Factors affecting calving difficulty
This week, I will put on my animal science hat for a while and discuss factors that come into play when calving difficulty or dystocia is an issue.
It is never fun for a cattle producer to lose a calf at birth or soon after birth. We will use natural service, artificial insemination and some embryo transfer in our small herd at home.
Earlier in the fall, we lost a calf from one of my daughter’s old show heifers. The now mature cow had always conceived AI first time and always calved unassisted. We bred her to a nationallyknown bull for 2018. In fact, we had a bull calf born on the place the year prior that weighed maybe 65 pounds at birth out of the same sire, but out of a different cow. The calf we lost was more than double the size of the calf the previous year.
Today, I will be sharing information on factors that affect calving difficulty. The hope is the information will help you not run into the same issue I had earlier in the fall. I will be using a revised publication by Ted G. Dyer, former UGA Extension animal scientist, for reference.
Sire selection is one of the first management decisions to consider in regards to calving difficulty. Keep in mind that there are sires or bulls in each breed that can cause calving difficulty when bred to certain cows.
Over the years, some breeds of cattle have been blamed for calving problems. Just note, that the problems can happen in all cattle breeds. Some of the decisions have to be made based on the situation such as breeding heifers or cows.
You would want to use bulls that are proven in siring low birth weight calves when you are breeding heifers. When heifers mature into cows, they can be bred to bulls that may sire larger calves because they should be more capable of delivering safely these offspring. One tool is also being able to review past calving records for sires and even the EPDs — expected progeny differences — for the different bulls. There are EPDs on bulls that will help you look for calf birth weight and calving ease comparison. EPDs can be used to compared bulls within the same breed to the breed average for that particular trait.
Keep in mind that there are accuracy values when looking at an EPD for a certain bull such as birth weight EPD that should be considered. A young bull may have few reported calves to the breed association so the accuracy may be low.
In our Calhoun HERD program, all of the heifers are bred artificially to a nationally known calving ease bull. When we select that sire, it would be one with high accuracy for that birth weight EPD trait. EPDs can help take out some of the guesswork in sire selection as a tool.
Our information states, by using EPDs, producers can evaluate genetic potential of sires and reduce the occurrence of dystocia by lowering calving birth weights and using bulls with a history of high calving ease. Keep in mind there can be some variation in each calf crop. Temperature can have a significant impact on calf birth weight. In fact, environmental factors are related to approximately 55 percent of calving difficulties. Note, that birth weights can vary from year to year in a herd where the same genetics and management techniques are used.
Studies have shown that calves born in the fall weigh less than calves born in winter and spring months. This increase in fetal weight during the winter months is most likely related to the increased nutrition intake from supplemental feeding by the cow, according to our information. As the cow takes in more nutrition in those months, the nutrient flow to the fetus increases so there is increased growth rate in the unborn calf. Most fetal growth is in the last three months prior to calving.
In regards to calving problems, there should be less issues with fall calving as compared to winter and spring. On the flip side, try to stay away from summer calving due to heat and humidity stress to the calves. This will reduce growth rate.
There is data on the effects of different feeding levels on dystocia and birth weights. High feeding levels pre-calving did not show significant impact on birth weight or dystocia. Now, reduced feeding levels did show reduced cow weight gain, decreased milk production, more issues with scours and then reduced pregnancy rate in the cows.
If growing your own replacement heifers, keep in mind that heifers grown on low nutritional diets can relate to an increase in dystocia when calving those heifers outs.
Finally, abnormal calf presentations at birth will be a portion of calving difficulties. All cattle producers should become versed in the calving process. Many producers are able to assist cattle in difficult birth situations, but note that at times you may need expert help from an large animal veterinarian.
Keep in mind that the only thing worse than doing nothing for a calf in an abnormal presentation is to do everything wrong before calling the vet.