The impact of extremes on fetal calf development 

Ever wonder why calves born in the fall sometimes seem smaller and lighter than their spring counterparts? Research indicates heat can be a factor in the fetal development of a calf. Additionally, drought conditions can also impact the growth of a calf in utero, depending on the management practices of the cattle operation.  

Heat Can Impact Development

According to experts, most of the research on the impact of environmental heat on fetal development has been conducted in dairy breeds. 

When the temperature rises, a cow’s body launches a wave of reactions in order to cool down. “Heat exposure shifts blood flow from internal organs to the periphery of the animal to increase heat dissipation,” Craig Payne, DVM, extension veterinarian with the University of Missouri, explained.

 When a cow’s body makes this shift to combat the stress of heat, the blood flow to the cow’s uterus decreases. 

“If that decrease flow persists, placental development is compromised which in turn, restricts the amount of oxygen and nutrients going to the fetus resulting in a reduced growth rate,” Payne said. “Such is the reason why the average birthweight of fall born calves is less than spring born calves.”  

However, some producers may wonder about the impact that heat and drought may have on their cows’ due dates. Payne said he is not aware of any research that demonstrates chronic heat stress leads to premature births.  

Drought Impact on Growth

The impact drought conditions have on the birthweight of calves can be tied to whether cows received proper nutrition during gestation. 

The supplemental feeding practices of the cattle operation during forage scarce conditions play a role in the development of the fetus. 

“In cases where nutrient restriction has occurred, the impact on birthweight depends on a variety of things including severity and length of the restriction, time during gestation in which the restriction occurs and animal maturity,” Payne shared.

Payne emphasizes what producers may want to focus on regarding this topic is to recognize that nutrient restriction during gestation has been demonstrated to have an impact on the lifelong performance of progeny. This is often referred to as fetal programming. The concept of fetal programming centers around research that indicates a cow’s nutrition during gestation has a lasting impact on the health and performance of her calf.       

Impact on Later Gestation Stages

The harsh, dry summer producers just experienced could impact cows in their second and third periods of gestation. Though most of the research in this area has occurred in dairy cattle, the findings are worth noting for beef cattle as well.

Cows heat stressed during late gestation have impaired mammary growth and less milk production in the following lactation. In addition, their immune system function can be compromised. Lastly, if cows fail to receive enough nutrients during the later stages of gestation, they can incur other problems as well. “Regarding nutrient restriction, loss of body condition going into calving season can result in decreased colostrum production, prolonged parturition/increased dystocia and increased postpartum interval,” Payne added. 


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