Cattle, buffaloes, sheep and goats in India emit an estimated 9.25-14.2 million tonnes of methane annually – a sizable proportion of the around 90 mt methane emitted by livestock across the world. This is a cause for serious concern, given that methane is a very potent greenhouse gas.
With this in mind, an Indian Council of Agricultural Research (ICAR) institute has developed an anti-methanogenic feed supplement, called ‘Harit Dhara’. When given to bovines and sheep, it not only cuts down their methane emissions by 17-20 per cent, but also results in higher milk production and bodyweight gain.
“An average lactating cow or buffalo in India emits around 200 litres of methane per day, while it is 85-95 litres for young growing heifers and 20-25 litres for adult sheep. Feeding Harit Dhara can reduce these by a fifth. For a cow producing 200 litres (143 g) of methane, it translates into 0.714 kg less of CO2 equivalent emissions daily or 261 kg per year (1 litre methane=0.714 g; 1 kg methane=25 kg CO2),” Dr Raghavendra Bhatta, director of the ICAR’s National Institute of Animal Nutrition and Physiology (NIANP) at Bengaluru, told The Indian Express.
Methane is produced by animals having rumen, in the first of their four stomachs, where the plant material they eat – cellulose, fibre, starch and sugars – gets fermented or broken down by microorganisms prior to further digestion and nutrient absorption. Carbohydrate fermentation leads to production of CO2 and hydrogen. These are used as substrate by archaea – microbes in the rumen with structure similar to bacteria – to produce methane, which the animals then expel through burping.
Harit Dhara acts by decreasing the population of protozoa microbes in the rumen, responsible for hydrogen production and making it available to the archaea for reduction of CO2 to methane. Tropical plants containing tannins – bitter and astringent chemical compounds – are known to suppress or remove protozoa from the rumen.
“Our product has been prepared using condensed and hydrolysable tannin-rich plant-based sources abundantly available in the country. Harit Dhara roughly costs Rs 6/kg and it is to be fed only to animals aged above three months having fully functional rumen. Our recommended daily dosage is 500 g for adult cattle and buffaloes, 150 g for growing bovines and 50 g for adult sheep,” said Bhatta.
However, lowering of enteric methane emissions may not sufficient economic justification for farmers to feed Harit Dhara. What NIANP’s anti-methanogenic feed supplement also does is change the composition of the volatile fatty acids that are the end-products of rumen fermentation (along with hydrogen and CO2).
“Fermentation continues as before, but there is more production of propionic acid now in proportion to acetic and butyric acid. Since propionic acid provides much of the energy for lactose (milk sugar) production and body weight gain, there is economic benefit too from feeding of Harit Dhara. The biological energy loss from methane emission can be rechanneled and utilised by the animal for milk production and growth,” explained Bhatta.
According to him, feeding 500 g Harit Dhara to lactating cattle and buffaloes would increase milk output by 300-400 ml/animal/day. The additional weight gain will, likewise, be 20-25 g/day from 150g for growing bovines and about 7 g/day from 50 g for adult sheep. At Rs 30/litre milk price, the benefit-cost ratio for the dairy farmer works out to 3:1.
“We have done field validation and filed a patent for Harit Dhara. Compound animal feed manufacturers can also incorporate it into their products by replacing wheat or de-oiled rice bran. Farmers wouldn’t have to, then, separately feed Harit Dhara to their animals,” added Bhatta.
The 2019 Livestock Census showed India’s cattle population at 193.46 million, along with 109.85 million buffaloes, 148.88 million goats and 74.26 million sheep. Being largely fed on agricultural residues – wheat/paddy straw and maize, sorghum or bajra stover – ruminants in India tend to produce 50-100% higher methane than their industrialised country counterparts that are given more easily fermentable/digestible concentrates, silages and green fodder.