Evaluation of modified [³⁵S]methionine and [³⁵S]casein preparations as supplements for sheep

Abstract

I . Doses of ~-[~~S]methionine (2 g) and r5S]casein (20 g) were given to sheep in the diet or via the abomasum, and the patterns of 35S-labelling in blood, wool and excreta were studied during the 7 d following administration of the dose.2. Doses given via the abomasum resulted in substantial labelling of the plasma proteins and wool; only small amounts of the dose were recovered in the urine and faeces. In contrast, doses given in the diet resulted in much less labelling of plasma proteins and wool and ingreater losses in excreta. These results provide the basis of a rapid system for testing the effectiveness of various methods of protecting methionine and casein from degradation in the rumen. From the patterns obtained with N-formyl-~~-[~~S]methionine and [36S]polymethionine (mol. wt 7-8 x 104) it appears unlikely that these compounds would stimulate wool growth if given as dietary supplements. 4.[S6S]Casein which had been treated with an 8 % aqueous solution of formaldehyde gave results which showed that the casein had been protected from destruction in the rumen without markedly reducing its subsequent digestibility. Treatment of [35S]casein with excess,formaldehyde (a 40 % aqueous solution) gave a product which was completely indigestible. . It is concluded that the radioisotope technique could be applied to other [35S]amino acids or their derivatives and to other [35S]proteins, and should also be applicable to larger ruminants such as cattle.

Plasma Amino Acid Patterns in Sheep Receiving Abomasal Infusions of Methionine and Cystine

“…total amino acids, branched-chain amino acids, serine, and glycine) should have been evident. This result is in accord with the general failure of methionine as a dietary supplement for wool growth (see Reis et al 1973), and with the evidence of Downes et al (1970) for the poor utilization of dietary supplements of [35S] methionine. The results do not support the suggestion of Bird (1972) and Bird and Moir (1972) that the degradation of methionine in the rumen may be sufficiently slow for dietary supplements to stimulate wool growth.…”

“…Disulphide-bound cystine in plasma (Downes et al 1965) was estimated as the difference between total plasma cyst(e)ine and free cyst(e)ine as measured in the amino acid analytical system described above; results were expressed as half-cystine residues. Total plasma cyst(e)ine was measured by a procedure based on the method of Gaitonde (1967), using dithiothreitol (Cleland 1964 to convert free and disulphide-bound cystine to cysteine.…”

Metabolic Fate of Parenterally Administered Sulphur-Containing Amino Acids in Sheep and Effects on Growth and Composition of Wool

“…Furthermore, in the sheep which received 40 g of DL-[35S]methionine intraperitoneally, no change in the rate of wool growth was detected even though 17% of the dose of 35S was incorporated into the wool, an amount in the range (15-30%) observed with 2 g doses administered abomasally (Downes et al 1970). This also fits in with the previous results (Reis 1967) showing that large supplements of methionine are associated with enhanced production of high sulphur proteins in wool without any overall effect on the rate of wool growth (Gillespie and Reis 1966).…”

“…Also, when L-cysteine (2 gjday) or L-methionine (2, 5 gjday) was infused intravenously or intraperitoneally there was a rapid increase in wool growth, the main increase occuring during the first 8 days. Although there may be differences in the metabolism of cysteine and cystine in the sheep, their overall effects on wool growth have been found to be similar (Downes et al 1970). A 12-day supplementation period with measurements made between days 8 and 12 should therefore be sufficient to evaluate the wool growth response to an amino acid supplement.…”

Methionine Substitutes in Ruminant Nutrition I: Stability of Nitrogenous Compounds Related to Methionine during In Vitro Incubation with Rumen Microorganisms

“…This suggests that performance could be improved by providing additional amino acids to the postruminal digestive tract. This hypothesis is supported by responses in nitrogen balance or wool growth obtained during postruminal infusions of protein or amino acids (10- 14) and parenteral administration of methionine (15). The possibilities for effecting such improvement through dietary additions of amino acids are severely limited by the instability of amino acids in the rumen (16,17).…”