[Nutritional physiology studies in pigs on the evaluation of modified proteins. 1. Results of the estimation of N-turnover, apparent and true digestibility of proteins in addition to apparent and true absorption of amino acids in the entire digestive tract]

[Results of lysine utilization in growing monogastric animals with special reference to various lysine sources]

Object of investigations was to estimate lysine efficiency from different lysine sources (lysinemonohydrochloride and lysinesulfate resp.) for rats, piglets and broiler chickens to reach a higher level of calculation of lysine supply. Lysine limiting diets were based on wheat, soybean meal and wheat gluten, supplemented with different levels of lysine sources under investigation. Balance trials (rat, piglet, chicken) and growth trails with analyses of body composition (chicken) were done to estimate N-balance resp. N-deposition. N-utilization model from Gebhardt (1966) and its further development for efficiency estimation of feed amino acids were used for data calculation. Results allow conclusion, that there are no differences in utilization of lysine from lysinemonohydrochloride and lysinesulfate. Limitations of efficiency resulting from differences in time course of absorption between protein bound and free lysine were not observed under ad lib. feeding conditions.

[Mechanism of action of lysine in relation to its form of supply in swine]

It was the aim of this study to check the maximum value of lysine efficiency in feed proteins used as yet for the ascertainment of amino acid efficiency coefficients (cf. Liebert and Gebhardt 1988 b). For this purpose N balance measurements were carried out with 5 female pigs (30-35 kg LW) under conditions of continuous lysine infusion (duration of infusion 12 hours) through subclavian indwelling catheters with the help of a proven N utilization model. Based on defined limiting relations in the wheat/wheat gluten ration used, the lysine efficiency coefficient for infused lysine could be ascertained according to the difference method as 1.03, i.e., slightly above the maximum value for lysine efficiency determined up to now. The current standard of maximum lysine efficiency was determined as bc-1 Lys = 102, which is the basis of further calculations of lysine efficiency coefficients.

[Evaluation of the protein quality of silaged corn ear products with different crude fiber contents]

The assessment of the protein quality of silaged maize ear products was carried out on the basis of crude protein and amino acid analyses and of N balance measurings with growing pigs including comparative studies with maize corns and cereals. The differences found in the amino acid concentrations between the individual maize ear products could be verified on the basis of the analysed values of husks, cobs and corns. There were no significant differences in the parameters of total protein utilization (PNu, b-value) between the studied silages. The differing crude fibre content resulted, however, in reverse shifts in N excretion in faeces and urine, i.e. diminished protein digestibility was compensated by improved intermediary utilization.

[The activity of and requirements for selected amino acids in growing female swine. 2. Methionine and cystine]

The methionine/cystine efficiency of ten protein sources including that of different charges of the same protein source was ascertained in N balance experiments with a total of 60 female pigs in the live weight range of 35-50 kg. The variability of the derived sulfur amino acids (SAS) efficiency coefficient (Csas) ranged between 0.64... 0.91 based on the SAS efficiency of casein as a standard. There was an analogous differentiation for the derived requirement values on the basis of the analysed methionine/cystine values of the proteins. For a protein retention of 100 g/day and a live weight of 40 kg, 6.2g methionine/cystine was ascertained based on the highest SAS efficiency (Csas = 1) as yet.

[Activity of and requirement for selected amino acids in growing female pigs. 1. Lysine]

In N balance experiments with a total 59 growing female pigs in the live weight range of 33 to 55 kg the lysine efficiency (bc-1 value) and the lysine efficiency coefficient (kLys) of various cereal proteins were ascertained under the consideration of various charges and varieties. The range of kLys = 0.65 ... 0.96 shows a wide spectrum of lysine efficiency, which results in an analogous differentiation of the derived lysine requirement values. Assuming kLys = 1.0 (lysine efficiency 100%, i.e. the maximum value for bc-1 found as yet for native proteins) a daily lysine requirement (efficient amino acid) of 8.9, 10.8 and 12.6 g resp. was ascertained for 100 g daily protein retention at 30, 40 and 50 kg live weight resp.

