A standard weed management system (system I) had a higher return above variable costs than did an intensive weed management system (system II) for two eastern Colorado cropping rotations. For continuous corn (Zea mays L.), the return above variable costs averaged $18.85/ha more under system I than under system II. For a barley (Hordeum vulgare L.)-corn-sugarbeet (Beta vulgaris L.) rotation, the return above variable costs averaged $20.48/ha more under System I than under System II. Based on alternative input (herbicide) and product prices, higher herbicide costs favored the standard weed management system, whereas higher crop prices favored the weed management system with the higher yields adjusted for quality. The probability that returns above variable costs differed between the two weed management systems depended upon the level of product prices and herbicide costs.

Grass and broadleaf weed densities and seed numbers, weed control practices, and grain yields were included in a bioeconomic model that evaluates alternative weed management strategies for continuous corn (Zea mays L.). Weed seed numbers in soil and herbicide carry-over provided intertemporal links. Four weed management strategies – two fixed, one mixed, and one flexible – were evaluated with annualized net returns as the performance indicator. The flexible strategy (weed control based on observed conditions) had the largest annualized net return for high and low initial weed seed numbers. The fixed weed management strategy (weed control predetermined) of an annual application of only a preemergence herbicide ranked second in terms of annualized net returns for high weed seed numbers. The mixed weed management strategy of alternative year applications of preemergence herbicide and “as needed” applications of postemergence herbicide ranked second for low initial weed seed numbers. The fixed weed management strategy of alternate year application of preemergence herbicide only generated the lowest annualized net return, regardless of initial weed seed numbers.

Six years of data collected from two shifts of Cornell random bred control matings each year are analysed. Approximately 900 progeny were tested per year from 50 sires mated to 250 dams.

Means for the important economic traits are presented by years and regressions for nine such traits, together with their standard deviations, are shown. The only significant regressions are those for both egg production and specific gravity score in shift II. An abnormally low egg production the first year for this shift is considered responsible for this result and the reality of the regression is discounted.

Genetic variances are presented by trait and year. Year to year variability is evident, but no trends are indicated.

Estimates of heritability and genetic correlations between traits are presented. These estimates are considered to be quite reliable and will be useful as estimates of genetic parameters when this population is used in selection experiments. Estimates of heritability from the sire components of variance were as follows: 8-week body-weight, 0·29; 32-week body-weight, 0·48; 55-week body-weight, 0·44; age at maturity, 0·09; egg production to 500 days, 0·07; 32-week egg-weight, 0·51; 55-week egg-weight, 0·53; USDA albumen score, 0·29; blood spot score, 0·13; and specific gravity score, 0·34.

Important maternal effects were found for 8, 32 and 55-week body-weight, sexual maturity and egg production. Selection programmes should take into consideration the fact that maternal effects accounted for 13% of the total variation in egg production. Genetic correlations utilizing combined sire and dam components revealed no serious antagonisms between egg production and other economic traits. However, this conclusion must be considered in the light of what influence maternal effects may have, since correlations computed from sire and dam components separately may have opposite signs and be important.

The many negative estimates of interaction components (SH, genetic by environment) and (I, sire by dam) indicate that these elements of the model contributed little to the variation of the traits studied.

The structural complexity of the right ventricle has made quantitative evaluation difficult. Conventional cross-sectional echocardiographic methods are limited by geometric assumptions and the position of the planes used for imaging. Previous reports have demonstrated accurate three-dimensional echocardiographic quantitation of the right ventricle in-vitro and in experimental animals. We adapted a previously described method for three-dimensional reconstruction of the left ventricle to compute right ventricular volume and ejection fraction in a clinical setting.

We examined 29 patients aged from 2 to 42 years with pulmonary hypertension, by three-dimensional echocardiography and resonance imaging. Correlation and agreement were calculated for volumes and ejection fractions. Three-dimensional echocardiographic reconstruction, when compared to resonance imaging, yielded r values of 0.95 and 0.93, and mean differences (bias) of 31% ± 19% and 33% ± 18%, for systolic and diastolic volumes respectively. Interobserver variability was low (12.9% and 8.0%). Ejection fraction as calculated by three-dimensional echocardiography showed close agreement with resonance images (bias=l% ±7%). Three dimensional echocardiography is now a method of measuring right ventricular ejection fraction in the clinical setting which produces results comparable to those of resonance imaging. Volume measurements correlated well for systole and diastole, but consistently underestimated values produced from resonance images.

Efficient management techniques in sheep production must take particular account of the pattern of reproductive behaviour and its application in the manipulation of reproductive processes. Conventionally in the UK, the advancement of the breeding season has been achieved by the use of progesterone-impregnated sponges and pregnant mare's serum gonadotrophin (PMSG). The ‘ram effect’ has been shown to be a powerful and cheap way of controlling the time of mating of sheep. The objective of the present study was to investigate the value of using different methods of teasing for the stimulation of ovarian activity in an early lambing flock.