**6. Alteration in mechanism of male reproduction by heat stress**

The Bulls make up short of the herd, and their reproduction is straightly linked to the fertilisation of oocytes. In order to generate health of bull viability, and genetically modified potential ideas in bulls genes. In mammal species have unique physiological regulation known as thermoregulation that protect the reproductive activities from the climatic circumstances. The testicular temperature for spermatogenesis in bulls cannot go above 33–34°c [14] through spermatogonia to elongated spermatids, spermatogenesis mechanism of bovine is multifaceted which take 61 days to complete their process [17]. However, the timing of spermatozoa exposure to heat stress, as well as the time and withdrawal from heat stress. It is difficult to differentiate that at which phase of spermatogenesis the spermatozoa get affected by heat stress. The collecting ejaculate at the time of spermatogenesis phase denotes that heat stress disturbs the spermatogenesis cycle. Inefficient histone replacement by protamine's, resulting in sperm chromatin conformation shifts, is the cause of cell vulnerability at certain particular periods [17]. Hyperthermia has a detrimental impact on testicular function. The adverse impact of heat stress on reproductive tissue as show impact such as lack of germ cell, low morphology, lack of sperm count. According to requirements of specific cell the DNA of sperm nucleus arranged on basis of requirements. The specific type nuclear protein present in spermatozoon's which sets chromatin in more condensed structure between 6 to 20 times as compared to nucleosome-bound DNA, nucleus [17]. During spermatogenesis, heat stress alter the conformation of chromatin of sperm which further imbalance the conformation of DNA methylation which further represent in reorganisation of zygote [17]. The high compaction is due to the substitution of histone-bounded with chromatin with protamine-bounded with chromatin, which is needed for the secure liberation of DNA of sperm of oocyte in the female reproductive tract under the depletion of oxidative stress. Furthermore, the tremendously condensed sperm nucleus inhibits sperm DNA transcription. Protamine deficiency in the sperm nucleus causes DNA damage, which can result in male sub-fertility or infertility [17]. The heat stress increase the level of thiobarbituric acid reactive substance (TBARs) and also level of oxidative marker vice versa decreasing the level of

### **Figure 2.**

*Impact of heat stress on reproductive efficiency of male reproduction.*

glutathione peroxidise (GPx) and enzyme related to antioxidant in seminal plasma of bovines [14]. Bulls plasma luteinizing hormone (LH) levels are reduced by heat stress [14]. The reproductive efficiency of males gets majorly reduced by the impact of heat stress (**Figure 2**).

### **7. Impact of heatstress on embryo development**

The impact of heat stress can cause major impact on maturation of oocyte and development of oocyte competence. The fertilised females under the influence heat stress decline the embryo quality in cattle's [14]. During the fertilisation and implantation of embryo experience towards following phases such as cell proliferation, alteration in patterns of gene expression and cell differentiation. The heat stress significantly inhibits embryo growth 48–72 hours after fertilisation, which correspond to the 8–16 cell stage [14]. After this point, heat stress shows less impact on development and so on cell proliferation [14]. The embryos shows especially vulnerable to maternal heat stress in earliest phase of development as further as development processes the sensitivity towards heat stress. The proportion at which maturation of embryo take place to blastocyst stage after the 8th day of oestrus was decline. When lactating of cattle's were demonstrated on day 1 heat stress impact on oestrus (1-2 cell stage embryo). However, heat stress does not show any impact on blastocyst phase on eighth day [2].

The zygotic genome activation (ZGA) phase occurs at the 4th to 8th cell stage in cattle's [14] is the most vulnerable to heat stress in cow embryos. After the zygotic genome activation heat stress alter the conformation structure of chromatin of embryonic cell [14] potentially disrupting gene expression. Thus, heat stress causes apoptosis in embryonic cells in cattle's [14], and rabbits in addition to maturing oocytes [14].

