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Effect of Ambient Temperature and Humidity on Plasma Cortisol in Sheep
Br. vel.). (1982). 138, 175
EFFECT OF AMBIENT TEMPERATURE AND HUMIDITY ON PLASMA CORTISOL IN SHEEP
BY
V. H .
GUERRI N I* AN D
H . B ERTC HI NG ER
Department of Physiology, Pharmacology and Toxicology, Faculty of Veterinary Science, OnderslejJoort OJ 10, Rejmblic of South Africa
SU M MA RY
Pl as ma co rti so l, water inta ke, urin e o utput a nd th e packed ce ll vo lum e (PC V ) were d e termin ed in six adult M erin o we th e rs ex posed to ho t-humid , ho t-dry, cool-humid a nd coo l-dry environm en ts . Th e te mpera ture-humidity ind ex (THI ) was used to d e termin e th e co mbin ed effect of a mbi en t tempera ture a nd humidi ty on th e va lu es meas ured . T he lowes t m ea n p las m a co rti sol va lu es ( 19·03 ± 6· 23 nm ol/ 1) we re fou nd durin g ex pos ure to th e hot- humid environm ent a nd the hig hes t (43·64 ± 9·86 nm ol/ 1) during expos ure to th e cool-humid environm e nt. During exposure to th e ho t-dry a nd cool-dry environm ents, m ea n pl as m a co rti so l leve ls ra nged bet wee n 32·53 nm ol/ 1 a nd 4 1·56 nm ol/ 1. In creased THI va lu es were co rrelated with d ecreased pl as m a co rti so l (P <0·005) . Sh ee p whi ch h ad hig h pl as m a corti so l levels (3 2·2 1 to 58·6 1 nm ol/ 1) co nsum ed less wate r a nd ha d a lower urin e o u tpu t but a hig her PC V va lue th a n s hee p whi ch had low pl as ma co rti so l leve ls (8· 13 to 32· 13 n mol/1). In a ll th e shee p in creased pl as ma co rti so l was co rrela ted wi th d ec reased water in ta ke (P < 0·005), decreased urin e outpu t (P < 0·005) , bu t in c reased PC V (P
I NTRO D UCT I ON
E xperim e n ts ca r ried out in s heep by Ro binson & M orri s ( 1960), a nd late r by ';:'i lton , W eig l & Bu cha na n ( I 975) showed th a t d ur ing the first d ays of ex pos ure to a ho t environm e nt , pl as ma co rti so l in creased . If ex pos ure to th e hot enviro nm en t was p rolo nged p las ma co rti so l d ecreased. M o re rece ntl y, Ing ra ha m , Sta nl ey & W agner • Prese nt add ress: I.e M ils d ' /\ la ux, l.ot isscmcm Cadi lh ac, /\v . Vill ene uve d ' /\ngo ul cmc, M o n tpc lli c r 3•f I 00, Fra nee.
176
BRI T I SH V ETER I N ARY JOU RNA L, 138,2
( 1979) found simil a r res u lts in cattle w hi ch h a d b ee n exposed to a h o t e nv iro nm en t. In s h eep , th e initi a l in crease in co rti co id s o n ex p os ure to a h o t enviro nm e n t m ay occur as a respo n se to s tress, wh e reas th e d ec rease in pl as m a co rti sol durin g pro lo n ged h ea t expos ure m ay b e rel a ted to a d a p tat io n to st ress ful co nditi o n s (Til to n et al., 19 75). Beca use pl as m a co rti sol va lu es a r e m o difi ed b y s tress, clim a ti c eva lu a ti o ns mu st includ e th e str ess indu ced by hi g h a mbi ent humidi ty during ex pos ure to a h o t o r a coo l en v iro nm ent ( K elly & Bo nd , 197 1) . I t is fo r thi s reaso n th a t th e te mpe r a tu re- humi d ity ind ex (THI ) whi c h co mbin es th e e ffect o f a mbi en t te mpe ra ture a nd humidity o n a nim a ls w as fo rmul a ted ( I ng ra h a m et al., 19 79) . U nfo rtun a te ly, th e e ffect o f ex pos ure to a humid enviro nm e nt as co mp a red to a dr y en v iro nm e nt o n th e pl as m a co rti so l va lu es o f rumin a nts h as ra re ly bee n d escrib ed. Th ese findin gs U"11d e rlin e th e n eed to d e termin e p las m a co rtiso l in s h ee p ex p osed to diffe re nt e nviro nm e n ta l te mpe r a tures a nd humidi ty. Expe rim ents ca rri ed o ut b y Ba lfo ur ( 1962), with ca ttl e, a nd b y f a n a nd hi s co ll a b ora tors ( 19 7 5), with s h ee p , s ho wed th a t co rti coid s exe rted s ig nifi ca nt soci i u Illre ta ining ac tivi ty . O 'Co nn o r & V e rn ey ( 194·2) m a inta in ed th at th e prin c ipa l p las m a g lu coco rti co id s acco unted fo r 30 to 4 0% o f t h e sod ium-re ta inin g ac ti vit y in m a n . On th e o th er h a nd , exp erim ents h ave s ho wn th a t sod ium losses in c rease wh e n s h ee p a re ex posed to h o t enviro nm e nts (Co llin s & \ 1Ve in e r, 1968 ). R ece ntl y, Gu e rrini , K os te r & Bertchinge r ( 1980 ) d e m o nstra ted th a t th e urin e vo lum e o f s h ee p in cr eased durin g expos ure to a h o t-humid , a h ot-dry, a nd eve n a coo l- humid e nv iro nm e nt. In th e sa m e ex perim e nt, w a ter inta ke in c reased durin g b o th h o t e n v iro nm e nts but d ecreased o n ex p os ure to th e coo l-humid enviro nm e n t. Beca use bo th e n v iro nm e n ta l a nd co rti so l level ch a n ges m ay a ffec t bod y w a ter b a la n ce (Co ll in s & \A/e in e r, 1968; F a n el al. , 1975), th e re is a n eed to es ta blis h th e rel a ti o n s hip b e tw ee n pl as m a co rti so l co n ce n tra ti o n , urin e o utput a nd wa ter int a ke in s h ee p durin g expos ure to diffe re nt en v iro nm ents. L ee, R o u sse l & B ea t ty ( 1976) s h o wed th at hig h b lood co rti so l va lu es in c reased t h e pro du c ti o n o f red bl ood ce ll s in ca tt le. I n rece nt rev iew s, G u y to n ( 197 1) a nd H a rp e r , R o dw e ll & M ayes ( 1977) fo und th a t th e re was a p os itiv e co rre lat io n be tw ee n pl as m a co rti so l a nd PCV . Ex p e rim ents ca rri ed o ut in s h eep (G u e rrini et al. , 1980 ) s h ow ed th a t h o t- humid expos ure d ecreased PCV ; in co ntras t, ex p os ure to a h o t-dry e nv iro nm e nt in cr eased PCV . Beca use co rti so l m ay indu ce red ce ll produ ct io n , a nd e n v iro nm e n ta l c h a nges th e m se lves m ay a ffect PC V , th e re is a n eed to s tud y th e re la ti o ns hip b e twee n PCV a nd pl as m a co rt iso l in s h eep ex posed to diffe r ent e nv iro nm e nt s. The purpose o f th e prese nt ex p e r im e n t was to d esc rib e th e e ffect o f te m pe ra ture and humidi ty o n p las m a co rtiso l in s h ee p. A t th e sa m e tim e, th e e ffect of p las m a co rti so l c h a nges o n w a te r int a ke, urin e o utput a n d PCV we re in ves ti gated .
