Andrew N Thompson

Improving ewe reproductive performance remains a priority for the Australian sheep industry. Here we present a protocol for veterinary practitioners to investigate cases of poor reproductive performance. The proposed methodology can be readily adapted to account for resources available and risk factors specific to the farm in question. This protocol will allow practitioners to determine the (a) timing and (b) likely causes of foetal/lamb loss to inform strategies targeted at improving reproductive performance.

Split paternity rates in multiple born lambs of syndicate-mated Merino flocks have previously not been reported, primarily due to the cost of genotyping. Pedigree data from litters born to genetically diverse syndicate mated ewes in three Merino Lifetime Productivity flocks across Australia were analysed to examine rates of split paternity, or heteropaternal superfecundation. Over three joinings at three sites, 1082 twin or triplet litters were marked, of which 577 were heteropaternal (53.3%). There was no effect of age of dam, year of birth, sire or maternal grandsire on heteropaternity rates. These high rates of heteropaternity confirm the need to genotype all progeny from multiple births in syndicate mated flocks to ensure accurate genetic evaluation. INTRODUCTION Split paternity, or heteropaternal superfecundation, occurs when females are successfully mated by multiple males during the same oestrus cycle. Decreased costs of determining paternity using DNA means that it is now feasible to obtain pedigrees from syndicate mating which may have some practical advantages over single-sire mating. Being able to syndicate mate sheep and determine parentage using DNA requires less paddocks than single sire joining and reduced labour in terms of feeding, labour for lambing rounds (preparation for lambing through identification of dams and mothering up) together with less disturbance during the lambing period as well less risk of failed matings with infertile single-sire mated rams. Very little data about heteropaternal superfecundation has been published for either sheep or cattle. In cattle, where twinning rates are traditionally very low (1-5% depending on breed), McClure et al. (2017) examined rates of heteropaternal superfecundation in Irish herds, citing data from the Irish Cattle Breeding Federation database. They reported that, with an average of 1.7% twin rates, 0.98% of these were heteropaternal. By contrast, in syndicate-mated sheep, surprisingly high levels of heteropaternity, detected by DNA technology, have recently been reported for flocks in Ireland under relatively intensive conditions (Berry et al. 2020). The only information on the occurrence or frequency of heteropaternity in multiple-born lambs in naturally mated Merinos showed even higher levels (46-59%) in lambs born in 2012-2015 as part of the Merinolink Genomic Validation Project (Martin 2016). We predicted that heteropaternity would also be high in extensively run Merino flocks in different parts of Australia with varying genotypes. We tested this in three naturally mated Merino flocks in Western Australia and New South Wales over 2-3 years. We also examined the effect of heteropaternity on total weaning weight of litters to see if there was any difference in the weaning weights of single-sired twin lambs compared to heteropaternal twins.

Selection of Merino sheep for use in breeding programs includes the combination of visual assessment and measurement of production traits. Genetic evaluation of these assessments and traits takes into account non-genetic effects to improve the accuracy of breeding value predictions. The hypothesis tested in this paper was that visual classing assessment of sheep on a traditional three-point and a novel five-point visual scoring system are heritable and both are also affected by non-genetic effects such as birth and rearing type. Using data from the first two years of classing ewes in the Merino Lifetime Productivity project at Pingelly, WA, moderate heritability estimates were observed for both scoring systems (0.24±0.08 for three-point and 0.17±0.07 for five-point). Both traits were moderately repeatable (0.31-0.36+0.03). Birth and rear type impacted visual scoring grades significantly, indicating that they should be accounted for when visually classing Merino sheep. INTRODUCTION Merino sheep breeding routinely combines objectively measured production selection and visual assessment to improve the quality and quantity of wool produced as well as improve structure and conformation. Merino sheep classing by visual selection is based on a number of subjectively assessed traits such as wool quality, quantity and conformation, assessed by professional sheep classers using different scoring systems to class animals into different categories (Brown et al. 2002; Robinson et al. 2007). When used in conjunction with estimated breeding values for production traits, visual classing can add value to selecting superior animals for replacement, with greater accuracy and efficiency than using a single method alone (Mortimer et al. 2010). Genetic evaluation of Merino production data includes accounting for any fixed effects or non-genetic factors, such as birth type (whether the animal was born as a single or multiple), rear type (whether the animal was raised as a single or multiple), the age of the dam, the date of birth of the animal and whether that animal was born to a maiden or experienced mature ewe (Hadfield and Kruuk 2007; Brown et al. 2016). These non-genetic factors influence the phenotype of the animal and can often influence how it is classed visually. For example, twin born and reared lambs are typically smaller and produce broader and less wool than single counterparts (Swan et al. 2008, Thompson et al. 2011a,b). Accurate estimates of these fixed effects need to be included when estimating breeding values, to ensure accurate estimates of genetic merit. Research has shown that visually assessed classer grades have a heritability between 0.12 and 0.2 and have favourable genetic and phenotypic correlations with liveweight, wool quality and structural traits (Mortimer et al. 2009). These subjectively measured traits are also significantly influenced by birth type, rear type and other non-genetic factors. In addition, Clarke and Thompson (2021) found that classers were influenced by subjective assessments of liveweight, clean fleece weight and fibre diameter when grading of animals. In this study non-genetic factors had a significant effect on classing outcomes such that at the first seven month old professional classing 69% of the culls were twins and only 31% were singles. Conversely 70% of the tops were singles and only 30% were twins. The current study uses an expanded data set from the Merino Lifetime