### **8. Mitigation strategies for reduction of heat stress**

The heat stress impact on cattle's result in considerable financial losses as well as expensive for farmers, but there are following reduction method for heat stress to recoup any of these losses by implementing appropriate heat stress mitigation

*Adverse Impact of Heat Stress on Bovine Development: Causes and Strategies for Mitigation DOI: http://dx.doi.org/10.5772/intechopen.99307*

strategies. These techniques may be used individually or in combination to improve outcomes by ensuring the best possible atmosphere for farm animals to working farmers are more likely to follow policies that are both cost-effective and incorporate indigenous expertise. Environmental adjustment has traditionally been used to reduce heat load, with the focus on (i) minimising sunlight (ii) increasing air movement [12]. On the other hand wetting of cattle has been subject of research [12] observed that the causes of cooling in day and night, the utilisation of movement of air and water, management of heat load can be measured with help of changes in rectal temperature, respiration time and DMI. There many availabilities of mitigation option for farmers and producers such as (I) oestrus detection (ii) nutritional management (iii) genetic manipulation (iv) antioxidant (v) pharmaceutical treatment (vi) adaptation and acclimation (vii) embryo transfer. In light of antibiotic resistance, nutritional methods are becoming more common. In science also genetics is well known responsible for thermo tolerance capacity, gene identification in cattle's for making them cope up with heat resistance is a new area of research. Individual livestock systems must be assessed for mitigation opportunities to ensure that the mitigation techniques put in place turn into an efficient method for dropping the impact of heat stress in that venture.

### **8.1 Detection of oestrus and injection at oestrus**

Due to the extreme shorter length and lower strength of oestrus, it is difficult to detect. Using a variety of heat detection methods, such as tail-head-paint combined with visual oestrus detection, podometer, pressure enabled patches, and electronic devices put on the tail and head, may boost dairy cow reproductive efficiency. The detection rate for oestrus can be improved by rising the time and several number of visual study [18]. At the time of summer, using an entire male to detect heat at night and early in the morning can improve detection performance [18]. This method suppresses heat stress of oestrus might be hormonal as suggest that indicates heat stress decreases the level of estradiol-17 levels and vice versa increase the secretion level of adrenocorticotrophic which can protect oestrus conduction under the influence of estradiol-induced. The physical lethargy exhibited by heat-stressed cattle's is also likely to reduce oestrus. The other method used for increase fertility in the summer the injection of GnRH are inject during oestrus. According to some studies, when lactating cattle's were vaccinated with GnRH at observed oestrus during the summer, the conception rate increased from 18–29%. The cattle's which are lactating dairy cattle's given GnRH injections at the first indication of status heat during the summer and autumn months had higher conception rates (56%) than untreated (41%) monitors [18]. Heat stress decline the time duration and harshness of oestrus, which leads to an increase in anoestrus and silent ovulation. In order to increase fertility, the timed artificial insemination (TAI) protocol is used for effective oestrus detection and timely insemination. The hormonal therapies have been designed to synchronise ovulation times, allowing for the use of fixed TAI without the need for oestrus detection. The TAI protocol is known as ovary synchronisation content of insemination of gonadotropin-releasing hormone (GnRH) (day 0), prostaglandin F2 (day 7) and GnRH (day 9) and a hormonal therapies, followed by artificial insemination 16-20 hours after the second GnRH hormonal treatment [19]. When coupled with TAI, the ovary synchronisation protocol can successfully synchronise ovulation in cattle's can also enhance conception rate [19]. Under subtropical environmental conditions, the Centre for Inherited Disease Research (CIDR) synchronisation and Pre-synchronisation protocols are also used to increase the rate of conception and rate of pregnancy of Holstein cattle's [19]. This TAI protocol has the potential to minimise reproductive efficiency losses in cattle due to poor oestrus detection in the summer.

