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King B.J.,Charles Sturt University | King B.J.,Co operative Research Center for Future Farm Industries | Robertson S.M.,Charles Sturt University | Robertson S.M.,Co operative Research Center for Future Farm Industries | And 3 more authors.
Animal Reproduction Science | Year: 2010

This study evaluated the ability of short-term grazing of live=green pasture to increase ovulation rate during late summer when annual pasture is generally dead and of low quality. Ovulation rates, measured by the number of corpora lutea, were compared between 4 nutritional treatments: senesced phalaris (Phalaris aquatica), phalaris plus 500. g lupin grain per day, lucerne (Medicago sativa) or chicory (Chicorum intybus) pastures. The study used 100 Merino ewes per treatment, divided between 2 replicates. The experiment was repeated in 3 years; February 2006, and January 2007 and 2008. Oestrus was synchronised and the ewes grazed the pastures for 9 days prior to ovulation at times corresponding to days 8-17 of the cycle in 2006, and days 6-14 in 2007 and 2008. The proportion of ewes producing multiple ovulations was higher (P<0.05) in the lucerne and chicory (0.36, 0.38) than the phalaris (0.27), and intermediate in the lupin (0.33) treatment. Regression analysis showed that the proportion of ewes with multiple ovulations increased with the quantity of live herbage (P<0.04). Responses were achieved even at low levels of live herbage with 90% of the maximum proportion of multiples occurring at 350. kg DM/ha. It is concluded that providing short-term grazing of live chicory or lucerne to ewes can increase ovulation rates relative to ewes grazing senesced phalaris and to levels similar to those achieved by lupin grain supplementation. © 2010.


Robertson S.M.,Charles Sturt University | Robertson S.M.,Co operative Research Center for Future Farm Industries | Friend M.A.,Charles Sturt University | Friend M.A.,Co operative Research Center for Future Farm Industries | And 4 more authors.
Animal Production Science | Year: 2011

Abstract Perinatal lamb mortality is a major source of reproductive loss, particularly for twins. A study was conducted to determine whether provision of shelter in the form of shrub belts (a 'maternity ward') could increase survival of twin lambs compared with hedgerows, and whether hedgerows improve survival of single lambs compared with unsheltered paddocks. Measurements were recorded for Merino Poll Dorset cross twin lambs born in hedgerows (phalaris or hessian) or shrub belts and single lambs born in hedgerows or unsheltered paddocks over the years 20072009. Records for 382 single and 726 twin lambs were used. The survival of single lambs was not increased (P = 0.06) by hedgerow shelter. The survival of twin lambs in shrubs was 10% higher (P < 0.05) than that in hessian hedgerow shelter in 20082009 (0.77 cf. 0.70), associated with a reduction in deaths from starvation and/or mismothering and/or exposure. The hessian shelter was associated with an increased (P < 0.05) growth rate to weaning of single lambs, but the growth rates of twin lambs were lower (P < 0.05) in shrub than in hessian shelter. In 2010, a second study of 178 twin Merino Poll Dorset cross lambs found that survival of lambs born alive was not improved by shrubs compared with unsheltered paddocks (0.80 versus 0.77; P > 0.05). It is concluded that shrub belts which forced twin-bearing ewes to lamb in a sheltered environment reduced perinatal mortality in one of three datasets, but was not repeated. The shrubs take time to establish, and the benefit will be small if weather is mild during lambing. © 2011 CSIRO.


Gulliver C.E.,Charles Sturt University | Gulliver C.E.,Co operative Research Center for Future Farm Industries | Friend M.A.,Charles Sturt University | Friend M.A.,Co operative Research Center for Future Farm Industries | And 7 more authors.
Lipids | Year: 2013

Diets high in omega-6 polyunsaturated fatty acids (n-6) are associated with increased prostaglandin F2α (PGF2α) synthesis in cattle, however, the specific effects on the potential prostaglandin response to an oxytocin challenge in sheep have not been reported. The aim of the current study was to determine whether oxytocin-stimulated PGF 2α was significantly increased when ewes were fed a diet high in n-6 compared with a control diet low in n-6. Merino x Border Leicester ewes (n = 30) received one of two dietary treatments, either high in n-6 (70 % oat grain) or low in n-6 (control diet, 100 % cereal/legume silage). Ewes consumed the diets for 44 days prior to two consecutive oxytocin challenges. Plasma n-6 and PGF2α metabolite (PGFM) concentrations following oxytocin challenge were greater (P < 0.05) when ewes were fed a diet high in n-6 compared with the control diet. A higher availability of n-6 may have lead to an increased in vivo synthesis of PGF2α, however, further research is required to determine the exact mechanisms involved. © 2012 AOCS.