M ATERI A LS AND M ET HO DS
S ix a dult L ete ll e w e th e rs we ig hing betw ee n 48 a n d 52 kg we re use d fo r th e ex p e rim e n t. Th e s h ee p we r e ke pt in a n e n closed c h a m be r a nd ex posed to three tes t e n v iro nm e nts, eac h las tin g fo ur w ee ks: h o t- humid w ith hig h a m b ie nt te m pe ra tures (29 to 32°C) a nd humidity (89 to 9 7%), h o t- d ry wi th hi g h a mbi e n t te mp e ra tures (29 to 32°C) but lo w humidit y (4 9 to 53%), a nd coo l- humid w ith low a mbi en t te m pera t u res ( 18 to I9°C)
ENVIRO N1v1 ENT AND PLASMA CORT ISOL IN S H EE P
177
but high humidity (92 to 96%). Studies were a lso und erta ken ove r fo ur 'control' period s in a coo l-d ry e nviro nm ent each of three wee ks duration, befo re , betw ee n a nd a fte r th e three tes t pe ri od s. In th ese co ntrol period s th e a mbi ent tem perat ure range was 19 to 23°C a nd a mbi ent humidity range 54 to 6 1% . Milled lu ce rn e grass a nd wate r were suppli ed each d ay be tw ee n 0800 a nd 08 30 h . Each d a y, wa ter inta ke and urin e output were m eas ured at 0800 h. Ambi ent tem p eratures a nd humidity were reco rd ed co ntinu ous ly on a tam bo ur h ygrograp h (C ase ll a, London ) whi ch w as reg ul a rly ca librated to a ± 4% error m a rg in ; th e recordings a t 0800 h each d ay were used fo r stat isti ca l a na lys is . T he te mpe rat ure a nd humidi ty we re not a ll owed to va ry by m ore than ± 4% durin g a ny 24- h period . Blood samples were co ll ec ted fro m th e jugu la r vein eve ry seventh d ay be tw ee n 0800 a nd 0830 h. T he pac ked ce ll vo lum e was determ in ed b y the mi croca pill a ry me thod. Dupli ca te p las m a co rti so l concentrations were th en d etermin ed b y radioimmunoassay (Ba um , Ind o r & La nd o n, 1974·). M ea ns , sta nd a rd d evi a tion s a nd stand a rd e rro rs were ca lcul a ted a nd lin ea r regress ion a na lyses were used to test th e co-va ri a nce be tween th e va lu es m eas ured . Th e THI values were d e termin ed using th e equ a tion: THI = ( Tc~ b )- (0· 55- 0·55RH) (T ell>- 58) wh ere T ell> was the dry bu lb te mp erat ure, a nd RH was amb ient rela tive humidity ex pressed as a pa rt of I (Kell y & Bo nd , 197 1) .
RESUL.TS
Of th e six sheep studi ed , three co nsiste ntly had lower m ea n pl as m a co rti so l co nce ntra ti ons (8· 13 to 32·13 nmo l/ 1) th a n th e o th er three (32·2 1 to 58·6 1 nm o l/ 1) wh en exposed to the different environm ental conditions. Fo r thi s reaso n in prese ntin g the res ults in Fi g . I a nd Tab le 1 f th e shee p were divided into ' low' an d ' hi g h' g ro ups res pe ctively. T a bl e I shows the li nea r co rrel a tion s betwee n a ll th e va ri a b les m eas ured , i.e. hae m atoc rit, pl as m a co rti so l co nce ntrat io n , urin e output a nd wa ter intak e , w hen the s hee p were ex posed to d iffe rent enviro nm enta l co nditio ns.
TABLE I
SIMPL E CO RR ELATIO NS OF PL.ASiv! A CO RTI SO L \VITH THE TE MP ERATURE H U MIDITY I N DE X JTI-II J, WATER I NTAK E, UR I NE OU TP UT AND PAC KED C ELL VOLUME ( PCV) I N SI X SHEEP EXPOSED T O HOT -H UM ID , I-l OT-DRY AND COO L- H U MID ENV IR ON ME NTS
environments
Hal-f humid
Hot-f dl)'
Cool-f humid
-0·38 -0·30 -0·39 0·53
-0·40 -038 0·40
- 0·7 1 -05 1 0· 38
- 0·30 -0. 40 0·55
il ll*
THI unit s
VVa ter intake 1/ day U rin e outputl / day PC V %
* 144 pa irs tes ted .
t
24 pa irs tes ted .
