What is a digestibility trial or test on an animal?

Answer 1

In the 5th edition of 'Animal Nutrition' by McDonald et al (1995), there is a chapter on the evaluation of food digestibility which includes a description of a digestibility trial. On page 222 of Chapter 10 from 'Animal Nutrition' states: "In a digestibility trial, the food under investigation is given to the animal in known amounts and the output of faeces measured. More than one animal is used, firstly because animals, even when of the same species, and and sex, differ slightly in their digestive ability, and secondly because replication allows more opportunity for detecting errors of measurement" The book goes on to explain that in most cases when conducting digestibility trials on mammals, it is best to use males as it is easier to collect the faeces and urine separately from male animals. Special apparatus is required to collect separate urine and faeces from female animals. Animals used in the trial should be healthy and docile to ensure an accurate measure of digestibility of a healthy animal that is not in work is aquired. Small animals may be placed in metabolism cages which separate urine and faeces by an arrangement of sieves (many examples of these can be found by doing an image search for "metabolism cage"). Larger animals, such as cattle or horses, are fitted with harness and faeces collection bags made of an impervious material, such as rubber (again, there are a number of pictorial examples of this on the internet. I found the best search term was: harness faeces collection bag). The food used in the trial should be thoroughly mixed beforehand to obtain a uniform composition. The food is given to the trial animals for at least a week before collection of faeces begins, in order to accustom the animals to the diet and to clear the gastrointestinal tract of residues from previous foods. This preliminary period is followed by a period when food intake and faecal output are recorded. This experimental period is usually 5 to 14 days long, with longer periods being desirable as they give greater accuracy. In all digestibility trials, and particularly those involving ruminants, it is highly desirable that meals should be given at the same time each day and that the amounts of food eaten should not vary from day to day. The trial is completed by analysing samples of the food used and the faeces collected. This information was largely obtained from the following refernces: P. McDonald, R. A. Edwards, J. F. D. Greenhalgh, C. A. Morgan (1995), Animal Nutrition,5th edition, Longman Singapore Publishers (Pte) Ltd.