The COMA report on The Nutritional Aspects of Cardiovascular Disease (1994) recommended that the intake of long chain n-3 polyunsaturated fatty acids, including eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), by the UK population should double. EPA and DHA in the human diet are derived principally from oily fish. The aim of this experiment was to determine the effect of increasing levels of fish oil in the diet at two levels of vitamin E supplementation, on intake, milk production, the extent of uptake of EPA and DHA into milk fat at levels exceeding those investigated to date, and the effect of a dietary supplement of vitamin E on fatty acid content.

Lipids are commonly used in ruminant diets to increase the energy density of the ration and increasingly to manipulate the fatty acid (FA) composition of the final product (meat or milk). However, lipids may have negative effects on rumen function and in particular on the extent of carbohydrate digestion, which is accompanied by alterations in volatile fatty acid proportions, towards less acetate and more propionate. These alternations are more pronounced for lipids high in polyunsaturated fatty acids particularly linolenic acid (18:3n-3; found in linseed). However, there is some evidence to suggest that the opposite is true for longer chain C20 FAs, found in fish oil (Doreau and Chilliard, 1996). This experiment has examined the impact of lipid sources differing in their FA composition (saturated compared polyunsaturated FA) on digestion of nutrients in the rumen and small intestine.

Feeding fat to increase metabolisable energy content of lactation rations for dairy cows is now a common practice. It generally increases milk yield but decreases milk protein concentration. In North America whole oil seeds (cotton seeds, soya beans, sunflower seeds, etc.) containing high levels of linoleic acid are often fed as a fat source in a total mixed ration (TMR). Rape seed has also been fed and provides higher levels of oleic acid, but rape seed must be processed to be digested. Historically dietary fats for dairy cows have been rendered inert in the rumen to minimise negative effects on fibre digestion. In North America it is now recognised that unsaturated fats fed as whole oil seeds in a TMR do not have deleterious effects on digestion or intake, but these rations typically do not contain grass. Therefore our objective was to determine the intake and lactation response to feeding whole oil seeds (cotton seed and rape seed) in a grass silage-based ration and compare the response to that obtained using a rumen protected fat source as a positive control.

Rumen bacteria convert polyunsaturated C18 fatty acids to stearic acid (CI8:0) by biohydrogenation. Intermediates include a family of cis/trans isomers of linoleic acid known as conjugated linoleic acid (CLA) and a family of trans isomers of oleic acid (C18:1), chiefly trans-11 C18:1. Trans fatty acids inhibit milk fat synthesis in cows, an effect which Griinari et al. (1997) attributed specifically to trans-10 C18:1. Biohydrogenation intermediates can be incorporated directly into milk. In humans, trans C18:1 in hydrogenated vegetable oil (chiefly trans-9 C18:1) mimic saturated fatty acids as a risk factor for heart disease (Judd et al., 1994) and may inhibit milk fat synthesis. CLA may be anticarcinogenic (Parodi, 1997). It is important, therefore, to understand the effect of dairy cow nutrition on biohydrogenation intermediates.

Methane is an unavoidable product of rumen fermentation. Reduction of rumen methanogenesis can lead to an improved exploitation of nutrient energy and a decrease of methane emissions in the environment. The objective of this study was to investigate the effect of several fat and tannin containing feedstuffs on the production of CH4 and concommitant CO2 using the in vitro system „Hohenheim Gas Test” (STEINGAß & MENKE 1986). Special emphasis was directed to the suitability of the method to measure the effect of various substrates on rumen methanogenesis. Another objective was to investigate to what extent increasing fat or tannin contents in the diet of the donor sheep affect methanogenesis in vitro.

The current milk quota regime within the European Community restricts both the volume and butterfat content of milk supplies from farms. Reduction in the butterfat concentration of milk enables an increase in liquid milk supplies, provided that the national butterfat base has been exceeded. In a concurrent study (Keady and Mayne, 1998) inclusion of fish oil in the diet of lactating dairy cows depressed butterfat content by up to 15 g/kg, consequently increasing the volume of milk which may be supplied in a quota situation by 0.27. The aim of the present study was to examine if the effects of fish oil inclusion on milk fat content were mediated via changes in rumen fermentation parameters.

Oil in fat-filled milk powders is the major source of energy in calf milk replacers. Choice of oil source is determined by nutritive value (chiefly digestibility), functionality (avoidance of breaking the emulsion) and, increasingly, customer preference for oils of purely vegetable origin. One alternative to the use of traditional oil sources such as lard and fish oil, is coconut oil, which is rich in highly digestible medium-chain length fatty acids (particularly C12:0), but relatively deficient in essential long-chain polyunsaturated fatty acids such as linolenic acid. The objective of this experiment was to compare the effects on calf performance of oil source within milk replacers.