What are we looking for when we do a Bull Breeding Soundness Exam?

Bull Breeding Soundness Examinations.

Often cow-calf producers look at bull breeding soundness exams as merely a semen evaluation. Many times as veterinarians we do not explain everything that we are doing, nor do we explain what each part of the evaluation means and its significance. The following article explains the different parts of a complete "Bull Breeding Soundness exam" and how it is important for the producer.

A bull breeding soundness evaluation is a prediction of a bull's potential reproductive capacity. It includes:

1. Physical examination of abnormalities that could interfere with the desire and ability of the bull to breed

2. Libido or serving capacity test and observations of the bull during the breeding season

3. Examination of the genital organs, including: the penis, scrotal circumference measurement, scrotal and testicular palpation, and rectal examination to palpate the internal genital organs

4 Semen evaluation

Under ideal conditions, a complete breeding soundness exam should be done yearly on every bull prior to the breeding season. However, it is often impractical for a veterinarian to do everything listed above in order to completely evaluate each bull. Often a producer needs to evaluate its libido and ability to physically get the job done.

Body condition score: Ideal should be about 6, too fat or too thin causes decreased sperm production, and in some instances sterility.

Feet & Legs: Lameness can impair the ability of a bull to breed. There are also some undesirable genetic traits that a bull can pass on to its offspring that can affect locomotion.

Eyes: Good eyesight is usually necessary in natural mating situations.

Rectal Examination: is necessary to palpate the pelvic urethra, prostate, vesicular glands, ampullae, vas deferens, and internal inguinal rings. The most common finding is usually seminal vesiculitis.

Scrotum and its Contents: Problems often identified are soft testicles, sometimes due to fat deposits making the scrotal circumference larger from fat not testicular volume. Many of these bulls undergo testicular degeneration and may not recover. Asymmetry of the testicles, hernia, dermatitis, cryptorchids, lack of mobility, epididymitis, and others can affect fertility.

Penis/Prepuce: Conditions easily seen at the time of electroejaculation are ruptured corpus cavernosum, adhesions, persistent frenulum, hair rings, penile fibropapilloma. Some conditions need to be diagnosed by watching the bull mate. If protrusion and/or erection does not occur during the electroejaculation it is imperative that the producer observes the bull mating at the beginning of the breeding season.

Scrotal Circumference: its significance is often overlooked by producers. Bulls with large scrotal circumference is a reflection of large testicles, this correlates with more semen production and sperm cell production, greater sperm motility. Bulls with below minimum scrotal circumference and produce satisfactory semen can perform with low breeding pressure. However, in moderate to high breeding pressure they do not perform well. There is also a high correlation between scrotal circumference measurements in bulls and the age at which female progeny reach puberty. Sires with above average testicle size produce progeny that reach puberty at an earlier age. There are differences among breeds: Minimum recommended Scrotal Circumference (CM)

Weather conditions can play a roll when obtaining scrotal circumferences. When the temperature is below 32⁰ F most measurements will not be accurate. If temperatures are between 32⁰ and 50⁰ F, care must be taken to ensure an accurate measurement.

Semen Evaluation: Motility is an estimation of the number of sperm cells with good aggressive forward movement and given a rating of: Very Good, Good, Fair, or Poor. The minimum rating that is acceptable is a Fair Rating.

Morphology is the number of normally shaped sperm cells. The abnormalities are divided into primary abnormalities and secondary abnormalities. A minimum recommended number of normal cells is 70%.

If any of the above categories shows a below minimum standard, the bull is classified as either unsatisfactory or deferred and then retested once the problem has had time to be resolved.

High serving-capacity bulls with large scrotal circumference can be mated successfully to a larger number of females than bulls with less reproductive capacity. It is not unusual for a dominant bull to breed up to 70% of the female cattle, therefore it is vital that these bulls have a high breeding capacity and be in good physical condition. With good quality bulls a bull-to-breeding female ratio of 1:25 is plenty for range conditions, and a ratio of 1:50 in smaller pastures is adequate. Higher numbers may just be an unnecessary expense. The fertility, libido, and mating ability are more important than the breeding female ratio.

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