The influence of rumen volatile fatty acids on blood metabolites and body composition of growing lambs

Abstract

Changes in the body composition, blood metabolites and rumen volatile fatty acids were measured in growing 12-week-old lambs fed whole-loose barley or ground barley pelleted with minerals for 10 weeks. Feeding whole-loose barley produced a propionic type of rumen fermentation and ground barley pelleted with minerals, an acetic acid type.The propionic type of fermentation was associated with a significant increase in the plasma concentrations of glucose and insulin, a reduction in the concentrations of plasma urea, and a reduction in almost all of the plasma amino acids, particularly alanine, methionine, valine, isoleucine and leucine. There was also a significant increase in the amount of body fat and dry matter, a higher level of protein per kg fat free empty body weight, and a more efficient utilization of dietary energy in the animals with a propionic acid type of fermentation.The elevation in the concentration of rumen propionic acid produced two important changes. It increased the supply of the main glucogenic precursor propionate, which probably reduces the body's requirement for alternative gluconeogenic precursors, and it stimulated directly and/or indirectly the pancreatic secretion of insulin. The latter is most likely responsible for the efficient peripheral utilization of glucose and other nutrients in lambs with a propionic acid type of rumen fermentation.Thus, a propionic type of fermentation is associated with an increase in the plasma levels of glucose and insulin, an increase in fat deposition and an increase in the efficiency of ME retention; all of these factors contribute to the improved performance of this group of lambs compared to those with an acetic acid type of fermentation.