Biomedical Engineering Reference
In-Depth Information
of timed artificial insemination on fertility in
summer has been investigated, and the results
suggest that exogenous hormone administration
can help overcome the effects of heat stress and
reduce summer infertility in cattle (Wolfenson
et al.
1994
; De La Sota et al.
1998
) .
The use of fixed time insemination (AI) has
the distinct advantage of not requiring the detec-
tion of oestrus and effective synchronisation
methods for fixed time AI have been developed.
They are based on administration of GnRH or
hCG to induce ovulation, followed by a luteolytic
dose of prostaglandin F
2a
6-7 days later and a
second treatment with GnRH or hCG 24-60 h
after the luteolytic treatment to induce a fertile
ovulation (Schmitt et al.
1996b
; Pursley et al.
1995,
1997
). During summer, these programmes
did not increase the number of cows pregnant to
the fixed time insemination, but they did increase
the number of cows pregnant by 120 days post-
partum and reduced the numbers of days open
(Almier et al.
2002
; Cartmill et al.
1999
) . These
results suggest that the principal benefit of these
treatments is to induce cyclicity and the develop-
ment of normal corpora lutea leading to good
fertility. These approaches lead to an increase in
the number of pregnant cows by increasing the
number of inseminations at oestrus.
days open, as well as increasing milk yield with
a significant return on investment (Avendano-
Reyes et al.
2006
; Urdaz et al.
2006
) . In addition
to thermal stress alleviation or proper cooling,
changing management practices may also help
reduce the severity of heat stress on animals
during summer or hot-humid conditions. There
should be at least 38-45 square feet of shade per
mature dairy cow to reduce solar radiation.
Spray and fan systems should be used in the
holding pen, over feeding areas, over the
feeding areas in some free stall barns and under
shades on dry lot dairies in arid climates. Exit
lane cooling is an inexpensive way to cool cows
as they leave the parlour. Providing enough
access to water during heat stress is critical.
Water needs increase 1.2-2 times during heat
stress conditions. Lactating cattle require 130-
175 l/day of water/day. Since milk is approxi-
mately 90% water, water intake is vital for milk
production and to maintain thermal homeosta-
sis. Various other attempts have been made to
overcome the effects of heat stress on fertility,
including the use of shade, fans, air-condition-
ing and sprinkler systems to cool animals during
summer (Igono et al.
1987
; Bucklin et al.
1991
;
Huber
1996
; Hansen
1997
; Aggarwal
2009
) .
The most widely used methods are cooling
systems that mist the cows with water from
overhead sprays and cool the air. The use of the
animal cooling systems has produced some
improvement of fertility, but they are unable
to match the level of normal winter fertility
(Armstrong
1994
; Huber
1996
) .
In a study on Tharparkar cows, the average
age at first conception was lower in cows kept
under comfort conditions (with shelter), that is,
23.87 months as against 25.88 months in animals
under stress condition (Razdan
1965
) . It was
found that physiological maturity was attained by
the animals in both normal and heat-stressed cows
simultaneously, but either the ova did not survive
or the inseminations were not successful due to
excessive heat loads on the animal.
Hot-humid environments have been asso-
ciated with low milk production and poor
reproductive efficiency (Hafez
1968
) because of
increased metabolic heat production associated
10.3
Improving Summer Fertility
It takes approximately 40-50 days for antral fol-
licles to develop into large dominant follicles
and ovulate (Roth et al.
2001b
) . If heat stress
occurs during this time period, both the follicle
and oocyte inside the follicle become damaged.
Once ovulation occurs, the damaged oocyte has
reduced chances of fertilising and developing
into a viable embryo. Cooling dry cows may
reduce heat stress effects on the antral follicle
destined to ovulate 40-50 days later, which
coincides with the start of most breeding peri-
ods and possibly increases first service concep-
tion rates. Heat alleviation or cooling dry cows
with feed line sprinklers, fans and shades has
been observed to be beneficial for reducing ser-
vices per conception, reproductive culls and
