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Studies on the breeding season and reproduction of the ewe Part III. The breeding season and artificial light Part IV. Studies on the reproduction of the ewe Part V. Mating behaviour and pregnancy diagnosis

Published online by Cambridge University Press:  27 March 2009

E. S. E. Hafez
E. S. E. Hafez
Affiliation:
School of Agriculture, University of Cambridge, and Faculty of Agriculture, Cairo, Egypt
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During the course of three breeding seasons, daily observations of oestrus were undertaken on the following groups of ewes, all of which were running with ochred rams. One hundred and twenty ewes (pure bred and first-cross) of different breeds and ages, running with vasectomized rams under natural conditions. Twenty-eight grade Suffolk ewes fed on a submaintenance diet. Eighteen grade Suffolk ewes running with a fertile ram. Twenty ewes of several breeds exposed to artificial light.

The effects of heredity (breed and individual), environment (season, year and nutrition), age and artificial light on the breeding season and related phenomena have been investigated. The results and conclusions were as follows:

1. (a) There are breed differences in the extent of the breeding season, cycle length, incidence of silent heat and duration of heat (Table 29). (b) The duration of the breeding season is related to the geographical origin (latitude and altitude) of the breed, (c) The duration of the breeding season of the first-cross is intermediate between that of the two parents, (d) Individual differences in the number of oestrous cycles per ewe per season were more marked in the mountain breeds.

2. (a) Of the ewe lambs, 79% exhibited oestrus during the shortest days only of the first breeding season. Their breeding season is not spread evenly about the shortest day as it is with adults. (b) The occurrence and length of the breeding season in ewe lambs is associated with early birth dates or with higher growth rates.

3. (a) Significant differences exist between breeds in the age at first oestrus. (b) Ewe lambs born early in the season showed their first oestrus at later age and heavier weight than those born late.

4. Annual differences in the duration of the breeding season, cycle length, incidence of silent heat and occurrence of first oestrus were negligible.

5. (a) Submaintenance diet had no effect on the onset of the breeding season, but it converted oestrus into silent heat. Conception occurred less frequently after periods of underfeeding. (b) At high latitudes nutrition has only a minor effect on the breeding season of the ewe.

6. (a) A constant high ratio of artificial darkness (8 hr. light: 16 hr. darkness) hastened the onset of the breeding season some 57 and 27 days in the two experimental groups. (b) A constant high ratio of artificial light (16 hr. light: 8 hr. darkness) hastened the end of the breeding season some 104 days on an average (in one experimental group), (c) There were breed differences in the latency of initiation and of cessation of the induced breeding season, (d) In the induced breeding season cycles of ovulation preceded the first oestrus, (e) Two thresholds of pituitary activity are suggested, one for the onset of ovulation, and the other for the manifestation of oestrus.

7. (a) A high frequency of cycles outside the normal range (14–19 days) was observed in the mountain breeds and in ewe lambs. (b) The shortest average cycle length coincided with the shortest days of the year.

8. A high frequency of silent heats (during the breeding season) was observed in the mountain breeds, in ewe lambs and during the second half of the breeding season.

9. Oestrus was of longer duration in adults and yearlings than in ewe lambs.

10. (a) Post-partum heat occurred in 56% of Suffolk ewes with an average lactation anoestrus of 35 days. (b) There is a relationship between the early onset of the breeding season and the incidence of post-partum heat, (c) Conception post-partum is partly inhibited by lactation.

11. Mating behaviour was observed in animals of several breeds and ages (three patterns were recorded for ewes and eight patterns for rams).

12. Irregular columnar cells in the vaginal smear of the ewe characterized late pregnancy.

In addition, the breeding season of wild and domestic sheep was reviewed in relation to the environment with special reference to the length of daylight.

