Effect of feeding selenium-fertilized alfalfa hay on performance of weaned beef calves.

Selenium (Se) is an essential micronutrient in cattle, and Se-deficiency can affect morbidity and mortality. Calves may have greater Se requirements during periods of stress, such as during the transitional period between weaning and movement to a feedlot. Previously, we showed that feeding Se-fertilized forage increases whole-blood (WB) Se concentrations in mature beef cows. Our current objective was to test whether feeding Se-fertilized forage increases WB-Se concentrations and performance in weaned beef calves. Recently weaned beef calves (n = 60) were blocked by body weight, randomly assigned to 4 groups, and fed an alfalfa hay based diet for 7 wk, which was harvested from fields fertilized with sodium-selenate at a rate of 0, 22.5, 45.0, or 89.9 g Se/ha. Blood samples were collected weekly and analyzed for WB-Se concentrations. Body weight and health status of calves were monitored during the 7-wk feeding trial. Increasing application rates of Se fertilizer resulted in increased alfalfa hay Se content for that cutting of alfalfa (0.07, 0.95, 1.55, 3.26 mg Se/kg dry matter for Se application rates of 0, 22.5, 45.0, or 89.9 g Se/ha, respectively). Feeding Se-fertilized alfalfa hay during the 7-wk preconditioning period increased WB-Se concentrations (P Linear<0.001) and body weights (P Linear = 0.002) depending upon the Se-application rate. Based upon our results we suggest that soil-Se fertilization is a potential management tool to improve Se-status and performance in weaned calves in areas with low soil-Se concentrations.

Standardized procedure for measurement of nasal potential difference: an outcome measure in multicenter cystic fibrosis clinical trials.

Patients with cystic fibrosis (CF) can be discriminated from healthy subjects by measurement of the nasal potential difference, which has become a useful outcome measure for therapies directed toward correcting defective electrolyte transport in CF. A standard operating procedure was developed by a CF Foundation clinical trials network, to be followed by all sites performing collaborative studies. Key variables in the measurement included type of voltmeter, exploring probe, reference electrodes, and solutions used to assess both sodium transport and chloride conductance. Eight sites submitted data on 3-8 normal and 4-5 CF subjects. Baseline voltage, an index of sodium transport, was -18.2 +/- 8.3 mV (mean +/- SD) for normals, and -45.3 +/- 11.4 mV for CF patients. There was no CFTR-mediated chloride secretion in CF subjects, as evidenced by the lack of response to perfusion with zero chloride + beta agonist solutions (+3.2 +/- 3.5 mV) vs. that in normals (-23.7 +/- 10.2 mV). The standardized nasal potential difference measurement minimizes variability between operators and study sites. Valid and consistent results can be attained with trained operators and attention to technical details. These data demonstrate the procedure to be sufficient for multicenter studies in the CF Foundation network.