TABLE II !'vi EJ\N ±SO WATER INTAKE, UR I NE OUTPUT, BODY WE I GH T AN D PA C KED CE LL VOL UME I N SIX MER I NO WETHERS OF WH I C H T H REE HAD CONS I STENTLY 'H I GH' AND T H REE ' LO W ' PLASMA CO RT I SO L LEVELS D UR I NG EXPOSURE TO HOT-HUMID, HOT-DRY , COO L-HUMID AND COO L -DRY ENV I RONMENTS
Hot-humid High
Low
High
Cool-dry
Cool-humid
Hot-dry Low
H igh
Low
High
26·2 1 ± 9·53 3·40 ± 0·55 2·02 ± 0·73 36·58 ± 2·8 1
42·03 ± 19·52 3·29 ± 0·36 0·89 ± 0·38 38·62 ± 4·06
Low 2
Pl as ma co rt iso l n mo l/ I * vV ate r int a ke !/ da y Urin e out put !/ d ay
PVC%* Bod y weight kg *
t t
27·91 ± 17·2 1 3·34· ± 1·04· 1· 17 ± 0·82 35·08 ± 3·23 53·20 ± 2·20
10·3 1 ± 4·23 4·47 ± 1· 10 1· 18 ± 1·01 3 1·50 ± 2·93
60·74 ± 20·3 1 4·63 ± 0·77 0·93 ± 0·43 36·50 ± 3·65 54·70 ± 1·40
19· 12 ± 9·43 5· 78 ± 0·69 1· 91 ± 0·2 1 33·50 ± 2·87
59· 58 ± 22·76 2·64 ± 0·9 1 1·37 ± 0·35 38·60 ± 3·22 56·00 ± 1·80
21·52 ± 13·86 3·99 ± 0·49 1·32 ± 0· 16 35·54 ± 2·52 53·60 ± 1·30
* 24 measurements made during exposure to hot-humid , ho t-dry and cool- humid environm ents and 72 durin g coo l-dry exposu re. 168 m eas ure ments m ad e d urin g hot- hum id , hot-dry and cool-humid exposure a nd 504 du rin g cool-dry exposure.
t
> :::0 -<
'-
0
c
:::0
2
_> r
ENVIRONMENT AND PLASMA CORT ISOL IN SHEEP
179
45 ~
0
> 35
u
CL
25
w
-"" 0
c w 0
~
w c
...... 0
E
c 0
"'
Fig . I . M ea n urin e o utput , wa te r int a ke and PCV in M erin o sheep with high (n = 3) . an d low (n = 3) 0 plas m a cort iso l leve ls. The a nim a ls were exposed to ho t-humid (A), hot-dry ( B) a nd cool-humid (C) tes t en viro nm e nt s a nd a coo l-dry (D ) co mro l environment. Th e upper bar lin e represc m s ha lf o f th e s tanda rd deviation. Durin g each tes t env iro nment , 24 blood sa mples a nd 168 wa ter in take a nd urine output m eas urement s were ta ke n. Durin g com rol enviro nm e nt s, 72 bl ood sa mples a nd 501 wate r int a ke a nd urin e ou tput measu rcmem s were ta ken.
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BRITISH VETER INARY .J OU RNAL , 138 ,2
Th e lowest mea n individu a l plasma co rti sol level s were reco rd ed during ex pos ure to th e hot- humid en vi ron men t a nd th e hig hes t in th e coo l-humid co nditi o ns. In c re ased THT va lu es were statis ti call y co rrela ted (? < 0·005) with d ec reased p las ma co rti so l levels. Th e three sh ee p which h ad hi g h p lasma co rti so l va lues co ns um ed less wa te r (?< 0·05) a nd h a d a low er urin e o utput (P < O·Ol) but a hig h e r PCV (P < O·OOI) th a n the three sh ee p whi ch h ad lower p lasma cort isol va lu es (Fig. I) wh en ex posed to eac h of th e fo ur env iro nm e nts. \l\lithin each env iron m ent, individu a l body weights were no t sign ifi ca ntl y d iffe ren t. Lin ea r regress ion a n a lyses s howed th a t in a ll the s hee p increased pla s ma co rti so l conce ntra tion was related to d ecreased wa ter int a ke in the hot- humid (P < 0·05) a nd hot-d ry (? < 0·00 5) environme nts, a nd to d ecreased urine ou tput in the ho t-humid (P < 0·05), hot-dry (P
Th e p las m a cort iso l co ncentra tion was d e te rmin ed in cat tle by Cabe ll o ( 1980) wh o reported values ranging between 22 ·4·5 a nd 160·05 nm o l/ 1. In ex p e rim e nt s with ca t tle, Hud so n et al. ( 1976) found a m ea n plasma co rti so l conce ntra ti o n of 6 ng/ ml. Dur ing stress st udi es with shee p , Ti lton el al. ( 1975) found pla sm a co rti so l va lu es th a t ra nged between 2·53 ng/ ml a nd 6·29 ng/ ml. The ra nge of plasm a corti so l co nce ntra ti o ns fou nd in the prese nt experim e nt were s imil a r to th ose fou nd in prev io us tr ia ls with rumin a n ts. During ex pos ure to a hot-humid e nvironm e nt , m ea n p las m a cortisol co nce ntrat io n decreased betw ee n 70 % a nd 96% when co mp a red with th e sa me va lue s found in coo ldry cond iti o ns. In creased THI va lues were co rrela ted (P < 0·005) with d ecreased pl as m a corti so l. Thes e fin d in gs merely co nfirm the resu lts of previou s tri a ls. In g ra h a m el al. ( 1979) fou nd th a t prolonged hea t expos ure d e pressed pl as m a co rti so l in cat t le; T il to n et al. ( 1975) found simi lar results in sheep. Of interest, however, was th e findin g th at p lasma cort iso l levels we re d epressed throu g hout ho t-humid expos ure. Thi s resu lt s uggested th a t ifTHT va lu es rem a in ed a bove 84, p las m a co rti so l re m a in ed depressed . P las m a co rti so l m ay have in c reased during th e firs t d ays of h ea t exposure as h as bee n previously obse rved in ca ttl e (A lva rez & J o hn so n , 19 73) a nd sh ee p (T il ton el a!., 197 5). In the pres ent ex pe rim ent pl as m a samples were no t co ll ected until seve n days a ft e r expos ure began, therefore , we were unab le to desc ribe a h ypot h et ica l in c rease of pl as m a cort iso l during the firs t days of heat ex posure. The ad rena l co rti so l di sch a rge durin g th e initi a l ph ases of h eat exposure may have acco unt ed fo r a n ult e rior d e pl e tion of th e horm o n e (Rh ynes & Ewin g, 1973). Thi s ph eno m e no n m ay exp la in w h y pl as m a cortiso l a pp ea red to d ec rease durin g prol o nged hea t ex posu re . Th e res u lts show th a t pl as m a co rti so l co nce ntra tio n de creas ed s ig nifica ntl y (P < 0·005) more durin g ex po sure to a ho t-h u mid environment t ha n to a ho t-dry one.
