Influence of the Temperature and the Genotype of the HSP90AA1 Gene over Sperm Chromatin Stability in Manchega Rams

The present study addresses the effect of heat stress on males' reproduction ability. For that, we have evaluated the sperm DNA fragmentation (DFI) by SCSA of ejaculates incubated at 37°C during 0, 24 and 48 hours after its collection, as a way to mimic the temperature circumstances to which spermatozoa will be subject to in the ewe uterus. The effects of temperature and temperature-humidity index (THI) from day 60 prior collection to the date of semen collection on DFI were examined. To better understand the causes determining the sensitivity of spermatozoa to heat, this study was conducted in 60 males with alternative genotypes for the SNP G/C−660 of the HSP90AA1 promoter, which encode for the Hsp90α protein. The Hsp90α protein predominates in the brain and testis, and its role in spermatogenesis has been described in several species. Ridge regression analyses showed that days 29 to 35 and 7 to 14 before sperm collection (bsc) were the most critical regarding the effect of heat stress over DFI values. Mixed model analyses revealed that DFI increases over a threshold of 30°C for maximum temperature and 22 for THI at days 29 to 35 and 7 to 14 bsc only in animals carrying the GG−660 genotype. The period 29–35 bsc coincide with the meiosis I process for which the effect of the Hsp90α has been described in mice. The period 7–14 bsc may correspond with later stages of the meiosis II and early stages of epididymal maturation in which the replacement of histones by protamines occurs. Because of GG−660 genotype has been associated to lower levels of HSP90AA1 expression, suboptimal amounts of HSP90AA1 mRNA in GG−660 animals under heat stress conditions make spermatozoa DNA more susceptible to be fragmented. Thus, selecting against the GG−660 genotype could decrease the DNA fragmentation and spermatozoa thermal susceptibility in the heat season, and its putative subsequent fertility gainsPublishe

Adaptation strategies to counter climate change impact on sheep

Climate change has proved to impose potential negative effects on species survival, ecosystems stability and sustainable livestock production around the globe. Among the various environmental factors, heat stress is well known for its harmful effects on livestock and related production losses. Sheep exposed to heat stress show lower body growth and hide quality and compromised reproductive functions in both males and females. Adapting to the changing climate requires appropriate manipulations in the production system by taking into account the positive effects and attempting to diminish the negative effects of climate change. The highly adapted indigenous breeds identified by marker-assisted selection can be used as an efficient tool for developing thermotolerant breeds through improved breeding programmes. Promotion of such breeds can improve production efficiency and may lead to fewer greenhouse gas emissions. Further, the local people, especially women, are good managers of natural resources and possess excellent skills to utilize the natural resources efficiently. Hence, occasional training and a participatory research approach into the roles of women assist the tackling of climate change in the rural areas. In addition, well-organized early warning systems avoid severe damage due to unexpected disasters by providing sufficient time to prepare effective responses. Development of skilled disease surveillance supported with effective health services may effectively control the spread of climate change-related diseases in sheep. Furthermore, the production system requires improved water resource management to provide sufficient water for sheep production in the arid and semi-arid regions. Cultivation of drought-tolerant fodder varieties in extremely hot areas is an efficient adaptive strategy to ensure sufficient supply of feed during scarcity periods. Finally, strengthening extension services and building awareness through capacity-building programmes helps the livestock keepers to improve their adaptive capacities against climate change. Adaptation strategies related to cold stress include advanced cold-tolerant breeding programmes, migration in extreme winter and adoption of proper cold management practices. According to the predictions by various international bodies, the consequences of climate change will be on the rise in the future. Hence, adequate cost-effective management strategies appear to be the immediate need of the hour for adapting sheep production systems to the changing climate

Measurement of severity of heat stress in sheep

Animals show optimum growth, health, and productivity within a range of environmental temperatures. Exposure of the sheep to higher temperature leads to heat stress, which negatively affects their well-being and productivity. In addition to ambient temperature (AT), other climatic factors like humidity (RH), wind speed (WS), and solar radiation (SR) also influence the degree of heat stress in sheep. Further, climate change caused a higher rate of temperature increase in the tropical region. Hence, there is an urgent necessity to develop a simple, reliable, and easy method to assess the degree of heat stress in sheep particularly during summer. In the mid-twentieth century, temperature-humidity index (THI) was introduced to evaluate the severity of summer stress and was extended to dairy animals as a tool to explain the welfare of the animals. Moreover, several THI equations were developed by various scientists based on prevailing AT and RH. However, the main drawback of the THI was that it did not account for other weather parameters like WS and SR, even though they also equally influenced the level of heat stress in animals. Research efforts pertain to establishing a suitable thermal index by incorporating all cardinal weather parameters. With this background, heat load index (HLI) was developed as an alternative to THI relating RH, WS, and black-globe temperature (accounts both AT and SR). The few other modern indices available to assess the severity of heat stress in sheep are black-globe temperature-humidity index (BGTHI), thermal comfort index (TCI), and global comprehension index (GCI). In addition to weather indices, some physiological indices are also used to assess heat stress in sheep. Physiological responses like rectal temperature and respiration rate are considered as good indicators of heat stress in sheep. Moreover, strong correlations between blood parameters like hemoglobin, packed cell volume, and endocrine parameters such as cortisol and thyroid hormones production are well established in sheep. Further, genomics and proteomics tools are providing advanced options to evaluate the adaptation processes of sheep. Some of the genes identified in sheep during heat stress are heat shock protein, heat shock factor-1, thyroid hormone receptor, and prolactin receptor genes. Besides, the identified thermo-tolerant genes could be used as an ideal marker for assessing the level of heat stress and may be further utilized for marker-assisted selection breeding programs to develop superior thermo-tolerant breeds