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Fatty acid metabolism may vary in dairy cows with high and low residual feed intake.

M. J. Martin



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Fatty acid metabolism may vary in dairy cows with high and low residual feed intake.
M. J. Martin*1, R. S. Pralle1, K. A. Weigel1, Z. Zhou2, H. M. White1. 1University of Wisconsin Madison Madison, WI, 2Michigan State University East Lansing, MI.

Mammary uptake and sequestration of triglycerides has been demonstrated to be greater in cows with lower residual feed intake (RFI). The objective of this study was to evaluate the differences in blood metabolites and markers of hepatic function between multiparous cows with high and low RFI as determined during 7-wk feed efficiency studies (n = 3). Calculated RFI was determined by regressing energy intake on milk energy output, median DIM, metabolic BW, and ΔBW (PROC MIXED, SAS 9.4). Cows were ranked by RFI and the top (HighRFI; feed inefficient) and bottom (LowRFI; feed efficient) 15% of phenotypic RFI (n = 18/group) were selected. Plasma and serum samples were taken concurrently from the tail vessel (TV) and the subcutaneous abdominal vein (MV). TV samples were analyzed for aspartate aminotransferase, alanine aminotransferase, and albumin. TV and MV samples were analyzed for blood urea nitrogen, lactate, carnitine, and acylcarnitines. Mammary arterial-venous difference (AVdiff) was calculated and variables were transformed as needed. The effect of RFI group was determined using PROC GLIMMIX with fixed effect of group and accounted for heterogeneity of variance. Data are presented as (mean [95%CI]). LowRFI cows had lower (P = 0.01) TV concentrations of C3-carnitine (0.86 �M [0.69,1.06] vs 1.31 �M [1.04,1.64]) and C4-carnitine (0.25 �M [0.22,0.28] vs 0.33 �M [0.29,0.37]), while TV C18:1-carnitine tended (P = 0.08) to be greater in LowRFI cows. Concentrations of C4-OH-carnitine were greater (P = 0.01) and C18:1-carnitine tended to be greater (P = 0.10) in the MV of LowRFI cows. Interestingly, AVdiff of C4-OH-carnitine was lower (P = 0.01) and C3-carnitine and C4-carnitine tended (P < 0.10) to be lower in LowRFI cows. There were no differences in concentration or AVdiff of other markers quantified. Although acylcarnitine exchange across mitochondrial membranes and between tissues is not fully understood, acylcarnitines are intermediates of fatty acid oxidation and may serve as markers of metabolism. Differences in circulating acylcarnitine concentrations suggest potential differences in fatty acid metabolism between high and low RFI cows.

Keywords: acylcarnitine, feed efficiency, arterial-venous difference.