Effects of (DTrp6-Des-Gly10-ProNH29)-luteinizing hormone-releasing hormone ethylamide on the estrous cycle, weight gain, and feed efficiency in feedlot heifers.

Subcutaneous implantation of pelleted (DTrp6-Des Gly10-ProNH29)-luteinizing hormone-releasing hormone in 3 heifers (at a total dose of approx 5 microgram/0.45 kg of body weight) shortly after ovulation did not affect the ongoing luteal phase, but prevented the next expected estrus and ovulation. The effect was reversible and estrus was reestablished 16 and 19 days after pellet removal. The subsequent luteal phase concentrations of plasma progesterone appeared to be below normal concentrations. In a 2nd study, 25 heifers were implanted subcutaneously twice, 56 days apart, at random stages of the cycle. The mean number of estrous episodes over the 112 days of observation was decreased from 5.56 in controls (n = 25) to 1.12 in treated (n = 25) heifers. This suppression of estrus was not associated with change in live weight gain or food intake.