Gestation

Gestation is termed as the period of intrauterine embryonic and fetal development. The duration of gestation is calculated as the interval from fertile service to parturition and is genetically determined among the mammalian species. The gestation length varies from species to species. For example, the gestation period is approximately 270-290 days in cattle, 145-155 days in goats and sheep, and 305-320 days in buffalo. Moreover, gestation length has a positive correlation with the size of the animals. Small-sized animals usually have shorter gestation periods than larger ones, with some exceptions. However, various factors might influence gestation length in mammals, such as the age of the dam, fetal sex coupled with other environmental factors like season, feed, etc. In general, older cows carry calves longer than their younger counterparts. The gestation length for male calves is usually 2-4 days longer than for females. Based on the characteristic features of embryonic and fetal development, gestation length can be categorized into three trimesters: the first, second and third, each approximately three months long in cattle. The first trimester spans from 1st to 12th week, where zygote cleavage, pre-implantation embryonic development, implantation, and fetal development occur. At this stage, fetal length increases more rapidly than its weight. The second phase spans until the 26th week of pregnancy when the slow growth of the fetus is noticed. The third trimester starts from the 27th week until the end of the cow’s pregnancy. The rapid growth of the fetus is characterized at this stage, and about 70% of the calf’s development takes place during this period. [Mohammad Shamsul Alam Bhuiyan]