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Evaluation of the relationship between ruminal pH and milk de novo fatty acid proportion in early-lactating dairy cows.

R. Fukumori

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06-24-2020

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Abstract:

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Evaluation of the relationship between ruminal pH and milk de novo fatty acid proportion in early-lactating dairy cows.
R. Fukumori*1, W. Shi2, S. Oikawa1, M. Oba2. 1Rakuno Gakuen University Ebetsu, Hokkaido, Japan, 2University of Alberta Edmonton, AB, Canada.

The objective of this study was to evaluate the relationship between rumen pH and proportion of de novo fatty acids (DNFA) in milk and milk fat, determined by Fourier transform infrared spectroscopy, in lactating dairy cows. Data were collected from 18 multiparous Holstein cows, fitted with a rumen cannula, fed one of experimental diets differing in starch content (22.1 or 28.3%) with or without supplementation of a Saccharomyces cerevisiae fermentation product (NutriTek, Diamond V Inc., Cedar Rapids, IA) in a previous study. Milk was sampled on d 7 and 21 after calving, and concentrations of milk fat, de novo fatty acids (DNFA; C6 to C14), mixed origin fatty acids (C16 and C17), and preformed fatty acids (≥C18) were analyzed using CombiScope FTIR A600 (Delta Instruments, Drachten, the Netherlands). Rumen pH was recorded in the ventral sac every 30 s continuously for 72 h, on d 7 to 9 and 21 to 23 after calving, using a pH measurement system (LRCpH; Dascor, Escondido, CA). Pearson correlation coefficients were used to determine the relationship between rumen pH variables and milk fat variables. Milk fat DNFA (g/100 g FA) was positively correlated with nadir (r = 0.428, P < 0.01) and mean rumen pH (r = 0.471, P < 0.01), and negatively correlated with duration (r = −0.511, P < 0.01) and area below rumen pH 5.8 (r = −0.520, P < 0.01) although milk fat content did not have any relationship with rumen pH variables in this study. The coefficients of determination between rumen pH variables and DNFA were greater in milk fat DNFA (g/100 g FA) than milk DNFA (g/100 g milk), suggesting that milk fat DNFA (g/100 g FA) is an appropriate measurement variable to predict low rumen pH even for cows in early lactation. A regression analysis suggests that cows with subacute rumen acidosis, defined as rumen pH below 5.8 for more than 5 h/d, had milk fat DNFA concentration of 21.9 g/100 g FA or lower. This study showed that milk fat DNFA was correlated with rumen pH variables, and that it has a potential to be used to identify cows with subacute rumen acidosis.

Keywords: de novo fatty acids, rumen pH, subacute ruminal acidosis.