Digesta Flow Research Articles

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. Cr2O3 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-NH2 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.

Concurrent studies of the flow of digesta in the duodenum and of exocrine pancreatic secretion of calves. 2. The effects of addition of fat to skim milk and of 'severe' preheating treatment of spray-dried skim-milk powder.

1. The duodenal flow of digesta and the concurrent pancreatic secretion were compared when six Ayrshire calves, with duodenal re-entrant and pancreatic sac cannulas, were fed on three reconstituted milks. The diets were: reconstituted, ‘mildly’ preheated, spray-dried skim-milk powder (SK); the same skim milk containing 20 g fat/l (SKF); and reconstituted, ‘severely’ preheated skim-milk powder containing 20 g fat/l (HSKF). The calves were fed ad lib. from teats twice daily from 9 to 21 d of age, each diet being offered for 4 d. Collections of duodenal digesta and pancreatic secretions were made for 12 h after the fourth and eighth meals on each diet.2. The calves tended to have the highest liquid intakes when diet SK was given. After adjustment for differences in intake, diet SK resulted in the appearance of more hydrogen, chloride and potassium ions but less undigested protein nitrogen in the duodenal digesta than with either diet SKF or HSKF.3. Compared with diets SK and SKF, the whey fluids from diet HSKF took significantly longer to leave the abomasum, less H+ passed through the duodenum during the first 6 h after feeding and less Cl− during the whole postprandial period. More undigested protein N and fat from diet HSKF passed through the duodenum during the first 6 h after feeding, although this difference was significant only for protein N during the 1st hour after feeding.4. Over the 12 h postprandial period, the duodenal digesta contained almost exactly the same quantities of polyethylene glycol (PEG), N and fat as those in the meal. The total volume of digesta was 2.25 l greater than the quantity of milk ingested. When the hourly duodenal flows of PEG and fluid were expressed as the square root of the hourly quantities recovered, the pattern of abomasal emptying was rectilinear. The flows of N and fat were curvilinear, when expressed on the same basis.5. The concentration of ‘sodium-free’chloride in the duodenal digesta, in excess of that ingested in the milk, was used as an indicator of the quantity of acid secreted by the abomasum. The relative quantity of acid secreted was greatest with diet SK and least with diet HSKF.6. The pancreatic secretion of fluid was highest during the period 5–9 h after feeding but the secretion of enzyme activity was highest during the first 2 h after feeding.7. Considerable variability in the secretion of enzyme activity was observed and the rate of secretion did not appear to be related to any component of the duodenal digesta.8. Diet SKF was associated with a greater volume of pancreatic secretion and more pancreatic protease secretion than either diet SK or HSKF, but most amylase activity was secreted when diet HSKF was given. Evidence is presented which suggests that pancreatic enzyme activity adaptation occurred when diet HSKF was offered in succession to diet SK or SKF. The secretion of trypsin activity did not differ between diets.

Factors limiting the intake of feed by sheep. VIII.* The roughage requirement of the ruminant lamb fed on concentrate diets based on wheat

The voluntary feed consumption (VFC) and body weight gain of lambs initially 12 weeks old and weighing 22 kg were measured when diets based on whole wheat grain and varying in straw content were offered. The basal diet comprised, on an organic matter (OM) basis, about 82 parts whole wheat grain and 18 parts protein concentrate; ground wheaten straw was added to provide diets with 2%, 7% or 13% straw. Daily VFC, expressed in relation to body weight in kg0.75 (BW0.75), increased from 85.6 with 2% straw through 90.4 with 7% straw to 94.2 with 13% straw. The corresponding OM digesti bilities were calculated to range from 84.8 to 77.6%. However, the intake of digestible OM and the rate of body weight gain were not affected by the straw content of the diet, the respective mean values for all lambs being 73g/day BW0.75 and 293 g/day. Lambs initially 25 weeks old and weighing 38 kg were offered a diet (2% straw) based on wheat in which the wheat was presented either as whole grains or in ground and pelleted form. With the whole grain diet the daily rates of OM intake, digestible OM intake and body weight gain were 75.6 g/ BW0.75, 64.7 and 254 g respectively; the corresponding values with the ground grain diet were about 20% lower. Studies involving the slaughter of animals showed that a large proportion of the wheat grain consumed reached the rumen in the form of whole grains and these contributed significantly to the dry matter of the ruminal digesta. The rate of ruminal digestion of whole wheat grains was slow (37% in 96 hr) when the sheep were given a diet based on wheat. By contrast, when a roughage diet was consumed the rate was high (81% in 96 hr). Fractured grain was rapidly digested in the rumen (67% in 20 hr). The mean residence time of water-soluble marker in the rumen and the rate of digesta flow from the rumen were greater in fistulated sheep given a whole grain diet than with a ground grain diet. The diets also differed with respect to the concentration of potassium in rumen liquor, the rumen potassium pool size and the rate of flow of sodium and volatile fatty acids to the omasum. It was concluded that the roughage requirement of the ruminant lamb fed on concentrate diets based on whole wheat did not exceed the equivalent of 2 g ground straw per 100 g diet. The possibility of a higher roughage requirement with ground wheat diets is suggested. ___________________ *Part VII, Aust. J. Agric. Res., 24: 387 (1973).

