R. G. Gunn

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

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.

Plasma FSH, LH, prolactin and progesterone profiles of Cheviot ewes with different levels of intake before and after mating, and associated effects on reproductive performance

Abstract Patterns of secretion of FSH, LH and prolactin were investigated in the luteal and follicular phases of the cycle prior to mating in Cheviot ewes on high and low intakes (approximately 3.0 and 0.8 kg DM per head per day) during the weeks before mating. Ewes on the high intake had a higher mean ovulation rate (1.95 vs 1.40; P No significant differences associated with intake were observed in the endocrine profiles during the luteal phase of the cycle before mating, indicating that differences in reproductive performance were not mediated by changes in endocrine profiles in this period. However, during periods of the subsequent follicular phase, ewes on a high intake had a higher LH pulse frequency, higher mean prolactin levels and non-significantly higher FSH levels. The preovulatory peaks of these hormones were not altered by the level of intake but the mean peak values for prolactin and LH were significantly higher in ewes with multiple ovulations than in those with single ovulations. Differences in endocrine status prior to mating were not associated with differences in luteal function after mating, as measured by circulating progesterone levels. However, mean progesterone levels were higher in ewes on a low intake after mating compared with those on a high intake.

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

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.

Effects of body condition and environmental stress on ovulation rate, embryo survival, and associated plasma follicle stimulating hormone, luteinizing hormone, prolactin and progesterone profiles in Scottish Blackface ewes

In a 2 × 2 factorial experiment, half of each of two groups of ewes in high (20 ewes) or low body condition (20 ewes) were subjected to procedures designed to simulate normal management and climatic stresses, and the effects of these treatments on ovulation rate, embryo survival and endocrine status were investigated. The mean ovulation rate of ewes in the high condition group was significantly higher than that of ewes in the low condition group (1·8 v. 11) ( P Circulating follicle stimulating hormone, luteinizing hormone and prolactin levels were recorded in the peri-ovulatory period. Mean circulating follicle stimulating hormone levels were similar in three of the treatment groups but were generally lower in ewes in the low condition/stressed group. This difference was significant in some of the sampling periods. Neither basal levels of luteinizing hormone nor the size of the pre-ovulatory luteinizing hormone surge were significantly affected by level of body condition or stress but the surge began earlier in ewes in the low condition groups. The difference in timing was not, however, related to ovulation rate. Circulating prolactin levels were consistently and often significantly lower in ewes in poor condition ( P While ovulation rate was affected by body condition, the recorded progesterone profiles during the first 2 weeks after mating suggest that luteal function was not affected by any of the treatments applied.

Effects of high levels of body condition and food intake on plasma follicle stimulating hormone, luteinizing hormone, prolactin and progesterone profiles around mating in Greyface ewes

Two groups of 19 Border Leicester cf × Scottish Blackface 9 ewes were fed so that ewes of one group were in a very high level of body condition at mating (mean score 3·35) and had a high level of intake. Ewes of the second group were in moderately high condition (mean score 2·74) and were given a live-weight maintenance ration. Ewes in the high group had a higher ovulation rate than those of the moderate group (3·36 v . 2·33) but a lower number of embryos per ewe mated (1·16 v . 1·42). Mean follicle stimulating hormone profiles were similar for ewes of the two groups during the luteal and follicular phases of the cycle before mating and during the subsequent oestrus. Mean prolactin concentrations were higher in ewes of the high group during the follicular phase and oestrus but not during the luteal phase. Mean luteinizing hormone (LH) concentrations were higher in ewes of the high group during the follicular phase and oestrus but not during the luteal phase. Mean LH concentrations were similar for the two groups at all times but the frequency of LH pulses was higher in the high group during the follicular phase. Ewes that were not pregnant at slaughter had abnormal progesterone profiles following mating, abnormal pre-ovulatory LH surges or failed to show oestrus. These abnormalities were not related to gonadotrophin profiles prior to oestrus.

Fertility in Cheviot ewes. 3. The effect of level of nutrition before and after mating on ovulation rate and early embryo mortality in South Country Cheviot ewes in moderate condition at mating

One hundred and twenty South Country Cheviot hill ewes were differentially group-fed indoors over a 2-month period to achieve either moderately-good or poor body condition. Over 5 weeks prior to mating, ewes in moderately-good condition were brought down in condition by restricted feeding and ewes in poor body condition were raised in condition by a high level of feeding. The ewes were thus in moderate condition at mating. During the first 4 weeks after mating, half the ewes from each original condition group were fed at a high level and the other half were fed at a low level. Ewes were killed either on return to service or at 30 ± 10 days forcounts of corpora lutea and viable embryos. Ovulation rate was not significantly related to the level of pre-mating food intake at the condition level studied, although the trend was positive. Embryo mortality, as ova loss, was reduced by a high level of post-mating food intake but was increased by a high level of pre-mating intake. This latter result, however, may be influenced by the experimental confounding of high pre-mating food intake and very low initial body condition. The greatest loss was incurred by ewes, originally in poor condition, which were fed at a high pre-mating level and a low post-mating level. Potential lambing rate at slaughter was not affected by the level of food intake either before or after mating although the trend was for a low level of post-mating intake to be associated with an increase in the proportion of barren ewes.