EN ViRO NMEN T AN D PLASMA CORTISOL I N SH EE P
18 1
This findin g s uggests th a t during h eat expos ure th e ve ry humid environm en t depressed co rti so l va lu es furth er . In a ddition , it und erlin ed the need to relate the TH I , a nd not a mbient tempera ture a lone, with blood para m e ters in o rd er to determine th e effects of clim a te on rumin a nts . In gram & M o unt (1975) fo und that sheep were less stressed in a hot-dry enviro nm ent than in a hot- humid one . I f th e ex tent o f the d ecrease in pl as ma co rti sol durin g h eat ex pos ure is a n acc ura te indi cation of the degree of chro nic stress in sh ee p , the res ults of th e present ex perim ent s uggest th at th e shee p were less stressed during th e ho t-dry env iro nm ent than during th e ho t-humid o ne . Th e lowest THI va lu es (63 to 65) w ere hig hl y co rrela ted (? < 0·005) with the hig hes t plas ma cortisol va lu es (66 to 96 nmol / 1). Simil a rl y, th e hig hest THI va lu es (84 to 88) were hig hly co rrel a ted with the lowes t pl as m a cort iso l va lu es (4 to 7 nmol / 1). In contras t, inte rmed iate THI va lu es (65 to 70) were not statisti ca lly re lated (P < 0·3) with interm ediate p las ma co rti so l va lu es (40 to 50 nmol/1). Th ese findin gs indi ca te th a t extrem e, rather th a n intermedi a te, THI va lu es were like ly to produ ce sig nifi ca n t cha nges in the pl as m a co rti sol va lu es of sh ee p . In o rd er th erefor e to induce sig nifi ca nt co rti co id cha nges due to ex posu re to diffe rent a mbi ent tempera tures a nd humidity , THI va lues a bove 80 o r below 60 sho uld b e so ug ht. Th e res ults a lso s how th a t the shee p which ha d hig h pl as m a co rti sol values co ns um ed less wa te r a nd had a lower urin e o u tput than sheep with hig h pl asma co rti so l levels. In additi o n , lin ea r regress ion a na lys is indi cates th at in creased pl as m a co r tiso l was co rrela ted with d ecreased wa ter inta ke (? < 0·005) a nd d ecreased urin e output (?< 0·005) in a ll th e shee p throughout th e ex perim ent. Th ese findin gs concur with those of Fa n et al. ( 1975) in ex pe rim ents o n shee p a nd those o f O 'Con no r & V ern ey ( 1942) who m a inta in ed th a t co rti coi d s exerted sig nifi ca n t sodium-re tai ning act ivity. Fan et al. ( 19 75) obse rved that wa ter in ta ke a nd urin a ry sod ium d ec reased in shee p whi ch had been infu sed w ith co rti co id s whil e at the sa m e time p las m a sod ium co nce ntra tion in c reased . In the prese nt ex perim ent , wa ter in take m ay have d ecreased when co rti so l in creased because water a nd sodium losses d ecreased . Th ese findings s ugges t th at hig h co rti so l leve ls exe rt sig nifi ca nt water a nd sodium -reta ining ac tivity during ex pos ure to coo l enviro nm ents. In co ntrast, in th e hot-humid environ m e nt , low co rti so l values m ay have bee n related to th e in creased urin e output a nd in creased urin a ry sodium losses o bse rved. It sho uld be noted th a t various a utho rs (C ollin s & W ein er , 1968; Thompson, 1973) reco rd th at sodium losses in creased in sh ee p exposed to hot en v iro nm ents. Th ese findin gs co ntras ts with the we ll- known ph e nom eno n of redu ct ion in sod ium loss in m a n when exposed to hot e nvironm ents. Th e prese nt expe rim ent shows th a t in c reased pl as m a co rti so l is co rrelated w ith a n in creased PCV (P< O·OO I ). Th e lin ea r relat io nship be tw ee n th ese pa ra m ete rs was sign ifi ca nt d urin g each ex pos ure peri od. Thi s findin g indi cates th at pl as m a cortiso l cha nges caused by environ m enta l m odifi cat io ns we re ab le to a ffec t red bl ood ce ll produ ct io n o r PCV . Lee et al. ( 1976) observed simil a r effects in cat tl e. Th e res ults of the present ex p erim ent s uppo rt th e we ll- es ta blis hed co nce p t that cort iso l in creases red bl ood ce ll produ cti o n (G u y to n , 197 1). The hi g hly sig nifi ca nt co rre latio n found between pl as m a cortisol a nd PCV s ugges ts th at PCV m ay be a n acc ura te m eas ure o f p las m a co rti so l a nd hen ce of the st ress stat us o f rumin a n ts. Th e determinat io n of plas ma co rti so l leve ls therefore sho uld be accompan ied by a n assess m ent o f PCV during hea t-s tress s tudi es in rumin a nts.
BRITISH VETERINARY JOURNAL, 138,2
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ALVAREZ, M. B. & j OHNSON, H . D . ( 1973)Joumal of Dail)' Science 566, 189. BALfOUR, W. E. ( 1962). British Medical Bulletin 18 (2), 11 4. BAUM, C. K., I NDOR, R. & LANDON,] . ( 1974). Clinica Chimica !lela 5, 147. CABELLO , G. ( 1980). British Veterinary j ournal 136, 160. COLI. INS, K.]. & WEINER,]. S. ( 1968). Ph}'siological Reviews 48, 785 . FA N, ]. S. K., COGHLAN, ]. P., DENTON, D. A., ODDIE, C . j., SCOGG INS, B. A. & SHUI.Kf.S, A. A. ( 1975). American J oumal of Plrysiology 228, 1695. GUERRINI, V. H., KOSTER, N. & BERTCHINGER, H . (1980) . !lmel"ican j oumalofJ!eterinOIJ' l?esearch 41, 185 1. GUYTON, A. C. (1971). Textbook of .Medical Plrysiology. Phi lade lphi a: W. B. Saunders. H ARPER, H. A., RODWELl., V. \11/ . & MAYES, P. A. ( 1977). Review of Plrysiological Chemisl1J'· Ca lifornia: Lange. HUDSON, S., MULLFORD, M. , \>VHITI"LESTONE, V•i. G. & PAYNE, E. ( 1976 ). J oumalofDair_yScience
59, 744. I NGRAM, L. D. & MOUNT, E. L. ( 1975). Topics in En vironmental Ph)'Siology and Medicine; Man a111/ Animals in Hot Environments. New York: Springer-Verlag. I NGRAM, R. H., STANLEY, R. W. & \'\1AGNER, W . ( 1979). Americanjoumal of VeterinaT)' Research 40, 1792. KELLY, C. F. & BONO, T. E. ( 1971) . Bioclimalic Factors and Their Measurement: il Guide /o Environmental Research on Animals. W as hin gto n DC: Nationa l Academy of Sciences. LEE, j . A., ROUSSEL, j. D . & BEATTY, j. F. ( 1976)Joumal of Dail)' Science 59, I 04·. O'CONNOR, W . J. & V ERNEY, E. B. ( 1942) . Quarterly Journal of Exj;erimental PhJ> Siology 31, 393. RHYNES, W . E. & EW ING, L. L. (1973). j oumalof!lnimalScience 36, 189. R0131NSON, K. W. & MORRIS, L. R . (1960). !lustralianjoumal of!lgriwltural Research 11 ,236. THOMPSON, G. E. ( 197 3). J oumal of Dail)' Research 40, 4-41 . Tn.TON , j . E., WEIGL, R. M. & BUCHANAN, M. L. ( 1975). J oumal of Animal Science 41, 382 .
