Influence of incremental zeranol implant doses on the chemical and physical characteristics of third metacarpal bone and chemical composition of liver and soft tissue from feedlot steers.

Chemical and physical characteristics of third metacarpal bones and liver and rib soft tissue composition from feedlot steers were determined. Steers were selected (32 from each experimental location) to represent the range in slaughter weight and composition for each treatment group in three (total n = 1,088) feedlot experiments. Steers were implanted with 0, 24, 36, 48, 60, 72, 84, or 96 mg of zeranol at approximately 140 d before slaughter. Cattle at each location were fed for the same number of days and slaughtered as a group. Zeranol dose had no effect on the chemical composition of bone, liver, or rib soft tissue with the following exceptions: zeranol decreased (P < .01) bone Ca concentration and increased (P < .07) liver P concentration. Zeranol implantation decreased medullary cavity anterioposterior (AP) diameters and AP cortical width (P < .08). Loads withstood by the bones up to flexure (P < .08) and the strain at flexure (P < .09) were inversely related to the quadratic of zeranol dose. However, modulus of elasticity at flexure and breaking increased numerically with zeranol dose. Stress withstood by bones at flexure was greater (P < .09) for implanted steers. Strain data indicate that metacarpals from steers receiving zeranol would exhibit less deformation upon loading to flexure (P < .09) than controls. These data indicate that administration of intermediate doses of zeranol altered bone deposition of Ca, which resulted in modified third metacarpal physical and mechanical characteristics.

Effects of different doses of zeranol on growth, hemoglobin, and carcass traits in veal calves.

Effects of different doses of zeranol on ADG, hemoglobin (Hb), feed efficiency (FE), and carcass traits were evaluated in special-fed veal calves in two trials. On d 0, calves were implanted subcutaneously in the middle third of the ear with either 0 (control, placebo pellet), 12, 24, 36, or 48 mg of zeranol. Trial 1 was conducted from February through May 1990 with 120 Holstein bull calves (17 to 21 d of age on d 0) and Trial 2 was conducted from May through August 1991 with 100 Holstein bull calves (24 to 28 d of age d 0). Calves were fed on an individual calf basis. Calves in Trial 1 that were implanted with 48 mg of zeranol had improved FE (P < .05) and ADG (P < .05) during Period 1 (0 to 43 d). No significant differences in ADG or FE were observed among treatments in Trial 2. Hemoglobin levels at slaughter averaged 7.88 +/- .096 and 8.19 +/- .149 g/dL over all treatments for Trials 1 and 2, respectively. The only postslaughter trait affected by zeranol dose was testicular weight. In both trials, testicular weight at slaughter decreased (P < .05) with increasing doses of zeranol. Dressing percentage tended to be higher for 48-mg implants than for controls but the difference was not significant. There were no significant zeranol dose effects on longissimus muscle area, flank color, carcass conformation, or percentage of fore- vs hind-quarter weight. These results indicated that higher doses of zeranol improved ADG and FE during the first 6 wk after the trial period (to 8 wk of age), decreased testicular weight, and increased hide-on carcass dressing percentage for calves implanted with 48 mg of zeranol compared with those that received 0 mg of zeranol.

Measurement of zeranol in plasma from three blood vessels in steers implanted with zeranol.

Zeranol (Z) is a widely used growth promotant; however, plasma Z profiles in cattle implanted with Z have not been characterized. This study was conducted to determine bovine plasma Z profiles. In Exp. 1, four steers (BW = 284.8 +/- 5.6 kg) were implanted with 108 mg of Z (Ralgro). To determine the effect of sampling site on plasma Z concentrations, blood was sampled by venipuncture from the maxillary vein ipsilateral (IMV) to the ear in which Z was implanted and from the ipsilateral (IJV) and contralateral (CJV) jugular veins of each steer. Samples were collected on d 1, 4, 6, 8, 11, and 13 after implantation and Z was assayed by RIA. There was an effect of sampling site (P < .01). The overall mean plasma Z concentrations and 95% confidence intervals (CI) for each vessel were 282 (CI: 172 to 463), 135 (CI: 85 to 215), and 67 (CI: 42 to 106) pg/mL for the IMV, IJV, and CJV, respectively. Plasma Z concentration was higher (P < .05) in IMV than in IJV and higher (P < .05) in IJV than in CJV. In Exp. 2, nine steers (BW = 316.7 +/- 10.0 kg) were implanted with 108 mg of Z and IMV blood was collected on d 0, 1, 3, 7, 10, 14, 17, 21, 28, 35, 42, 56, 63, 73, and 91 after implantation. Day affected plasma Z concentration (P < .01); plasma Z was elevated above preimplantation levels for 91 d (P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Tumor necrosis factor as a potential mediator of acute metabolic and hormonal responses to endotoxemia in calves.

