Fertilization in the Pig

Abstract

Observations were made on ova recovered from mated, from inseminated and from unmated sows killed at varying intervals up to 144 hr after the onset of heat. The morphological findings on pene¬ trated, pronucleate and cleaved ova are described.The timing of the events that precede and follow fertilization is examined. The cumulus cell mass (egg-plug) was found around ova only from sows killed less than 8 hr after mating. Spermatozoa were not found in the cumulus until 5| hr after mating. Penetration and pronucleus formation occurred not earlier than 6 hr after mating. The first cleavage in normal mated pigs occurred 21 hr after mating. Some cleaved ova were recovered earlier than this from sows after 'delayed' mating. The distribution of ova at different stages of cleavage is recorded for sows killed at varying intervals after mating or insemination.Three of a total of 1677 ova resembled primarily oocytes; all other detectable abnormalities could have arisen in originally normal ova.The number of spermatozoa on the zona pellucida tended to increase with advancing stages of development, but counts of spermatozoa on ova at the same stage of cleavage recovered at different intervals after mating furnished no evidence that cleavage rate is increased by increas¬ ing sperm numbers.In unfixed ova from unmated sows, spontaneous fragmentation was observed with increasing frequency after 72 hr from the onset of heat ; degenerative changes were identified in fixed and stained ova 48 hr after the onset of heat. Cleaved (fragmented) ova from unmated pigs never showed a normal nuclear pattern.The findings are discussed.

Sperm: Egg ratios and putative molecular signals to modulate gamete interactions in polytocous mammals

“…However, an incisive quantitative regulation of sperm progression from the isthmus reservoir becomes less important once the egg's defense mechanism against polyspermy has been established. As noted elsewhere (Hancock, 1961;Hunter and Leglise, 1971), the stability of the block to polyspermy in, for example, pig eggs is such that 200-400 sperm heads may penetrate into the outer portion of the zona without compromising the ploidy of the zygote.…”

Egg Transfer in the Sow

“…The biggest previous litter is one of four pigs born as a result of the tubai transfer of nine eggs to one sow (Kvasnickii, 1951). The two pigs born as a result of egg transfer reported by Pomeroy ( 1960) (Pomeroy, 1955) when they are still at the four-cell stage (Hancock, 1961) (Averill & Rowson, 1958 (Hancock, 1961 …”

Sperm transport and reservoirs in the pig oviduct in relation to the time of ovulation

“…A single primary oocyte with a conspicuous germinal vesicle was also recovered (see Hancock, 1961); this presumably atretic egg contained 25-30 spermatozoa in the cortex of the vitellus. The flagellum still seemed to be attached to each sperm head, even though the dimensions of the sperm heads were approximately 50% larger than those of spermatozoa still outside this egg (see Polge & Dziuk, 1965).…”