Milk production and composition, and progeny performance in young ewes with high merit for rapid growth and muscle and fat accumulation.

In ewe lambs, acceleration of growth and accumulation of both muscle and fat leads to earlier sexual maturity and better reproductive performance. The next stage in the development of this theme is to test whether these aspects of growth in young ewes affect milk production in their first lactation and the growth of their first progeny. We studied 75 young Merino ewes that had known phenotypic values for depth of eye muscle (EMD) and fat (FAT), and known Australian Sheep Breeding Values for post-weaning weight (PWT) and depths of eye muscle (PEMD) and fat (PFAT). They lambed for the first time at 1 year of age. Their lambs were weighed weekly from birth to weaning at 10 weeks to determine live weight gain and weaning weight. Progeny birth weight was positively associated with live weight gain and weaning weight (P0.05). The PWT of the sire was positively associated with live weight gain (P0.05). The concentrations of fat, protein, lactose and total solids in the milk were not affected by the phenotype or genotype of the mothers or of the sires of the mothers, or by the sex of the progeny (P>0.05). We conclude that selection of young Merino ewes for better growth, and more rapid accumulation of muscle and fat, will lead to progeny that are heavier at birth, grow faster and are heavier at weaning. Moreover, milk production and composition do not seem to be affected by the genetic merit of the mother for post-weaning live weight or PEMD or PFAT. Therefore, Merino ewes can lamb at 1 year of age without affecting the production objectives of the Merino sheep industry.

Reproduction in the marsupial dibbler, Parantechinus apicalis; differences between island and mainland populations.

Details of the reproductive endocrinology of the dibbler, Parantechinus apicalis, an endangered member of the Family Dasyuridae, are presented from two geographically-separated populations, living either on the mainland or on islands in Jurien Bay, Western Australia. Plasma free cortisol in males measured in the island population during 1998/9 did not differ between the breeding and non-breeding season, but during the March rut in 2000, when males died after breeding, free cortisol levels were significantly raised. Post-mating mortality in dibbler males is facultative, rather than obligatory and the cortisol data implicate the same physiological sequelae described in other dasyurids. In females, a single annual oestrus was recorded during late summer to autumn in both populations with an onset earlier by 12 days in the mainland animals. Faecal steroids excreted as progesterone metabolites (PM) and oestradiol-17ß were measured during the annual oestrous period and showed significantly higher PM concentrations in island animals. Oestradiol, although raised, was not different between the two populations. A profile of PM levels throughout gestation revealed a small peak at the time of ovulation, followed by slowly rising levels to peak 8 days before birth, indicating slow development of the corpora lutea. Using collective data, the presumptive day of ovulation could be identified, allowing the calculation of a presumptive gestation length of 45days in dibblers from mainland populations. This gestation length compares with that of a related species, Pseudantechinus macdonnellensis, reported at 45-55 days. A surprising finding is the significantly shorter gestation period of approximately 38 days in island animals compared with those from the mainland. This and other differences between reproductive parameters of island and mainland populations are discussed in the context of the 'island syndrome'.

The yield and composition of milk in Sarda, Awassi, and Merino sheep milked unilaterally at different frequencies.

Sarda (n = 8), Awassi (n = 8), and Merino (n = 8) ewes were subjected unilaterally to once-daily milking (ODM) or twice daily milking (TDM) to test the hypothesis that the two breeds highly selected for milk production (Sarda and Awassi) would not respond as much to a change in the frequency of milking as the Merino, a wool sheep that has not been selected for dairy production. Milk composition and somatic cell count (SCC) were also assessed to determine if the changes in milking frequency affected milk quality. Milk yield was 24% and 18% lower in ODM udder halves than TDM udder halves in Sarda and Awassi breeds, respectively. The yield loss due to ODM was similar to that observed in Merino ewes (23%) and did not support our hypothesis. Fat content did not differ significantly in any breeds between ODM and TDM udder halves. Protein content was higher in the milk of ODM than TDM udder halves in Sarda and Merino ewes. The SCC was influenced by milking treatment only in the Sarda ewes, with high values observed in the milk of ODM udder halves. The same trend was observed in the Awassi and Merino breeds, but the differences were not significant. The effects on milk yield, composition, and SCC caused by ODM were completely reversed when TDM was resumed. This suggests that in sheep flocks the milk yield losses due to short-time suppression of one daily milking, for example, on festive days, are low and temporary.

Quantification of naltrexone and 6,beta-naltrexol in plasma and milk using gas chromatography-mass spectrometry. Application to studies in the lactating sheep.

A selective gas chromatography-mass spectrometry method using solid-phase extraction has been developed for the detection and quantification of naltrexone and its metabolite, 6,beta-naltrexol in plasma and milk from humans and sheep at pharmacologically relevant concentrations. Di- or tri-acetyl derivatives were formed and quantified by selected-ion monitoring. Recoveries of naltrexone (30 microg/l) and 6,beta-naltrexol (250 microg/l) from both human plasma and milk were greater than 70%. Intra-assay and inter-day precision ranged from 3 to 21% for naltrexone and 2-18% for 6,beta-naltrexol for all matrices investigated, with an overall mean accuracy of 104% for naltrexone, and 99% for 6,beta-naltrexol. Human samples containing these analytes were stable for at least 3 weeks at -20 degrees C or 6 weeks at -80 degrees C. Analysis of the plasma and milk from the lactating sheep showed mean milk-to-plasma ratios of 55 for naltrexone and 3 for 6,beta-naltrexol.