Current Progressive Dairy digital edition

Environmental impacts on calf growth and feed efficiency

Mike Van Amburgh and Kaitlin Andrews Published on 22 May 2015

calves and hutches

As preparations are made for warmer weather, heat stress is often thought of as a problem that should be avoided in lactating cows due to lost performance and possibly lost cows.



However, the effects of heat stress on replacement animals tends to be overlooked. Should heat stress be considered as a problem in calves? If so, how much does it affect growth rates and heifer-raising costs in the summer?

Last summer, as a joint project between Cornell University’s PRO-Dairy program and the department of animal science, we looked at environmental impact on calf growth from an economic standpoint across multiple herds in New York state.

By the end of the project, we found that even when heat stress wasn’t expected to be an issue, growth rates were being affected, and the cost per pound of gain was rising with summer temperatures. Since summer is typically thought of as being a less expensive time to raise calves, we began investigating where this increased cost was coming from.

Be mindful of temperature,but don’t ignore humidity

During the months of June and July, temperature and relative humidity were recorded within multiple calf facilities using data loggers and interpreted using the temperature-humidity index (THI, index values that combine temperature with relative humidity for an index value representative of the level of heat stress).

Throughout the summer, accuracy of the data loggers was monitored by comparing the logger inside the facility to one outside the facility, along with external validation against nearby certified weather stations.


The statistics to sum up this region of upstate New York for June and July are in Table 1.


Even in a summer that seemed fairly mild, the effect of humidity influencing heat stress in these calves could be observed. Calves can be fairly resilient in the heat when the barn cools off at night to temperatures at which they are comfortable (THI less than 70).

However, during the days the barn does not effectively cool, nor has heat abated, ADG begins to decline due to heat stress. This stress was best demonstrated in two neighboring farms less than 10 miles from one another, shown in Table 2as Farms A and B. Farm C was a farm from the group that had similar environmental conditions but was greater than 10 miles away.

calf farms

Lower average daily gains ledto increased heifer-raising costs

Lactating cows’ economic productivity is typically measured as income over feed cost (IOFC). We applied this same concept to calves to understand what the true efficiency of calf-rearing programs were and what the difference in cost was among different observed environmental conditions.


In Table 3, neighboring farms had similar environmental conditions as based on the THI; however, Farm B spent a higher number of days outside of the thermoneutral zone (TNZ). This table accounts for the number of days where the farm spent more than 18 hours outside the TNZ. Eighteen hours was chosen as a measure of a full day since the six remaining hours would not be equivalent to a full night of cooling in the barn.

temperature humidity index

When calves are subject to consecutive days spent outside of the TNZ, their maintenance requirements increase through panting and increased respiration rate. In this case, and this is most commonly the case with heat stress, performance was lost as average daily gain (ADG) and feed efficiency dropped due to the increased maintenance cost.

Looking at Table 4, the feed cost per animal per day is listed to note differences between farms in the heifer-raising programs. In this scenario, the farm with lowest feed cost was found to have the highest cost per pound of gain due to the low feed efficiency of the heifers. This could be partly explained by the increased maintenance cost due to the heat stress calves experienced.

Feed cost and measured gain

Are hutches betterfor mitigating heat stress?

Within this project, several hutch systems were represented and a trend of heat stress similar to that of Farm C in Table 4 was found. A pattern was observed across all farms housing calves in hutches. The temperature inside the hutch was nearly always recorded as hotter and more of a heat-stress condition for calves than the ambient conditions.

Calves have a tendency to lie in an area not in direct sunlight, sometimes leading them to lie in the hutches even when the hutch is hotter than the ambient temperature; doing so puts the calves in a higher THI environment. This concept was shown in Farm C, where the highest cost per pound of gain in an environment that had the highest THI also had the lowest feed efficiency.

How do we alleviate heat stress and minimize performance losses?

There are many ways to mitigate heat stress in calves, and the most important factors are familiar. Calves require ventilation, shade and fresh cool water. For existing hutch systems, adding shade cloth over the rows could provide shading to the hutches and the outdoor pen area of the hutch.

Propping the back of the hutch up a few inches could increase the circulation of fresh air within the hutch, resulting in cooler calves. Approaching heat-stress mitigation in barns is slightly more challenging, but adding measures that increase circulation of fresh air at the nose level of the calf will help reduce heat stress and thwart risk for opportunistic respiratory infections that develop in hot humid summer barns.

Working with agricultural engineers or experts in the areas of calf management and calf-barn ventilation can be useful in solving a heat-stress situation on your farm.

Ultimately, heat stress in the dog days of summer is nearly inevitable, but steps can still be taken to reduce its effects, better maintain average daily gains and optimize on-farm heifer-raising costs throughout all seasons. PD

Kaitlin Andrews is a graduate student in Cornell University’s Department of Animal Science.

Calves have a tendency to lie in an area not in direct sunlight, sometimes leading them to lie in the hutches even when the hutch is hotter than the ambient temperature ... Photo byPDstaff.

mike van amburgh

Mike Van Amburgh
Departmentof Animal Science
Cornell University