Metabolic adaptation to experimentally increased glucose demand in ruminants.

Abstract

Four Dorset wethers were studied in a Latin square design with 72-h periods to determine the metabolic adaptations that occur in support of increased glucose demand in ruminants. Wethers injected at 8-h intervals with excipient or a total of .5, 1.0, or 2.0 g/d of phlorizin excreted an average of 0, 72.7, 97.9, and 98.5 g/d of glucose into the urine, respectively. Both acute (2 to 24 h after the first injection) and chronic (8-h intervals from 8 to 72 h after the first injection) adaptations of plasma variables to phlorizin treatment were assessed. Concentrations of plasma glucose decreased linearly with increasing phlorizin dose during the 1st 24 h of treatment and tended to decrease linearly with phlorizin dose during 8 to 72 h of treatment. Urea N tended to increase linearly during 2 to 24 h and increased linearly during 8 to 72 h. Nonesterified fatty acids increased linearly with phlorizin injection during the entire treatment period. beta-Hydroxybutyrate increased quadratically with phlorizin injection during 2 to 24 h and tended to increase quadratically during 8 to 72 h. The ratio of insulin to glucagon tended to decrease linearly with phlorizin injection during the 1st 24 h but was unaffected from 8 to 72 h. Triiodothyronine, but not thyroxine, tended to decrease linearly with phlorizin injection during 8 to 72 h. Cortisol was not affected by treatment. Digestibilities of energy and N were not affected by treatment. Urinary energy excretion increased with phlorizin injection in proportion to the amounts of glucose excreted into the urine. These data indicate that phlorizin-treated wethers largely adapted to phlorizin treatment by 24 h after the first injection and are a suitable model for further investigations of hepatic adaptation to increased glucose demand in ruminants.

Whole body glucose turnover in growing and non-productive adult ruminants: meta-analysis and review

“…In lactating or pregnant ruminants, glucose turnover is clearly affected by changes in glucose requirements [12,[74][75][76]. In adult sheep, glucose turnover was better correlated with energy balance than with intake level, suggesting that the nutritional status of the animal had at least as much influence as the supply of glucose precursors [32].…”

Substrate oxidation by isolated ovine enterocytes is increased by phlorizin-induced glucosuria

“…Phlorizin injections decreased concentrations of glucose and insulin in plasma from lactating cows (Amaral-Phillips et al 1993). Consistent with metabolic adaptations to an increased glucose demand, phlorizin injection did not affect daily dry matter intake, milk production, or milk composition in dairy cows (Amaral-Phillips et al 1993) and resulted in only a transient decrease in concentrations of glucose in plasma from growing wethers (Overton et al 1998). The hepatic capacity to convert carbon from propionate into glucose was increased in phlorizin-treated steers (Veenhuizen et al 1988) and wethers (Overton et al 1999).…”

“…Phlorizininduced glucosuria in growing wethers has been used as a model to examine hepatic adaptations to increased glucose demand in ruminants (Overton et al 1998). Phlorizin injections decreased concentrations of glucose and insulin in plasma from lactating cows (Amaral-Phillips et al 1993).…”

“…This work was part of a larger study designed to examine homeorhetic adaptations to an increased glucose demand in ruminants (Overton et al 1998;Overton et al 1999 …”

Passage of nutrients into the duodenum and their postruminal digestion in cows fed crushed and ground maize

“…The extent of microbial proteosynthesis and supply of the animal not only with microbial protein but also with amino acids depend upon the amount of fermentable energy in the rumen (Owens et al, 1986;Huntington, 1997). For this reason synchronization of carbohydrate fermentation and release of nitrogen are of great importance for the synthesis of ruminal microbial proteins and their passage into the small intestine (Herrera-Saldana et al, 1990;Aldrich et al, 1993;Overton et al, 1998).…”