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SUMMARY1. Analysis of voltage-clamped noise has been used to investigate the operation of glutamate receptors and associated channels at the locust nerve-muscle junction.Channels opened by glutamate and an agonist have been compared.2. Glutamate-induced current fluctuations have a power spectrum with a single (1/frequency2) component which fits a simple model for the operation of channels. The form of the spectra for glutamate voltage noise and for 'background' noise has been determined.3. The single channel conductance was estimated from the spectra, y glutamate = 122 + 0*4 (s.E.) pS. This estimate is independent of membrane potential and of the amplitude of membrane current change produced by glutamate.4. The rate constant, a, for the closing of glutamate-operated channels depends exponentially on membrane potential, conforming to the equation a = a-e llvm (, = 0-26 + 0*014 msec-1, v = 0 0054 + 0-001 msec-1); the duration of the channel lifetime (r) decrease with hyperpolarization. Membrane potential dependence of a reduces as temperature is lowered.5. For glutamate-operated channels, the temperature dependence of x and y fits the Arrhenius equation; a and y decrease exponentially as a function of T-1 (0K) with a discrete change in slope at about 6 'C, indicating a change in the activation energies of the respective rate processes.6. Spectra of quisqualate-induced current fluctuations have the same form as spectra for glutamate noise. The single channel conductance was estimated from the spectra, y quisqualate = 120 + 3 9 (s.E.) pS.7. The rate constant, a, for the closing of quisqualate-induced channels depends exponentially on membrane potential. The duration of the open state for quisqualate channels was 2*2 times longer than for glutamate channels.8. For glutamate receptors the voltage-sensitivity of the channel life-time is in the opposite direction to that of ACh receptors in vertebrate muscle. Possible explanations for the sharp change in the activation energy of the rate processes associated with the channel are discussed.

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The established association between milk production and SCC in dairy cattle is increasingly used to estimate lost production due to mastitis. Such cost estimates are used to make decisions regarding cost effective mastitis prevention and control. It is therefore important to verify the relationship between SCC and milk production using data from different areas of the country and by using different analytical methodology. Our study used the 1985 to 1986 Michigan DHIA data base and analyzed daily milk production records rather than lactation summary records as used in the past. One advantage to our approach was that it did not give equal weight to all lactations, regardless of their duration. Also, it enabled inclusion of cows that had incomplete lactations caused by culling, or had other reasons for removal from the herd. A statistical model was constructed to predict milk production on the basis of herd, cow within herd, stage in lactation, month of calving, lactation, and SCC. The data base contained 397,172 milk test records obtained from Michigan DHIA from 504 Holstein herds in Michigan's lower peninsula. Our final model predicted 78% of the variation in milk production. Prediction of milk loss for each herd was highly correlated (r = .98) with the prediction model adopted by most DHIA organizations. Our model predicted that the mean herd lost a mean of 1.17 kg of milk/cow per d associated with SCC.

Knowledge of genetic relationships between characteristics of lactation curves and lactation yields is essential for joint selection for both. An equation, yt = atbexp(-ct), was chosen to depict individual lactation curves for 5,927 first lactations by Holsteins in 557 herds in Michigan Dairy Herd Improvement where yt is daily milk yield at day t in lactation, a is yield at time zero, b is ascent to peak, and c is decline after peak. Genetic correlations for 305-day milk yield with initial production (a), ascent to peak (b), descent after peak (c), and peak yield were -.37, .40, 0, and .91. From empirical results from applied selection indexes, selecting for both increase of ascent to peak and peak yield did not decrease 305-day milk substantially. Rankings of sires on these indexes were similar to their rankings on milk yield alone. Attempts to decrease peak yield and increase persistency decreased milk yield greatly.

Ammonia, hydrogen sulfide and swine-house dust at continuous aerial levels as high as or higher than those normally encountered in enclosed swine-finishing houses had little or no effect on rate of body-weight gain and respiratory-tract structure of 92 healthy pigs in seven trials. The trials were of 17 to 109 days' duration, involved air pollutants alone and in various combinations and were conducted in air-pollutant exposure chambers. (