CONTROL OF OVULATION WITH A GNRH ANALOG IN GILTS AND SOWS

Methods for the control of ovulation with GnRH or the GnRH analog D-Ph e(6)-LHRH(GnRH-A), were evaluated in gilts and sows as the last step i n development of a fixed-time Al protocol. This involved 3 field trial s using 2,744 gilts (10 units) and 71,628 sows (33 units). In Trial 1, the GnRH-A (75 mu g,) was given subsequent to treatment with altrenog est for cycle control or eCG for the stimulation of uniform folicle de velopment in gilts. The release of LH was followed by ovulations which commenced within 36.4 +/- 3.3 hr and were terminated at 39.0 +/- 2.8 hr after administration of GnRH-A. This degree of synchronization of o vulations enabled the use of fixed-time Al. Consequently, subsequent t o pretreatment with altrenogest and eCG, in 10 production units 1,285 gilts received 50 mu g GnRH-A and 1,459 gilts 500 lU hCG serving as po sitive controls (Trial 2); all the gilts were inseminated 24 and 42 hr after treatment. Pregnancy rate and piglet index (n of piglets per 10 0 first inseminations) following GnRH-A vs hCG were 78.8% and 779 vs 7 4.4% and 728, respectively (P<0.05). In field trials with first litter gilts and multiparous sows (33 units holding from 250 to 6,000 sows), 1,000 lU eCG was used for estrus control after weaning and 25 mu g or 50 mu g GnRH-A were given 55 to 58 hours after eCG (n=19,954 and 20,7 01) (Trial 3). Sows treated during the same time period with 300 mu g GnRH plus 300 1U. hCG (n=30,973) served as positive controls; all sows were inseminated 24 and 42 hours after treatment. Pregnancy rates for 50 mu g GnRH-A, 25 mu g GnRHa and 300 mu g GnRH plus 300 1U hCG were 83.0%, 81.7% and 80.7%, and the piglet indices 913, 899 and 880, respe ctively (P<0.05). Unit size and parity had significant effects on fert ility and productivity. In all studies, results with 50 mu g GnRH-A we re superior. In year-long studies, highest levels of fertility in resp onse to these treatments were seen from December to May.