Some effects of variation in carbohydrate and nitrogen intakes on the chemical composition of mixed rumen bacteria from young steers

By A. B. McAllan and R. Bailey-Wood

Vol. 37 (1977), no. I

Page 61, lines 2 and 3 should read:

The CP content was lowest in samples from calves receiving diet 2b (dried fescue and glucose) and highest in samples from calves receiving diet 1b (dried fescue only)

1. Published results have been used to study the relationships between nitrogen retention (NR), body-weight (W) and N intake in the pig.

2. The general decrease in maximal NR (g/d per kg W0.75) with increasing W (kg) was curvilinear for values of W from 1.5 to 45: NR = 3.324−0.098 W+0.001 W2; and rectilinear for values of W from 45 to 165: NR = 1.252−0.006 W. Values for protein requirements derived from these equations agreed closely with published estimates.

3. The slopes of the curves for NR (g/d per kg W0.75) v. N intake (g/d) decreased as W (kg) increased from about 2.5 to 190. After extrapolation to a proposed common intercept on the NR axis of -150 mg N/d per kg W0.75, regression analysis of the intercepts of these curves on the N-intake axis v. W gave an estimate of N requirements for maintenance of 246±19 mg/d per kg W0.75.

4. The results also indicated that at low N intakes net protein utilization (N retention+ total obligatory N losses ÷ N intake) was essentially independent of W, whereas the gross efficiency of N utilization (NR ÷ N intake) was influenced by both W and N intake.

1. In three separate experiments, four groups of five to eight young male rats were fed either (i) a high-protein diet, for which the net dietary protein: total metabolizable energy ratio (NDp:E) was 0.1 (HP diet); or (ii) a low-protein diet, for which NDP:E was 0.04 (LP diet). In both these groups, food intake was ad lib In group (iii) the HP diet was given in an amount approximately equal to that taken by the LP group fed ad lib. (HP-restricted). In group (iv) rats were fasted for 48 h after receiving the HP diet (HP-fasted). Each experiment lasted 4 weeks.

2. In the LP and HP-restricted groups, food intake was about 50% of that of the HP rats, while body-weight, after 4 weeks on diet was about 35% and 55% of that of HP rats, for LP and HP-restricted respectively. Both groups of malnourished rats gained some weight during the experiment.

3. Measurements of oral glucose tolerance and plasma insulin levels were made in the fourth week. LP and HP-restricted rats both showed low fasting insulin levels and low insulin to glucose ratios during the glucose tolerance tests; the LP rats were more seriously affected.

4. At the end of the fourth week the rats were killed and blood, liver and gastrocnemius muscle were analysed. LP rats showed specifically and consistently low values for haemoglobin and plasma protein concentration, and low activities of hepatic glucose-6-phosphatase (EC 3.1.3.9) and of alanine aminotransferase (EC 2.6.1.2) in liver and muscle. The activity of hepatic aspartate aminotransferase (EC 2.6.1.1) was, if anything, increased. The plasma amino acid concentrations and ratios showed a specific fall in branched-chain amino acids. Liver fat concentration was consistently elevated. The HP-restricted rats had normal values for haemoglobin, plasma protein and liver fat, and near-normal values for plasma amino acids. Hepatic alanine aminotransferase showed increased activity compared with HP rats, but muscle alanine aminotransferase showed reduced activity. The HP-fasted rats had increased haemoglobin, plasma protein and liver fat concentration, and very low liver glycogen concentrations. Hepatic alanine aminotransferase activity was elevated. Plasma alanine concentration was specifically reduced.

5. The results are consistent with suppression of gluconeogenesis, liver dysfunction and essential amino acid deprivation in LP rats. These biochemical changes found in rats on a low intake of a diet of low protein and high carbohydrate value are similar to those found in kwashiorkor. An equally low intake of a diet of good protein value (HP-restricted) led to marginally better growth, accompanied by biochemical signs of increased gluconeogenesis, analogous to those reported for nutritional marasmus. This nutritional state was not biochemically identical with that of acute fasting.

