Biomedical subjects

D R Lindsay

Publications and source records attributed to D R Lindsay.

At least 19 recordsLinked to original sources

PubMed1991

Ovariectomized does do not require progesterone priming for oestrous behaviour.

Ewes need to be primed with progesterone in order to achieve sensitivity to oestrogen. This relationship was examined in goats. In experiment 1 the median effective dose of oestradiol benzoate (ODB) required to induce oestrus during the breeding season (July) in progesterone-primed ovariectomized does was 15 micrograms, a dose similar to that reported to be required in ewes. In experiment 2 (initiated in March) the requirement for progesterone priming before injection of ODB to induce oestrus after a period without any exogenous hormone treatment, was compared in goats and sheep. Without progesterone priming, ovariectomized does were sensitive to doses of ODB between 20 and 80 micrograms, whereas ewes were not. This indicates that, unlike sheep, goats may not require progesterone priming in order to exhibit oestrus at the beginning of the breeding season. After being primed with progesterone, ewes were more sensitive to ODB than were does. In primed ewes the median effective dose of ODB was 12 micrograms whereas in does it was 27 micrograms. These differences may be due to a seasonal effect on oestrous behaviour or differences in sensitivity to oestrogen between the species.

Animals↗

PubMed1988

Secretion of LH, FSH and oestradiol-17 beta during the follicular phase of the oestrous cycle in the ewe.

Plasma concentrations of LH, FSH and oestradiol-17 beta were measured in blood samples taken at 15 min intervals for 48 h during the follicular phase of four Merino ewes. The amplitude of pulses of LH and the mean concentration of LH were higher at the beginning of the follicular phase, 36-24 h before the preovulatory surge of LH (amplitude 2.4 ng ml-1, mean concentration 3.9 ng ml-1), than at the end, 24-0 h before the preovulatory surge (amplitude 1.2 +/- 0.1 ng ml-1; mean concentration 1.4 +/- 0.1 ng ml-1). There was no change in the inter-pulse interval during this time (mean 74 +/- 5 min). Over the same period, oestradiol levels increased from 7-8 pg ml-1 to a peak of 10-15 pg ml-1. Mean FSH concentrations declined (36-24 h: 3.6 ng ml-1 vs 24-0 h: 1.8 +/- 0.3 ng ml-1) before rising at the time of the preovulatory surge of LH and again 24 h later. It was concluded that the biphasic response of LH to oestrogen that is seen in ovariectomized ewes may also operate during the follicular phase of the oestrous cycle in entire ewes.

Animals↗

PubMed1988

The number of spermatozoa, the number of ovulations per ewe, and immunization against androstenedione affect fertility and prolificacy of sheep.

Ewes that were untreated, fed lupins or fed lupins and immunized against androstenedione were artificially inseminated. The percentage of ewes pregnant at 36-45 days after insemination (fertility) was 8% higher in ewes that had more than one ovulation than in those that had only one ovulation. Maximum fertility was achieved with 50 x 10(6) spermatozoa and this did not vary with the number of ovulations that ewes had. Among the pregnant, twin-ovulating ewes, embryo survival increased as the number of spermatozoa inseminated increased from 25 x 10(6) to 400 x 10(6). Immunization of ewes against androstenedione increased ovulation rate but reduced fertility, and reduced embryo survival among twin-ovulation ewes.

Androstenedione↗

PubMed1988

Effects of breed, ovarian steroids and season on the pulsatile secretion of LH in ovariectomized ewes.

The effects of season and of oestradiol and progesterone on the tonic secretion of LH were studied in ovariectomized Merino and Suffolk ewes, two breeds which differ markedly in the seasonal pattern of their reproductive activity. In the absence of exogenous steroids, the frequency of LH pulses was lower and the amplitude of the pulses was higher in anoestrus than in the breeding season for Merino and Suffolk ewes 30 days after ovariectomy. In long-term (190 days) ovariectomized ewes, this seasonal change in LH secretion was observed in Suffolk ewes only. During seasonal anoestrus, treatment of ewes with subcutaneous oestradiol-17 beta implants (3, 6 or 12 mm in length) decreased the frequency of LH pulses in a dose-dependent manner, with Suffolk ewes being far more sensitive to the inhibitory effects of oestradiol than Merino ewes. The lowest dose of oestradiol (3 mm) had no effect on the secretion of LH in Merino ewes, but reduced secretion in Suffolk ewes. Treatment of ewes with the highest dose of oestradiol (12 mm) completely abolished LH pulses in Suffolk ewes, whereas infrequent pulses remained evident in Merino ewes. During the breeding season, oestradiol alone had no effect on the pulsatile release of LH in either breed, but in combination with progesterone there was a significant reduction in LH pulse frequency. Progesterone effectively decreased LH secretion in both breeds in both seasons. It was concluded that differences between breeds in the 'depth' of anoestrus could be related to differences in the sensitivity of the hypothalamus to both negative feedback by oestradiol and the direct effects of photoperiod.

Animals↗

PubMed1988

Reproductive behaviour in survival: a comparison between wild and domestic sheep.

The recorded behaviour of wild species of Ovis at the beginning of the breeding season supports the proposal that mating is synchronized by the 'ram effect', a phenomenon already described in domestic sheep. Animals separate into exclusive male flocks, and flocks of females and young animals for most of the year. They reunite just before the rutting season. At lambing there appear to be behavioural mechanisms that ensure that ewes lamb in close proximity to one another. It is hypothesized that these behavioural characteristics of wild sheep help protect the newborn and that much of the reproductive and maternal behaviour of domestic sheep may be traced to comparable behaviour in wild species.

Animals↗

PubMed1975

Influence of the presence of rams on the timing of ovulation and discharge of LH in ewes.

The influence of the presence of the male on the ovulation process was investigated in ewes after oestrus control by progestagens (intravaginal fluorogestone acetate) and PMSG. Permanent contact with the rams throughout oestrus accelerates the ovulation and the appearance of the LH surge. The results suggest that the action of the presence of the male on ovulation is mediated by way of the ovulatory surge of LH.

Animals↗

PubMed1975