26 April 1996

Concentrate use balancing act

PROFIT from milk in April and May depends on maximising use of grazed grass. Target intake for spring calving herds is 16-18kg a day of grass dry matter for cows averaging 25 litres.

But speaking at the 50th Irish Grassland Association conference in Limerick, Pat Dillon of the Moorepark Research Centre, Co Cork, warned that low grass intakes before and during the breeding season would lower pregnancy rates. Supplements, therefore, would be necessary as either extra grass or concentrates. But although feeding supplements at grass to such cows would safeguard fertility when grass intakes were low, it was uneconomic (see table).

This is reflected in a trial carried out at Moorepark from April 93 to mid-June 94. Grass growth was poor and grazing conditions difficult. The trial set out to study the effect of concentrate feeding on performance of early lactation dairy cows. One herd was fed grazed grass only, the other grazed grass and 2kg concentrates, and the other grazed grass and 4kg concentrates. The spring calving cows were stocked at 5.25/ha (2.1/acre) and grass grazed to 8cm (3in).

On the grazing-only trial average grass intake was only 14.6kg a cow (see table) compared with total intakes of 16.1kg DM and 17.5kg DM for the 2kg and 4kg systems, respectively.

"The low intakes on the grazed grass only regime reduced fertility," said Dr Dillon. Submission rate for all three herds was good. With good herd detection, 82-91% of cows were inseminated in the first three weeks of AI. But only 36% of those on the grass-only diet were in-calf to first service. This compares with 64% for the cows on grass plus 4kg of concentrates. Dr Dillon said the decrease fertility was a result of weight loss in the grass-only herd.

When grazing conditions failed to supply 16-18kg grass DM, 2kg a cow of supplement would be needed to safeguard fertility provided management was good.

&#8226 More conference reports on the use of grazed grass and how to estimate pasture cover next week. &#42


Effect of concentrate feeding on the performance of dairy cows in early lactation*

Treatment

GrassGrass +Grass +

only2kg conc4kg conc

Grass DM intake (kg a day)14.614.313.9

Total DM intake (kg DM a day)14.616.117.5

Milk yield (litres a day)23.4424.4125.41

Fat (%)3.693.643.58

Protein (%)3.303.323.30

Liveweight change (kg)-0.50+0.04-0.08

Margin a cow a day (£)5.465.425.31

*Average for April to mid-June 93 and 94.