The digestibility of dietary protein in the ruminant: Endogenous nitrogen excretion on a low nitrogen diet and in starvation

Effect of feed restriction on nutrient utilization, growth and metabolic profile in crossbred calves

Present study elucidated the effect of feed restriction on growth, nutrient utilizationand metabolic profile in crossbred calves. Eighteen crossbred male calves (Bos Taurus x Bos indicus) of about 4–6 months age and 85.7±5.6 kg body weight were randomly divided into 3 groups (Control, T–15 and T-30) of 6 each in completely randomised design. The calves in control group were fed ad libitum as per predicted requirement; while in group T-15 and T-30 calves were fed 15 and 30% restricted diets of predicted requirements. Daily intake of DM and OM was significantly (P<0.05) higher in control group relative to T-30, however, T-15 had an intermediate position. Digestibility coefficient of DM and OM was significantly (P<0.01) higher in T-30 group as compared to control and T-15 groups. Efficiency of N-utilization was better (P<0.01) in T-30 and T-15 groups than control. BW gain (kg) and average daily gain (ADG; g) were significantly (P<0.01) higher in control and T-15 groups as compared to T-30. Feed conversion ratio (FCR) of calves was better (P<0.01) in T-15 as compared to T-30. Haematological parameters and serum enzymes did not differ significantly (P>0.05) among treatment groups. However, serum glucose, total protein, albumin and serum urea were found to be significantly (P<0.01) lower in T-30. Present study concluded that dietary restriction at 15% level was efficient and at par with the control group having no feed restriction.

The physiology of the honey possum, Tarsipes rostratus, a small marsupial with a suite of highly specialised characters: a review

Field and laboratory studies of the iconic nectarivorous and 'pollenivorous' honey possum, Tarsipes rostratus, are reviewed with the aim of identifying aspects of its physiology that are as yet poorly understood and needed to implement management strategies for its long-term conservation. Dietary specialisations include the loss of teeth, a modified gut with a high rate of passage, exceptionally low minimum nitrogen requirements, an apparently high basal metabolic rate and a permanently polyuric kidney. In contrast, its reproductive physiology is plesiomorphic, combining aspects such as a post-partum oestrus, embryonic diapause, photoperiodicity and extended maternal care that are usually separate characteristics of other marsupial groups. In common with a number of other marsupials, the honey possum has the potential for trichromatic colour vision and has been the subject of several studies attempting to correlate visual quality with ecological realities. Field physiological studies have established its high rates of nectar and pollen intake needed to maintain energy balance and highlight the need for a constant intake from floral sources. Early allometric studies suggesting that the honey possum's relatively low reproductive rate may be linked to a diet limited in protein have not been supported and nitrogen intakes in the field exceed by a factor of 10 the animal's basic requirements for balance. Measurements of rates of protein turnover in field-caught lactating females suggest that they divert nitrogen from the protein pool to milk production by reducing rates of degradation, rather than by increasing rates of synthesis of protein. Although not yet an endangered species, the honey possum's habitat has been drastically reduced since European occupation of Australia and future-targeted research on the animal's unique physiology and habitat linkage is needed that can be translated into effective management practices. Only then will its long-term survival be assured.

Comparative digestibility of wholemeal and white breads and the effect of the degree of fineness of grinding on the former

1. Loaves were baked from three types of wheaten flour made from the same grist; a straight run white flour of 73% extraction, a finely ground wholemeal (100% extraction) and a medium ground wholemeal (100% extraction). Bread from each was consumed by six persons for periods of 11–12 days. The daily consumption was 530–630 g. dry weight of bread and, in addition, 37 g. margarine, 284 c.c. milk, 72 g. marmalade jelly and 284 c.c. of mild ale.

2. The total energy, nitrogen and fibre of the food consumed and of the faeces excreted over a period of 7 days were determined. Assuming that the foods other than bread were wholly digestible, the average percentage absorption of energy, nitrogen and fibre from the white bread was 96·1, 91·1, and 65·8 respectively; from the fine wholemeal bread it was 86·9, 85·3 and 14 respectively and from the coarser ground wholemeal 87·1, 85·7 and 9·7 respectively.

3. The nitrogen intake per 100 g. of the wholemeal bread eaten, was 2·91; of the white bread 2·70 g. This advantage was, however, neutralized by the greater amount of nitrogen lost in the faeces when wholemeal was taken, so that the average net gain of nitrogen to the body was 2·46 and 2·49 respectively per 100 g. dry weight of bread consumed.

4. The loss of 9% more of the energy of the bread in the faeces from wholemeal than from white bread is largely accounted for by the undigested cell envelopes and woody fibre in the bran. The greater utilization of the fibre of the white bread is in accordance with the observations of Rubner who showed that the cell membranes of the endosperm were of different composition from those of the bran cells and were more readily attacked by bacteria in the gut.

5. The range of individual variations in the utilization of the energy of the breads were: for white bread 95·4–96·8% and for wholemeal 85·4–88·7%. In the utilization of nitrogen these were: for white bread 88·2–94·1%, and for wholemeal 78·5–89·6%. The same subjects showed the better utilization of both energy and nitrogen.

6. The fineness of grinding of the wholemeal within the range used made no significant difference to the utilization of either energy or nitrogen.

The digestibility of English and Canadian wheats with special reference to the digestibility of wheat protein by man

1. Two men and four women carried out digestibility experiments on English and Canadian wheats at 90 and 80% extractions. The flour was the only source of protein and contributed 77−93% of the total dietary calories.

2. At 90% extraction the digestibility of the diets in terms of calories was unaffected by the source of the flour and amounted to 93·3%. At 80% extraction the digestibility of the diet containing English wheat amounted to 95·6% and of those containing Manitoba wheat to 96·7%. The difference is attributed to mild intestinal upsets on the English flour.

