School of Biosciences

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Phil Garnsworthy

Emeritus Professor of Dairy Science,



Note that Phil is an Emeritus Professor, so does not take on new PhD students.

Expertise Summary

Phil's research encompasses all aspect of dairy science with particular emphasis on nutrition.

Recent research projects include:

Feed efficiency and sustainability of dairy systems

Variation in methane emissions by individual dairy cows measured on-farm

Nutritive value of co-products from the bioethanol industry

Rumen function in relation to the microbiome, the cow genome, and digestive efficiency

Manipulation of milk fatty acid profile by nutrition and genetics

Nutritional strategies for enhancing dairy cow fertility

Research Summary

Phil's main area of interest lies in the nutrition of dairy cows and how to maximise efficiency of feed utilization for milk production without compromising reproductive performance, thereby… read more

Recent Publications

Current Research

Phil's main area of interest lies in the nutrition of dairy cows and how to maximise efficiency of feed utilization for milk production without compromising reproductive performance, thereby minimising environmental impact.

Current projects focus on Whole Farm Feed Efficiency and reducing the Carbon Footprint of Dairy Farms.

Phil led a Research Partnership funded by AHDB, the UK dairy industry body, investigating Animal Health, Welfare and Nutrition. Partners in the project were the Nottingham Vet School, Harper Adams University College, RVC, Bristol University, SAC and IBERS.

Phil has presented invited keynote papers at international conferences in more than 30 countries and regularly gives talks to advisors and farmers about the findings of his research.

Past Research

Methane and ammonia emissions

Phil developed a model to calculate the impact of dairy systems on environmental emissions, which is based on nutritional and physiological principles, rather than standard values per animal. The primary driver of total emissions at the herd or national level is the number of animals per unit of output. This is heavily influenced by fertility and the model shows that if fertility of UK cows was improved to the level achieved by the best herds, national methane and ammonia emissions would be reduced by approximately 20%.

In 2007 Phil and his team developed a novel method for measuring methane emissions by individual dairy cows during milking. This involves sampling the breath of cows and recording how often they belch. With funding from Defra, the method was calibrated against daily methane output by cows in respiration chambers. The method is currently being used to assess variability among thousands of cows on commercial dairy farms to inform the national greenhouse gas inventory.

Phil was a partner in the 7.7m Euro EU FP7 project RuminOmics, which connected the animal genome, gastrointestinal microbiomes and nutrition to improve digestion efficiency and the environmental impacts of ruminant livestock production. The main finding was a core rumen microbiome that is heritable and related to methane emissions and feed efficiency.

Body condition score in dairy cows

Interest in body condition score of dairy cows started when Phil was registered for a PhD at Aberdeen University. Whilst studying voluntary food intake, he tried to explain why dairy cows have a delay between peak milk yield and maximum appetite. At that time, advisers recommended calving cows with a condition score of 3.5 to allow them to "milk off their backs". In two experiments, he demonstrated that body fat inhibits food intake so the delay was actually caused by management practices. Thin cows (condition score 2 at calving) had greater appetites and produced milk directly from food, which is more efficient. Maximum appetite of thin cows coincided with peak milk yield. In later experiments at Nottingham Phil showed that body fat mobilisation is dependent not only on the degree of fatness, but also on dietary protein and energy concentrations. As a result of this series of experiments, recommended condition scores at calving have been reduced. The work has been replicated and inspired novel research and updated recommendations throughout the world.

Milk composition

Phil has conducted several large studies on nutritional and genetic factors influencing milk fatty acid composition. The primary aim is to improve the fatty acid profile of milk by reducing the proportion of saturated fatty acids and increasing proportions of monounsaturated and polyunsaturated fatty acids. Of particular interest is conjugated linoleic acids (CLA), which potentially have tremendous health benefits for humans. They are anticarcinogenic, anti-diabetic and anti-atherogenic; they alter nutrient partitioning away from body fat and improve the immune system. A major source of CLA is cow's milk. Phil led studies looking at seasonal variation in the CLA content of milk and mechanisms by which CLA is produced by cows in the rumen and mammary gland. This work showed that 80% of CLA is synthesised in the mammary gland via the desaturase enzyme system. In a study of 10,000 cows, it was shown that desaturase activity has a heritability of 30%, so there are opportunities to breed cows for healthier milk.

Food intake prediction

The main limitation to milk production by dairy cows is food intake. Phil investigated the use of alkanes for measuring food intake of cows fed under group conditions. Alkanes are inert waxes found naturally in plants and have been used for predicting intake in grazing sheep. Phil developed the technique for cows fed on silage so that intake can be predicted from a sample of faeces from representative cows. Subsequently, he found that near-infrared spectroscopy can also provide accurate measurements of food intake from faecal samples.

Rumen synchrony

Studies of rumen fermentation have concentrated on synchronising the supply of energy and nitrogen to rumen microbes. A computer model was developed that predicted the hourly supply of nutrients from degradation characteristics of feed ingredients. In sheep, synchronising energy and nitrogen supply leads to significant increases in microbial efficiency of nitrogen capture. The work was extended to lactating dairy cows, but it was found that these animals have various strategies for overcoming the effects of asynchronous diets. Diet selection and control of meal size and feeding pattern are two strategies. Recycling of nitrogen in the rumen is doubled with asynchronous diets and the rumen microbes increase their storage of polysaccharides.


In collaboration with Bob Webb at Nottingham, the Roslin Institute and SAC Aberdeen, Phil demonstrated that nutrition has major influences on fertility in dairy cows and beef heifers. Diets designed to increase blood insulin concentrations led to earlier resumption of cyclic activity and improved conception rates in postpartum dairy cows. However, although pregnancy rates are increased by a high-insulin diet, very high concentrations of insulin may be detrimental to embryo development. The project also investigated effects of individual dietary components on plasma insulin in dairy cows, in order to develop models to predict the implications of different feeding strategies for reproduction. Using this information, dietary strategies were designed to alter blood insulin at critical stages of the reproductive cycle resulting in significant improvements in pregnancy rate.

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