Lactational Responses to Postruminal Administration of Proteins and Amino Acids

Response of Lactating Dairy Cows to Abomasal Infusion of Amino Acids

Rumen Bypass and Protection of Proteins and Amino Acids

Manipulation of rumen fermentation

Four experiments were carried out to identify and quantify the limiting amino acids (AA) in rumen microbial protein (RMP). A method was developed which involved first, an assessment of the efficiency of utilization of absorbed AA-nitrogen (U) of RMP, defined as the retention of AA-N from RMP absorbed from the small intestine, and second, addition of a mixture of AA similar to the absorbed AA profile in a quantity defined by the U of RMP and equal to (1-U)/U. Third, it involved removal of each AA in turn and measurement of the resultant N retention. Using this approach it was possible to calculate both the order and extent of AA limitations in RMP. Apart from methionine which was found to be the most limiting AA, only lysine, arginine and histidine reduced N retention when omitted, and accordingly only these AA were limiting in RMP. The method is discussed in detail and the amount of supplementary AA required to utilize RMP fully is calculated.

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The nutritive value of rumen micro-organisms in ruminants. 4. The limiting amino acids of microbial protein in growing sheep determined by a new approach.

The qualitative amino acid adequacy of ruminally synthesized protein for growing lambs was evaluated by nitrogen retention responses to abomasal infusions of amino acids. The experimental animals were fed a controlled level of semipurified diet containing urea as the sole nitrogen source. Methionine alone con sistently increased nitrogen retention above isonitrogenous urea-infused controls. Lysine produced a positive nitrogen retention response only after supplemental methionine was provided. Threonine increased nitrogen retention only when infused concurrently with methionine and lysine. The data suggested that the limiting order of essential amino acids for growing lambs fed urea as the sole nitrogen source was: 1) methio nine, 2) lysine and 3) threonine. An abomasal supplement of the combination of methionine, lysine and threonine increased nitrogen retention 60% above the urea infusion control values. Tryptophan, histidine or leucine did not significantly in fluence nitrogen retention when infused with methionine, lysine and threonine. Methionine was also shown to be the first limiting essential amino acid when non specific amino nitrogen needs were supplied by glutamic acid. Plasma amino acid patterns appeared responsive to infusions and may provide an index of amino acid status in the growing lamb.

J. Kaminski

Papers

Qualitative assessment of supplemental amino acid needs for growing lambs fed urea as the sole nitrogen source

Effect of feed consumption on plasma amino acid concentrations in lambs.