The dynamic behavior of feed efficiency in primiparous dairy cattle

摘要

A variety of measures are currently used to evaluatefeed efficiency in livestock, with some of the mostpopular being the linear regression of nutrient intake onthe various energy sinks of the cohort being evaluated.The adoption of novel on-farm technologies has greatlyincreased the breadth and depth of data being collectedon a daily basis, which creates the opportunity forthe implementation of more advanced feed efficiencymodels. The objectives of the current study were toleverage data collected using high-throughput biometrictechnologies to evaluate changes of early-lactationfeed efficiency on a daily basis and to develop a novelmeasure of feed efficiency based on the NRC net energymodel. Daily records of nutrient intake, fat- andprotein-corrected milk yield, body weight, and bodycondition score were used to model 7 different indicesof feed efficiency (gross feed efficiency, return over feedcosts, residual feed intake, residual net energy intake,and net energy efficiencies of lactation, maintenance,and body reserve flux) in primiparous Holstein heifers(n = 40) from 0 to 150 d in milk. We observedthat feed efficiency was dynamic and fluctuated overthe course of the experimental period regardless of theefficiency measure used, but most measures followedsimilar trends in changes of efficiency on a day-to-daybasis. Of the measures evaluated, return over feed costswould be most suited for management purposes dueto practicality and simplicity, whereas other measures,such as the efficiency of net energy flux to and frombody reserves, present potential targets for inclusion inbreeding goals. Net energy efficiency of lactation wasestimated to have higher repeatability compared withresidual feed or energy intake, which may reduce thetime required to estimate whole-lactation efficiency.Because decreased net energy balance was strongly correlatedwith increased efficiency for all indices evaluated,future work investigating the associations of feedefficiency with the magnitude and duration of negativeenergy balance is warranted.