And in this area of research, the term “life span” has a far reach. Laporta, a University of Wisconsin associate professor of lactation physiology, and other researchers have winnowed out data showing that during late gestation, the dam and in utero calf are not the only ones affected by heat stress: the resulting heifer calf’s oocytes will carry epigenetic damage into the third generation.
Long-standing research shows that heat abatement during pregnancy can be beneficial, as the cow herself is going through mammary development during this time. Exposure to extreme heat can hinder secretory capacity and reduce production. Laporta cited more than a dozen studies which support the use of heat abatement in various stages of gestation. And it stands to reason that the in utero calf would also benefit from cooling methods — research bears that out, especially during the last trimester when key cellular events, most of the fetal weight gain, and metabolic and endocrine programming can be negatively impacted by environmental stressors, including heat.
These cellular processes are all heat sensitive, Laporta said, and exposure in utero can lead to shortfalls across several metrics, especially across the lifetime of the daughter. It starts with reduced gestation length and hampered IgG absorption, and even after the first 12 months, heifers are shorter and smaller than those not exposed to heat stress during fetal development.
They also fall short of production expectations, Laporta noted. Still more research has recently confirmed a growing suspicion: the heat-stressed calves in utero, in addition to their lower yields, can also pass on negative traits to their female offspring — now two generations away from the original heat stress event. The indirect exposure of this third generation can result in smaller mammary duct structure, fat pads, and parenchyma.
With a potential three generations at risk — the herd, the replacement herd, and the replacements of the replacements — Laporta offered up several studies around heat mitigation methods for different stages: dry periods, growing and pregnant heifers, and calves. All showed improvement in short-term thermoregulation using respiration rates and skin or rectal temperature as metrics, whether the cooling methods were fans; fans and misters; or positive pressure, continuous airflow systems custom-designed for the study.
Laporta emphasized that although cooling measures have positive and quantifiable benefits at all the life stages studied, the dry period should be a priority, as the cow, her daughter fetus, and the oocytes which will eventually become her granddaughters are all susceptible to suboptimal outcomes due to heat stress. She pointed out that the likelihood of temperatures reaching the danger zone is rising in regions where heat historically has not been an issue, so more awareness and attention to cooling infrastructure is key in getting ahead of the thermometer, and protecting the next generations of the herd.
