Does Heat Stress Affect Immune Function in Dairy Cows?

a Knowledge Summary by

Michael Steele BSc(Hons), BVSc, MRCVS1*

1Dairy Consultant, 10 Granborough Road, Winslow, Buckinghamshire, MK18 3BP
*Corresponding Author (

Vol 1, Issue 3 (2016)

Published: 14 Sep 2016

Reviewed by: James Breen (BVSc PhD DCHP MRCVS)

Next Review date: 20 Jan 2018

DOI: 10.18849/VE.V1I3.39

Clinical bottom line

Heat stress appears to generally suppress innate immune function in both dry and lactating dairy cows. Immune effects that are decreased include cytokine production, proliferation of immune cells, migration of lymphocytes to the udder and cell viability. This may lead to an increase in the risk of clinical diseases such as mastitis and metritis.


In dairy cows experiencing heat stress (in most papers defined as a temperature/humidity index of >65 at the lowest threshold (Bernabucci, 2014), vs. cows in environmentally cooled conditions, is innate immune functionality affected?

Clinical scenario

A previously published review revealed that cows experiencing high temperature humidity indices reduce milk yields beyond that expected of the reduction in dry matter intake (Baumgard, 2013) and therefore do not appear to experience ketosis. It is clear however, that cows experience some discomfort. The innate immune system is the first line of defense against invading pathogens, and any factor which suppresses the efficiency of this protection increases the risk of diseases (Kehrli, 1989).


Thompson (2014)
Population: Multiparous dairy cows in the dry period
Sample size: 15 cooled dry cows and 15 heat stressed cows. 5 from each group were induced Streptococcus uberis IMI at 5DIM
Intervention details: THI in non-cooled conditions was 77.9-78.3. Cooling involved fans, water sprinklers and shade in this group
Study design: Cohort Study
Outcome Studied: Rectal temperature, respiratory rate, milk yield and composition, blood parameters: Immune response genes (TLR2, IL1-β, IL6, IL8, IL10, and TNFα)
Main Findings
(relevant to PICO question):

Cooled dry cows had:

  • Lower temperature and respiratory rate,
  • Higher milk yield (no change in composition) by 3.8L/d
  • Higher neutrophil count after IMI
  • Higher IL10
  • Higher TLR2
  • All other cytokines had no difference
  • Very low cow numbers
  • Measured over 0-36 hours post IMI for cytokines and to 40 weeks into lactation for physiology
  • All cows were cooled after calving
  • Insufficient power to conclude an effect on milk yield, however, any numerical effects seen are valid as the primiparous group were not included

Collier (2008)
Population: Dairy cows experiencing heat stress >35°C
Sample size: NA
Intervention details: NA
Study design: Review of cohort studies
Outcome Studied: NA
Main Findings
(relevant to PICO question):

Gene expression changes to heat above 35°C include:

  • activation of heat shock transcription factor 1 HSTF1
  • increased expression of heat shock proteins (HSP)
  • increased glucose and amino acid oxidation and reduced fatty acid metabolism
  • endocrine system activation of the stress response
  • immune system activation via extracellular secretion of HSP
Limitations: NA

Kamwanja (1994)
Population: Lymphocytes from 3 breeds of heifers
Sample size: 12 heifers of Angus, Brahman and Senepol
Intervention details: Killing lymphocytes after incubation at 45°C for 1 or 12 hours
Study design: Cohort study on lymphocyte populations
Outcome Studied:

Viability of lymphocytes and HSP production when killed after 45°C for 1 hour or 12 hours

Main Findings
(relevant to PICO question):

Decrease in viability at 45°C in Brahman and Senepol

Limitations: In vitro work with little relevance to in vivo effects

Elvinger (1992)
Population: Dairy cows during lactation
Sample size: 34 cows at parity 1-8 and DIM 30-209 given either bST or placebo (16 in control, 18 in bST treated group). On day 10 after initialising placebo or bST cows were placed in cross over heat stress and normalised environments)
Intervention details: Heat stress (35-44°C) or normalised (26-33°C)
Study design: Cohort study (cross-over)
Outcome Studied: Temperature, respiratory, cortisol, milk yield, lymphocyte numbers (CD4+ and 8+)
Main Findings
(relevant to PICO question):
  • Heat stress increased rectal temperatures, respiration rates, and plasma cortisol concentrations and decreased milk yield
  • No discernible effects on immune function due to bST
  • Heat stress reduced lymphocyte migration to udder
  • Very low cow numbers
  • Cows ranged from lactation 1-8 with no specification as to numbers in each lactation. This may affect yield results (lactation 1 cows give less milk than lactation >1).

