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Early Weaning Improved Reproductive Performance of Cows

The objective of a collaborative study between USDA, Montana State Univ., and American Simmental Assoc. scientists was to determine the effects of early weaning vs. normal weaning time on cow reproductive performance. A total of 357 Angus and Angus x Simmental cows were assigned to one of two treatments: 1) calves were weaned early at 80 days at the time of prostaglandin (PGF) injection and start of AI breeding; or 2) calves were weaned at a normal age of approximately 215 days. Estrous cycles of all cows were synchronized for AI breeding. Bulls were turned out with cows beginning 2 weeks after AI for the remainder of a 50-day breeding season.

  • Pregnancy rates from AI were significantly higher (P<0.05) for early weaned cows than for normal weaned cows (66% vs. 54%).
  • Overall breeding season rates tended to favor cows that were early weaned compared to normal weaned cows (94% vs. 89%).
  • Date of conception was 7 days earlier for early weaned cows.
  • Early weaned cows gained more weight during the grazing season and were 79 lbs heavier than normal weaned cows at the time of normal weaning.
The authors concluded that early weaning at the start of a synchronized breeding season increased AI pregnancy rates and cow weights at the time of normal weaning and that early weaning may be a viable alternative to that of culling cows during periods of low forage production (Geary et al. 2006. Proc. Western Sec. ASAS. 57: 99).

[December 19th, 2006]


Dr. Rick Rasby, Professor of Animal Science
Animal Science, University of Nebraska - Lincoln, Lincoln, NE

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