Genetic parameters and trends for lamb survival following long-term divergent selection for number of lambs weaned in the Elsenburg Merino flock
C. L. Nel
A B D , A. A. Swan C , K. Dzama A , A. J. Scholtz B and S. W. P. Cloete A B
+ Author Affiliations
- Author Affiliations
A Department of Animal Sciences, Stellenbosch University, Merriman Avenue, Stellenbosch, 7602 South Africa.
B Directorate: Animal Sciences, Western Cape Department of Agriculture, Muldersvlei Road, Elsenburg, 7607 South Africa.
C Animal Genetics and Breeding Unit, University of New England, Ring Road, Armidale, NSW 2351, Australia.
D Corresponding author. Email: NeliusN@elsenburg.com
Animal Production Science - https://doi.org/10.1071/AN21198
Submitted: 9 April 2021 Accepted: 11 August 2021 Published online: 5 October 2021
Journal compilation © CSIRO 2021 Open Access CC BY-NC-ND
Abstract
Context: Mortality of new-born lambs is well known to have important implications for both animal production and welfare. Improving survival rates by genetic selection is very desirable, but the low heritability of survival traits challenges the prospect of useful genetic gain.
Aim: This study aimed to derive genetic and environmental parameters for lamb survival in the Elsenburg Merino resource flock. It also investigated correlations to possible indicator traits birthweight and birth coat score and reported genetic progress in breeding values for lamb survival following 33 years of divergent selection.
Methods: The flock was divergently selected for number of lambs weaned and was separated by the High (positive) and Low (negative) selection groups. The pedigree file identified 8138 lambs as the progeny of 273 sires and 2062 dams. The study considered total survival from birth to weaning (Tsv) that was also partitioned into perinatal survival to 3 days of age, and the remaining period. Variance components were derived by linear mixed models by using the ASREML® program. Genetic trends were derived by predicting mean breeding values for selection groups within each year and evaluated by fitting linear and broken-stick regression models.
Results: Predicted Tsv of H-line lambs (0.81 ± 0.01) was higher (P < 0.01) than that of L-line lambs (0.68 ± 0.01). Heritability was significant but low for survival traits (0.03–0.07), moderate for birthweight (0.16) and high for birth coat score (0.54). Genetic trends of the H-line trended divergently (P < 0.01) to the L-line for survival traits, but a changepoint (P < 0.01) in trend suggested that the H-line reached a selection plateau following 19–22 years of selection. Preceding this period, the rate of genetic change equalled ~1% of the mean for Tsv.
Conclusions: Despite the low heritability of survival, the genetic trends reported in this study contradicted the premise that genetic selection is not a worthwhile method to reduce incidences of lamb mortality.
Implications: It is recommended that lamb survival phenotypes should be recorded and incorporated into indices individually where possible, but composite traits are a viable alternative.
Keywords: sheep, (co)variance components, mortality, breeding values, heritability.
References
Afolayan RA, Fogarty NM, Gilmour AR, Ingham VM, Gaunt GM, Cummins LJ (2008) Reproductive performance and genetic parameters in first cross ewes from different maternal genotypes. Journal of Animal Science 86, 804–814.| Reproductive performance and genetic parameters in first cross ewes from different maternal genotypes.Crossref | GoogleScholarGoogle Scholar | 18156352PubMed |
Al-Shorepy SA, Notter DR (1998) Genetic parameters for lamb birth weight in spring and autumn lambing. Animal Science 67, 327–332.
| Genetic parameters for lamb birth weight in spring and autumn lambing.Crossref | GoogleScholarGoogle Scholar |
Alexander G (1961) Temperature regulation in the new-born lamb. iii. Effect of environmental temperature on metabolic rate, body temperatures, and respiratory quotient. Australian Journal of Agricultural Research 12, 1152–1174.
| Temperature regulation in the new-born lamb. iii. Effect of environmental temperature on metabolic rate, body temperatures, and respiratory quotient.Crossref | GoogleScholarGoogle Scholar |
Alexander G (1984) Constraints to lamb survival. In ‘Reproduction of sheep’. (Eds D Lindsay, D Pearce) pp. 199–209. (Australian Academy of Science and the Australian Wool Corporation: Melbourne, Vic., Australia)
Alexander G, Lynch JJ, Mottershead BE, Donnelly JB (1980) Reduction in lamb mortality by means of grass wind-breaks: results of a five-year study. Proceedings of the Australian Society of Animal Production 13, 329–331.
