FERTILIZATION AND DEVELOPMENT OF PIG FOLLICULAR OOCYTES

A. D. LEMAN, P. J. DZIUK
1971 Reproduction  
The capacity of follicular oocytes for normal fertilization has been tested in hamsters (Barros & Austin, 1967) , sheep (Woody, Alliston & Ulberg, 1961) and rabbits (Noyes, 1952; Chang, 1955). Follicular oocytes of rabbits and hamsters were fertilized at a reduced rate but no sheep oocytes developed. Dziuk & Dickmann (1965) have proposed that the block to polyspermy develops concomitantly with oocyte maturation. The following experiments were conducted to test whether pig follicular oocytes
more » ... d be fertilized normally and what proportion would become polyspermic. In Trial I, eight cyclic gilts were injected with 500 i.u. hcg during late prooestrus to induce ovulation. Ovulation was assumed to occur 40 to 42 hr after hcg (Hunter & Polge, 1966; Baker, Dziuk & Norton, 1967) . Each gilt was artificially inseminated about 20 hr after hcg and then, between 24 and 28 hr after hcg, each was subjected to laparotomy and one ovary was removed. From this ovary, oocytes were recovered by puncturing the follicles of 5 to 10 mm in diameter with a 16-gauge needle and flushing them vigorously with sterile tissue-culture medium 199. The recovery of follicular oocytes was scheduled to correspond with the occurrence of the first meiotic metaphase (Hunter & Polge, 1966). These isolated oocytes in the cumulus mass were then transferred into the oviduct with no adjacent ovary. One follicular oocyte from each ovary was retained for microscopic examination to verify the stage of meiotic develop¬ ment. The oocytes from the intact ovary served as controls and ovulation occurred naturally. Between 46 and 52 hr after hcg, gilts were again subjected to laparotomy and the eggs were recovered from each oviduct separately, isolated and examined as fresh and stained whole mounts by phase-contrast microscopy (Baker et al., 1967) . The penetration of one spermatozoon through the zona pellucida, the presence of two pronuclei, or a cleaved egg with two pronuclei were the criteria for classification of eggs as normally fertilized. More than one spermatozoon inside the zona pellucida and more than two pronuclei were criteria for classifi¬ cation as polyspermic (Hancock, 1959). The results of Trial I are given in Table 1 . In five of the eight gilts, one or more of the follicular oocytes were apparently fertilized normally. The mean fertilization rate was 45 % for follicular oocytes and 84 % for naturally ovulated oocytes. Analysis by the paired t test indicated that a significantly (P<0-05) higher proportion of the naturally ovulated oocytes was fertilized. The stage of
doi:10.1530/jrf.0.0260387 pmid:5569655 fatcat:7cdzu7az2fgovgvtqtaflrt64a