Elvinger (1991)
Population: Heat stressed lactating dairy cows
Sample size: NA
Intervention details: Incubated lymphocytes in high or low temperatures to see viability
Study design: Case study
Outcome Studied: Viability of leukocytes incubated at 38°C and 42°C
Main Findings
(relevant to PICO question):

During spring THI was 72 and in the summer it was 79.

In summer:

  • DNA synthesis was lower
  • Immunolglobulin M secretion was higher
  • Plasma cortisol was higher (2ng vs >4ng/ml before calving, not after)
Limitations: The cows weren’t grouped Variation in feed possible and other management factors (stocking etc.)

Lacetera (2006)
Population: Comparing leukocytes from BRS and HOL lactating dairy cows
Sample size: 5 BRS and 5 HOL cows
Intervention details: Incubation of PMNs at 39°C and 43°C
Study design: Cohort study
Outcome Studied: PMN: Proliferation HSP72 synthesis
Main Findings
(relevant to PICO question):
  • PMNs from BRS breed appeared to have a lower tolerance to heat. BRS is supposed to be a more heat tolerant breed.
  • Heightened temperature
  • Lowered ROS activity
  • Higher HSP72 synthesis in BRS but not HOL
  • HOL appeared to have a more tolerant effect to higher temperatures than BRS
  • Low numbers of cows, however the study is comparing cells rather than cows
  • HSP72 synthesis may not be conclusive as it is unclear whether or not pre-or post-transcription levels on mRNA are determined.

Lacetera (2005)
Population: Transition HOL dairy cows (dry and in early lactation)
Sample size: 34 cows. 28 calving in spring and 12 in summer. During spring THI averaged 72 and in the summer it averaged 79.
Intervention details: Comparing cows calving in spring and summer
Study design: Cohort study
Outcome Studied: Blood (leukocytes) taken weekly, from -4wk to +4wk around calving
Main Findings
(relevant to PICO question):

In summer:

  • DNA synthesis was lower
  • IgM secretion was higher
  • Plasma cortisol was higher (2ng vs >4ng/ml before calving, not after)
  • Very low cow numbers
  • Many more cows in winter group vs summer group
  • Variation in feed possible and other management factors (stocking etc.) from spring to summer. This may have affected physiological factors

Do Amaral (2010 and 2011)
Population: Comparing lymphocyte function in heat stressed and cooled multiparous lactating cows
Sample size: 21 heat stressed and 16 cooled lactating cows (from 42 days pre calving)
Intervention details: Cooling system had fans and sprinklers active at greater than 21°C
Study design: Cohort study
Outcome Studied: mRNA expression of prolactin receptor PRL-R, Suppressor of cytokine activity proteins SOCS-1, SOCS-2, SOCS-3, cytokine-inducible SH2-containing protein, and heat shock protein 70 typed at Kilodalton A5 (or HSPA5)
Main Findings
(relevant to PICO question):

Heat stress:

  • Had greater prolactin (PRL) in plasma
  • Had lower lymphocyte proliferation
  • Had lower SOCS (suppressors of cytokine function) levels
  • Had lower TNFα expression
  • Had lower PRL receptor expression
  • Low cow numbers
  • Did not concentrate on many innate, Th1 parameters
  • Did not mention the difference in temperature of cooled vs heat stressed groups

Lacetera (2002)
Population: Transition dairy cows in spring and summer
Sample size: 20 spring calving cows and 9 summer calving cows
Intervention details:

spring THI 58

Summer THI 72

Study design: Cohort study
Outcome Studied:
  • Rectal temperature
  • Respiratory rate
  • Proliferation of PMNs
  • Colostrum Ig levels
Main Findings
(relevant to PICO question):

Summer vs spring:

  • Increased rectal temperature
  • Increased respiratory rate
  • No effect on proliferation or colostrum Ig levels
Limitations: May be different management systems at different times, small cow numbers and very moderate THI for heat

Appraisal, application and reflection

There are relatively few papers directly addressing the effects of heat stress on immune function specifically, especially those concentrating on non-specific, innate effects that may be significant to the development of subsequent diseases. However, there are some agreements between the above papers that physiological effects are apparent as well as immune suppressive effects in temperature and humidity levels over THI levels at greater than or equal to 72.

