I. Expt I . Five 150 kg steers with ruminal, abomasal and ileal cannulas were given 3000 g oaten chaff daily plus pelleted supplement with no added nitrogen (diet A) or 50 g N/d as urea (diet B), casein (diet C), casein and formaldehyde-treated casein (HCHO-casein) (50: 50 w/w; diet D) and HCHO-casein (diet E), in a 5 x 5 Latin square design. The basal diet and supplement were fed in eight equal increments at intervals of 3 h. Proportions of dry matter and organic matter digested in the stomach and whole tract were greater for diets B, C, D and E than for diet A. Total volatile fatty acid levels in the rumen and the proportion of acetic acid were lower, and the proportion of propionic acid higher on diet A than on the other diets. Rumen ammonia levels were lower on diets A, D and E than on diets B and C. N flows at the abomasum, ileum and rectum were lower on diet A than on the other diets; abomasal flows and apparent intestinal absorptions of amino acids were higher on diets D and E than on diets A, B and C. Efficiencies of bacterial protein synthesis were 15, 15, 14, 13 and IZ g bacterial N/kg OM truly digested in the stomach on diets A, B, C, D and E respectively. found that there was an increased flow of microbial protein from the stomach. These observations indicate that microbial growth in the rumen of animals eating a low protein diet may be restricted by the supply of peptides and amino acids, with a concomitant reduction in the rate of cellulose digestion in the rumen. Since the rate of digestion and retention time in the rumen are major determinants of the voluntary food intake of low quality roughages (Thornton & Minson, 1973) it is possible that their intake may be limited by the supply of peptides and free amino acids to rumen micro-organisms.We investigated this possiblity by supplying iso-nitrogenous amounts of urea, soluble protein (casein) or digestible by-pass protein (HCHO-casein) to steers fed oaten chaff. EXPERIMENTAL
Six Friesian heifers (c. 300 kg) fitted with cannulas were given diets of wheat straw sprayed with NaOH (4.4 % wlw) and essential minerals either with or without urea (3% w/w). The total protozoal numbers in the rumen fluid were not significantly different between dietary trcatments (mean 6.2 X 104/ml). However, there were more holotrichs and medium-size entodiniomorph protozoa in the rumen fluid of the cattle given the HU and LU diets than the Hand L diets. Protozoal counts in the omasal fluid were 44% of those in rumen fluid. The apparent digestibilities of OM and neutral-detergent fibre (NDF) in the stomach and in the total tract were lower with high than low feed intakes. The urea supplement enhanced the digestibilities of OM and NDF in the stomach and in the total tract. The total nitrogen (N) and non-ammonia N (NAN) flowing to the omasum and to the duodenum per unit of N intake were significantly greater with the low than the high feed intakes and with urea supplementation of the diets than without urea supplementation. The proportions of total microbial N and bacterial N in omasal NAN were higher with the supplement of urea than the unsupplemented straw. The bacterial N in the NAN flowing to the omasum was lower for the high than the low intakes. Concentrations of ammonia-N and total volatile fatty acids in rumen fluid were higher for the ureasupplemented straw than the unsupplemented straw. The high level of feed intake was associated with higher water volume and solid contents in the rumen.
An experiment was conducted with 60 male Friesian calves between 5 and 11 weeks of age. The experiment was a 5 x 2 x 2 factorial design. The five major treatments were the inclusion of 20 or 40 % ground wheat straw or 20, 40 or 60 % ground lucerne in a pelleted diet. A methane inhibitor was included in the diet given to 30 of the calves. The diets were given alone or with a chaffed wheat straw supplement ad libitum. All diets contained 2% sodium bicarbonate. The weight gain of the calves was greater with the diets containing ground lucerne than with those containing ground wheat straw, but in both cases weight gains were reduced with increasing roughage content of the diets. The efficiency of feed conversion showed a similar trend. The supplementation of the diets with chaffed wheat straw did not affect the performance of the calves. The inclusion of the methane inhibitor in the diets improved the weight gains and efficiency of feed conversion. The daily retention of nitrogen in the calves showed a similar trend to the growth rates. The molar percentage of acetate in the rumen increased as the roughage content of the diets increased while the proportions of propionate, butyrate and valerate decreased. The inclusion of the methane inhibitor in the diets decreased the concentration of total volatile fatty acids (VFA) in the rumen and increased the molar percentage of propionate, butyrate and valerate.
There are a number of individual components which can be added to make the total endogenous nitrogen flow. Corring (1975) found that pancreatic secretions amounted to 3-4 g N/d for the 45 kg pig or 11 7; of the dietary N intake. Horszczaruk et al. (1974) estimated from studies with isolated loops ofjejunum that the total endogenous N secretions in the intestines could be 1CL22 g/d.Zebrowska et al. (1975) fitted 50 kg pigs with re-entrant cannulas in the duodenum and ileum and estimated endogenous N secretion to be 5-7 g/d at the duodenum and 3 g/d at the ileum. However, subsequently Low & Zebrowska (1977) found that these values were influenced by the technique of digesta collection.The flow of N to the duodenum, jejunum, ileum and faeces in two pigs given a protein-free diet was measured by Wilson & Leibholz (1981 b), but more information is required on the flow of endogenous N in all parts of the digestive tract, and this was measured in the present experiment, both by regression analysis and by giving an N-free diet to young pigs.
1. Forty pigs between 23 and 51 d of age were given ad lib. diets containing wheat and one of five protein concentrates: meat meal A, meat meal B, soya-bean meal, milk and lupins (Lupinus augustifolius). Twenty of these pigs were given indigestible markers from 51 to 56 d of age and were killed at 56 d of age.2. The diets containing meat meals A and B, soya-bean meal and milk contained 2.3 g total methionine/kg and the diet containing lupins contained 2.1 g/kg.3. A further forty pigs of the same age were given the same diets supplemented with 1 g synthetic methionine/kg. 4. The weight gains and feed conversion ratios of the pigs given the diets containing 2.1-2.3 g methionine and 3.1-3.3 g methionine/kg were not significantly different.5. The weight gains of the pigs given lupins (2.1 g methionine/kg) were less than those of the pigs given the diets containing 2.3 g methionine/kg.6. The apparent digestibility of dry matter (DM) and nitrogen was less for the diets containing the meat meals (0.75 and 0.78 respectively) than for those containing the other protein concentrates (0.80 and 0.84).7. The retention times in the large intestine of the diets containing soya-bean meal and lupins were 965 and 1083 min which were greater than those of the diets containing the other protein concentrates, mean 732 min.8. The major site of N digestion and absorption for the diet containing milk was the area of the small intestine 25-50% of total length from the pylorus, while for the other protein concentrates the major site was 5&75% of its total length from the pylorus.9. The digestion and absorption of N in the large intestine was less (3.4%) for the diet containing milk than for those containing the other protein concentrates (7.5-1 1.3%).10. The apparent digestibility of the methionine to the ileum for the five diets ranged from 0.74 to 0.86 while the calculated retention of the apparently-absorbed methionine was 1.00. It was suggested that methionine digestibility could be used as an indicator of availability.11. The calculated retention of apparently absorbed N in the carcass was 0.71 for the pigs given the diet containing milk and 0.51-0.58 for the pigs given the other diets.
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