The effect of frequency of feeding on the flow and composition of duodenal digesta in sheep given straw-based diets.

1. The effect of feeding sheep at two different frequencies (once hourly and once daily) on the flow of digesta, dry matter, and starch to the duodenum was assessed by fitting sheep with re-entrant cannulas in the proximal duodenum and giving them, at each feeding frequency, rations differing in the particle size of the roughage component.2. Frequent feeding resulted in a less variable daily pattern of flow of digesta and a significant increase (P < 0·01) in the total daily volume flowing to the duodenum. Altering the particle size of the ration did not affect the flow of digesta at either feeding frequency.3. The pattern of flow of dry matter followed very closely that of the flow of digesta, but there was a significant (P < 0·001) interaction between feeding frequency and particle size of the ration which affected the flow of starch to the duodenum. As a result, more starch entered the duodenum when both the frequency of feeding and the particle size of the ration were increased.

Concurrent studies on the flow of digesta in the duodenum and of exocrine pancreatic secretion of calves. The collection of the exocrine pancreatic secretion from a duodenal cannula.

1. Two surgical techniques were developed in the calf to study the role of pancreatic secretion in digestion. The secretion was collected through a cannula placed in a small sac of duodenum into which the pancreatic duct drained. The continuity of the duodenum was re-established in the first technique by duodenal re-entrant cannulas, and in the second technique by end-to-end anastomosis of the duodenum with a cannula placed cranial to the anastomosis to return the pancreatic secretion. The accessory pancreatic duct was ligated.2. The flows of digesta through the duodenum of milk-fed calves were 5505, 6369 and 7709 ml/12 h at 7, 24 and 63 d of age respectively, similar to values reported previously in the literature. In a 12 h collection period 297, 441 and 602 ml pancreatic fluid were secreted by calves of 7, 24 and 63 d of age respectively. The secretion from the mucosa of the duodenal sac was 40 ml/12 h in two other calves.3. The rate of secretion from the pancreas varied markedly in milk-fed calves, being lowest 2–3 h and highest 6–10 h after feeding. Changes in the concentration of chloride and bicarbonate with pancreatic secretion rate were indicative of a secretin stimulus to secretion.4. The rates of inactivation of pancreatic enzymes collected from the duodenal sac were measured at 4°, 20° and 39°.

Studies on the amount and composition of digesta flowing through the duodenum of dairy cows. 2. Sites of net absorption of magnesium and calcium from the alimentary tract.

Two cows were fitted with re-entrant duodenal cannulas, and four with T-piece duodenal annulas. Balance trials were carried out, the cows receiving either a winter ration, or freshly-mown herbage. Direct measurements were made of the flow of digesta, and of the amounts of Mg and Ca in both duodenal and faecal samples. Also indirect measurements were made of these parameters, using polyethylene glycol and chromium sesquioxide indicators. Net Ca absorption was restricted to the intestines, and, at high Mg intake, net Mg absorption was also largely intestinal, though too large an error attached to the indirect measurement of Mg absorption rates for reliable conclusions to be drawn. There was considerable secretion of Ca proximal to the duodenum. (Abstract retrieved from CAB Abstracts by CABI’s permission)

