Milk Production and Growth of Identical Twin Heifers Calving for the First Time at Two and Three Years of Age

Abstract

Summary Five identical-twin heifers, calving for the first time at 3 yr., were more persistent in lactation than their mates, which started their second lactation at 3 yr. The early-calving heifers reached a higher peak production than did the late-calving heifers, but ended the lactation with slightly less total milk, on the average. Four- and five-year lactations did not appear to be affected by the age of first calving. Growth or body size was not affected by the different ages of freshening after both groups had completed one or more lactations.