Abstract #M271
Section: Ruminant Nutrition (posters)
Session: Ruminant Nutrition I
Format: Poster
Day/Time: Monday 7:30 AM–9:30 AM
Location: Exhibit Hall A
Session: Ruminant Nutrition I
Format: Poster
Day/Time: Monday 7:30 AM–9:30 AM
Location: Exhibit Hall A
# M271
Comparison of residual feed intake, net energy, and economic models of feed efficiency in dairy cattle.
Dave J. Seymour*1, Filippo Miglior1, Gail Ritchie1, Vern R. Osborne1, John P. Cant1, Angela Cánovas1, 1University of Guelph, Guelph, ON, Canada.
Key Words: feed efficiency, net energy, residual feed intake (RFI)
Comparison of residual feed intake, net energy, and economic models of feed efficiency in dairy cattle.
Dave J. Seymour*1, Filippo Miglior1, Gail Ritchie1, Vern R. Osborne1, John P. Cant1, Angela Cánovas1, 1University of Guelph, Guelph, ON, Canada.
Feed efficiency is an economically important trait across livestock species and is of growing importance as a breeding goal in dairy cattle. One of the most widely used measures of feed efficiency is residual feed intake (RFI), which uses a regression method to rank animals based on predicted dry matter intake. The objective of this study was to compare RFI rankings to net energy- and economic-based rankings of feed efficiency in dairy cattle. 6,654 daily records from 93 primiparous lactating Holstein cows ranging from 0 to 150 d postpartum were selected for analysis from a larger data set based on completeness of records. RFI was calculated using a mixed model with week of lactation, milk energy content, metabolic BW, and BW change as covariates. Net energy efficiency was calculated as the energy content of milk as a proportion of dietary net energy for lactation (NEL) intake. Lastly, return over feed cost was calculated as the difference between the producer milk price based on component yields and the cost of TMR dry matter consumed. Animal ranks based on RFI and net energy were highly correlated (0.872), whereas return over feed cost ranking was moderately correlated with both RFI (0.668) and net energy (0.619). Both net energy (R2 = 0.95, P < 0.01) and RFI (R2 = 0.75, P < 0.01) ranks were negatively associated with mean daily net energy balance, suggesting that more feed efficient animals meet the energy demands of lactation by mobilizing body energy reserves to supplement that obtained from the diet. Return over feed cost rank was poorly associated (R2 = 0.29, P < 0.01) with net energy balance. This model does not account for the costs associated with persistent negative energy balance (e.g., metabolic disorders), and as such the maximal output may not reflect the optimal output. With the addition of body condition score data, as well as records over the course of an entire lactation, future work will be able to more accurately characterize net energy flow and identify animal characteristics regarding mobilization of body reserves and the relationship to feed efficiency.
Key Words: feed efficiency, net energy, residual feed intake (RFI)