Akademik Veri Yönetim Sistemi
15.Ulusal Zootekni Öğrenci Kongresi , Adana, Türkiye, 9 - 11 Mayıs 2022, cilt.1, ss.96-97
Heat stress (HS) is a condition characterized by high ambient temperature and humidity. Twothirds of the calves' development takes place in the last two months of pregnancy; during this
rapid growth period of fetus, the stress of the mothers negatively affects the offspring. Feed
consumption, milk production, reproduction, udder development, morbidity and mortality rate
and immunity are adversely affected in dairy cows exposed to heat stress and economic loses.
Low birth weight (about 9%) in calves and low milk yield in the next lactations are obtained
in dairy cows exposed to stress in the last period of pregnancy. In heat stress condition, the
blood flow to the placenta and nutrients transfers to embryo decrease, also, placental
hormones circulation decrease in the mothers exposed to heat stress in the late period of
pregnancy, and the cause give birth earlier. Calves with low birth weight can only compensate
for the weight loss in a long period of one year. Reduced birth weight of calves due to in utero
stress can be attributed fetal hyperthermia and impaired placental function and so, a shorter
gestation period. In-utero heat stressed calves have lower plasma concentrations of insulin,
insulinlike growth factor-I, prolactin and but no difference in glucose, or β-hydroxybutyrate
(BHBA) and non-esterified fatty acid (NEFA) plasma concentrations.. Normally, postpartum
calves are not exposed to metabolic stress due to the lack of production, and therefore they are
less affected by environmental heat stress than adult animals. However, studies have shown
that calves exposed to postnatal heat stress also have a decline in growth, an increase in
morbidity and death rates in calves. For a successful calf production, in the prenatal and
postnatal periods calves must be protected from heat stress.