Biomedical Engineering Reference
In-Depth Information
affected by heat and 12 h of water deprivation,
than H Friesians and goats (Kamal et al.
1982
) .
In general, buffalo cows' volume of water
intake (free water ± water through feedstuffs),
metabolic water, water voided (faeces ± urine)
and water vaporisation were 20.9, 1.6, 17.3 and
5.3 L in winter season and 36.8, 2.3, 20.0 and
19.2 L, respectively, in summer season. The water
input (intake ± metabolic) was observed to be
about twofold in summer. Water vaporisation
increased by four times in summer as that of
winter. Voided water showed slight seasonal dif-
ference (Pal et al.
1975
). In Friesian cows, the
water inputs for free, dietary and metabolic water
were 19.05, 0.41 and 1.35 L/day, respectively,
under mild climate (16°C and 62% RH) and
31.16, 0.37 and 1.24 L/day, respectively, under
hot climate (39°C and 62% RH, for 7 h daily over
11 days). The water outputs for urinary, faecal and
total evaporative water losses were 7.07, 7.72 and
6.02 L/day under mild climate, respectively, and
were 9.61, 7.61 and 13.33 L/day, respectively,
under hot climate. The differences in all compo-
nents between the two climatic conditions were
significant except for faecal water output (Kamal
et al.
1982
). Particularly, chronic heat exposure
of 6- and 12-month-old buffalo calves was
accompanied with increases in total body water
content (8.52 and 9.63%), free water intake
(25.16 and 56.41%), total water intake (28.49 and
48.34%), urine excretion (24.79 and 108.0%) and
evaporative water loss (51.15 and 69.37%),
respectively. Significant decreases were also
observed in 6- and 12-month-old buffalo calves
in total body solids content (15.73 and 16.12%),
metabolic water (20.84 and 16.81%) and faecal
water excretion (36.42 and 8.49%), respectively
(Nessim
2004
). In order to maintain total body
water content at a relatively constant level, it
is important that a continuous water supply must
be provided.
reduced heart rates, profuse sweating (Blazquez
et al.
1994
), decreased feed intake (NRC
1981
) as
well as reduced milk production (Abdel-Bary
et al.
1992
). Physical responses to heat stress in
dairy cows are breed specific (Finch
1986
) , with
the
B
.
indicus
and other tropical breeds being less
responsive to thermal stress than
B
.
taurus
cattle.
The differences in response to heat stress between
cattle breeds are attributed to varying levels of
adaptability to hot environments. Sharma et al.
(
1983
) showed that, within
B
.
taurus
dairy cattle
breeds, the Jersey was less sensitive to thermal
stress than the Holstein-Friesian.
6.3
Sweating and Panting
Sweating plays an important role in heat
loss mechanisms of crossbred cattle. Excess heat
is dissipated by evaporation of sweat as a pro-
tective mechanism of the body against over-
heating. Though crossbreds have a limited
sweating capacity as compared to zebu animal,
they are able to increase sweating rate and dou-
bled the rate of evaporation from skin at ambient
temperature of 38°C and relative humidity of
59% (Upadhyay and Aggarwal
1997
) . The
efficiency of function and total output of sweat
glands can be increased by continuous exposure
to hot conditions. Crossbreds also increase pul-
monary frequency and ventilation rate in an
attempt to maintain a thermal equilibrium during
exercise under heat stress (Upadhyay and
Aggarwal
1997
). In buffaloes, pulmonary func-
tions increase with increase in ambient tem-
perature. Under mild hot conditions, low
respiratory frequency of buffaloes and high
volume of O
2
consumption and low pulmonary
volume may contribute partially to an improved
efficiency of energy utilisation, thus affecting
thermal equilibrium in buffaloes. Respiratory
evaporation has been found to be more important
in maintaining thermal homeostasis than sweat-
ing under hot conditions in buffaloes (Aggarwal
and Upadhyay
1998
; Fig.
3
) .
Increase in water evaporation in response to
increased ambient temperature was found in buf-
faloes and cattle by many workers (Kellaway and
6.2
Physiological Responses
Responses of the cow to temperatures above the
TNZ include raised respiration rates and rectal
temperature (Omar et al.
1996
) , panting, drooling,
