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| Pregnant sheep |
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| Pregnant cow |
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| Pregnant pig |
Animals grow in stages.
1. PRENATAL GROWTH
Stages of prenatal growth
i. Blastocist stage
During this stage, the dividing zygote will yield millions of cells which are enclosed within the zonapellucidal and this is called blastocist.
Blastocist is a ball of many cells enclosed by a membrane called zonapellucidal. During this stage, the Blastocist feeds from the uterus by means of diffusion.
In the Ewe for instance, one to three or four lambs are normally produced but up to ten eggs maybe fertilized during fertilization or during mating particularly when when females are super ovulated. The Blastocist stage following fertilization will last for about 10days in sheep and pigs and 11days in cattle.
ii. Embryonic stage
This is the second stage in prenatal growth. Cell differentiation into tissues and organs are beginning to show or manifest. These differentiating cells have a very high priority for nutrients. The size of the embryo is not greatly influenced by the nutritional status of the mother, however, very small weight increase occur at this stage. This embryonic stage last from 10-34 days in sheep, 10-36 days in the pig and. 1-45 days in cattle.
iii. Foetal stage
After the Embryonic stage, the plancenta continues to grow and the extent of this growth determines the amount of nutrition which the young animal may receive during this stage. Major growth in weight and composition occur in this phase. At this stage of growth, the nutrition of the foetus is derived by nutrients diffusing from maternal blood through the placenta. The size of the placenta usually varies with the size of the uterus and therefore the size of the mother will influence the size of the foetus at birth. However, the genetics of the sire determines the upper limit of the size at birth in large mothers but the size of the placenta limits the potentials of the foetus in the small mother. At this stage, the individual has taken the shape and form of the animal
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Post Natal growth
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