The relationship in the cow between milk-fat secretion and ruminal volatile fatty acids

Abstract

I . The effect of reducing the hay and of increasing the proportions of concentrate and flaked maize in the diet of cows on the secretion of milk fat and its component fatty acids and on the proportions of volatile fatty acids in the rumen liquor has been studied. 2. The low-hay diet caused a fall in the milk fat content to about half of the values in the initial control period and the secretion of all the major fatty acids in the milk was reduced. The general pattern of change in the proportions of rumen VFA during the change to the low-hay diet was a decrease in acetic acid, an increase in propionic and n-valeric acids, relatively little change in n-butyric acid and also an increase in the concentration of lactic acid. Approximately 60 % of the variation in milk fat content during the change of diet was associated with the increase in propionic acid. 3. In cows established on the low-hay diet there were marked variations in the relative proportions of acetic and propionic acids, but there was no related change in milk fat content. On return of the animals to the high-hay diet, recovery of the initial proportions of acetic, propionic and valeric acids occurred within about 4 days but the recovery in milk fat content was not complete until 2-3 weeks had elapsed. 4. Although the intraruminal infusion of acetic acid in cows on the low-hay diet caused increases and decreases respectively in the molar proportions of acetic and propionic acids in the rumen, an increase in milk fat content was observed amounting to only one-quarter of the loss associated with the transfer to the low-hay diet; there was no characteristic pattern of increase in the yields of the individual fatty acids of milk fat.No consistent effects of intraruminal infusions of butyric acid, in cows on the low-hay diet, on the yield of milk fat or of the individual fatty acids were observed.There is much circumstantial evidence that the fall in milk fat content frequently observed in milking cows during a change from a diet containing a usual amount of hay to one containing only a small amount is related to the associated decreased and increased proportions of acetic and propionic acids respectively in the volatile fatty acids of the rumen digesta. Marked variations from cow to cow in the extent and rapidity of the fall in fat content are, however, observed, and on the abrupt return of cows from a diet low in hay to one containing a usual amount, the recovery of the original fat content is not immediate but takes place progressively over a period of up to 3 weeks (Balch, Balch, Bartlett, Cox & Rowland, 1952; King & Hemken, 1962; Storry & Rook, 1 9 6 5~) .Also when intraruminal additions of dilute acetic acid or of sodium acetate are given to cows receiving a diet low in hay and in whose milk the fat content has been depressed, the observed increases in milk fat content vary widely from cow to cow (Stoddard, ruminal volatile fatty acids that occur during a change from a diet containing a usual amount of hay to one containing only a small amount, and of...

Ammonium salts of fatty acids for milk production 1. The effect of feeding a salt solution containing ammonium acetate on the yield and composition of milk produced by Jersey cows fed hay/concentrate diets

“…Such diets with a high roughage content would be likely to produce a relatively high proportion of acetate to propionate in the end-products of rumen fermentation (Bath and Rook, 1963), and would be associated with the maintenance of a high milk fat percentage (Storry and Rook, 1966), as was the case in this instance. Such diets with a high roughage content would be likely to produce a relatively high proportion of acetate to propionate in the end-products of rumen fermentation (Bath and Rook, 1963), and would be associated with the maintenance of a high milk fat percentage (Storry and Rook, 1966), as was the case in this instance.…”

Perturbation Dynamics of the Rumen Microbiota in Response to Exogenous Butyrate

“…Intraruminal infusion of VFAs, including butyrate, has been used to study the effect of nutrient supply on milk secretion [5] and nutrient partition, liver physiology, lipid metabolism, and rumen wall development, as well as ruminal pH maintenance [6]–[8]. A decreased ratio of glucogenic (propionate)/lipogenic (acetate and butyrate) in ruminal VFAs could decrease hepatic gluconeogenesis [9], leading to a reduction in milk fat secretion [10]. Steady-state ruminal butyrate concentration reflects a delicate balance between butyrate production by rumen microbes and its clearance, mainly via epithelial absorption.…”

Effect of Low-Roughage Diets on the Microflora and Lipid Metabolism in the Rumen

“…Hydrolysis of the complex dietary lipids is necessary before isomerization and hydrogenation of the fatty acids can take place (15). When cows are fed low-roughage diets, particularly those which depress milk fat secretion, the changes in the fatty acid composition of lipids of milk (25), blood plasma (9,21,27), digesta (29,33), and adipose tissue (30) suggest that hydrogenation in the rumen of dietary unsaturated acids may be reduced. Reductions in the numbers of ciliate protozoa have been associated with reduced hydrogenation (6), and lower numbers of these organisms and of the bacterium Butyrivibrio fibrisolvens, which also actively hydrogenates (23), are known to occur with lowroughage rations (4,18,24).…”