Some observations on the digestibility of food by sheep, and on related problems

Abstract

When, in nutritional studies, it is necessary to determine the losses of a particular nutrient in the faeces, two techniques are employed to ensure that the faeces collected are representative of the intake of food. The first consists of feeding a marker substance, such as carmine, immediately before and at the end of the experiment. This allows a separation of the faeces produced from the food given in the interval, and is the technique employed with non-ruminant species.With ruminants, however, the use of markers does not result in a clear separation of the faeces marking the beginning and end of the period. Consequently, the method employed to obtain accurate digestion coefficients with ruminants is to give the experimental ration in exact quantities for long periods, in order to ensure that a 'steady state' of faecal excretion is reached, and then to collect the faeces excreted during a measured interval of time. If refusal of food occurs on a particular day, the method is invalid, and so the amount of food given is usually kept small to avoid refusal. The low planes of nutrition which are thus employed are not desirable if results are to be applied in practical feeding (Schneider, 1954). Nor can the method be used where intake is voluntary or uncontrolled, because the faeces produced during a particular 24 h period are not simply referable to the food intake in some previous 24 h period.In the course of experiments designed to study the effect of methods of fodder preparation and nutritional plane on the energy metabolism of sheep, information was obtained on the passage of food through the digestive tract, its digestibility, and the diurnal variation in the amounts of dry matter and water excreted. This information is presented here, and the results have been examined in some detail in order to elucidate the problems involved in the determination of digestibility coefficients in ruminants. It has been found that the time relationships involved in the passage of food through the gut give rise to equations which allow the prediction of the errors of digestibility coefficients, the digestibility coefficients themselves and the diurnal pattern of faeces excretion. They also permit the estimation of the gut contents or 'fill' of the animal under a variety of feeding systems and show what precautions must be taken in the conduct of digestibility trials. EXPERIMENTAL Animals and technique for studying digestibilityThe six wether sheep used as experimental animals were harnessed for the separate collection of faeces and were housed in individual cages. Each sheep was given 600,

Diurnal Changes in the Concentrations of Micro-organisms in the Rumens of Sheep Fed Limited Diets Once Daily: WITH AN APPENDIX ON THE KINETICS OF RUMEN MICROBES AND FLOW

“…Previous studies of the kinetics of feed particles in the rumen (Blaxter, Graham & Wainman, 1956;Brandt & Thacker, 1958;Garner, 1964) have made the basic assumption of steady-state flow, i.e. it has been assumed that movements of water into and out of the rumen were constant and equal, so that the volume remained constant.…”

Effect of dietary molasses on the site and extent of digestion of nutrients in sheep fed broiler litter

“…Although the DM concentration of the faeces was significantly lower for the 15% molasses treatment than for the other two treatments, this was probably not caused by a laxative effect of the molasses. Blaxter et al (1956) observed differences in faecal DM concentration when the rate of passage of diets through the digestive tract differed. They concluded that a high rate of passage of digesta through the colon limits the time available for water absorption from the digesta.…”

Degradabilidade ruminal da cama de frango e do feno de capim coast-cross e avaliação de modelos matemáticos para estimativa da taxa de passagem de partículas

“…Os resultados sugerem que o modelo biexponencial Grovum-Williams, amplamente utilizado na literatura, se mostrou inapropriado para descrever a cinética de passagem das partículas pelo trato digestivo, o que pode ser atribuído à lenta ascensão na concentração de indicador nas fezes observada em quase todos os animais estudados (Figura 2), não obedecendo ao OLIVEIRA et al padrão teórico da curva de observações descrito por BLAXTER et al (1956) taram comportamento parecido quanto aos desvios padronizados. Pode-se observar que ambos superestimaram ou subestimaram algumas seções da distribuição residual, não apresentando boa aderência aos dados observados.…”

“…A curva de excreção do marcador é, então, ajustada a um modelo matemático para determinar os coeficientes relacionados à passagem das partículas. BLAXTER et al (1956) foram os primeiros a demonstrar que a curva de excreção fecal do marcador pode ser descrita matematicamente como a soma de dois componentes exponenciais e um tempo de atraso no processo de remoção. Ainda de acordo com esses autores, o turnover mais rápido (>k ou k 1 ) representa a saída das partículas do rúmen e o mais lento (<k ou k 2 ), o tempo gasto para as partículas deixarem o abomaso e aparecerem nas fezes, e a constante τ, o tempo de atraso.…”