Genetic Basis of Estrous in Bovine: A Review

Worldwide there is a lot of interest in bovine as an animal to meet the growing demand of meat and milk in developing countries, but the productive potential of bovine is a major constraint leading to low productivity. The major reason for this low productivity is due to slow reproductive efficiency that is caused by late maturity, poor expression of estrous, silent heat, irregular estrous cyclicity, seasonality in breeding and anoestrous condition. Out of all these reasons of low productivity the major reason is that bovine’s exhibit silent heat that is not easily detectable. Estrous cycle as previously been discussed by many researchers is majorly affected by environmental and nutritional factors. The major focus in this paper is that apart from environmental and nutritional factors, genetic factors also play an important role in controlling the estrous behavior in bovine. Through different techniques like RT-PCR, Microarray, PCR-RFLP, SNP etc it has been estimated that almost 269 genes plays a significant role in estrous behavior. These genes undergo some significant changes at transcript levels during estrous cycle. By going through different papers and previously published papers it has been found that there are some major genes involved in controlling estrous behavior in bovine. Until now lot of research have been done in this aspect to find different polymorphisms in order find the different genes associated with estrous in bovine. Among the 269 gene the most studied genes and their related polymorphisms include CYP11A1, CYP19A1, CYP17A1, HSD17B, HSD3B, ER?, ER?, OXT, AVP, Leptin, and IGF1, GnRH, GnRH-R, etc. The gene CCK, POMC, MCHR1, GABRA6, HTR2A and DRD2 these are released in at least one brain area but are related to the modulation of emotional states like anxiety and also are involved in sexual motivation. The gene CYP19A1 belonging to P450 family is the major gene involved in the production of estrogen, a hormone that plays a significant role in estrous cycle. CYP11A1 is involved in the conversion of cholesterol into estrogen or steroids with pregnenolone formed. The estrogen receptors are the transcriptional factors that bind to estrogen and regulate their transcriptions. These have two isoforms ER? and ER? each are encoded by separate genes ER1 and ER2 respectively. Other than this some genes like oxytocin gene OXT. It is released in the brain where it acts on specific oxytocin receptor eliciting the behaviors like mating and partner bonding. In the presence of estrogen it is involved in mating. It is also involved in controlling the length of estrous. AVP gene is also involved in estrous behavior, whose expression is under the influence of progesterone and estrogen. Hence from the above mentioned discussion it can be concluded that apart from environmental, nutritional factors genetics also plays a pivotal role in controlling the estrous behavior in bovine.