Genetics

How to do a bull breeding soundness evaluation + VIDEO

Beef Central, 07/02/2023

Given that a beef business is essentially driven by the number of animals it can sell, their weight and price, then there is a need to focus on the relative areas that will drive that profit.

Research has shown fertility is often five to ten times more important than price received in terms of northern Australian enterprise profitability. Optimising fertility performance is obviously a big issue for all northern beef herds.

Producers can often spend a lot of effort in selection of replacement females, and frequently become so focused on the environment of their production system, they fail to place the necessary emphasis on genetic selection of herd sires. The herd sires set the direction of profitability for many years to come.

Selection of sires based on appearance alone has limited has limited the beef industry’s rate of gain. Only about 10–15pc of the 30,000 plus replacement bulls needed to fill requirements in northern Australia each year are currently sold with any fertility measurement describing their function.

This has to improve if the industry is going to continue to make significant genetic progress.

The Australian Cattle Veterinarians Association has determined that fertility is the ability of a bull to achieve, by natural service, a pregnancy rate of 60pc and 90pc in 50 normally cycling females, within three and nine weeks of mating, respectively.

The beef industry is focused on profitability producing a calf from each breeder within a 365 day interval. The stud industry must have the same focus if they wish to remain viable and relevant.

How can fertility be improved?

Objective information in the form of BullCheck or Veterinary Bull Breeding Soundness Evaluation (VBBSE), previously known as Bull Breeding Soundness Evaluation (BBSE), in terms of “what we see” (phenotype) is essential and BreedPlan EBVs are necessary from a genetic perspective.

The VBBSE was developed by vets to standardise bull fertility testing and to provide a consistent descriptor of bull fertility. The evaluation indicates whether a bull has met a set of standards for key fertility components which indicate whether a bull has a high probability of being fertile.

The components are:

  • Scrotal circumference (cm) and tone or resilience
  • Physical examination for faults in the head, legs, joints, feet, sheath and penis
  • Semen analysis for motility,
  • Morphology (or structure of the individual sperm cells), and
  • Mating behaviour / mating ability.

The Australian Cattle Veterinarians oversees the VBBSE practices with appropriate certification. The certificate provides a standard of assessment for veterinary evaluation of the various reproductive traits important to beef producers.

This evaluation is conducted prior to sale and details the identification of the sire, date and location where the evaluation was conducted, the assessments made and relevant disease information. It is purely an evaluation of a range of measures on that date on which it was done and does not provide any guarantee or imply the number of calves that the bull will sire in either single or multiple sire matings.

The VBBSE is not a genetic evaluation of reproductive traits, but an indication of the animal’s present reproductive function. However, this certificate is far superior to ‘the lack of’ or ‘distorted’ information that is frequently available to many bull buyers. This evaluation can also be conducted on property as an annual bull test prior to mating to identify any bull that is declining in fertility.

A summary of the five components of bull fertility in the VBBSE follows:

Scrotum: Scrotal circumference/size (SS) in centimetres where testes shape is within normal range. The current recommendations for tropically adapted bulls are a minimum scrotal size of 32cm (and average is 34–36cm) for a two-year-old bull.

Physical: Within the constraints of a standard examination, there is no evidence of any general physical/structural condition or of a physical condition of the reproductive tract indicating sub-fertility or infertility. This evaluation will identify structurally unsound bulls in legs, feet, sheath and general structure.

Semen: Crush-side assessment indicates that the semen is within normal range for motility, colour and percent progressively motile and is suitable for laboratory evaluation.

Morphology: Semen examination of percent normal sperm using high power magnification to ensure minimum standards for normal function are achieved.

Serving: The bull is able to serve normally as demonstrated in a standard test and shows no evidence of fertility limiting defects.

The resultant certificate should be sought-out by bull buyers when choosing between bulls as they also provide details of aspects of the evaluation that cannot be seen in the live animal e.g. percent normal spermatozoa and mating behavior details (if conducted).

Many producers are comfortable in discussing the feet, leg and joint structures in animals and are confident in making a selection decision to purchase or otherwise or use a bull based on what they see. The features of a bull that are clearly visible need little reinforcing in the selection process.

However what we cannot see, without a microscope, often needs a little explanation.

Understanding the morphology and why it is important

Morphology in a VBBSE is basically the ‘structure’ of individual sperm cells. The structural attributes that are not clearly visible (or that require a microscope to view) are frequently just as important, if not more important as far as affecting a bulls fertility.

Unlike the female that has her ‘quota’ of eggs at the start of life, the bull is continuously producing semen within the tubules in the testicles. The testicles are about 2°C cooler than body temperature. Between the head, body and tail of the epididymis there is a long tube for storage and maturation of the spermatozoa produced.

This production pipeline takes about 6–8 weeks from the start of production to when the semen is ready for ejaculation. As semen is continually produced, unused semen is excreted in the urine of all bulls.

So can a bull’s fertility change?

How often do we think about what affect various treatments we apply to a bull, have on his fertility? For example, when a bull is bought at a sale after being ‘stuffed full of feed’ (or more nicely put ‘prepared for sale’) and we then ‘let him down’ (reduce his weight considerably); do we affect his fertility? When a new bull has a fight with the current herd sires and is lame for a few days; does that affect his fertility? In fact any stress that we place on a bull, either as part of our production system or our husbandry program, can affect the quality or structure of the spermatozoa in the continuous production of semen from within the testicles to each of the storage glands along the reproductive tract.

Can we examine and categorize the semen produced by a bull?

Yes. Many breeders will be aware that upon the collection of semen either by electro-ejaculation or rectal massage, semen is examined crush-side for colour (no blood or urine staining allowed) and density of spermatozoa which is ranked on a 1 (clear to cloudy) to 5 (thick creamy colour) basis. In addition, when using low power magnification, the amount of swirl or vigorous swimming motion of all the spermatozoa is scored on a 1 (no swirl; generalized flickering of individual sperm only) to 5 (fast distinct swirl with continuous dark waves) basis. Once completed, the percentage of individual sperm that are swimming forward freely and independently is recorded. This assessment is a compulsory measure of fertility to meet BBSE standards. Based on extensive research the ACV has determined that a threshold of 30% progressively motile sperm is a pass on a BBSE. In addition, the sample must be free of large numbers of pus cells.

The final evaluation of the semen is the percentage of individual spermatozoa that are structurally normal – the morphology. To record the % Normal sperm, a sample of the semen collection is placed in a small tube with a special diluent and sent off to one of the accredited morphologists. The morphologist will examine 100 individual spermatozoa and record all the abnormalities present.

The morphologist report will detail the % Normal sperm and the percentages of abnormalities. The % Normal threshold indicated by the ACV is >70% Normal for bulls used in single sire mating or for Artifical Breeding (AI), and >50% normal for bulls used in multiple sire mating. However some producers may choose to use bulls with higher than 50% Normal. This trait is heritable, and is genetically correlated to the interval from calving to first oestrus cycle after calving in females (i.e. in the daughters).

 

Source: FutureBeef

 

 

 

 

 

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