[The influence of cellulose and various starches in feed on nitrogen metabolism in growing swine]

In N-balance experiments with a total of 49 female fattening pigs with a live weight between 33 and 47 kg the influence of cellulose supplements (exchanger principle) and changing quotas of maize starch and maize soak starch in semisynthetic feed mixtures on parameters of N-utilization was studied. The results show that there may be a positive influence of the supplement of cellulose on total N utilization (b-value, Gebhardt, 1963). One can conclude that, apart from a shift of the ways of N-excretion through faeces and urine, the utilization of products of microbial protein synthesis for N-retention is possible to a nutrition-physiologically relevant degree. The influence of the kind of starch on N-utilization was small.

[Nitrogen metabolism in growing swine with special reference to the efficacy of lysine from various lysine sources]

The results of measurings of N-metabolism in relation to the utilisation of the limiting amino acids are discussed on the basis of N-balance experiments with 20 growing female pigs (live weight 35-40 kg) with lysine-limited, highly digestible synthetic feed mixtures. Based on an N-utilisation model (Gebhardt, 1963), conclusions are drawn concerning the effectivity of lysine from various lysine sources. In accordance with literature, differences between synthetic lysine and microbial lysine concentrate could not be observed.

[Absorption and use of differently structured protein isolates by rats]

Differently structured isolated proteins with the same amino acid composition were tested with growing albino rats in an N-balance and absorption experiment. The following items were tested: --isolated horse bean protein --hydrolysed isolated horse bean protein with an amino acid supplement to make up for losses due to hydrolysis --horse bean protein-casein (1:1) fibres --isolated horse bean protein with an amino acid supplement to achieve the same amino acid concentrations as in the horse bean protein-casein fibres. The lowest digestibility and utilisation values were ascertained for the hydrolysed protein. Endogenous N-excretion calculated according to the isotope dilution method was higher than for intact proteins, the transport of the chyme in the digestive tract and the true absorption of N in the small intestine had significantly diminished. In comparison with horse bean protein supplemented with amino acids, the horse bean protein-casein fibres showed decreased protein utilisation and increased endogenous N-excretion. Independent of the protein fed and of the time after feeding a relatively constant endogenous N-quota of approximately 70% could be ascertained in the chyme in the small intestine. In contrast to this, the relation between exogenous and endogenous N determined from the contents of the large intestine proved to be dependent on the intermediary utilisation of the protein fed.

[Relation between creatinine excretion in the urine and feed protein quality in the growing pig]

N-balance experiments, in which creatinine excretion in urine was measured, were carried out with 80 female fattening pigs. 16 protein sources of different quality were used. In addition to that, an N-increase experiment--protein quality remaining the same--and N-free experiment and results from literature were included into the assessment. The b-value (Gebhardt, 1963) served as the criterion for protein quality. The creatinine coefficient (mg creatinine in urine per kg live weight and day) could be determined as 40.2. There was a direct relation between the N-balance value and creatinine excretion, not however, in the N-increase experiment. Significant relations to the protein quality (b-value, Gebhardt, 1963) could only be established when N-excretion in urine was included.

[Physiological nutrition studies of swine for the evaluation of modified proteins. 3. Relationship between the true and apparent N digestibility and amino acid absorption of the small intestines and the parameters of N metabolism]

Modified proteins were tested in absorption investigations with eight pigs with ileocaecal re-entrant cannulae. The apparent digestibility up to the end of the small intestines showed considerable differences between the feed proteins (77-93%). The same differences could be observed with regard to the apparent absorption of amino acids. Concerning the true N-digestibility resp. the true absorption of the amino acids in the above mentioned section of the intestinal tract there were hardly any differences between the proteins given. The results show that there is a relation between the amount of endogenous N in the chyme at the end of the small intestines and the protein consumed. The amount of endogenous N in the chyme in the small intestines influence N-excretion in urine and thus the intermediary utilisation of feed protein. From the point of view of nutrition physiology it follows that the spun vicia-faba protein/casein (1 : 1) fibres (C) approximate best the value of casein (A). While the treatment of this mixed protein with dyaldehyde starch had a negligible effect on the ascertained parameters only, the treatment of the same protein with aluminium chloride diminished its value more. The isolated vicia-faba (B) was the poorest of the modified proteins tested.