Robertson S.M.,Charles Sturt University | Robertson S.M.,Co operative Research Center for Future Farm Industries | Southwell A.F.,Charles Sturt University | Southwell A.F.,Co operative Research Center for Future Farm Industries | And 2 more authors.
Animal Production Science | Year: 2014

Month of joining and lamb sale strategy influence both the quantity and so value of lamb produced, and the feed required, so are important management decisions contributing to the profitability of sheep systems. Simulation modelling was used to evaluate the impact on gross margins of three lamb sale strategies for different months of joining and varying stocking rates. A flock of purchased Merino ewes producing crossbred lambs in southern Australia was modelled between 1971 and 2011. April joining produced higher gross margins than November or January only if the number of ewes per hectare was increased to potential carrying capacity. At the optimum stocking rate for each month of joining, three sale policies - a flexible lamb sale policy (where lambs were sold depending on seasonal conditions); selling lambs in December; or selling at 45-kg liveweight, all produced a similar mean gross margin, but the feed resources required were least using the flexible strategy (April-joined mean 195 ± 253 s.d. kg/ha for flexible compared with 219 ± 270 kg/ha if selling December or 1085 ± 459 kg/ha if sold at 45 kg). Mean gross margin differed between sale strategies by up to AU $66/ha if the optimal stocking rate was not used. These results suggest that the most advantageous lamb sale strategy will vary with both month of joining and stocking rate used, and should be considered when optimising sheep management systems. © CSIRO 2014.


Gulliver C.E.,Charles Sturt University | Gulliver C.E.,Co operative Research Center for Future Farm Industries | Friend M.A.,Charles Sturt University | Friend M.A.,Co operative Research Center for Future Farm Industries | And 5 more authors.
Animal Production Science | Year: 2013

Diets high in omega-6 (n-6) fatty acids in mice have been associated with a higher proportion of female offspring, however, the specific effects of dietary fatty acids on the sex ratio of sheep has not previously been reported. The aim of the present study was to determine whether feeding ewes a diet differing in n-6 for 6 weeks before and 3 weeks following conception would increase the proportion of female lambs born. Merino × Border Leicester ewes (n = 296) were allocated to receive either a diet high in n-6 (70% oat grain, 8% cottonseed meal, High n-6 diet) or, a control diet low in n-6 (88% legume silage, Low n-6 diet), for 42 or 53 days before and 17 days after conception, using a stratified block randomisation procedure based on body condition score and liveweight. Following synchronisation, oestrus was detected daily during natural mating with rams. After mating, all ewes grazed improved pastures as one group until lambing. Plasma n-6 concentrations were greater (P < 0.001), the time to parturition was shorter (P < 0.001) and the proportion of female offspring was higher (58.2 vs 43.5%, P = 0.010) when ewes were fed the High n-6 diet compared with the Low n-6 diet. Further research is required to determine whether the observed differences in sex ratio were due to specific alterations in n-6 fatty acids, or other differences in the diets not specifically related to n-6 such as saturated fat or energy density. Copyright © CSIRO 2013.


Broster J.C.,Charles Sturt University | Broster J.C.,Co operative Research Center for Future Farm Industries | Rathbone D.P.,Charles Sturt University | Robertson S.M.,Charles Sturt University | And 5 more authors.
Animal Production Science | Year: 2012

This experiment used contact loggers and GPS collars to evaluate the effect of stocking rate during lambing on ewe movement and contact levels between animals. Twin-bearing Merino ewes were placed in 0.5-ha paddocks sheltered with rows of hessian at stocking rates of 16 and 30 ewes/ha for the low and high stocking rates, respectively. The ewes did not spend more time in more sheltered areas of the paddock, and use of shelter was not influenced by stocking rate. Ewes at the high stocking rate travelled 11% farther per day but crossed through the hessian rows 37% less than ewes at the low stocking rate. Stocking rate did not change the level of contact between ewes, but higher levels of contact were shown between ewes and their lambs at the high stocking rate. The results suggest that the interaction between ewes and their lambs is modified by stocking rate and/or flock size for small groups lambing in shelter rows. © 2012 CSIRO.


