The effects of the isocaloric replacement of part of the dietary concentrate mixture by 5 % lauric acid (99 % pure) or by 10 % of myristic (95 % pure), palmitic (96 % pure) or stearic (94 % pure) on the yield and composition of milk fat was investigated in 2 feeding experiments with a total of 10 cows in mid-lactation. The concentrate mixtures were given with a high-roughage diet that supplied 9-1 or 7-7 kg hay/day in expts 1 and 2, respectively.In expt 1 the inclusion of myristic acid in the diet decreased the yields of milk and solids-not-fat (SNF), but increased the percentage of fat in the milk without altering the fat yield. When stearic or palmitic acid was included in the diet there was an increase in milk fat yield; palmitic acid caused the greater increase. In expt 2 the inclusion of lauric acid in the diet did not appear to affect the yields of milk or SNF but it caused large reductions in the percentage of fat in the milk and in the yield of fat.In expt 1 the inclusion of myristic acid increased the yields and percentages of 14:0, 14:1 and 16:1 in the milk fat and decreased the yields and percentages of the short-chain fatty acids (4:0-8:0), 16:0, 18:0 and 18:1. When palmitic acid was included in the diet there were increases in the yields and percentages of 16:0 and 16:1 in the milk fat and decreases in the yields and percentages of 10:0, 12:0, 14:0, 18:0 and 18:1. The inclusion of stearic acid in the diet increased the yields and percentages of 18:0 and 18:1 in the milk fat and decreased the yields and percentages of 12:0 and 16:0. In expt 2 the inclusion of lauric acid in the diet increased the yield and percentage of 12:0, and in 1 cow the content of 14:0 in the milk fat; there were reductions in the yields and percentages of all the other fatty acids in the milk fat. There was no evidence of any marked elongation of the carbon chains of 12:0 and 14:0 in the mammary gland to form 16:0 or 18:0.In expt 1 the incorporation of myristic acid in the diet decreased the concentration of total steam-volatile fatty acids in rumen liquor. The inclusion of either myristic, palmitic or stearic acid in the diet had little effect on the relative proportions of the individual volatile acids in the rumen liquor. In expt 2 the addition of lauric acid to the diet reduced the acetic acid: propionic acid ratio in the rumen liquor.
SummaryThe effects of the isocaloric replacement of starch in the concentrate by either 5 or 10% ‘stearic acid’ (85% pure) or by 10% ‘palmitic acid’ (85% pure) on the yield and composition of milk were investigated in a feeding experiment with 12 cows in mid-lactation. The concentrate mixtures were given with a high-roughage diet that supplied 4.4 kg of hay and 2·7kg of sugar-beet pulp/day.The inclusion of 5% ‘stearic acid’ in the concentrate mixture resulted in increases in the yields of milk, milk fat, solids-not-fat (SNF) and lactose and a reduction in the content of protein in the milk, whereas, when the level of ‘stearic acid’ in the concentrate was increased to 10%, there was an increase in only the yield of milk and a reduction in the contents but not in the yields of SNF and protein in the milk. The inclusion of 10% ‘palmitic acid’ in the concentrate mixture also reduced the contents of SNF and protein in the milk but produced increases in the yields of milk, milk fat and lactose and also in the content of fat in the milk.None of the dietary treatments resulted in any changes in the concentration of blood glucose.
SummaryThe apparent digestibility coefficients of the various constituents of diets containing myristic, palmitic or stearic acids have been determined in an experiment with 8 sheep.The inclusion of myristic acid in the diet had no effect on the digestibility coefficient of total dry matter or crude protein, but it decreased the digestibility coefficients of crude fibre and nitrogen-free-extractives and increased the digestibility coefficients of fat and minerals. When palmitic acid was included in the diet there were decreases in the digestibility coefficients of total dry matter, crude fibre and nitrogen-free-extractives. The inclusion of stearic acid in the diet resulted in decreases in the digestibility coefficients of dry matter and nitrogen-free-extractives. There was an inverse relationship between the melting points and the digestibility coefficients of the added fatty acids.The findings of this investigation are discussed in relation to the results of a previous study on the effects of these dietary fatty acids on the yield and composition of cow's milk.
The effects of the isocaloric replacement of starch in a low-fat concentrate mixture by either 5 or 10% 'stearic acid' (85% pure) or 10% 'palmitic acid' (85% pure) on the yield and composition of milk fat were investigated in a feeding experiment with 12 cows in mid-lactation. The concentrate mixtures were given with a highroughage diet that supplied daily 4-4 kg of hay and 2-7 kg of sugar-beet pulp.The inclusion of 5 or 10 % 'stearic acid' in the concentrate mixture decreased the concentrations and yields of 10:0, 12:0, 14:0, 14:1, 16:0 and 16:1 in the milk fat but increased the concentrations and yields of 18:0 and 18:1. When the concentrate mixture contained 10 % 'stearic acid' the decreases in the yields of the shorter chain acids and the increases in the yields of 18:0 and 18:1 in the milk fat were more pronounced than when the concentrate mixture contained 5% 'stearic acid'. The inclusion of 10% 'stearic acid' in the concentrate mixture also decreased the concentrations of 6:0 and 18:2 in the milk fat. The inclusion of 10 % ' palmitic acid' in the concentrate mixture decreased the concentrations of 6:0, 8:0, 10:0, 12:0, 14:0, 14:1, 18:0 and 18:2 in the milk fat but increased the concentrations of 16:0 and 16:1. This dietary treatment also reduced the yields of 6:0, 10:0, 12:0, 14:0 and 18:2 but increased the yields of 4:0, 16:0 and 16:1 in the milk fat. The inclusion of 5% 'stearic acid' or 10% 'palmitic acid' in the concentrate mixture increased the yield of total milk fat.The inclusion of 10% 'palmitic acid' or 10% 'stearic acid' in the concentrate mixture increased the relative proportions of propionic and iso-butyric acids in the rumen liquor but decreased the proportions of ^-butyric and valeric acids. The inclusion of ' stearic acid' at the level of 5 % in the concentrate mixture increased the relative proportions of iso-butyric and iso-valeric acids but decreased the proportion of butyric acid in the rumen liquor.In a previous investigation (Steele & Moore, 1968 c) it was shown that when the diet of the cow was supplemented with 600 g/day of palmitic or stearic acids there were large increases in the yields of palmitic and palmitoleic acids or of stearic and oleic acids in the milk fat. The increased yields of C 16 and C 18 fatty acids were accompanied by decreased secretions of C 10 , C 12 and C M fatty acids in the milk fat. These changes occurred in spite of the fact that the palmitic or stearic acid was added to a basal diet that already supplied 450 g of total fatty acids (mainly C 16 and C 18 acids) per day; the yield of total fatty acids in the milk of the cows during the experiment was also
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