Cows were selected from the Agri-Food and Biosciences Institute dairy herd, and were within the top 1% of the Holstein-Friesian population within the UK in terms of PLI. Cows had a mean pre-experimental milk yield of 31.6 (±6.53 SD) kg/d, and were a mean of 131 DIM (range = 30–240 d) at the start of the experiment.