**3. Alteration in the mechanism of female reproduction by heat stress**

Cattles reported an elevated occurrence of early embryo development during warm seasons for a variety of reasons. Heat stress leads to may adverse conditions at various phases of female reproduction (**Figure 1**). The direct impact of heat stress on oocyte competence and follicular is one of the major cause [2]. Furthermore, adverse impact of heat stress on cattle's super ovulation response, as well as the number and quality of recovered embryos [2]. The heat stress also reduces weight along with diameter of the corpus luteum, as well as the amount of progesterone it releases and the consistency of the oocytes, both contributes to pregnancy loss. The heat stress changes the endometrial environment by up regulating glycoprotein 2 and neurotensin, which can lead to infertility during the summer [11]. All of these reasons decrease the rate of fertilisation and the quality of any resulting embryos, raising the risk of pregnancy failure and lowering reproductive success. On the other hand, beef cattle [11] and dairy cattle have both shown this behaviour. The rate of conception in lactating cattle's decreases as the strength of the heat stress increases. The heat stress event can also affect conception rates from the month before breeding to two weeks after breeding [12]. In addition to these, heat stress is also linked to a smaller concepts scale, which could affect maternal pregnancy recognition and corpus luteum function [12]. Furthermore, heat stress has been linked to a compromised pregnancy during the pre-implantation phase, with an increased risk of foetal loss between days 21 to 30 of pregnancy [12]. The lack of blood flow in uterine can also show impact on nutrients supplementation to embryo and also lesser the secretion of hormones of uterus [12], can further have complicate things. The lactation of dairy cow is primarily effected by heat stress. During heat stress, non-lactating dairy animals and beef cattle are far less likely to become infertile. The conception rates in Holsteins decreased in the summer in Florida for lactating cattle's but not for non-lactating heifers [13]. However, the large amount of quantity of heat emission can process to lactation in the cattle's but the lactating cow is particularly vulnerable to heat stress. The lactation in cattle's will experience hyperthermia (high body temperature) at temperatures as low as 77-284°F [13].

**Figure 1.** *Impact of heat stress at various phase of female reproduction.*
