The placenta is fully developed by the third month of pregnancy. At four months of gestation,
a calf has developed to the size of a small cat. Nutritional requirements to maintain the pregnancy are still relatively low, but there are significant fetal developments during mid pregnancy.
Muscle development occurs at two different stages of pregnancy. Muscle fibres are initially developed in mid pregnancy. Genetics provides the “code” as to how much muscle the animal will have, but the total muscle mass is influenced and possibly limited by the amount of protein in the ration. Comparing cows that grazed a low quality pasture (6 to 7% protein) for 60 days during mid pregnancy versus a higher quality pasture (11% protein) found that cows on the low protein pasture delivered a calf that was 4 pounds lighter than the higher quality pasture. Researchers evaluated the two groups of calves and found that weaning weights for the low protein pasture were 30 pounds and 48 pounds lighter at slaughter compared to calves from the “higher protein pasture”.
Heifers born to the cows that grazed lower quality pasture had smaller ovaries and luteal tissue. Luteal tissue produces progesterone which is needed to maintain pregnancy. Long et al., (2012) speculated that the ability of the heifer to conceive the first calf could be reduced because of the reduced organ size.
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Here is the article that was referenced:
Long, N. M., M. J. Prado-Cooper, C. R. Krehbiel, U. DeSilva, and R. P. Wettemann. 2010. Effects of Nutrient Restriction of Bovine Dams during Early Gestation on Postnatal Growth, Carcass and Organ Compositions, and Gene Expression in Adipose Tissue and Muscle. J. Anim. Sci. 88:3251–3261.