Sex Ratio in Sheep

Napier, K. M.; Mullaney, PD

doi:10.1530/jrf.0.0390391

Cited by 8 publications

(8 citation statements)

References 4 publications

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“…Significantly more males were born to ewes with singles than to ewes with twins or triplets. This is in keeping with earlier findings (Johansson and Hansson 1943;Napier and Mullaney 1974;Rasmussen 1941;Skjervold 1979). Significantly more females were born to ewes with triplets.…”

Section: Discussionsupporting

confidence: 93%

“…However, in the last 2 years of the study the sex ratios were above 50%. This is in keeping with the findings of Napier and Mullaney (1974). This finding needs an explanation.…”

Section: Discussionsupporting

confidence: 91%

“…In these studies the sex ratio (expressed throughout this paper as the percentage of males) varies from 48.4% to 49.5%. Napier and Mullaney (1974) found a sex ratio of 50.8%. Investigators looking at the difference in the sex ratio of single, twin and triplet births have found that ewes with single lambs produce a higher proportion of males than ewes with twin or triplet births (Johansson and Hansson 1943;Napier and Mullaney 1974;Rasmussen 1941).…”

Section: Introductionmentioning

confidence: 95%

“…Napier and Mullaney (1974) found a sex ratio of 50.8%. Investigators looking at the difference in the sex ratio of single, twin and triplet births have found that ewes with single lambs produce a higher proportion of males than ewes with twin or triplet births (Johansson and Hansson 1943;Napier and Mullaney 1974;Rasmussen 1941). However, in these studies data have been obtained from sources such as the herd book records of sheep breeding associations (Johansson and Hansson 1943), which may produce a rather selective if not abnormal sample, or the combination of such data over a number of years into one large sample (Chapman and Lush 1932;Rasmussen 1941).…”

Section: Introductionmentioning

confidence: 95%

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Birth sex ratios in sheep over six lambing seasons

Kent¹

1992

Behav Ecol Sociobiol

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The birth sex ratio of a commercial flock of Suffolk x sheep, Ovis aries, were studied over six consecutive lambing seasons. In all, data from 1820 lambs were recorded and analysed. The overall birth sex ratio was 49.56% male lambs. Significantly more males (56.23%) were born to ewes with single lambs than to ewes with like-sex twins (47.73%). Significantly more female lambs were born to ewes with triplet births (41.79% male). A significant difference in the birth sex ratio was observed between the first and second half of the lambing season, among like-sex pairs of twin lambs. More males were born in the first half (51.43%) and significantly more females (43.59% male) in the second half of the lambing season. The results are discussed with reference to the theory of Trivers and Willard (1973).

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Section: Discussionsupporting

confidence: 93%

“…However, in the last 2 years of the study the sex ratios were above 50%. This is in keeping with the findings of Napier and Mullaney (1974). This finding needs an explanation.…”

Section: Discussionsupporting

confidence: 91%

Section: Introductionmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 95%

See 2 more Smart Citations

Birth sex ratios in sheep over six lambing seasons

Kent¹

1992

Behav Ecol Sociobiol

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“…Rate ρ , i.e. the probability that an offspring born alive was a female, was set to 0.5 [42–44]. The age at first parturition was set to 10 months [45].…”

Section: Methodsmentioning

confidence: 99%

Modelling the Dynamics of Post-Vaccination Immunity Rate in a Population of Sahelian Sheep after a Vaccination Campaign against Peste des Petits Ruminants Virus

2016

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BackgroundPeste des petits ruminants (PPR) is an acute infectious viral disease affecting domestic small ruminants (sheep and goats) and some wild ruminant species in Africa, the Middle East and Asia. A global PPR control strategy based on mass vaccination—in regions where PPR is endemic—was recently designed and launched by international organizations. Sahelian Africa is one of the most challenging endemic regions for PPR control. Indeed, strong seasonal and annual variations in mating, mortality and offtake rates result in a complex population dynamics which might in turn alter the population post-vaccination immunity rate (PIR), and thus be important to consider for the implementation of vaccination campaigns.MethodsIn a context of preventive vaccination in epidemiological units without PPR virus transmission, we developed a predictive, dynamic model based on a seasonal matrix population model to simulate PIR dynamics. This model was mostly calibrated with demographic and epidemiological parameters estimated from a long-term follow-up survey of small ruminant herds. We used it to simulate the PIR dynamics following a single PPR vaccination campaign in a Sahelian sheep population, and to assess the effects of (i) changes in offtake rate related to the Tabaski (a Muslim feast following the lunar calendar), and (ii) the date of implementation of the vaccination campaigns.ResultsThe persistence of PIR was not influenced by the Tabaski date. Decreasing the vaccination coverage from 100 to 80% had limited effects on PIR. However, lower vaccination coverage did not provide sufficient immunity rates (PIR < 70%). As a trade-off between model predictions and other considerations like animal physiological status, and suitability for livestock farmers, we would suggest to implement vaccination campaigns in September-October. This model is a first step towards better decision support for animal health authorities. It might be adapted to other species, livestock farming systems or diseases.

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Increasing the proportion of female lambs by feeding Merino ewes a diet high in omega-6 fatty acids around mating

2016

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In previous experiments, the proportion of female lambs was higher when BL × Merino ewes were offered a diet high in omega-6 (n-6) than when offered one low in n-6 around joining. The aim of the current study was to determine whether the proportion of female lambs increases when Merino ewes are fed a diet high in n-6 and to further test the effect of time of feeding relative to mating. Ewes were fed a low n-6 (ryegrass silage) or high n-6 (oats and cottonseed meal) diet for ~40 days pre-mating or 40 days pre- and 17 days post-mating. Liveweight, fat score, plasma fatty acid status and lamb sex were determined. The concentration of plasma n-6 was higher (P < 0.001) and the time to oestrus shorter (P < 0.001) when ewes received the high n-6 compared with the low n-6 diet. The proportion of female lambs was higher when ewes were fed the high n-6 compared with the low n-6 diet either pre-mating only (71.3% vs 48.7%, P = 0.017) or both pre- and post-mating (69.6% vs 37.3%, P < 0.001). The sex ratio differed from an expected 50 : 50 when ewes were fed the high n-6 diet (P < 0.001), but not the low n-6 diet (P = 0.223). The effect of the high n-6 diet on the sex ratio of lambs in Merino ewes may act pre-conception, as the effect of the diet was not greater when ewes were fed both pre- and post-mating. Altering diet to increase female lamb proportions may be economically viable to producers of first-cross ewes.

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Sex Ratio in Sheep

Cited by 8 publications

References 4 publications

Birth sex ratios in sheep over six lambing seasons

Birth sex ratios in sheep over six lambing seasons

Modelling the Dynamics of Post-Vaccination Immunity Rate in a Population of Sahelian Sheep after a Vaccination Campaign against Peste des Petits Ruminants Virus

Increasing the proportion of female lambs by feeding Merino ewes a diet high in omega-6 fatty acids around mating

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