Animal Production Science
Volume 56 Number 4 2016
Sheep Reproduction: Part 2
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
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
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.
AN14579The impact of selecting for increased ewe fat level on reproduction and its potential to reduce supplementary feeding in a commercial composite flock
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.
AN15090Season and reproductive status rather than genetic factors influence change in ewe weight and fat over time. 4. Genetic relationships of ewe weight and fat score with fleece, reproduction and milk traits
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
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.
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
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.
AN14957Variation in physiological profiles may explain breed differences in neonatal lamb thermoregulation
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.
AN15085Supplementation of Merino ewes with cholecalciferol in late pregnancy improves the vitamin D status of ewes and lambs at birth but is not correlated with an improvement in immune function in lambs
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.
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.
AN14419Environmental and genetic factors influence the liveweight of adult Merino and Border Leicester × Merino ewes across multiple sites and years
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.
AN15217Whole-body fatness is a good predictor of phenotypic feed and liveweight efficiency in adult Merino ewes fed a poor-quality diet
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.