Effect of growth rate and mating age of dairy heifers on subsequent production over four years

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Abstract
An experiment was conducted using Friesian heifers in a Mediterranean environment to examine the effect of growth rate to mating and mating age on subsequent production. Heifers were mated at 12, 15, 18 or 24 months of age and at target mating weights of either 250 or 300 kg liveweight. Differential feeding ceased at the end of mating but, after calving, cows were grazed at one of two stocking rates. There were 64 cows in the milking phase of the experiment. Liveweight and production were measured over four lactations. There were no differences in production associated with target weight. Productions over four lactations for heifers first mated at 12, 15, 18 or 24 months were 15 500, 17 683, 16 779 and 18 855 kg fat-corrected milk, respectively. It was concluded that when differential feeding was discontinued at first mating, and feed was then not restricted up to calving, lifetime production was comparable whether heifers were mated at 48 or 58% of mature weight. Calving at less than 24 months of age could not be recommended.