Cow Calf: Factors Affecting Conception Rate
Why do some cows breed back more successfully than other cows in the same herd? Why do herd conception rates vary from year to year? Body condition and nutrition can offer some explanation. Research has demonstrated that cows in poor body condition and/or under nutrient stress will have lower conception rates and take longer to rebreed compared to cows in good body condition and provided with a ration meeting nutrient requirements. But, are there other factors that can affect re-breeding and conception rates? I want to summarize a presentation from Dr. James K. West, DVM and director of the embryo transfer unit veterinary service at Iowa State University, in which he lists both non-infectious and infectious causes for reduced conception rates in beef herd.
Some non-infectious factors that can reduce conception rates include: lethal genes, polyspermy, endocrine disorders, elevated blood urea nitrogen, heat stress and handling/transportation stress. Lethal genes and polyspermy (fertilization of the egg with more than one sperm, which is a lethal condition) both refer to genetic factors that do not allow a viable pregnancy to occur. Endocrine disorders result in short or irregular heat cycles or a condition where not enough progesterone is produced to sustain a pregnancy. With these 3 factors the producer has little control and culling is probably the best option for the producer.