Further Observations on the Seasonal Variation in Worm Egg Output in Scottish Hill Sheep

Morgan, D. O.; Parnell, I. W.; Rayski, C.

doi:10.1017/s0022149x00019180

“…The levels of FEC observed in Soay sheep were generally comparable to those observed in untreated domestic hill sheep in Scotland (Morgan et al 1950). Mean natural log(summer FEC) was considerably higher and relatively less variable in males than in females (CV ϭ 50.5% vs. 90.3%, respectively).…”

Section: Resultssupporting

confidence: 67%

Positive Genetic Correlation Between Parasite Resistance and Body Size in a Free-Living Ungulate Population

Coltman

¹

,

Pilkington

²

,

Kruuk

³

et al. 2001

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Parasite resistance and body size are subject to directional natural selection in a population of feral Soay sheep (Ovis aries) on the island of St. Kilda, Scotland. Classical evolutionary theory predicts that directional selection should erode additive genetic variation and favor the maintenance of alleles that have negative pleiotropic effects on other traits associated with fitness. Contrary to these predictions, in this study we show that there is considerable additive genetic variation for both parasite resistance, measured as fecal egg count (FEC), and body size, measured as weight and hindleg length, and that there are positive genetic correlations between parasite resistance and body size in both sexes. Body size traits had higher heritabilities than parasite resistance. This was not due to low levels of additive genetic variation for parasite resistance, but was a consequence of high levels of residual variance in FEC. Measured as coefficients of variation, levels of additive genetic variation for FEC were actually higher than for weight or hindleg length. High levels of additive genetic variation for parasite resistance may be maintained by a number of mechanisms including high mutational input, balancing selection, antagonistic pleiotropy, and host-parasite coevolution. The positive genetic correlation between parasite resistance and body size, a trait also subject to sexual selection in males, suggests that parasite resistance and growth are not traded off in Soay sheep, but rather that genetically resistant individuals also experience superior growth.

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“…Matched weight, hindleg length, and summer FEC data were available for 493 males (N ϭ 687 observations) and 576 females (N ϭ 1250 observations; Table 1). The levels of FEC observed in Soay sheep were generally comparable to those observed in untreated domestic hill sheep in Scotland (Morgan et al 1950). Mean natural log(summer FEC) was considerably higher and relatively less variable in males than in females (CV ϭ 50.5% vs. 90.3%, respectively).…”

Section: Resultssupporting

confidence: 67%

Positive Genetic Correlation Between Parasite Resistance and Body Size in a Free-Living Ungulate Population

Coltman¹,

Pilkington²,

Kruuk³

et al. 2001

Evol

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Parasite resistance and body size are subject to directional natural selection in a population of feral Soay sheep (Ovis aries) on the island of St. Kilda, Scotland. Classical evolutionary theory predicts that directional selection should erode additive genetic variation and favor the maintenance of alleles that have negative pleiotropic effects on other traits associated with fitness. Contrary to these predictions, in this study we show that there is considerable additive genetic variation for both parasite resistance, measured as fecal egg count (FEC), and body size, measured as weight and hindleg length, and that there are positive genetic correlations between parasite resistance and body size in both sexes. Body size traits had higher heritabilities than parasite resistance. This was not due to low levels of additive genetic variation for parasite resistance, but was a consequence of high levels of residual variance in FEC. Measured as coefficients of variation, levels of additive genetic variation for FEC were actually higher than for weight or hindleg length. High levels of additive genetic variation for parasite resistance may be maintained by a number of mechanisms including high mutational input, balancing selection, antagonistic pleiotropy, and host-parasite coevolution. The positive genetic correlation between parasite resistance and body size, a trait also subject to sexual selection in males, suggests that parasite resistance and growth are not traded off in Soay sheep, but rather that genetically resistant individuals also experience superior growth.

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“…Lambing occurred during the six weeb following 22 August, and the post-parturient rise established by several workers (Morgan, Parnell, and Rayski 1950;Parnell, Dunn, and Mackintosh 1954;Spedding and Brown 1956;Brunsdon 1964) occurred in October. This rise was evident in the more intensively stocked paddocks, but not in 7 and II, where the stocking rate was low and adequate feed was available.…”

Section: Discussionmentioning

confidence: 98%

“…INTRODUCTION 573 Morgan, Parnell, andRayski (1950, 1951), and Parnell, Dunn, and Mackintosh (1954), have found Nematode parasItIsm to be of consequence in Scottish hill sheep, and, because of the lack of information in New Zealand, the authors took the opportunity to investigate Nematode parasitism in hill-country breeding ewes at the Te Awa sub-station of Grasslands Division, D.S.I.R. The trials at Te Awa have been concerned with the improvement of hill pastures, and, more recently, with the effects of an increase in stocking rate on pasture and animal production.…”

mentioning

confidence: 99%

A study of Nematode parasitism in hill-country breeding ewes

Tetley¹,

Langford²

1965

New Zealand Journal of Agricultural Research

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A two-year study of Nematode parasitism has been carried out on Romney breeding ewes run at stocking rates ranging from three to seven ewes per acre.Total egg numbers of the ewes at the low stocking rates were consistently lower than those at the high stocking rates, but results indicated that egg numbers rarely reached a level considered to be detrimental to sheep health (i.e .. above 2,000 eggs per g faeces moist weight).A post-parturient rise in egg numbers occurred at high but not at low stocking rates. Ostertagia spp. were mainly responsible for this rise but BUllostomum trigollocephaillm predominated in the egg counts throughout the rest of the year. Some large numbers of B. trigonocephalum worms were found in a few dead or extremely emaciated sheep. Bunostomum egg numbers were significantly higher in the ewes at high stocking rates without cattle than at low stocking rates. Numbers in ewes at high stocking rates with cattle were intermediate.

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Further Observations on the Seasonal Variation in Worm Egg Output in Scottish Hill Sheep

Cited by 55 publications

References 2 publications

Positive Genetic Correlation Between Parasite Resistance and Body Size in a Free-Living Ungulate Population

Positive Genetic Correlation Between Parasite Resistance and Body Size in a Free-Living Ungulate Population

Positive Genetic Correlation Between Parasite Resistance and Body Size in a Free-Living Ungulate Population

A study of Nematode parasitism in hill-country breeding ewes

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