Amer PR, McEwan JC, Dodds KG, Davis GH (1999) Economic values for ewe prolificacy and lamb survival in New Zealand sheep. Livestock Production Science 58, 75–90.
| Economic values for ewe prolificacy and lamb survival in New Zealand sheep.Crossref | GoogleScholarGoogle Scholar |
Atkins KD (1980) Selection for skin folds and fertility. Proceedings of the Australian Society of Animal Production 13, 174–176.
Barwick SA, Leymaster KA, Keele JW, Harvey WR (1990) Estimates of genetic parameters for lamb survival to weaning and birth weight in the US Suffolk. Proceedings of the Association for the Advancement of Animal Breeding and Genetics 8, 331–334.
Behrendt R, Van Burgel AJ, Bailey A, Barber P, Curnow M, Gordon DJ, Edwards JEH, Oldham CM, Thompson AN (2011) On-farm paddock-scale comparisons across southern Australia confirm that increasing the nutrition of Merino ewes improves their production and the lifetime performance of their progeny. Animal Production Science 51, 805–812.
| On-farm paddock-scale comparisons across southern Australia confirm that increasing the nutrition of Merino ewes improves their production and the lifetime performance of their progeny.Crossref | GoogleScholarGoogle Scholar |
Binns SH, Cox IJ, Rizvi S, Green LE (2002) Risk factors for lamb mortality on UK sheep farms. Preventive Veterinary Medicine 52, 287–303.
| Risk factors for lamb mortality on UK sheep farms.Crossref | GoogleScholarGoogle Scholar | 11849723PubMed |
Bradford GE (1972) The role of maternal effects in animal breeding: VII. Maternal effects in sheep. Journal of Animal Science 35, 1324–1334.
| The role of maternal effects in animal breeding: VII. Maternal effects in sheep.Crossref | GoogleScholarGoogle Scholar | 4570696PubMed |
Brien F, Hebart ML, Hocking Edwards JE, Greeff JC, Hart KW, Refshauge G, Gaunt G, Behrendt R, Thomson K, Hinch G, Geenty KG, Van Der Werf JHJ (2009) Genetics of lamb survival: preliminary studies of the information nucleus flock. Proceedings of the Association for the Advancement in Animal Breeding and Genetics 18, 108–111.
Brien FD, Hebart ML, Smith DH, Edwards JEH, Greeff JC, Hart KW, Refshauge G, Bird-Gardiner TL, Gaunt G, Behrendt R, Robertson MW, Hinch GN, Geenty KG, Van Der Werf JHJ (2010) Opportunities for genetic improvement of lamb survival. Animal Production Science 50, 1017–1025.
| Opportunities for genetic improvement of lamb survival.Crossref | GoogleScholarGoogle Scholar |
Brien FD, Hinch GN, van der Werf JHJ, Brown DJ, Swan AA (2011) Selection strategies for the genetic improvement of reproductive performance in sheep. Proceedings of the Association for the Advancement in Animal Breeding and Genetics 19, 151–158.
Brien FD, Cloete SWP, Fogarty NM, Greeff JC, Hebart ML, Hiendleder S, Edwards JEH, Kelly JM, Kind KL, Kleemann DO, Plush KL, Miller DR (2014) A review of the genetic and epigenetic factors affecting lamb survival. Animal Production Science 54, 667–693.
| A review of the genetic and epigenetic factors affecting lamb survival.Crossref | GoogleScholarGoogle Scholar |
Bunter KL, Brown DJ (2015) Revisiting total weaning weight as a selection criterion. Proceedings of the Association for the Advancement of Animal Breeding and Genetics 21, 201–204.
