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Relationship between early lactation body condition score and mid-lactation feed efficiency in primiparous Holstein cows
Feed efficiency is increasingly becoming an important trait to consider when selecting profitable dairy cows. With that comes 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. The goal of this study was to determine if residual feed intake (RFI) measured in mid-lactation was related to early lactation body condition scores (BCS) in primiparous Holstein cows. Weekly BCS up to 45 DIM were observed on all first lactation Holstein cows at the Iowa State University dairy farm from 2012 to 2014. Beginning at approximately 50 DIM, all clinically healthy cows had daily milk production measured and feed intake recorded using a Calan Broadbent feeding system for approximately 60 days. During this time, weekly body weights, BCS, and milk component data were also collected. In total 255 cows had all of these data recorded. Early lactation BCS was predicted for days without observations. Three early lactation BCS traits were generated: average daily change in BCS during the first 25 DIM, average daily change in BCS during the first 45 DIM, and BCS at calving, measured as the average predicted BCS for DIM 3 through 5. RFI was calculated as the error term in the regression of DMI on milk energy, change in body weight, and metabolic body weight. Fixed effects of replicate and DIM were included. Differences in the early lactation BCS traits were assessed for the 20 most and 20 least feed efficient cows using a mixed model. RFI for the 20 feed efficient cows was less than -1.66 and greater than 1.69 for the feed inefficient cows. DMI for the efficient cows averaged 18.5 kg per day and 24.2 kg per day for inefficient cows. The difference in average BCS at calving was insignificant at 3.87 for efficient cows and 3.66 for inefficient cows. Change in BCS during the first 25 DIM and during the first 45 DIM did not differ by feed efficiency group. From this study, we conclude that cows differing on RFI as measured during mid-lactation do not experience significant differences in body tissue mobilization during early lactation. We appreciate the support from the USDA National Needs Graduate Fellowship Competitive Grant no. 2013-38420-20496 and the Agriculture and food Research Initiative Competitive Grant no. 2011-68004-30340.
Keywords: body condition score, residual feed intake, feed efficiency