COMPARATIVE-EVALUATION OF 3 DAIRY CROSSBRED GENOTYPES .1. GROWTH TRAITS AND REPRODUCTION IN HEIFERS

A comparative evaluation of performance until A.I. incorporation and r eproduction during the heifer stage of 196 animals corresponding to th e genotypes 3/4 Holstein 1/4 Zebu genotypes (44), 5/8 Holstein 3/8 Zeb u (95) and 5/8 Holstein 3/8 Criollo (57) reared under the same managem ent and feeding conditions, was carried out. For the analysis, a model of fixed effects which included as sources of variation the genotype (3) and the consecutive period of birth (4) for the growth traits unti l animals entered AI or the consecutive period of their entrance to AI (3) for the reproductive traits, was used. The measurements studied w ere: age (A), initial liveweight (ILW) and weight for age (WFA) at ent ering AI, AI entrance-insemination interval (AIEI), entrance to AI to conception (ECI), services per conception (S/C) and age at first calvi ng (CA). Differences between genotypes were only found tn age and weig ht at AI entrance, which were attributed more to management aspects th an to genetic causes, since these were not evident in the weight for a ge. Similarly, there were no differences between genotypes for the dif ferent reproductive traits studied in heifers. The general means with their respective standard errors were 19.61 +/- 0.22 months, 297.68 +/ - 1.68 kg and 0.507 +/- 0.006 kg/day for IA, ILW amd WFA. respectively , while the corresponding values were of 65.30 days; 98.54 days, 1.73 and 31.98 months for AIEI, ECI, S/C and CA in that order. It is conclu ded that there are no differences of biological importance in the grow th rate between the genotypes compared, nor in the reproductive perfor mance in the heifer stage.