Py. Chouinard et al., DIETARY SOYBEANS EXTRUDED AT DIFFERENT TEMPERATURES - MILK-COMPOSITION AND IN-SITU FATTY-ACID REACTIONS, Journal of dairy science, 80(11), 1997, pp. 2913-2924
Twenty-four multiparous Holstein cows, 4 of which were ruminally fistu
lated, were assigned to one of four diets containing full-fat soybeans
, either raw or extruded at 120, 130, or 140 degrees C. Our hypothesis
was that the extrusion of full-fat soybeans, as well as the extrusion
temperature, would affect the bypass of fatty acids in the rumen and,
thus, would modify the fatty acid profile of milk fat. Total mixed di
ets containing 23.7% soybeans (percentage of DM) were fed for 8 wk. Mi
lk yield was lower, and the proportion of milk CP was higher, for cows
fed raw soybeans than for cows fed extruded soybeans. Compared with r
aw soybeans, extruded soybeans increased the concentration of Delta-11
-trans-C-18:1 from 2.72 to 11.41% in milk fat but had no effect on yie
ld or percentage of milk fat. Polyunsaturated fatty acids of raw soybe
ans disappeared more rapidly than did those of extruded soybeans from
bags incubated in the rumen of fistulated cows. However, more Delta-11
-trans-C-18:1 and C-18:0 appeared in bags containing extruded soybeans
than in bags containing raw soybeans. Extrusion of full-fat soybeans
influenced the metabolism of fatty acids in the rumen and the fatty ac
id profile of milk fat, but the temperature of extrusion had only mino
r effects on these parameters.