Nitrogen isotopic fractionation to predict nitrogen-use efficiency of lactating Holstein Friesian dairy cows

摘要

Whilst N isotopic fractionation shows considerable potential as a phenotyping tool, it will be necessary to consider parity and other sources of variation in body protein change when using it to predict NUE of dairy cows.Several previous studies with sheep, beef cattle and dairy cattle have demonstrated a negative relationship between Feed Conversion Efficiency or Nitrogen-use efficiency (NUE) and the extent of isotopic fractionation of Nitrogen isotopes (15N and 14N; see meta-analysis by Cantalapiedra-Hijar et al., 2018). Nitrogen isotopic fractionation is usually expressed as the difference in 515N between the diet and product protein (usually measured in plasma, milk or muscle samples; in this case A15N is milk 515N- feed 515N). There is considerable unexplained variation around this relationship with dairy cows and the current study used samples taken from the Langhill Experiment, where cows undergo continuous measurements of NUE, to try to explain more of the variation.