Relationships between early postnatal growth and metabolic function of 16-month-old female offspring born to ewes exposed to different environments during pregnancy.

It was hypothesized that exposure of the fetus to adverse conditions in utero due to either maternal constraint or nutrition may result in developmental adaptations altering metabolism and postnatal growth of the offspring. Heavy (H) and light (L) Romney dams (G0) were allocated to ad libitum (A) or maintenance (M) nutritional regimens, from day 21-day 140 of pregnancy. Female twin-born offspring (G1) born to the dams in the four treatment groups will be referred to as HA-ewes, LA-ewes, HM-ewes and LM-ewes. At 16 months of age, offspring were catheterized and given intravenous insulin tolerance test (ITT), glucose tolerance test (GTT) and epinephrine tolerance test challenges to assess their glucose and fat metabolism in relation to their birth weight and postnatal growth. In HA-ewes, the regression coefficients of growth rates prior to puberty on insulin and glucose curves in response to GTT (InsAUCGTT) and ITT (GluAUCITT), respectively, were different from 0 (P < 0.05) and were different from the regression coefficients of HM-ewes. This may indicate that HA-ewes may have showed puberty-related insulin resistance at 16 months of age with increasing growth rates prior to puberty compared to HM- or LM-ewes. In HM-ewes, the regression coefficients of growth rates after puberty on InsAUCGTT and GluAUCITT were different from 0 (P < 0.05) and were different from those of HA-ewes. These results may indicate that offspring born to heavy dams fed maintenance during pregnancy and with greater postnatal growth rates after puberty could develop glucose intolerance and insulin resistance in later life.

Dam and granddam feeding during pregnancy in sheep affects milk supply in offspring and reproductive performance in grand-offspring.

In temperate climates, the cost of providing feed is greater in winter than in other seasons, causing ewes to be fed restricted rations during some periods of pregnancy. Epidemiological information indicates that undernutrition of the fetus may affect its health and performance in later life (i.e., fetal programming), and these effects may be passed between generations. The primary focus of the results presented in this paper is to examine the effects of feeding levels during pregnancy on a variety of traits from offspring at the fetal stage to 3.5 yr of age and also traits in the grand-offspring. Two studies are reported in which ewes were fed restricted diets during pregnancy, with a variety of fetal traits, offspring traits up to 3.5 yr of age, or grand-offspring traits up to 8 mo of age being measured. Study 2 also considered differences in dam size (heavy vs. light). In study 1, several fetal mammary gland measures indicated that milking ability may be enhanced in offspring from dams fed ad libitum during pregnancy. However, study 2 showed that mammary mass was greater in fetuses from dams fed at maintenance during pregnancy and that contemporaries of these fetuses produced greater protein and lactose yields in their first lactation. In the second lactation, the advantages in protein and lactose yields did not reoccur and ewes from ad libitum-fed dams produced greater fat yield. In study 2, grand-offspring whose granddams were fed at maintenance levels during pregnancy were lighter at birth in both the first and second parturitions than those whose granddams were fed ad libitum during pregnancy. First-parity grand-offspring whose granddams were fed maintenance levels during pregnancy achieved heavier BW by 40 to 50 d of age in the first lactation, which reflected the greater protein and lactose yields; however, no BW differences were present in second-parity lambs at the same age. A smaller proportion of first-parity ewe grand-offspring from heavy granddams that were fed ad libitum during pregnancy reached puberty at approximately 8 mo of age relative to the other granddam size and feeding groups. These results indicate that dam nutrition can affect the yield and composition of milk in their offspring and the BW and reproductive capability of their grand-offspring. Molecular and physiological mechanisms for these changes are being sought.

Effects of ewe size and nutrition on fetal mammary gland development and lactational performance of offspring at their first lactation.

