The influence of high environmental temperature on physi ol og ical react ions in general , and on blood compos it i on in p art ic- ular , depends on mahy factors , but mostly on moi sture loss by sweat ing. We have noted previously how man , a profusely sweat ing species , on exposure to high environment al temperatures , tends to become dehydrated w ith a consequent reduct ion in s erum volume. This increases the dry blood res idue. With c att l e , however , the mo isture los s i s bel ieved t o be relat ively low , and al so there
i s s ome evidence ( Brody) that cows tend rather to be hydrated
at high air temper atures and ur ine volume is increased , instead of decreased as in man , s o that the conc entrat ion of blood
cons t ituent s should t end to decreas e. "Swe at ing" �es of c attle - Indian breeds , may tend to react l ike man , but the
l i t erature i s sp ars e regarding influence of t emp erature on
Ind i an breeds and is oft en confused by having European breeds in the discus s i on as well.
( a ) Controlled
The only obs ervat ions on blood c omposit ion under controlled c ondi t i ons have been �ar r i ed out by Rieck and Lee ( 61 ) and
Erody ( 104) et al. The former found with Jers ey c ows at high
a ir t emperatures a marked fall in inorganic phosphate to 2. 95 mg. per lOO ml. b lood from 4. 96 , and a small drop in s erum c alcium from 10. 58 mg. per lOO ml. blood to 8. 64. A decrease
in bl ood sugar from 55. 22 mg. per lOO ml. blood to 44. 5 , was i n no way correlated with r i ses of temperature or humidity.
M e an red cell c ount showed no s igni f i c ant var i at i on. With c alves blood calc ium phosphorus , sugar and erithrocyt e l evel s , were unaffected.
On the other hand , Brody found that blood inorganic
phosphorus increased as t emperatures rose above 85°F. C alcium
declined somewhat , but due more to advanc ing l actat ion than t o
t emperatur e s . There was l ittle or no effect o� haemoglobin,
s eemed to decl ine definit ely aft er 85°F. The mos t marked
change , Brody found , v: as the creat inine which ro se to high levels.
Though having no data on creat inine level of the blood , a po ss ible exp l anat i on of thi s r j. se w as thought t o b e due t o a
damming up of creat inine as a result o f reduced met ab ol i s�
( b ) Field
Duckworth and Rattray ( 10 5 ) have reviewed the l iterature
on the haematology and Bos Taurus and Bos Ind icus c at tle. Many
w orkers have claimed higher erithrocyte counts in trop ical
breeds and al s o h igh leucocyte c ount s , and Duckwo rth and Ratt ray
i n their experiments with � bred Hol st e in c at t l e have subst ant i at ed thes e claims.
Manre s s a et al ( 106 ) ( 107) , working in the Phi l l ipp ine s , report s that haemoglob in l evel s could be used as a gu ide i n e v a luat ing adaptabil ity of the animals t o given environment al
c ondit ions. Nat ive Phill ippine and Nell ore oxen have higher
haemoglob in l evel s than imp ort ed exotic breeds. Crosses betwe en
indigenous and exot i c a resulted in int ermedi at e va lues. These indexes of Nel lore c attle are not s ignifi c antly di fferent from
those of the ex0t ic breeds in the ir own c ount ry , but imp o rt ed stock all show the decline. Th i s suggests that high a ir t emper ature depres ses haemoglobin levels and Manres s a et al t o ok
hourly sampl es of blood for a 24 hour per iod on 6 c onsecut i ve d ays and found a negat ive correl at i on between air t emperature and haemoglobin l evels throughout the day , in Nellom cattle.
A fu rther study showed that the number of red b l o od cel ls, spec ific gravity of the blood, and pho s phorus c a l c ium r at io s in the b l o od , have a p o s it ive relation t o the ab il ity of an imal s
t o adapt thems elves to hot temperature cond i t i ons. The
h igher value s of these factors were found in tho s e animal s o f
greatest adaptability. On the other h and , uric ac id, serum
phosphate, and s i ze of red blood cells were inversely correlat ed
to adaptability.
Bonsma ( 90 ) , S outh Afr i c a , without g iving any evidenc e
i f body temperature rises at high a ir temperature. Als o b l ood sugar cont ent , a lkal inity , and the non-prote in nitrogen l e vel s , are higher than in t emperat e c l imat es. The serum c alcium
i s als o high ' perhaps due to a plent ifUl supply of vit amin D
with the abundant sunshine c aus ing increased abs orpt ion of c alc ium. Bonsma also t a lks about the blood chlorides which d ecrease at high t emperatures.
B i s schop ( 108 ) at Onderst ep oort , South Afri c a , on the b a s i s o f two years work report s that Afri cander c attle have higher red cell count s and s how higher values for haemogl ob in and red p rec ipitat e than do the Fre i s i an and Red Poll c attle. He a l s o noted the s ame t endency for s ome of the other chemi cal c onst it uents.
1. Trop ical breeds of cattle have more erithrocytes and leucocytes than t emperate breeds.
2. The l it eratu re as a whole d oes not give a c lear cut determinat ion of the influence of cl imat ic element s on blood compos i t i on. Some few of the cl aims have not always been
b acked by exper iment al dat a. Great var i ab i l ity in the result s s e ems to be m maj or fact or cloua_ing the work. The blo od
p icture aspect of environment al phys iol ogy has not rece ived as much attent i on as other s ect ions.