Dry Cow Heat Stress Abatement

It has been well established that heat stress during the dry period negatively affects milk production in subsequent lactations in a sub-tropical environment (Tao et al. 2011). More recently, a study at the Miner Institute in Northern New York indicated reduced 21-day milk yield and gestation lengths due to heat stress in the late dry period. (Fread, 2023). Although it may be a lesser impact than in a subtropical climate, this study showed that heat stress affects dry cows in a moderate climate and heat abatement should be considered in the Northeast as summer is approaching.

Weather data from the National Oceanic and Atmospheric Administration (NOAA) for the University Park Airport in University Park, Pennsylvania was collected to estimate the level of heat stress in Pennsylvania. The summer months of June, July, and August from 2018-2022 were evaluated. During the 92 days between June 1^st and August 31^st, the average Temperature Humidity Index (THI) was greater than or equal to 68 for 1100 hours, representing 50% of the time. Both lactating and dry dairy animals will begin to experience heat stress at or above a THI of 68. The 1100 hours seen in Pennsylvania are more time above a THI of 68 than seen in the study conducted in Northern New York, indicating that the impacts of heat stress on dry cows in Pennsylvania would be more severe.

When considering heat abatement for dry cows, installing both sprinklers and fans is essential, as Fread (2023) showed that fans alone are not sufficient cooling for dry cows in the Northeast. The Penn State Extension DIP 411 plan (Tyson et al. 2005) gives a housing option for 35 far off dry and pre-fresh cows and is sized for a total herd of 150 to 175 milking cows. This plan was used to design an example heat abatement system, including circulation fans over the stalls, feed bunk, and maternity pens, along with a feed line sprinkler. This system includes eleven 50-inch panel fans, each consuming approximately 1 kilowatt of energy when running. The feed line sprinkler comprises 164 feet of sprinkler pipe with 24 nozzles using 0.75 gallons per minute with a 1 minute on time every 15 minutes. The heat abatement system described above would cost an estimated $19,000 to install.

Using weather data from NOAA for the University Park Airport, between June 1 and August 31, there are an estimated 1600 hours per year when the temperature is above 65°F and 800 hours when it is 72°F or above in PA. The heat abatement system described above uses a set point of 65°F for circulation fans and 72°F for the feed line sprinkler. This yielded a fan energy use of 17,600 kWh and a water use of 57,600 gallons for the system for the hot summer months of June to August. To estimate an operating cost for this heat abatement system, an electric cost of 14.5¢ per kWh was used. It was also assumed that half of the water used in the sprinklers system would become part of the manure system and must be hauled as manure at the cost of 1¢ per gallon. This gives a total of $2552 for electricity and $288 for manure handling for the system to operate for three months.

A 2016 study of the economics of cooling dry cools (Ferreira et al. 2016) estimated that dry cows who are housed under no heat abatement in Pennsylvania lose over 1,000 pounds of milk in their subsequent lactation. Using normal cow flow through a housing system, approximately 45 animals would be housed in the shelter shown in the DIP 411 plan during a 3-month period. Below is a partial budget for adding a heat abatement system to this example shelter.

Added Income:

• 45 cows with 1,000 lb each of additional milk at $18.00 per cwt: $8100
• Total = $8100

Added Costs:

• Added Feed (1lb dry matter for 2.5lb of milk at 10.5¢ per lb): $1890
• Electricity (14.5¢ per kWh): $2552
• Manure Handling: $288
• Added investments: Annual Amortization ($19,000 for 7 years @5%): $3,284
• Total = $8,014

Added Return Per Year: $86

Added Return Per Cow (45 Total): $1.92

The partial budget shows a very slim profit potential of the heat abatement system based only on additional milk income. What is not included are the health costs associated with increased standing and decreased feed intake due to heat stress. Increased standing time and decreased dry matter intake can impact foot health, body weight loss, reduced immunity, lower pregnancy rates, and other herd health issues. Additionally, a heat abatement system should have a useful life longer than 7 years, so after the capital investment is paid back the profit margin increases. In short, it pays to cool dry cows, even here in the Northeast US. So, before the heat of summer gets here take some time to evaluate your dry cow housing for heat abatement. Your dairy may be leaving some money on the table.

References:

Tao, J.W. Bubolz, B.C. do Amaral, I.M. Thompson, M.J. Hayen, S.E. Johnson, G.E. Dahl. 2011. Effect of heat stress during the dry period on mammary gland development. DS 94: 5976-5986.

Fread, Emily. 2023. "Effects of Late Gestation Episodic Heat Stress in the Northeastern United States on Holstein Dams and their Calves". Graduate College Dissertations and Theses. 1637. The University of Vermont.

F.C. Ferreira, R.S., Gennari, G.E. Dahl, A. De Vries. 2016. Economic feasibility of cooling dry cows across the United States. JDS 99: 9931-9941.

NOAA Local Climatological Data.

Tyson, J. T., R. E. Graves, D. F. McFarland, T. H. Wilson. 2005. Dry Cow Maternity Freestall Shelter DIP 411.

Gehrett, S., Beck, T. 2023. Personal Communications.