Manipulation of energy- and protein supply during the dry period can affect milk production and composition in the next lactation (Moorby et al, 1996). These studies also demonstrated considerable between-animal variation in responses which may relate to previous nutritional history. This problem was addressed in the current experiment by (i) developing enhanced assessments of animal condition; and (ii) monitoring performance over successive lactations. The second half of the first lactation is a critical phase, particularly for young heifers, since they have to balance the competing demands of pregnancy, growth and a persistent lactation. Berg and Ekern (1993) showed that underfeeding heifers had a residual effect on milk production and composition in their second lactation.

Forty-five Holstein Friesian heifers, which calved from September to December 1994, were selected for this work; 23 of the animals calved at approximately 3 years of age (‘3’), 22 at approximately 2 years of age (‘2’). Thirty-eight animals completed the experiment (to the end of their second lactation) and data from these animals are used here. The animals were maintained on a complete diet until April 1995 when they were offered 8 kg/day of concentrate with ad libitum grass silage for 3 weeks of covariance recording.