6. The results are discussed in terms of the consistency of the rat model, and its contribution to understanding biochemical changes found in infant malnutrition.

1. Twenty-four energy and nitrogen balances were determined using twenty-four crossbred cows (Brown Swiss × Sahiwal) during their midstage of lactation. Energy balances were estimated by subtracting milk energy and heat production from the metabolizable energy (me) intake. Heat production was estimated by indirect calorimetry, by collection and analysis of respiratory gases. The cows were given amounts corresponding to 90, 110 and 130 % of the me and 90 and 110% of the digestible crude protein (DCP) standards of the (US) National Research Council (1966).

2. Energy requirements were estimated by partitioning the me intake for maintenance, milk production and energy gain or loss by multiple regression of energy balance values. Heat production (and thus energy balance) was corrected for excess N intake.

3. Energy requirements for maintenance were 585.18, 580.17 and 574.41 kJ me/kg body-weight0.75 per d for cows in negative balance, cows in positive balance and for all cows, respectively.

4. The efficiency of utilization of me for milk production was 68.52, 65.48 and 66.12% respectively, for cows in negative balance, for cows in positive balance and all cows. Energy required per kg fat-corrected milk production was 4.580, 4.791 and 4.746 MJ me for the respective groups of cows.

5. The efficiency of utilization of me for tissue gain was 67.67 and 64.86 % for cows in positive balance and for all cows respectively.

The absorption, transport and distribution of α-[3H]tocopherol were greatly decreased in protein deficiency. This was reflected in the subcellular distribution of α-[3H]tocopherol in livers of protein-deficient rats. The ratio, bound: free for α-[3H]tocopherol, also decreased in both serum and liver cytosol. After protein refeeding, absorption, transport and distribution patterns of α-[3H]tocopherol for the protein-deficient rats were restored to patterns similar to those of control animals.

1. Two series of protein feeding-stuffs each consisting of a fish meal, meat-and-bone meal, soya-bean meal, groundnut meal and sunflower-seed meal were analysed for total amino acid composition and evaluated, both individually and combined in all possible pairs, as supplements to cereal-based diets for growing chicks by the total protein efficiency (g weight gain/g protein consumed; TPE) procedure. Each pair of feeding-stuffs provided 120 g supplementary protein/kg diet and the diet was made up so that the relative amounts of protein provided by each of the pair of constituents were (w/w): 120:0, 100:20, 80:40, 60:60, 40:80, 20:100 and 0:120 respectively, in addition to 60 g protein/kg provided by cereals.

2. In all but one of the twenty pairs of feeding-stuffs studied the mixtures exhibited a marked synergistic effect in that the TPE value was higher than the appropriately weighted mean of the TPE values obtained with the individual components.

3. Neither chemical score ([amount of limiting amino acid/the chick's requirement for the same amino acid] × 100) nor essential amino acid index; geometric mean for the ratio, amount of essential amino acid: the chick's requirement for that amino acid, for all ten essential amino acids) calculated from the amino acid composition of the dietary constituents could be used routinely to predict the results of the chick growth test, although chemical score did parallel the TPE values in some instances. In a number of instances, mixtures containing an apparently less favourable amino acid composition than one of the components of the mixture gave a higher TPE value.

4. It seems likely that the relative proportions of a number of amino acids determine the optimum combination of a mixture of proteins. The removal of amino acid deficiencies alone is not sufficient to ensure that a given mixture of proteins produces optimum performance in growing chickens.

1. Two experiments were done with Pietrain and Large White pigs (about 50 kg body-weight) to determine whether fat mobilization is enhanced in the stress-sensitive Pietrains (which also produce pale, soft, exudative (PSE) meat).

