Preparing your bull for the breeding season


Source: Ministry of Agriculture, Food and Rural Affairs

The breeding season for bulls is short but intense. Consequently, when the breeding season begins your bull must be ready to go and have the appearance of a well-muscled athlete. The bull needs all that physical fitness as he will spend a significant amount of time following cows rather than feeding over the course of the breeding season. To deliver success with calves on the ground, your bull must be in good nutritional and physical shape when the breeding season rolls around.

Preparing your bull for the current year’s breeding season begins at the end of the previous year’s breeding season. This article discusses key considerations to get maximum performance out of your bull.

Bull Nutrition

Bulls should be body condition scored between 30 and 60 days prior to turnout (the earlier the better!). An ideal pre-breeding target body condition score (BCS) is between 3 and 3.5. A bull with a BCS of 2 or less should be deemed unsatisfactory for use as the animal is unlikely to be able to perform adequately over the intensive breeding season. Equally, bulls classed as obese should not be used as semen quality is likely to be affected due to fat deposition in the scrotum. Fat interferes with thermo-regulation – an important component of quality sperm production. Bulls that are marginally under the ideal BCS 60 days out from breeding will benefit from being put on a higher plane of nutrition. Attempting to get thin bulls to an ideal BCS will often lead to bulls getting fat rather than fit. Fat bulls have poorer semen quality and from a libido perspective are often lazy.

Yearling bulls need a diet containing 13.5 – 14% crude protein with no more than 60% grain. The inclusion of forage in the diet should increase as the young bull matures. Mature bulls will be adequately supplied with a 12% crude protein diet. Often this protein requirement can be met by offering moderate to good quality forage. Mineral supplementation is critical, as an adequate supply of minerals (particularly vitamins A & E and zinc) are important to build the bull’s physical fitness and to prime the reproductive system for the breeding season ahead.

Over the course of the breeding season bulls can lose between 220 and 330 lbs in weight, even on very good pasture. Once the breeding season is complete, your bull needs to be placed on good pasture, have access to good quality forage over the winter, and have continued access to minerals and water so that he can regain his strength and fitness.

Foot Trimming

Foot trimming should be carried out at least 30 days and ideally 60 days out from the start of the breeding season. This will give time for the hoof to recover from the effects of trimming and, if there are any hoof issues detected, to give time for those issues to be treated.


The time leading up to breeding season is also a good time to revisit and execute your annual vaccination protocol. Bulls should be vaccinated with the same vaccines used on the cows. In Ontario, vaccination against BVD and IBR should be considered standard practice. Vaccination against leptospirosis and camplyobacteriosis (Vibrosis) may be more herd-specific and producers should consult with their veterinarian for direction. Vaccinations should be given at least 60 days prior to the start of the breeding season as, with all vaccines, there is a risk of fever. Sperm produced during a fever are abnormal and infertility can last up to 2 months after such an event.

Parasite and Fly Control

Parasite and fly control should be carried out to ensure bulls can maintain peak physical performance. In Ontario, dewormer is typically given in the fall. There is little in the literature about the risk of infertility from using wormers on bulls, but if a dewormer is needed during the breeding season, consult with a veterinarian to make sure the products used is appropriate. Fly control is important as flies can be a nuisance and a distraction for bulls. Producers should read product labels carefully to ensure the product to be used is safe for use on breeding bulls and follow the instructions carefully.

Eye Lesions

Eye lesions in mature bulls occur more frequently than is often realised. Eyes should be examined for vision compromising conditions such as cataracts, corneal opacity or carcinoma. The mouth should be examined for signs of injury or lesions that may impact the ability of the animal to feed properly. Feet and legs should be examined for signs of lameness or for any conformational defect that could lead to lameness in the future.

Managing Infertility

Research by the University of Georgia has shown that a sub fertile bull when used on a 35-cow herd produces 4,560 lbs less of weaned calf than a fertile bull. Total infertility in bulls is rare and is defined as the inability to impregnate. However, many bulls are or may become “sub-fertile” for a variety of reasons. We define fertile bulls as mature bulls capable of impregnating 60% and 90% of a 50-cow herd within 3 and 9 weeks of the breeding season, respectively, by natural service. A sub-fertile bull is a bull that can achieve pregnancies by natural service, but not at the rate achieved by fertile bulls when the opportunity exists.

