The selection of a bull is a limiting factor to a successful breeding program. Selecting a bull involves considering the bulls conformation, predicted birth and weaning weights, genetics, performance records, and libido. Breeding soundness exams are a simple and cost effective way to ensure the bulls being used are healthy and actually producing offspring.
This procedure involves four major aspects which are a physical or ultrasound exam, scrotal circumference measurement, semen motility, and semen morphology.
The physical exam involves visually examining the bull for development and soundness and the testicles for symmetry. Palpation can then be used to study overall development of the testes, testicular firmness, and abnormalities. It is important to study the bulls hooves, joints, and other aspects involved in mobility.
Scrotal circumference is measured using a flexible measuring tape to evaluate testicular development, size, and health. There are developmental standards depending on age and breed of the bull.
Semen is then collected using an electrode to stimulate the bull to ejaculate. The semen is examined under a microscope to determine sperm motility and morphology. Morphology assures the sperm is properly shaped and capable of fertilization. Sperm motility is evaluated by measuring live motile sperm to ensure a sufficient amount to reproduce.
The breeding soundness exams determines whether a bull is fit to breed but libido also plays a role in production. Libido can be tested in bulls by placing the bull in a pen with a restrained cycling cow and measuring the number of services during a set time, which is referred to as a serving capacity test. However, this is often not feasible for most ranchers so it is important to observe bulls in the field to assess his desire to breed, mounting ease, ability to achieve erection and extend the penis. Although bulls may be sound health wise, they may not have the desire or stamina to breed the required number of cows.
References:
- University notes
- https://www.merckvetmanual.com/management-and-nutrition/breeding-soundness-examination-of-the-male/breeding-soundness-examination-of-bulls