2. In Expt 1, plasma glucose and insulin concentrations and free fatty acid (FFA) concentrations and composition were measured in five Pietrains and five Large Whites after feeding, during an infusion of norepinephrine (2.5 μg/kg body-weight per min), 16 and 21 h after the withdrawal of food and following insulin administration (0.3 IU/kg body-weight). The entry rate of oleic acid was measured 4 h after feeding. Body composition and longissimus dorsi pH measurements were made on killing the pigs 4 d after the experiment.

3. After feeding, the Pietrains tended to have lower concentrations of glucose and insulin in plasma compared with the Large Whites, and higher concentrations of FFA. The Pietrains also had a faster entry rate of oleic acid into body tissues. In fasting (16 h) these differences in hormone and metabolite concentrations were also present and relationships between them and body development could be detected. Pietrains had higher concentrations of FFA and lower concentrations of insulin than Large Whites at a particular stage of the development of fat and muscle (subcutaneous fat weight÷longissimus muscle weight).

4. The fatty acid composition of FFA resembled that of the backfat triglycerides in fasting and during norepinephrine infusion but not in the fed state. In particular the proportion of fatty acid 18:1 was low in the fed pigs and that of 18:2 was high. The contrast in FFA composition between the fed and stimulated state was greater in the Large Whites.

5. The Pietrains were less sensitive to the antilipolytic action of insulin. Glucose and FFA concentrations were similar in both breeds during the norepinephrine infusion although insulin concentrations were increased to a larger extent in the Large Whites at the termination of the infusion.

6. In Expt 2, anaesthetized Pietrain and Large White pigs were given constant infusions of norepinephrine alone (2.5 μg/kg body-weight per min) and norepinephrine+propranolol (2 and 10 μg/kg body-weight per min) or phentolamine (2 and 10 μg/kg body-weight per min). The aim was to determine whether the breeds differed in their sensitivity to norepinephrine when conscious responses to the hormone were prevented.

7. When norepinephrine alone was infused, fat mobilization was greater in the Pietrain pigs and glucose concentrations were greater in the Large Whites. Propranolol markedly reduced the lipolytic action of norepinephrine, particularly in the Pietrain pigs studied, and phentolamine reduced its glycogenolytic action, particularly in the Large White pig.

8. It seems that the leanness of stress-sensitive, PSE-susceptible Pietrain pigs may be due to an enhanced fat mobilization under various conditions, associated with an impairment in insulin metabolism and a greater sensitivity to the β-adrenergic action of catecholamines on body fat stores.

1. Pullets were given from 1-d-old diets containing 1.6, 4.1, 8.1 and 12.0 g Mg/kg. Only small effects of these diets on live weight, food consumption, egg number, egg weights or egg-shell thickness were observed except at the highest level (12.0 g Mg/kg) which caused diarrhoea and an appreciable lowering of the live weight of growing pullets. A further group was given from point-of-lay a diet containing 9.3 g Mg/kg.

2. Eggs laid on 3 consecutive days from each of eighteen hens were collected at intervals of 3 weeks until the birds were 68.5 weeks old. Eggs laid on the 3rd day were used to determine the initial proportion of thick egg-white present and also the concentration of Mg, Ca, Na and K in the thick egg-white. Eggs laid on the 1st and 2nd days were stored at 20° for 20 d to establish the proportion of thick egg-white remaining after storage.

3. With the unsupplemented diet the proportion of residual thick egg-white after storage of eggs for 20 d at 20° was 306, 161 and 305 mg/g total egg-white when the hens were 26.5, 53.5 and 68.5 weeks of age respectively. When the diet containing 9.3 g Mg/kg was given, the proportion of thick egg-white after storage remained approximately 400 mg/g throughout the period of the trial.

4. The mean Mg concentration in the thick egg-white of eggs laid by hens given unsupplemented diets was 5.77 mm. The addition of extra Mg to the diet increased the content of Mg in the thick egg-white, for example when the diet contained 9.3 g Mg/kg the mean concentration rose to 7.69 mm.

