India is first in milk production in the world production, with 20 crore tons of milk from 20 cr. cows 10Cr.Buffaloes during the period of 2020-2021.This was possible only due to large scale crossbreeding of local breeds and non-descript breeds of cattle. Livestock plays an important role in the global economy. Among the environmental variables affecting animals, heat stress is one of the factors making animal production challenging in many parts of the world. Climate change effects are not only limited to crop production, but also affect livestock production, for example reduced milk yields and milk quality and reduced fertility.
Heat stress is one of the greatest challenges faced by dairy farmers in many regions of the world. The crossbred animals are more susceptible to heat stress. Heat stress in dairy animals is one of the leading causes of decreased production and fertility during summer months. In India, the summer temperature goes beyond 46°C which is 19°C above the upper critical temperature of dairy cattle. When the temperature exceeds 27 °C even with low humidity, the temperature is above the comfort zone for the high producing dairy cows. Humidity plays significant role in heat stress.
Common signs of heat-stressed animal include
- Animal moves to shade
- Water intake enhanced while feed intake reduced
- Prefers standing than lying down
- Increased respiration rate, body temperature (sometimes as high as 106 – 108°F.)
- Increased production of saliva
- Open-mouth panting
- Dry gums and mucous membranes due to dehydration
As dehydration becomes more severe, animals also may exhibit sunken eyes and an increased pulse rate. The “skin-pinch” test is another method to evaluate dehydration. To perform it, pinch or “tent” a fold of skin at the calf’s neck and observe how many seconds it takes to flatten. In normal animals, it will return to its regular position in less than two seconds. A flattening time of up to four seconds indicates the animal is up to 8% dehydrated. If it takes longer than that, even more serious, and potentially life-threatening, dehydration has set in.
Effects on milk production
Annual total milk loss due to thermal stress at the all-India level was 0.18 crore tones or approximately 2% of the total milk production of the country amounting to a whopping Rs. 2661.62 crores per year Upadhyay et al. The negative impact of global warming on total milk production in India is also estimated to about 1.5 crore tones by 2050.The decline in milk production due to Heat stress was 14% in early lactation and 35% in mid-lactation. Indeed, up to 10% of the variability in milk production has been attributed to the effect of climatic factors such as temperature.
According to scientists at the National Dairy Research Institute (NDRI), a pioneer institute in the field of dairy research, heat stress and poor maintenance of milch animals in the summer, particularly in May and June, leads to a decline of around 15 per cent to 20 per cent in milk production in crossbred cows and around 10 per cent to 15 per cent in buffaloes. In the humid months of July and August, it falls further to around 20 per cent to 25 per cent in crossbred cows and 20 per cent in buffaloes.
Haryana, Punjab, UP and Rajasthan are major contributors to milk production, but during summer, these states have temperature in excess of 44 degrees Celsius, which leads to reduction of milk yield
Effects on reproductive performance
Heat stress reduces the length and intensity of estrus besides increases incidence of anestrous and silent heat in farm animals. Heat stress affects the fertility and reproductive livestock performance by compromising the physiology reproductive tract, through hormonal imbalance, decreased oocyte quality and poor semen quality, and decreased embryo development and survival. In general, the percentage of conception rate was found to be reduced by 4.6% for each unit increase in temperature humidity index (THI) above 70, and heat stress during pregnancy further slows down the growth of the foetus and results in lower birth weight.
Some nutritional management tips to manage heat stress are:
- Provide high quality feeds like total mixed rations
- Increase the frequency of feedings
- Feed during cooler times of the day; feed a greater proportion of feed at night, 60 to 70% of feed
- Keep feed fresh as much as possible
- Provide high-quality forage
- Provide adequate fiber
- Heat stress can also be managed by spraying/ sprinkling water directly on the body of animals for a period of 1 to 5 minutes at an interval of 10- 30 minutes.
- Water intake increases by up to 50% as the THI approaches 80
- Use of electrolytes to replenish electrolytes losses.
Intake of sufficient cool water is probably the most important strategy for animals to undertake during heat stress.
Conclusion:
The body temperature and feed intake of dairy cows are affected by rising ambient temperature and humidity, which in turn affect milk production and reproduction.Mineral losses via sweating (primarily K) and changes in blood acid-base chemistry resulting from hyperventilation reduce blood bicarbonate and blood buffering capacity and increase urinary excretion of electrolytes. If animals are severely dehydrated due to heat stress, then animal should rehydrate with oral electrolytes.
Author: Dr. Deepak Kumar
GM -Sales and Marketing, Nutrition Division
Carus Laboratories Pvt. Ltd., Karnal
