Increased efficiency of microbial protein production in the rumen through manipulation of nutrients and rumen microbial populations

Summary

This project examined strategies to increase microbial protein (MCP) production within the rumen of cattle. It did this by examining the effect of specific nutrients and nutrient intake on the population of the dominant bacterial species in the rumen and the subsequent flow of MCP from the rumen. Microbial protein contributes on average 72% (and up to 100% with low quality forages) of the total protein supply to cattle. Temperate forages have high efficiency of microbial protein production (EMCP) within the rumen and tropical forages, with low crude protein (CP) content, have low EMCP which can be increased to the lower values used in the feeding standards with urea based supplements but never reach the higher values found with temperate forages.
It was hypothesized that limiting supply of specific nutrients (peptides, amino acids and branch chain fatty acids) and low dilution rate accounted for these differences through their effect on the bacterial species present. If EMCP on tropical forages could be increased to the higher levels achieved on temperate pasture, then live-weight gain would increase significantly. An algal supplement was investigated as a novel means of providing this package of nutrients which has the potential to be supplied via the drinking water.
The main findings of this project have been reported earlier (NBP0350, Final Report 30.09.2009), this addendum includes 454-pyrosequencing results from Experiments 3, 4 and 5 (of which some data was reported in the original final report) and two additional experiments conducted on the nutritive value of a range of algae species (Experiment 6) and cattle responses to algae species (Experiment 7),
1. Microbial genetic profile (MGP) in the rumen of steers offered algae or urea supplements determined by 454-pyrosequencing (Experiment 3).
2. Microbial genetic profile in the rumen of steers that were of divergent liveweight gain during the post-weaning period, determined by 454-pyrosequencing (Experiment 4).
3. Microbial genetic profile in the rumen of steers offered algae, cottonseed meal or urea supplements and the relationship with liveweight gain, determined by 454-pyrosequencing (Experiment 5).
4. Chemical composition and relative degradability of a range of algae species and commonly used protein supplements (Experiment 6).
5. Rumen function and MCP production of steers​ fed a low CP hay supplemented with various algae species and cottonseed meal (Experiment 7).

 
The main findings provided in this addendum include:Supplements of algae (Spirulina platensis) significantly increased MCP production and EMCP. No particular bacterial species (or groups of bacteria) were associated with the increased EMCP that was measured but greater diversity in the population of bacteria in the rumen was apparent in steers that received the Spirulina supplement (Experiment 3).  
There was no association between the rumen microbe genetic profile and post-weaning liveweight gain of steers. There was steer to steer variation in the rumen bacterial community but this was not related to post-weaning liveweight gain (Experiment 4).  
Liveweight gain was positively associated with the diversity of the bacterial population within the rumen of steers, as indicated by the number of operational taxonomic units present (Experiment 5).
Diversity within the rumen bacterial population was associated with N intake but did not vary between supplements per se (Experiment 5).
Increased rumen N supply increased the diversity of the rumen bacteria population but a large number of core bacteria remained relatively stable in response to increasing rumen N supply (Experiments 3, 4 and 5).
The composition and nutritive value of algae species is highly variable. Algae species may be useful supplements for animal production when used to meet specific nutrient deficiencies (Experiment 6).
Algae species with a high N content, such as Spirulina and Chlorella, can be supplied to steers on low CP basal diets with comparable results to traditionally used protein supplements, such as cottonseed meal (CSM) (Experiment 7).