An assessment of chromic oxide as an indigestible marker for digestion studies in sheep

SUMMARYFistulated cross-bred sheep were given, by means of continuous feeders, concentrate diets containing chromic oxide (Cr2O3). Dry-matter digestibility coefficients predicted from the faecal concentration of Cr2O3 were compared with those obtained by total collection of faeces, and the concentration of Cr2O3 in spot samples of faeces taken at different times of day was compared with that in faeces bulked over an 8-day collection period. The rate of flow of digesta from the abomasum and the partition of digestion between the stomach and intestines, calculated from the concentration of Cr2O3 in samples of abomasal digesta, were compared with values obtained using two markers, one of which remained in solution while the other was adsorbed by particulate matter.Récovery of Cr2O3 in the faeces ranged from 91 to 101% and predicted dry-matter digestibilities were similar to those obtained by total collection. There was no diurnal variation but there was marked random variation in the concentration of Cr2O3 in spot samples of faeces. Cr2O3 was shown to behave independently of the particulate matter in digesta and, as a single marker, it significantly underestimated the flow of digesta from the abomasum relative to the double marker method. Cr2O3 thus overestimated digestion in the stomach and underestimated digestion in the intestines. It was concluded that Cr2O3 was not a satisfactory marker for studies of the flow of digesta and hence the partition of digestion within the gastro-intestinal tract when digesta samples are taken from a simple cannula.

The flow of digesta, dry matter and starch to the duodenum in sheep given rations containing straw of varying particle size.

The flow of digesta, dry matter and starch to the duodenum in sheep given rations containing straw of varying particle size.

Studies on the amount and composition of digesta flowing through the duodenum of dairy cows. 1. Rate of flow of digesta measured direct and estimated indirect by the indicator dilution technique.

1. Feed intake and the output of faeces, urine and milk were recorded for 8 to 10 days on 2 Friesian cows, with duodenal re-entrant cannulae, receiving hay and concentrates or fresh-mown herbage at the early or mature growth stage. One cow was also given 50 g calcined magnesite daily. During and in the 5 days preceding the collection periods 100 g polyethylene glycol (PEG) and 5.25 g Cr2O3 were given twice daily into the rumen. The digesta were measured and sampled from the re-entrant cannulae for 120 h in the middle of each balance period. All of the administered PEG and Cr2O3 were recovered from the duodenal digesta and faeces. The PEG content of duodenal digesta reached a peak 3 to 4 h after administration, but no diurnal pattern was observed for Cr2O3. The contents of PEG, Cr2O3, DM, Ca and Mg in spot samples of duodenal digesta taken at 2-h intervals agreed well with proportional samples collected during the same hours. (Abstract retrieved from CAB Abstracts by CABI’s permission)

Amino acid composition of digesta taken from swine receiving diets containing soybean or rapeseed meals as sole source of protein.

The usefulness of amino acid digestibility measurements as indices of availability can be evaluated by comparing the amino acid composition of distal ileal digesta (where absorption is believed to be complete) with that in the rectum. Two semipurified diets containing either soybean or rapeseed oil meals were each fed to four castrated male pigs of 60 kg liveweight. The pigs were sacrified and samples of digesta were removed from the stomach, duodenum, jejunum, ileum, cecum, colon, and rectum. The concentrations of nitrogen and the proportions of 14 amino acids in the samples were studied. Digesta taken from the duodenum contained the greatest concentration of nitrogen; the nitrogen concentration decreased through the small intestine, and then remained constant through the large intestine. Comparing the ileal and rectal digesta, there were no significant differences in the proportions of valine, arginine, serine, tyrosine, threonine, phenylalanine, and aspartic acid for both diets. This was also true for lysine for the soybean meal diet and for methionine and alanine for the rapeseed meal diet, so that for these amino acids, digestibility should be a good estimate of availability. However, there were lower proportions of leucine plus glycine, proline, and glutamic acid in the rectal than in the ileal contents for both diets, and for lysine in the rapeseed meal diet, suggesting that digestibility values would overestimate availability. In contrast, there were higher proportions of isoleu-cine in the rectal than in the ileal contents for both diets, and of methionine and alanine for the soybean meal diet, suggesting that digestibilities would underestimate the availabilities of these amino acids.Partition of the digesta and the water-soluble digestion marker (polyethylene glycol) in the stomach precluded reliable quantitation of digesta flows through the ileum, but the experiment suggests that such quantitative measures would provide a basis for more valid estimates of amino acid availabilities than measurements of the amounts of amino acids voided in the feces.

