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Are odd- and branched-chain milk fatty acids potential indicators of forage intake in dairy cows?

Patel, Mikaela; Wredle, Ewa; Bertilsson, Jan


Odd- and branched‑chain fatty acids (OBCFA) have been suggested to be potential markers for duodenal flow of microbial protein and of volatile fatty acids in rumen fluid. These relationships may reflect the proportion of cellulolytic bacteria in the rumen with different forage:concentrate ratios. Thus, the milk OBCFA may be used as non-invasive tools for both researchers and farmers to assess nutrient related disorders in cows. It has also been shown that the OBCFA may be potential predictors of sub‑acute ruminal acidosis (SARA). In commercial herds, forage is often fed on group level and cows with low forage intake can therefore pass unnoticed, and health problems such as acidosis can arise. The objectives of the present study were to study the OBCFA composition in milk fat feeding three different silage:concentrate ratios in the diet and to study the correlation between fibre and OBCFA. The study included 50 cows >25 weeks of lactation. The diets were composed of the same feeds: grass silage and concentrate, but the silage:concentrate ratio differed between the diets: 50:50, 70:30 and 85:15 (on dry matter basis). Pooled milk samples were used in the analyses of milk composition and milk fatty acid profiles. Statistical differences between diets (P < 0.05) were determined using orthogonal polynomial contrasts and multiple regression analysis was performed on diet composition and OBCFA. Increasing the proportion of grass silage linearly increased the concentrations of C15:0, iso C15:0, C17:0 and total OBCFA (Table 1). There were no significant effects on milk fat, protein or lactose concentration. The concentration of total OBCFA showed the strongest positive correlation (P < 0.05) with dietary content of fibre (NDF), followed by C15:0 and iso C15:0 (R2 = 0.36, R2 = 0.28 and R2 = 0.24, respectively). Increasing the silage:concentrate ratio in diets for dairy cows, from 50:50 to 85:15 increased the concentrations of the linear odd-chain FA, iso C15:0 and total OBCFA in milk. The reflection of fibre content in milk OBCFA suggests that total OBCFA concentrations in milk may be useful to indicate forage intake under conditions when it is not possible to measure individual forage intake, and thus is a potential indicator to identify cows at risk of ruminal acidosis.

Published in

Title: Book of abstracts 15th International Conference on Production Disease in Farm Animals
ISBN: 978-91-576-9150-7
Publisher: SLU