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Maternal nutrition affects fetal development, with potential lifelong consequences. The study reported here compared the anatomical development (dimensions and organs) of twin fetuses at Day 140 of gestation, from 58 twin-bearing ewes fed at one of three different nutritional treatments in early pregnancy [Day 21–50, Low (LD21–50) versus Medium (MD21–50) versus High (HD21–50)] and one of two different nutritional treatments in mid- to late pregnancy (Day 50–140, Medium (MD50–140) versus High (HD50–140)]. There were no effects (P > 0.05) of either early or mid- to late pregnancy nutrition on placental weight and fetal bodyweight or size measurements at Day 140. Semitendinosus muscles from LD21–50-HD50–140 fetuses were heavier (P < 0.05) than those from LD21–50-MD50–140 and HD21–50-HD50–140 fetuses, and fetuses from LD21–50 dams had lighter (P < 0.05) mammary glands compared with those from MD21–50 and HD21–50 dams, even after adjustment for fetal weight. Maternal nutrition also affected (P < 0.05) the weights of the fetal thyroid and brain. These results suggest that farmers can limit ewe nutrition in early pregnancy with only minor effects on the fetus. To investigate potential lifetime effects, a larger cohort of these animals is currently being monitored.

This study set out to determine the stage of gestation at which maternal constraint on fetal growth occurs and whether pregnancy nutritional level could alleviate that constraint. One-hundred and thirty-eight Cheviot (C) and 114 Suffolk (S) ewes were split into two groups and bred with either 12 S or 12 C rams to generate four ewe/fetal groups CC (C dam and C sire), CSinC (crossbred fetus in C ewe), CSinS, and SS. At Day 21 of pregnancy (P21), half of the ewes in each of the four groups were randomly allocated to either a maintenance (M) or ad libitum (A) nutritional treatment, under pastoral grazing conditions. At P100, a subgroup of singleton-bearing ewes including ewes from all four groups (n = 55 in total) were euthanised (Study 1). Maternal, placental and fetal weights and sizes were recorded. The remaining ewes were fed to appetite from P140 and were allowed to lamb (n = 114 in total, Study 2) and lamb liveweights were recorded within 12 h of birth and at average days 30 and 100 (L30, L100) of lactation. In both studies, M ewes were lighter (P < 0.05) than A ewes, and CC and CSinC ewes were lighter (P < 0.05) than CSinS and SS ewes. In Study 1, maternal nutritional treatment had no effect (P > 0.05) on fetal bodyweight although fetuses from A ewes had heavier (P < 0.05) livers, spleens and thyroids than fetuses from M ewes. CC and CSinC fetuses were lighter (P < 0.01) than both CSinS and SS fetuses. In Study 2, lambs born to M ewes were lighter (P < 0.05) at birth and at L100 than lambs born to A ewes. CC lambs were lighter (P < 0.01) than CSinC, CSinS and SS lambs at birth. At L30 and L100, CC lambs were lighter (P < 0.05) than CSinC lambs, which, in turn, were lighter (P < 0.05) than both CSinS and SS lambs, which did not differ (P > 0.05). Combined, these studies indicate that maternal nutrition may have little impact on singleton-offspring development until late gestation while, in contrast, dam size affected fetal size by the end of the second trimester. These data suggest that the C ewe constrains the growth of the crossbred fetus well before a ‘physical’ constraint would be expected.

This study investigated whether selection for ewe size and nutrition during the previous pregnancy would affect the lactational performance of the ewe and liveweight gain of her lamb(s) in the subsequent year. A subgroup of singleton-bearing Romney ewes were milked once a week, for 7 consecutive weeks. Singleton-bearing ‘light’ ewes that gave birth to twins in the previous year had reduced milk yields from Day 21 of lactation (L21) onwards in the present year compared with those that gave birth to singletons in the previous year. Lambs born to light ewes had reduced liveweight gain from birth to L21 compared with those born to ‘heavy’ ewes. Singleton-bearing ewes in the present year that were fed maintenance and gave birth to twins in the previous year, produced less milk from L21 onwards compared with those that were maintenance-fed and singleton-bearing in the previous year. Singleton lambs born to milked ewes that were fed maintenance and gave birth to twins in the previous year, had lower liveweight gain from birth to L21 in the present year compared with lambs born to ewes fed maintenance and gave birth to singletons in the previous year. In the entire population, lambs born to ewes fed maintenance and that gave birth to twins in the previous year were lighter at L21 than lambs born to ewes fed ad libitum and bearing twins in the previous year. This indicates that if nutrition is suboptimal, or the ewes are lighter in the previous year, those that were twin-bearing are more likely to rear lighter lambs in the present year. Therefore, farmers need to take these points into consideration when devising feeding plans for the present year.