Bunter KL, Swan AA, Purvis IW, Brown D (2016) Pregnancy scanning can be used as a source of data for genetic evaluation of reproductive traits of ewes. Animal Production Science 56, 679–689.
| Pregnancy scanning can be used as a source of data for genetic evaluation of reproductive traits of ewes.Crossref | GoogleScholarGoogle Scholar |
Bunter KL, Swan AA, Brown DJ, Brien FD, Smith J (2018) Litter size at lambing influences genetic evaluation of maternal rearing ability. Animal Production Science 58, 791–800.
| Litter size at lambing influences genetic evaluation of maternal rearing ability.Crossref | GoogleScholarGoogle Scholar |
Bunter KL, Swan AA, Gurman PM, Boerner V, McMillan AJ, Brown DJ (2019) Evolution of genetic evaluation for ewe reproductive performance. Proceedings of the Association for the Advancement of Animal Breeding and Genetics 23, 560–563.
Bunter KL, Swan AA, Gurman PM, Brown DJ (2021) New genomically enhanced reproduction breeding values for Merino sheep allow targeted selection for conception rate, litter size and ewe rearing ability. Animal Production Science 61, 333–336.
| New genomically enhanced reproduction breeding values for Merino sheep allow targeted selection for conception rate, litter size and ewe rearing ability.Crossref | GoogleScholarGoogle Scholar |
Burfening PJ (1993) Direct and maternal genetic effects on lamb survival. Small Ruminant Research 11, 267–274.
| Direct and maternal genetic effects on lamb survival.Crossref | GoogleScholarGoogle Scholar |
Cloete SWP, Scholtz AJ (1998) Lamb survival in relation to lambing and neonatal behaviour in medium wool Merino lines divergently selected for multiple rearing ability. Australian Journal of Experimental Agriculture 38, 801–811.
| Lamb survival in relation to lambing and neonatal behaviour in medium wool Merino lines divergently selected for multiple rearing ability.Crossref | GoogleScholarGoogle Scholar |
Cloete SWP, Olivier JJ, Van Wyk JB, Erasmus GJ, Schoeman SJ (2003) Genetic parameters and trends for birth weight, birth coat score and weaning weight in Merino lines divergently selected for ewe multiple rearing ability. South African Journal of Animal Science 33, 248–256.
| Genetic parameters and trends for birth weight, birth coat score and weaning weight in Merino lines divergently selected for ewe multiple rearing ability.Crossref | GoogleScholarGoogle Scholar |
Cloete SWP, Gilmour AR, Olivier JJ, Van Wyk JB (2004) Genetic and phenotypic trends and parameters in reproduction, greasy fleece weight and liveweight in Merino lines divergently selected for multiple rearing ability. Australian Journal of Experimental Agriculture 44, 745–754.
| Genetic and phenotypic trends and parameters in reproduction, greasy fleece weight and liveweight in Merino lines divergently selected for multiple rearing ability.Crossref | GoogleScholarGoogle Scholar |
Cloete SWP, Olivier JJ, Olivier WJ (2007) Genetic change in South African Merino resource flocks. Proceedings of the Association for the Advancement of Animal Breeding and Genetics 17, 320–323.
Cloete SWP, Misztal I, Olivier JJ (2009) Genetic parameters and trends for lamb survival and birth weight in a Merino flock divergently selected for multiple rearing ability. Journal of Animal Science 87, 2196–2208.
| Genetic parameters and trends for lamb survival and birth weight in a Merino flock divergently selected for multiple rearing ability.Crossref | GoogleScholarGoogle Scholar |
Davies RB (1987) Hypothesis testing when a nuisance parameter is present only under the alternative. Biometrika 74, 33–43.
| Hypothesis testing when a nuisance parameter is present only under the alternative.Crossref | GoogleScholarGoogle Scholar |
Dwyer CM (2008a) Genetic and physiological determinants of maternal behavior and lamb survival: implications for low-input sheep management. Journal of Animal Science 86, E246–E258.
| Genetic and physiological determinants of maternal behavior and lamb survival: implications for low-input sheep management.Crossref | GoogleScholarGoogle Scholar | 17709772PubMed |
Dwyer CM (2008b) The welfare of the neonatal lamb. Small Ruminant Research 76, 31–41.
| The welfare of the neonatal lamb.Crossref | GoogleScholarGoogle Scholar |
Everett-Hincks JM, Cullen NG (2009) Genetic parameters for ewe rearing performance. Journal of Animal Science 87, 2753–2758.
