Biomedical Engineering Reference
In-Depth Information
reproductive functions. Thus, genetic selection for
thermal tolerance may be a necessity for future
livestock production system in tropical climate
for sustaining and optimising productivity under
global climate change conditions.
Genetic influences on regulation of body
temperature have been well studied in cattle. In
cattle, estimates of the heritability of rectal tem-
perature range from 0.25 to 0.65°C (Finch
1986
) .
There are distinct breed differences in thermo-
regulatory ability (Hammond et al.
1996
; Hansen
2004
; Pereira et al.
2008
) . One speci fi c gene
affecting body temperature regulation of cattle
during heat stress, the
slick
gene affecting hair
length, has been identified (Olson et al.
2003
;
Dikmen et al.
2008
), and there are undoubtedly
many others. The superior thermoregulatory abi-
lity of zebu cattle has been ascribed to lower
metabolic rate, reduced resistance to heat flow
from the body core to the periphery and proper-
ties of the hair coat (Hansen
2004
) . In addition to
these, many more metabolic and morphological
features differ in Zebu from Taurus cattle.
Thus, it is likely that the direct impact of global
warming (i.e. consequences for body temperature
regulation) on reproduction will be more severe
for domestic animals than other mammals. In
addition, the existence of allelic variation in
genes controlling body temperature regulation
and cellular resistance to heat shock indicates
that genetic adaptation to increasing global
temperature will be possible for many species.
9
Reproduction in Buffaloes
Buffaloes under natural conditions have been
observed to breed during specific period and,
therefore, are believed to be seasonal breeders.
However, this is not entirely true as buffaloes are
polyestral and may be observed to breed all year
round. The buffalo is also regarded as a difficult
breeder mainly because of its inherent suscep-
tibility to heat stress, and prolonged exposure to
high solar radiation during summer may cause
anoestrus and sub-oestrus. The irregular or
anoestrus conditions in buffalo affect and prolong
inter-calving periods resulting in economic loss
to the farmers. Heat stress on buffalo also affects
its feed intake and in turn the nutritional balance
and reproductive efficiency. The ideal or opti-
mum climatic conditions for buffalo growth and
reproduction as suggested by Payne (
1990
) are
air temperatures of 13-18°C combined with an
average relative humidity of 55-65%, a wind
velocity of 5-8 km/h and a medium level of
sunshine. However, these conditions are likely
to vary for different adapted and non-adapted
buffalo breeds under different conditions.
Buffaloes have acquired several morphological
features which reinforce their ability to thrive well
in tropical and hot-humid conditions. The melanin
pigmentation of buffalo skin is useful for defence
against ultraviolet rays. Hair density in adult buf-
falo is only one-eighth of that in cattle (Hafez et al.
1955
), thus facilitating dissipation of heat by
convection and radiation in open conditions. Low
number of sweat glands in buffalo compared to
cattle results in a lower efficiency of sweating in
buffalo than in cattle. Furthermore, the number of
sebaceous glands is lower in buffalo than in cattle;
8
Consequences of Actions of
Climate Change on
Reproduction for Species
Survival and Distribution
As has been clearly indicated, heat stress can
have profound effects on most aspects of repro-
ductive functions in male and female livestock,
and functions like gamete formation, embryonic
development and fetal growth and development
may be affected. The potential impact of heat
stress can be assessed by examining seasonal
trends in reproductive function of different live-
stock species. A study carried out in Spain indi-
cates that the proportion of inseminated dairy
cows that become pregnant during the warm
months of the year was 22.1 versus 43.1% of
cows inseminated in the cool season (López-
Gatius et al.
2004
). Indeed, the magnitude of the
summer decline in fertility is much less for non-
lactating heifers or cows producing low amounts
of milk than it is for cows with high milk yield
(Badinga et al.
1985
; Al-Katanani et al.
1999
) .
