H. Tagari

Solubility and net exchange of calcium, magnesium and phosphorus in digesta flowing along the gut of the sheep

1. The changes in the solubility of calcium, magnesium and phosphorus in digesta flowing along the intestinal tract and the net movement across the intestinal wall of these elements were determined in six rams, each equipped with three T-shaped cannulas; cannulas were placed in a total of six different sites of the small intestine. Cr2O3 was used as a marker substance to measure the rate of flow of the digesta. 2. The concentrations of soluble Ca, Mg and P decreased as digesta moved along the intestine. TheMgreatest fall in soluble Ca occurred after the first 3 m of the intestine, while a significant decrease in soluble Mg was found only at 15 and 25 m from the pylorus. The concentration of soluble P in digesta decreased until the 7 m site and then remained stable. In the faeces, the level of soluble Mg was approximately 4 times higher than, and that of Ca equal to, the levels of Mg and Ca found in digesta flowing through the upper intestine. Unlike Ca and Mg, a very low concentration of soluble P was found in the faeces. 3. In the duodenum, 84, 78 and 62% of the total Ca, Mg and P respectively were soluble, whereas in the digesta flowing through the terminal ileum the corresponding values were 3-2, 7-2 and 19% for Ca, Mg and P respectively. 4. The forestomachs and the colon were found to be the main sites of g net absorption; 1-12 mmol/h was apparently absorbed from the stomach and 1-05 mmol/h from the colon. The supper small intestine (1-3 m from the pylorus) appeared to be the major site of Ca and P absorption. 5. In the last 10 m of the small intestine, considerable amounts of minerals were secreted; 4-70, 0-96 and 1-85 mmol Ca, Mg and P/h respectively were added to the digesta flowing between 15 and 25 m from the pylorus. The effect of the increase in the pH of digesta along the small intestine on the solubility of these minerals is discussed.

The influence of heating on the nutritive value of soya-bean meal for ruminants

I t has been generally assumed that the nutritive value of protein feeds for ruminant animals is not influenced by the chemical and physical properties of the proteins. Several recent investigations have shown that proteins with a high solubility are degraded in the rumen to ammonia at a rate too rapid for efficient utilization. The rumen micro-organisms can then utilize only a relatively small part of the liberated ammonia for synthetic purposes. Excess ammonia diffuses into the blood and is converted in the liver into urea, and most of this urea is excreted in the urine, only a small amount being returned to the rumen through the saliva. Evidence was given by El-Shazly (1958) and Jasiorowski (1960) that the protein in green forages and hays is utilized to a greater extent when it is of low solubility, highly soluble proteins from similar feeds being utilized to a lesser degree. The beneficial effect of reducing the solubility of protein in concentrates by heating was first recognized by Chalmers, Cutherbertson & Synge (1954) and Chalmers & Synge (1954), and confirmed by Whitelaw, Preston & Dawson (1961) who found considerable advantage in the use of heat-treated groundnut meal in comparison with untreated groundnut meal. I t is well known that the full utilization of soya-bean meal for poultry feeding is obtained only by proper heating. The causes generally recognized as responsible for the improvement of soya-bean meal by heat treatment are irrelevant for ruminants. Since the solubility of protein of soya-bean meal decreases considerably on heating, we compared the utilization by ruminants of protein of soya-bean meals subjected to different heat treatments. Preliminary experiments carried out in a miniature artificial rumen showed a very significant decrease in the amount of ammonia liberated from heated soya-bean meal in comparison with the untreated soya-bean meal. These results led us to examine the utilization by sheep of three different kinds of soya-bean meal, the rate of liberation of ammonia in the rumen, changes in blood-urea concentration and nitrogen balance being used for assessing their value.

