Factors Influencing Reproductive Wastage in Victorian Sheep Flocks

Abstract

The cost to the national sheep industry of reproductive wastage has been estimated at around $839.6 Mil per annum (Jubb et. al. 2015). The Victorian sheep flock currently makes up 21% of the national flock with 8.9 Mil ewes, or 21% of the National breeding flock (MLA 2016 personal Communications) estimates of the financial penalty to the Victorian sheep industry from reproductive wastage would be approximately $176.3 Mil each year.<br/> This thesis was developed to investigate the conditions which lead to reproductive wastage in Victorian sheep flocks through a review of the available literature and an investigation of data collected from commercial Victorian sheep flocks involved in the Sentinel Flock Project (DPI Victoria).<br/> Twenty flocks of prime lamb and wool producing sheep were initially enlisted across the sheep production areas of Victoria to monitor factors influencing reproductive wastage, morbidity and mortality over a three year period. One flock retired from the project and another flock was added hence 21 flocks were assessed. As far as possible, the spread of these flocks represented the distribution of sheep across Victoria. Flocks were enlisted from the known contacts of the Department of Primary Industries Victoria, Meat and Wool Services Branch.<br/> Target flock size was 400 – 3000 breeding ewes. Both commercial and stud flocks were eligible for consideration. The flocks husbandry, management, reproductive performance and procedures were monitored for a period of three years and documented to evaluate the incidence reproductive wastage and livestock deaths in the participating flocks.<br/> Deaths were investigated to establish cause. According to need, the investigation included on-farm necropsy and/or the submission of samples to the Gribbles Veterinary Laboratory for analysis and diagnosis.<br/> Over the course of this investigation there were 82092 ewes scanned for pregnancy status including reproduction rate. The mean conception rates (number of feotus scanned per number of ewes joined) for ewes over the years 2009 to 2012 across seasons of joining (Autumn/Spring lambing's) in this work were, for the Merino Ewe x Merino Sire (MXM) 116.9%, Merino Ewe X Prime Sire (MXP) 126.7% and Prime Ewe x Prime Sire (PXP) 145.7%. The mean lamb marking (lambs marked /ewe joined) percentages were for the MXM ewes 84.6%, MXP ewes 103.2% and the PXP ewes marked 118.6%. This equated to a total loss of 23726 lambs from ultrasound scanning through to lamb-marking and a further 1107 lambs were lost from lamb-marking to weaning.<br/> Of the lambs lost from ultrasound scanning to lamb-marking the largest losses were attributed to Starvation mis-mothering (48%) followed by dystocic birth (25%) then primary predation (7%) and there were 7% which could not be diagnosed due to the state of the lamb carcass.<br/> The ewes in this study were monitored throughout the years of this work to determine the cause of loss. There were 1421 or 1.7% of ewes recorded as dying over the 2009 to 2012 period of this work. Investigations were carried out on a sample n=209) of these ewes to determine the cause of death. The primary cause of loss was due to endemic infectious disease (34%) followed by obstetrical disease (26%), then metabolic disease (13%). There were 17% of the ewes submitted for necropsy which were unable to be diagnosed as to cause of death due to the condition of the carcass.<br/> In this work conception was under the control of BCS for the MXM and MXP but genotype of the sire was significant for the PXP grouping. Birth weight of the lamb which was to a large degree under genetic control was a significant factor in survival of the lamb.