Economic and production efficiency aspects of variable energy density in the diets of identical twin calves

Despite the large amount of research evaluating the effects of various levels of nutrition on cattle growth, feedlot performance and carcass development, conflicting opinions remain. O'Donovan (1984), in a review article, summarized these studies in an attempt to find a common denominator that would help explain the variable but he had little success.

Obviously a major contributing factor to these diverse results would be extensive variation in experimental methodology. Cattle used in experimentation differ in biological type, age, sex, diet and previous environmental treatment. Investigations have been conducted restricting energy consumption so that animals lose weight, maintain their weight or gain weight (gains are limited below maximum gain potential). In addition, proportion of maximal weight gain by energy restricted animals varies considerably between studies. Type of restriction also is different. Cattle can be restricted by reducing total daily feed consumption, reducing dietary energy concentration through feed ingredient manipulation or combinations of both. Length of restriction periods also differs. Some researchers reported that cattle were maintained on low energy diets for the entire feeding period while others provided a period of high energy consumption or a refeeding period. Cattle subjected to these diverse growth limiting treatments then were compared to cattle consuming a common dietary treatmentcontinuously fed animals consuming high energy diets. Consequently, comparisons then were made with cattle at different or similar weights and various ages.