SUMMARYThe artificial fibre bag technique was evaluated for assessing the proportions of dietary D. M. and N which disappear in the rumen. The most important factor determining the variability in disappearance from bags incubated together was the sample size in relation to bag size. For incubation of 5 g air dry feed, a bag size of 17 ✗ 9 cm was found to be adequate. There were also variations in substrate disappearance between animals and between days of incubation. It was estimated that three sheep and the measurement of substrate disappearance twice were necessary in order to obtain acceptable repeatability.The technique was found to be satisfactory as a simple and rapid guide for measuring nutrients disappearance in the rumen such as protein degradation and carbohydrate fermentation. It has been used in subsequent work to measure the effect of features of the rumen environment, such as pH and NH3 concentration, on rate of fermentation.
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.
Fourty growing APRI male rabbits at the age of 5 weeks old were used to investigate the impact of partial replacement of concentrate feed mixture (CFM) CP by different levels of hydroponic barley (HB) on rabbits performance, digestibility, feeding value, some blood constituents and caecum microbial count. The changes in chemical composition of HB during 6, 7 and 8 days of growth period was also studied. Rabbits were randomly divided into four experimental groups (10 rabbits in each) and were housed in individual cages provided with continuous feeders and automatic water nipples during the experimental period (5-12 week of age). The first group was fed pelleted CFM diet with 16% CP (control, D1), while the 2 nd , 3 rd and 4 th groups were fed the control diet but 20, 40 and 60% of CP was replaced by HB (D2, D3 and D4, respectively) in a feeding trial which lasted for 7 weeks. At the end of the feeding trial, four digestibility trials were carried out on three rabbits of each treatment. Animals were fed the same tested diet as that in feeding trial. Three rabbits of each treatment were slaughtered at the end of digestibility trials. The main results generally showed that there was a tendency for gradual decreases in DM and NFE content, but increases in Ash, EE, CP and CF content by advancing age of sprouting. Rabbits fed D2 recorded the highest significantly (P < 0.05) values of digestion coefficients of CP and CF, while the lowest significantly (P < 0.05) values were recorded with rabbits fed D4 diet. There were positive significant (P<0.05) effect of feeding HB at levels of 20 and 40 % on concentrations of blood total protein, albumin and glucose. Rabbits fed HB diets (D2, D3 and D4) had significantly (P < 0.05) higher total viable count of bacteria in caecum compared with those fed the control diet without HB (D1). It may be concluded that replacing of HB at the rate of 20 or 40 % of CFM protein in growing rabbit diets had beneficial effects on most criteria studied. Higher level (60% of HB) used herein in rabbit diets is not recommended since it negatively affected nutrients digestibility and feeding values of tested diets.
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