Relative economic value of wool processing parameters for New Zealand strong wool between 2003 and 2007
Price trends for a total of 147,416 lots of wool in the strong wool segment of the New Zealand clip sold at auction between 1 July 2003 and 30 June 2007 were analysed by multiple regression analysis to determine the effect on price of five key characteristics known to affect wool processing performance. Changes in exchange rate were allowed for by covariance against the exchange rate of the US dollar on the day of the auction. The residual standard deviation within the data set was 20.4 c/kg clean. Mean values of the slope of the regression, or relative economic value, were 0.4 ± 0.2 c/ kg clean/mm change in barbe length, -1.9 ± 0.9 c/kg clean/μm change in mean fibre diameter, 2.5 ± 0.5 c/kg clean/CIE Y value change in brightness, -5.0 ± 0.6 c/kg clean/CIE Y-Z value change in intensity of yellowness and -16.8 ± 3.0 c/kg clean/% change in vegetable matter contamination. These estimated values align closely with values estimated in 1991 for the New Zealand clip as a whole confirming that despite the significant changes that have occurred within the wool processing industry the economic significance of individual wool characteristics to wool processors have not changed.
Wool staple tenacity in New Zealand Romney sheep: heritability estimates, correlated traits, and direct response to selection
A flock of New Zealand Romney sheep was established and selected as yearlings on the basis of fleece staple tenacity. The foundation flock was screened from contributing source flocks, with outliers of high or low staple tenacity as yearlings relative to the source flock mean contributing to a ‘high’ line and a ‘low’ line, respectively. A randomly selected control line was established because staple tenacity was known to be affected by yearly changes in feed supply. Staple tenacity of yearling fleeces was found to be heritable (0.41 ± 0.03). After 10 years of within-line selection, the line selected for increased staple tenacity had staples 53% stronger (33.9 N/mm2) than the control (22.1 N/mm2), while staples were 38% weaker in the line selected for decreased staple tenacity (13.8 N/mm2). Staple tenacity was genetically (0.67 ± 0.04) and phenotypically (0.44 ± 0.02) correlated with fibre diameter, and also with staple length (0.38 ± 0.07 and 0.32 ± 0.02, respectively). Longer, thicker fibres likely contributed to positive genetic (0.31 ± 0.07) and phenotypic (0.29 ± 0.02) correlations between staple tenacity and clean fleece weight. The indirect aim of selection was to improve fibre length after carding. Pooled wool samples were prepared from selection line groups of yearlings within sex each year, and a relationship between fibre length after carding measured on these samples and mean staple tenacity of the groups was observed (R2 = 0.514, P < 0.001). Within the tenth (last) year of selection, the high staple tenacity line produced the longest carded fibres (Hauteur: 103 mm) and the decreased staple tenacity line produced the shortest (87 mm), with the control line intermediate (96 mm).
Electrophysiological evidence that a subset of midbrain dopamine neurons integrate the reward signal induced by electrical stimulation of the posterior mesencephalon
This study was aimed at determining whether midbrain dopamine (DA) neurons are trans-synaptically activated by rewarding electrical stimulation applied near the midline in the posterior mesencephalon (PM), and in the affirmative, whether the increase in firing was proportional to the rewarding effectiveness of the stimulation. Experiments were performed on male Long-Evans rats trained to lever press to obtain 400 ms trains of cathodal rectangular pulses. Following the training period, curves relating the rates of responding to the stimulation frequencies were determined at two current intensities and reward thresholds were calculated for each animal. Each animal was then anesthetized with urethane (1.2 g/kg, i.p.) and firing rate of DA neurons were recorded before, during, and after each of 50 trains (1 train/3 s) of stimulation to the PM using stimulation parameters that either sustained near threshold responding (rewarding), or failed to sustain responding (non-rewarding), in the behavioral tests. A total of 24 DA cells were recorded from 13 behaviorally trained animals, and of these, 17 (71%) responded to rewarding stimulation by an increase in firing, five (21%) were unresponsive and two (8%) were inhibited. In 12 of the 17 cells that were activated, the increase in firing was proportional to the rewarding effectiveness of the stimulation rather than the total strength of the stimulation. These results provide evidence that a subset of midbrain DA neurons are trans-synaptically activated by rewarding PM stimulation and constitute a second, or subsequent, stage of the reward-relevant pathway that integrates the PM reward signal.