Andrew N Thompson

Ewes that lose less weight under restricted nutrition are potentially more profitable as less supplementary feeding is required or stocking rate can be increased. Heavier strains of Merino sheep have been shown to lose less weight when grazed on dry, poor pasture. Given that sire estimated breeding values (EBVs) for weight positively correlate with mature size, we hypothesise that adult ewes from sires with high EBVs for weight will have reduced annual fluctuation in weight. Spline functions were fitted to liveweight data for ewes from 8 Information Nucleus sites to determine annual weight change (max-mm-max) for each ewe. The 2 to 4 year olds were born between 2007 and 2009 and there were 5,242 records for 2,783 animals. Weights were corrected for conceptus and greasy fleece. Weight gain and loss were analysed using linear mixed effects models with fixed effects for site, breed, year, age, lamb birth type and rear type, and sire of the ewe was included as a random term. Sire EBVs for muscle, fat and growth and, ewe average annual liveweight (frame size) were included simultaneously as covariates. Ewes from sires with low EBVs for growth had no significant change in weight gain across a range of frame size (40-70 kg). In contrast ewes from high growth sires demonstrated similar weight gain at frame sizes of 40 kg, but increased in weight gain by 2.4 kg across the range of frame size. Contrary to our hypothesis, it was sires with less genetic potential for growth that produced progeny with reduced changes in liveweight. In both cases the magnitude of weight gain represented a diminishing proportion of frame size as it increased indicating phenotypically larger animals are more resilient to weight change. Ewes from high growth sires may require more careful management to minimise weight change, particularly when maintained at phenotypically higher weights.

Sheep in Australia can be bred to be more resilient to drought periods Resilient sheep lose less weight when grazing poor quality pasture. However, we do not know if breeding for weight change sheets reproduction. So we estimated genetic correlations between weight change and reproduction. We used ~6800 fully pedigreed Merino ewes managed at Katanning in Western Australia. Weight change was measured during mating (42 days) on poor pasture and during pregnancy (90 days) on poor and medium quality pasture on ~1900 2 year old ewes, ~1500 aged 3 and ~1100 aged 4. Reproduction traits were number of lambs and total weight of lambs born and weaned measured on ~5300 2 year old ewes, ~4900 aged 3 and ~3600 aged 4. We estimated genetic correlations (rg) between weight change and reproduction within age. Two year old ewes that gain weight during mating gave birth to more lambs (rg = 0.37±0. 18) and weaned more lambs (rg = 0.62±0.19). Two year old ewes that lost more weight during pregnancy weaned mow lambs (rg = 0.45± 0.19). In contrast, three year old ewes that gained weight during pregnancy weaned more lambs (rg = 0.65 ±0.30) and had a higher total birth weight (rg =0.42±0.17). All other correlations were low or had high standard errors. We concluded that young, immature ewes were more sensitive to weight change during mating because they had more difficulty getting pregnant compared to older, more fertile, ewes. Older ewes also had higher liner sizes that require more energy at lambing and lactation to produce healthy lambs. This means weight gain during pregnancy is more important for older ewes. In conclusion, breeding for resilience to drought periods improves reproduction in old ewes.

It has been thought that females must accumulate a certain mass of body fat before they can go through puberty and maintain fertility but this theory is being challenged because muscle development also seems to be linked to fecundity. Body fat and reproduction are linked physiologically by leptin, but a link among increased muscling and reproduction has not been explored. One possible link is follistatin (FS), a key player in the regulation of both muscle development and follicle-stimulating hormone secretion. We assessed the relationships between breeding values for muscling, the onset of puberty and fertility, and circulating PS concentrations in Merino ewe lambs (n=136) To detect onset of puberty, testosterone-treated wethers were run with the lambs from 6 to 8 months of age and then replaced by entire rams. Blood FS concentrations determined by RIA decreased as puberty approached and increased as conception approached. The proportion of ewe lambs that attained puberty decreased as FS values increased (P<0.05), but FS concentration had no effect on fertility. We conclude that FS secretion is related to the onset of puberty but not fertility of Merino ewe lambs. The data presented do not imply a cause-effect relationship; however, further research is necessary to clarify the effect of circulating FS on reproductive traits in Merino ewe lambs.

Background/question/methods: Two translocated populations of golden bandicoots (Isoodon auratus) were monitored following relocation from one island to another and to mainland Australia. We compared skeletal and mass measurements of the new populations to long-term monitoring data from the source populations. Results/conclusions: Bandicoots born at translocation sites were approximately 130% of the size of founder island population within 18 months of establishment. Translocated males increased in condition and females had a greater reproductive output at both new sites. The time of effectiveness took place in a single generation of at both mainland and island translocation sites, suggesting that the response is not one of evolution by natural selection. We conclude that ‘island dwarfism’ is driven by ecological processes of resource limitation in I. auratus.