7 June 1996



Is it economic to feed silage to cows while there is a surplus of grass to make

into silage? Mark Blackwell suggests not

TO close enough grass for silage-making, producers have been stocking cows at up to 7.4/ha (3/acre).

Average growth in mid-May of about 55kg/ha a day dry matter is almost sufficient to the meet the total feed demand of 3.8 cows a hectare (1.5/acre). That is 55 divided by 3.8 = 14.5kg DM a cow.

But that growth is insufficient to meet the feed demand of herds stocked at 7.4/ha. That is 55 divided by 7.4 = 7.4kg DM a cow.

This second herd would have to buffer feed almost half of the cows feed needs, or see a decline in pasture cover and under-feeding.

Producers in these two extremes have widely different goals and circumstances. But it invites the question: "Should silage be fed at the same time as the farm has a surplus of grass that is waiting to be made into silage?" The simple answer, no, would be more obvious to British farmers if they were feeding the silage out on to the grass and not in barns. If you could see the silage being eaten out in the field, and at the same time see good grass not being eaten, you would make the connection more easily.

The position is more obvious in New Zealand, where silage is fed out on to grass.

The second farmer is limiting his cows to such a small area that his stocking rate is, for the moment, 7.4/ha (3/acre). He is committed to buffer feeding unnecessarily. He will make more silage this spring and summer, so he can feed his cows what may be the same silage next spring and summer.

At times there is good reason for buffer feeding. For example, to help slow the grazing rotation down, to build up pasture cover, and meet the demands of freshly calved cows.

That has been described as positive substitution, which may be appropriate when pasture cover is below needs. But there comes a point every spring when pasture growth exceeds the possible feed demands of the herd. That is when substitution becomes potentially negative.

From this point there is little economic sense in feeding silage out with one hand while conserving grass silage with the other. &#42

Grass measurements


height (cm)kg/dm/ha