Influence of different fat supplements on digestibility and ruminal digestion in cows

In two trials each using 3 cows fitted with, rument cannulas, the effects of different lipid supplements on digestibility and ruminal digestion were analyzed. In trial 1, a control diet based on maize silage (C1) was compared to the same diet with a supplement of crude (untreated) bone fat (UF) and with a crystalline animal fat (CF). In trial 2, a control diet (C2) similar to diet C1 was compared to the same diet with a supplement of protein-coated (encapsulated) fat (EF). Fatty acid content in dry matter was 2.5% for control diets, 8.1 to 9.1% for supplemented diets. Apparent digestibility of nutrients, pH and volatile fatty acids in rumen juice, in sacco degradability of dry matter and cell walls were determined. Fat supply decreased organic matter digestibility in trial 1 (76.4, 67.8 and 68.8% in diets C1, UF and CF) and in trial 2(74.1 and 68.1% in diets C2 and EF). This decrease was due to a strongly negative action on cell wall digestion: 69.1, 53.7% and 57.3 in diets C1, UF and CF, 62.9 and 53.6% in diets C2 and EF, for NDF digestibility, and was related to a decrease in total volatile fatty acid concentration before feeding: 67.4, 46.7 and 47.7 mM in diets C1, UF and CF, 61.1 and 54.6 mM in diets C2 and EF. Acetate and butyrate decreased and propionate increased with lipid supply. The negative effect of fat on in sacco dry matter and cell wall degradation was moderate.