Plasma and liver metabolites and glucose kinetics as affected by prolonged ketonemia-glucosuria and fasting in steers

Metabolic adaptations associated with irreversible glucose loss are different to those observed during under-nutrition

In this study the hypothesis that irreversible glucose loss results in an 'uncoupling' of the somatotrophic axis (increasing plasma GH levels and decreasing plasma IGF-I) was tested. During periods of negative energy balance the somatotrophic axis respond by increasing plasma GH and decreasing plasma IGF-I levels. In turn, elevated GH repartitions nutrient by increasing lipolysis and protein synthesis, and decreases protein degradation. Irreversible glucose loss was induced using sub-cutaneous injections of phloridizin. Seven non-lactating cows were treated with 8g/day phloridizin (PHZ) and seven control animals (CTRL, 0g/day), while being restricted to a diet of 80% maintenance. PHZ treatment increased urinary glucose excretion (P<0.001), resulting in hypoglycemia (P<0.001). As a response to this glucose loss, the PHZ treated animals had elevated plasma NEFA (P<0.005) and BHBA (P<0.001) levels. Average plasma insulin concentrations were not altered with PHZ treatment (P=0.059). Plasma GH was not different between the two groups (P>0.1), whereas plasma IGF-I levels decreased significantly (P<0.001) with PHZ treatment. The decline in plasma IGF-I concentrations was mirrored by a decrease in the abundance of hepatic IGF-I mRNA (P=0.005), in addition the abundance of hepatic mRNA for both growth hormone receptors (GHR(tot) and GHR(1A)) was also decreased (P<0.05). Therefore, the irreversible glucose loss resulted in a partial 'uncoupling' of the somatotrophic axis, as no increase in plasma GH levels occurred although plasma IGF-I levels, hepatic IGF-I mRNA declined, and the abundance of liver GH receptor mRNA declined.

Sites, rates, and limits of starch digestion and glucose metabolism in growing cattle1

Growing cattle in the United States consume up to 6 kg of starch daily, mainly from corn or sorghum grain. Total tract apparent digestibility of starch usually ranges from 90 to 100% of starch intake. Ruminal starch digestion ranges from 75 to 80% of starch intake and is not greatly affected by intake over a range of 1 to 5 kg of starch/d. Starch apparently digested in the small intestine decreases from 80 to 34% as starch entering the small intestine increases from 0.2 to 2 kg/d. Starch apparently digested in the large intestine ranges from 44 to 46% of starch entering the large intestine. Approximately 70% of starch digested in the small intestine appears as glucose in the bloodstream. Within the range of starch intakes that do not cause rumen upsets, increasing starch (and energy) intake increases the amount of starch digested in the rumen, increases the supply of starch to the small intestine, increases starch digested in small intestine (albeit at reduced efficiency), and increases starch digested in the large intestine, such that total tract digestibility remains relatively constant. With increased starch intake, most of the starch is still digested in the rumen, but increasing amounts of starch escape ruminal and intestinal digestion, and disappear distal to the ileocecal junction. Again, within the range of starch intakes that do not cause rumen upsets, as starch intake increases, hepatic gluconeogenesis increases, glucose entry increases, and glucose irreversible loss increases, with a significant portion lost as CO2. The ability to increase use of dietary starch to support greater weight gains or improved marbling could come from increasing starch digestion in a healthy rumen or in the small intestine, but we conclude that the main limit to use of dietary starch to support live weight gain is digestion and absorption from the small intestine. Increased oxidation of glucose at greater starch intakes may alter energetic efficiency by sparing other oxidizable substrates, like amino acids.

Mixed ruminal microbes of cattle produce isopropanol in the presence of acetone but not 3-D-hydroxybutyrate

The objective was to evaluate the ability of mixed rumen microbes to synthesize isopropanol from acetone or 3-D-hydroxybutyrate. Rumen fluid from seven mature, nonpregnant, dry Holstein cows was incubated with starch or cellulose and additions of acetone, 3-D-hydroxybutyrate, or saline. Rumen fluid was analyzed for isopropanol after 0, 3, 6, and 9 h. No isopropanol was present in any sample at 0 h, and none was present in incubations containing saline or 3-D-hydroxybutyrate at any subsequent time. Incubations that included acetone produced small amounts of isopropanol from 0 to 3 and 3 to 6 h and significantly larger amounts from 6 to 9 h. With starch as the energy substrate, production from 6 to 9 h was 3.8 micromol/min per liter of rumen fluid and 3.7 micromol/min per liter with cellulose as the energy substrate; however, these values did not differ significantly. Mixed rumen microbes could synthesize isopropanol from acetone but not from 3-D-hydroxybutyrate, and rumen microbial metabolism of acetone was the likely source of plasma isopropanol seen in ketotic ruminants.

In vitro hepatic gluconeogenesis and ketogenesis as affected by prolonged ketonemia-glucosuria and fasting in steers

Both 1,3-butanediol, which causes ketonemia, and phlorizin, which causes glucosuria, were given to four steers for 28 days to determine effects of prolonged ketonemia and glucosuria on in vitro hepatic gluconeogenesis and ketogenesis. Treatments were: control ration; control with butanediol plus phlorizin; and fasting for 9 days. Liver slices, obtained by biopsy, were incubated with carbon-14 substrates. Substrate converted to glucose [mumol/(h X g liver)] during control, butanediol plus phlorizin, and fasting averaged 2.34, 7.21, and 12.00 for propionate; .99, 3.80, and 12.26 for lactate; .30, .76, and 2.20 for alanine; and 2.06, 5.37, and 5.78 for glycerol. Omission of calcium++ eliminated increases of gluconeogenesis caused by butanediol plus phlorizin and by fasting. Ketone bodies, octanoate, and bovine serum albumin did not affect glucose production markedly. Stearate inhibited gluconeogenesis during all periods except fasting. Production of beta-hydroxybutyrate [mumol/(h X g liver)] during control, butanediol plus phlorizin, and fasting averaged 2.07, 4.27, and 3.25 from butyrate and .06, .27, and .02 from palmitate. Results demonstrate that the gluconeogenic capacity of bovine liver is responsive to physiological and nutritional status.