| Sumario: | At the Regional Research Center "La Libertad" of ICA in Villavicencio, the offspring
of 183 cows of San Martinero, CebU and Angus-San Martinero breeds or cross
were assigned at calving time to two weaning ages of 7 and 9 months. All cows
were under grazing conditions, and had a mineral mix ad-libitum. The predominant
grasses were molasses grass 30%, jaragua grass 20% and native legumineus and
gramineous 50%. The calves were weighted at 210; 270; 365 and 540 days of age
and these weights were adjusted for age of the calf; additionally a group of 46 heifer
calves were left as replacement females, and their age at first calving was determined.
These variables were analyzed by least squares procedures with the apropiate linear
model for each variable that included the effect of sex and breed of the offspring,
and some first order interactions. At 270 days the calves weaned at 9 months of
age weighted 37.3 kg more than those weaned at 7 months of age; at 365 and 540
days the difference in weight was 25.3 and 17.9 kg, respectively, in favour of the
calves weaned at 9 months. In percentages this difference was 18.1% at 270 days,
11.4% at 365 and 7.0% at 540 days of age. The age at first calving of the replacement
heifers dit not differ significantly between the weaning ages: the overall mean was
1.452 days. The age of the dam did not significantly affected the age of first calving
of the heifers. Under grazzing conditions the decreasing differences in weight of
the calves weaned at 7 and 9 months of age did not influenced the age at firts calving
of heifers weaned at 7 months of age. This fact could mean that the differences
were minimized under the conditions of the "Piedemonte Llanero located in the
eastern region of Colombia.
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