Dr. Albert DeVries presented this material in a webinar for DAIReXNET on Monday, April 9th.

1. Supported by AFRI Competitive Grant no. 2010-85122-20623 from USDA-NIFA
Economics of Heat Stress:
Implications for Management
Albert De Vries
Department of Animal Sciences
University of Florida
Gainesville, Florida, USA
devries@ufl.edu
DAIReXNET Webinar, April 9, 2012

2. Topics
• Cost of heat stress, value of cooling
• Improved fertility in summer
• Sexed semen mix

3. Dairy heat stress losses in USA
St-Pierre et al. (2003)
• Feed intake 
• Milk production 
• Reproduction 
• Repro culling 
• Death 
Average losses due to heat stress
• Without any heat abatement:
$167 per cow per year
• With optimal heat abatement system:
$100 per cow per year

4. Annual production and economic losses in
6 states (minimum heat abatement)
Annual
Dry matter Repro
Milk  Days Deaths hours of Loss
State intake  culling 
(lbs/cow/yr) open   (%) heat stress ($/cow/yr)
(lbs/cow/yr) (%)
(%)
WI 201 403 9 0.6 0.1 9 72
CA 320 646 12 0.9 0.2 12 110
NM 370 745 23 2.2 0.5 20 168
AZ 798 1609 26 2.5 0.5 22 256
FL 1971 3975 59 8.0 1.7 49 676
TX 2196 4425 54 7.4 1.6 36 698
After St-Pierre et al. (2003)

5. Florida seasonal pregnancy rates 1976-2002
winter
summer
De Vries and Risco, 2005

6. Florida Observation
• Many seasonal breeding herds
– Calve in fall, breed in winter, dry in summer
• Preferably no calving in late spring/summer
– Heat stress during calving
– Death risk  (cows, calves)
– Milk production , fertility 
• Getting cows pregnant in summer:
 late spring / summer calving
• How important is it to get cows pregnant in summer?

7. Can we improve profitability
by improved fertility and
better insemination decisions?
A story of calving patterns

8. Systems approach
• Large spreadsheet(+) with heifers and cows, lactation
curves, fertility, feed intakes, labor, prices, etc.
• Decisions: replacement, insemination, calf raising
• Closed herd: sell surplus heifer calves + all bull calves
• Optimize profit per (milking) slot per year
• Heat stress effects on milk production, fertility, death
risk
• This is difficult 

9. Relative humidity, temperature and
temperature humidity index
for Orlando, Florida
max H
max F
THI
min H
min F

10. Seasonal herd
constraint: 1300 total cows
cows calved
heifer calves born
heifer calves kept
heifers calved

11. Seasonal herd
constraint: 1300 total cows
Cows present
Milk Cows milking
Open cows

12. • Increase probability of conception by 10%
• For example: 40% + 0.1 * 40% = 44%

13. +10% Probability of conception
constraint: 1300 total cows
Normal +10% Prob. conception
Profit/slot/year $728 $767
+$39/slot/year
heifers
cows

14. Inseminations
+10% probability of conception
constraint: 1300 total cows
cows
heifers

15. Delayed inseminations
+10% probability of conception
constraint: 1300 total cows
heifers
cows

16. Calvings
+10% probability of conception
constraint: 1300 total cows
cows
heifers

17. 1000 milking cows constraint

18. Seasonal herd
constraint: 1000 milking cows
Cows present
Milk Cows milking
Open cows

19. Inseminations
+10% probability of conception
constraint: 1000 milking cows
Normal +10% Prob. conception
Profit/milking slot/year $587 $647
+$60/slot/year
cows
heifers

20. Present and milking
+10% probability of conception
constraint: 1000 milking cows
present
milking

21. Delayed inseminations
+10% probability of conception
constraint: 1000 milking cows
heifers
cows cows

22. Calvings
+10% probability of conception
constraint: 1000 milking cows
cows
heifers

23. Sexed, fresh IVF embryo transfer in
summer increases conception rates
• Summer transfer of sexed in-vitro fertilized embryos
• 200% of conventional AI summer conception rate
• 88% heifer calves
Stewart et al. (2011)
• Economics?
• $90 per IVF-ET transfer
• $250 sold heifer calf, $50 sold bull calf
• Change in calving pattern

24. IVF-ET in summer: scenario A
conception rates and #inseminations, IVF-ET
All summer “breedings” with IVF-ET
No delayed inseminations
All calves sold, heifers purchased
1300 total cows constraint
conception rate
inseminations/ET

25. IVF-ET in summer: scenario A
Cows calved and milking
All summer “breedings” with IVF-ET
No delayed inseminations
All calves sold, heifers purchased
1300 total cows constraint
Value of IVF-ET:
-$4 /milking slot/year
milking
Normal: $779, IVF-ET: $775
calved

26. IVF-ET in summer: scenario B
conception rates and #inseminations, #IVF-ET
Optimal summer “breedings”
Allow delayed inseminations
1000 milking cows constraint
conception rate
inseminations/ET

27. IVF-ET in summer: scenario B
Cows calved and milking
Optimal summer “breedings”
Allow delayed inseminations
1000 milking cows constraint
Value of IVF-ET:
$88 /milking slot/year
milking Normal: $569, IVF-ET: $657
calved

28. Conventional, sexed semen,
and summer heat stress
• $20 conventional dairy semen
– Normal fertility
– 48% heifer calves
– Extra heifers calves sold for $250, bull calves $50
• $35 female sexed semen
– 80% of normal fertility
– 88% heifer calves
– Extra heifer calves sold for $250, bull calves $50
• What is the optimal mix?

29. Conventional and sexed semen mix
constraint: 1000 milking cows
conv. cows
sexed heifers
Profit conventional only: $587 / milking slot / year
Profit sexed + conventional: $624 / milking slot / year (+$37)

30. Summary
• Cooling dairy cows pays in hot climates
• Value of improving fertility in summer depends on
seasonality of cow performance (milk, fertility) and
herd constraints (parlor capacity, cash flow)
• Seasonality has major implications for optimal
insemination mix
Thank you
devries@ufl.edu