A RECENT Teagasc study has thrown some interesting light on the factors which determine dairy heifer efficiency post calving and how this can be made to impact beneficially on overall milking performance throughout her lifetime.
The work confirms that weight and age and weight at first calving are critical elements in achieving optimum production and fertility performance from replacement females.
Calving heifers less than two years of age (2YO) resulted in lower milk yields compared to heifers calving at 2YO (5,771kg and 5,905kg, respectively). Heifers calving at more than 2YO produced higher yields (5,992kg). Calving heifers less than 2YO resulted in lower first service conception rates when compared to older animals at first calving. However, no difference in empty rates was observed. With the exception of days open (lower for animals calving younger in first lactation) second lactation production and reproductive performance was unaffected by age at first calving.
Weight at first calving appeared to have a more long-term impact on animal performance. At first calving, light heifers (<530kg) produced significantly less milk compared to those calving at between 530kg and 600kg; 5,771kg and 5,905kg, respectively. Heavy heifers (>600kg) produced higher yields (6,130kg) compared to heifers calving down at 530kg to 600kg. Weight at first calving had no effect on milk composition.
Empty rate at the end of first lactation was slightly higher for the heavy heifers. Weight at first calving also had a significant effect on milk yield in second lactation. Light heifers (<530kg at first calving) produced, on average, 6,785kg in second lactation compared to heifers calving down at 530 to 600kg in first lactation, which produced 7,027kg.
Heavy heifers at first calving (>600kg) also produced higher yields in second lactation (7,301kg) compared to heifers calving down at 530 to 600kg. Milk composition was lower in second lactation for cows calving in first lactation at low body weights. Reproductive performance in second lactation was unaffected by weight at first calving.