It has been an unpredictable year so far, including the weather. Regardless of when the hot weather decides to hit, our best defense is to be prepared. We know that heat stress causes decreases in milk production and alters cow behavioral patterns, but what are some of the less known impacts of heat stress on dairy cattle well-being? Below are some interesting study results you may want to consider when deciding how to manage heat stress on your dairy.
- Immune system cytokines – Cows housed in a heat stress environment (temperature-humidity index > 68) had higher plasma concentrations of some key immune system cytokines. Higher concentrations of these cytokines (IL-1β, IL-6, IFN-ꝩ, and TNF-α) indicate that heat stress causes an inflammatory response in the cow’s body (Chen et al., 2018)
- Mucosal defense system – Housing cows in a heat stress environment also causes a stress-induced activation of the mucosal defense system in lactating cows (Koch et al., 2019). Of course, the more energy the cow’s system uses to cope with heat stress, the less energy that is available for milk production.
- In utero heat stress and calf immunity – Calves exposed to in utero heat stress have lower rates of peripheral blood mononuclear cell (PBMC) proliferation than calves not exposed to in utero heat stress (Tao et al., 2012). This effect can persist until the calves reach 56 days of age. PBMCs are the cells that make up the immune system, in which a low proliferation rate puts the calf at a health risk.
- In utero heat stress and calf health – Cows that were cooled during the dry period had heavier calves that also had lower body temperatures at calving than calves from cows housed under heat stress conditions during the dry period. Cooled cows also had calves that were more efficient at absorbing IgG from colostrum and gained 0.44 lb/day more than calves from heat-stressed cows (Laporta et al., 2017).
- In utero heat stress and calf IgG absorption – Calves born to cows exposed to heat stress during the dry period have lower serum IgG concentrations and higher serum cortisol concentrations than calves born to cows housed in a thermoneutral environment during the dry period (Almoosavi et al., 2020). Remember, cortisol is often referred to as the “stress hormone”
- In utero heat stress affects calf future performance – Heifers born to heat-stressed cows produce 16% less milk for the first 35 weeks of their first lactation than heifers born to cooled cows (Monteiro et al., 2016). Almost 20% more heifers from cooled cows reached their first lactation than heifers from heat-stressed cows.
- Feed supplements and cow performance – Supplements may help cows cope with heat stress. One supplement fed to heat-stressed cows resulted in lower cow rectal temperatures (Fabris et al., 2017). The same supplement fed to cooled cows resulted in 13% higher milk production than heat-stressed cows that were not fed the supplement.
10. Feed supplements and calf health – Feeding the supplement mentioned in #9 to cows during the dry period impacted calf health, depending on whether cooling was provided to the cows (Skibiel et al., 2017). Calf serum amyloid A (protein associated with inflammation) was higher in calves born to heat-stressed cows than cooled cows. Furthermore, neutrophil (a type of immune cell) function at 10 days of age was higher in calves born to cooled cows that received the supplement than cooled cows that did not receive the supplement.