1. A fish meal, meat meal, soya-bean meal, groundnut meal and sunflower-seed meal of known amino acid composition were evaluated individually, and combined in all possible pairs, by the estimation of net protein utilization (NPU) and protein efficiency ratio (body-weight gain:crude protein intake; per) using rats. Each pair provided a total of 100 g protein/ kg diet made up so that the amounts of the constituents were (w/w) 100:0, 80:20, 60:40, 20:80 and 0:100.

2. Marked synergistic effects were noted only for mixtures of sunflower-seed meal with soya-bean, fish and meat meals.

3. Chemical score ([amount of limiting amino acid/the rat's requirement for the same amino acid] × 100; CS), but not essential amino acid index; geometric mean for the ratio, amount of essential amino acid: the rat's requirement for that amino acid, for all ten essential amino acids; EAAI), successfully predicted the rankings of all mixtures except groundnut meal-meat meal and groundnut meal-soya-bean meal, by both per and NPU tests.

4. Although there is broad agreement linking results of per and NPU tests with results obtained by a more practical feeding trial in which the mixtures were evaluated as supplements to cereals, neither of these two standard tests is capable of predicting in every instance the advantages to be gained by mixing protein concentrates.

1. Protein and energy requirements of pigs weaned at 2 d of age were studied. In Expt 1, three diets with crude protein (CP; nitrogen × 6.38) and fat contents (g/kg dry matter (DM)) of 268, 260 (diet A); 216, 415 (diet B) and 264, 405 (diet C) were compared, with and without a supplement of 2 g DL-methionine/kg. Diets A and B contained skim milk and soya-bean oil only, in different proportions. Casein was added to diet C to equalize the CP content to that of diet A. In Expt 2, diets containing 290 or 315 g CP/kg DM were used with either 310 or 405 g fat/kg. The diets contained different proportions of skim milk, soya-bean oil and casein. The same diets as used in Expt 2 were used in Expt 3 but fed to a scale based on live weight which was 25% less than that used in Expts 1 and 2.

2. Methionine supplementation had no significant effect (P > 0.05) on the growth rate or feed: gain ratio of pigs from 2 to 28 d of age. The growth rate of the pigs from 2 to 28 d of age was significantly (P < 0.05) reduced when they were given the higher level of either CP or fat, with the exception that the effect of level of fat was not significant (P > 0.05) in Expt 3. The reduction in growth rate was associated with a decrease in feed intake. Feed: gain ratios were unaffected (P > 0.05) by the level of either CP or fat in the diet.

3. The higher protein level did increase the proportion of CP in the carcass DM (Expt 2 P < 0.01, Expt 3 P > 0.05) and gave an indication, which was not significant (P > 0.05), of improved N retention (g/d per kg live weight). The higher dietary fat level increased the proportion of lipid in the carcass DM, and this effect was significant (P < 0.05) in both Expts 2 and 3.

4. Diets containing additional casein were not fully consumed at the level of feeding used in Expt 2. This effect may be associated with the larger amounts of digesta in the stomachs of these pigs. Some differences in the composition of the digesta in the stomach were observed, but these did not affect the performance of the pigs.

5. It seems unlikely that either growth rate or feed:gain ratio (g DM consumed/g live-weight gain) can be improved by protein or energy levels exceeding those in a diet containing (g/kg DM) 730 skim milk (265–290 CP) and 310 fat. In this diet, containing (g/kg DM) 6.4 methionine and 3.5 cystine, sulphur amino acid requirements were satisfied.

1. Pigs consuming a diet containing 300 g linseed meal/kg and a pyridoxine supplement showed greater growth, nitrogen retention, blood packed cell volume and haemoglobin than those receiving only the basal diet.

2. Tryptophan-load tests on unsupplemented pigs revealed an increased excretion of kynurenine, Nα-acetylkynurenine and xanthurenic acid compared to those receiving additional pyridoxine.

