Abstract

The objective of this article was to emphasize effects of fetal exposure to hyperthermia and its consequences on future dairy cow performance. Fetal growth especially during late gestation depends on nutrients provided by dam via placenta. Thus, any factor that disrupts this relationship would be reflected in growing fetus biology and may have long-term negative effects on dairy cow performance and longevity. Decreased dry matter intake and milk yield as well as suppressed immunity have been shown in heat-stressed lactating dairy cattle. However, it seems that heat stress impacts on pregnant cow may be more drastic. Under high ambient temperatures, blood flows toward peripheral tissues instead of uterine and placenta to sustain thermoregulatory processes. Altered blood flow would result in decreased nutrient supply to placenta and fetus, thus compromising dam and calf biology. Stillbirth, calf prematurity, and lower birth weight are among the common consequence of hot environmental conditions resulting in lower weaning weight and subsequent poor heifer growth. Dairy heifers should de calved between 22-24 months of age for maximal milk production and minimal heifer rearing costs. Delayed calving can negatively impact herd economics. During fetal programming, nutritional and environmental challenges induce physiological changes in developing fetus which may have undesirable health and production consequences. Higher incidence of diarrhea in hot seasons may be due to higher microbial load in the calf environment and decreased immune function as a result of hyperthermia. The impact of hyperthermia on maternal and fetal immunity is probably associated with decreased postnatal calf ability to absorb colostral immune factors regardless of colostrum quality. Calves exposed to heat stress during late gestation might also produce lower milk than cooled calves. Thus, optimal dry cow management and adopting proper cooling systems in hot seasons can help prevent diseases and improve animal health and farm profitability.

Keywords: Hyperthermia; Fetal development; Animal health; Dry cow management; Farm economics