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Heifers Must Be the Correct Body Size, as Well as Age, at First Calving

Heifers Must Be the Correct Body Size, as Well as Age, at First Calving
By Jessica Cook 6 months ago

Holstein-Friesian heifers calving at 23 to 25 months of age have been shown to outperform later calving cows in terms of fertility, milk production and survival over their first 5 years of life. Recent research based on a large UK dataset of 396,000 pedigree Holstein and Holstein-Friesian heifers has provided further evidence to support first calving at 22 to 25 months. A lower calving age was associated with a reduced calving interval and reduced somatic cell count in lactation, an increased lifetime daily milk yield, and an increased chance of calving for a second time1. Heifers calving at 24 months had a mean daily lifetime yield of 14.9 kg, compared to animals calving at 36 months with a mean daily lifetime yield of only 12.8 kgs.

Getting Body Size Right

In addition to getting the timing right, it is also important to get the body size right. Heifers must calve at the right body weight – at first calving heifers should weigh 85 to 90% of mature body weight. If heifers calve down at lighter weights, they have a higher risk of calving difficulties, but they must also continue to grow to a greater extent after calving and this nutrient demand for growth will be at the expense of their fertility. To achieve both the target calving age and body weight, heifers must be well grown throughout the rearing period to ensure they weigh 55 to 60% of mature body weight at first breeding at 13 to 14 months of age.

Setting Targets

A growth rate of 0.7 to 0.8kg per day is generally recommended within the industry to achieve first calving at 24 months – but it is important to set a target growth rate for heifers on your farm, based on the mature body weight of cows within the herd.

Use the table below to calculate a growth rate target – you must know the mature body weight of cows in your herd (this is the weight of your cows in lactation 3, 100 to 120 days in milk). The mature body weight of Holstein-Friesian cows can vary considerably according to selection policy, so the mature body weight of cows within the herd must be measured.

Target Example information Insert your herd data here
Age at 1st calving 24 months
Age at 1st breeding (age at 1st calving minus 11 months)
13 - 14 months (in calf by 15
Mature weight of cows (measure at lactation 3+)
Weight at 1st breeding (multiply mature weight by 55%)
660 x 0.55 = 363kg
Weight gain required (body weight at 1st breeding minus birth weight of 40kg)
363 – 40 = 323kg
Average daily gain required up to 1st breeding (weight gain required divided by age at 1st breeding)
323 kg/13 months = 0.8kg/d

Achieving Targets

To ensure heifers have adequate body size at first calving, growth should be maximised during the milk feeding period when the ability to convert feed into growth most effectively is at its highest.

During the milk feeding period, a calf has a feed conversion rate of about 50% (i.e. 100g of feed = 50g of growth). As a guide, to achieve a growth rate of 800g per day, a calf would need to consume a total of 1600g of feed per day (e.g. 900g milk solids plus 700g starter feed = a total of 1600g). The feed conversion rate is however influenced by many management and environmental factors such as colostrum, environmental temperature, housing and disease status. For example, cold weather, wet beds and disease will all require a calf to use more of its feed nutrients to keep warm and support its immune system, meaning less feed is available to convert into growth.

Calving at 23 to 25 months minimises the non-productive stage of life but also results in improved udder health, better fertility, more milk and increased longevity. Based on the dataset of 396,000 heifers, the mean age at first calving for heifers in the UK was 29 months, with 40% calving for the first time at 30 months or older. There is therefore a huge opportunity to reduce the age at first calving and improve heifer performance. However in order for this to be successful targets must be set and a proactive approach from day one is essential to ensure every heifer enters the herd at 24 months with the correct body size.

Jessica CookJessica Cook

Young Animal Technical Specialist

Volac International

Reference:1Eastham NT, Coates A, Cripps P, Richardson H, Smith R and Oikonomou G (2018) Associations between age at first calving and subsequent lactation performance in UK Holstein and Holstein-Friesian dairy cows. PLOS ONE https://doi.org/10.1371/journal.pone.0197764