3. The results suggest that the unsupplemented pigs were marginally deficient in vitamin B6.

4. When the same diet was fed to rats there was no evidence of vitamin B6 deficiency.

1. A comparison was made of the composition of milk from front and rear teats in four sows. There were small and not significant differences in fat, protein and lactose contents, and in the fatty-acid composition of the milk fat with the exception of the 18:3 acid where the difference was also small but significant.

2. The effects of intravenous infusions of glucose and insulin in lactating sows on milk secretion and blood composition were investigated in two sows.

3. Intravenous infusion of glucose had no effect on blood plasma glucose concentration but increased the yields of lactose, protein and water.

4. Intravenous infusion of insulin depressed plasma glucose concentration and the yields of lactose and water. The yield of protein was unaffected.

5. It is concluded that differences between the non-ruminant (the sow) and the ruminant in the responses in milk secretion to glucose infusion may be related to differences in the sensitivity to insulin of mammary tissue.

1. A total of seven sheep fitted with re-entrant cannulas in the proximal duodenum were used in three experiments to measure the passage of dry matter (DM) in duodenal digesta.

2. Fifty-three 24 h measurements and ten 48 h measurements of DM flow were made in Expt 1. Coefficient of variation (CV) of these measurements was 22.1 % which was similar to variability reported for chromic oxide ‘corrected’ flows and for an estimate of day-to-day variation. DM flow on day 1 was 103.2 % (SE = 8.94) of flow on day 2 in 48 h measurements.

3. In two 3 × 3 Latin-square design experiments, duodenal DM flow was measured continuously over 72 h and on days 1, 2 and 3 DM flow was 100.4, 102.6 and 96.9 % (SE = 5.82) of mean flow (Expt 2) and 95.8, 101.2 and 103.0% (SE = 6.70) of mean flow (Expt 3) respectively.

4. It was concluded that no depression in duodenal DM flow occurred during the first 24 h of collection in these experiments and that the variability of repeated 24 h measurements of flow was within day-to-day variation.

1. Samples of rumen digesta were taken at different times after giving calves various dried forage or hay and cereal diets and mixed bacteria were separated.

2. For calves receiving dried forage only, the carbohydrate content of mixed bacteria varied with time after feeding, reaching a maximum of approximately 140 g/kg dry matter (DM) after 0.5-1 h, decreasing to about 60 g/kg DM after 4 h.

3. Replacement of part of the dried forage with glucose to give a similar metabolizable energy intake but approximately half as much nitrogen, produced a similar pattern of change with time after feeding but resulted in a markedly increased maximum bacterial carbohydrate content (approximately 230 g/kg DM). Addition of urea to this diet reduced the bacterial accumulation of carbohydrate to approximately the same level as was found in samples from calves receiving forage only diets. For the forage diets the carbohydrate content fell to 60-100 g/kg DM 4 h after feeding. For the hay and cereal diet the value was 170 g/kg DM at this time.

4. Changes in bacterial carbohydrate content were largely a result of changes in storage polysaccharide (α-dextran) content.

5. Crude protein (N × 6.25) and ash contents of mixed bacteria decreased after feeding with all-forage diets, but returned to approximately fasting levels within 4 h. At this time samples from calves receiving dried forage and glucose diets contained less CP and more ash (approximately 450 and 220 g/kg DM respectively) than those from calves given diets of dried forage only (approximately 525 and 180 g/kg DM respectively).

6. CP, total carbohydrate and ash content of mixed rumen bacteria contributed approximately 0.80 g/g DM.

7. Sodium, potassium, calcium, magnesium and phosphate accounted for approximately 0.50 g/g bacterial ash.

1. Nitrogen retention was measured in adult rats (250–350 g) subjected to the trauma of hind-leg fracture and given diets with or without arginine plus glycine supplementation. Observations were also recorded on excretion of creatine, creatinine, allantoin, and orotic acid. Liver and skeletal muscle transaminase activities were also determined.

