Our objective was to quantify changes in supply and use of nutrients and O2 by large-frame, multicatheterized beef steers as they grew from 235 to 525 kg BW. Steers consumed 5.25 to 9.87 kg DM/d of a 62% concentrate diet that provided 126 to 217 g N/d and 1 kg ADG. Steers were assigned to three groups (eight, nine, and eight steers each) that divided the BW range into thirds. Weights at first sampling for the three groups were 236, 319, and 445 kg, respectively. Each group was sampled twice. Groups were killed after the second sampling. Tissue weights and hindquarters (HQ) contents of fat, protein, and ash were measured. Blood flow, oxygen uptake, and net uptake or release of metabolites were regressed against functions of BW.75 to assess changes during growth. Blood flow in all tissues except liver and oxygen use by all tissues decreased per unit tissue weight as BW.75 and age increased. Changes with age per unit liver weight were as follows: decreased uptake of propionate and lactate, increased uptake of alpha-amino N and glutamine, decreased production of urea and glutamate, and increased production of acetate and beta-hydroxybutyrate. Glucose and urea production per unit liver weight was constant. Changes with age per unit HQ weight were as follows: increased uptake of glucose, decreased uptake of alpha-amino N and glutamate, decreased release of lactate, and increased release of glutamine. Weight of the portal-drained viscera (PDV) increased from 91 to 97 g/kg EBW as BW increased from 236 to 522 kg; PDV fat increased from 375 to 552 g/kg PDV tissues. Liver decreased from 16 to 12 g/kg EBW. Hindquarters decreased from 286 to 266 g/kg EBW; HQ protein was 200, 197, and 200 g/kg HQ tissue for Groups 1, 2, and 3, respectively. Corresponding fat was 131, 182, and 177 g/kg HQ tissue. Changes in net flux reflect changes in nutrient partitioning and tissue deposition as steers grew and aged.

Our objective was to quantify effects of age, weight, and body composition on responsiveness (Rmax or Rmin) and sensitivity (ED50) of several parameters of glucose metabolism to insulin in growing beef steers. Steers ate equal-sized meals every 2 h; the diet contained 62% concentrate and sustained 1 kg ADG. Treatments were euglycemic clamps at 10, 20, 40, 80, 160, and 320 mU.h-1.kg BW-1 of insulin infused into a mesenteric vein of seven younger (275 kg BW) and seven older (490 kg BW) steers. Most steers received three of the six treatments; two extra steers were added to compensate for missing data. Steers had blood vessel catheters and ultrasound flow probes that allowed measurement of net uptake or release of glucose and insulin by portal-drained viscera (PDV), liver, and hindquarters (HQ). Steady-state glucose infusion rate (SSGIR) was intrajugular glucose infused during treatments to maintain euglycemia. Within age groups, Rmax or Rmin and ED50 were estimated by nonlinear regression of glucose flux on arterial plasma insulin concentrations. Steers were killed after sampling, tissues were weighted, and HQ content of fat and protein was determined. Those data were used to predict tissue weights and HQ composition at the time of the euglycemic clamps. Predicted EBW (243 vs 444 kg), liver (4.24 vs 6.19 kg), and HQ (73 vs 122 kg) were heavier for older than for younger steers. Fat in HQ was higher for older than for younger steers (173 vs 134 g/kg), but protein was similar (198 g/kg). The ED50 (mU of insulin/L of plasma) for SSGIR (237 +/- 65 vs 113 +/- 22), liver glucose release (89 +/- 22 vs 44 +/- 11), total glucose entry (418 +/- 184 vs 125 +/- 20), and HQ glucose uptake (488 +/- 151 vs 243 +/- 78) was higher for older than for younger steers. The Rmax (mmol glucose.h-1.kg tissue-1) for SSGIR (2.68 +/- .22 vs 2.09 +/- .23) and HQ (3.08 +/- .33 vs 2.46 +/- .30) was higher for younger than for older steers. Liver glucose release decreased in response to insulin; Rmin (mmol glucose.h-1.kg liver-1) was higher for younger (36.0 +/- 6.9) than for older (24.7 +/- 3.2) steers. We conclude that as steers grew older, heavier, and fatter, their peripheral tissues and liver became less sensitive and less responsive to insulin.

Thirty mature chicken hens and 40 mature Japanese quail hens were used in an experiment to compare pathways of decoquinate (DQ) excretion. Labelled DQ was injected into chickens (.5 microCi via wing vein puncture) and quail (.25 microCi via cardiac puncture) on Day 0. Blood was sampled at 0, 1.5, 3, 6, 9, 12, 24, and 48 h postinjection. Eggs and excreta of chickens and quail were collected for 28 and 14 days, respectively, and analyzed for 14C. Six chickens and eight quail were sacrificed prior to 14C-DQ injection and also on Days 1, 7, 14, and 34 or 32 postinjection. Samples of liver, heart, kidney, bile, skin, fat, and muscle were analyzed for 14C. Blood rapidly cleared 14C in both species, and the half-time of 14C excretion via excreta was more rapid in quail (.37 day) than in chickens (.92 day). Little 14C was found in the eggs of quail (.32% of dose) and chickens (.17% of dose). Quail appeared to excrete peak amounts of detectable 14C 1 day earlier (Day 4) than chickens (Day 5). Liver contained the greatest concentration of 14C on Day 1 in both species. By the end of the experiment, less than 1% of the dose remained in liver or other organs. Results indicate that chickens and quail metabolize 14C-DQ at comparable rates and by similar pathways.