Rumen Bypass and Protection of Proteins and Amino Acids

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.

/pdf/the-nutritive-value-of-rumen-micro-organisms-in-ruminants-4-4zj8ugvw8d.pdf

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.

Highlight: A wealth of experimental data has been accumulated on quantitative intake of pen-fed livestock; such information has been widely employed to develop a keener nutritional knowledge of such animals. Data of this type are, however, distressingly lacking for grazing livestock. The procedures used for measuring intake by animals under grazing conditions have often been disappointing, and many have provided unreliable data. Forage intake measurements with grazing livestock are more commonly expressed as g DM or OM/Wk -75 or simply as a percent of body weight. Most estimates of inta gk e for cattle and sheep grazing ranges in Western United States fall within the range of 40 to 90 g DM/Wkg’” or from 1 to 2.8% of body weight. Intake usually decreases with advancing plant maturity.

/pdf/forage-intake-by-grazing-livestock-a-review-58m2ugh7f4.pdf

Forage intake by grazing livestock: a review.

Publisher Summary Dietary proteins, through digestion in the gastrointestinal tract, furnish amino acids and polypeptides, which are the raw materials needed to build the body proteins of animals. These body proteins essentially form the matrix of the living system; the centers around which the dynamic equilibria of life develop. This chapter focuses on the biological evaluation of these proteins. The biological value of a protein refers to the amount of nitrogen retained in the body of an animal. A new phase of research on the nutritive value of proteins includes mixtures of amino acids replacing proteins. The pattern of essential amino acids varies with the physiological state of the animal and with the species. The retention of nitrogen in the animal is a function of this pattern. The simplest method used to evaluate nitrogen retention in an animal is to determine the difference between nitrogen intake and nitrogen excreted. This difference, called nitrogen balance, shows whether an animal is maintaining, losing, or gaining nitrogen. Correlations between the nutritive value of a protein and the amino acid composition can be excellent, when the composition represents the pattern of amino acids, which are absorbed into the animal. Along with the evaluation through nitrogen balance, evaluation of proteins through growth and tissue regeneration is also presented.

Biological Evaluation of Proteins

In earlier work on the nitrogen metabolism of the young calf (Blaxter & Wood, 1951 a, c) the sole source of vitamin E in the diets was high-quality dried skim milk that had been packed in sealed tins. At the time it was thought that this source of vitamin E activity would be sufficient to protect the animal during the short-term experiments envisaged, especially in view of the very considerable difficulties that have been met in devising cattle diets containing little vitamin E (Gullickson, Palmer, Boyd, Nelson, Olson, Calverley & Boyer, 1949; Gullickson & Calverley, 1946). One of our early experiments, however, had to be abandoned owing to the onset of a syndrome in which vitamin E appeared to be involved. Six animals were affected 24-60 days after birth. The animals became very weak and unwilling to stand for more than a few minutes; the pastern joints became straightened ; the hind-legs crossed when attempts to walk were made ; there was a general ataxia, and the neck was outstretched in a very characteristic way. A tetany, not involving the extremities, was common during the latter stages and was seen only when the severely affected animal was placed on its feet. Relaxation of the musculature of the throat and inability to control movements of the tongue made drinking difficult and, in the terminal stages, the calves choked, owing to liquid food entering the trachea. Loss of hair at the bulbal base of the ear was always a common feature; the coat was staring and the skin thickened, the latter making superficial venesection difficult. In two animals oedema of the brisket and ascites were present. This was of rapid onset as judged by gains in body-weight and seemed to be associated with a slight exophthalmos. In these oedematous calves the pulse was highly erratic and generally increased in frequency. Death occurred suddenly if such signs of cardiac abnormality were present; otherwise the animals died following a period of prostration. At post-mortem examination ascitic fluid was found in the abdominal cavity, the carcass was generally slightly oedematous, and one constant feature was the rapidity of putrefactive change. The liver and kidneys were normal; the lungs were pneumonic and contained milk and blood. The heart was dilated in some animals, and slight white lesions were found in the walls of the left ventricle in one of those animals affected by oedema. The bones were calcified quite normally but some erosion of the articular cartilages was present. This, however, was also found in normal calves. The skeletal muscle was very pale and flabby, and the fat was a light

/pdf/the-nutrition-of-the-young-ayrshire-calf-2-a-spirometer-for-40w40festz.pdf

The nutrition of the young Ayrshire calf. 2. A spirometer for the determination of the respiratory exchange of the calf.

The Factorization of the Protein Requirements of Ruminants and of the Protein Values of Feeds, with Particular Reference to the Significance of the Metabolic Fecal Nitrogen

Kenneth L. Blaxter

Papers

The Factorization of the Protein Requirements of Ruminants and of the Protein Values of Feeds, with Particular Reference to the Significance of the Metabolic Fecal Nitrogen

Animal Agriculture in a global Context