Low Pregnancy Rate in a Spring-Calving Cow Herd
A 120-head commercial cow-calf herd calves in March and April on fescue pasture. At pregnancy check, 94 of 120 cows (78%) are pregnant after a 75-day breeding season, and 14 of 22 replacement heifers are pregnant. Mature cows average body condition score (BCS) 4.2 at calving; heifers average BCS 5 but weigh 690 lb, while mature cow weight is 1,250 lb. The only winter feed is fescue hay testing 7.8% crude protein and 52% TDN, fed free-choice from December through March, with no mineral supplement. Calves average 430 lb at weaning in October. The owner wants to keep all open cows, buy more hay, and add a protein tub. He asks whether the low pregnancy rate is caused by the bull.
1. Is the bull the most likely cause of the low pregnancy rate? Explain using the pregnancy rates, body condition, heifer weight, and feed data.
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The bull is not the most likely primary cause. A bull problem would usually depress pregnancy across all females, but the mature cow rate is about 82% (80 of 98) while the heifer rate is only 64% (14 of 22). The mature cows are thin at BCS 4.2, below the target of about 5 at calving, and the hay is low in protein and energy for late gestation and early lactation. The heifers weigh 690 lb, which is only 55% of the 1,250-lb mature weight; a common target is about 65%, or 812 lb, at breeding. Thin cows and underdeveloped heifers are more likely to be anestrous or fail to conceive early. A bull fertility check is still prudent, but nutrition and heifer development explain the pattern better than a single bull failure.
2. Prioritize three management changes and calculate the heifer target weight.
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First, cull or at least preg-check and market open cows rather than carrying them another year. Second, supplement the mature cow herd to reach BCS 5 before calving, using a protein and energy source rather than only more low-quality hay; a mineral supplement should also be provided. Third, develop the replacement heifers to reach about 812 lb before breeding (0.65 x 1,250 lb). At 690 lb, they need about 122 lb of gain, or roughly 1.5 to 2.0 lb per day over an 8- to 10-week development period, depending on timing. A protein tub alone will not fix a 7.8% crude protein hay and thin-cow problem. Prioritize the changes that affect the next calving and breeding season: body condition, heifer weight, and culling chronically open females.
3. The owner wants to keep all open cows and buy more hay. Evaluate that plan economically and recommend a better alternative.
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Keeping every open cow carries another year of feed, pasture, labor, and opportunity cost with no calf income, and a thin open cow is likely to fail again. Buying more of the same low-protein hay adds cost without correcting the energy and protein deficit. A better plan is to cull open mature cows, retain only young females with a clear nutrition-related reason for being open, and invest the feed savings in supplementing the productive cows and developing heifers. If forage is short, reducing herd size is often cheaper than buying hay of low quality. The decision should compare the cost per pregnancy achieved, not just the cost per ton of hay. A recorded breeding season and body condition scoring at calving and breeding will show whether the changes are working next year.