EFFECT OF A SINGLE INJECTION OF A LONG-ACTING GONADOTROPIN-RELEASING-HORMONE AGONIST ON PREPUBERTAL MALE AND FEMALE PIGS ON REPRODUCTIVE-ORGANS, GROWTH-PERFORMANCE AND SENSORY QUALITIES OF PORK ROASTS

Crossbred pigs (n = 200) were used to study the effects of a long-acti ng form of gonadotropin-releasing hormone (GnRH) agonist on the reprod uctive systems of male and female pigs and their growth performance an d sensory quality of pork roast. Treatment was a single injection of a controlled release formulation of GnRH agonist [D-Trp(6), des-Gly(10) ]-GnRH ethylamide to release 5 mu g/(kg x day) for 4 months beginning when the pigs were 66 +/- 2 days old. Pigs were allocated to five grou ps of 40 animals each: males castrated (CM) at 13 +/- 2 days, intact m ales (IM), treated males (TM), intact females (IF) and treated females (TF). Ovarian and uterine weights at slaughter averaged 3.67 and 79.8 g, respectively, in IF compared with 1.38 and 26.5 g in TF (P < 0.05) . Testicular weights were 203 g in IM and 36.8 g in TM (P < 0.05). Mic roscopic observations of the testes revealed an absence of sperm cells but the presence of germ cells. Steroid concentrations at slaughter f rom all pigs showed that intact males had significantly more testoster one in their serum (26.36 +/- 9.87 nmol/L) compared with TM, CM, IF or TF groups and that treated males had intermediate concentrations (12. 50 +/- 7.44 nmol/L) higher (P < 0.05) than those in CM and TF. Adminis tration of GnRH agonist during the growth period of male pigs had no c onsistent effect on growth performance, but as compared to IM pigs, so me of the carcass charasteristics such as meat ratio (49.1 vs 50.2% in TM and IM; P < 0.001), dressing percentage (77.5 vs 76.5% in TM and l M, P < 0.05) and average backfat (20.8 vs 17.6 mm in TM and IM; P < 0. 05) were modified by such a treatment. Meat quality, however, as deter mined by flavor and tenderness evaluations by sensory panelists, were similar (P < 0.05) in all groups and off-flavor scores were lower in T M than in IM (P < 0.001). As for males, backfat and meat ratio were di fferent in TF compared to IF (P < 0.05) and roast juiciness was higher in TF than IF (P < 0.05). These results suggest that GnRH agonist can reduce gonadal secretory activity to castration levels during the gro wth period of prepubertal male pigs and could be an alternative to sur gical castration in the pork industry with no negative effects on grow th and meat quality. No advantage to endocrine castration in females w as found.