Type
Research Article
Information
The Journal of Agricultural Science , Volume 42 , Issue 3 , July 1952 , pp. 232 - 265
Copyright
Copyright © Cambridge University Press 1952

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References

REFERENCES

Alongi, G. (1924). Rass.studi Sess. Eugen. 4, 85. (Quoted by Grant, 1934.)Google Scholar
Anderson, J. (1936). Emp. J. Exp. Agric. 4, 197.Google Scholar
Anderson, J. (1949). Personal communication.Google Scholar
Andreoni, R. (1938). Riv. Zootec. 15, 79. (A.B.A. 7, 19.)Google Scholar
Arauja, M. R. (1950). Personal communication.Google Scholar
Asdell, S. A. (1946). Patterns of Mammalian Reproduction, p. 360. New York: Comstock.Google Scholar
Asdell, S. A., de Alba, G. H. & Roberts, J. S. (1945). J. Anim. Sci. 4, 277.CrossRefGoogle Scholar
Atland, P. D. (1946). Anal. Rec. 96, 27.Google Scholar
Atland, P. D. (1949). J. Exp. Zool. 110, 1.CrossRefGoogle Scholar
Bailey, L. H. (1922). Cyclopedia of Farm Animals. New York: Macmillan.CrossRefGoogle Scholar
Baker, J. R. (1938). Tabul. Biol., Berl., 15, 333.Google Scholar
Baranov, A. G. (1941). Sovetsak. Zooteh. no. 1, 65. (A.B.A. 11, 31.)Google Scholar
Bartlett, A. D. (1857). Proc. Zool. Soc. Lond. 25, 105.CrossRefGoogle Scholar
Beach, F. A. (1947). Rec. Progr. Horm. Res. 1, 27.Google Scholar
Bell, T. D. (1945). Pr. Bull. N. Mex. Agric. Exp. Sta. no. 1003.Google Scholar
Bergé, S. (1942). Avl av sau og Geit, p. 17. Oslo: Grondahl and Sons, Forlag.Google Scholar
Bergé, S. (1949). Personal communication.Google Scholar
Bergerie Nationale, France (1949). Personal communication.Google Scholar
Bhattacharya, P. (1949). Personal communication.Google Scholar
Bissonnette, T. H. (1932). Proc. Roy. Soc. B, 110, 322.Google Scholar
Bissonnette, T. H. (1935). Anat. Rec. 63, 159.CrossRefGoogle Scholar
Bissonnette, T. H. (1937). Amer. Nat. 71, 525.Google Scholar
Bissonnette, T. H. (1941). Physiol. Zoöl. 14, 379.CrossRefGoogle Scholar
Bissonnette, T. H. (1951). Personal communication.Google Scholar
Bissonnette, T. H. & Czech, A. G. (1941). J. Wildlife Management, 5, 383.CrossRefGoogle Scholar
Bissonnette, T. H. & Wilson, E. (1939). Science, 89, 418.CrossRefGoogle Scholar
Blum, C. T. (1943). J. Hered. 34, 141.Google Scholar
Bonfert, A. (1933). Bid. Asoc. Med. Vet. Român. 45, 215. (A.B.A. 2, 114.)Google Scholar
Briggs, H. M. (1936). Bull. N. Dak. Agric. Exp. Sta. no. 285.Google Scholar
Briggs, H. M. (1949). Modern Breeds of Livestock, pp. 445 and 517. New York: Macmillan.Google Scholar
Briggs, H. M., Darlow, A. E., Hawkins, L. E., Welham, O. S. & Hauser, E. R. (1942). Bull. Okla. Agric. Exp. Sta. no. 255.Google Scholar
Brooks, C. M. & Gersh, I. (1941). Endocrinology, 28, 1.CrossRefGoogle Scholar
Bujatti, P. G. (1949). Riv. Zootec. 22, 195. (A.B.A. 17, 358.)Google Scholar
Burkhardt, J. (1947). J. Agric. Sci. 37, 64.CrossRefGoogle Scholar
Calkin, V. Z. (1948). Bjull. mosk. Obšč. Prirod. (Otd. biol.), 53, 31. (A.B.A. 17, 139.)Google Scholar
Cardas, A. & Nica, G. (1940). Züchtungskunde, 15, 86.Google Scholar
Casida, L. E. & McKenzie, F. F. (1932). Res. Bull. Mo. Agric. Exp. Sta. no. 170.Google Scholar
Chapman, A. B. (1935). Analysis of variation in the sexual cycle and some of its component phases. University of Wisconsin Ph.D. Thesis.Google Scholar
Clark, R. T. (1934). Anat. Rec. 60, 125.CrossRefGoogle Scholar
Cole, H. H., Hart, G. H. & Miller, R. F. (1945). Endocrinology, 36, 6.CrossRefGoogle Scholar
Cole, H. H. & Miller, R. F. (1931). Proc. Soc. Exp. Biol., N.Y., 28, 841.CrossRefGoogle Scholar
Cole, H. H. & Miller, R. F. (1935). Amer. J. Anat. 57, 39.CrossRefGoogle Scholar
Coleman, J. M. (1950). Agric. Gaz. N.S.W. 61, 440.Google Scholar
Combes, A. (1934). Union Ovine, 6, 254. (A.B.A. 2, 209.)Google Scholar
Cowie, A. T. (1948). Pregnancy Diagnosis Tests. A Review. Jt. Publ. no. 13. Commonw. Agric. Bur.Google Scholar
Cox, E. W. (1936). The Evolution of the Australian Merino. Sydney: Angus and Robertson Ltd.Google Scholar
Darlow, A. E. & Hawkins, L. E. (1931). Proc. Amer. Soc. Anim. Prod. p. 205.Google Scholar
Darwin, C. (1885). Animals and Plants under Domestication, p. 104. London.Google Scholar
Dassat, P. (1942). Ital. Agric. 79, 328.Google Scholar
Davis, W. B. & Taylor, W. P. (1939). J. Mammal. 20, 440.CrossRefGoogle Scholar
De Lange, M. (1950). Onderstepoort J. Vet. Sci. 24, 125.Google Scholar
Desclaux, P. (1944). C. R. Soc. Biol., Paris, 138, 347.Google Scholar
Eastoe, R. D., Sutton, P. B. & McDonald, J. (1948). Agric. Gaz. N.S.W. 59, 93.Google Scholar
Elapkin, A. C., Madsen, M. A. & Phillips, R. W. (1940). Bull. Utah Agric. Exp. Sta. no. 292.Google Scholar
Elpatjevskii, D. (1934). Ovcevodstvo, 7, 32. (A.B.A. 2, 323.)Google Scholar
Elwes, H. J. (1913). Guide to Primitive Breeds of Sheep and their Crosses, pp. 3 and 35. Edinburgh.Google Scholar
Engle, E. T. (1931). Endocrinology, 15, 405.CrossRefGoogle Scholar
Finlay, G. F. (1949). 14th Int. Vet. Congr. Lond., Sec. 5 (e), p. 5.Google Scholar
Folley, S. J. (1949). Brit. J. Nutrit. 3, 91.CrossRefGoogle Scholar
Fomenko, M. V., Judović, S. S., Loginova, N. V., Polovoeva, V. V. (1933). Trud. Asiat. N.-I. Inst. Ovcevod. 1, 21.Google Scholar
Fraps, R. M., Neher, B. H. & Rothchild, I. (1947). Endocrinology, 40, 241.CrossRefGoogle Scholar
Fraser, A. (1949). Sheep Husbandry, p. 89. London: Crosby Lockwood.Google Scholar
Frölich, G. (1931). Das Karakulschaf und seine Zucht. Munich. (A. B. A. 1, 58.)Google Scholar
Frost, N. M. (1942). J. Mammal. 23, 215.CrossRefGoogle Scholar
Gadola, A. (1933). Ann. Inst. sperm, zootec, Roma, 1, 201. (A.B.A. 3, 381.)Google Scholar
Golf, A. (1940). Z. Schafz. 29, 137. (A.B.A. 9, 115.)Google Scholar
Goot, H. (1949). N.Z. J. Sci. Tech. [Agric], 30, 330.Google Scholar
Granger, W. (1947). Aust. Vet. J. 23, 143.CrossRefGoogle Scholar
Grant, R. (1934). Trans. Roy. Soc. Edinb. 68, 1.CrossRefGoogle Scholar
Green, J. D. (1952). Amer. J. Anat. (in the Press).Google Scholar
Green, J. D. & Harris, G. W. (1947). J. Endocrinol. 5, 136.CrossRefGoogle Scholar
Greep, R. O. (1936). Proc. Soc. Exp. Biol., N.Y., 34, 754.CrossRefGoogle Scholar
Griswald, D. T. (1932). Proc. Amer. Soc. Anim. Prod. p. 181.Google Scholar
Guilbert, H. R. (1942). J. Anim. Sci. 1, 3.CrossRefGoogle Scholar
Hafez, E. S. E. (1950). Nature, Lond., 166, 822.CrossRefGoogle Scholar
Hafez, E. S. E. (1951 a). Naturwissenschaften, 38, 100.CrossRefGoogle Scholar
Hafez, E. S. E. (1951 b). Nature, Lond., 167, 777.CrossRefGoogle Scholar
Hafez, E. S. E. (1951 c). Nature, Lond., 168, 336.CrossRefGoogle Scholar
Hafez, E. S. E. (1951 d). Nature, Lond., 168, 1046.CrossRefGoogle Scholar
Hammond, J. (1921). J. Agric. Sci. 11, 337.CrossRefGoogle Scholar
Hammond, J. (1949 a). U.N. Sci. Conf. Conser. Util. Resources, no. 11 (6), 22.Google Scholar
Hammond, J. (1949 b). Brit. J. Nutrit. 3, 79.CrossRefGoogle Scholar
Hammond, J. jun. (1944). J. Agric. Sci. 34, 97.CrossRefGoogle Scholar
Hammond, J. jun. (1951). Nature, Lond., 167, 150.CrossRefGoogle Scholar
Hancock, J. L. (1949). 14th Int. Vet. Congr. Lond., Sec. 4(e), p. 5.Google Scholar
Hancock, J. L. & Rowlands, I. W. (1950). Personal communication.Google Scholar
Hansson, A. (1947). Physiology of Reproduction in Mink. Stockholm: Alb. Bonniers Boktryckeri.Google Scholar
Harris, G. W. (1947). J. Endocrinol. (Proc), 5, 17.Google Scholar
Harris, G. W. (1948). Physiol. Rev. 28, 139.CrossRefGoogle Scholar
Hart, D. S. (1950). J. Agric Sci. 40, 143.CrossRefGoogle Scholar
Hart, D. S. (1951). J. Exp. Biol. 28, 1.CrossRefGoogle Scholar
Hediger, G. (1950). Wild Animals in Captivity, p. 4. London: Butterfly Sci. Publ.Google Scholar
Henning, W. L. (1939). J. Agric. Res. 58, 565.Google Scholar
Hill, M. & Parkes, A. S. (1933). Proc. Roy. Soc. B, 113, 537.Google Scholar
Hill, M. & Parkes, A. S. (1934). Proc. Roy. Soc. B, 115, 14.Google Scholar
Hilzheimer, M. (1916). Brehms Tierleben, 13 Bd. (Quoted by Voss, 1950.)Google Scholar
Hindle, E. (1949). Records of Royal Zoological Society. London.Google Scholar
Höcker, U. (1938). Beiträge zur Kenntnis der Sexualvorgänge des Karakulschafes im Hinblick auf die Künstliche Besamung, Hon.-Diss. Halle.Google Scholar
Hoelzer, H. (1948). Dtsch. tierärztl. Wschr. 55, 136. (Nutr. Abstr. Rev. 19, 484.)Google Scholar
Holm, H. (1939). Vet. med. Diss. Hannover. Abstract in Berl. Munich, tierärztl. Wschr. (1941), p. 522. (A.B.A. 10, 165.)Google Scholar
Hugh, E. J. (1950). Personal communication.Google Scholar
Humphrey, G. C. & Kleinheinz, F. (1907). 24th Ann. Rep. Wis. Agric. Exp. Sta. p. 25.Google Scholar
Johansson, I. & Hansson, A. (1943). Annals Agric. Coll. Sweden, 2, 145.Google Scholar
Johnson, E. L. (1924). J. Agric. Res. 29, 491.Google Scholar
Kadgien, G. (1934). Dtsch. landw. Tierz. 38, 393. (A.B.A. 2, 214.)Google Scholar
Käppeli, J. (1908). Landw. Jb. Schweiz. 22, 53.Google Scholar
Kardymovič, M., Marsakova, A. & Pavljucuk, V. (1934). Probl. Zivotn, no. 5, p. 110.Google Scholar
Kelley, R. B. (1937). Bull. Coun. Sci. Industr. Res. Atist. no. 112.Google Scholar
Kelley, R. B. (1943). Pamphl. Aust. Wool Bd., no. 2, p. 23.Google Scholar
Kelley, R. B. (1946). Bull. Coun. Sci. Industr. Res. Aust. no. 205.Google Scholar
Kelley, R. B. & Shaw, H. E. B. (1939). J. Coun. Sci. Industr. Res. Aust. 12, 18.Google Scholar
Kelley, R. B. & Shaw, H. E. B. (1943). Bull. Coun. Sci. Industr. Res. Aust. no. 166.Google Scholar
Kennedy, J. F. & Bettenay, R. A. (1950). Aust. J. Agric. Sci. 1, 76.CrossRefGoogle Scholar
Khot, S. S. & Ramchandran, K. N. (1948). Indian Fmg. 9, 63.Google Scholar
Kirillov, V. (1944). Sovhoz. Proizvod. no. 12, p. 34. (A.B.A. 13, 148.)Google Scholar
Koch, W. (1944). Z. Tierz. Zücht. Biol. 57, 147.Google Scholar
Kopeikin, V. G. & Tulupova, N. A. (1940). Trud. vorosilovsk zootch-vet. Inst. no. 1, p. 67. (A.B.A. 14, 236.)Google Scholar
Krizenecky, J. (1949). Personal communication.Google Scholar
Kupfer, M. (1928). 13th and 14th Rep. Div. Vet. Ed. and Res. Union of S. Africa.Google Scholar
Labuscagne, F. J. (1948). Fmg. S. Afr. 23, 77.Google Scholar
Larrea, J. A. (1944). Rev. As. Ing. agrón. (Montevideo), 16 (4), 6. (A.B.A. 13, 93.)Google Scholar
Leroy, A. (1949). Personal communication.Google Scholar
Lesbouyries, G. (1949). Reproduction des Mammifères Domestiques, p. 369. Paris: Vigot Freres.Google Scholar
Lin, K., Tsai, C. & Wan, Y. S. (1932). Chin. J. Physiol. 6, 23.Google Scholar
Liversage, V. (1937). E. Afr. Agric. J. 2, 270.Google Scholar
Loginova, N. V. (1939). Trud. Inst. Ovcevod. Kozovod. no. 10, p. 91. (A.B.A. 9, 325.)Google Scholar
Low, D. (1842). The Breeds of the Domestic Animals of the British Island, vol. II, p. 35. London.Google Scholar
Lydekker, R. (1912). The Sheep and its Cousins, p. 46. London.CrossRefGoogle Scholar
Macomber, D. (1933). New Engl. J. Med. 209, 1160.CrossRefGoogle Scholar
McKenzie, F. F. (1928). Res Bull. Mo. Agric. Exp. Sta. no. 118.Google Scholar
McKenzie, F. F., Allen, E., Gurtherie, M. J., Warbritton, V., Terrill, C. E., Casida, L. E., Nahm, L. J. & Kennedy, J. W. (1933). Proc. Amer. Soc. Anim. Prod. p. 278.Google Scholar
McKenzie, F. F. & Phillips, R. W. (1930). Proc. Amer. Soc. Anim. Prod. p. 138.Google Scholar
McKenzie, F. F. & Phillips, R. W. (1932). Univ. Mo. Rep. (06 1932).Google Scholar
McKenzie, F. F. & Phillips, R. W. (1933). Bull. Mo. Agric. Exp. Sta. no. 328.Google Scholar
McKenzie, F. F. & Terrill, C. E. (1937). Res. Bull. Mo. Agric. Exp. Sta. no. 264.Google Scholar
Marais, I. P. (1936). Untersuehungen ü. d. Sexualzyklus bei Merinoschafen. Diss. Leipzig.Google Scholar
Marrian, G. F. & Parkes, A. S. (1929). Proc.Roy. Soc. B, 105, 248.Google Scholar
