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. 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. 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. 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 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. 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.

1. Measurements were made of energy balance by direct calorimetry, and of nitrogen balance in groups of lean and congenitally obese (‘fatty’) Zucker rats at body-weights of 200 and 350 g given a highly digestible semisynthetic diet at 14.0 or 18.4 g/rat per 24 h.

2. Losses of food energy and N in faeces were very small. The fatty rats lost much more N in urine than did lean rats. Despite this the proportion of gross energy that was metabolized was 0.92 for both fatty and lean rats.

3. In all trials, fatty rats lost a smaller proportion of metabolizable energy (ME) as heat and deposited less as protein than thin rats but deposited much more as fat.

4. The amounts of ME required to deposit 1 kJ of protein and 1 kJ of fat respectively were shown by regression analysis to be 2.25 (±0.16) and 1.36 (±0.06) kJ respectively. These values agree extremely closely with recent, more tentative, estimates based on assumptions as to maintenance requirement which the present experiments were able to circumvent. It may be concluded with confidence that the energy costs of depositing 1 g of protein or fat are almost identical at 53 kJ ME/g.

1. Three experiments were conducted on the ability of cats to utilize dietary carbohydrates. In two experiments, the digestibilities of carbohydrates were measured by the chromic oxide-marker technique using a balanced Latin-Square allocation of treatments: in the third experiment, the effect of age and diet on the activity of intestinal β-galactosidase (lactase) (EC 3.2.1.23) and β-fructofuranosidase (sucrase) (EC 3.2.1.26) of kittens was measured.

2. In Expt 1 the digestibilities of six individual carbohydrates, glucose, sucrose, lactose, dextrin, raw maize starch and wood cellulose added to a meat-based basal diet were measured.

3. In Expt 2, a similar meat-based basal diet was used and the effect of three processing methods (fine and coarse grinding, and cooking) on the apparent digestibility of the starch in maize and wheat grain was measured.

4. In Expt 3 the effects of the inclusion of either 200 g lactose or 200 g sucrose/kg in an all-meat diet and of age on the β-galactosidase and β-fructofuranosidase activities of the small intestine of weanling kittens were measured.

5. Adult cats efficiently (> 0.94) digested all six individual carbohydrates added to the diet with the exception of cellulose, which was indigestible. The digestibility coefficients of glucose, sucrose and lactose were significantly (P < 0.01) greater than that of starch. The inclusion of lactose caused diarrhoea in some cats and significantly (P < 0.01) reduced apparent digestibility of crude protein (nitrogen × 6.25) in the total ration.

6. Fine grinding significantly enhanced the digestion of starch in wheat and maize grain, but the effect was greatest for maize grain. Cooking had a similar effect to fine grinding for wheat grain, but an effect intermediate between coarse and fine grinding for maize grain.

7. Intestinal β-galactosidase activity decreased with age in kittens (71-106 d). Neither β-fructofuranosidase nor β-galactosidase activities were significantly affected by the addition of sucrose and lactose to the all-meat diet.

1. The first part of this study was designed to determine the increase in the amount of iron absorbed by hypothetical groups of subjects on the border-line of Fe deficiency when they were given meals fortified with ferrous sulphate. Two levels of Fe fortification were used (1.6 and 8.9 mg/meal) and the increase in the amount of Fe absorbed by the ‘border-line’ groups was 0.13 and 0.7 mg respectively.

2. Subjects which are on the border-line of Fe deficiency may be considered the target group of an Fe-fortification programme. Therefore the experimental model used can provide valuable information on the effects on the prevalence of Fe deficiency which can be expected when such a programme is introduced.

3. In the second part of the study, the bioavailability in man of reduced Fe with different physico-chemical properties was measured. Special emphasis was given to the relationship between the values obtained in vitro and in vivo.

4. The bioavailability was expressed as absorbability relative to that of ferrous sulphate. In four samples of hydrogen-reduced Fe the bioavailability ranged from 90 to 13%. The reduced-Fe products differed considerably with respect to solubility in hydrochloric acid (8–94% dissolved after 30 min), particle size distribution (91–1% < 7 μm) and reactive surface area (< 0.1–2.7 m2/g).