{r1ccej;/ed for jmblicalion 14 Jul.J' /981)
ANNOUNCEMENT TH I RD WORKSHOP ON H ORMONES IN fv!ILK
following the two successful Vl o rks ho ps held in London ( 1976) and Nottingham ( 1979) a third meeting is plan ned for T hu rsday, 15 Apri l 1982 to be held in the Conference Centre, A.R.C. In st itute of Animal Physiology , Babraham, Cambridge. The programme wi ll in clud e papers on methodology, and a pp li catio ns o f mi lk progeste rone and milk oest roge n tests. For further deta il s please contact: Dr R. B. H eap, A.R.C. Institute of Animal Phys iology, Babraham , Cambridge CB2 4A T.
EFFECT OF AMBIENT TEMPERATURE AND HUMIDITY ON PLASMA CORTISOL IN SHEEP
BY
V. H .
GUERRI N I* AN D
H . B ERTC HI NG ER
Department of Physiology, Pharmacology and Toxicology, Faculty of Veterinary Science, OnderslejJoort OJ 10, Rejmblic of South Africa
SU M MA RY
Pl as ma co rti so l, water inta ke, urin e o utput a nd th e packed ce ll vo lum e (PC V ) were d e termin ed in six adult M erin o we th e rs ex posed to ho t-humid , ho t-dry, cool-humid a nd coo l-dry environm en ts . Th e te mpera ture-humidity ind ex (THI ) was used to d e termin e th e co mbin ed effect of a mbi en t tempera ture a nd humidi ty on th e va lu es meas ured . T he lowes t m ea n p las m a co rti sol va lu es ( 19·03 ± 6· 23 nm ol/ 1) we re fou nd durin g ex pos ure to th e hot- humid environm ent a nd the hig hes t (43·64 ± 9·86 nm ol/ 1) during expos ure to th e cool-humid environm e nt. During exposure to th e ho t-dry a nd cool-dry environm ents, m ea n pl as m a co rti so l leve ls ra nged bet wee n 32·53 nm ol/ 1 a nd 4 1·56 nm ol/ 1. In creased THI va lu es were co rrelated with d ecreased pl as m a co rti so l (P <0·005) . Sh ee p whi ch h ad hig h pl as m a corti so l levels (3 2·2 1 to 58·6 1 nm ol/ 1) co nsum ed less wate r a nd ha d a lower urin e o u tpu t but a hig her PC V va lue th a n s hee p whi ch had low pl as ma co rti so l leve ls (8· 13 to 32· 13 n mol/1). In a ll th e shee p in creased pl as ma co rti so l was co rrela ted wi th d ec reased water in ta ke (P < 0·005), decreased urin e outpu t (P < 0·005) , bu t in c reased PC V (P
I NTRO D UCT I ON
E xperim e n ts ca r ried out in s heep by Ro binson & M orri s ( 1960), a nd late r by ';:'i lton , W eig l & Bu cha na n ( I 975) showed th a t d ur ing the first d ays of ex pos ure to a ho t environm e nt , pl as ma co rti so l in creased . If ex pos ure to th e hot enviro nm en t was p rolo nged p las ma co rti so l d ecreased. M o re rece ntl y, Ing ra ha m , Sta nl ey & W agner • Prese nt add ress: I.e M ils d ' /\ la ux, l.ot isscmcm Cadi lh ac, /\v . Vill ene uve d ' /\ngo ul cmc, M o n tpc lli c r 3•f I 00, Fra nee.
176
BRI T I SH V ETER I N ARY JOU RNA L, 138,2
( 1979) found simil a r res u lts in cattle w hi ch h a d b ee n exposed to a h o t e nv iro nm en t. In s h eep , th e initi a l in crease in co rti co id s o n ex p os ure to a h o t enviro nm e n t m ay occur as a respo n se to s tress, wh e reas th e d ec rease in pl as m a co rti sol durin g pro lo n ged h ea t expos ure m ay b e rel a ted to a d a p tat io n to st ress ful co nditi o n s (Til to n et al., 19 75). Beca use pl as m a co rti sol va lu es a r e m o difi ed b y s tress, clim a ti c eva lu a ti o ns mu st includ e th e str ess indu ced by hi g h a mbi ent humidi ty during ex pos ure to a h o t o r a coo l en v iro nm ent ( K elly & Bo nd , 197 1) . I t is fo r thi s reaso n th a t th e te mpe r a tu re- humi d ity ind ex (THI ) whi c h co mbin es th e e ffect o f a mbi en t te mpe ra ture a nd humidity o n a nim a ls w as fo rmul a ted ( I ng ra h a m et al., 19 79) . U nfo rtun a te ly, th e e ffect o f ex pos ure to a humid enviro nm e nt as co mp a red to a dr y en v iro nm e nt o n th e pl as m a co rti so l va lu es o f rumin a nts h as ra re ly bee n d escrib ed. Th ese findin gs U"11d e rlin e th e n eed to d e termin e p las m a co rtiso l in s h ee p ex p osed to diffe re nt e nviro nm e n ta l te mpe r a tures a nd humidi ty. Expe rim ents ca rri ed o ut b y Ba lfo ur ( 1962), with ca ttl e, a nd b y f a n a nd hi s co ll a b ora tors ( 19 7 5), with s h ee p , s ho wed th a t co rti coid s exe rted s ig nifi ca nt soci i u Illre ta ining ac tivi ty . O 'Co nn o r & V e rn ey ( 194·2) m a inta in ed th at th e prin c ipa l p las m a g lu coco rti co id s acco unted fo r 30 to 4 0% o f t h e sod ium-re ta inin g ac ti vit y in m a n . On th e o th er h a nd , exp erim ents h ave s ho wn th a t sod ium losses in c rease wh e n s h ee p a re ex posed to h o t enviro nm e nts (Co llin s & \ 1Ve in e r, 1968 ). R ece ntl y, Gu e rrini , K os te r & Bertchinge r ( 1980 ) d e m o nstra ted th a t th e urin e vo lum e o f s h ee p in cr eased durin g expos ure to a h o t-humid , a h ot-dry, a nd eve n a coo l- humid e nv iro nm e nt. In th e sa m e ex perim e nt, w a ter inta ke in c reased durin g b o th h o t e n v iro nm e nts but d ecreased o n ex p os ure