Sweating rate, rectal and skin temperatures and respiration rate were measured at weekly intervals from 7 days of age (for 4 weeks in Experiment 1; 6 weeks in Experiment 2) in winter- and summer-born Friesian calves exposed to a temperature of 39 degrees C dry bulb and 32 degrees C wet bulb in a climate chamber. Four calves were studied in each season in both experiments. In Experiment 1, ambient temperatures were from 3 degrees to 9 degrees C higher in early summer than in late winter. During each 39 degrees C exposure, sweating rate increased from basal levels of 40-90 to plateau levels of 120-300 g/m2 per h after 90-120 min. The increase in sweating rate with age was most pronounced in winter-born calves, but summer-born calves had higher values at 1 week of age (167 +/- 52.4 vs 94.4 +/- 30.1 g/m2 per h). Seasonal differences in ambient temperature were greater in Experiment 2 (11 degrees to 17 degrees C). In this case summer-born calves had higher sweating rates at each age (plateau values of 220-320 g/m2 per h), and showed a more rapid increase in sweating rate during each 39 degrees C exposure than winter-born calves (plateau values of 100-250 g/m2 per h). The results demonstrate major changes in sweating competence during the first 4-6 weeks of life in Friesian calves, a quite pronounced effect of season (ambient temperature) on the levels of sweating achieved, and indicate that low sweating rates in newborn calves are a contributing factor in deaths due to hyperthermia in semi-arid grazing areas.
The genus Bulbine Wolf has ~130 species in Africa and only seven species in Australia. Base chromosome numbers in African and Australian Bulbine are x = 7 and x = 12, respectively. This raises the possibility of Australian Bulbine being of polyploidy origin or, alternatively African Bulbine may have evolved through dysploid reduction. Previous chromosome counts in Bulbine glauca (Raf.) E.M.Watson were predominantly 2n = 46, with aneuploid numbers of 2n = 45, 44, 48, 47, 40 and 41 also being encountered within and between populations. Novel chromosome counts are presented here for a wide sample of populations of B. glauca, occurring on volcanic and granite outcrops along the New South Wales and Victorian tablelands and on granite outcrops in Tasmania. Chromosome numbers for Bulbine crassa D.I.Morris and Duretto is 2n = 26. The modal chromosome count for B. glauca is confirmed as 2n = 46 with no evidence of aneuploidy. The species complex shows a variable asymmetric karyotype across its distribution, indicating karyotypic evolution involving structural rearrangements. There appear to be six distinctive groups within the complex based on karyomorphology. Evolutionary changes in both B. glauca s. lat. and B. crassa appear to have not involved recent polyploidy. Variation in chromosome morphology across the B. glauca complex is consistent with our morphological evidence of more than one species.
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