Seasonal variation in the ovarian activity of Merino ewes

Fletcher, I. C.; Geytenbeek, PE

doi:10.1071/ea9700267

Cited by 16 publications

(12 citation statements)

References 6 publications

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“…The Merino ewe is one of the least seasonal of all sheep and it is commonly observed that some ewes are ovulating in the anoestrous season (Fletcher and Geytenbeek 1970;Wheeler and Land 1977;Oldham 1980). The proportion of ewes ovulating in the anoestrous season has also been found to vary widely between successive years (Pearce et al 1984).…”

Section: Introductionmentioning

confidence: 99%

“…The proportion of ewes ovulating in the anoestrous season has also been found to vary widely between successive years (Pearce et al 1984). Whether the proportion of Merino ewes ovulating at this time consists of some ewes which continue to ovulate or a high proportion of ewes having infrequent ovulations is not known mainly because successive ovarian observations in earlier studies have been too infrequent (Fletcher and Geytenbeek 1970;Oldham 1980). Studies in the Tasmanian Merino in Scotland have suggested that many ewes have infrequent ovulations in the anoestrous season (Wheeler and Land 1977).…”

Section: Introductionmentioning

confidence: 99%

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Ovulation in the Merino Ewe in the Breeding and Anoestrous Seasons

Pearce

Oldham²

1988

Aust. Jnl. Of Bio. Sci.

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The pattern of ovulation of Merino ewes was studied by repeated laparoscopy each 14 days in the anoestrous (n = 97) and breeding (n = 87) seasons. In the anoestrous season the proportion of ewes ovulating did not decrease below 11 070, 42% of ewes never ovulated and the remainder fluctuated between the two states. On 20 occasions a clear anovulatory period was interrupted by an isolated spontaneous ovulation. In the breeding season the overall mean proportion of ewes with corpora lutea or albicantia at laparoscopy was 87%, 54% of ewes ovulated regularly throughout while in another 31% absence of corpora lutea or albicantia coincided with the follicular phase of an oestrous cycle as evidenced by an appropriately aged corpora lutea at the next laparoscopy. Of the remaining 15% of the flock 3% had anovulatory periods greater than 14 days while the remainder experienced irregular ovulatory cycles - the majority due to short periods of anovulation but some ewes retained corpora lutea for longer than 14 days while others ovulated twice between successive laparoscopies.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Ovulation in the Merino Ewe in the Breeding and Anoestrous Seasons

Pearce

Oldham²

1988

Aust. Jnl. Of Bio. Sci.

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“…The experiment was conducted during February which is generally considered to be the beginning of the spontaneous breeding season for the Merino ewe in the southern hemisphere (Watson, 1952;Fletcher & Geytenbeek, 1970). Medium wool parous Merino ewes which had an initial liveweight of 44-8 + 0-4 kg (mean + s.e.m.)…”

Section: Methodsmentioning

confidence: 99%

Increases in ovulation rate in lupin-fed ewes are initiated by increases in protein digested post-ruminally

Nottle¹,

Pi²,

Seamark³

et al. 1988

Reproduction

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“…INTRODUCTION THERE is considerable evidence from several breeds of sheep that ovulation rate (number of ova shed per oestrus) increases from the commencement of the breeding season and then falls away at the end (Averill, 1959;Hulet and Foote, 1967;Fletcher and Geytenbeek, 1970;Wheeler and Land, 1977). Furthermore, this pattern of ovulation rate within the breeding season is normally translated into a similar pattern of lambs born per ewe lambing (Land, Dickinson and Read, 1969;Hendy and Bowman, 1974); this suggests that fertilization rate and early embryonic mortality do not vary markedly with season.…”

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confidence: 99%

The effect of body condition and time of mating on the reproductive performance of Masham ewes

1980

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Masham ewes were mated at three stages of the breeding season, early (15 September to 20 October), mid (20 October to 24 November) and late (15 December to 19 January), at two different body condition scores, 4 and 2, for 3 successive years. The mean scores achieved for body condition 4 were 3-6, 3-7 and 3-9 for early, mid and late respectively and for body condition 2 were 2-4, 2-3 and 2-2. In the late lambing flock more ewes were marked by vasectomized rams and less ewes were barren than in the early and mid flocks. The ewes in higher body condition at mating had significantly more triplets and fewer singles, and a higher lambing percentage (183 versus 165). This effect of body condition on litter size distribution was significant at each time of mating, with the ewes at the late mating producing significantly fewer triplets and more singles; this difference was caused by a reduction in the performance of the body condition 4 ewes in the late group. Young ewes in the body condition 4 group produced significantly fewer triplets and more singles than the mature ewes in the same body condition group, but at the lower body condition age had no effect on litter size distribution.

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Seasonal variation in the ovarian activity of Merino ewes

Cited by 16 publications

References 6 publications

Ovulation in the Merino Ewe in the Breeding and Anoestrous Seasons

Ovulation in the Merino Ewe in the Breeding and Anoestrous Seasons

Increases in ovulation rate in lupin-fed ewes are initiated by increases in protein digested post-ruminally

The effect of body condition and time of mating on the reproductive performance of Masham ewes

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