Crunch numbers on alternative fibre

13 Nov, 2018 04:00 AM
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Alternative fibre sources vary widely in nutritive value, digestibility and effective fibre value

When pasture is limited and supplies of fodder are reduced, farmer may need to consider using alternative fibre options that they may not have used before.

Dairy Australia program manager Cath Lescun said many alternative fibre sources were suitable for feeding to dairy stock provided they were supplemented with high energy feeds and protein sources as part of a balanced diet.

The alternative fibre sources vary widely in nutritive value, digestibility, effective fibre value, and may present risks such as ruminal acidosis, mycotoxins and chemical residues.

Alternative fibre sources that may be available depending on seasonal circumstances and location include almond hulls, palm kernel meal, cereal straw (barley, oats, triticale, wheat and rice straws) sugar cane and grape marc.

Fibre facts

Fibre is an essential ingredient in the diets of ruminant animals such as dairy cattle. It supplies energy, maintains normal, healthy rumen function, and in cows is utilised to produce milk fat.

The most commonly used chemical measure of the fibre content of a feed or a diet is Neutral Detergent Fibre (NDF).

The 'physically effective fibre value' of a feed or a diet is also critical. It refers to the ability of a feed to stimulate rumen contractions, stimulate chewing activity and production of saliva, which contains buffers that maintain the cow's ruminal pH in the optimal range (6.2-6.6) for growth of rumen microbes.

NDF intake should ideally be about 28 to 35 per cent of the total diet to maximise daily dry matter intake, however, cows can eat up to levels of 35pc of the diet with minimal impact on intake. Above 35pc NDF, dry matter intake will decline especially if the diet is forage based.

About 25pc of the fibre in the diet should have a fibre length of about 2.5 centimetres. Diets containing rapidly digested starch sources such as wheat should have higher levels of NDF (minimum 34pc).

A rule of thumb for NDF intake is 1pc of bodyweight as forage NDF or 1.2pc of bodyweight for total NDF intake. For example, a 600-kilogram cow can eat 6kg dry matter of NDF per day from forage or 7.2kg DM of NDF/day in the total diet.

If there is not enough long or 'effective' fibre, there will not be enough chewing during eating and ruminating, and therefore not enough saliva produced, leading to a drop in ruminal pH and increased risk of ruminal acidosis.

Cattle can suffer from two forms of ruminal acidosis:

  • For more information about fibre and alternative fibre sources go to the Fact Sheets at the Feed Shortage 2018-19 website at www.dairyaustralia.com.au/feedshortage. There is technical information about fibre, including the A-Z of fibre sources, and ruminal acidosis listed under the Feeding the Herd section.

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