REVIEW ▶▶▶
may be attributed to an increase in microbial fermentation and energy metabolism. So the animal’s efficiency can in- crease if a broader range of nutrients are more efficiently con- verted to metabolisable nutrients. The diversity of the rumen microbiome population also influences the efficiency of the animal, with a more uniform microbiome being associated with more efficient animals. Inefficient animals have a higher variation in micro-organism species and fermentation end-products.
Methane production and energy Enteric methane can result in 2 to 12% energy loss and highly efficient animals produce 20 to 26% less methane. Mitigation of methane emissions has become one of the focus points of today’s livestock production, as methane has a negative ef- fect on the environment and ruminants are one of the major producers of anthropogenic methane. The abundance of mi- crobes such as archaea, which influence methane emissions, can be reduced, resulting in more energy being available to the animal for production. The Methanobrevibacter and Methanosphaera species are two of the major methano- gen-producing species that tend to be more abundant in in- efficient animals. Researchers found that Proteobacteria were less abundant in animals that produced high levels of meth- ane and a high abundance of Succinivibrionaceae were found in cattle that produced low levels of methane.
Feed additives and production Knowledge gained from the interaction between the rumen microbiome and specific nutrients or nutrient groups can as- sist producers and nutritionists in manipulating diets to im- prove production efficiency and thus in practicing precision feeding. The addition of feed additives to ruminant diets is a nutritional aspect that can influence the rumen microbiome, ultimately improving the digestive and microbial efficiency, which leads to increased production. The ideal feed additive should improve digestive efficiency while reducing methane emissions and maintaining a stable ruminal pH to prevent ac- idosis. Acidosis is a common occurrence in animals fed high levels of grain in their diets, where an accumulation of lactic acid can lead to low pH and a damaged rumen. Ionophores, a type of antibiotic, is an additive that reduces harmful bacteria and methanogens, while promoting propionate-producing bacteria, thus reducing the risk of acidosis and methane emissions and increasing the animal’s production. As antibi- otics prevent the growth of bacteria, there are fewer bacteria that compete with the host animal. However, due to the risks of microbial resistance, the European Union has banned the use of antibiotics in animal feed.
Use of alternative additives Alternatives such as probiotics and essential oils, which can manipulate rumen microbial fermentation and thus
increase efficiency, need to be investigated. These naturally occurring additives can manipulate the rumen microbiome to perform more efficiently through an increase in the abundance of propionate-producing micro-organisms, a shift in the microbiome community to reduce less beneficial micro-organisms, or in the protection of the rumen as a buffer. Probiotics encourage the growth of beneficial strains of bacteria in the rumen at the expense of undesirable or harmful bacteria. They survive harsh conditions by attach- ing to the rumen lining to stabilise, balance and protect the rumen environment. Bacteria used as probiotics are mostly gram positive and they may include Bacillus, Pediococcus, Enterococcus, Streptococcus, Saccharomyces and Lactoba- cillus. An increase in growth and average daily gain was re- ported when probiotics were fed to finishing cattle; howev- er, the effect of probiotics on growth has not been consistent. The effect of probiotics on the rumen microbi- ome seems to depend on the bacterial strains used, as well as the dosage. Essential oils are made from plant secondary compounds that have antimicrobial properties and can re- duce harmful pathogens. They can influence the propor- tions of VFAs in a similar manner to that of ionophores by reducing bacteria that produce acetate, while increasing propionate-producing bacteria. Methanogens are also in- hibited by essential oils, thus reducing methane emissions. Combinations of essential oils have a geater impact on the rumen microbiome compared to essential oils from a single source. Examples of essential oils include carvacrol, eugen- ol, cinnamaldehyde and methanol. The effects of essential oils on the rumen microbiome are not consistent as they seem to affect the concentration of ammonia more than VFAs, with the potential to improve nitrogen and energy utilisation and thus increase efficiency.
Conclusion The rumen microbiome has a direct effect on the utilisation of the feed by the ruminant and thus on efficiency, but, for- tunately, it can be managed and manipulated through the addition of feed additives. The identification of microorgan- isms in efficient animals might result in strategies to in- crease their abundance in the rumen while reducing harm- ful or inefficient microbes. These strategies might result in a more efficient animal, reducing feed costs while maintain- ing or increasing production. It is also clear that more re- search needs to be done on the effect of feed additives on the rumen microbiome, as various contrasting effects are re- ported in literature. As the world becomes more aware of environmental challenges, strategies such as manipulating the rumen microbiome to increase efficiency and reduce methane emissions will become more important. It is there- fore imperative to further investigate and better understand the rumen microbiome.
▶ ALL ABOUT FEED | Volume 28, No. 6, 2020 25
PHOTO: RONALD HISSINK
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36
