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Will higher fat or energy levels in a calf’s diet increase growth rates?

There is good reason why farmers are keen to improve calf rearing, to ensure heifers produce their first calf at 24 months and remain in the milking herd for as long as possible.

In the Netherlands a recent survey found that most farmers use age as the main determinant for serving maiden heifers, targeting 25-26 months as age at first calving.

In contrast, farmers in the 1970s and 1980s sought to calve heifers at 21-22 months but this resulted in those animals exiting the herd prematurely.

We must therefore get the age of calving right to achieve the best return on the significant investment required to rear a heifer.

Feeding large volumes of milk to calves during the quota years, often used as a means to dispose of milk, was also a feature. This approach delayed weaning but as small herd sizes were common at that time it was not a major demand on cost or labour. However, when those heifers joined the herd, it did not increase average milk yield or any other parameter.

It is important that farm businesses are productive and that is why the cost of rearing a heifer must be balanced against its lifetime yield potential.

One option being promoted is to feed more energy to calves during the milk feeding phase but, as can be seen in Table 1 (Yohe et al 2021), increasing fat percentage by over 70% only raises the energy level by 12%.  In this trial, there was no difference in growth rates or any other measure achieved by increasing the level of fat from 18% to 30%.

Table 1 ( Yohe et al 2021)

  Product 1 Product 2 Product 3 Product 4
Crude protein % 22 22 23 23
Crude fat % 18 22 26 31
Lactose % 48 43 39 34
ME MJ/kg 19.6 20.2 21 21.9
Relative ME 100 103 107 112

Feeding calves aged four to five weeks any good milk replacer at 1kg/day can potentially make the calf milk look good and calves will enjoy drinking it. The calf will look good on the outside but it will curtail their digestive development significantly. It must be remembered that it is very important that other feeds are offered alongside calf milk, and calves are encouraged to eat them to promote development of the rumen and large intestine, to minimise growth checks and health issues post-weaning.

In Tables 2 and 3, we have broadly compared the intakes and performance of calves involved in two trials. There is a difference in the age of the calves starting these trials but the point we are keen to illustrate is that the calves in the second trial, who were offered less milk, were able to consume much greater volumes of dry feed. The data for their post-weaning performance shows that they had developed and adapted their digestive system and their microbiome to utilising dry feed.

Table 2

  Amado et al (2019) Product 1 Amado et al (2019) Product 2 Harper Adams trial (2016) Product 3
Crude protein 24 23 20
Crude fat 23 17 24
Lactose 38 44 45
ME MJ/kg 19.7 18.4 19.9
Relative ME 107 100 108

 

Table 3

  Product 1 Product 2 Product 3  (from 3 weeks of age)
CMR intake kgs 57 57 19
Dry feed intake kgs 41 (to 10 weeks on trial) 41 (to 10 weeks on trial) 201 (to 12 weeks on trial)
Growth rate to weaning kgs 0.64 0.66 0.65
Post weaning DLWG kgs Not recorded Not recorded 1.34
Rearing cost/day (milk and dry feed) £ 2.50 2.40 1.55

To offset the weaning check, with even high feeding rates 12- 14 week weaning is being recommended.

Using this as a barometer to produce a herd of 500 dairy cows, the cost of the feed, labour and housing equipment combined amounts to an additional £75,000 (0.5p/litre) compared to successful weaning at 8-10 weeks.

This significantly reduces farm productivity unless heifers are bred earlier or stay in the herd for longer. Many robust trials have failed to find any advantage to accelerating growth rates with milk only. (Morrison et al 2007, Kiezebrink et al 2015)

The evidence so far is that heifers pushed during any period are slower to ovulate therefore don’t breed earlier and those that are pushed to calf earlier have difficulty staying in the dairy herd due to health or fertility challenges.

While some heifers will naturally calve down earlier, the issue lies with pushing all heifers to meet that target.

We must focus on developing the calf’s digestive system and, as this is a key component in the calf’s immune system, this must be done at the animal’s pace.

Therefore, we must encourage dry feed intake in the first four weeks and ensure that this intake grows incrementally. By doing so, by the time the weaning process starts, dry feed will account for 60% of total energy intake.

Keeping fat intake to around 120-150g/day is key to encouraging dry feed intake and calf development.

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