Farm Tech

In The Paddock
Seasonal sheep and beef management tips April 2003

Supplementary feeds for sheep – Feed quality can be very important

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Key points

• ME levels are usually the best basis for assessing the quality of supplementary feeds
• High quality feed is needed to assure ewe or lamb liveweight gains
• Specialist forage crops have MEs of 12–13 MJ ME/kg DM if grazed at the correct growth stage
• Grains have MEs of 12–13.5 ME/kg DM
• Pasture silages and hay have MEs of 8.5–10.5. Most are suitable for maintenance feeding only
• For supplementary feeding to be economic, feed planning or budgeting is essential

Supplementary feeds play an important role on sheep and beef farms, especially in districts subject to drought and/or cold winters.

In seasons when feed is short, the choice of supplement can have a huge effect on future production and profitability.

Will it provide the nutrition needed by each class of stock? Is it priced fairly relative to other options?

Finding the answer to these questions begins with an analysis at any one of a number of labs throughout the country, most of which use NIR (Near Infra Red spectropy) technology. NIR results typically include:

• Soluble carbohydrates
• Acid detergent fibre (ADF)
• Neutral detergent fibre (NDF)
• Crude protein (CP)
• Crude fat
• Dry matter
• Organic matter digestibility
• Metabolisable energy (ME)
• Ash and some mineral estimates.

Soluble carbohydrates (sugars and starches) are highly digestible. NDF includes structural carbohydrates (cellulose and hemicellulose) and lignin. ADF includes cellulose and lignin.

Cellulose is readily broken down into sugars by fermentation in the rumen. Hemicellulose is only slowly broken down and lignin is virtually indigestible.

As a plant ages, it becomes less digestible as structural carbohydrate and lignin levels increase.

CP is made up of true protein (TP) and non-protein-nitrogen compounds like urea and nitrates. The NIR protein figure is described as crude protein, but is effectively a true protein figure.

TP is essential for the growth of young stock. The TP content of a crop also declines as a crop gets older. With silages, an estimate of ammonia nitrogen is given (see below).

The ME content of a crop is the best measure of its quality. In most supplementary feeding situations in New Zealand, energy is the limiting factor, so supplements should usually be purchased on an ME basis.

At least 10 per cent of a feed needs to be made up of soluble sugars and starch to allow normal fermentation and digestion to take place. Normal ranges are: pasture 10–15 per cent; pasture silage 2–7 per cent and maize silage 30–40 per cent.

Fibre is hard to digest and generally the lower the fibre the better the quality, but at least 20 per cent ADF or 30 per cent NDF is needed for normal rumen activity.

Normal fat levels are 2.5–4.5 per cent. Excess fat interferes with digestion.

A CP level of 7 per cent is adequate for maintenance; 10–14 per cent for growth and 15–17 per cent for lactation. Less than 7 per cent will cause protein deficiency, while more than 24 per cent will cause production problems.

For maintenance purposes, the ME content is relatively unimportant, especially if there is some pasture available. But if liveweight gain is being targeted, the ME content of the supplement is the key.

With lambs, the potential daily gain increases from 100 g/day to 400 g/day as the ME content increases above 10 MJ ME/kg DM. At 9 MJ ME/kg DM, lambs can consume a maintenance ration only. Below this, they will not be able to eat enough to even maintain weight. The same principles apply to ewes.

Feed quality of some supplements

Crops

Most summer and winter forages produce a good bulk of feed (8–12T DM/ha). They are 85 per cent digestible, have MEs of 12–13 MJ ME/kg DM and 15–25 per cent CP, if they are grazed before they start to go to seed. Good levels of gain can be obtained on these forages if they are not grazed too hard. Some animal health problems can occur with these feeds and gradual introduction is recommended.

Grains

Peas, lupins and barley can be used to supplement ewes. They are also suitable for lambs, but for marketing reasons they should not be used for lamb finishing.

Each 100 g of barley provides 10 per cent of the daily maintenance of a 60 kg ewe or 20 g/day gain. To avoid acidosis, gradual introduction to grain is essential.

Grains are 85 per cent DM, have 12–13.5 MJ ME/kg DM and 12–14 per cent CP. One kg of barley will provide 10.6 MJ ME (1.0 kg x 0.85 DM x 12.5 MJ ME/kg DM). Expect feed conversion ratios of the order of 5 to 1 with lambs.

Silage/hay and balage

Good pasture silage, balage and hay contains 8.5-10.5 MJ ME/kg DM and 12-20 per cent CP. These feeds are usually used for maintenance, but good quality silage can be used successfully to flush ewes.

If the silage is not wilted and has true protein levels (NIR CP level) less than 12–14 per cent, liveweight gains can be good but the flushing response is likely to be disappointing.

High ammonia N levels–greater than 10 per cent of total N–are a sign of poor silage quality.

Feed planning

To estimate the amount of supplementary feed needed, a proper feed plan or budget should be completed. This can have a huge bearing on whether supplementary feeding is profitable or not.

Estimates of feed on hand, crop and pasture growth rates, pasture covers and animal requirements are all required.

More information

The following publications are available free to farmers from Meat & Wool Innovation:

Supplementary Feeding. NZ Society of Animal Production Occasional publication No. 7.

A Guide to Improved Lamb Growth, Chapter 5.

A Guide to Feed Planning

In the Paddock, July 2001. Silage for ewes.

In The Paddock, December 2001. Prepare lambs well and they'll thrive on forage crops.

Your local farm consultant or veterinarian will also be able to help. Alternatively, contact your local Meat & Wool Innovation extension specialist: