Assessing the relevance of fluid dilution rate for ruminal metabolism in cattle and sheep
by Xiaoyu Zhang
Date of Examination:2023-01-31
Date of issue:2023-06-07
Advisor:Prof. Dr. Jürgen Hummel
Referee:Prof. Dr. Jürgen Hummel
Referee:Prof. Dr. Eva Schlecht
Persistent Address:
http://dx.doi.org/10.53846/goediss-9922
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Abstract
English
Ruminants evolved a forestomach in which plant materials are fermented with the help of ruminal symbiotic microbes. Ruminal microbes use the ingested materials to proliferate, and produce volatile fatty acids which are absorbed by host animals as energy and nutrient substrates, and carbon dioxide and methane as fermentation end products. The ingested solid materials are mixed with rumen fluid, and generally, the solid phase retain longer than the fluid phase. Both in vitro and animal studies indicated that a higher fluid dilution rate is related to a more efficient microbial growth and a lower methane emission. Additionally, in vitro studies as well as theoretical considerations suggested a reverse relationship between microbial yield and methane production, since both microbial synthesis and methanogenesis consume metabolic hydrogen. To test whether an increased fluid dilution rate is associated with increased microbial yield and decreased methane production in live animals, this study applied a saliva stimulant, pilocarpine, to modify liquid flow rate in cattle and sheep. Four non‐lactating cattle and three non-pregnant sheep were fed forage only (restricted to constant intake) in Latin square designs with oral pilocarpine doses. Measurements included feed and water intake, mean retention time (MRT) of fluid and particles in the reticulorumen and the total tract, ruminal microbial yield (via urinary purine bases or metabolic faecal nitrogen), methane emission, digestibility, rumen fluid parameters for both cattle and sheep, and chewing behaviour as well as reticular motility for cattle. Data were investigated using orthogonal polynomial contrasts. The fluid MRT was decreased via treatments for both cattle and sheep. The methane production via treatments for cattle was decreased, but not for sheep. The microbial yield based on urinary purine bases was not affected, but increased based on metabolic faecal nitrogen only for cattle. The ratio between particulate and fluid MRT was smaller for sheep than that for cattle, and was not affected by treatment. The apparent digestibility was not affected by treatment. In addition, this study suggested a correlation between chewing measures and MRT measures as indicated by the cattle experiment. The relationship between chewing behaviour and fluid MRT could be linked through saliva production via the masticatory‐salivary reflex, which indicates that chewing measures could emerge as easy‐to‐measure proxies for MRT characteristics. Our results showed methane production decreased, and microbial N yield increased indicated by metabolic faecal nitrogen by applying pilocarpine but only for cattle. The discrepancy between cattle and sheep might be related to the difference in ratios of the MRT of particles to fluid, which has been shown to be largely resistant to changes in diet type or feed intake. Whether setting the breeding target of shorter fluid MRT could contribute to less methane production and more microbial yield remains to be further investigated.
Keywords: ruminant; salivation; passage rate; methane; ruminal microbial yield