The Merino Lifetime Productivity project is evaluating the lifetime productivity of the ewe progeny of industry sires at five sites around Australia. Additional work at the Pingelly site is evaluating the productivity of the wether progeny. Liveweight, carcase traits and wool production data for wether progeny born in 2016 and 2017 have been collected. This paper presents a preliminary analysis of the value of production of the 2016 and 2017 drop wethers at yearling and adult age. The difference in value of production to 18-22 months of age between the top and bottom ranking sire groups was approximately $50 per head, excluding differences in mortality between sire groups. In future analyses the wether data will be compared to the productivity of the ewes as well as combined with ewe data to calculate flock profitability so comparisons can be drawn between sires in feed intake and whole-body energy.

Large pasture growth variation across years requires changes in optimal management between years, making breeding objectives difficult to calculate. We modeled a farm with Merino sheep bred for wool and meat in a Mediterranean environment where feed availability and prices vary widely between years. We calculated profit and economic values for 6 traits by optimizing management across 5 years using dynamic recursive analysis, comparing varying to average pasture growth and prices. Profit decreased for the varying scenario but economic values increased. Economic values for yearling live weight and fibre diameter increased most and were least sensitive to uncertain pasture growth, having least effect on energy requirements. These changes shifted selection response from wool towards meat and reproduction, mostly because reproduction had a higher genetic correlation with yearling weight than wool traits. Therefore, variation in pasture growth should be considered when developing sheep breeding programs.

Lamb producers have the option to market lambs at a range of slaughter weights. However, there are limited price premiums for heavier carcasses on a per kilogram basis. Any economic advantage of heavy lambs is realised by extra weight and not price. Both genetic and on-farm factors contribute to extra weight gain. Firstly, lamb weight and growth is correlated to its mature size and lambs from larger parents grow faster and reach heavier weights, but also have greater feed requirements. Secondly, stocking and reproductive rate account for the majority of variation in whole-farm profit, but increasing these also increases feed requirements. The production of heavy lambs is therefore a trade-off with maximising stocking and reproductive rate within the pool of available feed resources. We hypothesise that slaughter weight does not increase with mature size, due to the priority to increase stocking and reproductive rate for profit maximisation.

Ewes that lose less weight when there is a shortage of paddock feed are potentially more profitable because they require less supplementary feeding or can be grazed at higher stocking rates during autumn/winter (Young et al. 2011). Adams et al. (2006) have shown that sheep genotypes which lose more weight when underfed have lower metabolic reserves including fat. This paper tested the hypothesis that selection for increased fatness would reduce the rate of liveweight loss in adult Merino ewes when nutrition was restricted.

Merino ewes are the backbone of the Australian sheep industry and this is likely to be the case for some time. Stocking rate will remain a key profit driver in Merino enterprises and to maintain or improve profitability producers will need to continually adapt their production systems to deal with even larger changes in feed supply between seasons and years. The reproductive performance of the Merino ewe also needs to improve, largely through improving the survival of twin born lambs, to rebuild flock numbers and meet market demand for lamb and sheep meat. Increasing both stocking rates and reproductive performance need to be achieved in the context of producers wanting to run more sheep per person with less intervention and increased consumer demand for welfare friendly products. Improving genetics and matching sheep genotype to the production and management system will inevitably become more important. We believe this will include defining traits to more easily identify Merino sheep that are more robust, that lose less liveweight when faced with sub-optimum nutrition and that produce more progeny with higher survival rates both pre- and post-weaning. Increasing genetic fat is the prime candidate for increasing the robustness of Merino ewes and their progeny as the storage and mobilisation of fat is an important mechanism for all animals to cope with fluctuating environments. Fat is stored during favourable times and then mobilised to provide energy for fundamental functions when requirements exceed supply, such as during periods of limited nutrition or during late pregnancy and lactation. The amount of fat stored in fat depots in sheep can be increased by selection for higher subcutaneous fat depth, using Australian Sheep Breeding Values (ASBVs) from MERINOSELECT. However, from a genetic perspective, reducing the fatness of lamb to improve its appeal to the consumer has resulted in a general focus on selection for less fat in Australian sheep breeds. Merino sheep have also become leaner as a result of selection for higher fleece weights and the genetic association between higher fleece weight and reduced fatness (Huisman and Brown 2009). Defining the true value of fat requires an understanding of the effect it has on the value of lamb carcasses as well as its effects on the productivity of the sheep production system in different environments. In this paper we have reviewed published papers and our own unpublished work to test the hypothesis that Merino sheep that are genetically fatter will have improved performance especially under more restricted nutritional conditions.

Poor lamb survival is a major cause of reproductive inefficiency in sheep flocks in many countries. Since 2007, the Australian Cooperative Research Centre for Sheep Industry Innovation (the Sheep CRC) has had a major project on reproduction efficiency to help industry wean an extra 1 million lambs per year by 2014 from the national flock, the key target being improved neonatal lamb survival. In addition, work is also directed at improving post-weaning survival. This paper provides an overview of the project, its key findings and achievements to date, focussing on neonatal lamb survival.