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Volatile Fatty Acid Measurements on the Rumen Contents of Lambs Fed Rations of Various Physical Form¹

Iowa Agricultural and Home Economics Experiment Station, Ames

Abstract

A series of four experiments were conducted with lambs to determine the effects of the physical form of the ration and trace mineral supplementation on in vivo rumen molar proportions of volatile fatty acids. Total volatile fatty acid and pH measurements were also made. The ration contained 67% concentrate and 33% roughage. In two of these studies, fistulated lambs were used and in two studies intact lambs were used. The intact lambs appeared to be the better experimental subjects since, for reasons largely unexplained at this time, the effects of the ration treatments were not as pronounced when fistulated lambs were used. Despite these differences, the trends in all studies were similar.

The feeding of pelleted rations produced a narrowed acetate to propionate ratio in comparison to similar ground mixed ration. Long hay rations unexpectedly produced narrower acetate to propionate ratios than ground mixed rations. The percent of butyric acid was reduced and that of propionate raised by the addition of cobalt. Percents of iso-butyrate and iso-valerate were lowered and the percent of valerate raised under conditions that narrowed the acetate to propionate ratios. The total quantity of volatile fatty acids tended to be increased by feeding pelleted rations in comparison to ground mixed rations; however, this was not a consistent effect. Acetate to propionate ratios widened with increased length of time after feeding. Acetate production tended to peak approximately four hours after feeding for most rations. However, total acid production had not peaked by six hours on a long hay ration while a peak for ground mixed or pelleted rations was reached previous to two hours after feeding. Rations containing corn cobs produced narrower acetate to propionate ratios than similar rations containing alfalfa hay.

¹ Journal Paper No. J-4261 of the Iowa Agricultural and Home Economics Experiment Station, Ames, Iowa. Project No. 1208.