Effect of Level of Intake and Physical Form of the Diet on Plasma Glucose Concentration and Volatile Fatty Acid Absorption in Ruminants

Abstract

Summary An attempt was made to investigate some of the factors affecting plasma glucose concentration in sheep. A randomized complete block design was used to study the effects on plasma glucose concentrations of three feeds each fed at three levels of intake to sheep either 15 or 27 months old. The three rations were chopped hay, pelleted finely ground hay, and the pelleted mixture of 45% corn meal and 55% finely ground hay. At the medium and high levels of intake the plasma glucose concentrations of the animals receiving hay pellets or grain-hay pellets were higher (P To try to explain some of the differences in plasma glucose concentrations reported here, glucose and volatile fatty acid (VFA) absorption studies were conducted on six sheep fed either chopped or pelleted, ground hay. The method to measure the absorption of a given metabolite involves the serial sampling of blood from the portal vein and the carotid artery and the measurement of the portal blood flow rate during the same experimental period by a thermodilution method. There was essentially no glucose absorption from the gastrointestinal tract. In the rumen ingesta, there was a trend for the ratio of acetic to propionic acid to be lower when the test rations were fed in the pelleted, ground form. The relative proportions of VFA in the portal blood were markedly different from those in the rumen ingesta. Although the data are not sufficient to make definite conclusions concerning the effect of physical form of hay on the amounts of fatty acids absorbed, they demonstrated that appreciable amounts of formic acid, 47 to 13.4g per day, were absorbed. The total quantities of VFA absorbed per day ranged from 73 to 89g per day.