Well, we are in the middle of spring calving. I have seen and delivered some very large calves. So far the biggest was approximately 180 pounds of a set of twins. Most of us put all of the responsibility of large calves on the bull. Now, it is true that bulls can change your herd very fast and improve your herd the fastest. But, half of the genetics in the calf comes from its mother.
A calf gets 50 percent of its genetics from each of its parents. So, if the bull throws small calves and you end up with just a couple larger calves, I would put the blame on the cows. Plus, over the years I have noticed that older cows tend to have larger calves. Also, cows that are over fed during the last one to two months of pregnancy tend to have very large calves.
Now think about heritability of calving ease. I think it is only around a 0.2. Which means it is only around about 20 percent heritable, and environment has the other 80 percent heritability. This includes nutrition and feeding. Now, the genetic specialists may disagree with my numbers, but the principle is still sound. I am not a genetic specialist and always had a better time in other classes in school.
Feeding the cow for the last one to two months of gestation is where we are mainly maintaining them in the proper plane. I like to see our cows at a body condition score (BCS) of 6 when they are in their second trimester (4-6 months of gestation). Then the last trimester (7-9 months of gestation) we can just maintain them at this score. To do this we normally feed poorer quality hay. Now, if they are not at a BCS of 6 and lower we may have to feed them so they will gain. Remembering that by feeding to gain weight we might have to put up with larger calves being born.
Basically, we need to manage your cows’ nutrition throughout the whole year. I like cows to calve in at a BCS of 6 and then it is okay for cows’ to loose down to a BCS of 4-5 the first three months of lactation as long as we can gain it back. I like a cow that will give all she has to her calf and put more pounds on the hoof, quickly. Then after she has bred back I like her gaining again and gain back to that BCS of 6. With her at a 6 and probably in her second trimester of gestation, I like to back off and save my best feed for lactation. Just maintain her until she calves.
Bulls need to have their working clothes on for me. If they are either a 5-6 BCS, this is where I like to see them. If they loose 150-250 pounds breeding cows, that’s okay. I can normally put it back on them when I pull them out or start feeding them separately from the herd.
Dr. Tim E. O’Neill, DVM, owns Country Veterinary Service in Farmington, Ark.


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