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Featured researches published by D. A. Sim.


Animal Science | 1995

Effects of nutrition in utero and in early life on the subsequent lifetime reproductive performance of Scottish Blackface ewes in two management systems

R. G. Gunn; D. A. Sim; E. A. Hunter

Over 3 years, a flock of Scottish Blackface ewes was managed so that one-third of the ewes received a high level of nutrition during the last 100 days of pregnancy (P), one-third received a high level of nutrition during the first 100 days of lactation (L) and one-third received a low level of nutrition as derived from a hill grazing over the same two periods (C). From these ewes, 496 ewe lambs were retained at weaning (19 to 22 weeks of age), balanced for treatment, year and birth type. At 6 months of age half of the lambs, similarly balanced, were transferred to an upland grazing system (U) for three breeding years. The other half was retained on the same hill grazing as their mothers for the same period (H). At the end of the study, all ewes were fed to reduce the range in body condition at a synchronized mating and ovulation rates were determined at slaughter. Differences in live weight of ewes due to treatment between groups P, L and C had disappeared by 18 months. There were no pre-mating differences between treatments in live weight or body condition score except that ewes in group P had higher live weights than those in group C at condition scores greater than 2·75. There was little effect of grazing system on the differences between treatments in live weight or body condition score at 30 and 42 months but H ewes were heavier and fatter at 18 months of age. Ewe mortality was consistently less in group L than in groups P and C and on system H than on system U, although the differences were not statistically significant. Group L had fewer barren ewes than groups P and C, and barrenness was significantly greater in the U than the H system. Group C had proportionally more single than multiple births than either groups P or L. At the end of the study there were no differences between the treatments in the proportion of ewes successfully mated at the final mating nor in their ovulation rates in relation to pre-mating body condition. It is concluded that nutrition during either the lactation period or late pregnancy period can influence subsequent lifetime reproductive performance and that this was expressed through an effect on embryo or foetal loss since there were neither residual differences apparent in live weight or condition score nor in ovulation rate potential.


Animal production | 1991

Pre-mating herbage intake and the reproductive performance of north Country Cheviot ewes in different levels of body condition

R. G. Gunn; W. F. Smith; A. J. Senior; E. Barthram; D. A. Sim; E. A. Hunter

Over 4 years, a flock of mature North Country Cheviot ewes was grazed on different swards between weaning in August and mid October to achieve a range of condition scores at 5 weeks before mating (post-weaning period). During the subsequent 5 weeks before a synchronized mating (pre-mating period), all ewes were grazed on a perennial ryegrass/white clover sward, provided at high (H) or low (L) herbage masses (1600 to 2100 or 1200 to 1400 kg dry matter (DM) per ha, respectively). Ovulation rate was derived from the number of corpora lutea in 101 ewes slaughtered after first mating. Conception and lambing rates were derived from the number of lambs born to first mating of 406 ewes. In 2 out of the 4 years, 79 ewes were used to estimate herbage intake. There was no effect of post-weaning management on reproductive performance. Herbage intake and reproductive performance were examined in relation to the body condition of the ewes at 5 weeks before mating. On an H herbage mass pre-mating, herbage intake in the period immediately prior to mating was greatest in ewes in low body condition and declined significantly with increasing condition. On an L herbage mass pre-mating, herbage intake did not vary significantly with condition. Ovulation rate was low in ewes in low body condition (scores =≤·25) at 5 weeks before mating, increased significantly with increasing condition up to scores 2·50/2·75 but did not change significantly above such intermediate scores. Conception and lambing rates increased significantly with increasing body condition up to scores 2·50/2·75 and then decreased significantly as condition increased above these levels. These effects of body condition were greater on an L herbage mass pre-mating than they were on an H herbage mass. Ewes in the intermediate body condition scores of 2·50 and 2·75 at 5 weeks before mating had a low sensitivity to contemporary nutrition pre-mating. Such condition levels are therefore considered to be above the range of condition in the North Country Cheviot breed within which reproductive response is affected by contemporary nutrition pre-mating. The lower reproductive performance of ewes in high body condition (scores 3=3·00) at 5 weeks before mating was related to an increase in estimated ova and embryo loss and may be associated with a reduced herbage intake.