to th e coo l-humid enviro nm e n t. Beca use bo th e n v iro nm e n ta l a nd co rti so l level ch a n ges m ay a ffec t bod y w a ter b a la n ce (Co ll in s & \A/e in e r, 1968; F a n el al. , 1975), th e re is a n eed to es ta blis h th e rel a ti o n s hip b e tw ee n pl as m a co rti so l co n ce n tra ti o n , urin e o utput a nd wa ter int a ke in s h ee p durin g expos ure to diffe re nt en v iro nm ents. L ee, R o u sse l & B ea t ty ( 1976) s h o wed th at hig h b lood co rti so l va lu es in c reased t h e pro du c ti o n o f red bl ood ce ll s in ca tt le. I n rece nt rev iew s, G u y to n ( 197 1) a nd H a rp e r , R o dw e ll & M ayes ( 1977) fo und th a t th e re was a p os itiv e co rre lat io n be tw ee n pl as m a co rti so l a nd PCV . Ex p e rim ents ca rri ed o ut in s h eep (G u e rrini et al. , 1980 ) s h ow ed th a t h o t- humid expos ure d ecreased PCV ; in co ntras t, ex p os ure to a h o t-dry e nv iro nm e nt in cr eased PCV . Beca use co rti so l m ay indu ce red ce ll produ ct io n , a nd e n v iro nm e n ta l c h a nges th e m se lves m ay a ffect PC V , th e re is a n eed to s tud y th e re la ti o ns hip b e twee n PCV a nd pl as m a co rt iso l in s h eep ex posed to diffe r ent e nv iro nm e nt s. The purpose o f th e prese nt ex p e r im e n t was to d esc rib e th e e ffect o f te m pe ra ture and humidi ty o n p las m a co rtiso l in s h ee p. A t th e sa m e tim e, th e e ffect of p las m a co rti so l c h a nges o n w a te r int a ke, urin e o utput a n d PCV we re in ves ti gated .
M ATERI A LS AND M ET HO DS
S ix a dult L ete ll e w e th e rs we ig hing betw ee n 48 a n d 52 kg we re use d fo r th e ex p e rim e n t. Th e s h ee p we r e ke pt in a n e n closed c h a m be r a nd ex posed to three tes t e n v iro nm e nts, eac h las tin g fo ur w ee ks: h o t- humid w ith hig h a m b ie nt te m pe ra tures (29 to 32°C) a nd humidity (89 to 9 7%), h o t- d ry wi th hi g h a mbi e n t te mp e ra tures (29 to 32°C) but lo w humidit y (4 9 to 53%), a nd coo l- humid w ith low a mbi en t te m pera t u res ( 18 to I9°C)
ENVIRO N1v1 ENT AND PLASMA CORT ISOL IN S H EE P
177
but high humidity (92 to 96%). Studies were a lso und erta ken ove r fo ur 'control' period s in a coo l-d ry e nviro nm ent each of three wee ks duration, befo re , betw ee n a nd a fte r th e three tes t pe ri od s. In th ese co ntrol period s th e a mbi ent tem perat ure range was 19 to 23°C a nd a mbi ent humidity range 54 to 6 1% . Milled lu ce rn e grass a nd wate r were suppli ed each d ay be tw ee n 0800 a nd 08 30 h . Each d a y, wa ter inta ke and urin e output were m eas ured at 0800 h. Ambi ent tem p eratures a nd humidity were reco rd ed co ntinu ous ly on a tam bo ur h ygrograp h (C ase ll a, London ) whi ch w as reg ul a rly ca librated to a ± 4% error m a rg in ; th e recordings a t 0800 h each d ay were used fo r stat isti ca l a na lys is . T he te mpe rat ure a nd humidi ty we re not a ll owed to va ry by m ore than ± 4% durin g a ny 24- h period . Blood samples were co ll ec ted fro m th e jugu la r vein eve ry seventh d ay be tw ee n 0800 a nd 0830 h. T he pac ked ce ll vo lum e was determ in ed b y the mi croca pill a ry me thod. Dupli ca te p las m a co rti so l concentrations were th en d etermin ed b y radioimmunoassay (Ba um , Ind o r & La nd o n, 1974·). M ea ns , sta nd a rd d evi a tion s a nd stand a rd e rro rs were ca lcul a ted a nd lin ea r regress ion a na lyses were used to test th e co-va ri a nce be tween th e va lu es m eas ured . Th e THI values were d e termin ed using th e equ a tion: THI = ( Tc~ b )- (0· 55- 0·55RH) (T ell>- 58) wh ere T ell> was the dry bu lb te mp erat ure, a nd RH was amb ient rela tive humidity ex pressed as a pa rt of I (Kell y & Bo nd , 197 1) .
RESUL.TS
Of th e six sheep studi ed , three co nsiste ntly had lower m ea n pl as m a co rti so l co nce ntra ti ons (8· 13 to 32·13 nmo l/ 1) th a n th e o th er three (32·2 1 to 58·6 1 nm o l/ 1) wh en exposed to the different environm ental conditions. Fo r thi s reaso n in prese ntin g the res ults in Fi g . I a nd Tab le 1 f th e shee p were divided into ' low' an d ' hi g h' g ro ups res pe ctively. T a bl e I shows the li nea r co rrel a tion s betwee n a ll th e va ri a b les m eas ured , i.e. hae m atoc rit, pl as m a co rti so l co nce ntrat io n , urin e output a nd wa ter intak e , w hen the s hee p were ex posed to d iffe rent enviro nm enta l co nditio ns.
TABLE I
SIMPL E CO RR ELATIO NS OF PL.ASiv! A CO RTI SO L \VITH THE TE MP ERATURE H U MIDITY I N DE X JTI-II J, WATER I NTAK E, UR I NE OU TP UT AND PAC KED C ELL VOLUME ( PCV) I N SI X SHEEP EXPOSED T O HOT -H UM ID , I-l OT-DRY AND COO L- H U MID ENV IR ON ME NTS
environments
Hal-f humid
Hot-f dl)'
Cool-f humid
-0·38 -0·30 -0·39 0·53
-0·40 -038 0·40
- 0·7 1 -05 1 0· 38
- 0·30 -0. 40 0·55
il ll*
THI unit s
VVa ter intake 1/ day U rin e outputl / day PC V %
* 144 pa irs tes ted .
t
24 pa irs tes ted .
