In vitro characterization of ruminal fermentation and lipid metabolism in dairy diets associated with high versus low concentrations of conjugated linoleic acid in milk

Abstract

Conjugated linoleic acid (CLA) is an important bioactive fatty acid in ruminant milk due to its potential anticarcinogenic, anti-inflammatory, and antiatherogenic properties. However, milk CLA concentration varies considerably among dairy production systems, and the ruminal mechanisms underlying this variation remain poorly understood. This study aimed to evaluate rumen fermentation characteristics, nutrient digestibility, partial volatile fatty acid (VFA) profiles, methane production, and lipid biohydrogenation characteristics of diets associated with extremely high and low milk CLA concentrations. In total, 300 milk samples were collected from dairy farms in Pangalengan, Kebon Pedes, and Kunak. Fifteen diets associated with the highest milk CLA concentrations (>2.4% of milk fat) and fifteen diets associated with the lowest CLA concentrations (<0.92% of milk fat) were selected and reformulated according to field feeding practices. The diets were evaluated using in vitro fermentation and digestibility techniques. Measured parameters included ruminal pH, ammonia, total and partial VFAs, gas and methane production, microbial protein synthesis, nutrient digestibility, and unsaturated fatty acid biohydrogenation indices. Substantial variation was observed among diets in terms of fermentation, digestibility, and lipid metabolism. Total VFA concentration ranged from 93.37 to 144.37 mM, while methane production ranged from 5.03 to 23.31 mL/g dry matter (DM). Dry matter digestibility and organic matter digestibility ranged across 52.68–80.19% and 51.18–80.64%, respectively. Several high-CLA-associated diets exhibited relatively lower acetate-to-propionate ratios (1.80–1.96) and higher incomplete biohydrogenation (IBH) ratios, although substantial overlap occurred between high- and low-CLA-associated diets. This overlap indicated that general fermentation intensity alone could not fully explain CLA variation. Milk CLA variation showed relatively stronger associations with ruminal lipid biohydrogenation characteristics, particularly IBH and the persistence of unsaturated fatty acid intermediates, than with overall fermentation characteristics. However, substantial overlap among diets prevented the identification of a single VFA profile or biohydrogenation index as a consistent characteristic associated with milk CLA concentration.

Keywords

conjugated linoleic acid / rumen biohydrogenation / volatile fatty acids / in vitro fermentation / dairy cow nutrition

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