REPRODUCTIVE AND SOME PERI-NATAL VARIABLES IN A MIXED BREED BEEF-CATTLE HERD

Calving success (CS), days to calving (DC), birth weight (BW) and calv ing ease (CE) were studied in a mixed breed (Hereford, Jersey x Herefo rd and Simmental x Hereford) beef cattle herd. DC was not normally dis tributed and a number of transformations failed in normalising it. Rep eatabilities were estimated by analysis of variance. Inclusion (or exc lusion) of non calvers and the transformations studied had little effe ct on the repeatability of DC, which ranged from 0.10 to 0.12. The rep eatabilities for CS, BW and CE were 0.08, 0.26 and 0.03, respectively. The residual correlations of CS with DC and functions of DC were high (-0.68 or greater), whereas the correlations among DC and functions o f DC were close to one. The correlations of DC with BW and CE varied l ittle with the transformation applied to DC, ranging from 0.26 to 0.28 and 0.10 to 0.12, respectively. The correlation between BW and CE was 0.06. The study points to a number of problems associated with the us e of DC as a reproductive variable in beef cattle. It is concluded tha t although DC is currently a useful field reproductive variable, the s earch for appropriate female reproductive traits should continue.