Animal production | 1986

Effects of age and its relationship with body size on reproductive performance in Scottish Blackface ewes

R. G. Gunn; J. M. Doney; W. F. Smith; D. A. Sim

On a hill farm, the reproductive performance of Scottish Blackface ewes increases annually with increasing age up to 6 years and is positively related to pre-mating live weight. A group of Scottish Blackface ewe lambs was, from 5 months of age, preferentially managed over a 2-year period to accelerate the achievement of mature size, in order to study the relative importance of age and size to reproductive performance. Ovulation rate and early embryo mortality of these ewes at 31 months of age were compared with those of adult ewes of similar body size and condition at 79 months of age which had been reared conventionally in the same hill flock. Two comparisons were made, one between different age groups in the same year and the other retrospectively between different ages of the same age group. In the first comparison, the adult ewes had a slightly greater reproductive response which suggested a small effect of age per se but there was also the possibility of a genetic difference. In the second comparison, there was no difference in ovulation rate or potential lambing rate per pregnant ewe, but a trend towards greater wastage of twin-shed ova in the heavier and fatter younger ewes again suggested a small effect of age. At both ages, however, these ewes performed close to their adult genetic potential which suggested that the treatment of the young ewes was sufficient to overcome most of the limitations associated with age or size. Reproductive performance normally associated with young animals is therefore mainly an expression of their size relative to their maturity and the removal of the size limitation by higher levels of nutrition and more rapid growth can largely eliminate their poorer performance.


Animal production | 1991

A note on herbage intake by Greyface ewes on perennial ryegrass white clover swards in the autumn

R. G. Gunn; J. M. Doney; W. F. Smith; A. D. M. Smith; D. A. Sim; E. A. Hunter

The effects on herbage intake of changes of herbage mass associated with different stocking rates were studied in Greyface (Border Leicester × Scottish Blackface) ewes in the autumn. Intake was measured in 5-day periods in late September (PI), late October (P2) and late November (P3) on two established, perennial ryegrass/white clover swards (SI and S2). Both swards had previously been variably stocked to produce areas with a range in herbage masses, some of which were grazed continuously (G) at stocking rates declining from 18 to 6 ewes per ha. Intake was also measured in P2 and P3 on other areas of the swards which were ungrazed for 6 weeks in September and October (C) and then stocked at 18 ewes per ha. Intakes of dry matter, organic matter and digestible organic matter were 16 g, 10 g and 7·5 g/kg live weight, respectively. Organic matter digestibility was 075 in PI and P2 but declined in P3. Differences in herbage intake and digestibility arose largely because of differences between the swards in herbage mass, sward height and sward density. Ewes in condition scores > 3·00 in early September had lower intakes at all times than did thinner ewes. Changes in sward management associated with different strategies of use had little long-term effect on herbage intake. Keywords: digestibility, herbage, sheep, stocking rate.


Animal Science | 1991

The effect of level of nutrition prior to mating on the reproductive performance of ewes of two welsh breeds in different levels of body condition

R. G. Gunn; T. J. Maxwell; D. A. Sim; J. R. Jones; M. E. James


Animal production | 1983

Lactation performance, herbage intake and lamb growth of Scottish Blackface and East Friesland × Scottish Blackface ewes grazing hill or improved pasture

J. M. Doney; J. N. Peart; W. F. Smith; D. A. Sim


Animal production | 1984

Milk and herbage intake of suckled and artificially reared lambs at pasture as influenced by lactation pattern

J. M. Doney; A. D. M. Smith; D. A. Sim; D. Zygoyannis


Animal production | 1990

The effect of different pasture management strategies during the weaning-to-mating period on reproductive performance of Greyface ewes

R. G. Gunn; J. M. Doney; R. D. M. Agnew; W. F. Smith; D. A. Sim


Animal Science | 1992

The effect of feeding supplements in the autumn on the reproductive performance of grazing ewes 2. Feeding supplements in relation to sward height

R. G. Gunn; J. R. Jones; D. A. Sim


Animal production | 1988

The effect of sward height and active immunization against androstenedione on reproductive performance of ewes of two Welsh breeds in different body conditions

R. G. Gunn; S. M. Rhind; T. J. Maxwell; D. A. Sim; J. R. Jones; M. E. James

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