Endogenous Hormone Response and Fertility in Dairy Heifers Treated with Norgestomet and Estradiol Valerate2

Abstract

Seventy postpuberal dairy heifers were assigned to remain untreated (n = 26) or to receive the Syncro-Mate-B (SMB) treatment (n = 44). Untreated heifers were inseminated at 12 hr after detection of estrus, while SMB-treated heifers were inseminated either at 48 hr after implant removal (group 1) or at 12 hr after detection of estrus (group 2). Jugular blood was collected at regular intervals from four untreated heifers and from 20 SMB heifers. In untreated heifers, estradiol-17 beta (E) was unchanged throughout the estrous cycle. Progesterone (P) reached maximum concentrations during the luteal phase and then declined to less than 2 ng/ml before estrus. Follicle stimulating hormone (FSH) ranged between 50.1 and 100.2 ng/ml during the estrous cycle, then reached a peak (P less than .05) concentration of 516.2 ng/ml coincident with peak luteinizing hormone (LH) concentration at 12 hr after the detection of estrus. In SMB-treated heifers, plasma E increased by 12 hr after injection of estradiol valerate and then declined throughout the rest of the sampling period. P declined to less than 2 ng/ml by 24 hr after administration of the SMB treatment and remained low throughout the sampling period. FSH declined in response to SMB treatment, then reached a peak (P less than .05) concentration coincident with peak LH 40 hr after implant removal. First service pregnancy rates among the untreated, group 1 and group 2 heifers, were 65, 58 and 38%, respectively, and did not differ (P greater than .05). SMB treatment was effective in inducing luteolysis and in suppressing estrus and peak gonadotropin release. Intervals from implant removal until estrus and from implant removal until peak gonadotropin release were highly variable among SMB-treated animals.

Timing of Preovulatory Endocrine Events, Estrus and Ovulation in Brahman × Hereford Females Synchronized with Norgestomet and Estradiol Valerate

“…One of these three conceived to the artificial insemination. This variability was similar to that observed by Kazmer et al (1981) in dairy heifers synchronized with norgestomet and estradiol. Based on the low frequency of asynchronism observed in our study, we conclude that timing of the LH surge relative to estrus is not a major contributor to the low fertility reported for 48-h timed insemination.…”

“…The group consisted of two heifers that exhibited estrus later than 54 h after implant removal, five that were not observed in estrus, and three that had an LH surge later than 12 h after estrus. Zaied et al (1976), Spitzer et al (1978) and Kazmer et al (1981) found conception rates similar to those of the optimal timing group in cattle without Brahman breeding. It is apparent that heifers that displayed estrus later than 54 bEstrus < 54 h after implant removal and LH surge within 12 h after onset of estrus.…”

“…Partial attainment of this goal has been reached with regimens employing a synthetic progestogen (norgestomet) and estradiol valerate. Conception rates of over 50% to timed inseminations 48 h after norgestomet implant removal have been observed in Bos taurus cattle (Zaied et al, 1976;Kazmer et al, 1981). However, conception rates in Brahman and Brahman crossbred cattle treated and inseminated similarly have been substantially lower (Waiters et al, 1984;Williams and Kovacik, 1987).…”

Avaliação da reutilização de implantes contendo progestágenos para controle farmacológico do ciclo estral e ovulação em vacas de corte.

“…Como o horário da inseminação em relação à ovulação é um fator importante na taxa de concepção, trabalhos têm sido feitos com o objetivo de diminuir a variação no tempo de ovulação em animais sincronizados, visando melhor fertilidade (Kazmer et al, 1981) Apesar das suas vantagens, o número de fazendas que empregam o uso da inseminação artificial como rotina ainda é pequeno. No…”