| Genetic parameters for ewe rearing performance.Crossref | GoogleScholarGoogle Scholar | 19502504PubMed |
Everett-Hincks JM, Lopez-Villalobos N, Blair HT, Stafford KJ (2005) The effect of ewe maternal behaviour score on lamb and litter survival. Livestock Production Science 93, 51–61.
| The effect of ewe maternal behaviour score on lamb and litter survival.Crossref | GoogleScholarGoogle Scholar |
Everett-Hincks JM, Mathias-Davis HC, Greer GJ, Auvray BA, Dodds KG (2014) Genetic parameters for lamb birth weight, survival and death risk traits. Journal of Animal Science 92, 2885–2895.
| Genetic parameters for lamb birth weight, survival and death risk traits.Crossref | GoogleScholarGoogle Scholar | 24802039PubMed |
Falconer DS (1989) ‘Introduction to Quantitative Genetics.’ (Longmans Green/John Wiley & Sons: Harlow, Essex, UK)
Fogarty NM (1972) Crossbreeding for lamb production. 1. Survival and growth of first cross lambs. Australian Journal of Experimental Agriculture 12, 234–239.
| Crossbreeding for lamb production. 1. Survival and growth of first cross lambs.Crossref | GoogleScholarGoogle Scholar |
Fogarty NM, Ingham VM, Gilmour AR, Cummins LJ, Gaunt GM, Stafford J, Edwards JEH, Banks RG (2005) Genetic evaluation of crossbred lamb production. 1. Breed and fixed effects for birth and weaning weight of first-cross lambs, gestation length, and reproduction of base ewes. Australian Journal of Agricultural Research 56, 443–453.
| Genetic evaluation of crossbred lamb production. 1. Breed and fixed effects for birth and weaning weight of first-cross lambs, gestation length, and reproduction of base ewes.Crossref | GoogleScholarGoogle Scholar |
Fogarty NM, Safari E, Gilmour AR, Ingham VM, Atkins KD, Mortimer SI, Swan AA, Brien FD, Greeff JC, van der Werf JHJ (2006) Wool and meat genetics: the joint possibilities. International Journal of Sheep and Wool Science 54, 22–27.
Fozi MA, Van Der Werf JHJ, Swan AA (2005) The importance of accounting for maternal genetic effects in Australian fine-wool Merino breeding. Australian Journal of Agricultural Research 56, 789–796.
| The importance of accounting for maternal genetic effects in Australian fine-wool Merino breeding.Crossref | GoogleScholarGoogle Scholar |
Gama LT, Dickerson GE, Young LD, Leymaster KA (1991) Effects of breed, heterosis, age of dam, litter size, and birth weight on lamb mortality. Journal of Animal Science 69, 2727–2743.
| Effects of breed, heterosis, age of dam, litter size, and birth weight on lamb mortality.Crossref | GoogleScholarGoogle Scholar | 1885385PubMed |
Geenty KG, Brien FD, Hinch GN, Dobos RC, McCaskill M, Ball AJ, Behrendt R, Gore KP, Harden S, Hocking-Edwards JE, Hart K, van der Werf JHJ (2014) Reproductive performance in the Sheep CRC Information Nucleus across different sheep production environments in southern Australia. Animal Production Science 54, 715–726.
| Reproductive performance in the Sheep CRC Information Nucleus across different sheep production environments in southern Australia.Crossref | GoogleScholarGoogle Scholar |
Gilmour AR, Gogel BJ, Welham SJ (2015) ‘ASReml User Guide Release 4.1. Structural Specification.’ Available at www.vsni.co.uk
Gudex BW, Hickford JGH, Frampton CM (2005) Sire line differences in lamb losses from starvation-exposure. Proceedings of the New Zealand Society of Animal Production 65, 186–190.