## **8.2 Genetic manipulation**

The definite genes that regulate thermoregulation of body and also the cellular responsiveness towards hyperthermia have allelic variants in the mammalian gene pool. Thus, both natural and artificial genetic selection can influence how heat stress affects reproductive function [18]. The coat colour, hair length-controlling genes, and heat shock tolerance in cells are all traits that could be chosen. It may be possibilities to boost up thermal tolerance and also increase fertility in summer by genetically modifying or changing the biochemical properties of the embryo prior to transfer [18]. The recognition of genes plays a vital role in increasing resistivity of cells towards heat shock might led to the transfer of these into heat stress through the breeds sensitivity and transgenic techniques, resulting in cattle's with increasing resistance capacity to defect the heat stress. The selection of breeding animals would need to be given further thought. The performance-based livestock selection and the selection of best breeds based on the phenotypic behaviour with cost effective significant traits like high growth rates, has been practised for decades whereas, farmers can continue to selection of replacement breeds on the basis of individual results cost effective and based on their profits in significant traits in the coming years. According to [13], while genetic improvement initiatives continue to emphasise these economically significant traits, there is a risk that this could lead to a decrease in thermo-tolerance resistivity due to the connection between cattle productivity and also rising metabolism of heat output. The enhancement in metabolic heat output decline the thermo-neutral zone of the animals, which combination with seasonal variation, will make handling cattle in hot weather more difficult.

### **8.3 Nutritional management**

To reduce heat generation through nutrient utilisation inside the animal, choose and feed new, palatable, and high-quality forages as much as possible, feed ingredients with a high digestibility [18]. The animals that are stressed need carbohydrates that can be fermented quickly. The essential ingredients should have buffering capacity such as sodium bicarbonate (NaHCO3), magnesium oxide (MgO) and sodium sesquicarbonate (Na3H (CO3)2) to maintain a natural atmosphere by effectively lower the occurrence of acidosis in the rumen, which is a frequent occurrence in hot weather [18] even if they are not eating as much feed as they need, early lactation cattle's effected to heat stress can go even deeper into increase in negative energy balance. As a result of altered follicle growth and decreased oestrus activity, they are more likely to have poor reproductive efficiency. Any of the symptoms of heat stress can be reduced by feeding high-quality forages and healthy rations. Since potassium is the primary component of sweat gland secretion in cattle, it should also be increased in their diet. As compared to fibre and carbohydrates. The intake of fats in diet is more beneficial because it help to reduction of heat and lowers the metabolic heat. In heat stress conditions, the dry matter easily digestible and also observed decrease in protein-energy ratio. In heat stressed cattle's, feeds on superior quality low-degradable protein has been observed to increase milk productivity as a result, both the amount and type of protein consumed by heat-stressed cattle's and buffaloes are critical. By using supplemental niacin to cattle's diet can also help them cope with heat stress. The Palm oil supplementation increased DMI while lowering heat stress signs [5]. The NEBAL was strengthened by feeding conjugated linoleic acids during heat stress, but milk fat was depleted at the same time. Lipoic acid has been shown to have antioxidant and energetic-metabolism-promoting properties [5]. The Exogenous antioxidant nutrient supplementation such a vitamin C, A, and E, as well as trace minerals including zinc (Zn), manganese (Mn), copper

*Adverse Impact of Heat Stress on Bovine Development: Causes and Strategies for Mitigation DOI: http://dx.doi.org/10.5772/intechopen.99307*

(Cu), selenium (Se), chromium (Cr) and others, may be used to decline the adverse effect of environment [5]. The elements such as B-complex vitamins, ascorbic acid, tocopherol, rumen-protected by Niacin and Nicotinic acid [5] have all been found to be helpful. Thiazolidinedione's (TZDs) can boost HSP development [5] increase glucose utilisation [5] and boost energetic metabolism, making them a viable heat stress strategy. Dietary betaine, like TZDs, might be a better alternative in heat stressed lactating cattle's [5]. In heat stressed lactating cattle's, chromium supplementation has been shown to increase energy metabolism and performance [19]. There is evidence of the development of reactive oxygen species (ROS) by embryos growing at high body temperatures is one of the causes of embryonic death in heat stressed animals [13]. Efforts to increase the fertility of lactating cattle's subjected to heat stress by administering antioxidants have had mixed results [13].