Many environmental factors applied postnatally are known to affect milk production of the dam, but to date, the effects of different fetal environments on subsequent first lactational performance of the offspring have not been reported. Four hundred fifty heavy (H; 60.8 kg +/- 0.18) and 450 light (L; 42.5 kg +/- 0.17) dams were randomly allocated to ad libitum (A) or maintenance (M) nutritional regimens from d 21 until d 140 of pregnancy, under pastoral grazing conditions (HA, n = 151; HM, n = 153; LA, n = 155; LM, n = 153). At d 100 of pregnancy, a sub-group of twin-bearing dams was killed and fetal mammary glands collected. From 1 wk before lambing, all remaining dams were fed ad libitum until weaning. After weaning, female progeny were managed and fed under pastoral conditions as 1 group. At 2 yr of age, 72 twin-rearing ewe offspring were milked once a week for 7 wk. Fetuses from M-dams had heavier mammary glands (P = 0.03) compared with A-fetuses. Fetuses from H-dams had greater (P = 0.0008) mammary duct area compared with L-fetuses. At 2 yr of age, M-offspring had greater milk yields at d 7 (P = 0.02) and d 28 (P = 0.09) of lactation and tended to have greater accumulated milk yields (P = 0.11) compared with A-offspring. Ewes born to M-dams showed greater lactose percentage at d 14 (P = 0.002), d 21 (P = 0.06), and d 28 (P = 0.07) of lactation and greater (P = 0.049) accumulated lactose yields and CP (P = 0.06) yields compared with A-offspring. Ewes born to H-dams displayed greater milk yields at d 14 (P = 0.08) and d 21 (P = 0.02) and had greater accumulated milk yield (P = 0.08) and lactose yield (P = 0.04) compared with L-offspring. Lambs born to M-offspring were heavier at birth (P = 0.02) and grew faster until weaning (P = 0.02), matching the milk yield and composition data, compared with their ad libitum counterparts. Birth weight was not affected (P > 0.10) by grand dam size; however, lambs born to H-offspring grew faster from birth until d 49 of age (P = 0.03). In conclusion, dam nutrition during pregnancy affected the resulting milk production of the offspring and composition and growth of their lambs. In addition, dam size affected the milk production of the offspring, lactose yield, and growth of their lambs. These findings are important for furthering our understanding of how the environment to which the female fetus is exposed can affect her subsequent development and her ability to nourish the next generation.

Insulin regulation of amino-acid metabolism in the mammary gland of sheep in early lactation and fed fresh forage.

Insulin plays an important role in regulating the partitioning of nutrients to the mammary gland, particularly in lactating ruminants fed concentrate-based diets. There is evidence that the nutritional status of the animals might also affect their response to insulin. This is largely untested in early lactating ruminants fed fresh forage. To investigate nutritional effects on insulin response, 12 lactating sheep, housed indoors, were allocated to one of two treatment groups (hyperinsulinaemic euglycaemic clamp (HEC) or control) in a randomised block design and fed perennial ryegrass (Lolium perenne)/white clover (Trifolium repens) pasture. Mammary amino acid (AA) net uptake from plasma and utilisation for milk protein synthesis was measured during the 4th day of the HEC using arterio-venous concentration differences, and 1-13C-leucine was used to estimate whole body and mammary gland leucine kinetics. There was no change in feed intake, milk protein output and mammary blood flow during the HEC (P > 0.1). The HEC decreased (P < 0.1) the arterial concentrations of all essential AA (EAA) except histidine. The mammary net uptake of some EAA (isoleucine, leucine, methionine and phenylalanine) was reduced by the HEC (P < 0.1). Leucine oxidation in the mammary gland was not altered during the HEC (P > 0.1) but mammary protein synthesis was reduced by the HEC (P < 0.05). These results show that sheep mammary gland can adapt to changing AA precursor supply to maintain milk protein production during early lactation, when fed fresh forage. How this occurs remains unclear, and this area deserves further study.

The bone-muscle ratio of fetal lambs is affected more by maternal nutrition during pregnancy than by maternal size.

Bone formation and loss are related to the strain imposed on bone by muscle forces. Bone mineral content (BMC) and lean mass (LM) of fetal lambs was determined at day 140 of pregnancy in 8 groups of ewes, which were of either large or small body size, on either high (ad libitum) or maintenance pasture intake from day 21 of pregnancy, or carrying either singletons or twins. BMC and LM (using DXA scanning) of fetal hindquarters/spine were corrected to leg length. BMC and LM were less in twin than singleton groups (P < 0.001). Large ewes on high intake produced single fetuses with a (group mean) BMC/LM ratio that was higher (P < 0.002) than that in fetuses of large ewes with singletons on maintenance intake or twins on either high or maintenance intakes, the ratios of which were not different. In single fetuses from small ewes on high intake, the BMC/LM ratio was higher than those from small ewes with singletons on maintenance intake or twins on either high or maintenance intakes, the ratios of which were not different. The ratio was not different in singleton fetuses of ewes on high intake, whether they were large or small. Different fetal environments resulted in a given amount of muscle being associated with a higher or lower bone mass. Dietary intake during pregnancy was more important than maternal size in affecting the ratio. We conclude that intrauterine environmental factors may be important in determining bone mass postnatally, and possibly later in life.