Australian journal of biological sciences最新文献

The recorded behaviour of wild species of Ovis at the beginning of the breeding season supports the proposal that mating is synchronized by the 'ram effect', a phenomenon already described in domestic sheep. Animals separate into exclusive male flocks, and flocks of females and young animals for most of the year. They reunite just before the rutting season. At lambing there appear to be behavioural mechanisms that ensure that ewes lamb in close proximity to one another. It is hypothesized that these behavioural characteristics of wild sheep help protect the newborn and that much of the reproductive and maternal behaviour of domestic sheep may be traced to comparable behaviour in wild species.

The female sex hormone, oestrogen, plays a central role in breast cell proliferation in both the normal and malignant state. It controls transcription from several genes, including that for the progesterone receptor, and in endometrial tissue, via this receptor, it controls the gene for the enzyme oestrogen sulfotransferase. This enzyme may control the level of the oestrogen receptor by sulfurylating free oestradiol. To study the mode of transcriptional control exercised by oestrogen, bovine oestrogen sulfotransferase cDNA has been cloned and the nucleotide sequence determined. The message, of which 1812 bases have been sequenced, contains an open reading frame of 885 bases which encode a protein of 295 amino acids and a maximum apparent molecular weight of 34,600. The deduced protein sequence is supported by existing peptide sequence data and appears to contain a steroid-binding region. Some physico-chemical characteristics of the enzyme appear to differ markedly from those previously reported.

Three surveys of cattle for bluetongue (BLU) antibody were conducted over the years 1978-1980 in coastal areas of New South Wales. In each survey the samples were identified by age. The prevalence of BLU-group antibody, demonstrated in a gel diffusion precipitin test, was highest in the north and decreased progressively to the south. Antibody prevalence increased with age. However, according to variations in prevalence by age and region, it was concluded that the activity of relevant viruses was highly variable between years and was geographically discontinuous. Evidence is presented that much of the antibody found, especially in animals less than 4 years old, failed to persist from one year to another. Factors likely to contribute to more persistent reactions in older animals are discussed. Neutralizing antibodies to bluetongue virus serotypes 1 and 21 were demonstrated and prevalence of these was associated with location and age, as was that of group-specific antibody.

The ovariectomized ewe has been used to establish principles and procedures which have proved invaluable in controlled breeding in entire animals. Bioassays in the ovariectomized ewe, the end-point of oestrous behaviour, have been used to identify potent and rapidly metabolized progestagens which were subsequently used to control the time of oestrus and ovulation in cyclic ewes effectively, and to induce oestrus and ovulation in anoestrous ewes. Steroid hormone treatment of the ovariectomized ewe has been used to study relationships between the ovary and the pituitary-hypothalamic axis, to examine transport of embryos within the female tract and to establish the steroid hormone requirements of early pregnancy.

Responses to daily injections of bovine growth hormone (GH, 0.15 mg kg-1 liveweight), beginning on day 10 of lactation, were measured in lactating ewes. Milk yields of GH-treated ewes increased soon after commencement of injections and continued to increase for some 25 days before reaching plateau levels. By comparison, yields of ewes injected with excipient (controls) decreased over the experiment. There was a tendency for contents of milk fat to be higher and milk protein to be lower for GH-treated than for control ewes during the first 15-20 days after injections were started. At the beginning and over the first 15-20 days of the experiment feed intakes of both groups of ewes were similar, but thereafter intakes of GH-treated ewes gradually increased to reach plateau levels some 200-300 g day-1 higher than for control ewes by about day 35. Liveweights of both groups of ewes decreased during the first 2 weeks of treatment then increased, with GH-treated ewes losing, then gaining, more weight than control ewes. The efficiency of food utilization for milk production was higher for GH-treated than control ewes throughout the experiment but digestibility of food organic matter was not different during the eighth week of the experiment. At the end of the experiment, body composition, assessed by dilution of tritiated water, was similar for both groups of ewes. Differences in milk production were not sustained after withdrawal of GH injections. Measurements of tissue uptake of key metabolites were made on days 3 and 45 of GH treatment. On day 3, GH lowered uptake of glucose and non-esterified fatty acids by leg muscle tissue and increased mammary uptake of non-esterified fatty acids. By day 45 there were no apparent differences of tissue uptake of key metabolites. The results indicate that there is a biphasic response to exogenous GH in the lactating ruminant. It appears that initially GH affects nutrient partition thereby increasing supplies to the mammary gland of key nutrients for milk synthesis. In the longer term, GH increases feed intake, which provides sufficient nutrients to sustain increased milk production and also liveweight gain.

The stoichiometry of the two heavy chains of myosin in smooth muscle was determined by electrophoresing extracts of native myosin and of dissociated myosin on sodium dodecyl sulfate (SDS) 4%-polyacrylamide gels. The slower migrating heavy chain was 3.6 times more abundant in toad stomach, 2.3 in rabbit myometrium, 2.0 in rat femoral artery, 1.3 in guinea pig ileum, 0.93 in pig trachea and 0.69 in human bronchus, than the more rapidly migrating chain. Both heavy chains were identified as smooth muscle myosin by immunoblotting using antibodies to smooth muscle and non-muscle myosin. The unequal proportion of heavy chains suggested the possibility of native isoforms of myosin comprised of heavy-chain homodimers. To test this, native myosin extracts wer electrophoresed on non-dissociating (pyrophosphate) gels. When each band was individually analysed on SDS-polyacrylamide gel the slowest was found to be filamin and the other bands were myosin in which the relative proportion of the heavy chains was unchanged from that found in the original tissue extracts. Since this is incompatible with either a heterodimeric or a homodimeric arrangement it suggests that pyrophosphate gel electrophoresis is incapable of separating putative isoforms of native myosin.

Milk samples from captive potoroos were analysed for composition during weeks 3-25 of the lactation period. During pouch residence, up to week 16, carbohydrate levels were high, ranging from 9 g 100 ml-1 at week 5 to 15 g 100 ml-1 at week 15; fat levels were consistently low, at around 2 g 100 ml-1; protein levels gradually increased from 5 g 100 ml-1 before week 10 to 12 g 100 ml-1 at week 16. Growth rates during this period increased exponentially, from 1 g week-1 at week 3 to 40 g week-1 at week 16. Thereafter, as the young left the pouch, marked changes were seen in carbohydrate and fat levels: by week 25, carbohydrate levels had fallen to 2 g 100 ml-1, and fat levels had risen to 26 g 100 ml-1. Protein levels increased moderately, reaching 15 g 100 ml-1 by week 25. Growth rates further increased during this period, to reach 60 g week-1 by week 25. Thus, trends in milk composition previously observed in Macropus species were observed also in the potoroo, suggesting a consistent pattern across the macropodid family. Carbohydrate levels in potoroo milk tend to be higher than in other macropodids, but total milk intake is as important as composition in determining growth rates.