Effects of prepartum dam energy source on progeny growth, glucose tolerance, and carcass composition in beef and sheep

A series of experiments were conducted in cattle and sheep to investigate the effects of prepartum dietary energy source during gestation on pre- and postpartum dam performance as well as on progeny growth, insulin sensitivity, and carcass composition. The three dietary energy sources used for the experiments were hay or haylage (fiber, HAY); corn (starch, CORN); or dried distiller grains (fiber plus fat, DDGS) and diets were fed to dams at isoenergetic intakes during gestation.;In the first experiment beef cows were used to determine the effects of late gestation dietary energy source on fetal growth and prepartum maternal hormone and blood metabolites. Cows fed HAY and CORN achieved the experimental objective of having similar body weight and body condition score change during late gestation, however, cows fed DDGS had greater body weight gain. This suggests DDGS may have a greater energy value than expected based on published reviews when limit-fed during gestation to beef cows. Calves from cows fed CORN and DDGS had heavier birth weights than calves from cows fed HAY. Differences in plasma metabolites may indicate differences in maternal metabolism in late gestation due to dietary energy source, which may affect partitioning of nutrients between maternal and fetal tissues.;Progeny from the first experiment were weaned, and then fed a common finishing diet until the calves reached a common fat thickness. These progeny were then slaughtered. Differences in birth weight were still evident upon entry into the feedlot, as body weights were heavier for calves from cows fed CORN and DDGS than from those fed HAY. In contrast to arrival at the feedlot, carcass weights were lighter for calves from cows fed DDGS than from those fed CORN or HAY. Growth rate was not different among treatments from birth to slaughter, but calves from dams fed CORN were slaughtered at a younger age than calves from cows fed HAY or DDGS. Measures of carcass yield were not affected by treatment, whereas intramuscular fat (a component of USDA quality grade) was greater in calves from dams fed DDGS or HAY than from those fed CORN. In addition, initial insulin secretion in response to a glucose tolerance test was greater in calves from dams fed HAY than calves from dams fed CORN or DDGS and was associated with greater intramuscular fat content per unit of fat thickness.;In the second experiment, mature ewes were fed dietary treatments in mid- to lategestation to determine effects on ewe prepartum metabolic energy status, postnatal progeny performance, glucose tolerance and carcass composition. During mid-gestation ewe body weight gain and body condition score were similar among treatments and met the experimental objective, whereas during late gestation body weight gain and body condition score were less at parturition in ewes fed HAY than those fed CORN or DDGS. Similar to experiment one, lamb birth weights tended to be greater in lambs from ewes fed CORN and DDGS than in lambs from ewes fed HAY. Greater maternal glucose concentrations were observed in ewes fed CORN, whereas greater maternal insulin and BUN concentrations were observed in ewes fed DDGS. Increased glucose and amino acid supply, as indicated by maternal metabolic status, could explain the increase in birth weight in lambs from ewes fed DDGS and CORN compared with that of lambs from ewes fed HAY.;Overall growth rate from birth to slaughter was not different among treatments. Lambs from ewes fed DDGS vs. lambs from ewes fed CORN or HAY tended to have a greater initial insulin secretion due to glucose infusion in the glucose tolerance test. No difference was detected in HCW, fat thickness, proportion of seam fat, or intramuscular fat content among treatments. However, lambs from ewes fed DDGS vs. lambs from ewes fed CORN or HAY had a greater proportion of internal fat, less muscle, and lower calculated boneless trimmed retail cut percentage.;The first experiment was repeated, because isoenergetic intakes were not achieved in the first experiment, and may have confounded responses observed. Cow body weight gain was similar among treatments during late gestation, thus, this experimental objective was met. Cows fed HAY vs. cows fed CORN or DDGS had greater non-esterified fatty acids, lower blood urea nitrogen, and lower insulin concentrations postfeeding, as well as lower progeny birth weights. At 93 days of age, progeny's fed and fasted glucose and insulin concentrations were measured. Fasting glucose concentrations were greatest to least for calves from cows fed CORN, HAY, and DDGS, respectively, whereas fed glucose and insulin, and fasted insulin concentrations, were similar among treatments.;In all three experiments, prepartum energy source did not adversely affect postpartum cow or ewe performance. Together these results suggest prepartum energy sources, which may increase maternal glucose and amino acid supply to the fetus, impact fetal growth and alter postnatal insulin sensitivity and adipose tissue development. These alterations in fetal development have long-term effects on carcass composition.