Use of residual feed intake in Holsteins during early lactation shows potential to improve feed efficiency through genetic selection.

Improved feed efficiency is a primary goal in dairy production to reduce feed costs and nega- tive impacts of production on the environment. Esti- mates for efficiency of feed conversion to milk produc- tion based on residual feed intake (RFI) in dairy cattle are limited, primarily due to a lack of individual feed intake measurements for lactating cows. Feed intake was measured in Holstein cows during the first 90 d of lactation to estimate the heritability and repeatability of RFI, minimum test duration for evaluating RFI in early lactation, and its association with other production traits. Data were obtained from 453 lactations (214 heifers and 239 multiparous cows) from 292 individual cows from September 2007 to December 2011. Cows were housed in a free-stall barn and monitored for individual daily feed consumption using the GrowSafe 4000 Sys- tem (GrowSafe Systems, Ltd., Airdrie, AB, Canada). Animals were fed a total mixed ration 3 times daily, milked twice daily, and weighed every 10 to 14 d. Milk yield was measured at each milking. Feed DM percent- age was measured daily, and nutrient composition was analyzed from a weekly composite. Milk composition was analyzed weekly, alternating between morning and evening milking periods. Estimates of RFI were deter- mined as the difference between actual energy intake and predicted intake based on a linear model with fixed effects of parity (1, 2, ³ 3) and regressions on meta- bolic BW, ADG, and energy-corrected milk yield. Heri- tability was estimated to be moderate (0.36 ± 0.06), and repeatability was estimated at 0.56 across lactations. A test period through 53 d in milk (DIM) explained 81% of the variation provided by a test through 90 DIM. Multiple regression analysis indicated that high efficiency was associated with less time feeding per day and slower feeding rate, which may contribute to differences in RFI among cows. The heritability and repeatability of RFI suggest an opportunity to improve feed efficiency through genetic selection, which could reduce feed costs, manure output, and greenhouse gas emissions associated with dairy production.