Growth Effects of Regrouping Dairy Replacement Heifers with Lighter Weight and Younger Animals

Body weight and ADG of 2,817 Holstein heifers were monitored from their arrival (about 11 d old) to a commercial contract-heifer operation (Rancho Las Nieves, Mallén, Spain) through a final BW of about 400 kg to assess the effects of regrouping dairy replacement heifers with unacquainted and younger animals. Upon arrival heifers were kept individually, but were progressively grouped to form groups of about 120 animals at the age of 215 d and older. The BW of heifers was monitored at the approximate ages of 110, 160, 220, 270, 330, and 400 d. Heifers that were above a pre-established target BW at each check point were moved to a different pen, whereas those that did not reach a target BW at any of the monitored ages were kept (delayed) in the same pen and mixed with younger heifers that had met target BW transition into this group. Animals that were delayed were weighed approximately every 15 d until they reached the target BW corresponding to their age and were then moved up one group. At 50.87 ± 0.76 d before delayed heifers were regrouped, their ADG (794 ± 25.4 g/d) was lower (P < 0.001) than that of non-delayed heifers (996 ± 10.8 g/d); however, the ADG (1160 ± 25.6 g/d) of delayed heifers 18.15 ± 0.78 d after being regrouped with a new set of animals was greater (P < 0.001) than that of non-delayed heifers and greater than the ADG achieved before regrouping. Regrouping heifers that are growing below the average growth rate of their cohorts with a new set of younger and lighter animals resulted, in this study, in a dramatic increase in ADG.