Perinatal pathology in fetuses and newborn cattle of meat and dairy breeds is registered in 20,7–70,0% of cases, among beef breeds it is 7,0–48,9% and on the average it is 36.0%. Antenatal hypotrophy occurs in 9–21% of calves. The effect of Holstein-Friesian pregnant cows’ diet on the growth and development of fetus has been studied. Hypotrophy is differentiated according to the severity of metabolic changes (light and heavy), but according to the dischronation of skeletal and muscular systems (asymmetric and symmetric).

The cows involved in the experiment were under constant clinical observation. Upon reaching the pregnancy period of 2, 3, 4, 5, 6, 7, 8 and 9 months in 6 heads of cattle from each group the blood samples were collected, and then the cows were slaughtered to estimate the fetal development. Cows’ blood samples were collected before slaughter. During analyzing the fetuses their weight and sizes were determined. Cows’ blood analysis was designed to evaluate the metabolic and functional state of the liver. These blood tests showed that cows from the control group throughout the experiment remained clinically healthy, and metabolic profile was consistent with a particular gestational age. After 1 month after the change of diet, liver functions were disturbed in the cows of the experimental groups, the signs of parenchymatous hepatitis with severe fatty (adipose) degeneration, cytolysis and hepatodepression syndromes appeared. It is shown that in healthy cows fetal development is characterized not by the steady change of its length and weight. The most active fetus’s body weight increase is observed during 4^th, 7^th and 8^th months and its length increase is observed during 3^rd, 4^th, 6^th and 7^th months. The size of a body weight increase compared to mass of a body occurs more actively and terminates its active phase within the 7^th month. The body weight gain was completed within the 8^th month of development. The third month of development is characterized by asymmetry of the body, which is kept up to 180 days, thus, disproportional development of head, body and limbs occur during this period.

Using the feeding simulation method, the pregnant cows’ diet quality role in the development of the fetus is shown. The growth of fetuses from cows that were given toxic feed (before fertilization, gestational age 2, 5 and 7 months) was analyzed. Changing the diet for 30 days before insemination had no significant effect on the development of the fetus during the first three months of the development. The constitution of fetal body and limbs visually were not significantly different from the control, but had a smaller size. Besides, the growth of hair around the eyes, mouth and horns was ascertained after 4^th, 5^th and 6^th months, respectively. Changing the diet of cows on the 2^nd month of pregnancy led to the developmental disorders in 4-month-old fetuses as a decrease in the length of its body. Inspection of the fetuses showed that the constitution of body and limbs were not significantly different from the control, but had a smaller size. Hair growth in the area of the eyes and the mouth appeared on the 4^th month, in the area of the horns on 5^th and 7^th months of development. Changing the diet of cows on the 7^th month of pregnancy did not affect the length of the body of the fetus, but its body weight was significantly reduced. The constitution of the body and limbs of fetuses from cows that have changed the diet on 5^th and 7^th months of pregnancy visually were not significantly different from the control. However, the former from the 7^th month, the latter from the 8^th month of development appeared to have disproportion between the development of the axial skeleton and muscles with the tendency to decrease muscle mass. The critical periods of the development of fetuses with increased sensitivity to feeding disturbances of pregnant cows were highlighted. The most relevant is the critical period during which there is a significant inhibition of increase in the size and weight of the fetal (the 5^th month of pregnancy). In addition, in respect of the body weight the 6^th and 8^th months of prenatal development are critical. The analysis of hypotrophy manifestation peculiarities showed that feeding disturbances in non-pregnant cows and their presence during the whole pregnancy led to "symmetric hypotrophy". The presence of a negative food factor in the second half of pregnancy is the cause of asymmetric hypotrophy.

Key words: cattle, fetus, intrauterine growth, feeding.