The effects of coliform endotoxin (E) and recombinant bovine tumor necrosis factor alpha (TNF) were compared with respect to clinical signs of disease and changes in plasma metabolite and pituitary and pancreatic hormone concentrations in calves. In addition, changes in plasma TNF concentration during each challenge exposure were quantitated by use of radioimmunoassay. Healthy Holstein bull calves with mean body weight of 90 kg were each given, in order, on different days, saline solution (5.0 ml, IV, day 1, n = 4), E (type 055:B5, 1.0 micrograms/kg of body weight IV, day 2, n = 4) and TNF (5.0 micrograms/kg IV, day 9, n = 3). Jugular venous blood samples, rectal temperature reading, and PCV were obtained at hourly intervals before (2 hours) and after challenge exposure. The PCV increased (P less than 0.05) after E and TNF administrations for the first 5 hours, then returned to normal in calves given E, but decreased and remained low in calves given TNF through 24 hours. Plasma triglyceride and nonesterified free fatty acids concentrations were increased through 10 hours (P less than 0.05) after E administration, whereas triglyceride and nonesterified free fatty acids concentrations were not significantly affected by TNF administration. Increase in blood glucose concentration at 1 hour after administration of E and TNF was followed by prolonged hypoglycemia that lasted through 6 hours. Changes in plasma insulin concentration paralleled the observed changes in glucose concentration, initially increased at 2 hours after E and TNF (P less than 0.05) administrations, but then tended to decrease below control values thereafter.(ABSTRACT TRUNCATED AT 250 WORDS)

Radioimmunoassay for bovine tumor necrosis factor: concentrations and circulating molecular forms in bovine plasma.

Antisera against recombinant bovine tumor necrosis factor (rbTNF) were produced in rabbits immunized with rbTNF in Freund's complete adjuvant (F314) and used in a double antibody radioimmunoassay to measure plasma TNF. Assay standards were rbTNF. Iodination of rbTNF and chromatography on G-50 Sephadex with 50 mM EDTA, 0.1% BSA, 0.05 M phosphate buffer, pH 7.5 resulted in labelled rbTNF which was greater than 97% TCA precipitable (specific activity of 37.5 microCi/micrograms). F314 (1:80,000 dilution) bound 21% of 125I-rbTNF in a non-equilibrium assay at 4 C. Separation of bound and free 125I-rbTNF was accomplished by precipitation with goat anti-rabbit IgG prepared with 6% polyethyleneglycol (mw = 8000). Minimum detectable TNF was 4 pg/assay tube. Matrix effects of plasma were minimal. Recovery of rbTNF from plasma was linearly (recovered TNF = .932 * added TNF = .12; r = .99). Displacement curves of increasing amounts of plasma from calves challenged with endotoxin to effect an increase in endogenous TNF were parallel to the rbTNF standard curve. F314 failed to crossreact with any other cytokines tested except human TNF (less than 1%). Neither recombinant nor native bovine TNF significantly interacted with antisera for TNF of human or murine origin. Plasma TNF was acutely elevated in calves infused with endotoxin. Changes in plasma TNF were determined in samples from calves with chronic parasitic infection. Endogenous plasma TNF existed as a monomer with a molecular weight of 17,000, and was not bound to any plasma carrier protein. These data indicate that a specific RIA for bTNF capable of detecting changes in in vivo TNF levels has been established.