TABLE II !'vi EJ\N ±SO WATER INTAKE, UR I NE OUTPUT, BODY WE I GH T AN D PA C KED CE LL VOL UME I N SIX MER I NO WETHERS OF WH I C H T H REE HAD CONS I STENTLY 'H I GH' AND T H REE ' LO W ' PLASMA CO RT I SO L LEVELS D UR I NG EXPOSURE TO HOT-HUMID, HOT-DRY , COO L-HUMID AND COO L -DRY ENV I RONMENTS
Hot-humid High
Low
High
Cool-dry
Cool-humid
Hot-dry Low
H igh
Low
High
26·2 1 ± 9·53 3·40 ± 0·55 2·02 ± 0·73 36·58 ± 2·8 1
42·03 ± 19·52 3·29 ± 0·36 0·89 ± 0·38 38·62 ± 4·06
Low 2
Pl as ma co rt iso l n mo l/ I * vV ate r int a ke !/ da y Urin e out put !/ d ay
PVC%* Bod y weight kg *
t t
27·91 ± 17·2 1 3·34· ± 1·04· 1· 17 ± 0·82 35·08 ± 3·23 53·20 ± 2·20
10·3 1 ± 4·23 4·47 ± 1· 10 1· 18 ± 1·01 3 1·50 ± 2·93
60·74 ± 20·3 1 4·63 ± 0·77 0·93 ± 0·43 36·50 ± 3·65 54·70 ± 1·40
19· 12 ± 9·43 5· 78 ± 0·69 1· 91 ± 0·2 1 33·50 ± 2·87
59· 58 ± 22·76 2·64 ± 0·9 1 1·37 ± 0·35 38·60 ± 3·22 56·00 ± 1·80
21·52 ± 13·86 3·99 ± 0·49 1·32 ± 0· 16 35·54 ± 2·52 53·60 ± 1·30
* 24 measurements made during exposure to hot-humid , ho t-dry and cool- humid environm ents and 72 durin g coo l-dry exposu re. 168 m eas ure ments m ad e d urin g hot- hum id , hot-dry and cool-humid exposure a nd 504 du rin g cool-dry exposure.
t
> :::0 -<
'-
0
c
:::0
2
_> r
ENVIRONMENT AND PLASMA CORT ISOL IN SHEEP
179
45 ~
0
> 35
u
CL
25
w
-"" 0
c w 0
~
w c
...... 0
E
c 0
"'
Fig . I . M ea n urin e o utput , wa te r int a ke and PCV in M erin o sheep with high (n = 3) . an d low (n = 3) 0 plas m a cort iso l leve ls. The a nim a ls were exposed to ho t-humid (A), hot-dry ( B) a nd cool-humid (C) tes t en viro nm e nt s a nd a coo l-dry (D ) co mro l environment. Th e upper bar lin e represc m s ha lf o f th e s tanda rd deviation. Durin g each tes t env iro nment , 24 blood sa mples a nd 168 wa ter in take a nd urine output m eas urement s were ta ke n. Durin g com rol enviro nm e nt s, 72 bl ood sa mples a nd 501 wate r int a ke a nd urin e ou tput measu rcmem s were ta ken.
180
BRITISH VETER INARY .J OU RNAL , 138 ,2
Th e lowest mea n individu a l plasma co rti sol level s were reco rd ed during ex pos ure to th e hot- humid en vi ron men t a nd th e hig hes t in th e coo l-humid co nditi o ns. In c re ased THT va lu es were statis ti call y co rrela ted (? < 0·005) with d ec reased p las ma co rti so l levels. Th e three sh ee p which h ad hi g h p lasma co rti so l va lues co ns um ed less wa te r (?< 0·05) a nd h a d a low er urin e o utput (P < O·Ol) but a hig h e r PCV (P < O·OOI) th a n the three sh ee p whi ch h ad lower p lasma cort isol va lu es (Fig. I) wh en ex posed to eac h of th e fo ur env iro nm e nts. \l\lithin each env iron m ent, individu a l body weights were no t sign ifi ca ntl y d iffe ren t. Lin ea r regress ion a n a lyses s howed th a t in a ll the s hee p increased pla s ma co rti so l conce ntra tion was related to d ecreased wa ter int a ke in the hot- humid (P < 0·05) a nd hot-d ry (? < 0·00 5) environme nts, a nd to d ecreased urine ou tput in the ho t-humid (P < 0·05), hot-dry (P
Th e p las m a cort iso l co ncentra tion was d e te rmin ed in cat tle by Cabe ll o ( 1980) wh o reported values ranging between 22 ·4·5 a nd 160·05 nm o l/ 1. In ex p e rim e nt s with ca t tle, Hud so n et al. ( 1976) found a m ea n plasma co rti so l conce ntra ti o n of 6 ng/ ml. Dur ing stress st udi es with shee p , Ti lton el al. ( 1975) found pla sm a co rti so l va lu es th a t ra nged between 2·53 ng/ ml a nd 6·29 ng/ ml. The ra nge of plasm a corti so l co nce ntra ti o ns fou nd in the prese nt experim e nt were s imil a r to th ose fou nd in prev io us tr ia ls with rumin a n ts. During ex pos ure to a hot-humid e nvironm e nt , m ea n p las m a cortisol co nce ntrat io n decreased betw ee n 70 % a nd 96% when co mp a red with th e sa me va lue s found in coo ldry cond iti o ns. In creased THI va lues were co rrela ted (P < 0·005) with d ecreased pl as m a corti so l. Thes e fin d in gs merely co nfirm the resu lts of previou s tri a ls. In g ra h a m el al. ( 1979) fou nd th a t prolonged hea t expos ure d e pressed pl as m a co rti so l in cat t le; T il to n et al. ( 1975) found simi lar results in sheep. Of interest, however, was th e findin g th at p lasma cort iso l levels we re d epressed throu g hout ho t-humid expos ure. Thi s resu lt s uggested th a t ifTHT va lu es rem a in ed a bove 84, p las m a co rti so l re m a in ed depressed . P las m a co rti so l m ay have in c reased during th e firs t d ays of h ea t exposure as h as bee n previously obse rved in ca ttl e (A lva rez & J o hn so n , 19 73) a nd sh ee p (T il ton el a!., 197 5). In the pres ent ex pe rim ent pl as m a samples were no t co ll ected until seve n days a ft e r expos ure began, therefore , we were unab le to desc ribe a h ypot h et ica l in c rease of pl as m a cort iso l during the firs t days of heat ex posure. The ad rena l co rti so l di sch a rge durin g th e initi a l ph ases of h eat exposure may have acco unt ed fo r a n ult e rior d e pl e tion of th e horm o n e (Rh ynes & Ewin g, 1973). Thi s ph eno m e no n m ay exp la in w h y pl as m a cortiso l a pp ea red to d ec rease durin g prol o nged hea t ex posu re . Th e res u lts show th a t pl as m a co rti so l co nce ntra tio n de creas ed s ig nifica ntl y (P < 0·005) more durin g ex po sure to a ho t-h u mid environment t ha n to a ho t-dry one.
