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Relationship between Early Lactation BCS and Mid-Lactation Feed Efficiency in Dairy Cattle

and Implications The relationships between body condition score (BCS) observed during the first 45 days of lactation and two measures of feed efficiency, residual feed intake (RFI) and gross efficiency (GE) defined as milk energy / DMI, measured during mid-lactation were assessed in 255 first lactation Holstein cows. No significant differences in BCS at calving and at approximately 40 days in milk (DIM) nor in BCS loss during the first 25 and first 45 DIM were observed between the most feed efficient and feed inefficient cows when either RFI or GE was used as the measure of feed efficiency. However when feed efficiency was measured as GE, feed efficient cows had significantly lower BCS at 40 DIM. Our findings suggest that selection based on RFI as a measure of feed efficiency during mid-lactation should not impact BCS loss during early lactation. Introduction Feed efficiency, especially during mid-lactation when the cow is at peak feed intake and milk production, is becoming an increasingly important trait when selecting profitable dairy cows. However, there is the concern that selecting for a more feed efficient cow may inadvertently select for cows that undergo extreme body tissue loss to meet the demands of milk production. By measuring feed efficiency as RFI while accounting for BCS, we can keep feed efficiency phenotypically independent of body tissue change during the measurement period. However, this does not guarantee that feed efficiency will be unrelated to body tissue loss in early lactation when having adequate body tissue reserves is most critical for a smooth transition to lactation. The goal of this study was to determine if RFI measured in mid-lactation was related to early lactation BCS in Holstein cows. Additionally, we wanted to determine the relationship between early lactation BCS and the traditional measure of feed efficiency, GE, specifically milk energy produced per kg DMI.