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Description:
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Reproductive , maternal and weight traits were analyzed for Angus (A ) , Brahman
(B ) , Hereford (H ) , and Nellore (N ) straightbred cows ; F1 NA ; 3 /8N 5 /8A cows ; and four
breed composite cows (BANH ) at the McGregor Research Station in Central Texas .
Heterosis was estimated for calf crop born (CCB ) (n = 1 ,698 ) , calf crop weaned (CCW )
(n = 1 ,698 ) , calf survival (CS ) (n = 1 ,388 ) , birth weight (BW ) (n = 1380 ) , weaning
weight (WW ) (n = 1 ,198 ) , and cow weight at palpation (PWT ) (n = 1 ,929 ) by linear
contrasts for cow breed and cow breed group . F1 NA and the quarter breed composite
BANH dam group expressed significant (P < 0 .0001 ) heterosis for calf crop born and
calf crop weaned . The 3 /8 N 5 /8 Aa produced by matings of 3 /4 A 1 /4 N bulls to NA
dams expressed significantly more heterosis for CCB (P < 0 .0001 ) and CCW (P < 0 .01 ) ,
while the 3 /8 N 5 /8 Ac dams expressed less heterosis than predicted from the dominance
model for both traits .
For CS the 3 /8 N 5 /8 Aa expressed the same amount of heterosis as predicted
from the dominance model of 0 .05 , while the 3 /8 N 5 /8 Ab and 3 /8 N 5 /8 Ac dams
expressed less heterosis than predictions based on the dominance model . Heterosis
estimates were only significantly higher (P < 0 .10 ) for BANHb dams than expectations from the dominance model . For BW all the BANH cows expressed significant heterosis
except for the BANH2 cows which expressed significant (P < 0 .05 ) negative heterosis of
-0 .96 kg .
Calves out of F1 NA cows were heaviest at weaning with 239 kg . All BANH
cows expressed significant (P < 0 .0001 ) heterosis for weaning weight except for the
BANHc cows . These heterosis estimates were higher than those expected from the
dominance model for BANHb and BANH2 cows , while the heterosis estimate was
slightly lower in BANHa cows and similar for BANHc cows . All 3 /8 N 5 /8 A cows
expressed less heterosis for WW than prediction from the dominance model .
Nellore cows were the heaviest at four years of age with 542 kg . Only the
BANHb and BANHc cows expressed significant (P < 0 .05 ) heterosis for PWT . None of
the 3 /8 N 5 /8 A cows expressed heterosis for cow weight at palpation .
Results from this study showed that heterosis levels expressed by the different
crossbred cow types were generally equal or higher to those predicted by the dominance
model . |