Heat Stress Management of Dry Cows

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Heat Stress Affects Health and Production

Heat stress during late gestation negatively influences health and productivity of dairy cows in the subsequent lactation^1,2. Under commercial farm conditions in Florida, cows that were dry during the summer months (June, July and August) produced less milk during the subsequent lactation compared with all cows dry during cooler months (December, January and February). In addition, cows exposed to cooling during the dry period have decreased occurrence of postpartum diseases such as mastitis, respiratory problems, and retained fetal membranes compared with cows dried during hot months.

Heat Stress Affects Reproduction

Reproductive performance of lactating cows declines significantly during heat stress. Reproductive performance during the hot season is clearly associated with a change in patterns of estrus detection, a decrease in conception rate and an increase in days to first service in dairy cows. Under commercial settings, cows dried off during hot months have a significant increase in times bred, DIM to first breeding and DIM to pregnancy diagnosis in the first 150 DIM of the subsequent lactation. This suggests that the effects on fertility of dry period heat stress carry over into the next lactation. Therefore, under commercial settings, environmental management strategies designed to reduce heat stress during the dry period can help attain optimal lactation performance².

Indicators of Heat Stress

Rectal temperature and respiration rates are good indicators of heat stress in dry cows. Monitoring respiration rates is a practical management tool to determine if a cow is heat stressed. As part of a daily routine in a commercial dairy farm, a herdsperson can count breaths per minute. An excess of 65 bpm is an indicator of significant heat stress.

Countering Heat Stress

Housing dry cows in barns equipped with sprinklers, fans and shade results in increased milk production, and improved immune response on the subsequent lactation ³. However, cooled dry cows may have a higher incidence of ketosis, and tend to have a higher incidence of metritis and retained placenta versus heat stressed dry cows⁴.

Investment in Heat Stress Abatement Pays Off

Based upon these previous findings, the following is a synopsis of the economics of cooling cows during the dry period in Florida.

• Assumptions for 100 cow herd housed in an open sided, sand bedded freestall barn:

 Cost of a 20 cow freestall barn with fans and soakers: $1,700/stall = $34,000

Note that the cost may be slightly more per stall depending on the location of the dairy due to structural needs of the location.

• Other costs:

16 cases of ketosis = $1,600⁵.

8 cases of metritis = $2,400⁶.

Feed increase: 5.0 lbs dry matter/cow/day; $20/100 lbs of dry matter = $10/100 lbs milk.  This assumes that each 1 lb increase in milk requires 0.5 lb increase in DMI.

• Revenue from increased production:

9.9 lbs more milk/cow/day for 305 d = 3,020 lbs/year at $20 cwt= $61,000

Given the above assumption of costs and revenue for an example 100-cow herd, this could generate $27,000 of income over variable costs associated with health impacts and increased intake. Assuming that cows would be under heat stress conditions for 12 months, the cost would be paid off in 15 months. If the cows would be under heat stress for 6 months, then the investment would be paid off in 30 months.  Table 1 represents a summary of variable milk price and yield responses on returns to the producer when implementing dry period cooling. Note that feed price and other cost effects were held constant as for the example above. 

In summary, cooling cows during late gestation improves subsequent lactation performance. The severity of heat stress significantly influences the response and cost-benefit of heat abatement. In addition to the economic benefit, heat abatement positively affects health and welfare.

Table 1

Table 1: Potential costs, returns and payback estimates of heat stress abatement during the dry period in dairy cattle. Milk price ranges between $17.50 and $25.00/cwt milk, which represents a typical range throughout the US.  Barn cost represents the cost of a 20 dry cow freestall and increase in profit/cow/year is the ratio between the increase in profit/year and the total number of cows in the herd.  The milk yield increase varies from 3 to 9 lbs/day and is assumed to be consistent across the lactation.

Author Information

Izabella Toledo and Geoffrey Dahl

References

1. Tao, S., and G.E. Dahl. Invited review: Heat stress effects during late gestation on dry cows and their calves. Journal of Dairy Science. 2013. 96:4079-93.
2. Thompson, I.M. and G. E. Dahl. Dry-period seasonal effects on the subsequent lactation. Professional Animal Scientist. 2012. 28: 628-631.
3. Do Amaral, B. C., E.E. Connor, S. Tao, M. J. Hayen. J.W. Bubolz and G. E. Dahl. Heat stress abatement during the dry period influences metabolic gene expression and improves immune status in the transition period of dairy cows. Journal of Dairy Science. 2011. 94:86-96.
4. Thompson, I. M., A. P. A. Monteiro, G. E. Dahl, S. Tao, and B. M. Ahmed. Impact of dry period heat stress on milk yield, reproductive performance and health of dairy cows. J. Dairy Sci. 2014. Vol. 97(E-Suppl. 1):734.  Abstract #1493.
5. www.ProgressiveDairy.com (http://www.progressivedairy.com/dairy-basics/herd-health/6176-parturitio…)
6. Overton, M., J. Fetrow. Economics of Postpartum Health, in Proceedings Dairy Cattle Reproduction Council Annual Meeting 2008; 39-43.