Marshall, F. H. A. (1903). Trans. Boy. Soc. B, 196, 47.Google Scholar
Marshall, F. H. A. (1908 a). Sci. Progr. 7, 1.Google Scholar
Marshall, F. H. A. (1908 b). Trans. Highl. Agric. Soc. Scot. 20, 5th series, p. 139.Google Scholar
Marshall, F. H. A. (1922). The Physiology of Reproduction, 2nd ed.London: Longmans.Google Scholar
Marshall, F. H. A. (1937). Proc. Roy. Soc. B, 122, 413.Google Scholar
Marshall, F. H. A. (1942). Biol. Rev. 17, 68.CrossRefGoogle Scholar
Marshall, F. H. A. & Potts, G. G. (1924). Bull. U.S. Dep. Agric. no. 996.Google Scholar
Mason, K. E. & Wolfe, J. M. (1930). Anat. Rec. 45, 232.Google Scholar
Mata, E. G. & Cano, A. E. (1941). Gaceta Vet. 3, 67. (Biol. Abstr. 16, 13, 105.)Google Scholar
Maymone, B. (1949). Personal communication.Google Scholar
Mercier, E. & Salisbury, G. W. (1947 a). J. Dairy Sci. 30, 747.CrossRefGoogle Scholar
Mercier, E. & Salisbury, G. W. (1947 b). J. Dairy Sci. 30, 817.CrossRefGoogle Scholar
Meturer, D. (1950). Personal communication.Google Scholar
Mihiala, S. (1936). Ann. Inst. nat. Zootech. Rouman. 5, 190. (A.B.A. 6, 23.)Google Scholar
Miller, I. S. (1949). N.Z. J. Agric. 79, 227.Google Scholar
Miller, R. F., Hart, G. H. & Cole, H. H. (1942). Bull. Calif. Agric. Exp. Sta. no. 672.Google Scholar
Miller, W. C. & Day, F. T. (1939). J. R. Army Med. Cps, 10, 95.Google Scholar
Monge, C. (1943). Physiol. Rev. 23, 166.CrossRefGoogle Scholar
Moore, C. & Price, D. (1948). J. Exp. Zool. 108, 171.CrossRefGoogle Scholar
Morley, F. H. W. (1948). Aust. Vet. J. 24, 106.CrossRefGoogle Scholar
Mornet, F. H. W. (1939). Bull. Sero. Zootech. Epizool. Afr. occid. franç. 2, 1. (A.B.A. 7, 124.)Google Scholar
Moule, G. R. (1950). Aust. Vet. J. 26, 29.CrossRefGoogle Scholar
Nautical Almanac (1949). P. 464. London: H.M. Stationery Office.Google Scholar
Nelson, D. & Burrill, M. W. (1944). Fed. Amer. Soc. Exp. Biol. 3, 34.Google Scholar
Nichols, J. E. (1924). J. Minist. Agric. 31, 835.Google Scholar
Nichols, J. E. (1926). J. Minist. Agric. 33, 218.Google Scholar
Nichols, J. E. (1927). Z. indukt. Abstamm.- u. Vererb-Lehre, 34, 313.Google Scholar
Nichols, J. E. (1946). Rep. Proc. Brit. Soc. Anim. Prod., 5th open meeting, p. 26.Google Scholar
Opperman, J. G. S. (1949). Die Geslagsaktiwiteit Van Die Ooi. University of Pretoria B.Sc. thesis.Google Scholar
Oxford Advanced Atlas (1936). P. 1. Oxford: Bartholomew.Google Scholar
Palsson, H. (1950). Personal communication.Google Scholar
Papanicolaou, G. N.(1925). Proc. Soc. Exp. Biol., N.Y., 22, 436.CrossRefGoogle Scholar
Papanicolaou, G. N. (1933). Amer. J. Anat. 52, 519.CrossRefGoogle Scholar
Papanicolaou, G. N. & Stockard, G. R. (1920). Proc. Soc. Exp. Biol., N.Y., 17, 143.CrossRefGoogle Scholar
Parkes, A. S. (1929). Internal Secretions of the Ovary. London: Longmans, Green and Co.CrossRefGoogle Scholar
