In vitro degradation of choline from selected feedstuffs and choline supplements.
The objective of this experiment was to determine the extent of in vitro degradation of choline from barley, corn, corn gluten meal, cottonseed meal, fish meal, soybean meal, alfalfa hay, timothy hay, choline chloride, and choline stearate. During four individual fermentation runs, samples were incubated in vitro for .25, 1, 3, 6, 12, 18, 24, 36, and 48 h with an inoculum mixture containing rumen fluid obtained from a rumen-fistulated dairy cow fed 17.5% corn silage and 28.7% grass silage and 53.8% concentrate diet. Because of their low choline content (less than .68 mg/g) corn, corn gluten meal, alfalfa hay, and timothy hay gave erratic values for choline disappearance for different fermentation runs and times of incubation although disappearance tended to increase with time. Data for the rest of the feeds and choline supplements were analyzed using nonlinear regression procedure to obtain estimates of potentially degradable choline, rapidly degradable choline, and the rate of choline degradation in vitro. The mean estimates of rumen degradable choline (%) were 79.4, 84.7, 82.9, 83.8, 98.0, and 98.6 for barley, cottonseed meal, fish meal, soybean meal, choline stearate, and choline chloride, respectively. The results suggest that incorporating choline-rich feedstuffs in diets can only marginally increase the postruminal flow of choline in dairy cows.