2. When traumatized rats weighing approximately 250 g were given a diet with 200 g casein/ kg, supplemented with 20 g arginine and 10 g glycine/kg (EC diet) or a casein diet made isonitrogenous with the EC diet by addition of aspartic acid (C diet), a 60–70% increase in N retention was observed for the first 5 d post-injury for animals consuming the EC diet. A soyabean (S) diet, isonitrogenous to the diet containing 20% casein, supplemented with arginine and glycine was as effective as the EC diet in promoting significantly better N retention of traumatized rats (350 g) in comparison to rats given the C diet.

3. When the dietary casein content was reduced to 100 g/kg, supplements of 10 g arginine and 5 g glycine or 20 g arginine and 10 g glycine/kg did not improve N retention. It is suggested that both protein quality and protein quantity are important following injury.

4. An increased excretion of creatine was observed in traumatized rats given the high-protein diets supplemented with arginine and glycine. No consistent changes were noted for urine creatinine.

5. Urine allantoin levels remained stable after leg-fracture in rats consuming either the C or EC diets. Differences in the levels of urine orotic acid were found during both the pre- and post-injury periods in rats given the C, EC or S diets.

6. The mechanisms responsible for the improved N retention of traumatized rats consuming the high-protein diets with supplements of arginine and glycine may be related to the role of arginine both as a constituent of muscle tissue and as an intermediate in the urea cycle.

7. In traumatized rats fed the C or EC diets, liver transaminase activity increased whereas the transaminase activity in skeletal muscle decreased. These results support the recent concept that the increased excretion of N following injury arises from diminished reutilization of amino acids by muscle tissue without an acute increase in the rate of muscle catabolism.

1. A study was made in goats of the response in terms of milk production, nitrogen utilization, plasma amino acids and amino acid uptake by the mammary gland, to postruminal infusion of casein. Goats in early lactation, housed in metabolism cages, were fed on 2.5 kg basal ration/d (containing 111 g crude protein (N × 6.25)/kg) and were given, by infusion into the abomasum, 0, 15, 30 or 45 g casein/d.

2. Milk production increased from 2.41 kg/d on the basal ration to 2.52, 2.80 and 2.94 kg/d in response to infusions of 15, 30 and 45 g casein/d respectively. Milk composition was unaffected except for milk fat, which was slightly decreased during infusions of the higher levels of casein.

3. The goats were found to be in positive N balance on the basal ration. Milk N output increased with casein infusion; the increase was equivalent to a maximum of 49% of the infused N.

4. The concentration of glucose in arterial blood plasma was decreased at the highest level of casein infusion, but that of plasma urea N was unaffected by treatments.

5. Casein infusions increased the concentrations of total indispensable amino acids and the ratio, indispensable: dispensable amino acids in arterial plasma. Arterial concentrations and mammary extractions of most indispensable amino acids were increased, but only a few increases were statistically significant (P < 0.05).

6. Comparison of individual indispensable amino acids absorbed from the intestine with output in milk indicated that methionine was probably the first limiting amino acid.

7. The results of the experiment were compared to those of similar experiments with cows that have been reported by other workers. The possible ways in which the infused casein may have caused the responses were discussed. However, no firm conclusions regarding the mechanism involved could be drawn from the results of the present study.

1. Critical studies on the distribution of NT-methylhistidine (3-methylhistidine; Me-His) among organs and tissues in adult rats are reported. Adult rats contained 46.5 ± 3.6 mg Me-His/kg body-weight. Almost 90% of the Me-His in the body was recovered from skeletal muscle. These results support the hypothesis that fractional catabolic rates of myosin and actin in skeletal muscle can be estimated by measuring urinary excretion of Me-His.

2. Dietary protein level did not affect the total amount of Me-His in the body. However, urinary excretion of Me-His increased as dietary protein intake was increased.

3. From these results it was concluded that fractional catabolic rates of myosin and actin increase as dietary protein intake increases.