The impact of stress and selected environmental factors on cows' reproduction

The selection of cattle in terms of the increase in milk yield has been resulted in a negative energy balance of cows. A negative energy balance inhibits the growth of dominant follicles and the secretion of estradiol. This results in a decrease in the activity of ovaries. Furthermore, in high-yielding cows there is often a decrease in fertility. In addition, there are many factors influencing the cows' fertility. Unsuitable nutrition, litter in a barn, as well as the stress experienced by cows can reduce the reproductive rate of cattle. Oxidative stress can cause damage, the genetic material of oocytes, and endometrium damage. Metabolic stress can lead to a longer period of infertility. Furthermore, heat stress impairs the maturation of the dominant follicle and may cause placental retention. Chronic stress, e.g. in lameness or during transport, may cause changes in the secretion of reproductive hormones due to the high concentration of cortisol in the blood. Moreover, mycotoxins can cause miscarriage or inflammation of the uterus. Pesticides cause hormonal dysfunction in the hypothalamic-pituitary-gonadal axis. Dairy cattle should be provided with suitable conditions to obtain satisfactory production and reproductive rate.