Relationship of age and liveweight at first calving to subsequent lactation yields of Friesian heifers grazing tropical pastures

Abstract

The relationship between age at first calving, liveweight at first calving and milk yield in the first lactation was studied on 78 purebred Friesian heifers grazing tropical pastures without supplementation. In addition, 61 and 41 records of milk yield in the second and third lactations respectively were analysed for relationship to liveweight at first calving. Age at calving was not significantly related to milk yield in the first lactation, though liveweight at first calving was significantly related to milk yield in the first (r = 0·57;
P < 0·01), second (r = 0·51; P < 0·01) and third (r = 0·46; P < 0·01) lactations. The regression coefficient showed a slight, though non-significant, decrease with succeeding lactations. Possible explanations for this relationship and application of the results are discussed.