where IC carcasses had 1.19, 1.63, and 1.32 percentage units advantages over PC carcasses for boneless lean, bone-in lean, and total carcass cutting yields, respectively. While immunological castration had no impact on loin color scores, loins from IC carcasses had less marbling, were softer, and were slightly less tender than those from PC carcasses. The effects of immunological castration on carcass leanness were also seen when evaluating further processing characteristics where cured hams and bellies from IC carcasses had more moisture and less fat than those from PC carcasses. When evaluating the technologies together, RAC-fed IC pigs grew 29% faster and were 17% more feed efficient than control-fed PC pigs during the last 33 d of feeding. Furthermore, RAC-fed IC carcasses were 2% heavier, had 7% less fat, and were estimated to be 0.59 percentage units leaner than control-fed PC carcasses. In terms of carcass cutting yields, RAC- fed IC carcasses had 1.9, 2.4, and 2.0 percentage units greater boneless lean, bone-in lean, and total carcass cutting yields, respectively, than control-fed PC carcasses. The combination of the two technologies had no more impact on fresh meat quality than using either technology alone. The results from these studies support the ideas that these two technologies are additive in terms of effects on growth performance, carcass characteristics, and carcass cutting yields while having minimal impact on fresh meat quality