Parkes, A. S. & Hammond, J. (1940). Proc. Roy. Soc. Med. 33, 483.CrossRefGoogle Scholar
Pavsic, M. (1949). Personal communication.Google Scholar
Pearse, A. G. E. (1951). Personal communication.Google Scholar
Petrov, V. A. (1935). Probl. Zivotn. no. 2, p. 77. (A.B.A. 3, 389.)Google Scholar
Phillips, P. H., Lamb, A. R., Hart, E. B. & Bohstedt, G. (1933). Amer. J. Physiol. 106, 356.CrossRefGoogle Scholar
Phillips, R. W., Fraps, R. M. & Frank, A. H. (1945). Amer. J. Vet. Res. 6, 165.Google Scholar
Phillips, R. W., Schott, R. G. & Simmons, V. L. (1947). J. Anim. Sci. 6, 123.CrossRefGoogle Scholar
Polovceva, V. V. & Judović, S. S. (1939). Trud. Inst. Ovcevod. Kozovod. no. 10, p. 125. (A.B.A. 9, 326.)Google Scholar
Pomanski, E. A. & Stojanovskaja, V. I. (1936). Probl. Zivotn. no. 3, p. 77. (A.B.A. 4, 435.)Google Scholar
Puteani, E. V. (1940). Z. Schafz. 9, 89. (A.B.A. 9, 116.)Google Scholar
Quinlan, J. & Maré, G. (1931). 17th Rep. Dir. Vet. Ser. Anim. Ind. S. Afr. p. 663.Google Scholar
Quinlan, J., Roux, L. L. & Van Aswegen, W. G. (1939). Onderstepoort J. Vet. Sci. 12, 233.Google Scholar
Quinlan, J., Steyn, H. P. & De Vos, D. (1941). Onderstepoort J. Vet. Sci. 16, 243.Google Scholar
Rao, M. V. K. (1945). Indian Vet. J. 21, 414. (A.B.A. 14, 89.)Google Scholar
Ravenscrift, C. S. I. (1941). Univ. Pretoria B.Sc. thesis. (Quoted Opperman, 1949.)Google Scholar
Ravenscrift, C. S. I. (1945). Univ. Pretoria M.Sc. thesis. (Quoted Opperman, 1949.)Google Scholar
Richter, J. (1939). Hdb. Schafœuchf 1, 2. Aufl. (Quoted Voss, 1950.)Google Scholar
Richter, F. & Rittau, M. (1933). Arch. Tierernähr. Tierz. 9, 232.Google Scholar
Ring, J. R. (1945). Endocrinology, 37, 237.CrossRefGoogle Scholar
Roberts, E. (1921). J. Agric. Res. 22, 231.Google Scholar
Robinson, T. J. (1950 a). Personal communication.Google Scholar
Robinson, T. J. (1950 b). J. Agric. Sci. 40, 275.CrossRefGoogle Scholar
Roux, L. L. (1936). Onderstepoort J. Vet. Sci. 6, 465.Google Scholar
Rowlands, I. W. (1948). Vet. Rec. 60, 181.Google Scholar
Rumjancev, B. F., Butarin, N. S. & Denisov, V. F. (1933–1934). Trud. Kirgiz. Kompl. Exsp. 4, 15. (Quoted Asdell, 1946, p. 377.)Google Scholar
Russel, S. F. (1919). Bull. Okla. Agric. Exp. Stat. no. 126.Google Scholar
Schinckel, P. G. (1951). Personal communication.Google Scholar
Schott, R. G., Phillips, R. W. & Spencer, D. A. (1939). Proc. Amer. Soc. Anim. Prod. p. 347.Google Scholar
Scott, J. P. (1945). Comp. Psychol. Monogr. 18, 1. (Biol. Abstr. 19, no. 12214.)Google Scholar
Smirnov, L. (1935). Probl. Zivotn. no. 8, p. 7. (A.B.A. 4, 195.)Google Scholar
Smith, L. W. & Hussien, M. (1935). Agric. Live-Stk. India, 8, 126.Google Scholar
Spencer, C. E. (1943). J. Mammal. 24, 1.CrossRefGoogle Scholar
Stanica, P. (1939). Ann. Ist. nat. zootech. Rouman. 7, 90. (A.B.A. 8, 53.)Google Scholar
Stieve, H. (1934). Z. mikr.-anat. Forsch. (Abt. 11), 36, 481.Google Scholar
