Ruminal and total tract digestibilities in steers fed diets containing liquefied or prilled saturated fatty acids.

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Abstract
We studied the effects of the addition of liquefied vs prilled mostly saturated fatty acids (FA) to the concentrate portion of total mixed diets on ruminal and total tract digestibilities. Four Holstein steers (270 ± 23 kg) fitted with ruminal and duodenal cannulas were used in a 4 × 4 Latin square design with 21-d periods. Diets contained (DM basis) 30.0% corn silage, 22.2% chopped alfalfa hay, 25.0% ground shelled corn, 12.5% soybean meal, and 5% of one of the following fat sources: 1) prilled FA (PFA), 2) choice white grease (triglycerides) added in liquid form (LTG), 3) 2.5% PFA + 2.5% LTG, or 4) 2.5% liquefied PFA (LFA) + 2.5% LTG. Ad libitum OM intake was not different (P > .10) among diets (mean 7.8 kg/d). Ruminal digestibilities of OM (35.7, 39.9, 42.2, and 37.3% for Diets 1 to 4, respectively) were greatest (P < .10) for the combination of PFA + LTG and lowest for PFA alone. Ruminal digestibilities of NDF, ADF, and starch did not differ (P > .10) among diets. Total tract digestibilities of OM, NDF, and ADF were greater (P < .10) for the diet containing LTG alone than for the diet containing LFA + LTG because of trends for greater postruminal digestibilities. The LFA + LTG diet resulted in a greater proportion of acetate and lower proportion of propionate in ruminal fluid than PFA alone (P < .10). The acetate:propionate ratio (3.53, 2.96, 3.10, and 2.89 for Diets 1 to 4, respectively) was lower (P < .05) for LFA + LTG or LTG alone than for PFA alone. Postruminal and total tract digestibilities of total FA (66.0, 76.0, 71.2, and 68.9% for Diets 1 to 4, respectively) were lower (P < .05) for PFA than for other diets. Addition of saturated FA in liquid form resulted in digestibilities and ruminal effects similar to the same saturated FA added in prilled form.

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