Hall DG, Fogarty NM, Gilmour AR (1995) Performance of crossbred progeny of trangie fertility merino and booroola merino rams and poll dorset ewes 1. Lamb birth weight, survival and growth. Australian Journal of Experimental Agriculture 35, 1069–1074.
| Performance of crossbred progeny of trangie fertility merino and booroola merino rams and poll dorset ewes 1. Lamb birth weight, survival and growth.Crossref | GoogleScholarGoogle Scholar |
Hatcher S, Atkins KD, Safari E (2009) Phenotypic aspects of lamb survival in Australian Merino sheep. Journal of Animal Science 87, 2781–2790.
| Phenotypic aspects of lamb survival in Australian Merino sheep.Crossref | GoogleScholarGoogle Scholar | 19502501PubMed |
Hatcher S, Atkins KD, Safari E (2010) Lamb survival in Australian Merino Sheep: a genetic analysis. Journal of Animal Science 88, 3198–3205.
| Lamb survival in Australian Merino Sheep: a genetic analysis.Crossref | GoogleScholarGoogle Scholar | 20562357PubMed |
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 | 6667215PubMed |
Hebart ML, Brien FD, Jaensch KS, Smith DH, Walkom SF, Grimson RJ (2010) Genetics of reproductive efficiency: a study of Merino resource flocks in South Australia. Communication 0685. In ‘Proceedings of the 9th World Congress on Genetics Applied to Livestock Production’, Leipzig, Germany.
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 |
Hinch GN, Kelly RW, Owens JL, Crosbie SF (1983) Patterns of lamb survival in high fecundity Booroola flocks. Proceedings of the New Zealand Society of Animal Production 43, 29–32.
Kemper KE, Smith JL, Purvis IW (2003) The value of birthcoat score as an early age selection criterion for superfine Merino sheep. Proceedings of the Association for the Advancement of Animal Breeding and Genetics 15, 139–142.
Kilgour RJ (1992) Lambing potential and mortality in Merino sheep as ascertained by ultrasonography. Australian Journal of Experimental Agriculture 32, 311–313.
| Lambing potential and mortality in Merino sheep as ascertained by ultrasonography.Crossref | GoogleScholarGoogle Scholar |
Kleemann DO, Walker SK (2005) Fertility in South Australian commercial Merino flocks: sources of reproductive wastage. Theriogenology 63, 2075–2088.
| Fertility in South Australian commercial Merino flocks: sources of reproductive wastage.Crossref | GoogleScholarGoogle Scholar | 15826674PubMed |
Kleemann DO, Walker SK, Walkley JRW, Ponzoni RW, Smith DH, Grimson RJ, Seamark RF (1993) Effect of nutrition during pregnancy on birth weight and lamb survival in FecB Booroola × South Australian Merino ewes. Animal Reproduction Science 31, 213–224.
| Effect of nutrition during pregnancy on birth weight and lamb survival in FecB Booroola × South Australian Merino ewes.Crossref | GoogleScholarGoogle Scholar |
Kleemann DO, Quigley SP, Bright R, Scott Q (2000) Survival and growth of Damara, Dorper, Dorset, Rambouillet, South African Meat Merino first cross lambs in semi arid Queensland. Asian–Australasian Journal of Animal Sciences 13, 173
Knight TW, Lynch PR, Hall DRH, Hockey HUP (1988) Identification of factors contributing to the improved lamb survival in Marshall Romney sheep. New Zealand Journal of Agricultural Research 31, 259–271.
| Identification of factors contributing to the improved lamb survival in Marshall Romney sheep.Crossref | GoogleScholarGoogle Scholar |
Lopez-Villalobos N, Garrick DJ (1999) Genetic parameter estimates for lamb survival in Romney sheep. Proceedings of the New Zealand Society of Animal Production 59, 121–124.
Lynch JJ, Alexander G (1980) The effect of time since shearing on sheltering behaviour by Merino sheep. Proceedings of the Australian Society of Animal Production 13, 325–328.
Matos CAP, Thomas DL, Young LD, Gianola D (2000) Genetic analyses of lamb survival in Rambouillet and Finnsheep flocks by linear and threshold models. Animal Science 71, 227–234.
| Genetic analyses of lamb survival in Rambouillet and Finnsheep flocks by linear and threshold models.Crossref | GoogleScholarGoogle Scholar |
Maxa J, Sharifi AR, Pedersen J, Gauly M, Simianer H, Norberg E (2009) Genetic parameters and factors influencing survival to twenty-four hours after birth in Danish meat sheep breeds. Journal of Animal Science 87, 1888–1895.
