Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2019
Publication Date: 7/1/2019
Citation: Connor, E.E., Hutchison, J.L., Van Tassell, C.P., Cole, J.B. 2019. Defining the optimal period length and stage of growth or lactation to estimate residual feed intake in dairy cows. Journal of Dairy Science. 102(7):6131–6143. https://doi.org/10.3168/jds.2018-15407.
Interpretive Summary: Feed conversion efficiency in animal production is often estimated using residual feed intake (RFI), calculated as the difference between an animal’s actual feed (or energy) intake and its expected intake needed to support its level of production. Difficulty exists, however, in estimating RFI of dairy cattle due to changes in their energy requirements during growth as heifers and throughout the milk production cycle as cows. This work characterizes relationships among RFI measures in dairy cattle made during different stages of production and their utility in selection programs. The primary findings were that selection of the most efficient animals based on either RFI measured during heifer growth (between 10-14 months of age) or in cows during early lactation could reduce the feed requirement by approximately 8% relative to the herd average, with no apparent changes in energy-corrected milk yield, body weight, or rate of body weight gain. A test period of 70 to 80 days in duration between approximately days 150 to 265 of lactation should provide the best approximation of whole-lactation RFI for the least time and effort. Lastly, RFI measured during growth of heifers may serve as an indicator trait for RFI during lactation, and selection for heifers exhibiting low RFI during growth should improve overall herd feed efficiency during lactation.
Technical Abstract: Residual feed intake (RFI) is commonly used to assess animal feed efficiency and is calculated as the difference between observed and expected feed (or energy) intake typically derived from a multiple regression model of dry matter (or energy) intake on energy sinks, including maintenance, growth, or milk production. It is not clear what stage during the production cycle of the dairy cow is best to assess RFI. Here we characterize RFI in growing Holstein heifers (RFI_Growth; ~10 to 14 mo of age) and changes in RFI throughout a 305-d lactation (RFI_Lac) in conventionally managed U.S. Holstein cows to identify the most desirable testing scheme for RFI_Lac. Additionally, phenotypic correlations between RFI_Growth measured in Holstein heifers and RFI_Lac in their first 100 d of lactation (n = 130) were examined to determine the utility of RFI_Growth as a predictor of RFI_Lac and performance characteristics of lactating cows that were divergent in RFI_Growth as heifers. Mean energy intake of the least and most efficient growing heifers (+- 0.5 SD from mean RFI_Growth of 0) differed by 3.01 Mcal/d (1.2 kg/d DMI; P < 0.0001) but the groups showed no difference in mid-test body weight or ADG (P >= 0.76). Among cows evaluated for whole-lactation RFI_Lac, mean energy intake differed (P < 0.0001) by 8.66 Mcal/d (3.1 kg/d DMI) between the least and most efficient cows with no differences in ADG, ECM, or body weight (P >= 0.75). Correlation analysis between whole-lactation RFI_Lac (10 to 305 DIM) and periodic RFI_Lac indicated a test period of 70 to 80 d in duration surrounding day 186 of lactation (e.g., 150 to 265 DIM) provides the best approximation (r >= 0.90) of whole-lactation RFI_Lac. The correlation between RFI_Growth of heifers and RFI_Lac estimated during the first 100 DIM of the first lactation was 0.37 (P < 0.0001). Ranking of heifers as least, middle, or most efficient based on RFIGrowth (+- 0.5 SD from mean = least and most efficient) resulted in 43% maintaining the same ranking by RFI_Lac in the first lactation. On average, the most efficient heifers ate 3.27 Mcal/d ME less (P < 0.005; or 1.19 kg DMI) during the first 100 DIM than the least efficient heifers, but exhibited no differences in average energy-corrected milk yield, ADG, or BW (P >= 0.44). Thus, RFI_Growth may serve as an indicator trait for RFI_Lac, and selection for heifers exhibiting low RFI_Growth should improve overall herd feed efficiency during lactation.