14 January 2000

Top forage keeps yields up

Responding to pressure to

reduce feed costs without

compromising milk

production, one Nuffield

scholar looked at how to

maximise forage quality.

Marianne Curtis reports

DRIER silage, up-to-date analysis methods and comprehensive information on nutritional value of maize varieties will help improve forage quality and use, says Chichester-based independent ruminant nutritionist David Donaldson.

Mr Donaldson has visited France, Holland and the US as part of a Nuffield Farming Scholarship looking at milk production from different forage-based systems.

"The difference between having excellent forage and good forage is worth about 2-3kg of concentrate a cow a day," he says. "Yet despite improvements in varieties, cow genetics and nutrition, milk from forage has increased little in the UK over the past 15 years."

Maize has proved to be one forage where rapid progress can be made. In France, he found that more comprehensive information on maize varieties allowed better matching to particular systems. "France has more trial sites than the UK, which provides better information on varieties performance under different climatic and soil conditions.

"French research shows that the relationship between starch content and feed value is small because stem and leaves account for half the dry matter: The digestibility of this fraction can vary from 40% to more than 65%.

"Information on litres of milk a kg dry matter and digestibility means varieties can be ranked on an animal production basis in France. NIAB has ranked varieties on digestibility for the first time this year but more regional trials and animal production trials would help distinguish between them."

But analysis problems do not stop at variety and silage analysis results can vary considerably between labs, warns Mr Donaldson. "The Maize Growers Association sent samples of the same silage to five different labs and got five different results back.

"Some labs are also using outdated formulae and calibrating equipment incorrectly. To minimise the likelihood of an inaccurate analysis, select labs using the ME tick system and ask whether they are part of a ring test scheme." Ring tests provide a quality control method, enabling labs to check that results are comparable between them.

Whichever the lab – and for all silages – one result that is too low in many cases is dry matter, says Mr Donaldson. "The Dutch put great emphasis on making dry grass silage and using small clamps to reduce spoilage during feed out. Aiming for 30% dry matter grass silage will lead to higher intakes, better yields and lower lameness than wet, acidic silage."

This level of dry matter is easily achievable in Holland, where summers are warmer and crops lighter. But tedding and adequate wilting for 24-48 hours means higher dry matters are possible in the UK, says Mr Donaldson.

A good yardstick to determine whether silage is too acidic is to divide the amount of silage cows are eating by its pH. Figures over 10 indicate an acid load problem which will depress intakes and impair digestibility, he says.

SILAGEQUALITY

&#8226 Need consistency between labs.

&#8226 Need maize nutritional information.

&#8226 Increase grass silage dry matter.