
%0 Journal Article
%A Davis, GP 
%A Corbet, NJ 
%A Mackinnon, MJ 
%A Hetzel, DJS 
%A Entwistle, KW 
%A Dixon, R 
%T Response in female fertility and calf growth to selection for pregnancy rate in tropical beef cattle
%J Australian Journal of Agricultural Research
%D 1993/10/01
%V 44
%N 7
%P 1509-1521
%K tropical cattle;selection;fertility
%R https://doi.org/10.1071/AR9931509
%U https://www.publish.csiro.au/paper/AR9931509 
%X Direct response to divergent selection based on estimated breeding value for female pregnancy rate in a herd of Bos indicus cross cattle was evaluated along with correlated responses in calf survival, weaning rate, cow liveweight and calf growth. Pregnancy rates were significantly higher ( P < 0.05) in heifers of the High line compared with the Low line (High-Low=15¦ 5%) and in lactating 4-year-old cows (25¦9.5%) and in 3 of the 5 years of the study (average difference 24%). The Low line had significantly ( P < 0.05) higher pregnancy rates in 1 year (-16¦5.4%). These differences in pregnancy rates were reflected in weaning rates, but calf survival was only different between the lines in 2 of the 4 years analysed (-6¦ 3.0% in 1990 and 18¦6.5% in 1991). The High line had a significantly ( P < 0.05) shorter days to calving than the Low line in heifers (High=309¦2.2 days v. Low= 315¦2.5 days), lactating 3-year-old cows (3l5¦ 3.6 days v. 331¦4.1 days), non-lactating 3-year-old cows (301¦5.4 days v. 320¦4.6 days) and lactating 4-year-old cows (311¦3.9 days v. 336¦4.9 days). Differences between the lines in pre-weaning growth varied according to generation with significantly lower (P < 0.05) weaning weights (182¦3.1 kg v. 189¦3.3 kg) and pre-weaning growth (790¦17 g/day v. 826¦ 17 g/day) in first generation High line calves from foundation dams and no difference between the lines in second generation calves from first generation dams. Post-weaning growth was significantly higher ( P < 0.05) in High line calves (350¦ 5 g/day v. 327¦5 g/day). The results indicate that selection of sires on EBV for pregnancy rate leads to improved fertility in heifers and 4-year-old lactating cows without adverse effects on progeny growth. 
