Relationship between proxies of energy states and nitrogen use efficiency for Holstein cows in early lactation

The purposes of this study were to estimate the genetic parameters of the energy status indicator (C18:1 cis-9) of Holstein cows in early lactation and its relationship with nitrogen use efficiency (NUE) (predicted NUE and milk urea concentration). After editing, the data included 143,517 records within 5 to 50 days in milk from 52,198 cows, and 3,546 animals in the pedigree with 28,427 SNPs. Two multiple-trait repeatability models were used in this study. In early lactation, the average C18:1 cis-9 was gradually decreasing and was highest in May. The heritabilities of C18:1 cis-9 for primiparous and multiparous cows were 0.12 and 0.09, respectively. The C18:1 cis-9 had positive genetic correlations with predicted NUE (from 0.28 to 0.67), and weak genetic correlations with milk yield, milk urea concentration (from-0.15 to 0.14). This study suggests that breeding for NUE alone may enhance energy troubles in early lactation.