Genotype differences and their impact on digestive tract function of ruminants: a review

Hegarty, R. S.

doi:10.1071/ea02148

Cited by 71 publications

(41 citation statements)

References 54 publications

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“…This suggests that high genetic merit cows convert the energy and protein components of the feed more effectively than medium genetic merit cows. Crocker and Robison (2002) showed a genetic line effect on swine excreta with maternal line animals producing significantly less P, Ca, Cu, Zn and Fe than boar line or F1 cross animals and numerically lower N, NH 3 N and K. Hegarty (2004) reviewed the evidence for a genetic difference in gut function in ruminants covering genetic components of diet selection, eating rate, digestive kinetics and methane production. There were data to suggest that there are genetic differences in the amount of methane produced per unit feed intake.…”

Section: Mitigation As a Results Of Breeding For Improved Productivitymentioning

confidence: 99%

Developing breeding schemes to assist mitigation of greenhouse gas emissions

Wall¹,

Simm²,

Moran³

2010

Animal

183

158

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Genetic improvement of livestock is a particularly effective technology, producing permanent and cumulative changes in performance. This paper highlights some of the options for including mitigation in livestock breeding schemes, focusing on ruminant species, and details three routes through which genetic improvement can help to reduce emissions per kg product via: (i) improving productivity and efficiency, (ii) reducing wastage in the farming system and (iii) directly selecting on emissions, if or when these are measurable. Selecting on traits that improve the efficiency of the system (e.g. residual feed intake, longevity) will have a favourable effect on the overall emissions from the system. Specific examples of how genetic selection will have a favourable effect on emissions for UK dairy systems are described. The development of breeding schemes that incorporate environmental concerns is both desirable and possible. An example of how economic valuation of public good outcomes can be incorporated into UK dairy selection indices is given. This paper focuses on genetic selection tools using, on the whole, currently available traits and tools. However, new direct and indirect measurement techniques for emissions will improve the potential to reduce emissions by genetic selection. The complexities of global forces on defining selection objectives are also highlighted.

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Section: Mitigation As a Results Of Breeding For Improved Productivitymentioning

confidence: 99%

Developing breeding schemes to assist mitigation of greenhouse gas emissions

Wall¹,

Simm²,

Moran³

2010

Animal

183

158

View full text Add to dashboard Cite

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“…Most pertinent now is the potential to use less-and non-invasive tools in breeding for increased feed efficiency and reduced methane production. Hegarty (2004) outlined the basis for possible genetic differences in methane production. The availability of genomic tools means that our ability to select for these more complex traits is limited more by the availability of simple, rapid and low-cost phenotyping tools.…”

Section: Methods To Estimate Rumen Methanogen Abundancementioning

confidence: 99%

Chemical markers for rumen methanogens and methanogenesis

McCartney

Bull

Dewhurst

2013

Animal

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The targeting of mcrA or 16S rRNA genes by quantitative PCR (qPCR) has become the dominant method for quantifying methanogens in rumen. There are considerable discrepancies between estimates based on different primer sets, and the literature is equivocal about the relationship with methane production. There are a number of problems with qPCR, including low primer specificity, multiple copies of genes and multiple genomes per cell. Accordingly, we have investigated alternative markers for methanogens, on the basis of the distinctive ether lipids of archaeal cell membranes. The membranes of Archaea contain dialkyl glycerol ethers such as 2,3-diphytanayl-O-sn-glycerol (archaeol), and glycerol dialkyl glycerol tetraethers (GDGTs) such as caldarchaeol (GDGT-0) in different proportions. The relationships between estimates of methanogen abundance using qPCR and archaeol measurements varied across primers. Studies in other ecosystems have identified environmental effects on the profile of ether lipids in Archaea. There is a long history of analysing easily accessible samples, such as faeces, urine and milk, to provide information about digestion and metabolism in livestock without the need for intrusive procedures. Purine derivatives in urine and odd-chain fatty acids in milk have been used to study rumen function. The association between volatile fatty acid proportions and methane production is probably the basis for empirical relationships between milk fatty acid profiles and methane production. However, these studies have not yet identified consistent predictors. We have evaluated the relationship between faecal archaeol concentration and methane production across a range of diets in studies on beef and dairy cattle. Faecal archaeol is diagnostic for ruminant faeces being below the limit of detection in faeces from non-ruminant herbivores. The relationship between faecal archaeol and methane production was significant when comparing treatment means across diets, but appears to be subject to considerable between-animal variation. This variation was also evident in the weak relationship between archaeol concentrations in rumen digesta and faeces. We speculate that variation in the distribution and kinetics of methanogens in the rumen may affect the survival and functioning of Archaea in the rumen and therefore contribute to genetic variation in methane production. Indeed, variation in the relationship between the numbers of micro-organisms present in the rumen and those leaving the rumen may explain variation in relationships between methane production and both milk fatty acid profiles and faecal archaeol. As a result, microbial markers in the faeces and milk are unlikely to relate well back to methanogenesis in the rumen. This work has also highlighted the need to describe methanogen abundance in all rumen fractions and this may explain the difficulty interpreting results on the basis of samples taken using stomach tubes or rumenocentesis.

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“…It has been suggested that domestic ruminants could be selected for increased digestive efficiency, based on phenotypic characteristics of the way digesta moves through their digestive tract (Hegarty, 2004). Ruminants can actually be bred to differ in the mean retention time of digesta (Thompson et al, 1989;Smuts et al, 1995;Goopy et al, 2014).…”

Section: Digesta Washing Microbial Harvest Microbial Metabolismmentioning

confidence: 99%

Physiological adaptations of ruminants and their potential relevance for production systems

Clauss

Hummel

2017

R. Bras. Zootec.

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-Herbivores face the dilemma that the level of feed intake is negatively related to factors that determine digestive efficiency, such as thoroughness of ingesta comminution by chewing, and retention of digesta in the digestive tract. Ruminants have evolved particular adaptations to solve this dilemma. Most ruminants share the characteristic of "digesta washing": fluid moves through their digestive tract faster than particles, thus effectively washing very fine particles, such as bacteria, out of the digesta plug. As the forestomach is followed by auto-enzymatic digestion, this allows a continuous, increased harvest of microbes from the forestomach. True rumination only evolved twice, in the camelids and the true ruminants. These both evolved a density-dependent sorting mechanism based on physical separation of the digesta by the process of flotation and sedimentation, ensuring that the process of rumination is applied to large particles. Differences in this sorting mechanism might facilitate a faster digesta processing in true ruminants as compared with camelids. The hallmark of ruminant digestive anatomy is the omasum, in which the fluid required for both digesta washing and the reticular separation mechanism is re-absorbed. In ruminants of the tribe Bovini, the omasum has reached the largest size and this group has a particularly great forestomach fluid throughput. Increasing the degree of digesta washing even more should increase microbial harvest from the forestomach and reduce the susceptibility to acidosis. At the same time, it should result in a metabolic state of the microbiome more tuned towards biomass production and less towards methanogenesis. Enhancing the forestomach fluid throughput by selective breeding could represent a promising way to further advance the productivity of the ruminant digestive tract.

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Genotype differences and their impact on digestive tract function of ruminants: a review

Cited by 71 publications

References 54 publications

Developing breeding schemes to assist mitigation of greenhouse gas emissions

Developing breeding schemes to assist mitigation of greenhouse gas emissions

Chemical markers for rumen methanogens and methanogenesis

Physiological adaptations of ruminants and their potential relevance for production systems

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