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Food, fibre and pharmaceuticals from animals
Animal Production Science

Animal Production Science

Volume 56 Number 4 2016

Sheep Reproduction: Part 2

AN14517Grazing crops: implications for reproducing sheep

David G. Masters and Andrew N. Thompson
pp. 655-668

Grazing young crops presents new opportunities to increase production and profit in the wheat-sheep and high rainfall farming zones in Australia. Forage from young crops has a high nutritive value and is available to meet an increased demand for feed from reproducing ewes in winter. Grazing young crops comes with an increased risk of a range metabolic disturbances and nutritional imbalances. These risks can be minimised by regular monitoring of livestock and crop biomass and the provision of mineral supplements.

AN15202Economic value of pregnancy scanning and optimum nutritional management of dry, single- and twin-bearing Merino ewes

J. M. Young, R. Behrendt, M. Curnow, C. M. Oldham and A. N. Thompson
pp. 669-678

The profitability of scanning for pregnancy status and litter size is dependent on how the information is utilised. This work showed increased profitability when the nutrition of dry, single- and twin-bearing ewes was altered to increase the survival of twin-born lambs. These results will provide industry with increased confidence to implement scanning on commercial properties.

AN14630Pregnancy scanning can be used as a source of data for genetic evaluation of reproductive traits of ewes

Kim L. Bunter, Andrew A. Swan, Ian W. Purvis and Daniel Brown
pp. 679-689

Reproductive data for ewes consists of pregnancy scan and/or lambing results, and it is important that these alternative data sources provide similar and accurate information towards genetic evaluation. This study investigated the consistency of pregnancy scan data with lambing outcomes, and showed that pregnancy scan data could be used instead of lambing data for genetic evaluation. It is important that pregnancy scanning is performed accurately to maximise the accuracy of breeding values derived from pregnancy scan data.

Australian Merino breeders have to balance recording and selection across wool traits, meat attributes, worm resistance and reproduction rate. This study investigates the value of recording various trait combinations and the results clearly highlight that breeders should measure directly all important traits that contribute to farm profitability. Breeders should use multiple trait selection indexes that consider the value of, and relationships between, all these traits, rather than focusing on just one or two traits.

Analysis of a maternal composite stud flock in Holbrook, New South Wales indicated that selection for scanned post-weaning fat and muscle depth in lambs should lead to increased fat muscle and body condition in the breeding ewe. The influence of body composition traits on reproduction was weak. However, it is hypothesised that by genetically increasing post-weaning fat depth producers can reduce the demands for supplementary feeding.

The profitability of a sheep enterprise is greatly influenced by the ability of the ewe to produce a lamb annually. This paper examines the association between the liveweight and fat score of the adult ewe and key fleece, reproduction and milk traits. The genetic relationships between fat score and reproduction were generally low to negligible. The advantages of selecting for fat to improve the maternal performance of the ewe seem to be limited in enterprises where the production system can easily be adjusted to restrict the influence feed deficiencies.

AN15114Effect of previous reproductive performance on current reproductive rate in South Australian Merino ewes

David O. Kleemann, Simon K. Walker, Raul W. Ponzoni, Dennis R. Gifford, James R. W. Walkley, Darryl H. Smith, Richard J. Grimson, Kaylene S. Jaensch, Samuel F. Walkom and Forbes D. Brien
pp. 716-725

Poor reproductive performance of the Australian Merino may be due, in part, to the inability of ewes to recover body reserves by the next breeding cycle. However, this study shows that low liveweight and poor reproductive performance in any 1 year is not necessarily associated with previous reproductive performance. Genetic variation indicates that flock fertility could be improved by selection on previous records whilst gains in fecundity and survival could come from improved management.

AN15121Neonatal lamb mortality: factors associated with the death of Australian lambs

G. Refshauge, F. D. Brien, G. N. Hinch and R. van de Ven
pp. 726-735

For long-term reductions in neonatal lamb mortality to occur we first must understand the primary causes of death. In the present study, neonatal lambs dying within 5 days of birth were autopsied, revealing dystocia (9%), stillbirth (21%), brain injury (18%) and starvation-mismothering (25%). These findings are largely consistent for a wide range of environments using common sires and should be the attention of future research in the Australian sheep industry.

AN15099Thermogenesis and physiological maturity in neonatal lambs: a unifying concept in lamb survival

K. J. Plush, F. D. Brien, M. L. Hebart and P. I. Hynd
pp. 736-745

An informed understanding of a lamb’s ability to control temperature homeostasis will provide novel methods to improve lamb survival. This review has identified that while there are genetic and phenotypic factors that help explain variation in resistance to cooling, the physiological maturity of lambs immediately following birth is a likely determinant of cold resistance. Further work using definable models of cold resistance will elucidate this link with lamb maturity.

The ability to thermoregulate following birth is an important determinant of lamb survival. We have shown that glucose metabolism, in addition to birthweight, is a potential explanation as to why some lambs are better able to resist hypothermia than are others. This improved understanding of neonatal thermoregulation may lead to targeted options, such as nutritional manipulation of gluco-regulatory pathways, to increase lamb survival.

High levels of lamb mortality limit productivity in the sheep industry and may be contributed to by poor immune function in lambs. Vitamin D is known to improve immune function and therefore ewes were supplemented with large doses of vitamin D in late pregnancy, which increased the levels of vitamin D in the ewes and lambs at birth but did not improve immune function in the lambs. Further research is needed to determine the requirements for vitamin D in lambs and what levels of vitamin D are required to boost immune function.

AN14945Genetic evaluation of maternal behaviour and temperament in Australian sheep

D. J. Brown, N. M. Fogarty, C. L. Iker, D. M. Ferguson, D. Blache and G. M. Gaunt
pp. 767-774

The temperament and behaviour of ewes at lambing can impact on the survival of their newborn lambs. Maternal behaviour and temperament are moderately heritable (the former also repeatable), which means these traits can be improved by selection. Scoring maternal behaviour at lambing could be a useful trait to include in breeding programs aimed at improving overall reproduction rates in sheep flocks.

Liveweight change in the ewe flock during summer and autumn can affect farm profitability through effects on stocking rate, requirements for supplementary feeding, and productivity of the ewe and her progeny. Variation in liveweight change of ewes is primarily due to differences in environment and management. However, there are small beneficial associations between some breeding values and liveweight change in some environments.

Weight loss in adult ewes over summer–autumn is expensive due to costs such as feed and labour but also due to effects on reproductive success and ewe health. The concentration of leptin, an indicator of whole-body fat, was examined, and ewes with high concentrations of leptin had a lower daily intake when fed a poor-quality diet and lost less weight than did ewes with low concentrations of leptin. Maximising fat-tissue accretion via genetics and/or nutritional management could improve adult ewe efficiency during periods of poor nutrition.

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