HERITABILITY, REPEATABILITY AND ENVIRONME NT EFFECTS IN HEREFORD CATTLE .2. CALVING INTERVAL, PRODUCING ABILITY AND COW PRODUCTIVITY INDEX

Paternal half-sib analyses and least-square procedures were used to co mpute heritability estimates for calving intervals (IEP), mean calving interval (IMEP), most probably producing ability of the cow (HMMP), a nd cow productivity index (IMP) of two Hereford herds in Rio Grande do Sul. Year of previous calving accounted for a highly significant (P<0 .01) variation in IEP, in both herds, while age of dam at carving was not significant in herd B (P>0.05). Sex of previous calf was not signi ficant for IEP (P>0.05) in either herds. The sex by age of dam interac tion was a significant source of variation (P<0.01), only in herd A. L east-squares means for both herds were: A = 437 +/- 6.3 and B = 480 +/ - 15.3. Heritability estimates for all traits in both herds were: IEP = 0.01 +/- 0.06 and 0.12 +/- 0.16; IMEP = 0.06 +/- 0.19 and 0.28 +/- 0 .26; HMMP = 0.31 +/- 0.28 and 0.20 +/- 0.16 and IMP = 0.10 +/- 0.12 an d 0.22 +/- 0.25. Repeatability estimates for IEP in herd A and B were 0.18 +/- 0.06 and 0.17 +/- 0.05 respectively. These values obtained fo r IEP were low. Therefore, selection will result in little genetic pro gress.