Enzyme studies with the livers of chicks fed semi-synthetic diets containing crystalline amino acids and diammonium citrate

Protein-Sourced Feedstuffs for Aquatic Animals in Nutrition Research and Aquaculture

Aquatic animals have particularly high requirements for dietary amino acids (AAs) for health, survival, growth, development, and reproduction. These nutrients are usually provided from ingested proteins and may also be derived from supplemental crystalline AA. AAs are the building blocks of protein (a major component of tissue growth) and, therefore, are the determinants of the growth performance and feed efficiency of farmed fish. Because protein is generally the most expensive ingredient in aqua feeds, much attention has been directed to ensure that dietary protein feedstuff is of high quality and cost-effective for feeding fish, crustaceans, and other aquatic animals worldwide. Due to the rapid development of aquaculture worldwide and a limited source of fishmeal (the traditionally sole or primary source of AAs for aquatic animals), alternative protein sources must be identified to feed aquatic animals. Plant-sourced feedstuffs for aquatic animals include soybean meal, extruded soybean meal, fermented soybean meal, soybean protein concentrates, soybean protein isolates, leaf meal, hydrolyzed plant protein, wheat, wheat hydrolyzed protein, canola meal, cottonseed meal, peanut meal, sunflower meal, peas, rice, dried brewers grains, and dried distillers grains. Animal-sourced feedstuffs include fishmeal, fish paste, bone meal, meat and bone meal, poultry by-product meal, chicken by-product meal, chicken visceral digest, spray-dried poultry plasma, spray-dried egg product, hydrolyzed feather meal, intestine-mucosa product, peptones, blood meal (bovine or poultry), whey powder with high protein content, cheese powder, and insect meal. Microbial sources of protein feedstuffs include yeast protein and single-cell microbial protein (e.g., algae); they have more balanced AA profiles than most plant proteins for animal feeding. Animal-sourced ingredients can be used as a single source of dietary protein or in complementary combinations with plant and microbial sources of proteins. All protein feedstuffs must adequately provide functional AAs for aquatic animals.

The role of the gut microflora in the utilization of dietary urea by the chick

1. In a preliminary experiment, growth of conventional chicks given a basal diet containing adequate amounts of all the essential but none of the non-essential amino acids was improved by supplements of 10·3 g urea or 50·4 g glutamic acid/kg diet or both.

2. In the main study the effects of supplementing the basal diet with 2·6 g urea/kg were compared in groups of sixteen germ-free and conventional chicks.

3. The germ-free chicks did not benefit from the urea supplement whereas the conventional birds showed improved food conversion efficiency and significantly better growth.

4. In both environments nitrogen retention ((mg N intake – mg N excreted) ÷g food intake) was higher in the birds given urea, but N utilization ((mg N intake – mg N excreted) ÷ mg N intake) was reduced. This reduction was greater in the germ-free birds.

5. There was a small increase in plasma ammonia concentration in the germ-free birds given urea but a significantly greater increase in the corresponding conventional group.

6. Plasma uric acid concentrations were variable in both groups, and much lower than the normal range. They followed a similar pattern to the plasma ammonia values.

7. More insoluble N was excreted by the conventional chicks given urea than by the corresponding germ-free group, or by either group given the basal diet.

8. It was concluded that the gut micro-organisms are responsible for the growth-promoting effect of urea, presumably through release of ammonia by bacterial urease (EC3.5.1.5) and its consequent incorporation into amino acids.

In situ degradation and absorption of [15N]urea in chicken ceca

[15N]Urea was introduced (in situ) into a ligated cecal pouch of chickens to determine if it is degraded therein and absorbed into the blood as ammonia during the following 60 min. A mean of 49% of the introduced urea-15N was recovered from the blood of the mesenteric vein draining the cecal pouch and 26% was recovered from the cecal lumen fluid. Of the urea-15N introduced into the pouch, 4%, 2%, 15% and 5% were detected as urea, ammonia and non-protein fractions, except urea and ammonia, and proteins in the lumen fluid, respectively. Non-protein-15N, except urea and ammonia, protein-15N, urea-15N and ammonia-15N values recovered in the cecal venous blood were 10%, 19%, 18% and 2% of the introduced 15N, respectively. Urea concentration in the cecal venous blood increased from 0.71 mg to 3.13 mg per 100 ml for the first 15 min after introduction of urea-15N (P < 0.01) then decreased until 60 min. No significant change was found in blood ammonia concentration, however, despite a small increase during the period 15-45 min after urea-15N introduction. Ammonia-15N increased in the caecal venous blood for the first 30 min then decreased to a plateau level of 43% of the peak level. The rates of increase of urea-15N and non-protein-15N concentrations attained maxima in the blood as early as 15 min, then decreased linearly (P < 0.05). It is concluded that, although urea is actively degraded to ammonia in the ceca, it is mostly absorbed from the ceca, not in the form of ammonia, but as protein, urea and amino acids.