| Genetic parameters and factors influencing survival to twenty-four hours after birth in Danish meat sheep breeds.Crossref | GoogleScholarGoogle Scholar | 19251927PubMed |
McGuirk BJ, Bourke ME, Manwaring JM (1978) Hybrid vigour and lamb production. 2. Effects on survival and growth of first-cross lambs, and on wool and body measurements of hogget ewes. Australian Journal of Experimental Agriculture 18, 753–763.
| Hybrid vigour and lamb production. 2. Effects on survival and growth of first-cross lambs, and on wool and body measurements of hogget ewes.Crossref | GoogleScholarGoogle Scholar |
Morris CA, Hickey SM, Clarke JN (2000) Genetic and environmental factors affecting lamb survival at birth and through to weaning. New Zealand Journal of Agricultural Research 43, 515–524.
| Genetic and environmental factors affecting lamb survival at birth and through to weaning.Crossref | GoogleScholarGoogle Scholar |
Mortimer SI, Atkins KD (1997) Improvement of Merino reproductive performance through bloodline substitution and crossing. Proceedings of the Association for the Advancement of Animal Breeding and Genetics 12, 404–407.
Muggeo VMR (2008) Segmented: an R package to fit regression models with broken-line relationships. R News 8, 20–25.
Mullaney PD (1966) The relation of birth coat and lamb survival. Australian Journal of Experimental Agriculture 6, 84–87.
| The relation of birth coat and lamb survival.Crossref | GoogleScholarGoogle Scholar |
Muller A, Brand TS, Scholtz AJ, Kruger ACM, Cloete SWP (2020) Genetic and environmental parameters and trends for early growth and yearling traits in the Elsenburg Dormer resource flock. Small Ruminant Research 191, 106181
| Genetic and environmental parameters and trends for early growth and yearling traits in the Elsenburg Dormer resource flock.Crossref | GoogleScholarGoogle Scholar |
Nel CL, Cloete SWP, Kruger ACM, Dzama K (2021) Long term genetic selection for reproductive success affects neonatal lamb vitality across cold stress conditions. Journal of Thermal Biology 98, 102908
| Long term genetic selection for reproductive success affects neonatal lamb vitality across cold stress conditions.Crossref | GoogleScholarGoogle Scholar | 34016335PubMed |
Newman SA, Dodds KG, Clarke JN, Garrick DJ, McEwan JC (2000) The Sheep Improvement Limited (SIL) genetic engine. Proceedings of the New Zealand Society of Animal Production 60, 195–197.
Owens JL, Bindon BM, Edey TN, Piper LR (1985) Behaviour at parturition and lamb survival of Booroola Merino sheep. Livestock Production Science 13, 359–372.
| Behaviour at parturition and lamb survival of Booroola Merino sheep.Crossref | GoogleScholarGoogle Scholar |
Plush KJ, Brien FD, Hebart ML, Hynd PI (2016) Thermogenesis and physiological maturity in neonatal lambs: a unifying concept in lamb survival. Animal Production Science 56, 736–745.
| Thermogenesis and physiological maturity in neonatal lambs: a unifying concept in lamb survival.Crossref | GoogleScholarGoogle Scholar |
R Core Team (2020) R: a Language and Environment for Statistical Computing. Available at https://www.r-project.org/
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 |
Riggio V, Finocchiaro R, Bishop SC (2008) Genetic parameters for early lamb survival and growth in Scottish Blackface sheep. Journal of Animal Science 86, 1758–1764.
| Genetic parameters for early lamb survival and growth in Scottish Blackface sheep.Crossref | GoogleScholarGoogle Scholar | 18407992PubMed |
Robinson DL (1996) Models which might explain negative correlations between direct and maternal genetic effects. Livestock Production Science 45, 111–122.
| Models which might explain negative correlations between direct and maternal genetic effects.Crossref | GoogleScholarGoogle Scholar |
Safari E, Fogarty NM, Gilmour AR (2005) A review of genetic parameter estimates for wool, growth, meat and reproduction traits in sheep. Livestock Production Science 92, 271–289.
| A review of genetic parameter estimates for wool, growth, meat and reproduction traits in sheep.Crossref | GoogleScholarGoogle Scholar |
Safari E, Fogarty NM, Gilmour AR, Atkins KD, Mortimer SI, Swan AA, Brien FD, Greeff JC, Van Der Werf JHJ (2007) Across population genetic parameters for wool, growth, and reproduction traits in Australian Merino sheep. 1. Data structure and non-genetic effects. Australian Journal of Agricultural Research 58, 169–175.
