A model of reproductive efficiency in beef cows: effect of bull exposure and body condition at calving on the calving-conception interval

Blanc, F.; Blanc, J.; Dozias, D.; Agabriel, J.

9emes Rencontres autour des Recherches sur les Ruminants, Paris, France, 4-5 decembre 2002: 65-68


Accession: 003622453

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The efficiency of reproduction in a beef cattle herd is usually assessed by the percentage of pregnant cows, the postcalving anoestrus interval, the calving-conception interval and the calving interval. The length of these intervals is influenced by breeding management factors such as suckling intensity or bull exposure and by animal factors such as parity or body condition. The objective of this study was to quantify these effects and to formalize the interactions between some of the animal and breeding factors and to simulate their influences on the calving-conception interval. Two factors were taken into account in the model: the exposure to bull and the body condition score at calving. The model simulated the reproductive process in a herd where the individual cow was the unit being modelled. The reproductive process was viewed as a sequence of events (parturition, ovulation, conception), each of which takes a defined duration. With respect to reproduction, a cow could be in one of three possible states: open-not-cycling, open-cycling or pregnant. At the end of each reproductive event, factors following statistical distributions or empirical laws might change the status of the cow. Cows differed from each other by parity, calving date and body condition at calving. The parameters of the model were evaluated by fitting the model to data from primiparous (n=193) and multiparous (n=204) Charolais cows bred at the experimental station of Le Pin au Haras. The model's ability to simulate the calving-conception interval and its dispersion was tested using an independent set of data of primiparous Charolais cows reared at the experimental station of Laqueuille. The mean predicted calving-conception intervals were often overestimated (from 3-10 days) and predictions regarding postcalving anoestrus interval did not account for the observed dispersion between individuals. Further investigations are needed to improve the model.