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What’s behind target age at first calving? (Oct 2021)

Westpoint Farm Vet’s Tim Potter, who specialises in dairy and young stock, looks at the reasons why the industry target age at first calving, of 24 months old, is something all producers should aim for.

Data from the UK continues to highlight that many herds are calving heifers later than the target 24 months and are, therefore, missing out potential performance benefits. Studies have shown that calving at 24 months of age improves overall lifetime milk production by up to 13%, and work by the RVC has shown show that heifers which calf at two years give on average 25,000 litres of milk throughout their first five years, while those calving two months later give just 20,400 litres. The figures also reveal longevity is increased. Heifers calving at 24 months old have a 62% chance of remaining in the herd at five years old. Heifers calving at 26 months old have a significantly lower – 41% – chance of surviving past their fifth year.

That said, the benefits of calving at 24 months old are not only about production and longevity. Meeting the target also impacts profitability and efficiency. Rearing heifer replacements is a significant cost to any dairy business, which increases the longer the rearing period is. The cost of rearing a heifer that calves at 24 months old is approximately £1,500, but this increases to £1,800 if she calves at 26 months old and can be more than £3,000 if she calves for the first time at 32 months old.

Monitoring growth: keep heifers on track to calve at 24 months old

Environmental benefits

Another advantage of a lower age at first calving is a reduction in the number of non-productive females on farm – a huge benefit when housing space is at a premium. Calving heifers at 24 months old also speeds up the herd’s rate of genetic gain. Meeting calving age targets also offers environmental benefits. A heifer calving for the first time at 23 or 24 months old will have a significantly lower carbon footprint than older animals.

And it is important to remember it’s not simply a case of ‘how low can you go’ when it comes to age at first calving. Calving heifers too early (less than 21 months old) will have a negative impact on milk production and increase the risk of calving difficulties associated with them not being fully grown. When they calve for the first time, heifers should weigh between 85% and 90% of their mature body weight. If a heifer calves below this target, they will continue to grow after calving but she will have a greater nutrient requirement to support this growth, which will often come at the expense of fertility.

So the 24-month target is the sweet spot in terms of overall herd efficiency and maximising long-term performance – both in terms of milk production and fertility. It strikes a balance between the challenges encountered by calving heifers too young while also ensuring herds are running as efficiently as possible. Calving heifers at 24 months old also avoids negative impacts on lifetime performance and longevity, often seen when heifers calve for the first time at an older age.

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