Simulation of the Energy Costs Associated with Protein Turnover and Na+,K+-Transport in Growing Lambs

Abstract

A mathematical representation of the energy-requiring processes of protein turnover and Na+,K+-transport in the tissues of growing lambs is described. This model was then used to examine the relative contributions of these processes to ATP expenditure at two different growth rates (90-230 g/d). Protein turnover accounted for 19% of whole-body ATP expenditure at both growth rates examined, with the gastrointestinal tract (GIT), accounting for 25-27%, muscle for 21-26%, skin for 23-26% and liver for 13% of total protein turnover energy costs. The contribution of Na+,K+-transport increased from 18 to 23% of whole-body heat production as growth rate increased, with the GIT accounting for 39 and 50%, muscle for 17 and 10% and liver for 18 and 23% of total Na+,K+-transport costs at low and high nutrient inputs, respectively. Thus, protein turnover accounted for 19% of the increment in ATP expenditure due to the increased nutrient input at the higher rate of growth, while Na+,K+-transport accounted for 39%, and fat turnover and accretion accounted for 25%, leaving 17% of the ATP increment unaccounted for.

Energy metabolism by splanchnic tissues of mature sheep fed varying levels of lucerne hay cubes

“…However, the lower than 100% recovery of energy at levels above maintenance may be because of loss of heat of fermentation or energy retained in the PDV and liver as a result of BW gain. In addition, maintenance energy expenditure and metabolic activity of the gut increase with increasing intake of forages (Gill et al, 1989) because of increased gut tissue mass from fibrous feeds (McLeod and Baldwin, 2000). However, technical limits in the estimation of blood flow and arterial-venous differences or lack of data for unmeasured energy substrates such as nucleic acids and peptides cannot be excluded (Lindsay, 1993).…”

Physiology, regulation and multifunctional activity of the gut wall: a rationale for multicompartmental modelling

“…The immune system is an integral part of the GIT (Goddeeris et al 2002) and the majority of the immune cells in the whole body are located in the GIT. Energy costs involved in the immune response of the GIT may therefore be quantitatively far more important than that of the remainder of the body.…”

Effect of dietary corn silage inclusion on visceral organ mass, cellularity, and the protein expression of ATP synthase, Na+/K+-ATPase, proliferating cell nuclear antigen and ubiquitin in feedlot steers

“…In agreement with our observations, McLeod and Baldwin (2000) suggested that level of dietary roughage affects ruminal growth via changes in cellular hyperplasia (i.e., cell number). Goodlad (1981) reported that cell proliferation in ruminal epithelium was stimulated when changing the diet of the sheep from roughage to concentrate. Gaebel et al (1987) observed that the number of cell layers of the epithelium increased when changing the diet from 100% hay to 36% hay, was maintained or decreased when changing the diet from 36% hay to 10% hay, with the alterations being fully reversible.…”

“…Energy costs can be studied on whole body, tissue, cellular, or molecular levels. Cellular energy-consuming events such as ion transport, protein turnover, and cell proliferation are thought to be important in regulating energy metabolism in tissues (Milligan and Summers 1986;Gill et al 1989;McBride and Kelly 1990). These events represent basal metabolic rate and thermoregulatory functions at the cellular and molecular levels.…”