Pakistan by default is an agricultural country. Livestock is mainstay of the farming
communities and has exclusive position in national agenda of the development. It plays an
important role in poverty alleviation and can uplift the socioeconomic condition of our rural
masses. Livestock contribution to agricultural GDP is 55.9 % and its contribution to National
GDP is 11.8 % (Anonymous,2013-2014). Total cattle population of Pakistan is 39.7 M
(Anonymous, 2013-2014). Livestock, especially cattle, play an important role in agriculture
economy of Pakistan in form of milk, meat and draught power. Milk is one of the cheapest
sources of nutrition and is beneficial for the human health in all stages of life. Despite the
nutritional importance of milk, its per capita availability and consumption is low in our country.
This inadequacy is due to suboptimal performance of indigenous dairy cattle due to lack of
modern technologies in cattle farming.
Pakistan is blessed with the finest breeds of dairy cattle such as Sahiwal, Cholistani and
Red Sindhi. Sahiwal cattle breed initially named as Montgomery breed (Bos indicus) is one of
the important breeds of indigenous cattle in Pakistan having dairy characteristics. The average
milk yield is about 1500 liters per lactation with 4% butter fat. But still its potential of milk
production is far less as compared to the exotic breeds e.g. Holstein Friesian etc. This is
primarily due to compromised feeding and management and little attention in the past for the
selection and breed improvement in Sahiwal cows. Moreover, late age at maturity and longer
calving interval (Makuza and McDaniel 1996) are major reproductive issues in Sahiwal cows.
Introduction
2
Physiology of oestrus cycle has been extensively studied in Holstein cows ( ). With the
advent of ultrasonography in early 1980’s it became possible to study follicular and luteal
dynamics during the estrous cycle in detail in Bos taurus (Fortune 1994; Lucy et al. 1992; Savio
et al. 1988; Wolfenson et al. 1995), and some beef breeds of Bos indicus cattle (Bó et al. 2003;
Figueiredo et al. 1997) and in buffalo (bubalis bubalis) as well (Warriach and Ahmad 2007).
The benefit of these studies was that the information on follicular dynamics in Bos taurus breeds
has been used to manipulate the estrous cycle in order to improve estrus synchronization
(Thatcher et al. 1993; Twagiramungu et al. 1995; Wolfenson et al. 1994) fixed time artificial
insemination (FTAI) (Pursley et al. 1997; Schmitt et al. 1996a; Schmitt et al. 1996b;
Twagiramungu et al. 1995) and embryo transfer procedure (Mapletoft et al. 1994; Roberts et al.
1994).
Sahiwal is one of the established zebu cattle (bos indicus) milk breeds of tropical and
subtropical region. It is known for its remarkable power of endurance for hot climate, resistance
to ticks and other diseases and has high producing ability under harsh environment and low cost
of maintenance as compared to the Bos indicus and Bos taurus crossbreds. Due to its promising
dairy characteristics and better adaptation to tropical environmental conditions, both the semen
and female of this breed have been exported from Pakistan and in Africa and Australia.
Differences on the reproductive characteristics between Bos taurus and few breeds of Bos
indicus cattle have been reported like luteal tissue characteristics (Pathiraja et al. 1986), Graafian
follicle (DF) diameter (Figueiredo et al. 1997) and estrous cycle duration (Castilho et al. 1996).
However, surprisingly, there has been no thorough study on the reproductive physiology of the
estrous cycle in Sahiwal cows. Therefore, the objective of the present study is to determine the
Introduction
3
follicular dynamics, luteal tissue development and regression, estrous cycle length, timing of
ovulation, estrus signs and fertility.
It is hoped that these data will be helpful for improved assisted reproductive technology
e.g. AI, ET etc. (Andrabi and Maxwell., 2007), timing of the treatment of the various hormones
(Krininger et al., 2003) and development of new technologies like fixed time A.I, estrus
synchronization, super ovulation, embryo transfer in Sahiwal cows. Ultimately, these can
increase herd reproductive, productive performance and for preservation of Sahiwal cattle breed.