Effect of suckler cow genotype on energy requirements and performance in winter and subsequently at pasture

Three experiments using a total of 62 Charolais (C) and 110 Beef × × Holstein-Friesian (BF) spring-calving cows were carried out to determine the relative energy requirements of the genotypes.Cows were individually offered a restricted allowance of grass silage daily during the last 85 and 107 days pre partum in Experiments 1 and 2, respectively, and ad libitum grass silage during the last 93 days pre partum in Experiment 3. In all 3 experiments grass silage was offered ad libitum during the first 34 days of lactation.In Experiments 1 and 2, cows and calves were grazed together during the subsequent grazing seasons.When fed to appetite, silage dry matter intake was similar for both cow genotypes but was higher for the BF cows when expressed relative to live weight.For Experiments 1 and 2 combined, initial live weights and live weight changes to post-partum, over the indoor period and at pasture were 720 (s.e.14.1), 613 (s.e.8.4), -74 (s.e.4.0), -63 (s.e.2.7), -106 (s.e.6.0), -89 (s.e.4.0) and 120 (s.e.7.0), 88 (s.e.5.3) kg for C and BF cows, respectively.In Experiment 3 the corresponding initial live weights and live weight changes to post partum were 759 (s.e.12.3), 659 (s.e.9.1) and -63 (s.e.4.9) and -52 (s.e.3.5) kg.There was no effect of genotype on body condition score or adipose cell diameter or their changes.Plasma creatinine concentrations were higher (P < 0.001) in C cows than BF cows.It is concluded that the energy requirements of a 660 kg C cow are approximately equivalent to a 600 kg BF cow during late pregnancy.