Assessing neonatal lamb vigour

Neonatal lamb vigour has been identified as an important trait for the subsequent survival of the lamb. To date, time to perform critical early lamb behaviours, up to time to suckle, has been the most common method of assessing lamb vigour. The aim of this thesis was to identify and evaluate other methods of assessing vigour and assessing it at a time when the ewe would be moving from the birth site because this time is critical for the maintenance of contact between the ewe and the lamb. Improving the ease of assessing lamb vigour may also provide a practical tool for improving lamb survival through genetic selection on lamb vigour traits. A modified barrier test and the physiological response of lambs to a cold stress between four and six hours of age were used as novel methods for assessing lamb vigour. Cold stress was induced a number of ways including via noradrenaline injections, the use of an ice vest and simulation of cold weather conditions using fans and cold water. Responses to cold stress were measured using changes in rectal temperature collected continuously over the treatment period, the behavioural responses of the lamb during the cold challenge and their performance in the modified barrier test following the cold challenge. Differences in vigour due to variation in late pregnancy nutrition, breed and sire within breed were also assessed. Sires were selected from the Sheep CRCs information nucleus flock (INF) and correlations between the INF sire vigour score and time to suckle were determined. It was found that sub maintenance nutrition in late pregnancy had no effect on lamb vigour as measured by time to suckle. Sire breed did not account for differences in lamb vigour however within breed sire differences were found. There were high correlations between INF vigour score and time to suckle and rectal temperature at 10 minutes of age (0.77, -0.67 and -0.71 respectively). It was concluded that a modified barrier test could be used to assess lamb vigour after the lamb has suckled to provide information on the capacity of the lamb to respond to the ewe at a time when she may be moving from the birth site. The use of lamb vigour scoring as used in the INF may be a useful indirect selection criterion for improving lamb survival as it appears to be providing information on critical neonatal behaviours

Use of an ice vest to elicit a cold response in neonatal lambs

The ability of the neonatal lamb to respond to cold stress is considered vital to the likelihood of its survival in many sheep production systems. Various methods have been used to assess the neonatal lamb cold responses including progressively cooled water baths (Slee et al. 1990), temperature controlled chambers (Alexander 1961) and noradrenaline and other drug treatments which stimulate brown fat metabolism thereby mimicking a real cold exposure (Slee et al. 1987). This study compared body temperature responses induced by an ice vest to those induced by a noradrenaline challenge as a means of assessing individual lamb variation in cold responses

Sire effects on neonatal lamb vigour and following-behaviour

The ability of the lamb to maintain contact with the ewe as she moves away from the birth site is critical to the lamb's subsequent survival. If this contact is compromised then lamb loss is likely to occur due to starvation/mismothering. This study uses sires from the Sheep CRC Information Nucleus Flock to compare the effect of selection of sires within the Merino breed for high or low losses due to starvation/mismothering on neonatal lamb vigour. Lamb vigour was measured using conventional measures of time to perform early neonatal behaviours, early physiological measures (rectal temperatures and blood glucose), and performance in a modified barrier test while under physiological stress from cold exposure. Lambs were exposed to cold at a time (4-6 h after birth) when the ewe is likely to be moving away from the birth site and therefore when losses due to starvation/mismothering are likely to begin. Progeny from the high-loss sires were significantly (

Lamb survival, a challenge for the decades

Lamb survival to weaning is the major profit driver in the Australian sheep industry, and equally an important issue for animal welfare and ethical livestock production. Research aimed at improving lamb survival and reproductive efficiency remains consistently one of the highest- ranking priorities identified by industry consultation groups. The extensive body of knowledge generated by research efforts across Australia have led to comprehensive management guidelines and extension programs to support their uptake. Nevertheless, reported rates of loss in many regions remains higher than acceptable, despite lamb loss rates in general improving under improved management strategies. One of the biggest challenges is to break down this complex phenotype into measurable meaningful component traits. As for any complex phenotype, a combination of improved management and genetic selection may be most likely to lead to success but for either application, phenotypes must be less dependent on uncontrollable environmental influences than counts of losses. Dystocia has been conclusively shown to be one of the most important causes of lamb loss and development of approaches to measure incidence of dystocia will aid the development of new phenotypes to facilitate genetic and management strategies to improve lamb survival

Comparing spatial landscape utilisation estimates for livestock from land managers and GPS collars

Managers of extensive livestock systems often manage large numbers of livestock over vast land areas, much of which is not regularly or easily accessible. Managers in this situation need to make decisions about stocking rate and the length of grazing to balance productivity and pasture degradation similar to intensive systems. For extensive systems, these decisions are often based upon the estimated area that stock will actually occupy and graze rather than the total paddock size. Managers base their estimates on stock sighting and proximity to water points coupled with climatic conditions and pasture availability. This pilot study compared the spatial landscape utilisation (SLU) predictions of a land manager ('predicted SLU) with the 'actual SLU' as recorded by GPS tracking collars. Here the 'actual SLU' was defined as the area of a paddock over which cattle positions were recorded

Use of infrared thermal technology to detect changes in neonatal lamb temperature

The capacity to mount a response to cold stress is an important determinant of the probability of lamb survival (Slee, 1981). The aim of this experiment was to determine if changes in the body temperature of lambs born to ewes fed differentially during the last 50 days of pregnancy could be detected before and after a noradrenalin challenge using infrared thermal (IRT) technology. Ewes were oestrous synchronised, mated and maintained on pasture until day 100 after joining. At day 60 after mating, they were scanned for pregnancy and litter size. From day 100, single- or twin-bearing ewes were fed either an 80% or a 120% maintenance energy diet, resulting in four groups of ewes: single 80% (n=4, 8.4 MJ ME/day), twin 80% (n=5, 10.2 MJ ME/day), single 120% (n=5, 12.6 MJ ME/day) and twin 120% (n=4, 15.6 MJ ME/day). The ewes were penned individually indoors on day 143 of pregnancy. At 5.5 hours of age, temperature loggers were inserted into the rectums of the lambs. At 6 hours of age, lambs were given a noradrenalin injection (150 μg/kg) subcutaneously in the mid dorsal region. A dorsal IRT image of the lamb was taken immediately prior to and 30 min after the injection. A midline temperature profile from the shoulder to rump was extracted from the IRT image and the area under the curve (AUC) was calculated. The maximum temperature before and after the injection and the relative location of the maximum were recorded. Rectal temperature at the time of the injection and 30 min after the injection was determined. Data were analysed using litter size as a main effect and nutritional level (MJ ME/day) as a covariate

Variability in neonatal behaviour in single and twin lambs

The effect of litter size (LS) on the variability in neonatal behaviour in the context of lamb survival was investigated. Merino ewes (n=270) were oestrus synchronised in three mating groups (MG) 10 days apart and naturally mated. Eighteen ewes from each MG were selected, balanced for LS (singles and twins) following pregnancy scanning at day 60. Ewes were maintained on pasture until day 100 of pregnancy before being fed a concentrate ration in group pens. Ewes were housed five days prior to lambing, in individual pens. Video records from birth until three hours post partum were taken and times to stand, reach the udder, unsuccessfully and successfully suckle determined. At 10-15 minutes post partum, lambs were removed for blood sampling and morphometric and temperature measurement. MG3 lambs also had an infrared thermal image taken and consequently, were separated from their dams 1 minute longer (