Abstract
ON March 10, 1958, 111 Romney ewe lambs (group A) which had grazed continuously since weaning (December 12, 1957) on pastures dominant in red clover were joined with an additional 92 Romney ewe lambs (group B) for studies of their breeding season. This latter group had grazed, since weaning (December 11, 1957), on perennial rye-grass–white clover pastures. Vasectomized, ochred rams were run with these lambs from March 17, 1958, all being grazed together on perennial rye-grass–white clover pastures. All lambs were weighed on March 19, group A and group B having the same average live weight (71 lb.). On the same day, that is, within two days of joining with teasers, 29 lambs from group A but none from group B were found to have been marked. This sudden onset of œtrus from one group of lambs was unexpected in view of the previous results1 on the breeding season of Romney ewe lambs. Owing to the relatively early age at first œstrus shown by these lambs, laparotomy was performed within five days of observed œstrus to determine whether ovulation had occurred. Both the left and right ovaries of eight lambs were examined without finding any evidence of the existence of corpora lutea. Graafian follicles of varying sizes, however, were seen on most ovaries.
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CH'ANG, T. Reproductive Disturbances of Romney Ewe Lambs grazed on Red Clover (Trifolium pratense) Pastures. Nature 182, 1175 (1958). https://doi.org/10.1038/1821175a0
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DOI: https://doi.org/10.1038/1821175a0
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