The Sunday News
Mhlupeki Dube
THE influence of the bull on herd fertility in both dairy and beef herds is often overlooked with the focus being on management of heifer and cow fertility.
When cow management and infectious disease control are good then the limiting factor in herd fertility may be bull fertility rather than female factors. Bull fertility cannot be assumed and must be monitored by regular examination of bulls and breeding records.
Your bull should be active and ready to service cows and heifers that come on heat.
This is more so during the breeding season which for smallholder farmers tends to coincide with the beginning of the rainy season as cows improved their body condition ready to receive the bull.
Your bull therefore needs to be fertile so that it is equal to the task and does not waste productive time.
The reproductive performance of bulls is also influenced by the genetic constitution of the breed, climate, nutrition, age and disease.
For a bull to be fully fertile and perform to full potential each of the following components must be considered.
Libido (sex drive) and physical fitness, ability to achieve intromission and deposit semen in the vulva, production of sufficient quantities of high quality semen, absence of disease that could be transmitted to cows during breeding.
Many bulls fail to achieve normal fertility due to physical deformities such as lameness or injury.
When selecting young bulls avoid poor foot and leg conformation that may lead to subsequent problems in its adult age.
Avoid laminitis by sourcing bulls direct from breeders that are not culling. Bulls with physical deformities find it difficult to mount and service cows and that may have a drastic effect on the fertility of your herd.
Also avoid overfeeding your bulls (although this is highly unlike in smallholder farmers as bulls are underfed instead). Ensure bulls are fit and not fat prior to breeding. Obesity or conversely very poor body condition will depress fertility.
A number of conditions may affect the ability of a bull to mount and achieve normal intromission thus depositing semen in the correct place.
Various penile deviations can develop which prevent bulls from entering the vulva when trying to mate. The most common is corkscrew (spiral) deviation which is an acquired condition that can develop in bulls that have previously worked normally. Damage to the erect penis during service can result in penile rupture (haematoma) which may not be noticed immediately.
Swelling is seen in front of the scrotum which will slowly resolve but few bulls will return to use.
Prolapse of the prepuce can lead to damage and chronic inflammation which if neglected can lead to stricture and inability to serve.
There are also many conditions that can affect the production and quality of semen produced from the testicles.
Scrotal circumference gives an indication of adequacy of testicular tissue volume and has a direct relationship with fertility.
In addition to circumference it is important to look for bulls with good scrotal conformation. Bulls with tight, wedge shaped scrotums will be less able to regulate the temperature of their testicles and overheating can lead to reduction in semen quality. Bulls should achieve standards for scrotal circumference by certain ages and those that fail to reach these standards are likely to be sub-fertile due to failure of normal sperm production capacity. Bulls with small testicles will at best produce small quantities of normal semen and at worst may be infertile due to hypoplasia of sperm producing cells. In general bulls should have scrotal circumference of at least 30-32 centimetres at 24 months of age.
Infection of testicles (orchitis) can cause infertility and will cause initial swelling and then degeneration (shrinking) of affected testicles.
Infection of the internal accessory sex glands is another condition that can affect fertility in bulls and check up by a veterinarian can confirm and rectify this.
Bulls can also carry and transmit various infectious diseases and this can be prevented by vaccinating bulls against such diseases as vibriosis.
As a general practice to ensure fertility of your bull(s) you should adhere to a strict vaccination calendar against all diseases of economic importance that can afflict your herd.
Always monitor bull body condition and ensure that they are in good condition. Check for lameness or any physical deformities that may develop.
Always make it a habit to get a vet officer to inspect your bulls once in a while. This is a practice which most smallholder farmers fail to adopt primarily because they are weekend farmers and vet officers will be on weekend with their families and hence cannot just be bothered at no cost. Also most smallholder farmers have an aversion to pay for knowledge even if they are able to. Most importantly you need to keep track of your bull performance by careful observation of mating and recording keeping with regards to offspring and other related production issues.
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