Prudent forage and crop strategy

Informed decisions will mean feeds are fit for purpose and stack up on benefit-cost against alternatives, making sure extra costs for the likes of conserved feed or crop establishment are factored in.

Keep in mind that feeding over the following production periods has varying requirements f or optimum production:

• Liveweight maintenance of adult breeding stock

• Meeting body condition targets during mating then over pregnancy

• Milk production for top rearing of suckling progeny

• Good growth of progeny to target weights after weaning.

The nutrients usually indicating feed value are energy and protein, as these are the main drivers of productivity. Energy gives the oomph for production levels and protein provides the building blocks for milking, reproduction and growth.

Fortunately, our most common grass-clover pastures and forage crops meet the needs of our sheep and cattle except in areas where there are known soil deficiencies of essential minerals such as selenium, cobalt, copper, etc. These can be corrected in fertilisers or administered directly to animals. There’s a wide range of other forages and crops available to fill the gaps when pasture supply is limited. Decisions by farmers on which

FORAGES

to use have generally evolved over the years but need regular review with the help of colleagues or consultants.

Remember that the amounts of various rations fed, even though based on science, is not in itself an exact science. This is because there’s a whole host of variables due to environmental conditions, and often other random influences, that impact the level of feed needed. So there’s an element of judgement. In most cases, trial and error over the years and inbuilt ‘gut feeling’ that most farmers have, does the trick.

Comparing feeding value

As the key feed ingredient is energy, the metabolisable energy (ME) system has been adopted for farm animals worldwide. The relationship between gross energy in feeds and metabolisable energy available for production in animals is shown in the energy pathway diagram (Figure 1). Put simply, the net energy in feeds is available as ME to the animal for production after losses in faeces, urine and fermentation in the rumen.

This ME system is simple and easily applied. Quantities of ME in most pastures, forage crops and supplementary feeds are given in Table 1 (see over page) and are readily available online and in publications. A good place to find sheep and cattle energy requirements is the Beef + lamb NZ website https://beeflambnz.com where ‘Making every mating count’ and ‘Guide to NZ cattle farming’ have comprehensive tables. Handy feeding guidelines, including seasonal pasture production in various areas, are available on the Farmax site at http://www.farmax.co.nz

GUIDELINES FOR DIFFERENT PRODUCTION PERIODS

Recommendations here for use of forages and crops are based primarily on energy and protein requirements during different production periods. Remembering on-farm decisions will be influenced by practical aspects such as contour, soil type, seasonal growth conditions, etc, and importantly the cost of providing the feed.

Maintenance

Maintaining liveweight of adult ewes

or cows should aim to hold body condition score (BCS) just above the midpoint of the range, or 2.5+ for sheep and 5+ for cows. If animals drop below these BCS levels it should be top priority to recover again for the production periods of mating, mid-late pregnancy and milking.

The primary requirement for maintenance is energy with 60kg ewes needing about 11MJ ME/day and 400kg cows about 55MJ ME/day. Using values from Table 1 for summer dry and stalky pastures with an ME content of 8MJ ME/kg of drymatter (DM), ewes would need 11/8 = 1.4kg DM/day while cows would need 55/8 = 6.9kg DM/day. In other words, fed to appetite in both cases.

Another example using crops is that cows wintered on rape with an ME content of 12MJ ME/kg DM would need 55/12 = 4.6kg DM/day. Ewes on swedes with an ME content of 12.4MJ ME/kg DM would require 0.9kg DM/day.

A worked example of areas of crop needed each day for cows at maintenance on rape is given at the foot of Table 1. Similar methodology could be used to calculate areas for ewes wintered on swedes or other crops.

Use of hay or silage can be a viable alternative for maintenance feeding if pasture is in short supply.

Mating and pregnancy

For ewes heading towards mating in autumn, the aim should be to lift BCS by a half to one unit, or 3.5 to 7kg liveweight (each body condition score change is equivalent to about 7kg LW change).

This will need at least a 50% increase in feed intake of feed with a higher ME content for a period of 3 to 4 weeks. For breeding cows mated with calves at foot during summer-autumn, the priority will already be highest quality feed available to maintain good milking at the same time.

For both ewes and cows in mid-late pregnancy, the priority of maintaining body condition is difficult due to competition for space with rapidly developing foetuses. A higher ME content in feed of at least 11.5 megajoules (MJ) ME/kg DM will be required during this period to provide an additional 1–2.5MJ ME/day for ewes and 15–40MJ ME/day for cows. A range of forages and crops in Table 1 with such high energy levels will suffice if available in late pregnancy and fed to appetite. Bulky winter crops such as mangolds, swedes and turnips are of marginal value in late pregnancy, though higher drymatter crops such as fodder beet and rape with less bulk will allow greater energy intake.

Milk production

A generous supply of milk during the first 4–6 weeks of lactation is crucial in both breeding ewes and cows for good survival and early growth of suckling progeny. Continued feeding of high energy feeds from late pregnancy will achieve this, assuming in most cases quality leafy spring pasture will be available. If pasture supply is limited high energy supplements or crops will suffice without the intake restrictions experienced during mid-late pregnancy.

Young growing stock

Achievement of good growth rates in newly weaned lambs or calves requires high levels of both energy, at more than 11MJ ME/kg DM, and protein with a minimum of 18% of crude protein in drymatter. The need for protein is both to satisfy continued growth of the newly developed rumen and provide the building blocks for muscle deposition.

Generous allowances of grass-clover mixes and lucerne will provide this ideal mix of energy and protein in late winter-spring when optimum growth rates will be achieved, providing animal health is up to scratch. Other options to boost growth include use of herbs such as chicory and plantain in pasture mixes. These have the added advantage of being drought resistant with deep rooting systems. In addition, plantain contains tannins, as do legumes like Lotus corniculatus, and this protects protein from degradation in the rumen with associated production advantages.CW SHEEP table

• Ken Geenty is a primary industries consultant