Estimation of the relative bioavailability of inorganic selenium sources for poultry. 2. Tissue uptake of selenium from high dietary selenium concentrations.

An experiment was conducted with 192 day-old male Cobb chicks to study tissue uptake of Se as an estimate of the bioavailability of supplemental inorganic Se sources fed at high dietary concentrations. A basal corn-soybean meal diet (.18 mg Se/kg diet, dry matter basis) was supplemented with 0, 3, 6, or 9 mg Se/kg diet (as-fed basis) as either reagent grade Na2SeO3, CaSeO3, or Na2SeO3 plus fumed amorphous carrier or 6 mg Se/kg diet as either Na2SeO4 or Se metal, and fed for 1 wk. No toxic effects were noted as expressed by mortality; however, there was a reduction (P less than .01) in feed intake and daily gain when 9 mg Se/kg diet was fed, suggesting onset of toxicosis. Selenium concentration in liver, kidney, muscle, and plasma increased linearly (P less than .01) as dietary Se increased from all sources. Selenium metal produced lower (P less than .01) Se concentrations in kidney and muscle than other supplemental sources. Multiple regression slope ratios were used to estimate relative bioavailability values of 100, 103, 99, 112, and 83 for Na2SeO3, CaSeO3, Na2SeO3 + carrier, Na2SeO4, and Se metal, respectively. When these ratios were corrected for the analyzed dietary Se concentration, relative values were 100, 96, 94, 109, and 81 for the above sources, respectively.

Effects of time and dietary selenium concentration as sodium selenite on tissue selenium uptake by sheep.

Thirty crossbred wethers (60 kg avg initial wt) were used to study the time-dose response to dietary Se as sodium selenite (Na2SeO3). Sheep were fed a basal diet (.20 mg/kg Se, M basis) for 10 d; three wethers were killed and tissues were collected for controls. The remaining 27 sheep were assigned randomly to diets supplemented with either 3, 6 or 9 mg/kg Se (as-fed basis) from reagent grade Na2SeO3 and fed for 10, 20 or 30 d. Feed offered was restricted to 1,200 g daily and tap water was available ad libitum. Sheep were stunned and killed by exsanguination and liver, kidney, muscle, heart and spleen were removed and frozen for Se analysis. No toxic effects were noted as expressed by feed intake or hemoglobin concentration. Added dietary Se increased Se linearly (P less than .01) in liver, kidney, and serum. Selenium in liver, kidney and serum also increased (P less than .01) as time advanced. Serum, liver and kidney were more sensitive to dietary Se than were muscle, heart and spleen. Ten days appeared to be an adequate length of time for further Se bioassay studies of this nature. Reagent grade Na2SeO3 was nontoxic when fed to sheep for 30 d at levels up to 90 times the Se requirement.

Estimation of the relative biological availability of inorganic selenium sources for ruminants using tissue uptake of selenium.

An experiment was conducted to estimate the relative bioavailability of inorganic Se sources based on tissue Se deposition following supplementation at high dietary levels. Twenty-eight crossbred wethers averaging 50 kg initial weight were assigned randomly to seven treatments that were fed for 10 d. The basal diet contained .18 mg/kg Se (DM basis). Dietary Se was added at 0, 3, 6 or 9 mg/kg as reagent grade sodium selenite (Na2SeO3) and 6 mg/kg from either calcium selenite (CaSeO3), Na2SeO3 + fumed amorphous carrier or sodium selenate (Na2SeO4). There were four sheep per treatment group, housed in individual, raised pens with slatted floors. Daily feed intake was restricted to 1,200 g and tap water was available ad libitum. The basal diet was fed for a 10-d adjustment period, then sheep were fed experimental diets for 10 d. At the termination of the experiment, blood samples were taken; sheep were stunned and killed, and livers and kidneys were removed and frozen for Se analysis. There was a linear (P less than .001) uptake of Se in liver, kidney and serum. The CaSeO3 and Na2SeO4 sources resulted in greater (P less than .05) Se concentrations in liver and kidney than did Na2SeO3, but these differences were not significant when the analyzed dietary Se concentrations were used as a covariate in the statistical model. Based on linear and multiple linear regression slopes and average increases in serum, liver and kidney Se concentrations, estimated relative bioavailability values corrected for analyzed dietary concentration, were 100, 101, 90 and 133 for Na2SeO3, CaSeO3, Na2SeO3 + carrier and Na2SeO4, respectively.

Estimation of the relative bioavailability of inorganic selenium sources for poultry. 1. Effect of time and high dietary selenium on tissue selenium uptake.

An experiment was conducted with male broiler-type chicks to study the effect of time and high dietary Se concentration on tissue Se uptake. A basal corn-soybean meal diet (.2 mg/kg Se, DM basis) was supplemented with 0, 3, 6, or 9 mg/kg Se (as-fed basis) as Na2SeO3 and fed ad libitum for 1, 2, or 3 wk. No toxic effect of Se was observed as expressed by mortality; however, there was a reduction in daily feed intake (P less than .01) at 6 and 9 mg/kg added Se, particularly at 3 wk, suggesting developing toxicosis. Selenium concentration in all tissues studied increased linearly (P less than .001) as dietary Se increased, especially in kidney and liver. Coefficients of determination and lambda criterion values were greatest in plasma, followed by liver, muscle, and kidney. It appeared that 1 wk would be an adequate length of time for further Se bioavailability studies based on tissue Se uptake from diets containing 3 to 9 mg/kg added Se.

Phosphorus supplementation of Nellore steers fed Yaragua/Stylo mixture in the Peruvian tropics.

Twenty-four yearling 11-month old Nellore steers initially weighing 180 kg were assigned to three treatments in a randomised complete block experiment lasting 392 days. Animals grazed continuously either Yaragua grass (Hyparrhenia rufa) or Yaragua/Stylo legume (Stylosanthes guianensis) and received the following treatments: A) Control, Yaragua plus common salt, B) Yaragua/Stylo plus common salt, and C) Yaragua/Stylo plus dicalcium phosphate/common salt (1:1). Mineral consumption in the three groups averaged 52 g per animal day-1. At 13 months daily liveweight gains/steer were 0.182, 0.409 and 0.483 kg for treatments of Yaragua, Yaragua/Stylo, and Yaragua/Stylo plus dicalcium phosphate/common salt mixture. Daily liveweight gains per ha were 0.488, 1.289, and 1.522 kg steer-1 for Yaragua, Yaragua/Stylo plus common salt and Yaragua/Stylo plus dicalcium phosphate/common salt. Steers receiving a legume (stylo) in the diet more than doubled weight gains (P less than 0.05) compared to controls with dicalcium phosphate further (P less than 0.05) increasing these gains.