Genetic aspects of feed intake and efficiency in lactating dairy heifers.

In 1982, an experiment was initiated to study the relationships between feed intake and feed efficiency of young AI bulls, growing heifers and lactating heifers. This paper focuses on the genetic parameters for feed intake, production, and efficiency of lactating heifers. Measurements of feed intake, body weight and production were taken on 360 heifers during the first 105 days of lactation. The heifers were progeny of 38 sires; 125 of the heifers also had measurements on their dam. Heifers were fed a diet of 6 kg of concentrates and roughage ad libitum. Genetic parameters were estimated by REML fitting an animal model using a derivative-free algorithm. Heritability for roughage dry matter intake was 0.46. Heritability was 0.37 for gross feed efficiency and 0.19 for residual feed intake, which reflects the differences in energy intake after correcting for differences in metabolic body weight, weight change and production. The genetic correlation of 105-day production of fat- and protein-corrected milk with roughage intake was 0.61, with gross feed efficiency was −0.93, and with residual feed intake was close to zero. The correlated response in roughage intake when selection is on production is not large enough to cover the additional requirements due to the increased production. Intake capacity might be considered as an additional trait in the selection goal to avoid an increase in negative energy balance during early lactation