HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Garrett, W. N. Articles by Johnson, D. E. Search for Related Content PubMed Articles by Garrett, W. N. Articles by Johnson, D. E.

Nutritional Energetics of Ruminants

University of California, Davis 95616 and Colorado State University, Fort Collins 80523

Abstract

Research during the last 25 yr has resulted in several major advancements in knowledge regarding the nutritional energetics of ruminants. Respiration calorimetry became highly automated. Comparative slaughter techniques were made less tedious and expensive by the use of large capacity grinders and the ability to predict body composition with reasonable accuracy from carcass density. The use of deuterium oxide to estimate body water and, subsequently, body fat and protein may become a reliable technique to estimate energy balance. These technical improvements have led to a clearer understanding of those factors influencing the efficiency of metabolizable energy (ME) utilization. In general terms, maintenance and lactation are energetically more efficient processes than growth. The net efficiency of ME use by animals gaining fat and protein simultaneously is lower when the gained tissue contains a high proportion of protein. Net efficiency of protein deposition is lower than that of fat and lower than the efficiency of protein synthesis determined from known biochemical pathways (due in part to the energy costs of protein turnover). Several factors influence the metabolizability of a diet and consequently the efficiency of ME utilization-level of intake is important and site of digestion may also play a role. Associative effects are not usual in relation to energy utilization of balanced diets but if observed may also be related to intake and site of digestion. Another major advance has been the development of feeding standards which more completely consider differences in ME utilization. All newer feeding standards are based on net energy concepts although they differ in how the concepts are applied to practical production situations. Much remains to be accomplished. Maintenance energy requirements are large and the components of maintenance need to be clearly defined. Certainly tissue turnover and nutrient transport (ion transport particularly) are important. Why does the source of ME (roughage or grain) have such a marked influence on the efficiency of energy utilization and why is the efficiency of ME use for growth lower when measured by comparative slaughter than by respiration calorimetry? The importance of ion transport as a component of energy metabolism and the influence of ionophores on energy utilization deserves further study. The impact of the many gut X diet interactions on energy metabolism must be more fully assessed. Feeding standards can be made more precise but the translation of fundamental principals to practically useful production situations is not a simple task. Additional information is needed regarding the composition of animals (gained tissue), feed intake and gut-fill as influenced by environment, diet, species, breed and sex class.

Key Words: Energy Metabolism • Energetic Efficiency • Metabolizable Energy Utilization • Ruminants • Energy Balance

¹ Dept. of Anim. Sci., Univ. of California

² Dept. of Anim. Sci., Colorado State Univ.