The effect of growth rate on reproductive outcomes in replacement dairy heifers in seasonally calving, pasture-based systems

摘要

The effect of average daily gain (ADG) on reproductiveoutcomes in replacement dairy heifers wasinvestigated. All heifers were managed in the typicalIrish spring calving, pasture-based system, where theherd calves in 1 block between January and April andthe majority of the diet comprises grazed grass. Heifercalves (n = 399) from 7 herds were weighed at birthand at the beginning of the breeding season, and ADGwas calculated. Service dates and pregnancy diagnosisresults were recorded, and conception dates were calculated.Days open (DO) was defined as the number ofdays between the beginning of the breeding season andconception. Genetic data were retrieved from the IrishCattle Breeding Federation database. A Cox proportionalhazard model was constructed to identify variableswith a significant effect on DO. An acceleratedfailure time model was used to predict survival curvesand median survival times for different combinations ofthe significant variables. The ADG ranged from 0.41to 0.91 kg/d, with a median of 0.70 kg/d. Frailty effectof farm within year, maintenance subindex of theeconomic breeding index, and ADG had a significanteffect on DO. Derived from the final accelerated failuretime model, the predicted median DO for a heifer withan ADG of 0.40, 0.70, or 0.90 kg/d aged 443 d at thebeginning of the breeding season and with a maintenancesubindex in the second tercile were 27, 16, and11 d, respectively.