D. E. Larsen, DVM
I stepped through the small gate into the crowding ally behind the chute. Ag swung the tailgate open, and I grabbed the tail of this large Charolais cross heifer with my right hand. I worked my gloved left hand into her rectum. There was enough squeeze on her that she could bounce around.
I had been doing this for most of the day. We took some time for a lunch of a special soup Ag had made for the day. Homemade bread and a hearty soup would make the afternoon go faster. The most significant advantage of the lunch break was my left arm got a rest.
In the big cattle country, a cow doctor might have herds of 400 cattle to check every day for a couple of weeks. Their arms became accustomed to the workload. For me, it was one or two herds a week, and most of those herds were less than 100 cows. My arm was in shape enough to do over a hundred cows, but I had to rest it every chance I could.
I was skilled at rectal palpation. Using my left hand, I would first attempt to retract the uterus. This would bring the uterus into the pelvic canal where I could feel along the entire length. I would first feel the membranes slip between my fingers when I pinched the body of the uterus near the bifurcation. If present, this slip was a positive sign of pregnancy. Then I would explore down each horn of the uterus to find an amnionic sac or a fetus. Based on the size of the amnion sac or the fetal head, I could age the pregnancy to plus or minus 3 days.
A uterus with pregnancy over 90 days duration could seldom be retracted. One could usually find a fetal head by sweeping your hand along the length of the pregnant uterine horn. After 120 days of pregnancy, the fetus was generally out of reach until very late in pregnancy. Aging a pregnancy after 120 days was difficult, and getting between plus or minus 15 days was considered the best one could do. Inexperienced veterinarians could miss the age by months.
The obvious benefit of pregnancy exams in a commercial herd was to enable ranchers to cull the cows that were not pregnant. In that way, they would avoid the expense of winter feed for those cows. On rare occasions, I would detect a problem in the breeding program by finding a high number of open cows. Most of those problems could be seen by adequate observation during the breeding season.
The primary goal was to have cows fall into a 42 – 84-day pregnancy window. Cows outside that window would be culled. This would select for productive breeders, cows who would become pregnant on the first cycle she was exposed to the bulls. Then those cows not pregnant on the first cycle would have a second chance at pregnancy. By culling cows who could not breed back with two cycles, we were able to condense the calving season to a shorter time. This would allow ranchers to concentrate their observation of the calving and render help as needed. Having the age of pregnancy helped in knowing just when a cow was due to calve.
Failing to cull a cow who was outside the prescribed pregnancy window selected for infertility. First, you would have one cow that was a problematic breeder, then 5 years later, you would have that one cow and three of her daughters. The ball game was lost then.
It obviously would take several years of work to arrive at the desired calving window. With Ag’s herd, we probably had over 70% of the herd calving in the first 21 days of the calving season. This was ideal, and it allowed for some elective culling.
Elective culling would allow you to cull individuals based on other factors than fertility. Cows with better milk production would wean calves with a higher weaning weight. Cows with poor udder conformation might cause a lot of extra work at calving and could be susceptible to mastitis. In any herd, there are cows with behavior issues, culling them would reduce stress on the rancher and on the herd.
I always told my clients to cull the last cow in the chute. If you have 100 cows in the corral to work through the chute, there will always be the last cow. She is seldom last by chance.
Ag never listened to me on this point. She had to large Brahman cross cow that was almost impossible to get into the chute. So difficult, in fact, that I had only checked her one time. We would try and try to get her in the chute.
“Let’s just forget her,” Ag would say. “She is always pregnant. She is too mean to not be pregnant.”
“I am telling you, Ag, you need to get rid of that cow,” I would always say.
And true to form, after 5 years, there was the old mama cow and then 3 of her daughters, all trying to be the last one in the chute.