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Straw diet will slow down calf growth rate

In a series of UK-wide workshops organised by Alltech, American dairy expert Jud Heinrichs outlined his latest research on nutrition and science. Louise Hartley reports.

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Many farmers are still rearing heifers like their grandfathers did, even though nearly every other part of dairy farming has changed. That was the message Prof Heinrichs from Penn State University told his Cumbrian audience at a workshop jointly organised by Davidson Animal Feeds.

 

He said many farmers still provided heifers with 24-hour access to feed, whereas limited or precision feeding could meet the nutritional needs of their herds.

 

“We are now making much better quality forage than our grandfathers and keep more of our heifers inside, which lowers their nutritional requirements.

 

“Calves aged 6-9 months only need to be fed 2% of their body weight per day on average and, unlike lactating cows, there are no recommendations to feed heifers 24 hours per day.”

 

“Precision feeding usually results in providing 20% less feed than ad lib. When feed is eaten, young stock are not given any more – a concept which is sometimes difficult for farmers to get their heads round,” he said.

Digestible

"As intakes decrease, forage is digested in the rumen for longer and, as long as straw is replaced with a more digestible forage, feed efficiency can be improved by 4-5%.

 

“Typically, if an animal is growing too fast we slow it down by putting something undigestible, such as straw, into the diet – but that costs money. You are also allowing gut fill of the animal to dictate growth rate.”

 

Prof Heinrichs explained that the average piece of feed leaving the rumen of a calf, heifer or cow, was about 1.18mm and, considering the volume of material a lactating cow eats every day, he said this was pretty remarkable.

 

“Straw has a place in a lactating cow’s ration as a source of effective fibre, but younger animals with a smaller rumen hold straw in the rumen for days while it is chewed down to 1.18mm.

 

“Straw takes up valuable space in the rumen, limiting the amount of concentrate the calf is physically able to eat per day and, therefore, slows down the growth rate.

 

“Feeding forage which is of good quality and also digestible, such as hay, will pass through them quicker, allowing a high grain intake and better growth.”

 

To read this month’s digital edition of Dairy Farmer magazine click here

 

Prof Heinrichs also advised farmers not to grow their calves too fast pre-puberty. Data on Holstein heifers from around the world comparing average daily weight gain from birth to puberty and to first lactation milk production, showed a very clear and consistent trend, he said.

Growth rates

“Heifers which grew 800g/day before puberty gave the most milk in the first lactation, while those which grew 1kg/day or more yielded 450-900kg less in the first lactation.

 

This was due to excessive growth rates causing problems with mammary gland development.

 

“Thankfully the curve is rounded at the top, which means growth between 750-900g/day is good and will not result in a loss of yield. It would be almost impossible for every heifer to hit 800g/day,” he said.

 

“Accelerated growth was in vogue a few years ago, but all the data on pushing growth rates in young calves now suggests it is wrong. It is silly to spend extra money growing heifers too fast and losing out at the other end. (See panel).

 

Growth goals for heifer bredding

  • Double birth weight at 80- 90 days – calves should be grown at reasonable rates especially pre-weaning.
  • Age at first heat for Holsteins should be less than 11 months and Jerseys should be less than eight months. The aim is to have heifers cycling for a couple of months before breeding.
  • Breeding at 13-14 months – do not push back to 12 months.
  • Calve at 22-24 months -- UK average is currently 28.8-32 months.
  • Breeding weight should be 55% of mature body weight (MBW) ie a third lactation cow. There can be quite a variation in this value from farm to farm, so it is always best to work this out for your herd.
  • Weight at calving should 85-90% MBW. In terms of first lactation yield there is no point getting heifers larger – you only spend more money on rearing costs – but too small and they will produce less milk.

Appetite

 

The key was to keep calves healthy pre-weaning and set them up with a good appetite, and Prof Heinrichs said weaning should be done as young as six weeks old.

 

“The most expensive replacement animal on your farm per head per day is the pre-weaned dairy heifer. The first group after weaning is the cheapest and it is management which dictates when you move from one to the other.

 

“Dairy heifers are perfectly able to cope with being weaned at six weeks old. After puberty the sky is the limit in terms of growth rate, depending on how big they need to be before calving,” he said.

 

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