David L. Morris: Vet Column 2-21-11
Feeding pregnant animals, particularly in the latter half of gestation, can affect fetal growth. For animals such as sheep, which frequently bear multiple fetuses, nutrient intake prior to lambing is important. Previous studies in cattle, another ruminant, have indicated that winter-feeding systems that differ in primary energy source for spring calving cows can alter the subsequent birth weight of the progeny. Investigators from The Ohio State University recently studied the effects of feed source in gestating ewes on fetal growth.
High starch diets increase the amount of glucose in the liver which, in turn, stimulates the release of insulin. The resulting availability of nutrient supply in pregnant ewes is presented to the developing fetuses as well. As fetuses mature prior to lambing, the demand for nutrients increases; therefore, feeding programs in late gestation can make a difference. For this study, haylage, limit-fed corn, and limit-fed dried distillers grains were compared as the primary feed source during mid- and late-gestation in ewes.
Ninety mature crossbred Hampshire X Dorset ewes weighing approximately 180 pounds were used in this study at the Sheep Center of the Ohio Research and Development Center in Wooster, Ohio. Ewes were exposed to rams for 28 days and pregnancy was confirmed by ultrasound at 41 and 62 days following the introduction of the ram. At approximately 80 days of gestation, ewes were sorted by body weight, body condition score, number of fetuses, and sire.
Dietary treatments were one of three winter-feeding systems which differed in primary feed source. One group was fed free choice haylage from first cutting alfalfa and contained 13.7 percent crude protein. A second group was limit-fed corn. A third group was limit-fed dried distillers grains obtained from production on one day from a single ethanol plant. All diets were formulated to meet or exceed National Research Council (NRC) nutrient requirement for mid gestation and late gestation. The intake of corn and dried distillers grains diets were designed to be similar in energy intake to the free choice haylage. Once lambing occurred, all ewes were fed the same diet during lactation.
Results of this study indicated that during mid-gestation (day 60 to 115), body weight gain of ewes was similar among treatments. At day 115, ewes fed haylage had a lower body condition score than ewes limit-fed corn or limit-fed dried distillers grains. At lambing, ewes fed dried distillers grains were heavier followed by ewes limit-fed corn and lightest for ewes fed haylage. There was no difference due to ewe gestation diet on lamb body weight at weaning.
Ewe milk production and lamb preweaning average daily gain were not different between gestation diets. Ewes limit-fed corn and limit-fed dried distillers grains had higher body condition scores at lambing than those fed haylage. By weaning, however, ewes limit-fed dried distillers grains had higher body condition scores than ewes fed the other two diets.
Winter-feeding systems for gestating ewes which differ in dietary energy source and protein concentration during mid- and late-gestation can alter maternal metabolites. In this study, although changes in fetal growth were noted, pre-weaning progeny performance was not altered. Gestation feed costs were reduced for ewes limit-fed dried distillers grains. It should be noted that ewes fed dried distillers grains during gestation did have an increased incidence of ketosis just before lambing.
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