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Dietary Factors Affecting Volatile Fatty Acid Production in the Rumen¹

Iowa Agricultural and Home Economics Experiment Station, Ames

Abstract

Sodium bicarbonate and calcium carbonate additions to high concentrate-low roughage type diets were without effect in altering acetate-propionate ratios and total volatile fatty acid levels in lambs. Supplementary sodium bicarbonate tended to elevate ruminal Ph. Concurrent sodium bicarbonate and lactic acid supplementation produced ruminal propionate levels no higher than produced by lactic acid alone. Sodium bicarbonate and calcium carbonate additions had no effect on growth and carcass characteristics of fattening wether lambs.

Chlortetracycline supplementation of a high urea-high roughage lamb fattening ration tended to overcome the depressing effects of urea on carcass grade. Where no urea was included in these rations, chlortetracycline additions tended to widen acetate-propionate ratios and to elevate butyric acid levels. There appears to be an interaction between chlortetracycline and urea on acetate-propionate ratios and ruminal acetate levels.

Narrowed acetate-propionate ratios, higher butyric acid levels, lower total volatile fatty acid levels and lower pH's were produced in the 80% concentrate as compared to the 50% concentrate diets. While overall weight gains were similar between the two types of rations, higher carcass grades, higher dressing percent and higher percent separable fat resulted in the higher concentrate rations. In the second intact lamb trial, correlation was shown be-between ruminal butyric acid levels and carcass grade.

Rumen fluid buffering capacity measurements support the hypothesis that substances can enter the rumen from the blood stream or peritoneal cavity in the same manner that they are absorbed through the rumen wall.

¹ Journal Paper No. J-4258 of the Iowa Agricultural and Home Economics Experiment Station, Ames, Iowa. Project No. 1208.

² Present address: Rockefeller Foundation, Mexico City.