Summary
The birth sex ratio of a commercial flock of Suffolk × sheep, Ovis aries, were studied over six consecutive lambing seasons. In all, data from 1820 lambs were recorded and analysed. The overall birth sex ratio was 49.56% male lambs. Significantly more males (56.23%) were born to ewes with single lambs than to ewes with like-sex twins (47.73%). Significantly more female lambs were born to ewes with triplet births (41.79% male). A significant difference in the birth sex ratio was observed between the first and second half of the lambing season, among like-sex pairs of twin lambs. More males were born in the first half (51.43%) and significantly more females (43.59% male) in the second half of the lambing season. The results are discussed with reference to the theory of Trivers and Willard (1973).
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References
Burfening PJ (1972) Prenatal and postnatal competition among twin lambs. Anim Prod 15:61–66
Chapman AB, Lush JL (1932) Twinning, sex ratios and genetic variability in birth weight in sheep. J Hered 23:473–478
Clutton-Brock TH (1991) The evolution of parental care. Princeton University Press, Princeton, NJ
Clutton-Brock TH, Albon SD (1982) Parental investment in male and female offspring in mammals. In: King's College Sociobiology Group, Current problems in sociobiology. Cambridge University Press, Cambrige, UK, pp 223–247
Clutton-Brock TH, Iason GR (1986) Sex ratio variation in mammals. Q Rev Biol 61:339–374
Clutton-Brock TH, Albon SD, Guinness FE (1981) Parental investment in male and female offspring in polygynous mammals. Nature 289:487–491
Clutton-Brock TH, Albon SD, Guinness FE (1984) Maternal dominance, breeding success and birth sex ratio in red deer. Nature 308:358–360
Ewbank R (1964) Observations on the suckling habits of twin lambs. Anim Behav 12:34–37
Ewbank R (1967) Nursing and suckling behaviour among Clun Forest ewes and lambs. Anim Behav 15:251–258
Henning WL (1939) Prenatal and postnatal sex ratio in sheep. J Agric Res 58:565–580
Huck UW, Pratt NC, Labov JB, Lisk RD (1988) Effects of age and parity on litter size and offspring sex ratio in golden hamsters (Mesocricetus auratus). J Reprod Fert 83:209–214
Hulet CV, Krcanbrack SK, Blackwell RL, Price DA, Wilson LO (1962) Mating behaviour of the ram in the multiple sire pen. J Anim Sci 21:865–869
Hulet CV, Alexander G, Hafez ESE (1975) The behaviour of sheep. In: Hafez ESE (ed) The behaviour of domestic animals. Baillière Tindall, London, UK, pp 246–295
Johansson I, Hansson A (1943) The sex ratio and multiple births in sheep. Ann Agric Coll Sweden 11:145–171
Karam HA (1957) Multiple births and sex ratio in Rohamani sheep. J Anim Sci 16:990–997
Napier KM, Mullaney PD (1974) Sex ratio in sheep. J Reprod Fert 39:391–392
Owens JL, Bindon BM, Edey TN, Piper LR (1985) Behaviour at parturition and lamb survival of Booroola Merino sheep. Livestock Prod Sci 13:359–372
Rasmussen K (1941) A note on the effect of multiple births on the sex ratio in sheep. Scient Agric 21:759–760
Siegel S (1956) Nonparametric statistics for the behavioral sciences. McGraw-Hill, New York
Skjervold H (1979) Causes of variation in sex ratio and sex combination in multiple births in sheep. Livestock Prod Sci 6:387–396
Sokal RR, Rohlf FJ (1969) Biometry: The principles and practice of statistics in biological research. Freeman, San Francisco
Trivers RL, Willard DE (1973) Natural selection of parental ability to vary the sex ratio of offspring. Science 179:90–92
Williams GC (1979) The question of adaptive sex ratio in out-crossed vertebrates. Proc Roy Soc Lond B 205:567–580
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Kent, J. Birth sex ratios in sheep over six lambing seasons. Behav Ecol Sociobiol 30, 151–155 (1992). https://doi.org/10.1007/BF00166697
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DOI: https://doi.org/10.1007/BF00166697