Digesta flow through the rabbit large intestine.

Digesta flow through the rabbit large intestine.

Comparison of spot and continuous sampling for estimating duodenal digesta flow in sheep

Abstract The flow of duodenal digesta in sheep fed a diet of chopped dried grass was measured either by continuous 24-hour or spot sampling. Continuous samples were taken from sheep with re-entrant cannulae given chromic oxide paper (Cr2O3) as a flow-correction marker. Spot samples were taken from sheep with re-entrant or T-shaped (simple) cannulae given 103Ru-phenanthroline and 51Cr-EDTA as particulate and liquid phase markers respectively. No significant differences were obtained between the mean 24-hour flows of dry matter or liquid digesta measured by the two techniques, but spot sampling gave more variable results. Diurnal variations of duodenal digesta flow and marker concentrations in the continuously fed sheep showed that 103Ru-phenanthroline, 51Cr-EDTA, and PEG were more closely associated with their respective digesta phases than was Cr2O3.

Nitrogen metabolism in sheep. I. The effect of protein and energy intake on the flow of digesta into the duodenum and on the digestion and absorption of nutrients

The digestion of organic matter, nitrogen, and sulphur was measured in sheep fitted with re-entrant duodenal cannulae. The sheep were given 1.4, about 16, or 30 g of nitrogen per 24 hr from barley roughage with or without a nitrogen supplement of lucerne, wheat gluten, or casein. A further diet supplied 16.1 g of nitrogen per day but consisted of 83 % low-quality roughage compared with 50% in the other diets. The flow of digesta to the duodenum varied from 4.4 to 6.8 1. per 24 hr with dry matter intakes of 480–800 g per 24 hr. The sheep were fed hourly and watered continuously, and there was a more than 10-fold variation in the flow of digesta to the duodenum over 2-hr collection periods. The digestibility of organic matter was lower for the diet supplying 1.4 g of nitrogen per day than for the other diets. Between 77 and 96 % of the apparent digestion of organic matter occurred before the duodenum. In the sheep given 1.4 g of nitrogen per 24 hr, the flow of nitrogen to the duodenum was 4.8 g per 24 hr, while in the sheep given about 16 g of nitrogen daily the flow of nitrogen to the duodenum was 8.4–11.8 g per 24 hr. Only 35 % of the dietary intake of nitrogen reached the duodenum in the sheep given 30 g of nitrogen daily. The sheep given the diet containing 83 % low-quality roughage showed a lower retention of nitrogen than those given the other diets of similar nitrogen content. Between I and 9 % of the flow of nitrogen to the duodenum was in the form of ammonia. The flow of sulphur to the duodenum was between 33 and 55% of the dietary intake, while 72-99% of the apparent digestion of sulphur occurred before the duodenum. The digestibility of dietary sulphate sulphur was greater than that of the sulphur found in lucerne.

Digestion by sheep of concentrate diets containing formaldehyde-treated peanut meal

The effect of formaldehyde treatment of peanut meal on the digestion of barley-peanut meal diets was studied in fistulated crossbred sheep at two peanut meal and therefore dietary protein levels. There were no differences either between protein levels or due to treatment in the overall digestion of organic matter, but more of this digestion took place in the stomach when the low protein diets were given. Dietary starch was completely digested. There was no effect of protein level or of formaldehyde treatment on the partition of starch digestion between the stomach and the intestines. About 10% of the dietary nitrogen disappeared from the stomach when the high protein diet containing untreated peanut meal was given; treatment resulted in a small net gain of nitrogen in the stomach. There was a net gain of nitrogen in the stomach when the low protein diets were given, the gain tending to be greater when the peanut meal was treated. When the meal was treated, there was a small but not significant increase (c. 2%) for the low protein diet and a substantial increase (c. 31 %) for the high protein diet in the amount of crude protein digested in the intestines per unit of digestible organic matter intake. Changes observed in the composition and flow of digesta and in plasma urea and cc-amino nitrogen levels are discussed in relation to the digestion of organic matter and protein.

