The heat increment in fasting sheep of acetic acid partially neutralized with sodium hydroxide

I n previous work Armstrong & Blaxter (1957) found that when acetic acid was given to fasting sheep as the sole source of energy it was inefficiently utilized in the sparing of body tissues from oxidation.Five experiments gave a mean heat increment of 40.9 kcal/Ioo kcal of acid metabolized, a value which greatly exceeded the heat increments found when propionic or n-butyric acids were given.A noticeable feature of the experiments with acetic acid was the marked acidosis that developed when the acid was administered, and it was suggested that the high increments of heat might be associated with accumulation of acid.Respiration-chamber experiments by Moll- 1941) with milking cows given A.I.V. silage were cited in this regard, for they showed that severe acidosis due to mineral acid increased the heat increment and that neutralization of the acid reduced it.This paper describes three experiments in which fasting sheep were given acetic acid partially neutralized with sodium hydroxide in an attempt to prevent acidosis ; the results are compared with those previously reported when acetic-acid solutions were given.A brief account of some of the findings has been published (Armstrong, Blaxter & Graham, 1958). EXPERIMENTAL Animals.The experimental animals used were three castrated male sheep, P, S and T, each with a cannulated rumen.They had been used in the earlier experiments of & Blaxter (1957). Armstrong Plan of experiments.Three experiments were carried out, one with each sheep, and all conformed to the same plan.The fasted animal was confined in a respiration chamber and physiological saline (6.5 l./day) was dripped into the rumen at a constant rate by means of the continuous drip-feed pump described by Armstrong & Blaxter (1957).After 4 days a mixture of acetic acid partially neutralized with sodium hydroxide was added to the saline in sufficient amounts to supply 700 kcal daily and this solution was dripped into the rumen for 3 days.Saline was then given for a further 3 days.The management of the sheep before and after the experiment has been described by Armstrong & Blaxter (1957).Solutions of partially neutralized acetic acid.Table I gives details of the solutions infused in the experiments.It will be noted that the amounts of sodium ion in the acid solutions given to sheep P and sheep T were the same.The amount in the solution infused into sheep S was appreciably greater.