Time to act if you have underweight dairy replacement heifers

On many dairy farms, replacement heifers fail to reach target weights. The time between birth to first calving makes it very difficult for farmers to recognise the impact that their replacement strategies have on farm production and performance.

Ronan Mulligan, Dairy Advisor in Teagasc Claremorris, notes that lower survival rates to third lactation and reduced milk yields in subsequent lactations are just some of the consequences of failing to achieve the target weight for age when rearing replacement heifers.

Target weights

ICBF Herdplus has the ability to provide dairy farmers with a huge cohort of information. Within ICBF Herdplus, there are an array of tools available to farmers that aim to help farmers identify areas in which they can improve their overall farm performance.

Since October 2022, ICBF HerdPlus has added a new profile screen, which will allow farmers to record the weights of their replacement heifers in order to help determine if they are going to achieve their target weights.

The profile allows dairy farmers to benchmark heifer live weights against industry target weights for replacement dairy heifers based on age. This will help to identify any underweight heifers and ensure they are the correct weight by mating start date. This will ultimately lead to heifers calving down at the optimal age of 22-24 months and in turn will help to maximise farm profitability.

The importance of weighing

Weighing your dairy heifers is a key component of successful heifer rearing and plays an important role for a successful breeding season. Poor fertility in replacement heifers is often due to heifers being underweight at mating start date. This can be avoided if weight and weight gain of the heifers is regularly monitored.

Research has shown lower survival rates to third lactation and massively reduced levels of production are just some of the consequences of failing to achieve the target weight for age when rearing replacement heifers.

The maintenance sub-index is the main tool used to determine a cow’s projected mature body weight. The higher the maintenance sub-index, the lighter the cow. Table 1 below identifies the required percentage of bodyweight replacement heifers should be at during different stages in their lifetime. February-born weanling and yearling heifers should be 30% and 70% respectively of their pre-calving body weight on August 1^st if they’re to be successfully calved at two years of age.

Table 1: Target bodyweight guidelines for replacement heifers

Knowing the weights of your replacement dairy animals and reaching target weights on time is critical for successful calving at two years of age. Nationally, only 75% of heifers calve down at 22-26 months of age. 25% or around 80,000 heifers calve at over 26 months of age. This can have massive consequences on calving pattern, production and will ultimately increase costs on dairy farms.

Addressing underweight heifers

Weighing is necessary to identify underweight heifers or to ensure the other heifers in the herd are on course to achieve their desired liveweight come mating start date.

If not at the correct weight, supplementation should be provided immediately as it will become too late to address the issue of underweight heifers at mating start date next April or May. Heifers should be provided with top quality silage (75% DMD +) over the course of their first winter in order to improve performance and live weight gain. It’s also hugely important that replacement heifers have enough feed space when supplemented with meal at grass and also at housing during their first winter.

Grouping of lighter heifers can also be useful during the first winter, as it can allow farmers to prioritise this particular group of stock and give them extra supplementation during housing.

Early turnout for replacement heifers is also beneficial with higher weight gains usually achieved from pasture as oppose to winter diets. If the group of heifers are not uniform, lighter heifers should be prioritised and turned out first. These heifers should also be allocated some concentrates. Now is the time to act if you have underweight heifers in your herd.

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