Impact of Heat Stress on Dairy Cattle and Appropriate Strategy to Reduce Its Influence

1. Impact of Heat Stress on Dairy Cattle and Appropriate Strategy to Reduce Its Influence

2. Strategies to Reduce Heat Stress in Dairy CattleJ.F.Smith, R.J.Collier,J.P.Harner and B.J.BradfordWestern Dairy Nutrition Conference 2012 Dairy Heat Stress Road ShowT.Bilby, P.Hansen, A.DeVries and J.E.Santos Animal Science Department - College of Agriculture and Life Sciences

3. Cow Comfort & Behavior • Under U.S. conditions we improve cow comfort or take advantage of behavior when it improves performance • Milk production • Reproduction • Health

4. Grouping Strategies Cow Handling Facilities Freestall Design & Bedding Management Strategies Time Budgets Cow Comfort & Behavior Walking Distance Heat Stress Stocking Density Travel Lanes Flooring Surfaces Cold Stress Feeding Strategies Feedline Surfaces

5. Assumptions • Cow comfort is essential • Ability manage heat stress and cold stress • Time budgets • 12 to 14 hrs/day to rest • 6 hrs/day to eat and drink • Control lighting • Labor efficient • Bedding • Cow handling • Maximize milk production per cow

6. The cow is a furnace

8. An Example • Assume the skin temperature of a cow was 30°C • Temperature increase from 26°C to 28°C, cow would lose less heat to the air by conduction and convection. • Temperature of 34°C, cow experiences a net gain in heat from the air!

9. What does the example explain? • Sensible heat loss mechanisms become ineffective as the gradient between environmental temperature and cow temperature decrease (latent heat loss) • Latent heat loss refers to heat associated with the evaporation of water • Water is evaporated when produced on the skin as a result of sweating , rain, immersion in water, etc. or breath of air enters the respiratory system and is humidified • Converting water from the liquid to the gaseous phase requires large amounts of heat • Therefore, cows increase sweating rate and respiration rate to lose heat by evaporation

10. Basic Premise!

11. What is the Temperature Humidity Index (THI) • A formula based on dry bulb temperature (thermometer) and humidity that is used as an estimate of the magnitude of heat stress affecting a cow • Tdb - (0.55-(0.55*RH/100)*(Tdb– 58) • Accounts for both temperature and humidity • Heat threat threshold has been lowered from 72 to 68 • Impacts production and reproduction

12. Old THI Chart

13. New THI Chart

14. Revised Temperature Humidity Index For Lactating Dairy Cows • Stress Threshold (68) Respiration rate exceeds 60 BPM. Milk yield losses begin. Repro losses detectable. Rectal Temperature exceeds 38.5°C (101.3°F) • Mild-Moderate Stress (70) Respiration Rate Exceeds 75 BPM. Rectal Temperature exceeds 39°C (102.2°F) • Moderate-Severe Stress (80) Respiration Rate Exceeds 85 BPM Rectal Temperature exceeds 40 °C (104°F) • Severe Stress (90). Respiration Rate 120-140 BPM. Rectal Temperature exceeds 41 °C (106°F) Source: Bob Collier, Univ. of AZ

15. Accuracy of THI • THI not greatly affected by amount of shade, forced ventilation, and evaporative cooling provided to cows • Not very useful to identify which activities and routines during the day make cows susceptible to heat stress (loafing, the holding area or parlor)

16. Way to measure “internal” temperature

17. Vaginal Temperature Lot and shade Fans and mister

18. Parlor cooling

19. Negative Impact of Heat Stress • Milk Production • Reproduction • Health • Nutrition • Behavior

20. Heat Stressed Cows • Dry matter intake is reduced • Increase sweating and panting to maintain core body temperature • Maintenance requirements increase by as much as 35% • Energy is shifted from milk production to maintenance • Negative impacts on milk production, reproduction and health

21. Effects of Heat Stress Short Term ↑ Respiration Rate ↑ Rectal Temperature ↑ Water Intake ↑ Sweating ↓ Rate of Feed Passage ↓ Dry Matter Intake ↓ Blood Flow to Internal Organs ↓ Milk Production

22. Effects of Heat Stress Long Term • Future milk production? • Lower peaks • Poor reproductive performance • Health • Udder health • Lameness

23. Milk Production – per day

24. Smith et al

25. Smith et al

26. Smith et al

27. Effect of Cooling Dry Cows

28. Heat Stress and Reproduction • Heat impact on reproduction more pronounced as production increases - Consequences of higher levels of feed intake (al-Katanani et al 1999) • Follicle that ovulated today started growing 3-4 months ago. Heat affects the follicle for at least the last 26 days of growth • Damages the oocyte once it has been released from the follicle at ovulation • Early embryo sensitive to heat stress until day 3 of pregnancy when becomes insensitive to maternal hyperthermia • Short term rises in body temperature • Potential decrease 25 – 40% in conception rate • Increase of .9°F resulted in a 13% decrease in conception rate (Gwazdauskas et al , 1997) • Take Home – Cannot solve effects of heat stress by limiting insemination to cooler parts of the day. Smith et al

29. Effectiveness of cooling before and after breeding Dairy Heat Stress

30. Summer to winter ratios for conception rate in Israeli herds as affected by production level and intensity of cooling

31. Reproductive Impacts • Lower estradiol levels also cause a depression in estrus behavior • Cows are more difficult to find in heat • Heat detection decline during the summer month by 10-20% • Impact of chronic heat stress • Poorer quality corpora lutea that produce less progesterone • Risk of late embryonic loss and abortion is approximately 2 to 2.5 times greater for cows bred during and immediately following heat stress • Increase in twins Smith et al

32. Chronic heat stress depresses feed intake and prolongs the period of time required for a cow to reach positive energy balance • Causing excessive weight loss and delaying days to first ovulation • Changes calving patterns • Over stocking of transition facilities • Overcrowding these facilities leads to increases in post-calving health issues, decreased milk production and impaired future reproduction. Smith et al

36. Smith et al

38. Smith et al

39. Water Intake • Under thermal neutral conditions lactating cows will drink 35 g/day • Water intake increases 1.2 to 2.0 fold during heat stress!! • Need about 3.5 linear inches of drinking space per cow in housing areas • Multiple locations • Need water troughs going to and from the parlor • 10% of water consumption Smith et al

40. Water Availability in Freestalls • Freestall housing • Water at every crossover • Distance between crossovers will determine if adequate tank perimeter is provided • Water troughs can be placed on the outside walls Smith et al

41. Smith et al

42. Smith et al

43. Smith et al

44. Smith et al

47. Response to Shade • 1.8 to 4.1 kg of milk/cow/day • Design of shades in dry lots is important • Orientation of naturally ventilated freestall barns is critical • Sun angles Animal Science Department - College of Agriculture and Life Sciences

48. Smith et al

50. Shades in Dry Lot Housing Mature Cows • Shade • 45 to 50 ft2/cow (4.2 to 4.7 m2/cow) • North to South orientation • Minimum 14 feet or 4.3 meters high Smith et al