Association between growth rates, age at first calving and subsequent fertility, milk production and survival in Holstein-Friesian heifers

Abstract

Age\rat first calving (AFC) affects the profitability of dairy enterprises. This\rstudy examined the relationships between AFC and subsequent fertility, milk\rproduction and survival up to third calving in UK Holstein-Friesian heifers;\rStudy 1 comprised 134 consecutively born heifers from the same herd (AFC 764 ±\r8 days) and Study 2 contained 445 heifers born on 17 farms (AFC 796 ± 6 days).\rGrowth rates and fertility during rearing were monitored and animals were subsequently\rdivided into four AFC groups for analysis: 30 months. The actual AFC reflected both growth rate and heifer\rfertility, with later calving heifers already lighter by 6 months of age. The proportion conceiving to first service was highest (93% and 84% for Studies 1 and 2, respectively) for the youngest AFC group.\rFertility in the first lactation was best in cows calving at 23 - 25 months and worst in the oldest AFC group.\rMilk production parameters in the first and second lactations were broadly\rsimilar between AFC groups but significantly more heifers with an AFC 44% of their days alive spent\rin milk production compared with only 18% - 40% in cows calving at ≥26 months.\rHence cows with an AFC 0.75 kg/d\rup to 15 months and good heifer fertility and resulted in the best subsequent\rperformance.