Hydrogen Sulphide Production by Fermentation in Rumen and its Impact on Production and Health of Ruminants
Swati Thakur1*, Dhara Souvik2, Dangi Manita3, Madan Jyotsana1, Sandhu Sonia1
1 Department of Veterinary Physiology and Biochemistry, LUVAS, Hisar, Haryana, India
2 Department of Veterinary Gynaecology and Obstetrics, AAU Assam, India
3 Department of Animal Genetics and Breeding, LUVAS, Hisar, Haryana, India
(*swatithakur92@gmail.com)
Introduction
Hydrogen sulphide has many beneficial and toxic effects on health of the animals. Rumen fermentation plays a vital role in digestion and absorption of nutrients in ruminants. Dietary sulphur can be reduced into hydrogen sulphide (H2S) in the rumen during ruminal fermentation. H2S produced during fermentation is absorbed rapidly in to body of animals through intestinal wall. H2S may be toxic to the ruminants if produced in excess, can cause poliomyelitis. The production of H2S depends upon the population of sulphate reducing bacteria (SRB). H2S plays a role in physiological function and maintenance of gastrointestinal tract. H2S is oxidized successively in mitochondria to thiosulphate and afterwards to sulphite with sulphate as end product under physiological conditions. H2S accumulation in ruminants lead to toxic effects on the animals, may cause disorders like poliomyelitis.
Hydrogen sulphide toxicity in ruminants
Sulphur in the diet of ruminants can be reduced to hydrogen sulphide (H2S) during rumen fermentation. H2S is a toxic gas and its production in rumen may have certain detrimental effect on ruminants and may even induce poliomyelitis (PEM). PEM is a neuropathological condition of ruminants induced by a variety of neural metabolic disruptions such as altered thiamine status, water deprivation, sodium ion toxicosis, excess intake of sulphur and lead poisoning. H2S and its ionic forms are highly toxic having important effect on biological system and H2S interfere with cellular respiration in the similar way as hydrogen cyanide. H2S produced during rumen fermentation rapidly absorbed into the rumen wall and its rate of production depends upon sulphur level in the diet. Dietary sulphur in the form of sulphate given in ruminant’s diet is utilized by rumen micro-organisms to produce sulphides, lead to an increased concentration of H2S in the rumen. Episodes of excessive production and absorption of sulphides in rumen are a toxicological hazard in ruminants and high enough H2S ration can cause PEM and if not treated quickly the animal may die. H2S in brain may act as a neuromodulator. H2S levels in rumen above 2000 mg/L can precede the development of PEM and sometimes known as sulphur induced poliomyelitis (S-PEM). H2S concentration below 471.2 mg/L in rumen caused no toxic effect on animal health.
Rumen hydrogen sulphide production
Sulphate reducing anaerobic bacteria (SRB), reduce sulphate into H2S in rumen. SRB can also reduce thiosulphate and sulphite to H2S and utilize gaseous hydrogen ions.
Relationship between SRB and methanogens in rumen
There is a competitive and interactive relationship between SRB and methanogens. Methanogens and SRB compete for hydrogen for their metabolism, SRB reduces sulphate to sulphide and methanogens reduce CO2 to methane (CH4). The competitiveness of SRB and methanogens depends largely on the concentration of sulphate in rumen. If the concentration of sulphate in rumen reach a certain level, methane production can be suppressed. However, when sulphate concentration in rumen was very low, a symbiotic and mutually beneficial relationship formed between SRB and methanogens through hydrogen generation and interspecific hydrogen transfer. Thereby, decreasing sulphate may make SRB a hydrogen producer in rumen. Thermodynamically, affinity of matrix shown an advantage to SRB over methanogens in the hydrogen competition. Methanogens are unable to compete with SRB for hydrogen even though methanogens and SRB coexist. Hydrogen utilization of SRB is due to potential difference as hydrogen ions are more inclined to SRB as energy produced by sulphate reduction is more.
Factors influencing hydrogen sulphide production in rumen
- Dietary level of sulphur on rumen hydrogen sulphide production
The dietary level of sulphur and its utilization in rumen are positively correlated with the rate of H2S produced in rumen. Therefore, the level of sulphur in diet of ruminants is closely related to H2S production in rumen. A large amount of H2S was produced in rumen when ruminants were fed high sulphur diets by the action of SRB. Excessive sulphate in rumen (576 mg/L) affect the reducing ability of SRB. It may be indicated that dietary sulphur level affect H2S production in rumen by regulating SRB.
- Effect of ruminal pH on hydrogen sulphide production
High sulphur content in the diet lowers rumen pH in ruminants. H2S production from sulphide is a pH dependent process. The average pH of rumen account only 12% of H2S concentration changes in rumen, whereas, rumen protein sulphur intake account for 58% of rumen H2S concentration changes.
- Effect of dietary neutral detergent fibre (NDF) on rumen H2S production
Rumen pH is also affected by the factors other than dietary sulphur level, such as dietary NDF which may affect H2S production in rumen. H2S concentration in rumen decreased linearly with an increase in dietary content of roughage NDF. Higher dietary NDF can reduce H2S production in rumen. Although the exact mechanism of S-PEM are still unknown. It has been known that cattle fed a concentrate rich ration face a greater risk of S-PEM than those fed a high forage diet. This may suggest that increased dietary sulphur content in cattle consuming high forage diet could lower the potential risk of sulphur toxicity by adjusting SRB population in rumen.
Effect of ruminal hydrogen sulphide on ruminant’s health and production
Diets containing excess sulphur can be detrimental to animal health as it triggers production of H2S during rumen fermentation, resulting in to toxicity. Although, sulphur is regarded as an essential element in ruminants nutrition. However, excessive sulphur intake can reduce animal production and can cause respiratory, encephalic and enteric problems. Ruminal H2S overproduction directly results in to the development of polioencephalomalacia. Cattle growth is adversely affected by sub-acute intoxication of H2S production in rumen.
Ethanol based co-products usage in ruminant’s nutrition tend to increase sulphur concentration in the diet and is one of the main challenge. Therefore, inclusion of greater proportions ethanol based co-products in ruminant’s finishing rations has been prohibited. Supplementation of thiamine in diet helps to alleviate or prevent poliomyelitis in ruminants. H2S also plays an essential role in physiological functions and maintenance of the gastrointestinal tract.
Summary
Currently there are few studies on rumen H2S production. H2S is produced by reduction of sulphate in rumen by SRB and there is competitive relationship between SRB and methanogens. However, this is necessary to verify that H2S production in rumen is inhibited by increasing methanogens in the rumen. There are no evidences of increase in H2S concentration after reaching a critical value on increasing sulphur content in diet. The relationship between ruminal pH and H2S production and effect of NDF on H2S production further need experimental verification. In addition, endogenous production of H2S in rodents improved the normal physiology of gastrointestinal tract. Therefore, it is important to accentuate the vital role of GIT micro-flora for the normal physiological functioning of the host.
References
https://www.pashudhanpraharee.com/all-about-rumen-microbiology/
https://www.mdpi.com/2227-9717/8/9/1169
Wang, R. 2012. Physiological implications of hydrogen sulphide. Physiol. Rev. 92, 791–896.
Qian, K., Xu, J., Zu, H.C. and Cong, Y. 2020. Research progress of rumen hydrogen sulphide production in ruminants. Animal Science Journal, 91 (1).