A note on the effect of the direction of live-weight change about the time of mating on reproductive performance of Greyface ewes

Over 3 years, in Greyface ewes stocked at 10 or 15 per ha and mated in October (early) or November (late), lamb production at birth was related to the pattern of live-weight change of the individual ewe about mating. Based on weighings at 1·5- to 3-week intervals, ewes were grouped according to whether they were gaining (114 ewes), losing (221) or apparently maintaining weight (339) at the time of mating. Ewes losing weight produced significantly fewer lambs (1·58) than did ewes maintaining weight (1·78) while both produced significantly fewer lambs than did ewes gaining weight (1·96). Differences in lamb production between years (year 1 = 1·84, year 2 = 1·71, year 3 = 1·70) and times of mating (early = 1·82, late = 1·67) can be explained in terms of live weight at mating and the different proportions of ewes gaining, maintaining and losing weight. On the basis of earlier studies, it is suggested that the effect of direction of live-weight change operated on failure to conceive or on total loss of multiple-shed ova and was more important pre-mating than post mating.

Effect of body condition and pasture type on herbage intake, performance during lactation and subsequent ovulation rate in Scottish Blackface ewes

Scottish Blackface ewes in uniform, good, body condition at mating were differentially fed during pregnancy, such that two groups lost 0·15 to 0·20 (groups A and B) and one group gained 0·05 (group C) of maternal live weight by lambing time. The treatments had little effect on the number of lambs born per ewe lambing (1·39, 1·46 and 148 respectively). Prior to parturition, group A was transferred to a poor hill pasture, and groups B and C to an improved upland reseeded pasture. Herbage intake by six single- and six twin-suckling ewes from each group was estimated in the 3rd, 6th and 8th week after parturition, and mean daily milk production was estimated on 1 day following each intake measurement period. Herbage intake by six dry ewes in each of groups A and B was also estimated. There were significant differences amongst groups A, B and C, respectively, in mean organic matter digestibility of the herbage consumed (0·701, 0·771 and 0·773), mean daily digestible organic-matter intake (1·06, 1·46 and 1·46kg), mean live-weight change over the period ( –2·9, +5·4 and +l·3kg) and mean daily milk yield (0·64, 1·93 and 1·95 kg). By the following mating time, after grazing the same pasture from weaning, there was still a difference in body condition score according to pasture type during lactation (2·08, 2·36 and 2·29, respectively). Ovulation rate measured after mating was consistent with the direct effect of body condition (1·34, 1·56 and 1·52, respectively).

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

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.

The effect of different durations and times of high- level feeding prior to mating on the reproductive performance of Scottish Blackface ewes

One hundred and sixty-four Scottish Blackface ewes from two different farm sources were brought into a uniform moderately-poor level of body condition by early November. Five groups of approximately 33 ewes were then fed different amounts of pelleted dried grass and hay on pasture to achieve either high (H) or live-weight maintenance (M) levels of intake for different durations and at different times in the 36 days prior to mating at a synchronized oestrus. One group of ewes was fed the M level throughout, two groups were fed the H level for 18 days either preceded or followed by 18 days of the M level and two groups were fed the H level for 27 days either preceded or followed by 9 days of the M level. After mating, all ewes were fed the M level until slaughtered on return to service or at 28 (± 8) days after mating for counts of corpora lutea and viable embryos relating to first mating. The gain in body condition and live weight after 18 days of H feeding was about half that achieved after 27 days. Time of H feeding had no differential effect on gain in condition or live weight. H feeding increased ovulation rate only if fed immediately prior to mating. When a period of M feeding preceded mating, most of the advantage was lost, particularly with 18 days of M feeding after 18 days of H feeding. Embryo mortality measured as ova loss was not significantly affected by either the duration or time of H feeding, although there was a trend for loss to decrease with increasing duration. Potential lambing rate to first mating was therefore significantly increased by H feeding for 27 days even when followed by 9 days of M feeding prior to mating but was not significantly increased by H feeding for only 18 days even when fed immediately prior to mating. Differences in response were obtained from the ewes from the two sources. H feeding only produced a significant improvement in reproductive performance when potential was high and this was partly related to greater size. In populations with low potential, the provision of H feeding in the pre-mating period is therefore of doubtful economic advantage.