Robertson S.M.,Charles Sturt University | Robertson S.M.,Co operative Research Center for Future Farm Industries | King B.J.,Charles Sturt University | King B.J.,Co operative Research Center for Future Farm Industries | And 4 more authors.
Animal Production Science | Year: 2012

This experiment evaluated the effect of stocking intensity at lambing on lamb survival. A randomised block design with three replicates compared stocking rates of 16 and 30 ewes/ha. Twin-bearing Merino ewes (n = 69) that had been mated with Poll Dorset White Suffolk rams were placed in paddocks sheltered with rows of hessian, with 8 or 15 ewes per 0.5-ha plot for the low and high stocking rates, respectively. The survival of lambs born alive at the high stocking rate (63%) was 24% less (P = 0.002) than for those at the low stocking rate (83%), and was associated with a higher (P<0.05) proportion of lambs dying from starvation, mismothering or exposure. There were no differences (P>0.05) in lamb birthweight, marking weight, ewe liveweight or condition, suggesting nutritional conditions between the stocking rates were similar. The results suggest caution in using lambing strategies which require high stocking rates. © 2012 CSIRO.


Broster J.C.,Charles Sturt University | Broster J.C.,Co operative Research Center for Future Farm Industries | Robertson S.M.,Charles Sturt University | Robertson S.M.,Co operative Research Center for Future Farm Industries | And 5 more authors.
Animal Production Science | Year: 2012

The death of newborn lambs is a major factor influencing the reproductive efficiency of sheep enterprises. Adverse weather conditions (wind, precipitation and low temperature), either alone or in combination (chill index), can increase the level of newborn lamb mortality to over 50% of births for short periods through increased heat loss. The provision of shelter to reduce wind speed and therefore chill index (heat loss) has been shown to reduce lamb mortality; however, the reduction in mortality has been variable. This study used the decision support tool GrassGro to determine the likelihood of adverse weather conditions occurring at six locations across south-eastern Australia which varied widely in climate. Data were extracted for 24 consecutive weekly periods between May and October over 39 years (1968-2006) to evaluate daily precipitation, temperature, radiation, wind speed and chill index. The minimum, maximum and median values were calculated for all climatic factors for every week and year combination. The effectiveness of reducing wind speed to reduce the occurrence of a high chill index was also evaluated. The severity of these weather events varied between locations with the median weekly chill index rarely exceeding 1000 kJ/m2.h at Temora, but at both Hamilton and Orange this occurred in over two-thirds of the weeks examined. Reducing wind speed by 50% reduced the number of weeks with a median chill index exceeding 1000 kJ/m2.h in twice as many weeks at Hamilton and Yass compared with Orange. These results show that the potential for shelter to reduce chill index will vary according to the location and time of year. In locations where another climatic factor, such as low temperature or rainfall, has a greater influence on the chill index, shelter which only reduces wind speed, will be less effective than at locations where wind speed is the driver of chill index. © 2012 CSIRO.


Gulliver C.E.,Charles Sturt University | Gulliver C.E.,Co operative Research Center for Future Farm Industries | Friend M.A.,Charles Sturt University | Friend M.A.,Co operative Research Center for Future Farm Industries | And 4 more authors.
Animal Reproduction Science | Year: 2012

The positive effects of fat and energy supplementation on improvements in reproduction are well documented. However, the specific effects of omega-3 polyunsaturated fatty acids (n-3) on reproductive success in ruminants have not been examined in detail. While the link between n-3 and markers associated with reproduction, in particular, prostaglandin F 2α (PGF 2α) and the link between PGF 2α and reproductive outcomes are well established, evidence of a direct effect of high n-3 diets on measurable reproductive outcomes in ruminants is lacking. Therefore, the aim of the current review was to examine the effect of n-3 on a number of reproductive markers and measurable outcomes in sheep and cattle. There is strong evidence linking consumption of diets high in n-3 with reduced circulating peripheral inflammatory markers such as PGF 2α. Inflammatory eicosanoids including PGF 2α, in particular, can significantly affect reproduction outcomes such as the onset of oestrus, embryo survival and parturition. While there is also evidence linking n-3 supplementation with longer time to oestrus and parturition associated with reduced PGF 2α, the effects of n-3 on other measurable outcomes of reproductive success, such as pregnancy rate, embryo survival and intergenerational effects on the health and production of offspring are largely unknown. Similarly, the effects of diets high in n-3 or n-6 polyunsaturated fatty acids on male fertility are also unknown. © 2012 Elsevier B.V.

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