Protein digestion in the intestine of sheep

1. The rate of flow of digesta along the intestinal tract, and particularly the changes occurring in proteins during their passage through the intestine were determined in six rams; each animal was fistulated with three cannulas which involved six different sites of the intestine. Cr 2 O 3 was used as a marker substance to measure the rate of flow of the digesta. 2. In the sections of the intestine from 1 to 15 m posterior to the pylorus the amounts of water, dry matter and total nitrogen decreased gradually as a result of their absorption through the intestinal wall. The region of the intestine situated at a distance of 7–15 m from the pylorus was more active with respect to the absorption of N, whereas water and dry matter were adsorbed to a greater extent in the region from 1 to 7 m from the pylorus. 3. The only part of the intestine in which substantial increases of water, dry matter and total N were found was the section immediately distal to the pylorus, and these increases were caused by the inflow of bile, and pancreatic and duodenal juices. The net increase found beyond the entry of the common bile duct was 2.7 g protein N and 2.0 g non-protein N (NPN)/24 h. 4. The activities of trypsin, chymotrypsin and carboxypeptidase A and the ratio α-NH 2 NPN: protein N increased from the pylorus up to a distance of 7 m and decreased again from this point to a distance of 15 m from the pylorus. 5. In the sections of the intestine between 1 and 3 and between 3 and 7 m distant from the pylorus the extent of proteolysis exceeded considerably that of absorption of amino acids through the intestinal wall. This was concluded from the decrease in the rate of flow of protein amino acids (by 31% between 1 and 3 m distant from the pylorus and by 34% between 3 and 7 m) and the simultaneous increase in non-protein amino acids (by 20% in the region between 1 and 3 m) or no change in non-protein amino acids (between 3 and 7 m). 6. The relatively greater decrease in non-protein amino acids (by 57%) compared with that of protein amino acids (by 41%) occurring in the section 7 to 15 m distant from the pylorus showed that this is an area of most intensive absorption of amino acids. 7. In the lower section of the intestine, from 15 to 25 m distant from the pylorus, the total amount of amino acids showed almost no change; probably a net effect of loss and gain of amino acids mainly due to microbial activities. Increases in the dehydrogenase activity suggested enhancement of bacterial activity in this lower region of the intestine. 8. The supply of essential amino acids to the tissues of sheep is improved, compared with the amino acid composition of the diet, as the result of ruminal biosynthesis of essential amino acids and ruminal degradation of non-essential amino acids and preferential absorption of essential amino acids through the intestinal wall, particularly in the section of most intensive absorption, 7–15 m distant from the pylorus.

Comparison of rate of passage, fermentation rate and efficiency of digestion of high fiber diet in desert Bedouin goats compared to Swiss Saanen Goats

Fermentation and passage rate in the rumen and along the entire gut were measured in black Bedouin and Swiss Saanen goats fed a high fiber diet (Rhodes grass (Chloris guyana) supplemented with 10% alfalfa hay). The purpose of the study was to clarify the physiological basis that underlies advantages of Bedouin goats over non-desert goats in digesting high fiber based diets. Volume of fluid and rumen digesta particle distribution were similar for both breeds. Ability of Bedouin goats to consume amounts of hay equal to those consumed by Saanen goats, despite considerably longer retention time in the rumen, was related to their ability to maintain a higher digestion rate in the rumen. Microbial activity in the particulate fraction was higher in Bedouin goats than in Saanen goats, and this was reflected in total rumen fermentation, i.e., in significantly higher volatile fatty acid production rate and significantly higher volatile fatty acid concentrations. The ability of Bedouin goats to maintain a high fermentation rate in the rumen may be partially related to their ability to control rumen pH above levels which cause severe depression in rate of fermentation. The combination of higher fermentation rate and slower passage allows maximization of feed intake and digestibility in a given situation, as compared to non-desert ruminants.

Gross energy digestion and urea recycling in the desert black Bedouin goat

Abstract 1. 1. Gross energy digestion and urea recycling were measured in Bedouin goats inhabiting extreme deserts in the Middle East and compared to Swiss Saanen goats. 2. 2. The apparent gross energy digestibility of alfalfa hay and wheat straw in the black Bedouin goat were 6% and 33% respectively higher than in the Swiss goat. 3. 3. When the amount of alfalfa hay fed was restricted to about 60–70% of the ad lib consumption, recycling of urea in the Bedouin goats was maintained at rates (0.44g·N-urea [kg·day] −1 ) similar to those recorded when alfalfa hay was fed ad lib . In the Swiss goats a 30% drop was recorded. 4. 4. When wheat straw was the only feed, the amount of urea recycled by the Bedouin goats (0.18 g·Nurea [kg·day] −1 ) was more than twice the amount recycled by the Swiss goats. 5. 5. Supplementing the wheat straw to provide both breeds with equal amounts of digestible energy and nitrogen intake resulted in an increase in the amount of urea recycled in both breeds. The Bedouin goat, however, still recycled twice as much urea (0.3 g·N-urea [kg·day] −1 ) as the amount recycled by the Swiss goats. 6. 6. It was concluded that under adverse nutritional conditions the Bedouin goat possesses high potentials to both meet its caloric demands as well as to economise its nitrogen metabolism and the two characteristics are complementary to each other.

