Are your heifers reaching the correct weight?

Growing heifers well allows them to reach sexual maturity at an earlier age, allowing earlier breeding which results in a younger age at first calving.

The cost of rearing a heifer is reduced if her age at first calving is reduced.

It is also critical that heifers calve without difficulty, perform well in the dairy and get back in calf easily during their first lactation.

Australian data collected from a year-round calving herd showed the optimal age at first calving was 24 to 30 months of age, as these heifers had the highest first lactation production, highest estimated lifetime production and maximum days of productive life.

Heifers calving for the first time at greater than 30 months of age had decreased first lactation production and decreased days of productive life.

With more heifers entering the herd, the overall herd age will be younger. Younger animals tend to be more fertile and have fewer milk quality issues than older cows as they have had less opportunity to develop mammary infections.

A younger herd age also allows selective culling of older animals and any excess heifers can be sold locally or globally as an alternative source of income.

What is the correct weight for heifers?

The target body weight for a heifer at her first calving is 94 per cent of her mature body weight.

This will vary with breed and genetics.

For example, if the average ‘ideal’ mature cow in a herd is 600kg, a heifer should be calving at 564kg. And, if the average ideal mature body weight is 650kg, then heifers should be calving for the first time at 611kg.

Heavier heifers at first mating are more likely to show sexual activity than lighter heifers.

Therefore decisions around first mating should be based on body weight, not on age.

In seasonal and split calving herds, heifers at first mating may be between 13 and 15 months of age.

This means the youngest animal in the group must be sufficiently grown so there is the best chance for her to get in calf quickly and easily.

The target body weight at first mating is 60 per cent of her mature cow bodyweight.

Commonly smaller heifers are carried over to a younger group so they have more time to grow out prior to first mating.

This delay means there is an increased age at first calving which significantly reduces profitability as the heifer has taken more time and money to rear.

Long-term benefits of heavier heifers

After first calving, heavier heifers are more likely to show a heat prior to mating start date and have better first service conception rates than lighter heifers.

They also have fewer calving problems and have better transition into the milking herd. The impact of body weight on lactation performance has also been demonstrated.

Research has shown that a 50kg heavier heifer at first calving, will produce an extra 1041 litres of milk, 38.5kg butterfat and 42.5kg of protein over the first three lactations.

In addition to the positive effects on reproductive and lactation performance, heifers with a heavier body weight at first calving have increased longevity compared to poorly grown heifers. This is likely due to their improved fertility and fewer health problems.

How can I help my heifers achieve this?

An objective assessment of heifer performance can be achieved by monitoring growth between weaning and first calving.

This ensures that the average daily gain of heifers can be monitored so that they can achieve their target weights at the critical times of first mating and calving.

Small heifers can be identified early, allowing strategic intervention to reduce the risk of them being carried over to a younger group.

Routine animal husbandry procedures such as vaccination and drenching can be carried out at the same time as weighing to reduce any additional handling or stress.

It is worth discussing heifer performance with your veterinarian to enable correct analysis and interpretation of the data and accompanying nutritional advice.

Dr Gemma Chuck works for Apiam Animal Health in the dairy operations team where she writes technical service programs for farmers and vets.