Effects of a Single Injection of LHRH on the Response of Anestrous Ewes to the Introduction of Rams1

Abstract

Two methods of induction of ovulation were examined in Manchega ewes that were in postpartum anestrus during the nonbreeding season. The experiment was of 2 X 2 X 3 factorial design. The methods compared were introduction of rams and this treatment plus an im injection of 50 micrograms luteinizing hormone releasing hormone (LHRH) at the time rams were introduced. Variations in response due to month of treatment (April, May or June) and interval from lambing to treatment (1, 2 or 3 mo) and their interactions with type of treatment were examined. Responses studied were proportions of ewes showing increases in plasma progesterone at (a) 10 d or (b) 17 or 24 d post-treatment, or lambing by 200 d post-treatment, and interval from treatment to lambing for ewes that did lamb by 200 d. The formation of a corpus luteum was determined by concentrations of progesterone in plasma; a positive response was considered to be a concentration greater than .5 ng/ml (baseline values averaged .1 ng/ml). Overall, there was no benefit of LHRH above the response to introduction of males only, in any trait examined. There was a significant interaction of treatment with month of treatment on the proportion of ewes forming corpora lutea by 17 or 24 d after initiation of treatment. This proportion was lower in June (38 vs 66% in April and 82% in May) for ewes receiving LHRH, but did not differ among months (61 to 68%) for ewes exposed to males only.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence that Refractoriness to Long and Short Daylengths Regulates Seasonal Reproductive Transitions in Mediterranean Goats

“…Progesterone concentrations were determined in duplicate in 200 μl aliquots of plasma (following extraction with 3 ml fresh hexane) according to the radioimmunoassay method of López‐Sebastián et al. (1984).…”

Endogenous Circannual Cycles of Ovarian Activity and Changes in Prolactin and Melatonin Secretion in Wild and Domestic Female Sheep Maintained under a Long-Day Photoperiod1

“…The plasma progesterone concentration was determined in duplicate in 200-ll aliquots of plasma (following extraction with 3 ml fresh hexane) according to the radioimmunoassay method of López-Sebastián et al [31]. The assay sensitivity was 0.12 ng/ml, and the intra-and interassay coefficients of variation were 7.4% and 10.6%, respectively.…”

Influence of maternal environment on the number of transferable embryos obtained in response to superovulatory FSH treatments in ewes

“…Thereafter, the plasma was stored at -20 ºC until being assayed for hormone concentrations. Progesterone concentration was determined in individual plasma by radioimmunoassay as Embryo degeneration in superovulated ewesdescribed by Lopez-Sebastian et al [13]. Sensitivity was 0.06 ng·mL -1 and the interand intra-assay variation coefficients were 13.6 and 10.4%, respectively.…”