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Heifer calving at the correct age


Dairy replacement heifers are probably the most important animals on a farm producing milk, but at the same time do represent a huge cost to rear. It is therefore of vital importance that farmers manage their heifer rearing wisely and calve them around 24 months old to achieve the most efficient financial gain from their investments.


BY CHRIS MCCULLOUGH, FREELANCE JOURNALIST I


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A B C D E F G H I J Herd regions - anonymized K L M N O


n fact, research in the UK has shown that calving heifers at 24 months old has the ability to increase the overall lifetime performance of the animal by 13%. Around the world dairy farmers opt to run various dairy


heifer replacement rates, but usually it is around 20% to 35%. This means for every 100 cows in the herd, the farm rears 20 to 35 heifer calves each year to act as replacement stock one day in the main herd.


Heifer rearing It is estimated that the cost of rearing a dairy heifer up to 24 months old is around € 1,500 to € 1,800, depending on the system. With this in mind, it is vital that farmers realise the best economic potential of the replacement heifer by plan- ning her first calving at the correct age and weight. This rearing period of the animal’s life is all cost and creates


Figure 1 – Average age of first calving (months) in the anonymized UK herd regions.


no financial input. It has a direct effect on both the total cost of rearing and the time taken for each individual heifer to pay this investment back. Past studies have estimated that it takes, on average, one and a half lactations for the heifer to repay her investment in the rearing period, but this can range from one to six lactations. Replacement heifers are the main route to advance the ge- netic potential of the herd and in practice should be the best genetics on the farm. Research by various agricultural bodies shows the economic, land sparing and carbon footprint benefits of rearing heifers to join the milking herd are best at 24 months of age. However, a significant proportion of heifers still first calve well beyond 24 months of age. Increasing the average age at first calving in a 100-cow herd from 25 to 28 months can in- crease the rearing cost by 18%, which equates to an extra cost of € 6,500 per year for a typical 100-cow dairy herd. Some farmers are reluctant to calve their heifers for the first time at 24 months because they think it may affect the life- time performance of that animal. Other fears are that it could affect heifers’ ability to compete with adult cows, mostly dur- ing feeding times. Research to address these concerns was carried out by AFBI and AHDB in the UK, who analysed over seven million lactation records. The basis of this research in- cluded looking at the production of two million Holstein cows born after 2000 with age at first calving between 21 and 42 months. Cows were categorised based on their age at first calving into three levels: the low level had an age at first calv- ing of between 21 and 24 months, the middle level between 24 and 30 months, and the high level between 30 and 42 months.


First calving The average age at first calving of the cows assessed in Northern Ireland was found to be 28.5 months; however, it varied significantly across the regions of the UK (see Figure 1) with averages per region ranging from 28.1 to 30.5 months. Cows in the low level produced an average of 30,901 kg milk (energy corrected) in their lifetime, which is 1,137 kg and 3,570 kg more energy-corrected milk than the average for cows in the middle- and high-level categories (see Figure 2). For every extra month to the age of first calving, there is an average decrease of 16 days in the cow’s productive life


▶ DAIRY GLOBAL | Volume 9, No. 2, 2022 15


Age at first calving (months)


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