Vet Column 1-11-10
Fort Collins, Colo.
Milk is the sole source of nutrients for the newborn mammal. Survival and the potential for the offspring to reach adult reproductive potential are directly dependent upon the lactational success of their dams. Studies have shown that nutrition during fetal life affects fetal ovarian development, postnatal growth, reproductive performance and metabolism. It has also been shown that fetal mammary duct area is decreased by poorer dam nutrition during pregnancy.
Size of the dam affects fetal growth through the size of the placenta, which influence the nutrient supply to the developing fetus. Fetal development in small breeds of sheep, horses and pigs can be altered from the normal genetic potential by varying dam size, resulting in altered birth weight and postnatal growth. Restricted development of the mammary gland of female offspring born to dams with varying levels of gestational nutrition and its effects on subsequent milk production or milk composition have not been demonstrated.
To pursue this issue, investigators from Massey University in New Zealand recently reported on a sheep study comparing the effects of dam nutrition and dam size during gestation on fetal mammary gland development and the lactational performance of the resulting female offspring at 2-years-of-age.
Approximately 450 of the heaviest and 450 of the lightest mixed-age Romney ewes were selected from the extremes in a commercial flock of 2,900 ewes. All were artificially inseminated. Ewes were fed free choice or a maintenance ration. At 140 days of pregnancy, free choice fed dams weighed an average of 172.8 pounds; maintenance fed ewes weighed an average of 143.3 pounds.
Offspring born to the large dams weighed an average of 12.1 pounds and was different than offspring born to the lighter weight dams which weighed an average of 11.8 pounds at birth. Similarly, at weaning, large dam offspring weighed an average of 72.1 pounds and was different than the lighter weight dam offspring which weighed an average of 68.8 pounds at weaning.
Offspring born to ewes receiving free choice feed during gestation weighed an average of 12.5 pounds at birth and was different than the average birth weight of lambs born to maintenance fed ewes which was 11.5 pounds. At weaning, lambs born to ewes receiving free choice feed during gestation weighed an average of 72.3 pounds and was different than the weaning weight of offspring born to maintenance fed ewes during gestation which was 68.3 pounds.
After weaning, female progeny were managed and fed to nutritional requirements as one group under New Zealand commercial farming practice.
Results of this study indicate that offspring from ewes fed maintenance level from day 21 to 140 of gestation produced more milk as compared to ewes fed free choice amounts during this same period of gestation. Lambs born to the 2-year-old ewes exposed to maintenance fed dams during gestation were heavier at birth and grew faster until weaning than 2-year-old ewes exposed to free choice fed dams during gestation.
Ewe nutrition during pregnancy affects the resulting milk production of the offspring and composition and growth of their lambs. This study indicates that overfeeding ewes during gestation negatively affects the milk production and productivity of the replacement ewes.
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