The fundamentals of fertility in beef cattle

Llewellyn Angus, an animal scientist, Simbra/Simmentaler breeder, and SA Interbreed Judges Association examiner, says that grazing and fertility management are both crucial to profitable beef cattle farming. Here he shares the basic principles of managing fertility in a beef herd.

The fundamentals of fertility in beef cattle
Fertility is determined not only by genetic breeding, but by general herd management principles, such as maintaining good animal health.
Photo: Supplied
- Advertisement -

A livestock farmer is firstly a veld and pasture farmer. It is vital that the animals’ nutritional requirements are met, especially during breeding and when the cows are raising calves.

Moreover, the cattle should be fully fed in a relatively short period of grazing. This implies that the farm’s fodder flow must be sufficient throughout the year.

Arguably the most crucial aspect of grazing management after establishing the correct stocking rate is to ensure that a portion of the veld and pasture is given a periodic rest period comprising a full growing season.

- Advertisement -

The foremost economic factor of a cattle farming enterprise is fertility. It is five times more important than growth performance, which in turn is five times more important than carcass quality. Obviously, it is better to have a poorly performing calf than no calf at all.

Management & genetics
Fertility has both a management and a genetic component. The management component includes all those aspects, such as feeding correctly and maintaining animal health, that are your sole responsibility as a farmer.

It also includes maintaining strict breeding seasons in order to establish which animals are not reproducing. Breeding seasons make it far easier for you to use a veterinarian to determine which cows have failed to conceive.

Good management enables animals to produce and reproduce optimally. The genetic component of fertility is limited to 10% heritability. However, it is highly repeatable, so make sure to identify the cow families that calve every year.

Just to be clear: heritability is a reflection of the degree to which offspring performance is a reflection of the performance of their parents.

Repeatability is a measure of the strength of the relationship between repeated records. As a producer, knowing the repeatability of a trait can help you make culling decisions. You can also use repeatability as a measurement to predict early on how productive a cow will be over her lifetime in terms of milk production and calf weaning.

Breeding values
Select for genetic traits that are positively correlated with fertility, such as scrotal size and mature body mass, and consider the fertility index itself, such as days to calving. These are expressed as estimated breeding values (EBVs).

Remember, however, that if the animal’s feed and other requirements are not met, you cannot correct for this by selecting for higher fertility on a genetic level.

Scrotal size in bulls plays a major role in determining the fertility of the female offspring. It is true that bigger is better, but only up to a point. Look at the scrotal size or scrotal circumference EBVs of the bulls you buy, and physically examine scrotal development. Two equally well-developed testes with good epididymis development are very important.

Another key trait is mature weight, which should always be kept in check. The EBV for mature weight should ideally be around breed average. Your aim should be to breed cows that calve easily and produce fast-growing calves, but you don’t want breeding stock that are too large by the time they wean their first calf, because big cattle have high maintenance requirements. Moreover, animals that are heavy at maturity are often less productive.

The days-to-calving fertility index identifies bulls and cows that carry the genes producing fertile progeny. Animals that take less time to calve from the initial mating date have a better days-to-calving index and are thus more fertile.

This index also plays a large part in the overall economic indices for certain systems, such as a self-replacing feedlot.

Bull selection
A bull has a 50% genetic influence on a herd of females that he gets into calf. It’s therefore crucial to buy and use bulls with the correct fertility and growth attributes. The old adage, ‘A good bull is half your herd and a bad bull is your whole herd’, holds true.

Be sure to maintain the correct bull-to-cow ratio and to test bulls regularly for fertility and sexually transmitted diseases.

As a general guideline, a two-year-old bull should be able to cope with 20 females in a two- to three-month breeding season. At three years old, a bull should service 30 females within this time frame, and by four years, he should be able to breed with 40 females.

Early calvers are generally the more fertile animals. The shorter you make your calving season, the more fertile your herd will become. Ideally, 60% of your females should calve in the first 30 days of the season. By selling your late calvers, you also in effect shorten your breeding season.

Hybrid vigour increases fertility, growth and longevity, so it pays to crossbreed. But this must be carried out in a structured way, and good management is essential. A normal crisscrossing system or a three-way cross system can be followed.

It is also very important to choose a breed or type of cattle that is suited to your environment and farming system.

Under more extensive conditions (in large parts of the country), breeds with a certain mix of Bos taurus (for production) and B. indicus (for hardiness and adaptability) demonstrate greater fertililty. Under more intensive and higher-rainfall systems, B. taurus-type breeds do better.

Under extremely arid and hot conditions where the stocking rate is very low, indigenous B. indicus-type cattle and Brahmans fare best.

Email Llewellyn Angus at [email protected].