The reality of twins in beef cattle

While the incidence of twins in beef cattle is very low, there is the possibility that it could improve the rate of their reproduction, says the Agricultural Research Council.

The reality of twins in beef cattle
A complete economic assessment of the potential of twinning in beef cattle has never been conducted.
Photo: FW Archive

The concept of improving the rate of reproduction in beef cattle by selection for an increased rate of twinning has been debated with both optimism and pessimism since the early days of animal breeding.

With the success of selection for multiple births in sheep, there was hope that the technique would also work in cattle. In general, however, beef cattle farmers have been opposed to twin births due to the number of problems associated with twinning. Successful reproduction in a cow-calf production system is the cornerstone of biological and economic efficiency.

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Cattle evaluations have focused mainly on production traits, and genetic improvement in reproductive traits through the use of selection tools has been limited. It is globally accepted, however, that from an economic perspective, reproductive traits are twice as important as production traits in a cow- calf production system.

Reproduction of cattle is dependent on several factors, including breed type (for example Bos taurus or B. indicus), animal class and location. The interaction between environment, health, genetic factors and management also has a major influence on reproductive performance.

Twinning is rare
Cattle are uniparous: female animals are likely to produce only one offspring per gestation. In most beef cattle breeds, twinning is rare, with multiple births most likely being due to multiple ovulations with a frequency of not more than 1%.

In dairy breeds, by contrast, the frequency is between 3% and 5%. The regulation of the twinning rate has been achieved via embryo transfer, genetic selection, hormonal treatments or the immunologic suppression of hormones.

In cattle, twinning has advantages and disadvantages, depending on whether one is running a dairy or beef operation, and what production system is being used.

Genetic selection
The heritability of twinning, and indeed of most reproductive traits, is very low. Heritability (h2) for twinning rate has been estimated to be between 0,01 and 0,09.

However, it has been suggested that with genetic selection, twinning in cattle may be increased to a level of economic importance. This could be achieved through the use of selection criteria primarily focusing on multiple observations of ovulation rate when applied to replacement heifers and sires.

The genetic correlation between ovulation rate and twinning rate is 0,75 or higher. In cattle, the rate of twinning is regarded as a quantitative trait, which means that it is dependent on the combination of several genes modified by environmental factors.

With the development of new genetic technologies such as quantitative trait loci (a locus is a specific, fixed position on a chromosome where a particular gene or genetic marker is located) and marker-assisted selection, it may be possible to select more effectively for twinning in beef cattle.

If loci-affecting traits related to reproductive performance, including twinning, can be identified, DNA markers will be useful for selecting genetically superior animals for a number of reproductive traits, thus improving response to selection.

Disadvantages of twinning
Some disadvantages associated with twinning include lower calf survival rate, dystocia, stillbirths, abortions, calf abandonment, retained placentas, longer intervals between conceptions, increased culling rate (lower cow reproductive performance), and freemartin (infertile) heifers.

The lower productive performance in cows is caused mainly by increased difficulties
during the course of gestation, and a prolonged inter-calving period due to difficult births. Moreover, with the increase in twin births in a herd, the risk of unsuccessful reconceptions increases, and thereby the profitability of the herd decreases drastically. It has been reported that cows calving twins have longer calving intervals and increased culling rates than those carrying only one calf. In addition, twinning places the cow at greater risk for developing metabolic disorders such as ketosis and displaced abomasum.

Advantages of twinning
In theory, beef cattle productivity in a herd can be improved through an increase in prolificacy or an increase in the frequency of twins. When raising twins, a beef cow will most likely wean more total calf weight than a cow with only one calf.

Twinning therefore offers the potential for an increase in beef production efficiency in a herd. Researchers have illustrated the potential for a decrease in production costs of about 20% to 30% per unit of beef returns when an increase in total weight of calves is observed at weaning by means of twinning.

Below are some results from a number of research studies undertaken in the US and Canada:

  • Twins produce 108kg to 186kg more weight at weaning per cow than singletons do.
    Dams with twins produce 70,8% more calves compared with a single calf born, which results in an increase of 48,1% in weaning weight.
  • Twins cost about 24% more than a single calf due to veterinary assistance during birth, and health issues that may occur in twins.
  • A cow with twins produces up to 65,2% more kilograms of calf than a cow with a singleton.

Many studies have also shown that freemartin heifers do not have a negative effect on beef production systems. This is due to the larger number of calves within a herd that can be slaughtered after weaning.

In comparison with normal female calves, freemartins frequently produce a choice grade carcass, as there is more marbling in the longissimus muscle. Freemartins also generally have a higher birthweight than normal female calves.

Twinning in beef cattle, at least theoretically, presents a potentially new paradigm for cattle management and production systems. It therefore provides an opportunity to increase both reproductive and economic efficiency, although some of the potential economic gain will be compromised by the factors negatively associated with the trait, as already described.

Some of these problems may be overcome with changes in management, such as including pregnancy status checks to determine twin versus single gestations, appropriate nutrition for twin gestations, suitable calving facilities, and the early weaning of twin calves to facilitate rebreeding of the dam. Pre-calving diagnosis of twin pregnancies will enable better management at calving and allow for obstetrical assistance to be ready if required.

Intensive management needed
Twinning in beef cattle is a potential means of dramatically improving efficiency of beef production. However, a very high level of intensive management will be required for the twinning technology in beef cattle to increase economic productivity.

Improvements in genetics and/or management for dystocia, calf survival and rebreeding rate will be required to make any beef production system based on twinning economically feasible.

Interestingly, a complete economic assessment of the potential of twinning in beef cattle has never been conducted. Such an assessment is needed to determine whether the economic returns from the production of two calves per cow could offset the costs of labour, feed and herd health (intensive management of twin-producing dams and their calves), as well as other disadvantages associated with the trait.

In South Africa, the likelihood of achieving a workable system of twinning in beef cattle is low, as extensive production systems dominate beef cattle farming enterprises.

However, there may be a few cases where farmers have abundant feed resources and will be able to devote enough of their time to managing and caring for cows calving twins. Unfortunately, selection for twinning will be limited if only small numbers of animals are available.

Email Dr Ben Greyling of the Agricultural Research Council at [email protected].