The digestion of safflower oil-casein particles protected against ruminal hydrogenation in sheep

Three sheep were offered lucerne hay either alone or with a supplement of safflower oil-casein particles protected from microbial digestion by treatment with formaldehyde. The supplement provided an additional 70 g of long chain fatty acids and 9 g nitrogen. It was estimated that, as a result of providing the supplement, additional nutrients derived from the small intestine included about 10 g of nitrogen and 60 g of long chain fatty acids. About 38 g of these fatty acids was absorbed in polyunsaturated form. With the basal diet, negligible amounts of polyunsaturated acids were absorbed from the small intestine. The addition of safflower oil-casein particles was associated with slight but significant increases in the flow of digesta from the abomasum but had no effect on the volume of water in the rumen or on the rates of flow from the rumen or terminal ileum. It was calculated that the supplemented diet provided, per unit of organic matter intake, about 30% more metabolizable energy, 38% more net energy, and 70% more amino acids than the basal diet.

Digestion of two legumes and rumen bacterial growth in defaunated sheep

Defaunated sheep offered lucerne hay or dried red clover were used to study digestion in the stomach of dietary organic matter, plant cell wall constituents, and plant cell contents. Digestion in that section of the tract was, for dietary organic matter, 50 % with lucerne and 60% with red clover, for plant cell contents 65–70% with both diets, and for plant cell wall constituents 30% with lucerne and 60 % with red clover. Estimates of growth of rumen bacteria in these sheep indicated that about 32 g of bacterial organic matter and 23 g of bacterial crude protein were synthesized in the rumen for each 100 g of plant organic matter digested. Comparisons of apparent digestion in the stomach and intestines were made between the defaunated sheep and the same sheep carrying a normal population of rumen microorganisms. Levels of rumen ammonia were lower in the absence of protozoa. However, only small differences were observed in the flow of digesta along the tract and in the apparent digestion of organic matter and nitrogen in both the stomach and intestines as a result of defamation. Hence it is suggested that data on the digestion of forages obtained with defaunated sheep can be applied to sheep with rumen protozoa.

The effect of the physical form of the diet and the level of feeding on the digestion of dried grass by sheep.

AbstractIntact and rumen cannulated sheep were used to study the digestion of an artificially dried grass offered either in a chopped or a ground and pelleted form at energy intakes ranging from 1–3.2 × the energy requirement for meantenance. In each form of the grass the digestibility of all dietary constituents was depressed at high levels of feeding and, excepting ether extract, was lower in the ground and pelleted grass than in the chopped grass. The digestibility of organic matter (DOM) varied with treatment from 70.7–82.7% and for each form of grass was related to the level of feeding (LF) such that DOMC = 83.1–1.01 LF (P < 0.05) and DOMG = 84.6–4.12 LF (P < 0.001). Corresponding relation‐ships were observed between the mean retention time of food residues in the alimentary tract (MRT) and the level of feeding (LF) such that MRTC = 111.7–95.1 log LF (P < 0.001) and MRTG = 77.2–60.8 log LF (P < 0.001). Where animals were fed on ground and pelleted grass there were changes in rumen fermentation characterised by a lowered rumen pH and cellulolytic activity and by reduced concentrations of ammonia‐N and total short‐chain fatty acids in the rumen fluid. The percentage of acetic acid in the fermentation products was decreased and there were associated increases in the percentages of butyric acid and valeric acid.The results indicate that grinding and pelleting the grass was associated with a reduction in the digestibility of organic matter resulting partly from an increased rate of flow of digesta through the alimentary tract and partly from a reduction in cellulolytic activity in the rumen.