3. The apparent digestibility of the protein depended upon the amount of N in the wheat and fell as the extraction rose. A quantitative analysis of the results indicates that the protein in wheat flour of 90 and 80% extraction is completely digested and absorbed, and that the N found in the faeces is entirely derived from the secretions of the gut.

The Medical Research Council paid for the expenses of this investigation. We are very much indebted to Drs T. Moran, C. R. Jones and other members of the Cereals Research Station, St Albans, without whose help this study would hardly have been possible. We have also very much appreciated the help we have received from the subjects, Miss M. Costain, Miss C. M. Walsham, Miss E. Wilkinson and Mr R. Tayler, and also from Flt.-Sergeant Childs, who kindly made the bomb calorimeter determinations.

219. The nutritive value of proteins for milk production. V. The effect of high temperature and of season on the nutritive value of grass proteins, the supplementary effect of the maintenance ration on the production ration, and the effect of feeding a high-protein ration

1. As regards the nutritive value of artificially dried spring grass, the protein appears to be unaffected by the temperature of drying even to the extent of scorching the grass. Early autumn dried grass has a biological value intermediate between spring and late autumn grass, while linseed cake has a very low value.

2. The supplementary effect of the maintenance on the production ration has been shown when hay was substituted for straw in the maintenance ration together with a production protein intake of poor biological value.

3. With an excess of protein in the ration most of the excess nitrogen was excreted in the urine, while both the milk yield and the biological value of the food protein fell considerably. It is possible that, together with an adequate amount of lysine in the protein ingested, a certain mixture of amino-acids is essential before maximum milk yield can be obtained.

4. A study of the nitrogen metabolism shows that high-temperature drying has no effect, whereas marked effects were noted with the early autumn grass and more especially with the linseed cake. The hippuric acid nitrogen output decreased with the high-temperature dried grass, possibly the effect of a loss on drying of benzoic acid. With the high-protein diet an increased excretion of creatinine was noted with no alteration in the creatinine intake. The purin metabolism varies with the total nitrogen excretion, the allantoin increasing markedly in the high-protein period. This is due to an increased intake of purin base.

5. The sulphur metabolism shows the results to be expected from previous publications except in the case of the high-temperature dried grass. It appears that the high-temperature treatment has in some way affected the nature of the sulphur compounds in the grass, with a consequent diminution in the retention.

Nitrogen metabolism and renal function in the dik-dik antelope (Rhynchotragus kirkii)

Nitrogen metabolism and kidney function of the dik-dik antelope (Rhynchotragus kirkii) were studied under a range of controlled, experimental conditions and diets. Dik-dik antelope remained in nitrogen balance even when fed a diet low in protein and high in fibre. When fed a diet high in protein (20%) and water ad-libitum, 55.3% of the urea filtered by the kidney was reabsorbed. Limiting water intake increased urea reabsorption to 77.2%. The U/P urea concentrations were maintained at similar ratios on all diets, as well as during dehydration and solute loading. Minimum endogenous nitrogen excreted was 74mg/kg(0.75)/day. Dehydration (water deprivation) and solute loading (intraruminal infusion of 0.25M NaCl) had varying effects on nitrogen metabolism. It is concluded that the metabolic nitrogen economy of the dik-dik antelope is qualitatively similar to that of other domestic and wild ruminants.

Digestion, absorption and utilization of single-cell protein by the preruminant calf. The true digestibility of milk and bacterial protein and the apparent digestibility and utilization of their constituent amino acids

Two experiments of Latin square design were made, each with four Friesian bull calves fitted with re-entrant duodenal and ileal cannulas at 4-10 d of age. The calves were used to study the effect of giving milk-substitutes containing 0, 300, 500 and 700 g bacterial protein (Pruteen)/kg total protein on apparent digestibility of nitrogen fractions and amino acids and true digestibility of 3H-labelled milk protein and 35S-labelled bacterial protein in the small intestine. A third experiment of Latin square design with four intact Friesian calves was used to measure apparent digestibility of nutrients throughout the alimentary tract and retention of N, calcium and phosphorus. At the duodenum, volume of outflow, its pH, and outflow of total-N(TN), protein-N (PN) and non-protein-N (NPN) decreased with time after feeding. At the ileum, volume of outflow and TN outflow were unaffected by time after feeding but PN outflow decreased; NPN outflow at the ileum increased to a maximum 6 h after feeding and then declined. Increased inclusion of Pruteen did not affect the volume of outflow at the duodenum or ileum, but duodenal PN outflow increased. At the ileum, pH values were lower and TN, PN and NPN outflows were higher with increasing concentration of Pruteen in the diet. Apparent digestibility in the small intestine tended to decrease with greater amounts of Pruteen, but was only significant for NPN. Apparent digestibility from mouth to ileum significantly decreased for TN and PN as Pruteen inclusion increased. Amino acid concentration in duodenal outflow, with the exception of that of arginine, reflected intake. The total amount of each amino acid in ileal outflow increased and the apparent digestibility of most amino acids decreased with greater amounts of Pruteen in the diet. Apparent digestibility of nucleic acid-N from Pruteen was very high. True digestibility in the small intestine and between mouth and ileum of 3H-labelled milk protein was high and did not differ between dietary treatments. True digestibility of 35S-labelled Pruteen was low for the milk-protein diet and tended to increase linearly as more dietary Pruteen was included. Dry matter concentration in faeces and a high apparent digestibility throughout the whole alimentary tract of carbohydrates did not differ between treatments.(ABSTRACT TRUNCATED AT 400 WORDS)