Control of ovulation and fixed time insemination in heifers following cloprostenol

Short estrous cycles and estrous signs after premature ovulations induced with cloprostenol and gonadotropin-releasing hormone in cyclic dairy cows

The aim of the present study was to confirm earlier findings, obtained with a small number of animals, that gonadotropin-releasing hormone (GnRH) can shorten corpus luteum functional life when it is administered 24 h after cloprostenol (PG) treatments given 7-9 days after estrus. In addition, the effects of two treatments, PG alone or PG + GnRH given before mid-diestrus, on signs of estrus were studied. Sixty cows in farm conditions were used in the experiment. Eight days after natural estrus, they were given an intramuscularly (i.m.) treatment of cloprostenol (0.5 mg). The animals were then divided into two groups. One group (n = 25) received an i.m. treatment of gonadorelin (0.1 mg) 24 h after the PG treatment (PG + GnRH group), while another group (n = 35) served as controls without any further treatment (PG group). Estrous signs were recorded. Progesterone concentrations were measured from samples of whole milk. No short cycles were observed in the PG group, whereas 33% of the cows in the PG + GnRH group exhibited premature luteal regression (P < 0.05). Cloprostenol treatment on Day 8 had no effect on the intensity of the estrous signs. Instead, GnRH treatment 24 h after PG treatment weakened the estrous signs significantly (P < 0.01). It is concluded that GnRH administration 24 h after a PG treatment given 8 days after estrus can cause short estrous cycles in some cows on an individual basis.

Reproductive loss in high-producing dairy cattle: where will it end?

The dairy industry in the United States has changed dramatically in the last decade. Milk production per cow has increased steadily because of a combination of improved management, better nutrition, and intense genetic selection. Dairy farms are larger, and nearly 30% of the dairy cows in the United States are on farms with 500 or more cows. The shift toward more productive cows and larger herds is associated with a decrease in reproductive efficiency. Cows with the greatest milk production have the highest incidence of infertility, but epidemiological studies suggest that, in addition to milk production, other factors are probably decreasing reproductive efficiency in our dairy herds. The reproductive physiology of dairy cows has changed over the past 50 yr, and physiological adaptations to high milk production may explain part of the reproductive decline. Critical areas for new research include control of the estrous cycle, metabolic effects of lactation on reproduction, mechanisms linking disease to reproduction, and early embryonic mortality. Solving reproductive loss in dairy cows will not be easy because only a small number of research groups study reproduction in postpartum dairy cows. Therefore, the present research base will need to be expanded. For this to occur, research funding must be increased above its current level and a renewed emphasis must be placed on solving the emerging crisis of infertility in dairy cows.

Conception rates in repeat-breeders and dairy cattle with unobserved estrus after prostaglandin F2 alpha and gonadotropin-releasing hormone

In Experiment 1, cows with a history of at least two previous unsuccessful inseminations were allocated to four groups. At the repeated estrus (third or greater service), some of the cows were inseminated according to the a.m.-p.m. rule (Controls, n = 83), or received i.m. 100 mug gonadotropin-releasing hormone (GnRH, n = 32) within 30 sec after insemination. Ovaries of the remaining cows to be treated were palpated during the anticipated ensuing luteal phase to determine the presence of a corpus luteum. Cows found to have luteal tissue received i.m. 25 mg prostaglandin F(2)-alpha (PGF(2)-alpha) and were inseminated after detected estrus or at 72 and 96 h after PGF(2)-alpha in the absence of estrus. Cows given PGF(2)-alpha either received no further treatment (PGF(2)-alpha, n = 40) or were given i.m. 100 mug GnRH (PGF(2)-alpha + GnRH, n = 29) after insemination or at 72 h after PGF(2)-alpha in the absence of estrus. Conception rate of control cows (39%) was similar to that of cows given PGF(2)-alpha (40%) or PGF(2)-alpha + GnRH (43%), but it tended to be lower (P = 0.13) than that of cows given only GnRH at insemination (54%). In Experiment 2, cows with unobserved estrus and diagnosed not pregnant (palpation) were palpated to detect a corpus luteum. Cows with luteal tissue received i.m. PGF(2)-alpha (n = 52) or PGF(2)-alpha + GnRH (n = 45) and were inseminated as described above. Conception rates were similar (39% vs 33%, respectively). In Experiment 3, cows in a large commercial dairy with (n = 93) or without (n = 420) previous reproductive problems were given i.m. 100 mug GnRH after insemination (n = 169) or were left untreated (n = 344) at repeat services (third and fourth services). Treatment with GnRH improved (P < 0.05) conception in normal (47% vs 36%) and abnormal (25% vs 12%) repeat-breeding cows. Treatment with PGF(2)-alpha alone or in conjunction with GnRH failed to further improve conception rates and only delayed intervals to rebreeding when administered during the luteal phase after the repeated estrus. The use of GnRH failed to reduce intervals from treatment to insemination or improve conception in cows with unobserved estrus compared to treatment with PGF(2)-alpha alone.

Gonadotropin-releasing hormone and conception of Holsteins

Effects of gonadotropin-releasing hormone (100 micrograms) and time of artificial insemination on fertility, were examined in lactating dairy cows at first, second, and third services. Inseminations were either soon after detected estrus (0 h) or 12 h later, and cows were given gonadotropin-releasing hormone or saline after inseminations. Conception at first service was not improved by hormone treatment. But conception rates at repeat services were improved by nearly 21% when cows were treated with gonadotropin-releasing hormone within 30 s after insemination. Inseminations soon after detection of estrus (0 h) followed by hormone treatment resulted in the highest conception rates for all services. Time of the insemination (0 versus 12 h) had no effect on conception. Administering gonadotropin-releasing hormone at repeat services should improve conception rate of lactating dairy cows.