Researchers from PCC have found out the cellular response of livestock toward heat and environmental condition in the Philippines.

In a study titled “The Role of Heat Shock Protein (HSP70) Gene Expression in Blood Lymphocytes of Water Buffaloes” done by Excel Rio Maylem, Shanemae Rivera, Gerald Ramos, Eufrocina Atabay, Edwin Atabay, and Emma Venturina, HSP70 expression was detected in the blood lymphocytes of water buffaloes.

HSP70 was noted as a potential indicator of heat stress in livestock. As a member of the family of HSP, a gene responsible for counteracting the effect of the continuously changing climate, HSP70 is deemed as the most inducible and highly sensitive form in its family.

A total of 20 Bulgarian Murrah buffaloes and two native carabaos were used in the study. Ten from these animals were donor bulls from the PCC National Bull Farm in Digdig, Carranglan, Nueva Ecija while the remaining 12 were buffalo cows from the institutional herd of the PCC National Headquarters and Gene Pool in Science City of Munoz, Nueva Ecija.

The study was conducted last January 2016 to June 2018 with a budget of PhP5,305,200.00 from the Department of Agriculture-Biotechology Program.

Methodology

The researchers performed blood collection and isolation of peripheral blood mononuclear cells (PBMCs), RNA extraction, and quantitative RT-PCR analysis.

Cows were grouped according to their age and lactation period. All of them were fed with a mixture of grasses, silage and concentrates and given water ad libitum. House pens were opened to allow continuous flow of air. 

Blood samples, meanwhile, were also collected for the analysis of HSP70 gene expression during the hot dry (May-July), hot wet (August-October), cool wet (November-January) and cool dry (February-April) seasons for the determination of its response to elevated temperatures. For physiological responses; respiration rate (RR), pulse rate (PR) and rectal temperature (RT) data were recorded on the same date before blood collection. Cows were grouped into three: low calving interval (300-400), mid calving interval (401-599) and high calving interval (600-700).

These were then followed by the isolation of PBMCs, RNA extraction and quantitative RT-PCR analysis using technical protocols.

Results

Observations were made on the different levels of HSP70 expression of individual bulls and cows.

Highly significant (P<0.05) expression of HSP70 was recorded during hot-dry months (May to July) which is approximately 2.6 to 2.7-fold change higher than the cold-dry months (February to April). This shows that the animals are more stressed during the former months compared to other months such as cold-dry months, hot-wet months (August to October) and cool-wet months (November to January) of the year.

Furthermore, moderately positive correlation was also observed between HSP70 and minimum temperature (þ=0.38), maximum temperature (þ=0.44), rainfall (þ=0.37) and strong negative correlation for relative humidity (RH) (þ=-0.42). This inferred that temperature, rainfall and unabated fluctuation of relative humidity brought by climate change greatly affects the expression of HSP70 in the blood lymphocyte of water buffaloes and imposed a deleterious effect on animal reproduction and production. Therefore, any change in this environmental condition leads to escalation of HSP70 relative expression level.

Physiological parameters, meanwhile, like rectal temperature (RT) (þ=0.42) and pulse rate (PR) (þ=0.33) had a moderate correlation to HSP70 while respiratory rate (RR) (þ=0.17) and semen quality traits including semen volume, sperm motility and concentration had no significant correlation. This means that an increase in PR and RT could also signify animals experiencing heat stress.

In terms of fertility, a two-fold higher gene expression of HSP70 on high calving-interval cows (P<0.05) was recorded compared to low-interval cows (1.30) and mid-interval cows (1.21). This showed that cows with more HSP70 expression are more heat-stressed which is considered to be a contributory reason to why the animals have a high calving interval, or lower fertility rate.

Based on the overall results, the researchers concluded that understanding the cellular response of livestock animals to heat stress will allow the identification of the animal’s intrinsic thermotolerance to heat and the changing climate in the Philippines.  This can serve as a lead in providing interventions to address the detrimental effect of heat stress in the livestock sector.

On the side, the HSP70 in blood lymphocytes can be a potential indicator of heat stress in water buffaloes and its varying expression levels can be used as a valuable reason for the differences on its length of calving interval leading to fertility rate. This then leads to the utilization of HSP70 for the management of heat stress and its effect on reproduction in water buffaloes.