| Across population genetic parameters for wool, growth, and reproduction traits in Australian Merino sheep. 1. Data structure and non-genetic effects.Crossref | GoogleScholarGoogle Scholar |
Sawalha RM, Conington J, Brotherstone S, Villanueva B (2007) Analyses of lamb survival of Scottish Blackface sheep. Animal 1, 151–157.
| Analyses of lamb survival of Scottish Blackface sheep.Crossref | GoogleScholarGoogle Scholar | 22444218PubMed |
Schoeman SJ, Cloete SWP, Olivier JJ (2010) Returns on investment in sheep and goat breeding in South Africa. Livestock Science 130, 70–82.
| Returns on investment in sheep and goat breeding in South Africa.Crossref | GoogleScholarGoogle Scholar |
Slee J (1978) The effects of breed, birthcoat and body weight on the cold resistance of newborn lambs. Animal Production 27, 43–49.
| The effects of breed, birthcoat and body weight on the cold resistance of newborn lambs.Crossref | GoogleScholarGoogle Scholar |
Slee J, Alexander G, Bradley LR, Jackson N, Stevens D (1991) Genetic aspects of cold resistance and related characters in newborn Merino lambs. Australian Journal of Experimental Agriculture 31, 175–182.
| Genetic aspects of cold resistance and related characters in newborn Merino lambs.Crossref | GoogleScholarGoogle Scholar |
Smith GM (1977) Factors affecting birth weight, dystocia and preweaning survival in sheep. Journal of Animal Science 44, 745–753.
| Factors affecting birth weight, dystocia and preweaning survival in sheep.Crossref | GoogleScholarGoogle Scholar | 558970PubMed |
Snowder GD, Fogarty NM (2009) Composite trait selection to improve reproduction and ewe productivity: a review. Animal Production Science 49, 9–16.
| Composite trait selection to improve reproduction and ewe productivity: a review.Crossref | GoogleScholarGoogle Scholar |
Snyman MA, Erasmus GJ, van Wyk JB, Olivier JJ (1995) Direct and maternal (co) variance components and heritability estimates for body weight at different ages and fleece traits in Afrino sheep. Livestock Production Science 44, 229–235.
| Direct and maternal (co) variance components and heritability estimates for body weight at different ages and fleece traits in Afrino sheep.Crossref | GoogleScholarGoogle Scholar |
Southey BR, Rodriguez-Zas SL, Leymaster KA (2001) Survival analysis of lamb mortality in a terminal sire composite population. Journal of Animal Science 79, 2298–2306.
| Survival analysis of lamb mortality in a terminal sire composite population.Crossref | GoogleScholarGoogle Scholar | 11583416PubMed |
Swan AA (2009) The economics of litter size in meat sheep. In ‘Use FecB (Booroola) gene in sheep breeding programs: proceedings of the Helen Newton Turner Memorial International Workshop’, Pune, India, 10–12 November 2008, pp. 173–176.
Swan AA, Piper LR, Brewer HG, Purvis IW (2001) Genetic variation in reproductive performance of fine wool Merinos. Proceedings of the Association for the Advancement of Animal Breeding and Genetics 14, 417–420.
Vanderick S, Auvray B, Newman SA, Dodds KG, Gengler N, Everett-Hincks JM (2015) Derivation of a new lamb survival trait for the New Zealand sheep industry. Journal of Animal Science 93, 3765–3772.
| Derivation of a new lamb survival trait for the New Zealand sheep industry.Crossref | GoogleScholarGoogle Scholar | 26440155PubMed |
Welsh CS, Garrick DJ, Enns RM, Nicoll GB (2006) Threshold model analysis of lamb survivability in Romney sheep. New Zealand Journal of Agricultural Research 49, 411–418.
| Threshold model analysis of lamb survivability in Romney sheep.Crossref | GoogleScholarGoogle Scholar |
Wickham H (2016) ‘ggplot2: Elegant Graphics for Data Analysis.’ (Springer-Verlag: New York, NY, USA) Available at https://ggplot2.tidyverse.org