5. The relationships found between physico-chemical information and bioavailability indicated that reactive surface area and dissolution rate were better predictors of the bioavailability than the particle size.

1. Mixed rumen bacteria were grown in vitro in a medium containing [U-14C]adenine. Radioactivity was incorporated into the purine bases of the nucleic acids.

2. Labelled bacteria were incubated with a nitrogen-deficient cell-free medium (medium A), a protozoa-free supernatant suspension from a slow-speed centrifuging of a steer's rumen contents (medium B) and whole rumen contents of a steer (medium C). Mean (six experiments) proportional rates of release of radioactivity(/h) were significantly greater for medium A (0.140) than for media B or C (0.055 and 0.043 respectively). Some of the radioactivity accumulated in the cell-free media; some was lost, partially as carbon dioxide.

3. Calculation from this and other information indicated that about 30% of bacterial nucleic acids may turn over in the rumen even in the absence of protozoa.

1. A study was made in goats of the response in terms of milk production, nitrogen utilization, plasma amino acids and glucose kinetics to postruminal infusions of glucose and casein. Goats in mid-lactation, housed in metabolism cages, were fed on 2 kg basal ration (containing 112 g crude protein (N × 6.25)/kg)/d alone (control) and with daily infusions into the abomasum of 45 g casein or 45 g glucose.

2. Milk production increased with casein infusion (P < 0.01), but not with glucose infusion, being 1.59, 1.86 and 1.62 kg/d with the control, casein and glucose infusions respectively. Milk composition was unaffected except for milk fat, which was decreased by the glucose infusion.

3. The goats were in positive N balance on the basal ration. Milk N output increased with casein infusion, by an amount equivalent to 27% of the infused N.

4. The concentration of dispensable amino acids in arterial plasma was decreased with casein infusion and increased with glucose infusion.

5. Glucose kinetic measurements with control, casein and glucose infusions indicated that pool sizes were 247, 279 and 302 mg/kg live weight0.75, and irreversible losses were 5.5, 6.7 and 7.0 mg/kg live weight0.75 per min respectively. The differences between the results obtained from the glucose and casein infusions were not significant (P < 0.05).

6. The results of the experiment indicate that the increased milk production obtained when casein was infused was not due to enhanced gluconeogenesis.

1. Six Caucasian male Massachusetts Institute of Technology students participated in a 77–87 d metabolic balance study to determine the adequacy of the 1973 FAO/WHO egg protein allowance for men (0.57 g/kg body-weight per d). Each subject was given an initial energy allowance calculated to meet his particular requirements, and these intakes were raised by increments of 10% approximately every 2 weeks until a slightly positive balance was achieved. Each individual's energy intake was maintained at this final level for the remainder of the study.

2. At energy intakes sufficient to meet their estimated requirements, five of six subjects were in negative nitrogen balance. In five subjects, N balance improved with increased energy intake until N balance was achieved. The mean change in N balance was 0.335 mg N/additional kJ consumed. All of the subjects gained weight at the higher energy intakes.

3. Serum aspartate aminotransferase and alanine aminotransferase activities increased with continued intake of the experimental diet and reached abnormal levels in five of the six subjects. In the two subjects showing the earliest increases in serum transferase activity, the levels returned towards normal when protein intake was raised to 0.73–1.0 g/kg body-weight per d. All subjects showed normal serum transferase values on an ad lib. diet 2–3 weeks after termination of the study.

4. The findings indicate that at energy intakes necessary to bring subjects into slightly positive N balance at the level of 0.57 g egg protein/kg per d, a significant proportion of young adults continue to gain weight for as long as 70 d.

5. These findings suggest that the 1973 FAO/WHO safe allowance of 0.57 g egg protein/kg per d is not sufficient for most healthy young men receiving dietary energy intakes appropriate for long-term maintenance of body-weight.

