Metabolism and thermoregulation in the springhare (Pedetes capensis).

Springhares are large, nocturnally active, diurnally fossorial rodents that typically inhabit arid and semi-arid areas. This lifestyle means that they need to balance excessive heat loss when foraging at night against insufficient heat loss in a potentially warm, humid burrow and both of these against the need to minimize water turnover and energy requirements. In this study we investigated metabolism and thermoregulation in these animals. Basal metabolic rate averaged 8.62+/-1.37 J g(-1) h(-1) and minimum thermal conductance 0.386+/-0.062 J g(-1) h(-1) degrees C(-1). These were higher and lower than expected, respectively. This, along with a relatively low, lower critical temperature and broad thermal neutral zone indicate that springhares are physiologically well suited to the low night-time temperatures, which they typically encounter. Body temperatures were quite labile but springhares became hyperthermic at temperatures above 30 degrees C suggesting that they are poor thermoregulators at high temperatures. This is attributed to their seldom, if ever, encountering temperatures in this range. Insufficient heat loss under normal resting conditions does not appear to be a problem, as springhares inhabit deep burrows in which the temperature never exceeds the upper critical temperature. Excess heat generated during vigorous underground exercise is presumably stored and dissipated to the cool night air or the cooler soil when subsequently resting. Water turnover and energy expenditure are presumably adequately addressed by other physiological and behavioural characteristics.

Osmoregulation and water balance in the springhare (Pedetes capensis).

Springhares are large rodents that live in arid and semi-arid regions of Africa. We deprived springhares of water for periods of up to 7 days to determine what physiological adaptations. If any, enable them to survive in and regions without drinking. During water deprivation, springhares lost up to 30% body weight and produced a mean maximum urine concentration of 2548 mosmol kg-1 with a maximum of 3076 mosmol kg-1 in an individual animal. Haematocrit and plasma sodium and potassium concentrations were well regulated throughout water deprivation at 47.5 +/- 3.8% and 132.6 +/- 7.4 mmol l-1 and 3.5 +/- 0.7 mmol l-1, respectively, while plasma osmolality increased slightly from 293 +/- 12.5 mosmol kg-1 to 324 +/- 7.3 mosmol kg-1. Springhares thus appeared to be good osmoregulators and were able to maintain plasma volume during 7 days of water deprivation. In addition to the production of a relatively concentrated urine, water loss was limited by the lowered solute load and faecal water loss achieved by a reduction in food consumption and by the production of very dry faeces. These abilities, together with a favourable burrow microclimate and nocturnal activity pattern, enable them to survive in arid regions.

Mortality in near-term ostrich embryos during artificial incubation.

1. The ostrich industry in South Africa (and elsewhere) experiences a high rate of embryo mortality during artificial incubation of eggs. Most of this mortality takes place in the last l0-l4 d of incubation. 2. We carried out post-mortem examinations on 111 embryos that died within this period to assess the causes of this mortality. 3. Malpositioning and severe oedema were the predominant symptoms of dead-in shell embryos with 55% being malpositioned and 41% showing severe oedema. Of these, 22 embryos (24%) showed both symptoms. Malpositioning generally results from incorrect setting of the eggs or inadequate turning and oedema was significantly correlated with the amount of water lost from the eggs which in turn was correlated with egg size. 4. Myopathy, gross lesions of internal organs, haemorrhage, bacterial infections and congenital deformities were found in less than 10% of chicks examined for these symptoms.