Rates of rumen fermentation in relation to ammonia concentration

Abstract

1. Four sheep were fed from automatic continuous feeders on whole barley fortified with graded levels of a urea solution. This approach was to a large extent successful in maintaining relatively steady states of rumen ammonia concentration.2. Rates of barley fermentation in the rumen at various rumen NHI concentrations were assessed by measuring the disappearance of barley dry matter from polyester bags suspended in the rumen of these sheep.3. The minimal NH:, concentration for maximal rate of fermentation was estimated as 235 mg/l rumen fluid.The optimal ammonia concentration of rumen fluid may be defined as that which results either in the maximum rate of fermentation in the rumen or that which allows the maximum production of microbial protein per unit of substrate fermented. The two definitions may not always coincide; for instance Orskov, Fraser & McDonald (1972) showed with a barley feed that the microbial protein produced per unit of substrate fermented was not altered as a result of urea supplementation while the extent of rumen fermentation and digestibility was increased.The rate at which rumen fermentation proceeds has a great influence on both total and digestible feed intakes (Balch & Campling, 1962) and therefore feed intake may be reduced if NH, concentration is limiting the rate of fermentation.Diurnal variation in all constituents of rumen fluid, generally associated with the time of feeding, make it difficult to estimate optimal rumen NH, concentration. A steady state of rumen fermentation can be achieved by continuous feeding. Although urea can also be infused continuously, its absorption into grains (Orskov, Smart & Mehrez, 1974) offers another simple method for stabilizing rumen NH, concentration.The use of the 'polyester bag' technique (Mehrez & IZIrskov, 1977) enabled us to determine rapidly and accurately the rate of substrate fermentation in the rumen.This present experiment was carried out to investigate the relationship between rumen NH, concentration and rate of fermentation.

Kikuyu (Pennisetum clandestinum) pasture for sheep. 2. Production and nutritional status of ewes with or without lupin (Lupinus albus) supplementation

“…A low energy content will also limit the utilisation of non-protein nitrogen (NPN) in the rumen for providing microbial protein (MP) to the animal (Satter & Roffler 1977), resulting in an accumulation of ammonia in the rumen (Leng 1990). On the other hand, sufficient protein is essential to provide ammonia-nitrogen (NH3-N) for normal microbial growth (Satter & Slyter 1974) and optimal rumen fermentation (Mehrez et al 1977). In the case of low NH3-N concentration, both MP production and intake may be reduced.…”

Degradabilidade in Situ da Matéria Seca e Proteína Bruta das Silagens de Seis Genótipos de Sorgo (Sorghum bicolor (L.) Moench) em Diferentes Estádios de Maturação

“…Entretanto, estes valores estariam sempre aquém daqueles considerados ótimos (23,5 mg/100 mL) por Mehrez et al (1977) em vacas de alta produção, para se atingir o máximo em fermentação microbiana.…”

“…Esses parâmetros cinéticos são importantes porque eles não só descrevem a digestão, mas também caracterizam as propriedades intrínsecas dos alimentos que limitam sua disponibilidade aos ruminantes (Mertens, 1993). De acordo com Mehrez et al (1977), os modelos semi-logarítmicos ou exponenciais são apropriados para o estudo da degradação das forrageiras. Orskov & McDonald (1979) sugeriram um modelo exponencial para auxiliar no estudo da degradação de forrageiras no rúmen e uma equação baseada no princípio de redução do material durante a incubação, no estudo da degradação em função do tempo de incubação no rúmen.…”

CHANGES IN AMMONIA CONCENTRATION, BACTERIAL COUNTS, pH AND VOLATILE FATTY ACID CONCENTRATION IN RUMEN OF COWS FED ALFALFA HAY OR CONCENTRATE: UREA-CORN SILAGE

“…The evidence indicated that there was a metabolic adaptation in the rumen for better utilization of ammonia. Concentrations of amino acids and peptides were nearly 1 mM in the rumen fluid throughout the day and increased to 3 Roffler and Satter (1975a,b) did not always correctly predict lactation response in cattle fed urea or ammonlatreated corn silage (Huber 1975 (Mehrez et al 1977) is higher than the 5 mg/tOO mL suggested by Satter and Slyter (1914 …”