Comparison of the efficiency of proteins contained in lucerne hay and soya-bean meal for sheep

I . In four feeding experiments with sheep the utilization of proteins contained in lucerne hay and of those in toasted soya-bean meal (SBM), representing a roughage and concentrate feed respectively, were examined. The ration of one group of animals contained lucerne hay as sole source of digestible protein and that of the other SBM. 2. Measurements of the nitrogen balance showed clearly the superiority of lucerne hay as protein source compared with soya-bean meal; this arose from the greater N retention found with the lucerne hay ration. 3. The influence of both rations on the metabolic pathways of the proteins was examined by following the changes of concentration of various metabolites in the rumen contents and of blood urea at different intervals after feeding. 4. Concentrations of urea found in the blood of the sheep given lucerne hay were lower than those of the other group, a finding which is in agreement with the results of the balance experiments. 5 . The concentrations of NH,-Nandof aminoacidsin the rumen liquor were higher in sheep given lucerne hay than in those given SBM. These concentrations appeared to be related to the differences between the soluble non-protein N contents of the two feeds. 6 . The results agree with the finding from in vitro experiments that rumen liquor from sheep receiving lucerne hay promoted greater synthesis of protein than rumen liquor from sheep receiving SBM. 7. Total bacterial activity as measured by the reduction of triphenyltetrazolium chloride (dehydrogenase activity) was much higher in the rumen liquor of sheep given lucerne hay than when SBM was given. 8. The concentrations of volatile fatty acids (C,-C,) were much higher in the rumen liquor in sheep on the lucerne hay diet than in those on the SBM diet. After meals of the lucerne hay diet, the concentrations of acids higher than Cz, particularly those of valeric acid, exceeded those present in the rumen liquor of the animals kept on the SBM diet. 9. Proline and alanine appeared in relatively higher concentrations in the rumen liquor than the other amino acids determined, and these two acids together with valine disappeared very rapidly. The possible conversion of these amino acids into valeric acid is considered. It is suggested that valeric acid found in relatively high concentrations in rumen liquor of sheep given lucerne hay may be due in part to the deamination of proline, which likewise disappeared very rapidly together with alanine and valine.

Mammary Uptake, Portal-Drained Visceral Flux, and Hepatic Metabolism of Free and Peptide-Bound Amino Acids in Cows Fed Steam-Flaked or Dry-Rolled Sorghum Grain Diets

Our objectives were to measure net fluxes of free AA (FAA) and peptide-bound AA (PBAA) across portal-drained viscera, liver, splanchnic tissues, and mammary tissues, and milk AA output of lactating Holstein cows (n = 8, 86 +/- 8 d in milk). Cows were fed an alfalfa-based total mixed ration containing 40% steam-flaked (SFS) or dry-rolled (DRS) sorghum grain. The total mixed rations were offered at 12-h intervals in a crossover design. Blood samples were obtained from indwelling catheters in portal, hepatic, and mammary veins and from mesenteric or costoabdominal arteries every 2 h from each cow and diet. Intake of dry matter was 17.9 and 18.6 kg/d of the SFS and DRS diets, respectively, but dropped to 16.3 kg/d for cows fed the SFS diet in the last 3 experimental days, sampling day included. Milk and milk crude protein yields (kg/12-h sampling) were 13.85 vs. 13.25 and 0.425 vs. 0.396 for cows fed SFS or DRS, respectively, and were not affected by the considerable drop in dry matter intake of cows fed the SFS diet during the last 3 experimental days. The portal-drained visceral flux of total essential FAA was 417 and 442 g/12 h (SEM 63) in cows fed SFS and DRS, respectively. However, the portal-drained visceral flux of 7 essential PBAA out of the 9 determined was numerically greater in cows fed the SFS diet, and total essential PBAA in that treatment was 77.4 +/- 22.2 compared with 35.4 +/- 50.2 g/12 h for cows fed the DRS diet. This phenomenon was again observed in a greater total splanchnic flux (FAA + PBAA) of 462 and 371 g/12 h in SFS- and DRS-fed cows, respectively. Mammary uptake of essential AA from both pools (free and peptide bound), and recovery of essential AA in milk, was again numerically higher in SFS-fed cows. In addition to FAA, quantifying the contribution of PBAA may improve our understanding of tissue use of AA substrates, and this may ultimately lead to improved diet formulations with respect to intestinal absorption and mammary uptake of AA.

