THE OVUM OR THE EGG
Ovulated eggs are larger than sperm in all species, despite the fact that they differ in size and appearance among many species. The existence of a substance in the yolk called duetoplasm accounts for the ovum’s large size.
In goat and rabbit eggs, the amount of yolk material in the cytoplasm is greater, but in mare eggs, it is less. Cows have the smallest eggs among domestic animals, while rabbits have the largest. The layers of cells known as the cumulus oophorus and corona radiata envelop freshly ovulated eggs. These cells have cytoplasmic extensions that interdigitate with the microvilli on the egg’s vitelline surface. The purpose of these extensions is to carry nutrients into the egg. However, the connections are broken and the cells are separated from the egg after ovulation as a result of ciliary movement and fibrinolytic enzymes found in the oviduct. Sperm enzymes may also cause these cells to be removed during fertilization. The vitelline membrane and the zona pellucida are the two membrane structures found in the ovum. The ovum contains the nucleus (in the metaphase II stage), the endoplasmic reticulum, multivesicular bodies, and all other common organelles. Furthermore, cortical granules are located directly below the vitelline membrane. The eggs of various domestic animals exhibit a number of anomalies, such as giant, small, oval, or flat eggs, ruptured zona pellucida, and absence of cortical granules.21.8
Source:
Rana Tanmoy (ed.). Principles of Veterinary Animal Physiology. CRC Press,2026. — 290 p.. 2026
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