Last August, I had the privilege of presenting at the Western Beef Association Bull Select workshop hosted by Bardoo Charolais in Capel. The day was a deep dive into BREEDPLAN and EBVs and how to use them to select the right bull for your enterprise.
My task was to talk about the steps you can take to help ensure that the bull you buy performs and lasts as expected. For me, the cornerstone of this is a thorough pre-purchase examination. As a member of the Australian Cattle Veterinarians, I am a bit biased, however, it is hard to go past the Veterinary Bull Breeding Soundness Examination (VBBSE) as a comprehensive framework for bull testing. This is branded as BULLCHECK and requires the examiner to have passed a written test and demonstrated the practical skills necessary to carry out the examination in a safe and effective manner.
The VBBSE is a set of prescribed assessments which are divided into 5 components:
A general physical examination including structure (conformation) and reproductive tract
An examination of the testes and measurement of scrotal size
A serving assessment to evaluate libido and mating ability
Collection and crush-side assessment of a semen sample
Laboratory examination of sperm morphology
The examination should be seen as a risk reduction exercise. The components serve to cumulatively reduce the risk of buying a sub-fertile bull or one that will become sub-fertile or 'break-down' in the future. In one situation it may be judged sufficient to carry out 1,2 and 4 on the list and in another, such as for a high value sale bull, a comprehensive1-5 assessment would be more appropriate.
Below are a few examples of the many issues that can be detected and may lead to a Q, qualified or X, cross, result for each stage of the exam:
1
Persistent Frenulum
Penile Ulcers
Seminal Vesiculitis
Corkscrew claws
Cracks in the hoof
Distended hock joints (risk of OCD)
Lameness
Eye cancers
2
Orchitis (testicular inflammation)
Inguinal Hernia
Testicular degeneration
Low scrotal circumference
3
Spiral deviation of the penis (Corkscrew)
Ventral deviation of the penis
Muscoskeletal disorders
Poor libido
4
Semen with low progressive motility
Blood or pus in the ejaculate
5
An unacceptable level of abnormal sperm
A higher than threshold level of individual morphological defects in the sperm such as vacuoles teratoid, proximal cytoplasmic droplets, abnormal tails etc.
Vaccination
In addition to the pre-purchase exam, another form of insurance is a comprehensive vaccination programme to help to protect the health of the bull as well as to prevent disease which will affect the fertility and health of breeding females.
A good resource for recommendations on suitable vaccinations for breeding bulls is Immune Ready Vaccine Recommendations - Immune Ready. This is a cross-industry initiative providing guidelines on vaccination for different classes of sale stock. The vaccinations are split into core vaccines which are appropriate in most situations, those which are appropriate in some situations and those which are not necessary.
The essentials for breeding bulls are:
7 in 1 combined Clostridial and Leptospirosis vaccine
Vibrio, Campylobacter vaccine
Pestivirus, BVDV vaccine (bulls should also be tested for BVD virus antigen)
The use of some IBR vaccines to protect against infectious balanoposthitis (IPB) is becoming more common. 'Exploding pizzle syndrome', especially in young bulls, is where a bull breaks down with ulceration and swelling of the prepuce. This is thought to be connected with IPB caused by bovine herpes virus, a virus which which also leads to IBR.
It should be remembered that some countries' import requirements are sensitive to IBR seroconversion, so if bulls are destined for export, advice should be sought from the exporter prior to vaccination.
Freezing
So, you've got a bull which has a tick for all sections of the VBBSE and you want to freeze the semen. It looks good crush-side and under the microscope so should make for a good AI bull, right?
Not necessarily, not all bull semen freezes well. Individual sperm vary in how well they can resist the whole freeze-thaw process. It can have negative effects on the sperm's capacitance reaction, motility, speed and mitochondrial activity.
Depending on where the semen has been sourced and the quality control processes in place, it is a good idea to crack a straw or 2 open to examine it under the microscope prior to the start of an AI programme. Unfortunately, this won't expose all the potential flaws in the semen however a trained eye should be able at least check the mass and progressive motility of the thawed semen.
Thawing
The temperature of liquid nitrogen is -196 degrees C. Below -130 degrees the frozen sperm is very stable and in theory should be perfectly preserved for hundreds of years. However, if the temperature of the sperm rises to above -130 degrees and back below again, then damage occurs due to recrystallisation. The degree of damage depends on the temperature that the sperm reaches and how long it remains at this temperature. Above -80 degrees the damage to the sperm can be severe.
The temperature in the neck of AI tanks tends to vary from -78 up to room temperature. It is very important that the straws are handled carefully to avoid or minimise exposure to these higher temperatures.
Ensure that the liquid nitrogen level is regularly topped up so that the raised cylinders contain liquid. This can buy more time and reduce the chance of damage to the sperm. Where possible, set up the tank so that semen not being used remains submersed in the liquid nitrogen at the bottom of the flask rather than being constantly lifted to the neck.
Comentarios