EN ViRO NMEN T AN D PLASMA CORTISOL I N SH EE P
18 1
This findin g s uggests th a t during h eat expos ure th e ve ry humid environm en t depressed co rti so l va lu es furth er . In a ddition , it und erlin ed the need to relate the TH I , a nd not a mbient tempera ture a lone, with blood para m e ters in o rd er to determine th e effects of clim a te on rumin a nts . In gram & M o unt (1975) fo und that sheep were less stressed in a hot-dry enviro nm ent than in a hot- humid one . I f th e ex tent o f the d ecrease in pl as ma co rti sol durin g h eat ex pos ure is a n acc ura te indi cation of the degree of chro nic stress in sh ee p , the res ults of th e present ex perim ent s uggest th at th e shee p were less stressed during th e ho t-dry env iro nm ent than during th e ho t-humid o ne . Th e lowest THI va lu es (63 to 65) w ere hig hl y co rrela ted (? < 0·005) with the hig hes t plas ma cortisol va lu es (66 to 96 nmol / 1). Simil a rl y, th e hig hest THI va lu es (84 to 88) were hig hly co rrel a ted with the lowes t pl as m a cort iso l va lu es (4 to 7 nmol / 1). In contras t, inte rmed iate THI va lu es (65 to 70) were not statisti ca lly re lated (P < 0·3) with interm ediate p las ma co rti so l va lu es (40 to 50 nmol/1). Th ese findin gs indi ca te th a t extrem e, rather th a n intermedi a te, THI va lu es were like ly to produ ce sig nifi ca n t cha nges in the pl as m a co rti sol va lu es of sh ee p . In o rd er th erefor e to induce sig nifi ca nt co rti co id cha nges due to ex posu re to diffe rent a mbi ent tempera tures a nd humidity , THI va lues a bove 80 o r below 60 sho uld b e so ug ht. Th e res ults a lso s how th a t the shee p which ha d hig h pl as m a co rti sol values co ns um ed less wa te r a nd had a lower urin e o u tput than sheep with hig h pl asma co rti so l levels. In additi o n , lin ea r regress ion a na lys is indi cates th at in creased pl as m a co r tiso l was co rrela ted with d ecreased wa ter inta ke (? < 0·005) a nd d ecreased urin e output (?< 0·005) in a ll th e shee p throughout th e ex perim ent. Th ese findin gs concur with those of Fa n et al. ( 1975) in ex pe rim ents o n shee p a nd those o f O 'Con no r & V ern ey ( 1942) who m a inta in ed th a t co rti coi d s exerted sig nifi ca n t sodium-re tai ning act ivity. Fan et al. ( 19 75) obse rved that wa ter in ta ke a nd urin a ry sod ium d ec reased in shee p whi ch had been infu sed w ith co rti co id s whil e at the sa m e time p las m a sod ium co nce ntra tion in c reased . In the prese nt ex perim ent , wa ter in take m ay have d ecreased when co rti so l in creased because water a nd sodium losses d ecreased . Th ese findings s ugges t th at hig h co rti so l leve ls exe rt sig nifi ca nt water a nd sodium -reta ining ac tivity during ex pos ure to coo l enviro nm ents. In co ntrast, in th e hot-humid environ m e nt , low co rti so l values m ay have bee n related to th e in creased urin e output a nd in creased urin a ry sodium losses o bse rved. It sho uld be noted th a t various a utho rs (C ollin s & W ein er , 1968; Thompson, 1973) reco rd th at sodium losses in creased in sh ee p exposed to hot en v iro nm ents. Th ese findin gs co ntras ts with the we ll- known ph e nom eno n of redu ct ion in sod ium loss in m a n when exposed to hot e nvironm ents. Th e prese nt expe rim ent shows th a t in c reased pl as m a co rti so l is co rrelated w ith a n in creased PCV (P< O·OO I ). Th e lin ea r relat io nship be tw ee n th ese pa ra m ete rs was sign ifi ca nt d urin g each ex pos ure peri od. Thi s findin g indi cates th at pl as m a cortiso l cha nges caused by environ m enta l m odifi cat io ns we re ab le to a ffec t red bl ood ce ll produ ct io n o r PCV . Lee et al. ( 1976) observed simil a r effects in cat tl e. Th e res ults of the present ex p erim ent s uppo rt th e we ll- es ta blis hed co nce p t that cort iso l in creases red bl ood ce ll produ cti o n (G u y to n , 197 1). The hi g hly sig nifi ca nt co rre latio n found between pl as m a cortisol a nd PCV s ugges ts th at PCV m ay be a n acc ura te m eas ure o f p las m a co rti so l a nd hen ce of the st ress stat us o f rumin a n ts. Th e determinat io n of plas ma co rti so l leve ls therefore sho uld be accompan ied by a n assess m ent o f PCV during hea t-s tress s tudi es in rumin a nts.
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{r1ccej;/ed for jmblicalion 14 Jul.J' /981)
ANNOUNCEMENT TH I RD WORKSHOP ON H ORMONES IN fv!ILK
following the two successful Vl o rks ho ps held in London ( 1976) and Nottingham ( 1979) a third meeting is plan ned for T hu rsday, 15 Apri l 1982 to be held in the Conference Centre, A.R.C. In st itute of Animal Physiology , Babraham, Cambridge. The programme wi ll in clud e papers on methodology, and a pp li catio ns o f mi lk progeste rone and milk oest roge n tests. For further deta il s please contact: Dr R. B. H eap, A.R.C. Institute of Animal Phys iology, Babraham , Cambridge CB2 4A T.