FROM AUTUMN/WINTER BEEFTALK

Beef producers can improve the efficiency of their enterprise by better managing reproductive performance in their herds, which has flow-on benefits for marketing, nutritional management and disease control. 

Seasonal mating and pregnancy testing are the two main components of reproductive management. Pregnancy testing breeding cows contributes to reproductive management in two key ways: it allows productive animals to be identified, and identifies non-performers for culling.

INDENTIFYING PERFORMERS AND NON-PERFORMERS

Scientific and anecdotal evidence shows that fertility is the most economical trait for which cattle should be selected. Estimates vary, but most authorities suggest that 40 to 60% of our selection effort and management practices should be directed toward improving and maximising reproductive performance.

Reproductive rates vary between properties and with seasons. Accurate figures for the whole of the Queensland beef herd are not available but the percentage of cows calving within a 12 month inter-calving interval is thought to be in the range of 50 to 70%.

From a genetic perspective, while reproductive ability may be highly repeatable, it is not highly heritable. If a cow calves early this year, then there is a good chance she will continue to do so in following years. However it does not necessarily follow that her daughters will be early calvers.

Cows that don’t provide a calf each year should be sold for slaughter and replaced by cows/heifers that do.

PREG STATUS AT SLAUGHTER

Unfortunately, abattoir surveys in Queensland indicate that approximately 60% of cows are pregnant when slaughtered. This means a lot of productive cows are being killed whilst many non-productive cows remain in the herd.

At present foetal blood at slaughter provides financially increased returns, but this incentive should not outweigh the best management decisions for the enterprise. In most cases, the owners didn’t know their cows were pregnant or weren’t aware of the economic losses incurred by selling pregnant females. The value of these losses is difficult to accurately assess, but it probably runs into tens of millions dollars per year in Queensland.

These economic losses are associated with the reduced reproductive performance of the herd, and the reduced value of the slaughtered animals. Meat quality drops markedly during pregnancy. The further advanced the pregnancy, the more adverse the effects. Pregnant cows are less able to withstand stress and are hence more likely to have a higher incidence of ‘dark cutters’, lower dressing percentages and lower carcass yields.

WHEN TO PREG-TEST

The most convenient time for most producers is at weaning, when it is relatively easy to cull empty cows. Pregnancy testing when cows and calves are yarded for weaning also avoids the difficulties that come with identifying and drafting cows and calves after they have been returned to the paddock. Seasonal mating (where bulls are removed for a certain period of the year) means that all weaning, pregnancy testing and culling can be completed at the one time, resulting in labour cost savings. 

An additional benefit of pregnancy testing at weaning is that non-productive cows can be unloaded from the property before the period of most nutritional stress (i.e. Winter). April through to early June is the ideal time to wean and pregnancy-test cows. In dry seasons, weaning earlier can improve conception rates during the following calving season.

OPTIONS FOR PREGNANCY TESTING

The pregnancy status of breeders can be evaluated in many ways, including

• keeping records of cycling activity
• hormone assays of body fluids such as milk, blood or urine
• beta-mode ultrasonography
• real-time ultra-sound devices
• measuring the electrical conductivity of vaginal and cervical mucus; and
• rectal palpation.

However not all pregnancy testing is accurate. The abattoir surveys mentioned above also revealed that of the cows that had been preg-tested empty by various methods, 38% were in fact pregnant. Almost half of these were in the middle or last third of pregnancy. 

None of these testing methods has proven suitable for use in all circumstances. To date the cheapest and most effective method for pregnancy testing cattle in most situations is rectal palpation.

RECTAL PALPATION

Pregnancy testing by rectal palpation is not a simple technique. It requires a degree of skill and there are some risks for the operator and the cow/calf. 

Pregnancy testing involves close handling of cattle, which entails some danger for even the most experienced operator. 

Pregnancy testing of cows less than 13 weeks pregnant has been known to cause abortions. These losses are minimal if the testing is performed by an experienced operator, but may be up to 10% if performed in a rough manner by inexperienced persons. For this reason all early pregnancy testing, wherever possible, should be done by a skilled operator. Beef producers who are adequately trained are able to safely and accurately pregnancy-test cows that are more than 13 weeks in calf. Generally, the more advanced the pregnancy, the easier the diagnosis.

For most properties the most convenient opportunity for testing at least 13 weeks after the bulls have been removed is at weaning. 

Accurate pregnancy testing which indicates the foetus’s age is far superior to a simple pregnant-or-empty decision. Foetal ageing is useful for detecting some reproductive diseases as well as assessing bull function during the mating period.