Making the most of recording calving data

Calving Ease EBVs provide an estimate of genetic differences in the ability of calves to be born unassisted from two-year-old heifers. Calving Ease EBVs are calculated from three main sources of information, being calving difficulty scores, birth weights and gestation length records. Calving difficulty scores are by far the most important of these sources.

Why Should Calving Difficulty Scores be Recorded?

Calving difficulty can have a negative impact on the profitability of a herd as it can lead to increased calf, heifer and cow mortality, slower re-breeding performance and/or additional expense (which can be considerable) associated with increased labour and veterinary services.

While a number of studies have shown birth weight to be the most important genetic factor influencing calving difficulty, there are a number of additional genetic factors that also have an influence. These include calf shape, pelvic area and the calving “will” of the dam. Calving difficulty scores capture all of these factors and therefore give breeders the opportunity to make more genetic improvement for ease of calving than is possible if selecting on birth weight alone.

Calving difficulty should be measured at birth using a 1-6 scale as per the table below.

What Considerations should be made when Recording Calving Difficulty Scores?

• If calving difficulty score is either blank or zero (0), it is interpreted as no score recorded NOT as a score of no calving difficulty (unassisted). All calves that are unassisted should be given a score of 1.
• Calving difficulty scores should be recorded for all calves, and not just those that had difficult or easy births. Calving difficulty scores should also be recorded for stillborn/dead calves; this information is useful for calculating the Calving Ease EBVs of close relatives (e.g. sire and dam).
• There needs to be some level of calving difficulty in the herd for the calving difficulty scores to be used effectively by the BREEDPLAN analysis. That is, simply scoring all births in a herd with a calving difficulty score of 1 will not identify any genetic differences in ease of calving.
• As is also the case with birth weight, a birth management group should be recorded alongside the calving difficulty score if there have been different treatments of the females prior to calving that may have affected calving difficulty. For example, where cows have had different levels of feed availability prior to calving.
• When calculating the Calving Ease EBVs, calving difficulty scores of 3 and 4 are grouped together. Calving difficulty scores 5 & 6 are excluded from the BREEDPLAN analysis as these are considered non-genetic in origin.

What considerations should be made when recording Birth Weights?

• Birth weight should be recorded for the whole calf crop. Without comparisons to the other calves, “occasional” measurements are of no value and can actually be misleading. Recording birth weight for dead calves is particularly important.
• There are significant fluctuations in the weight of a calf over its first week of life. Therefore, it is important to weigh calves as close to birth as possible. Ideally, measure birth weight within 24 hours of birth.
• Do not guess birth weight or use girth/chest size to estimate birth weight.
• A birth management group should be recorded if there are different treatments of the females prior to calving that may affect birth weight. For example, where one group of cows have had different feed availability. A separate birth management group should also be assigned if the weight of the calf has been affected by special circumstances (e.g. premature calves, the dam was sick etc.)

How does Breedplan use Gestation Length?

Gestation Length EBVs provide an estimate of genetic differences between the period from the date of conception (i.e. when the female gets in calf) to when the subsequent calf is born. Shorter gestation length is generally associated with lighter birth weight, improved calving ease and improved re-breeding performance among dams. In addition, calves born with a shorter gestation length may be heavier at weaning due to more days of growth.

Gestation Length EBVs are calculated from both the conception date and date of birth records for calves conceived by either AI or Natural Service Mating.

The information that needs to be recorded for the calculation of Gestation Length EBVs includes:

• the date of birth details for each calf
• the mating (or AI) date of any AI or natural service mating

Importantly, you do not need to calculate the gestation length for each calf. BREEDPLAN will calculate this from the information specified above.  Gestation length data can be submitted at the time of calf registration by using the AI/Natural Service date box.