Effects of barley treatment with lactic acid and using of different sources of dietary fat on performance, milk fatty acid profiles, and microbial protein synthesis in lactation Holstein cows

Compared to corn, barley starch is rapidly degraded in the rumen, leading to an accumulation of VFA and eventually resulting in acidosis. Recently, the use of organic acids has been effective in reducing of barley (as dry roll) starch degradation in the rumen. Oilseeds can be used in lactating cow diet and can produce milk with a more favorable fatty acid profile for human nutrition. Therefore, the objectives of this study were to evaluate the effects of ground barley grain treated with lactic acid (LA), dietary fat sources and their interaction on performance, milk fatty acid profile and microbial protein synthesis in early lactating Holstein cows.

To evaluate the effects of barley treatment and dietary fat sources on performance, ruminal and blood parameters twelve multiparous Holstein cows in early lactation were used in a replicated 4×4 Latin square design with a 2×2 factorial arrangement of treatments. Ground barley steeped in water (Barley-W) or in 1 % LA solution (Barley-LA) in equal quantity (wt/vol) for 48 h before adding to the TMR. Dietary fat source were extruded flaxseed (EF) and extruded soybean (ES). Accordingly, experimental treatments were: 1) barley treated with water (Barley-W) + extruded flaxseed (EF), 2) barley treated with water (Barley-W) + extruded soybean (ES), 3) barley treated with LA (Barley-LA) + extruded flaxseed (EF), 4) barley treated with LA (Barley-LA) + extruded soybean (ES).

Dry matter intake and milk yield were not affected by experimental treatments. Milk fat content and milk fat yield were greater in cows fed Barley-LA compared to cows fed Barley-W. More milk fat content was produced by cows fed ES compared to EF. Concentrations of Σ n-3 and Σ n-6 were greater and lower Σ n-6 respectively in milk from cows fed EF compared with those fed ES. The ratio Σ n-6/Σ n-3 was lower in milk from cows fed EF compared with those fed ES. The barley grain treatment and dietary fat source had no effects on milk concentration of C18:2c9t11 (CLA) and microbial protein synthesis, and their interactions between these factors were not significant.

In conclusion, treating ground barley grain with LA and the use of EF and ES as dietary fat sources did not influence the performance of early-lactation Holstein cows. Milk fat content and milk fat yield were greater in cows fed Barley-LA compared to those fed Barley-W. Concentrations of Σ n-3 and Σ n-6 were greater and lower Σ n-6 respectively in milk from cows fed EF compared with those fed ES. Contrary to our hypothesis, milk concentration of C18:2c9t11 (CLA) and microbial protein synthesis were not affected by barley treated with LA, dietary fat sources and Interaction between them.