9 March 2001

EVALUATING THE ECONOMICS OF ADDITIVES

PRODUCERS are paid for milk fat and protein yield and carcass weight but not for improvement in silage analysis figures, so the most important selection criteria for an additive is that it increases animal performance.

Reporting his research findings, Tim Keady said that when compared with untreated silages, formic acid was found to give an economic response under difficult ensiling conditions, but not under easy or moderate ones.

Sulphuric acid improved silage fermentation, but gave no evidence of improved carcass gain or milk yields in relation to untreated silage.

Molasses and sugar beet pulp were found to have no appreciable effect on performance and he advised feeding these products as dry feeds during winter, rather than putting them in the clamp as an additive.

Bacterial types

Bacterial inoculants were found to be effective at increasing milk yields by an average of 1.3kg/cow a day – the mean of 16 studies. However, Dr Keady warned that bacterial inoculants vary greatly in terms of bacterial composition and counts.

"When selecting an inoculant it is essential that the product applies at least 100,000 bacteria for every 1g of grass, but preferably 1 million. There must also be plenty of research evidence to show a product will work in conditions relevant to the farm situation."

Further research revealed that using a diet wagon to feed less than 10kg of concentrate a day will not increase milk yield or composition – relative to out-of-parlour feeders, and costly protein sources are also a waste of money as they result in no increased performance.

"However, studies showed a 6% increase in yield when cows were fed between 14-15kg/head a day of concentrates in the total mixed ration, but fat content fell by 0.08%."

Regardless of silage quality, as starch content of concentrates increased from 4% to 33% there was no improvement in milk yield, but protein rose by 0.15% and fat yield decreased by 0.11%.

There was also no economic response from feeding expensive protected soya bean, when compared with low-cost sources of digestible undegradable protein (DUP), such as straight soya bean meal, he added.

Myth shattered

Dr Keady shattered another myth when he told the audience that there was no benefit in adding straw to a ration.

"Straw decreases ME intake, lowers milk yield and has no affect on milk composition, and it is more expensive than many other feeds in Northern Ireland, when expressed in terms of cost/unit of energy." &#42