Minimising calving difficulties - Before breeding

Heifers tend to have more calving difficulties than mature cows. Their selection and management can play a large part in minimising potential problems.

Ensuring that heifers are well grown is vital to minimising calving problems. They must be managed carefully to ensure they keep growing steadily to reach their mature size targets. Ideally, they should be managed as a separate group, given access to good quality grazing and given supplements during the winter, according to silage quality. Regular weighing is essential to keep them on track to meet their liveweight targets.

Target: heifers should be 85% of their mature liveweight at calving. 

Calving difficulties in heifers are often attributed to poorly grown heifers or oversized calves born from an inappropriately selected bull. The key to minimising these problems is to make sure that heifers are well grown and mated with an easy-calving sire.

Restricting feed in the last month of pregnancy can increase calving difficulties and affect colostrum production. Rations should be formulated to meet all nutrient requirements at this stage of pregnancy, recognising that heifers require more protein (at least 11% crude protein in dry matter) than mature cows because they are still growing.

To reduce the risk of dystocia in heifers:

• Aim for heifers to be 65% of their mature body weight at the start of the breeding season
• Keep heifers growing and aim for 85% of their mature body weight at first calving
• Mate heifers and small cows to easy-calving bulls
• Do not restrict feed in the last month of pregnancy because this can increase calving problems and reduce colostrum quality
• Plan to calve heifers early in the calving season so they have more time to recover from calving before the next breeding season.

There is increasing interest in the value of measuring pelvic area as part of a pre-breeding check that is carried out by a vet before breeding heifers. Assessing the pelvic area at this stage allows identification of heifers with abnormally shaped or particularly small pelvises so that a decision can be made as to whether or not to breed from them. The pre-breeding check should also cover structural soundness, weight-for-age, BCS and an assessment of the reproductive tract.

It is vital that breeding bulls are fit and fertile at the start of the breeding season to maintain a compact calving season. Carrying out a bull MOT and a fertility test can identify sires that are infertile or subfertile. This should be done in plenty of time before the start of the breeding season so that, if necessary, an alternative bull can be sourced or artificial insemination (AI) planned.

Bulls with lower than optimum fertility may still impregnate cows, but at a lower rate, which will extend the calving period. Late-calving cows are more prone to gaining condition, especially if on good quality grass, which can increase the likelihood of calving issues.

Birth weight and gestation length can both affect the ease with which calves are born, yet neither can be assessed visually when choosing a bull. For this reason, it is critical to make a sire choice based on EBVs to minimise calving difficulties.

EBVs can be used to select bulls that produce calves with a shorter gestation length and lower birth weight, which consequently calve easily. At the same time, careful sire choice should identify calves that have good growth and/or maternal traits, depending on whether the calf is destined to be a breeding heifer or for beef production.

There are two types of calving ease EBVs:

• Calving ease (direct) – identifies bulls whose progeny will be born more easily
• Calving ease (maternal/daughters) – identifies bulls whose female progeny will calve easily. 

You can check the figures for current or prospective bulls, or for bulls being used for AI, by entering the ear number into the respective breed society database.

Check the bulls’ EBVs for:

• Birth weight – look for figures that are lower than the average for the breed
• Calving ease – look for figures that are better than breed average
• Gestation length – a negative figure means a shorter gestation, which will tend to result in a smaller calf that is born more easily
• Maternal calving ease when breeding replacements – a figure higher than breed average is preferable

The information on these pages was compiled by Katie Thorley, AHDB Beef & Lamb and David Black, Paragon Veterinary Group and reviewed by Dr Alexander Corbishley, University of Edinburgh.