Reproductive performance of Zebu compared with Charolais × Zebu females in a humid tropical environment

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Abstract
SUMMARY: Components of reproductive efficiency of Zebu-type and Charolais × Zebu-type (1/2, 3/4 and 7/8) females were compared. Zebus had longer mean intervals from calving to first service (57·8 days) and from calving to conception (46·0 days). Least squares means for both traits were respectively 129·8 and 145·1 days. Correspondingly, in the Charolais cross group 26·4% more cows were detected in oestrus within 180 days of calving, and 31·4% more conceived in the same period. Least squares means for these traits were respectively 80·7 and 50·5%.No significant differences were found between the two breeding types either in number of services per conception or in the percentage conceiving by artificial insemination (of those showing oestrus) both for lactating and dry females. A higher percentage of oestrus cycles of normal duration was found in Charolais cross (72·9 %) than in Zebus (63·1%). Gestation lengths of Zebus (Indu-Brasil sires) and Charolais cross (Charolais and Simmental sires) were respectively 288·8 and 283·1 days.The main difference between breed types was the longer lactation anoestrus shown by Zebus. These were very sensitive to seasonal effects, showing a cyclical time trend with peaks of shorter anoestrous periods for cows calving in January–February–March, and longer ones for cows calving in July–August–September. Related traits followed parallel cycles. Charolais cross cows showed less variation than Zebus.