Most papers compare cooled cows to heat stressed cows and either focus on outcomes in vivo or from leukocytes taken from the cows and subsequent functions in vitro.

Cows or leukocytes in cooled conditions appear to have:

Methodology Section

Search Strategy
Databases searched and dates covered: Used 3 databases: PubMed, CAB Abstracts (1973-2015) accessed on the OVID platform) and Google Scholar. PubMed did not achieve many hits (5) so I tried Google Scholar. PubMed also had too many results to process when using immun*, so I had to restrict to (immune OR immunity).

Hit 16,400 results. Filtered to 2000-2016, After the first 4 pages, virtually none were relevant to the PICO.

Search terms: ((((cow$ AND cattle AND bovi*))) AND heat stress) AND ((immune OR immunity)) – PubMed

does heat stress affect dairy cow immun* - Google Scholar

(cow$ AND cattle AND bovi* AND heat stress AND (immune OR immunity)).mp   - CAB Abstracts

Dates searches performed: 18th March, 2016

Exclusion / Inclusion Criteria
Exclusion: NA
Inclusion: Relevance to PICO, sufficient evidence level, answers the clinical question

Search Outcome


Number of results

Excluded – Relevance to PICO

Total relevant papers


17 12 5

Google Scholar

16,400 16,394 6

CAB Abstracts

53 47 6

Total relevant papers when duplicates removed


Conflict of Interest

The author declares no conflict of interest


  1. Baumgard, L.H, and Rhoads, R.P. (2013) Effects of Heat Stress on Postabsorptive Metabolism and Energetics. Annual Reviews in Animal Biosciences, 1 (1), pp. 311-337.
  2. Bernabucci, U. et al. (2014) The Effects of Heat Stress in Italian Holstein Dairy Cattle. Journal of Dairy Science, 97 (1), pp. 471-486.
  3. Collier, R.J. et al. (2008) Invited Review: Genes Involved in the Bovine Heat Stress Response. Journal of Dairy Science, 91 (2), pp. 445-454.
  4. Do Amaral, B.C. et al. (2010) Heat Stress Abatement during the Dry Period Influences Prolactin Signaling in Lymphocytes. Domestic animal endocrinology, 38 (1), pp. 38-45.
  5. Do Amaral B.C. et al. (2011) 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, 94 (1), pp. 86-96.
  6. Elvinger, F. Hansen, P.J. and Natzke, R.P. (1991) Modulation of Function of Bovine Polymorphonuclear Leukocytes and Lymphocytes by High Temperature in Vitro and in Vivo. American Journal of Veterinary Research, 52 (10), pp. 1692-1798.
  7. Elvinger, F. Natzke, R.P, and Hansen, P.J. (1992) Interactions of Heat Stress and Bovine Somatotropin Affecting Physiology and Immunology of Lactating Cows. Journal of Dairy Science, 75 (2), pp. 449-462.
  8. Kamwanja, L.A. et al. (1994) Responses of Bovine Lymphocytes to Heat Shock as Modified by Breed and Antioxidant Status. Journal of Animal Science, 72 (2) pp. 438-444.
  9. Kehrli, M.E. Nonnecke, B.J. and Roth, J.A. (1989) Alterations in Bovine Neutrophil Function during the Periparturient Period. American Journal of Veterinary Research, 50 (2) , pp. 207-214.
  10. Lacetera, N. et al. (2002) Moderate Summer Heat Stress Does Not Modify Immunological Parameters of Holstein Dairy Cows. International Journal of Biometeorology 46, no. 1 (2002): 33-37.
  11. Lacetera, N. et al. (2006) Heat Stress Elicits Different Responses in Peripheral Blood Mononuclear Cells from Brown Swiss and Holstein Cows. Journal of Dairy Science, 89 (12), pp. 4606-4612.
  12. Lacetera, N. et al. (2005) Lymphocyte Functions in Dairy Cows in Hot Environment. International Journal of Biometeorology, 50 (2), pp. 105-110.
  13. Thompson, I.M. (2014) Effect of Cooling during the Dry Period on Immune Response after Streptococcus Uberis Intramammary Infection Challenge of Dairy Cows. Journal of Dairy Science, 97 (12), pp. 7426-7436.

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