1. Rats were undernourished in early life by feeding their mothers a restricted quantity of a good-quality diet throughout lactation. Their undernutrition continued postweaning from 25 to 42 d of age, after which they were fed ad lib. Control rats were well nourished at all times.

2. Behavioural assessment of thirst was carried out on adult males. These were deprived of water for 23 h/d throughout the period of testing. Compared to control rats, previously-undernourished (PU) rats pressed a lever at a higher rate in a Skinner box to gain a water reward, drank more frequently during their first 5 min in an unfamiliar cage, and tended to run more quickly down an alleyway for water. PU rats also drank more (/kg body-weighta0.75) of a quinine solution (1 g/l) when this was available to them ad lib. as their only source of fluid.

3. A second group of rats was growth-retarded during gestation and the suckling and early postweaning periods. The rats had free access to food from 42 d of age. In adulthood their ad lib. food and water consumption was measured. PU males ate and drank more (/kg body-weight0.75) than control males.

4. These results indicate that adult rats which have been undernourished in early life display increased thirst. An attempt is made to explain this finding, together with their previously-demonstrated enhanced hunger drive, purely in terms of gross anatomical and physiological differences.

1. A comparison has been made of the products of lipolysis of the fat in cow's milk by salivary and pancreatic lipases (EC 3.1.1.3) from a preruminant calf.

2. It was confirmed that salivary lipase releases short-chain acids preferentially, particularly butyric and caproic acids. This was not only true initially but also as the course of lipolysis progressed. Even after 60 min incubation the longer-chain acids were only released to about one-twentieth of the extent of butyric acid.

3. Although pancreatic lipase also initially released proportionately more butyric acid than other fatty acids, within 30 min the longer-chain acids were released to about half the extent of butyric acid.

4. Since the over-all extent of lipolysis by salivary lipase was limited by its inability to release long-chain acids, the release of these acids (which comprise two-thirds of the total fatty acids of milk fat) in the calf is likely to be dependent on the subsequent action of pancreatic lipase.

5. The release of fatty acids by pancreatic lipase was enhanced by pre-incubating milk fat with salivary lipase.

1. Growth in weight and height in 152 children between the ages of 0.6 and 3 years was investigated in Keneba, a rural Gambian village. By 1 year of age the average weight-for-age of the children was only 75% of the Jelliffe (1966) standard.

2. The relationship between the prevalence of nine different categories of diseases and growth was investigated to determine the quantitative contribution of the diseases to the growth faltering observed. There was a highly significant negative relationship between gastroenteritis and both weight gain and height gain. The only other disease category having a similar relationship was malaria, but in this instance only with weight gain.

3. Although over-all growth in weight and height was considerably below the standard values, multiple regression analysis indicated that after the age of 1 year, except in July and August, normal and sometimes slow ‘catch-up’ growth would be possible in the absence of gastroenteritis.

4. Attention is drawn to the limitations of the use of anthropometry in a settled village community as the only criterion by which dietary adequacy can be judged.

1. The retention of ferric- and ferrous-iron was determined in guinea-pigs and monkeys using 55Fe and 59Fe.

2. The bioavailability of Fe from two typical Indian diets based on rice and wheat was determined in humans and monkeys using a 59Fe tracer and whole-body counting.

3. The retention ratio, ferric-Fe; ferrous-Fe was 0.90 in guinea-pigs and 0.33 in monkeys, indicating that monkeys absorb ferrous-Fe preferentially.

4. In monkeys retention of Fe from the test diets, as from ferrous ascorbate was lower than that in humans.

5. When food-Fe retention was expressed in relation to inorganic-Fe retention the value for retention ratio, food Fe: inorganic Fe in monkeys was similar to that in human subjects.

6. The results indicate that the monkey can be used as a model to study Fe absorption from human diets.

1. A relationship was found between selenium concentrations and glutathione peroxidase (EC 1.11.1.9) activities in whole blood of 264 New Zealand residents (r 0.71, P < 0.001).

2. New Zealand residents returning from visits overseas of 7 months to 3 years had elevated blood Se, but normal GSH-Px activities, whereas for some new settlers in New Zealand both Se and GSH-Px activities were high.