As high summer temperatures give way to cooler fall weather, the seasonal transition offers relief from heat stress. But even with more comfortable daytime highs, the herd may feel the aftereffects of heat stress for several more months. Now’s the time to assess how hot weather may have damaged your herd’s reproductive performance. Take a look backRecords analysis is a good starting point for herd assessment. Producers should check three key measurements for signs of a drop in performance.

1. Pregnancy rate
The starting point for reproductive analysis, pregnancy rate, is an easy way to identify performance slips. Most herds’ rates will decline during the summer months, but a realistic goal is to maintain a 21-day pregnancy rate within two to three percentage points of the herd’s yearly average. If the pregnancy rate drops by more than three to five percentage points, further analysis is needed.

2. Percent of milking herd pregnant
Normally about 10 percent of the milking herd will become pregnant each month. During heat stress that number can drop to 5 percent or less a month. When reaching this type of reduction in new pregnancies, cooling options may be warranted.

3. Early embryonic death
Body temperatures of 103°F to 103.5°F or more for any time during the day will increase incidence of early embryonic death. Normal losses on pregnancy re-examination are about 5 percent, but levels as high as 15 percent can be seen after periods of heat stress. This increases the importance of rechecking pregnancies after summer to identify open cows. Monitoring cow body temperatures using current technology can identify when heat stress is occurring.

Plan the recovery
Whenever a producer notices a decline in reproductive performance, the natural inclination is to get cows bred back as quickly as possible. However, it is important to carefully plan breeding to avoid having a large group calving at the same time. When future calving dates are bunched, transition and calving facilities can become overcrowded. This can lead to metabolic problems and reductions in early lactation performance, as well as affect future reproductive productivity.


Producers who find their herd’s reproductive performance in need of a rebound should utilize synchronization protocols to get cows bred back. Even during the summer heat stress, estrus synchronization and artificial insemination will result in greater fertility than visual heat detection and natural service. Aggressive identification and resynchronization of open cows are important parts of reproductive performance recovery.

To prevent large numbers of cows from calving at the same time, producers may want to consider adjusting the voluntary waiting period for cows calving in late summer and early fall. This can allow animals to regain condition following calving and improve breeding success. Adjusting heifer breeding by starting some animals earlier during summer can help to smooth out the calving distribution. Planned scheduling of reproduction is a possible way to avoid some of the consequences of overcrowding the transition area.

Consult your key farm advisers, especially the herd veterinarian, before making major changes in reproductive protocols.

Cow cooling pays
After you have overcome the reproductive difficulties of summer and while the season’s heat stress is still top-of-mind, make plans for next year to avoid the financial consequences of decreased reproductive performance.

Economic analysis places the value of each pregnancy to be between $200 and $400. If we consider a 1,000-cow dairy operation experiencing 50 fewer confirmed pregnancies per month due to heat-related effects, the dollars can be significant. Using $300 per confirmed pregnancy, the dairy is losing $15,000 a month.

Reproductive performance is not the only aspect of herd performance affected by heat stress. If the same 1,000-cow herd could improve milk production through cow cooling by just one pound of milk per cow per day, it could generate $3,000 more profit per month in marginal milk income (assuming a milk price of $14 per hundredweight and marginal feed cost of $4 per hundredweight).

This simple, conservative analysis demonstrates potential performance gains of $18,000 a month as a result of cow cooling. Additional gains can be found in improved peak milk, milk quality and lameness rates to offset the costs for equipment and utilities. With that kind of payback, it’s worth spending time to plan and install improved cooling systems for next season.

Cooling priorities
Cow cooling should be the first priority when planning systems to combat heat stress. Producers may start with exit lane cooling and then focus on making cows comfortable in the parlor.

1. Exit lanes
Install exit lane sprinklers in the return alley, along with water troughs. Cows will consume more than 30 percent of their daily water intake within a half hour after milking.

2. Milking parlor
The milking center should be a comfortable environment for cows to enter. Install fans to maintain air movement and keep workers and cows comfortable, as well as improve equipment performance. Fans and misters or soakers in the holding area help to alleviate heat stress when cows are crowded together before milking.

3. At the feedbunk
Fans and sprinklers at the feedbunk should be a staple on most dairies. Target air movement of 5 to 7 miles per hour and constant re-wetting of cows.

4. Resting areas
Fans and misters are needed to keep cows comfortable. Maintaining bedding quality is important and in drylot herds, pens may need to be dragged twice-a-day.

5. Drinking water
Clean and cool water must be abundantly available. Routinely check the water temperature of drinking troughs in hot sunlight. Cows will drink from 25 to 50 percent more water when air temperatures are 80°F to 90°F or above.

Maintenance of heat cooling systems, including fans, spray nozzles, soaker lines and so forth, is important and should be scheduled and monitored to maximize the return on the investment in cooling.

Producers who aggressively manage their reproduction programs can help ensure the full productivity of their herd, creating opportunities for extra operation revenues. Work with the veterinarian to assess the herd’s reproductive status coming out of the hot summer months. Aggressive use of synchronization programs can help improve breeding success and prevent bottlenecks down the road – not only in summer but year-round. PD

Stephen Smalley