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 (steelemi@elanco.com)








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.




Question

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).




Acronyms:

	IMI=intramammary infections;
	DIM=Days in Milk;
	Resp=respiration;
	TLR=Toll-like receptor;
	IL=interleukin;
	TNF=tumour necrosis factor;
	Temp=temperature;
	HSTF=heat shock transcription factor;
	HSP=heat shock protein;
	bST=bovine somatotropin;
	THI=temperature humidity index;
	BRS=Brown Swiss;
	HOL=Holstein;
	PMN=polymorphonuclear leukocytes;
	Th1=T-helper 1 response;
	Ig=immunoglobulin







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


	Limitations:		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


	Limitations:		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


	Limitations:		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)


	Limitations:		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


	Limitations:		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:

	Lower rectal temperatures
	Lower respiratory rates
	Lower cortisol levels in plasma
	Higher milk yield (3.8L/d)
	Higher IL10,2, neutrophil count, Lower TNF α, Lower suppressors of cytokine function
	Higher viability of leukocytes
	No effect on Ig levels in colostrum
	Better migration of lymphocytes to udder
	Higher prolactin receptor expression
	Lower prolactin production
	Higher heat shock transcription factor HSTF1 and heat shock protein HSP72 expression (but(B. U. Lacetera N. 2006) states that the function of the latter molecule remains unknown) but post-transcriptive effects are not determined.




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
	
Database

	
Number of results

	
Excluded – Relevance to PICO

	
Total relevant papers


	
NCBI PubMed

	17	12	5
	
Google Scholar

	16,400	16,394	6
	
CAB Abstracts

	53	47	6
	
Total relevant papers when duplicates removed

	9









      


Conflict of Interest

      
The author declares no conflict of interest






      


References

      

	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. http://dx.doi.org/10.1146/annurev-animal-031412-103644
	Bernabucci, U. et al. (2014) The Effects of Heat Stress in Italian Holstein Dairy Cattle. Journal of Dairy Science, 97 (1), pp. 471-486. http://dx.doi.org/10.3168/jds.2013-6611
	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. http://dx.doi.org/10.3168/jds.2007-0540
	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. http://dx.doi.org/10.1016/j.domaniend.2009.07.005
	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. http://dx.doi.org/10.3168/jds.2009-3004
	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.
	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. http://dx.doi.org/10.3168/jds.S0022-0302(92)77781-9
	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.
	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.
	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. http://dx.doi.org/10.1007/s00484-001-0115-x
	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. http://dx.doi.org/10.3168/jds.S0022-0302(06)72510-3
	Lacetera, N. et al. (2005) Lymphocyte Functions in Dairy Cows in Hot Environment. International Journal of Biometeorology, 50 (2), pp. 105-110. http://dx.doi.org/10.1007/s00484-005-0273-3
	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. http://dx.doi.org/10.3168/jds.2013-7621







  
Intellectual Property Rights

    Authors of Knowledge Summaries submitted to RCVS Knowledge for publication will retain copyright in their work, but will be required to grant to RCVS Knowledge an exclusive licence of the rights of copyright in the materials including but not limited to the right to publish, re-publish, transmit, sell, distribute and otherwise use the materials in all languages and all media throughout the world, and to licence or permit others to do so.

    Authors will be required to complete a licence for publication form, and will in return retain certain rights as detailed on the form.