Role of caeca in the nitrogen nutrition of the chicken fed on a moderate protein diet or a low protein diet plus urea

1. A study was carried out to investigate whether the back-flow of urine into the caeca benefits the nitrogen economy of adult cockerels fed on a diet containing 100 g protein/kg and when dietary urea is absorbed, excreted into urine and utilised. 2. No significant effects of colostomy on nitrogen utilisation were observed in chickens fed on 100 g/kg protein diet, whereas colostomy was highly effective in decreasing it in chickens on a diet containing 50 g protein/kg plus urea (P < 0.05). 3. Nitrogen utilisation in conventional birds was significantly less when a diet of moderate protein content was fed than when a low protein diet plus urea was fed, but the opposite effect was seen with colostomised birds (P < 0.05). 4. Colostomy increased urea excretion (nitrogen/kg body weight/day) from 4 to 9 mg in chickens fed on the moderate protein diet, but greatly, from 45 to 182 mg, in those fed on the low protein diet plus urea (P < 0.05). 5. Blood urea concentration increased by about 20 mg per 100 ml in 3 h, a value which was maintained up to 6 h but which returned to the prefeeding concentration at 24 h; both control and colostomised chickens on the low protein diet plus urea responded similarly. 6. After feeding urea, half the daily excretion of urea was observed to occur within 6 and 9 h, respectively, in control and colostomised chickens.(ABSTRACT TRUNCATED AT 250 WORDS)

Occurrence of intraportally-infused urea-15N in the urine of domestic fowl

1. Measurements were made in situ to determine the occurrence of intraportally infused urea-15N in ureteral urine of the fowl. 2. Of the total amount of infused urea-15N, 15% was excreted intact into the urine (90% of urinary total 15N) whereas 9% remained unchanged in the blood (78% of blood non-protein-15N). 3. The proportions of non-protein-15N in the blood, liver and kidney were 12, 3 and 1%, respectively of the infused 15N. Protein-15N was 3% of that infused in blood and much less in liver and kidney. 4. About 1% of the infused 15N was observed in the urinary uric acid, and 3% of the infused 15N in non-protein N, other than urea, ammonia and glutamine amide N, of blood and liver. 5. No appreciable amounts of 15N were present in ammonia and glutamine amide N of blood, liver or kidney and in uric acid of liver or kidney. 6. The caecal contents contained about 1% of the infused 15N with 15% of this as ammonia-15N. 7. It is concluded that intraportal urea is mostly excreted unchanged into ureteral urine of the fowl.

On caecal synthesis and absorption of amino acids and their importance for nitrogen recycling in willow ptarmigan (Lagopus lagopus lagopus)

The willow ptarmigan has two large caeca housing dense populations of microorganisms. Urine, containing uric acid, is transported from the cloaca into the caeca when these are filled. Here the uric acid is rapidly broken down, suggesting that the caeca take part in a recycling of excretory nitrogen. In this work it is shown that ammonia produced by the uric acid decomposition is incorporated into new amino acids in a glutamic dehydrogenase catalyzed reaction. We have, however, not been able to detect any absorption of amino acids from the caeca, indicating that nitrogen recycling via the amino acid route does not occur.

The use of growth and liver aspartate aminotransferase to assess the effect of source of non-essential nitrogen on pyridoxine depletion, repletion and requirements of chicks

1. Two experiments were carried out to study the relationship between growth, liver aspartate aminotransferase (Asp AT) and dietary pyridoxine to determine the pyridoxine requirement of chicks fed on diets containing crystalline essential amino acids with glutamic acid (GA) or diammonium citrate (DAHC) as the non-essential nitrogen source. 2. In one experiment purified diets containing isolated soy-protein with 0 or 3 mg pyridoxine/kg were used. The deficient chicks were significantly lighter, coverted food less efficiently and liver Asp AT activity was decreased. When deficient chicks were offered an adequate diet performance improved and Asp AT activity rapidly increased. 3. In the second experiment diets containing crystalline amino acids GA or DAHC combined with 0, 1 or 3 mg pyridoxine/kg (GA: 0, GA: 1, GA: 3, DAHC: 1, DAHC:3) were used. Growth rates of chicks fed on GA: 1 and GA: 3 were similar, whereas chicks fed on DAHC: 1 were significantly lighter than those given DAHC: 3. The growth data indicated a pyridoxine requirement for chicks fed on the GA diets of not more than 1mg/kg and of more than 1 mg/kg in those fed on diets containing DAHC. Asp AT activity varied significantly with dietary content of pyridoxine but not with the nitrogen source. When Asp AT activity was used to assess pyridoxine requirements, there was nof difference between chicks fed on GA or DAHC diets.