A new approach to the quantitative estimation of nitrogen metabolic pathways in the rumen

Rumen nitrogen metabolism values were estimated by the use of a single injection of 15(NH4)2SO4 into the rumen of sheep and consecutive 15N enrichment measurements in the rumen ammonia pool, rumen non-NH3-N (NAN) pool, rumen purine pool and blood urea-N (BUN) pool for a period of 24 h. Synthesis and degradation of N compounds in the rumen and passage of N to and from the rumen were evaluated on a chemical rather than a microbial basis; microbial fractions were not separated. This model was examined in two experiments. In Expt 1 a ram (55 kg) was given a semi-synthetic diet (1067 g dry matter (DM), 22.8 g N) in which soya-bean meal provided over 90% of the N. In Expt 2, two rams (45 kg) were given in three consecutive periods a semi-synthetic basal diet containing: (1) roasted soya-bean meal (SBM, 725 g DM, 14.8 g N/d); or (2) fishmeal (FM, 728 g DM, 15.5 g N/d); or (3) raw soya-bean meal (RSBM, 724 g DM, 13.8 g N/d). In all these rations, the main protein source provided over 90% of the N. In Expt 1, 68.3% of N intake was degraded directly to NH3 in the rumen, 21.2% escaped rumen degradation and 10.5% was incorporated into stable N compounds in the rumen. Net NH3 transfer to the blood was 30.4%, NH3 flow from the rumen was 6.6% and rumen NAN output was 63% of N intake. In Expt 2, rumen NAN output was larger (7.67, 14.36 and 8.89 g N/d for diets containing SBM, FM and RSBM respectively; P less than 0.05) and net NH3 loss to the blood was smaller (6.1, 0.39 and 4.17 g N/d for diets SBM, FM and RSBM respectively; P less than 0.05) for diet FM as compared with the soya-bean diets. The percentage of rumen NAN that was synthesized from NH3 was larger for diet RSBM (36.4, 40.3 and 49.1 for diets SBM, FM and RSBM respectively; P less than 0.05) than for the other two rations. NH3 pool sizes (g N) were 0.463, 0.385 and 0.301 for diets SBM, FM and RSBM respectively (P less than 0.05), while their hourly turnover rates were 15.8, 26.1 and 5.12 for diets SBM, FM and RSBM respectively (P less than 0.01), indicating no correlation between pool size and its turnover rate.(ABSTRACT TRUNCATED AT 400 WORDS)

Assessment of duodenal amino acid profile in dairy cows by the in situ method

Abstract In situ evaluation of the duodenal amino acid (AA) profile was attempted in a 4 × 4 Latin square study using four lactating Holstein cows fitted with ruminal and duodenal cannulas. Dietary supplemental crude protein (CP) sources, making up 40% of the dietary CP, were: soybean meal, cottonseed meal, corn gluten meal or urea. Duodenal flow of organic matter (OM) and CP was determined in vivo by means of constant infusion of ytterbium and chromium, and predicted in situ from rumen degradation. Purines were used as microbial markers. In situ calculation of the AA profile, expressed as g AA in 100 g of total AAs, was based on the composition of AA in feed and in isolated bacteria as well as on in situ rumen degradation of OM and CP. The AA profile in the duodenum when assessed in vivo was affected by the nature of the supplemental protein; in situ assessment of the AA profile resulted in comparable profiles. The data are interpreted to suggest that the in situ method enables prediction of the profile of AA (g AA/100 g total AA) flowing to the duodenum, and that the undegraded portion of supplemented protein affects that profile.

Evaluation of protein flow to the duodenum in dairy cattle by the in sacco method

Abstract In situ evaluation of the amount and composition of duodenal crude protein flow was examined in a 4×4 Latin square study using four lactating Holstein cows fitted with ruminal and duodenal cannulas. Dietary supplemental CP sources, making up 40% of the dietary CP, were: soybean meal, cottonseed meal, corn gluten meal or urea. Duodenal flow of organic matter (OM) and CP was determined in vivo by means of constant infusion of Yb and Cr, and was predicted in situ from rumen degradation. Purines were used as microbial markers. The two methods of estimating ruminally undegraded protein ranked the diets similarly. Microbial CP (1.9 to 2.1 kg/d) was estimated to make up 57% to 68% of the duodenal CP flow in the experimental diets. Efficiency of microbial protein synthesis were 201 (SEM 16) g CP/kg OM truly digested in the rumen, and 224 (SEM 18) g CP/kg OM disappearing in the rumen. Data are interpreted to suggest that the in situ method enables a prediction of total protein flow to the duodenum which is comparable to that obtained using the in vivo method. The added practicality of the former method renders it advantageous.