8 November 1996

Complete diet feeds

not all magic

Do high merit cows need to be fed fancy complete diets suplying high levels of concentrates? Sue Rider puts the question to Northern Ireland researchers

COMPLETE diet feeding offers a small but consistent increase in milk yield compared with out-of-parlour feeding, but there is no lift in total dry matter intakes and milk composition.

"Many of the perceived benefits of complete diet feeding are not there when different feeding regimes are compared on a level playing field," says Des Patterson, researcher at the Agricultural Research Institute, at Hillsbor-ough, Northern Ireland.

He is convinced that complete diet feeding does not work the magic farmers tell us it does.

"Our trials have shown only a small performance benefit and that is at high levels of concentrate feeding – 14kg a cow a day – at lower levels that increase might not be there at all."

Trials at Hillsborough feeding up to 11kg of concentrate a cow a day as a complete diet showed no improvement in cow performance compared with a silage and concentrate regime with the concentrate offered as three feeds a day.

Recent work has compared the response of high, medium and low merit cows to electronic, out-of-parlour compared with complete diet feeding when average concentrate intakes were 14kg a day a cow.

Average dry matter intakes were no higher for the complete diet-fed cows, and milk composition no better, but fat and protein yields were up 2%. Results were unaffected by the genetic merit of the cows.

Lack of response in intake with complete diet feeding is in contrast, says Dr Patterson, to previous studies which have shown a trend towards higher feed intake. "This could be because concentrates were offered three times daily in the out-of-parlour treatment – minimising rumen disturbance.

"Out-of-parlour feeding can then give similar feed intake and milk production results as complete diet systems, even at high concentrate levels," says Dr Patterson. He concedes that the complete diet mixer can handle a wider range of concentrate feeds and cheap by-products. But on the flip side its capital, machinery and labour costs can be high.

"The complete diet system is also trickier to manage for there is a tendency to over-feed concentrates. This can produce fat cows and reduce conception rates," explains Dr Patterson.

He offers two explanations as to why some producers do see big improvements in milk yield and composition on complete diet systems.

"Its likely they were feeding high levels of concentrate twice daily through the parlour – this can depress yield." Moving to three times a day feeding or an out-of-parlour system would overcome this, he suggests. "Alternatively, if concentrate feeding was only moderate, yields could have been restricted by a deficiency in the silage feeding system – poor availability, for example. A complete diet can solve this – but its a very expensive solution to a simple problem."

Des Patterson: Complete diets do not work the magic we are told.


WINTER FEEDING


&#8226 High merit cows producemore milk at every concentrate level.

&#8226 Perform better off grass when more winter concentrate fed.

&#8226 At high concentrate levels silage quality is not so important.


WINTER MEETING

Grass and Forage for Cattle of High Genetic Merit is the theme of the British Grassland Societys winter meeting to be held on Mon and Tues, Nov 25 and 26. Full details available from the BGS office (01734-318189).