Estimation of risk factors associated with difficult birth in ewes
B. J. Horton A B E , R. Corkrey A C and G. N. Hinch A DA CRC for Sheep Industry Innovation, Armidale, NSW 2350, Australia.
B Tasmanian Institute of Agriculture, University of Tasmania, Launceston, Tas. 7250, Australia.
C Tasmanian Institute of Agriculture, University of Tasmania, Hobart, Tas. 7005, Australia.
D University of New England, Armidale, NSW 2350, Australia.
E Corresponding author. Email: brian.horton@utas.edu.au
Animal Production Science 58(6) 1125-1132 https://doi.org/10.1071/AN16339
Submitted: 23 May 2016 Accepted: 14 November 2016 Published: 23 January 2017
Abstract
In eight closely recorded Australian Merino and crossbred sheep flocks, all lamb deaths were examined and the cause of deaths identified if possible. Dystocia was identified as one of the major causes of lamb death and this study examined factors that could be used to identify ewes at high risk of dystocia, either to avoid dystocia or to assist with early intervention where possible. Dystocia was least common in lambs of ~4.8 kg, but there was a higher risk at both lower and higher birthweights. Dystocia with both low and high birthweight was more common in older ewes, ranging from negligible low birthweight dystocia in ewes less than 3 years old at lambing, to 5% in older ewes. Low birthweight dystocia increased with increasing litter size, with 40% dystocia in ewes at least 4 years of age with triplets. In contrast, high birthweight dystocia was not affected by litter size. A previous record of low birthweight dystocia was a risk factor for future low birthweight dystocia, but the same relationship was not observed for high birthweight dystocia. A high lambing ease score (difficult birth) with high birthweight was a risk factor for future high birthweight dystocia, but this was not the case for low birthweight dystocia. These differences between the risk factors for low and high birthweight dystocia suggest that they have different causes. High ewe liveweight and condition score during pregnancy may be additional indicators of the risk of dystocia, particularly for ewes with high liveweight in the first 60 days of pregnancy. For most ewes dystocia was difficult to predict, but there was a small proportion of ewes with a very high risk of dystocia and if these could be identified in advance they could be monitored much more closely than the rest of the flock.
Additional keywords: animal reproduction, animal welfare, lambing, lamb survival, twinning.
References
Brien FD, Hebart ML, Smith DH, Hocking Edwards JE, Greeff JC, Hart KW, Refshauge G, Bird-Gardner TL, Gaunt G, Behrendt R, Robertson MW, Hinch GN, Geenty KG (2010) Opportunities for genetic improvement of lamb survival. Animal Production Science 50, 1017–1025.| Opportunities for genetic improvement of lamb survival.Crossref | GoogleScholarGoogle Scholar |
Brown DJ, Jones RM, Hinch GN (2014) Genetic parameters for lamb autopsy traits. Animal Production Science 54, 736–744.
| Genetic parameters for lamb autopsy traits.Crossref | GoogleScholarGoogle Scholar |
Cloete SWP, Scholtz AJ, Ten Hoope JM, Lombard PJA, Franken MC (1998) Ease of birth relation to pelvic dimensions, litter weight and conformation of sheep. Small Ruminant Research 31, 51–60.
| Ease of birth relation to pelvic dimensions, litter weight and conformation of sheep.Crossref | GoogleScholarGoogle Scholar |
Fogarty NM, Banks RG, van der Werf JHJ, Ball AJ, Gibson JP (2007) The information nucleus – a new concept to enhance sheep industry genetic improvement. Proceedings of the Association for Advances in Animal Breeding and Genetics 17, 29–32.
George JM (1975) The incidence of dystocia in fine-wool Merino ewes. Australian Veterinary Journal 51, 262–265.
| The incidence of dystocia in fine-wool Merino ewes.Crossref | GoogleScholarGoogle Scholar | 1:STN:280:DyaE28%2FhvVaitQ%3D%3D&md5=12d8f8f217342d11d4d49cbd4fef2d38CAS |
George JM (1976) The incidence of dystocia in Dorset Horn ewes. Australian Veterinary Journal 52, 519–523.
| The incidence of dystocia in Dorset Horn ewes.Crossref | GoogleScholarGoogle Scholar | 1:STN:280:DyaE2s7htFKqtQ%3D%3D&md5=db072a657fa9e1a02d7c1afa9380d042CAS |
Haughey KG (1983) Selective breeding for rearing ability as an aid to improving lamb survival. Australian Veterinary Journal 60, 361–363.
| Selective breeding for rearing ability as an aid to improving lamb survival.Crossref | GoogleScholarGoogle Scholar | 1:STN:280:DyaL2c7islOksQ%3D%3D&md5=8e2903a8bc0baae4a4864a0e9ce239a8CAS |
Hinch GN, Brien F (2014) Lamb survival in Australian flocks: a review. Animal Production Science 54, 656–666.
| Lamb survival in Australian flocks: a review.Crossref | GoogleScholarGoogle Scholar |
Kelly RW (1992) Nutrition and placental development. Proceedings of the Nutrition Society of Australia 17, 203–211.
Li L, Brown DJ (2016) Estimation of genetic parameters for lambing ease, birthweight and gestation length in Australian sheep. Animal Production Science 56, 934–940.
| Estimation of genetic parameters for lambing ease, birthweight and gestation length in Australian sheep.Crossref | GoogleScholarGoogle Scholar |
Mellor DJ, Stafford KJ (2004) Animal welfare implications of neonatal mortality and morbidity in farm animals. Veterinary Journal (London, England) 168, 118–133.
| Animal welfare implications of neonatal mortality and morbidity in farm animals.Crossref | GoogleScholarGoogle Scholar | 1:STN:280:DC%2BD2czpvFWntQ%3D%3D&md5=ce76f162d7f2214a61f26e68af3f4482CAS |
Refshauge G, Brien FD, Hinch GN, van de Ven R (2016) Neonatal lamb mortality: factors associated with the death of Australian lambs. Animal Production Science 56, 726–735.
| Neonatal lamb mortality: factors associated with the death of Australian lambs.Crossref | GoogleScholarGoogle Scholar |
Young JM, Saul G, Behrendt R, Byrne F, McCaskill M, Kearney GA, Thompson AN (2014) The economic benefits of providing shelter to reduce the mortality of twin lambs in south-western Victoria. Animal Production Science 54, 773–782.
| The economic benefits of providing shelter to reduce the mortality of twin lambs in south-western Victoria.Crossref | GoogleScholarGoogle Scholar |
