J.T. Reid

BODY WATER ESTIMATIONS IN RELATION TO BODY COMPOSITION AND INDIRECT CALORIMETRY IN RUMINANTS

Further progress in the evaluation of feeding methods and dietary characteristics for ruminants, in the improvement of meat quality and in the selection of the genotype of the parent stock of meat-producing animals, requires that attention be given to at least the gross chemical composition of the body. In accord with modern trends in human dietary regimens, greater emphasis is ostensibly being given to the genetic selection of livestock and to feeding schemes which will produce meat containing more protein and less fat. For the most part, however, the criteria being employed currently are body weight gain and certain visual estimates. In this report some of the limitations of body weight and the slaughterchemical analysis method as means of estimating the chemical composition and the energy exchange in the ruminant will be examined. In addition the body composition of the ovine and bovine will be systematized and accounts will be given of the degree of success with which the chemical composition and energy value of the living ruminant have been estimated by several means.

The influence of dietary fat on fat metabolism and body Fat deposition in meal-feeding and nibbling rats

1. An experiment was done with rats (body-weight 160 g) to study the effects on fat metabolism and body composition of low (10 g/kg)- or high (140 g/kg)- fat diets fed as one meal for one 4 h period/d (meal-feeders) or as six spaced meals/d (nibblers). The daily energy intake/unit metabolic body-weight (body-weight 0.73) was the same for all four groups, and this level of intake was about 80% of that consumed by rats allowed unrestricted access to the low-fat diet. The experimental period was 76 d. 2. Rats given the high-fat diet deposited more body fat/d and, as a result, grew faster and were energetically more efficient than rats given the low-fat diet depressed de novo lipogenesis from glucose in epididymal and perirenal fat pads, whose fatty acid composition resembled that of the diet. 3. For both diets meal-feeders had greater stomach plus small intestine weights than nibblers and had higher plasma free fatty acid levels, when they were killed 15 h after their last meal. 4. Meal-feeders given the low-fat diet had the greatest rate of lipogenesis for fat pads. 5. Meal-feeders given the high-fat deposited less of the main dietary fatty acids in their fat pads. 6. There was no evidence that meal-feeders eating a high-fat diet adapt their metabolism completely that they become more efficient utlizers than those nibbling this diet. Meal-feeders eating the low-fat diet became no fatter than nibblers of this diet, possibly because they were eating less than their daily ad lib. intake.

An equation, suitable for computer use, based on the ARC feeding system to determine the energy requirements of growing and fattening cattle

Based on the Agricultural Research Councils feeding system, equations were developed that allow the calculation of the metabolizable energy requirements for maintenance and weight gain by cattle, separately or combined. A general equation was developed for the straight-forward calculation of the total metabolizable energy requirements of growing and fattening cattle for any combination of body weight, rate of weight gain, age, level of muscular work, and metabolizable energy concentration of the diet. The estimates of energy requirement made by the use of this equation are in excellent agreement with those made by the Agricultural Research Council using an iterative method. In addition to avoiding the awkward iterative process, the equations proposed are readily adaptable to computer use.