22 May 1998

Use gestation EBVs

ESTIMATED breeding values for gestation length introduced last year should be used as a selection tool for commercial suckler herds, especially those breeding replacement heifers.

Thats the message of Signet consultant Geoff Fish, based on findings of an SAC study. This used two Simmental bulls, one with a high EBV for gestation length and one with a much lower figure, and compared the calving performance of their daughters.

Results of the study, which began in 1994, showed cows sired by the bull which now has a -4.7 EBV for gestation length had 4.4kg lighter calves, five-day shorter pregnancies and almost all calves were born naturally. Over a third of the other bulls calves were born with assistance. The gestation length and calving ease EBVs for these two bulls reflect actual differences recorded in the study, adds Mr Fish.

In addition, Simmental cross daughters from both these bulls were bred to a Limousin bull. Daughters of the bull with the shorter gestation length had shorter pregnancies themselves, calving four days earlier and unassisted. Two of the other bulls 12 daughters needed assistance at calving.

"This suggests producers should use bulls with a negative EBV for gestation length when breeding replacement heifers, alongside other EBVs such as 200 day growth rate," he says.