Level of food intake and the passage of markers and nitrogen along the alimentary tract of sheep

1. The relative rates of passage of polyethylene glycol (PEG) and lignin through the alimentary tracts of sheep were examined through the ratio of these two markers in the fodder and in the contents of various segments of the gut. A much faster turnover of PEG than of lignin in the stomach compartments suggested that samples from these organs could not be representative of the digesta flowing through them. Average PEG:lignin ratios in the small and large intestines were close to the ratio in the fodder, indicating that sampling from the duo-denum in the living animal could possibly yield material representative of that flowing from the stomach to the small intestine. Similar results were obtained for high and low levels of fodder intake.2. A procedure was developed for automatic sampling from the duodenum for prolonged periods, and the material collected was shown to be representative of digesta flow. Simpler methods of sampling from the duodenum were shown to be liable to relatively large errors.3. The amount of nitrogen reaching the duodenum in sheep given lucerne hay pellets was found to be equivalent to practically 100 % of the dietary N, whether the intake of fodder was 600 g/d or 1500 g/d.

Influence of the physical form of a barley grain and barley straw diet on nitrogen metabolism in sheep

Summary(1) Two wether sheep fitted with ruminal and duodenal re-entrant cannulas were used to study the influence of the physical form of a barley grain and barley straw diet and intraruminal addition of ammonium salts (mainly acetate) on digestibility of dietary constituents, the flow of digesta to the duodenum and the composition of digesta from the rumen and duodenum.(2). Grinding and pelleting of the diet depressed the digestibility of crude fibre and increased that of the nitrogen-free extract and addition of ammonium salts increased the digestibility of crude fibre. The effects of the physical form of the diet on the composition of the short-chain fatty acids of rumen liquor were not consistent and the addition of ammonium salts produced changes over and above those attributable to the small amounts of acids in the mixture. The extreme values observed for the molar proportion of propionic acid were 12·3 and 38·1% and the corresponding values for η-butyric acid were 28·1 and 9·0%.(3). Variations in the flow of nitrogenous materials to the duodenum were related more to the pattern of fermentation established in the rumen than to the experimental treatments. There was a highly significant relationship between the molar proportion of propionic acid and the abomasal output of nitrogen and also the abomasal output of α-ε-diaminopimelic acid and α-linked glucose polymers. The amino acid composition of duodenal digesta differed from that of the diet—in particular the proportion of glutamic acid was decreased and the proportions of aspartic acid, alanine, lysine and histidine were increased—but differences in composition between treatments and between animals were small.(4). The faecal output of nitrogen differed little between animals and between treatments, but nitrogen retention was significantly increased during the intraruminal infusion of ammonium salts.

Factors limiting the intake of feed by sheep. V. Feed intake and the productive performance of the ruminant lamb in relation to the quantity of crude protein digested in the intestines

The voluntary feed consumption (VFC), liveweight increase, and wool growth of lambs, initially 9-10 weeks old and weighing 22 kg, were measured over 6 weeks when pelleted diets of differing protein content were offered. The crude protein contents of the diets, on a dry matter basis, were 11.7% (LP diet), 15.8% (MP diet), and 19.1 % (HP diet). The digestion of the HP and LP diets was studied, with use of markers, in similar lambs prepared with stomach fistulae. VFC, expressed as grams dry matter/day/kg body weight0.75, was 82 (SE�3) with the LP diet, 94�3 with the MP diet, and 97�4 with the HP diet. The dietary crude protein intakes were 110, 178, and 220 g/day with the LP, MP, and HP diets respectively and the corresponding quantities of crude protein (6.25 x nitrogen in forms other than ammonia) apparently digested in the intestines (DCP,) were 75, 134, and 179 g/day. The LP and HP diets provided about 12 and 23 g DCP1/lOO g digestible organic matter respectively; the value for the MP diet was estimated to be 18 g DCP1/100 g. The rates of liveweight increase were 153 � 16, 240�9, and 267�12 g/day with the LP, MP, and HP diets respectively. Wool production was the same with the MP and HP diets but lower with the LP diet. The level of intake of DCP1 and the DCP1/digestible organic matter ratio had little effect on the gross chemical composition of the lambs, as estimated indirectly from tritiated water space. The levels of essential amino acids in peripheral blood plasma were generally in the order HP diet > MP diet > LP diet. Digesta flow from the rumen and abomasum, rumen volume, ruminal volatile fatty acid concentration, and pH of ruminal digesta were similar with the LP and HP diets. It was concluded that a level of about 18 g DCP1/100 g digestible organic matter was adequate for the expression of maximum VFC and that concentrations in excess of this would have little enhancing effect on liveweight gain or wool production under conditions of ad libitum feeding.