Once a heifer was in calf, managing her feed intake had no
influence on the size of the fetus, research has shown.
Sheep and Beef Council director Seamus Sullivan told a Meat
and Wool New Zealand field day at Millers Flat that
restricting feeding early in the pregnancy of first-calving
heifers did not affect the size of the newborn calf because
the heifer used her own reserves to support the growing
fetus.
Because of that, he said there were no negative consequences
from restricting feed.
The issue of calving difficulty in first-calving heifers, or
dystocia, was a hot topic at the Millers Flat field day, but
Mr Sullivan said the only known solutions were bull
selection, to have heifers as well grown as possible before
mating and keeping a close eye on them during calving.
He said research showed heifers that were assisted with
calving performed as well as non-assisted heifers in terms of
weaning weight, milk intake and future breeding. While feed
intake during pregnancy had no effect, any changes in birth
weight were usually accompanied by a similar changes in the
live weight of the heifer at calving, so not reducing the
problem of feto-maternal disproportion, the greatest cause of
dystocia in heifers.
In cows, Mr Sullivan said the greatest cause of dystocia was
the result of malpresentation of the fetus.
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