The juggling act

Ruminants are adapted to convert fibre into the energy needed to produce milk and meat, but total input needs to be balanced for optimum production.

The joy of life is that the more you know about something, the more you realise how little you know about it. Take the process of balancing a ration for a cow. Feeding standards prescribe the quantities of protein and energy required in terms of maintenance, butterfat and milk yield. I exclude formulations for total mixed rations, where intake can be measured fairly accurately and correlated with the cow’s performance.

If we examine the complexity of the fibre component in a ration, the issue becomes more complex. Neutral detergent fibre (NDF) is the portion of cell wall material in any forage. It is the most reliable predictor of how much dry matter equivalent a cow will consume. An increase in NDF means poorer quality forage and hence a lower intake. A 5% increase in NDF results in a 6% drop in milk yield. Decreasing the NDF component will increase milk production.

Acid detergent fibre (ADF) is the percentage of indigestible fibre in the forage. A 1% increase in ADF reduces the daily milk yield of a cow by 0,3l. So how do we apply these principles in practice? The NDF value of oat straw is 70%; oat silage has an NDF content of 63% – a difference of 7%. So if the average daily yield of the herd is 25l/cow on oat silage and the herd is switched to oat straw, the expected milk decrease will be 2,1l/cow/day.

The obvious solution to this dilemma is to graze or ensile forage before lignification progresses too far. Grain crops must be ensiled at the soft dough stage. But cows need the type of hay that can promote rumen eructations and rumination to ensure rumen motility.

Malcolm Stewart-Burger founded the Society of Master Dairymen and designed the Maxi Milk System. He is currently a part-time consultant to Nutex Feeds and De Heus. Contact Malcolm at [email protected]. Please state ‘Milking for profit’ in the subject line of your email.