Role of Prostaglandin  F_2α to Improve Breeding Efficiency in Dairy Cows

The breeding efficiency of dairy animals is directly related to the prosperity of dairy industry. Repeat breeding is one of the important reproductive disorders in dairy cattle and results in higher economic losses in dairy herds (Katagiri, 2011). The incidences of repeat breeding have been reported varying from herd to herd however, it ranged from 5 to 30 per cent (Yusuf et al, 2010). The variable incidence may be attributed to the heterogeneity or multi factorial causes of repeat breedng syndrome and the effect of locality and season (Ali et al, 2009). However, major causes of sub-fertility caused by repeat breeding can be divided into two categories: fertilization failure and embryonic death (Amiridis et al, 2009). Any deviation or prolongation in the breeding rhythm results in a progressive economic loss due to widening of the dry period, reduced calving, lactations during the life span of the animal, increasing culling and replacement cost, wasting semen and insemination cost and loosing genetic gain through increased generation interval (El-Khadrawy et al, 2011; Osman-Ergene, 2012) Low pregnancy rate in repeat breeding cow with delayed or an ovulatory condition may be attributed to hormonal imbalance together with uterine infection. Further, the synchrony between embryo survival and maternal environment is essential to restore normal fertility in repeat breeding animals. It can be maintained by correlation of adequate luteal function either by exogenous supplementation of progesterone or stimulations of steroidogenesis by use of leutinizing hormone. Administration of GnRH or hCG at the time of insemination favours LH surge, which results in improved pregnancyrate (Methwe et al, 2013). However, response to such therapy has been reported different in different animals (Sharma et al, 2003). During the last few years, several studies have been attempted to treat infertility in cows by using controlled internal drug release (CIDR), hormonal treatments such as gonadotropin releasing hormone (GnRH), gonadotropins (GnRH), estrogen and prostaglandin F (PGF2a) (Metwelly, 2006). Further, some of these hormones used for induction of lactation in repeat breeding cows which later showed better reproductive performance (Sharma, 2018). However, the most frequent use of these hormones in different combinations serves as an ultimate goal for improving the reproductive efficiency in cows. Likewise, numerous protocols are used in cow e.g., double dose PGF2alpha at 11 days intervals and GnRH injection the time of insemination. Under the field conditions, very fewer trials were conducted for the management of repeat breeding. Repeat breeding (RB), defined as cows failure to conceive from 3 or more regularly spaced services in the absence of detectable abnormalities, is a costly problem for the dairy producer . Repeat breeding is one of the major reproductive problem affecting reproductive efficiency and economy of milk production in cross bred dairy cows. Early embryonic mortality and fertilization failure are two major causes for repeat breeding syndrome in cows . The suggested maternal factors involved in repeat breeding syndrome in cow include the maternal age , genetic factor , uterine infection , hormonal dysfunctions , inadequate follicular growth  and inadequate nutrition  . The bull factors suggested as a possible cause of repeat breeding syndrome include bull fertility and semen quality . The environmental and management factors influencing repeat breeding syndrome include the lactational stress, size of the livestock, milk yield or calving season . Other managemental factors correlated to the incidence of repeat breeding syndrome include calving difficulty , estrus detection  , hygiene at artificial insemination and parturition  , improper site of deposition of semen in the female genital tract  , time of deposition and heat stress . Prostaglandin F2α (PGF2α) and its analogues are widely used as a luteolytic agent for the treatment of uterine conditions in dairy cattle reproduction. Consequently, a double protocol in which PGF2α given at a 7, 11 or 14 d interval was developed so that cows at a stage in the estrous cycle other than diestrus would have a functional corpus luteum when they received the second PGF2α dose . Following the second injection of PGF2α, the animals were inseminated either during detected estrus or at a fixed time which is usually between 72 to 80 h . The fixed time artificial insemination was generally carried out between 72 to 80 h as most animals treated were likely to have a synchronized estrus. The use of endogenous PGF2α have been shown as an essential part of ovulation process  , known to increase of uterine and oviductal contractility  which affects the sperm transport. There are few studies focused on the effect of PGF2α administration at the time of AI on pregnancy rate  . Oxytocin is used to increase conception rate by improving the sperm transport in the female reproductive tract of several species  . Clitoral massage which probably releases oxytocin following artificial insemination increased pregnancy in beef cows but not in beef heifers or dairy cows . But in another study, it had hardly any effect on pregnancy in cows. Cloprostenol is a synthetic prostaglandin F analogue. It is a FP(Prostaglandin F) receptor agonist, which shows 2α powerful luteolytic effects. It also stimulates the contraction of uterine and bronchial smooth muscle and produces vasoconstriction in some vessels. Anoestrous may be due to some conditions like abnormal pregnancy, early pregnancy, pyometra, endometritis, retention of placenta, maceration and mummification. So, get rid of this conditions cloprostenol is widely used. It has been now in vogue to administer PGF or its analogue in early 2α postpartum cows and buffaloes in order to hasten early resumption of cyclic ovarian activity and thereby to increase the reproductive efficiency. To improve reproductive efficiency, it is necessary to inseminate cows early in the breeding season so that, thereby achieving a more compact calving season. Breeding efficiency is increased by means of synchronization of estrus, conception rate and pregnancy rate. Estrus synchronization can be achieved by lysis of corpus luteum by administration of prostaglandin (PGF ) or its synthetic analogue on 5-17 2α days of the estrus cycle. The cows will return to estrus within 3-5 days. The effective therapeutic doses for cloprostenol are 500 µg in cattle and 175 µg in pigs. However, for R-cloprostenol, the recommended doses are: 150 µg in cattle and 75 µg in pigs. In both cases, it is administered by the intramuscular route.

Compiled  & Shared by- Team, LITD (Livestock Institute of Training & Development)

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