Factors that affect fertility in a feral population of sheep

Jewell, P. A.

doi:10.1111/j.1096-3642.1989.tb02310.x

Cited by 26 publications

(8 citation statements)

References 15 publications

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“…Fourteen other male lambs, caught concurrently, were tagged but not castrated to serve as controls (entire rams) see Table I. These lambs were caught over what proved to be the peak of the lambing period between 14 April and 22 April (median date April 19/20, see Jewell, 1989). An additional 16 male lambs (not shown in Table I) and 54 ewe lambs were tagged.…”

Section: Mulloch Mormentioning

confidence: 99%

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Survival and behaviour of castrated Soay sheep (Ovis aries) in a feral island population on Hirta, St. Kilda, Scotland

Jewell

1997

Journal of Zoology

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With 5 figures in the text)The free-living population of Soay sheep on the island of Hirta, St. Kilda, in the Outer Hebrides, has been intensively studied since 1959. The present study was initiated to throw light on the causes of the high mortality rate of adult rams in comparison to that of ewes. In 1978, 1979 and 1980, a total of 72 male lambs was castrated within a day or two of birth. The survival of these castrates has been much longer than that of the entire rams, marked as controls, and longer than that of ewes of the cohorts of the same years. The daily activity pattern of the castrates was similar to that of ewes rather than that of rams. In particular, during the rut the castrates spent most of the daylight hours grazing, in contrast to the rams who were continuously moving and involved in agonistic and sexual encounters. This study substantiates the earlier assertion that the costs in energy of reproduction are a major cause of mortality in temperate zone ungulates. The social organization of some castrates was similar to that of females in that they remained with the home-range group of ewes into which they were born, but other individuals resembled males in that these castrates clubbed together in their own groups. These patterns of behaviour persisted throughout life.

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Section: Mulloch Mormentioning

confidence: 99%

“…A visit to Hirta between 23 October and 21 November 1984 covered the first half of the rut (as judged from the median date of lambing, 23 April 1985, see Jewell, 1989). The castrates were still associated in the conspicuous all-castrate home-range groups.…”

Section: Social Organizationmentioning

confidence: 99%

Survival and behaviour of castrated Soay sheep (Ovis aries) in a feral island population on Hirta, St. Kilda, Scotland

Jewell

1997

Journal of Zoology

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“…Scottish Blackface (BF) and Shetland (SH) sheep are two breeds whose reproductive activity is highly seasonal (Hafez, 1952;Jewell, 1989), commensurate with the seasonal environments in which they are found. In contrast, polled Dorset Horn sheep (DT), although fairly closely related to primitive United Kingdom breeds (Ryder, 1964), have been genetically influenced by Mediterranean genotypes and have less seasonal reproductive activity (Hafez, 1952).…”

Section: Introductionmentioning

confidence: 99%

Seasonal variation of voluntary food intake and metabolic rate in three contrasting breeds of sheep

Iason¹,

Sim

Foreman³

et al. 1994

Anim. Sci.

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1994). Seasonal variation of voluntary food intake and metabolic rate in three contrasting breeds of sheep. AbstractVoluntary food intake (VFI) of chopped timothy hay and metabolic rate were each measured in each month of the year in six non-breeding ewes of each of three breeds. Metabolic rate was measured using indirect calorimetry over a range of food intakes and adjusted for intake to an estimated maintenance metabolic rate (MMR). The breeds compared were the Dorset Horn (DT), Scottish Blackface (BF) and Shetland (SH), the first being less seasonal in reproductive and other characteristics than the other two which are hill or northern latitude breeds. There was significant overall variation between months in VFI which was higher in the summer (July to September) than in the winter (December to February) months (P < 0-001). There was a significant breed X month interaction (P < 0-01), the seasonal effect being most strongly observed in the BF and SH ewes, whose VFI in summer was proportionately 0-1 greater than the year-round mean but was 0-1 lower in the winter. The DT ewes showed much less seasonal variation in VFI. There was no overall difference in VFI between breeeds (DT: 43-7; BF: 49-5; SH: 48-1 g dry matter per M 075 live weight per day, P > 0-1). Although MMR varied significantly between months (P < 0-001), there was no systematic variation between summer and winter. There was no significant breed X month interaction, but the MMR differed significantly (P < 0-001) between breeds giving a high overall MMR in BF (DT: 322-7; BF: 356-6; SH: 324-5 kf/kg M 075 per day). No significant correlation existed (P > 0-05) between the monthly mean MMR and VFI in any of the breeds. The causal relationship between seasonal cycles of basal metabolic rate and VFI is questioned.

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“…Density-dependent effects on reproduction have been reported in wild bighorn sheep (Jorgenson et al 1993), but findings from feral sheep elsewhere are inconsistent ; reproduction declined with increasing density on Campbell Island (Taylor el al 1970) but showed no relation to density on the island of Hirta (Grubb 1974a;Clutton-Brock et al 1991). Artificial selection on domestic sheep can effect patterns of fertility, but how these patterns change in feral sheep under natural selection may be influenced by breed, the new environment, and time since feralization (Rudge 1986;Jewell 1989). The effects of natural selection may also vary within a population ; the frequency of wool loss among Santa Cruz Island sheep, potentially an adaptive, derived character, varied greatly across the island (Van Vuren and Hedrick 1989).…”

Section: Discussionmentioning

confidence: 98%

“…Domestication involves intense artificial selection for certain traits, potentially at the expense of fertility (Cockrem and Clarke 1976;Jewell 1989). Feralization involves the release from artificial selection, potentially followed by natural selection in the new environment (Regnault 1976;Rudge 1986).…”

Section: Introductionmentioning

confidence: 99%

Density, reproduction, and group size in feral sheep on Santa Cruz Island, California, USA

Bowen¹,

Vuren²

1999

Mamm

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We evaluated the relationship between density, reproduction, and group size in an island population of feral sheep in which density varied greatly geographically. We expected that reproduction would vary inversely with density, and that groups would be smallest in high density areas because of low recruitment of offspring into social groups. We found no inverse relationship between density and reproduction in feral sheep, for uncertain reasons. We did find a positive relationship between reproduction and group size, but the relationship was weak, suggesting that factors besides recruitment of offspring play a dominant role in group formation and composition.Resume. -Nous avons tente d'evaluer les relations qui existent entre la densite, la reproduction et la taille des troupeaux dans une population insulaire de moutons domestiques retournes ä la vie sauvage dont la densite varie beaucoup geographiquement. Nous nous attendions ä ce que la reproduction varie en function inverse de la densite, et que les troupeaux soient plus petits dans des zones de densite elevee ä cause du faible renfort des jeunes dans les groupes sociaux. Pour des raisons mal determinees, nous avons irouve qu'il n'y avait pas une relation inverse entre la densite et la reproduction de ces moutons. Nous avons par contre mis en evidence une relation positive quoique faible entre la reproduction et la taille du troupeau, ce qui suggere que le renfort des jeunes joue un role essentiel dans la formation et la composition du troupeau.

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Factors that affect fertility in a feral population of sheep

Cited by 26 publications

References 15 publications

Survival and behaviour of castrated Soay sheep (Ovis aries) in a feral island population on Hirta, St. Kilda, Scotland

Survival and behaviour of castrated Soay sheep (Ovis aries) in a feral island population on Hirta, St. Kilda, Scotland

Seasonal variation of voluntary food intake and metabolic rate in three contrasting breeds of sheep

Density, reproduction, and group size in feral sheep on Santa Cruz Island, California, USA

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