Aromatase inhibitors: A new approach for controlling ovarian function in cattle.

Numerous treatments and protocols have been used to control the reproductive cycle in cattle, with varying effectiveness and many involving the administration of steroid hormones. Steroid hormones, such as estradiol, are perceived as having a negative impact on consumer health. This internationally shared opinion has led to a ban on the use of steroid hormones in food producing animals in many countries (i.

Synchronization of ovulation in cattle with an aromatase inhibitor-based protocol.

A study was designed to determine the effect of stage of the estrous cycle on the proportion of animals that ovulated and the synchrony of ovulation of heifers treated with an aromatase inhibitor-based protocol. Forty-eight heifers were treated intramuscularly with 500 μg of cloprostenol (PGF) followed by 100 μg of GnRH 24 hours later to serve as control data for comparison of the ovulatory response to a subsequent aromatase inhibitor protocol. Daily ultrasound examinations were done to determine the incidence of and interval to ovulation.

Effect of vehicle and route of administration of letrozole on ovarian function in a bovine model.

The objective of this study was to determine the effects of vehicle and route of administration of letrozole on ovarian function in sexually mature beef heifers. On Day 3 (Day 0=ovulation), heifers were assigned randomly to four treatment groups and given 1mgkg(-1) letrozole intravenously (iv, n=10) or intramuscularly (im, n=10) or given a placebo iv (control iv, n=5) or im (control im, n=5). The interwave interval was longer in heifers treated with letrozole im than in im and iv controls (11.

Effects of a non-steroidal aromatase inhibitor on ovarian function in cattle.

Effects of the non-steroidal aromatase inhibitor letrozole on ovarian function in cattle were determined. The hypothesis that letrozole would arrest growth of the dominant follicle, resulting in emergence of a new follicular wave at a predictable post-treatment interval, was tested. Heifers were assigned randomly to four groups 4 days after follicular ablation (~2½ days after wave emergence) and given intravenous doses of 500 (n = 9), 250 (n = 10), or 125 µg kg⁻¹ (n = 10) letrozole or phosphate-buffered saline (controls; n = 10).