Nutrition of the ewe at various stages of pregnancy is known to affect ewe and offspring performance. However, little is known regarding the potential interactions among differing maternal nutrition regimens in early and mid–late pregnancy. The objective of the present study was to examine the effects and potential interactions of three pastoral nutritional treatments from Day 21 of pregnancy (P21) to P50 (Sub-maintenanceP21–50 (total liveweight change achieved, SMP21-50, –0.15 ± 0.02 kg/day) v. MaintenanceP21–50 (MP21-50,–0.02 ± 0.02 kg/day) v. Ad libitumP21–50 (AdP21-50,0.15 ± 0.02 kg/day) and two pastoral nutritional treatments from P50 to P139 [MaintenanceP50–139 (designed to match change in conceptus mass, total liveweight change achieved, 0.19 ± 0.01 kg/day) v. Ad libitumP50–139 (0.26 ± 0.01 kg/day)] on 382 twin-bearing ewes and their offspring until 91 days after the mid-point of lambing (L91). Ewe liveweight and condition scores in pregnancy and lactation, and lamb liveweights, indices of colostrum uptake and survival were recorded. There were no interactions between nutritional periods for lamb liveweight, apparent colostrum intake and survival, and ewe liveweight, condition score and total weight of lamb per ewe at the end of the study. At L91, ewe nutritional treatment during P21–50 or P50–139 had no effect on either ewe liveweight or body condition score. Ewe nutritional treatment during P21–50 had no effect on lamb birthweight. Lambs born to AdP50–139 ewes were lighter (P < 0.05) than those born to MP50–139 ewes (5.32 ± 0.04 v. 5.48 ± 0.04 kg, respectively). Ewe nutritional treatment during P21–50 or P50–139 had no (P > 0.05) effect on indices of colostrum uptake in lambs at 24–36 h of age. At L91, ewe nutritional treatment during P21–50 or P50–139 had no effect on lamb liveweight, survival or total weight of lamb per ewe. In conclusion, although considerable differences in ewe liveweight were observed during pregnancy, the nutritional treatments had no effect on the production parameters measured at the end of the study. These results indicate, first, that farmers can use early pregnancy as a period to control ewe nutrition when ewes are offered at least pregnancy maintenance levels of nutrition in the mid–late pregnancy period and, second, that there is no advantage from offering twin-bearing ewes a level of nutrition above their pregnancy maintenance requirements in mid–late pregnancy.

Little is known about the long-term metabolic effects of maternal constraint on the offspring and whether a possible interaction of dam size and nutrition during gestation exists, affecting postnatal metabolic functions in the offspring. Four hundred and fifty heavy (H) (60.8 ± 0.18 kg) and 450 light (L) (42.5 ± 0.17 kg) Romney dams were allocated to ad libitum (A) or maintenance (M) nutritional regimens under New Zealand pastoral grazing conditions, from Day 21 to 140 after insemination. One week before lambing, all dams and offspring were managed as one group and provided with ad libitum feeding. At 16 months of age, female twin-born offspring (n = 12 per size by nutrition group) were catheterised and given intravenous insulin (0.15 IU/kg) (ITT), glucose (0.17 g/kg) (GTT) and epinephrine (1 μg/kg) (ETT) challenges to assess their glucose and fat metabolism and adrenal function. No effects of dam size or interactions between dam size and dam nutrition were found on glucose or fat metabolism or adrenal function. In response to the ETT, M-dam offspring showed greater (P < 0.05) peak glucose concentrations, increased (P < 0.05) glucose area under the curve and tended (P < 0.10) to have increased maximum change in glucose and non-esterified free fatty acid concentrations compared with A-ewes. No effects of dam nutrition were found on glucose tolerance, insulin resistance or adrenal function in response to GTT and ITT. In conclusion, dam size had no effect on glucose metabolism, adrenal function or fat metabolism in 16-month-old female twin offspring. Dam nutrition during pregnancy from Day 21 to 140 had no major effect on glucose metabolism, adrenal function or lipolysis; however, it did potentially affect gluconeogenesis and/or glycogenolysis, as increased glucose concentrations in ewes born to M-fed dams were observed in response to ETT. These results indicate that M-ewes could have an advantage over A-ewes in physiological stressful situations in life (e.g. pregnancy, lactation) as their liver may be able to supply more glucose to support their growing conceptus and milk production to increase the chances of survival of their offspring.