Heat stress in gestating dairy cows impairs performance of future generations

Heat stress in gestating dairy cows impairs performance of future generations
Number of dairy cows (dry and milking) per state (USDA-ERS, 2019) and number of heat stress days per state (NOAA, 2019). Taller bars represent more cows within each cow number range. A heat stress was declared when average daily temperature-humidity index was equal to or greater than 68. The number of heat stress days per state in each year from 2007 to 2013 was calculated and averaged across the years. Credit: Journal of Dairy Science

It is estimated that in the United States, environmental heat stress in cows costs the dairy industry more than $1.5 billion annually due to decreased milk production, impaired reproductive performance, increased rates of illness, and shortened lifespans. But what effects do heat stress in pregnant cows have on the productivity and health of their female offspring in the future, and how much might this affect dairy producers' costs? In a recent article appearing in the Journal of Dairy Science, scientists from the University of Florida and the University of California, Davis investigated the performance and profitability of two future generations of cows born to mothers exposed to heat stress during pregnancy.

According to senior author Jimena Laporta, Ph.D., of the Department of Animal Sciences at the University of Florida, Gainesville, FL, USA, previous research has found that heifers born to cows that are heat-stressed during late gestation grow to be smaller and produce on average five kilograms per day less milk in their first lactation, compared with heifers born to dams that were cooled during the hottest days of the year.

"This suggests a permanent effect of fetal environment on genetic expression in adulthood," said Laporta. "We hypothesized that exposure of pregnant cows to during late gestation will impair daughters' and granddaughters' lifetime performances."

The authors' first objective was to measure the carryover effects of maternal exposure to heat stress during late gestation on milk yield, , and survival rates of daughters and granddaughters. Their second was to estimate the related to those outcomes across the United States. Laporta and colleagues pooled and analyzed data collected over a 10-year period on performance of Holstein cows in Florida, the state with the greatest number of heat stress days per year. This gave them information on the lifespans, productivity, and reproductive performance of two successive generations of cows born to dams exposed to heat stress during pregnancy and those born to dams that were provided active cooling during heat stress periods.

The authors found that, as expected, daughters and granddaughters of heat-stressed cows showed negative effects in rates of survival from birth to first calving, length of productive lifespan, and milk performance, including milk yields and nutrient contents through the first three lactations. The team calculated that these impairments translate to considerable annual costs to dairy producers in the United States, with nationwide losses, based on the US average milk price from 2010 to 2015, of up to $595 million annually.

Laporta notes that lactating cows tend to be the focus of heat reduction strategies, possibly because the effects of overheating are more immediately evident among them than among nonlactating pregnant cows, for which the damage may become apparent only later, when they resume milking. But considering the hidden costs that carry over to future generations of cows and the likelihood of increased stress due to , Laporta and colleagues consider cooling techniques for dry cows—such as the use of fans and sprinkler systems—crucial to the continued success of the US .

More information: J. Laporta et al, Late-gestation heat stress impairs daughter and granddaughter lifetime performance, Journal of Dairy Science (2020). DOI: 10.3168/jds.2020-18154

Journal information: Journal of Dairy Science

Provided by Elsevier

Citation: Heat stress in gestating dairy cows impairs performance of future generations (2020, July 16) retrieved 15 June 2024 from https://phys.org/news/2020-07-stress-gestating-dairy-cows-impairs.html
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