Improvement of Genetic Potential
By: John Winder, The Noble Foundation
Genetic potential also plays a pivotal role in the reproductive process. Vast differences exist in reproductive potentials among cattle. However, improvement of potential for reproduction is not as straight forward as most other traits because animals do not express reproductive deficiencies until later in life. Researchers, however, have developed techniques to improve fertility indirectly. Let me give you a few examples. First, genetic differences exist within breeds for age at puberty. This trait is very difficult to measure in females (you have to watch them for months to determine when they first cycle). However, in the male, it is easy to establish the relative time he reaches sexual maturity. This can be established by simply measuring the circumference of his scrotum. In most breeds, puberty occurs when scrotal circumference exceeds about 32 cm.
When cow-calf producers select yearling bulls with large scrotal circumference (> 32 cm), daughters tend to reach puberty earlier. Furthermore, daughters of bulls with large scrotal circumferences tend to be more reproductively efficient throughout their productive lives. Another method for enhancing reproductive performance potential is to simply breed heifers as yearlings in a short breeding season (45 days). In other words, if you make it difficult for heifers to breed the first time, only the most fertile will enter the herd. Of course, it is always a good practice to cull non-pregnant cows at the end of the breeding season. However, this has only a minor effect on genetic potential. Cows have often produced daughters that are kept as replacements before being culled.
In general, we need to address reproductive potential early in life. Some new approaches are currently under investigation at various locations including the Noble Foundation.
Finally, remember cows are very much like a factory. Raw materials that enter the factory include grass, supplements and water. The product of the "cow factory" is a calf at weaning time. As with any factory, efficiency is measured as outputs relative to inputs. Our "cow factory" is extremely inefficient when she fails to breed.