Sykes, J. F. & Cole, C. L. (1944). Quart. Bull. Mich. Agric. Exp. Sta. 26, 250.Google Scholar
Terrill, C. E. (1935). Proc. Amer. Soc. Anim. Prod. p. 153.Google Scholar
Terrill, C. E. & Stoehr, J. A. (1939). Proc. Amer. Soc. Anim. Prod. p. 369.Google Scholar
Thompson, D. S. (1942). J. Dep. Agric. S. Aust. 45, 478.Google Scholar
Truscott, B. L. (1944). J. Comp. Neurol. 80, 235.CrossRefGoogle Scholar
Udoljskii, D. M., Gladkov, P. F., Čumin, N. P., Barljaeva, E. V. & Demidenko, E. A. (1940). Inst. Životn. Kratk. otč vypol temal plana, p. 89. (A.B.A. 12, 28.)Google Scholar
Underwood, E. J. & Shier, F. L. (1941). J. Dep. Agric. W. Aust. 18, 13.Google Scholar
Underwood, E. J. & Shier, F. L. (1942). J. Dep. Agric. W. Aust. 19, 176.Google Scholar
Underwood, E. J., Shier, F. L. & Davenport, N. (1944). J. Dep. Agric. W. Aust. 21, 1.Google Scholar
Usakova, S. A. & Fudelj, T. N. (1941). Trud. Jaroslavsk oblast. opyt. Stanc Zivotn. p. 93. (A.B.A. 14, 236.)Google Scholar
U.S.D.A. (1948). Rep. Bur. Anim. Industr., U.S. Dep. Agric. p. 23.Google Scholar
U.S.D.A. (1949). Rep. Bur. Anim. Industr., U.S. Dep. Agric. p. 22.Google Scholar
Vasques-Lobez, E. (1949). J. Endocrinol. 6, 158.Google Scholar
Villegas, V. (1928). Philipp. Agric. 17, 477.Google Scholar
Vorster, T. H. (1950). Personal communication.Google Scholar
Voss, G. (1950). Noue Ergebnisse und Probleme der Zoologie, p. 1028. Leipzig.Google Scholar
De Vuyst, A. (1949). Personal communication.Google Scholar
Walker, D. E. (1943). The breeding season, oestrus, and the oestrous cycle in New Zealand ewes. Univ. N. Zealand M.Sc. thesis.Google Scholar
Wallace, R. (1923). Farm Live Stock of Great Britain, 5th ed., p. 664. Edinburgh: Oliver and Boyd.Google Scholar
Walton, A. (1950). Proc. Soc. Study Fertility, no. 1, p. 40.Google Scholar
Warbritton, V. & McKenzie, F. F. (1937). Res. Bull. Mo. Agric. Exp. Sta. no. 257.Google Scholar
Warnick, A. C., Wiggins, E. L., Casida, L. E., Grummer, R. H. & Chapman, A. B. (1949). J. Anim. Sci. 8, 646.CrossRefGoogle Scholar
Watson, R. H. (1950). Personal communication.Google Scholar
Whetham, E. O. (1933). J. Agric. Sci. 23, 383.CrossRefGoogle Scholar
Whitaker, W. L. (1940). J. Exp. Zool. 83, 33.CrossRefGoogle Scholar
Whitehurst, V. E., Groun, R. M., Phillips, R. W. & Spencer, D. A. (1947). Fla. Agric. Exp. Sta. Bull. 429, 34.Google Scholar
Wilcke, H. L. (1939). Poult. Sci. 18, 236.CrossRefGoogle Scholar
Wood, R. O. (1937). A Survey of Sheep Management in Great Britain. London.Google Scholar
Wrightson, J. (1908). Sheep, Breeds and Management. London: Vinton and Co.CrossRefGoogle Scholar
Yeates, N. T. M. (1949). J. Agric. Sci. 39, 1.CrossRefGoogle Scholar
Young, W. C. (1941). Quart. Rev. Biol. 16, 135.CrossRefGoogle Scholar
Zarkzewsky, S. (1949). Report from Institute of Biology. Santiago. (Personal communication.)Google Scholar
Zuckerman, S. (1948). J. Anat., Lond. (Proc), 83, 63.Google Scholar