Carrying out breeding soundness examinations is an important exercise to identify potentially sub-fertile bulls and to avoid the substantial economic losses these bulls can cause. A bovine soundness examination should be carried out by a qualified veterinarian or technician. It is not a cheap examination but considering the substantial economic cost of a sub-fertile bull, it’s well worth the annual investment.

Diagram of the reproductive tract of the bull

Figure 1. Diagram of the reproductive tract of the bull. Image adopted from: Hamilton, T., 2006.

To carry out a breeding soundness exam, the veterinarian requires access to the scrotum and sheath. Therefore, the bull must be properly restrained. A rump bar should be used to avoid getting kicked when measuring and palpating the testicles. Bulls should stand on non-slip flooring material (rubber flooring is ideal) to avoid the bull losing its footing during examination. Bulls must have the ability to move backwards and forwards during examination. In many cases, a simple halter is the better solution to using a head gate.

A visual assessment of the scrotum shape should be made prior to any physical examination. A normal scrotum has a pendulous shape with a well-defined neck, an ideal shape for thermoregulation. Straight sided and wedge-shaped scrotums are associated with small testicles and excess fat in the scrotum.

Careful physical examination of the scrotum is important to detect problems not visibly apparent. The scrotal skin should be smooth, elastic and the testicles should move freely within the scrotum. Thickening of the scrotal skin can be indicative of trauma and, if inflamed, will cause heating of the testicles and a tendency for them to be held higher in the body. Photosensitivity in some bulls can cause oedema and swelling of the scrotum.

Scrotal circumference (SC) is a critical component of a breeding soundness examination. Scrotal circumference is highly correlated with paired testes weight, daily sperm production and sperm quality. Bulls with above average SC reach puberty earlier and this trait is highly heritable in female offspring.

Seasonal variation in scrotal circumference is commonly observed but these changes should not exceed 1 – 2 cm. An SC decline of 2 – 4 cm between the date of examination and the start of the breeding season can indicate a problem with testicular degeneration and may not be simply a result of loss in bodyweight. Recovery, if it occurs, can take months.

Table 1. Minimum recommended scrotal circumference in various breeds for breeding soundness

Age (Months)
Minimum Scrotal Circumference (cm)
Angus Charolais Maine Anjou
Blonde d’Aquitaine

Adopted from (Hamilton, T., 2006)

Palpation of the sheath is important to detect the presence of any abnormal swelling. A penile rupture/haematoma is a painful swelling of the sheath close to the scrotum. This is caused by sudden movements of the cow during intromission or when young bulls mount each other. If untreated, these bulls find mating difficult and painful.

Sperm collection, examination and analyses is an important component of a breeding soundness exam. Semen should be analysed for motility, sperm count, and identification of the significance of abnormal sperm. The threshold for the % normal sperm in a sample is 70%. The presence of foreign cells in the semen is often noted as this may indicate the presence of inflammation elsewhere in the reproductive system.

Other Considerations

Understanding the social behaviour of bulls is critically important for their successful management and to reduce the risk of fighting injuries. Seniority and social ranking are determined by age and are established in the holding paddock prior to the breeding season. It is not a good practice to mix bulls of different ages together in the breeding paddock as the older bulls will inhibit the breeding activity of the younger animal, particularly when there are a low number of cows in estrus. Research has shown that breeding rates are higher when bulls of similar age are mixed together compared to mixing bulls of different ages.

In Summary

Proper management and breeding assessment of bulls prior to the breeding season is critical for the economic wellbeing of any cow calf operation.

Carrying out these simple checks well in advance of the breeding season will provide enough time for a replacement to be found, if that is necessary.


  • Chenoweth, P. 2002. Bull Breeding Soundness Exams and Beyond. Proceedings: The Applied Reproductive Strategies in Beef Cattle Workshop, September 5-6 2002, Manhattan, Kansas.
  • Hamilton, T. 2004. Beef Bull Fertility. OMAFRA Factsheet 410/20
  • Handley, J. 1997. Selecting Beef Bulls. OMAFRA
  • Jones, L. 2019. Economics of beef bulls: Selection and Fertility. Progressive Cattlemen, Vol. 9, Issue 4.
  • Palmer, C. 2016. Management and Breeding Soundness of Mature Bulls. Veterinary Clinics: Food Animal Practise, 32:479-492
  • Penny, C. 2010. Examination of Bulls for Breeding Soundness, Published by Zoetis UK Ltd.
  • Potter, B. 2016. Bull Selection in Ontario. OMAFRA.


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