RESUMO
Evidence supports a causal link between anomalous intestinal function and impaired performance in dairy cows. Consequently, digesta pH values obtained from colon, cecum, and rectum are increasingly used to monitor intestinal function in dairy cows. We conducted a study to describe the daily dynamics of fecal pH in lactating dairy cows. The study lasted 4 d and individual records of dry matter intake, milk yield, and fecal pH were taken. Samples of feces were taken every 4 h during the 4-d study, and sampling time was adjusted ahead by 1 h daily so that a sample was obtained for each 1-h interval of the day. Data were analyzed using a mixed-effect model including time as fixed effect and cow as a random factor. We performed a cosinor analysis using pH data at different time points to determine whether fecal pH followed a biorhythmic pattern. On average, cows consumed 19.1 ± 1.55 kg/d of dry matter and produced 26.3 ± 4.16 kg/d of milk. The most relevant results confirmed a biorhythmic pattern for feces pH around feeding time: mesor (midline estimating statistic of rhythm) 6.20, amplitude 0.28, and acrophase 5.66. Additionally, we found a positive relationship between dry matter intake and amplitude, possibly because of an increase in the amount of fermentable carbohydrate reaching the hindgut in response to increasing intake. When using fecal pH as an indicator of intestinal function, it is critical to obtain samples at several time points to capture its daily rhythmicity and to report sampling time relative to feeding.
RESUMO
Periodic feed restriction is used in cattle production to reduce feed costs. When normal feed levels are resumed, cattle catch up to a normal weight by an acceleration of normal growth rate, known as compensatory growth, which is not yet fully understood. Illumina Miseq Phylogenetic marker amplicon sequencing of DNA extracted from rumen contents of 55 bulls showed that restriction of feed (70% concentrate, 30% grass silage) for 125 days, to levels that caused a 60% reduction of growth rate, resulted in a large increase of relative abundance of Methanobrevibacter gottschalkii clade (designated as OTU-M7), and a large reduction of an uncharacterised Succinivibrionaceae species (designated as OTU-S3004). There was a strong negative Spearman correlation (ρ = -0.72, P = <1x10(-20)) between relative abundances of OTU-3004 and OTU-M7 in the liquid rumen fraction. There was also a significant increase in acetate:propionate ratio (A:P) in feed restricted animals that showed a negative Spearman correlation (ρ = -0.69, P = <1x10(-20)) with the relative abundance of OTU-S3004 in the rumen liquid fraction but not the solid fraction, and a strong positive Spearman correlation with OTU-M7 in the rumen liquid (ρ = 0.74, P = <1x10(-20)) and solid (ρ = 0.69, P = <1x10(-20)) fractions. Reduced A:P ratios in the rumen are associated with increased feed efficiency and reduced production of methane which has a global warming potential (GWP 100 years) of 28. Succinivibrionaceae growth in the rumen was previously suggested to reduce methane emissions as some members of this family utilise hydrogen, which is also utilised by methanogens for methanogenesis, to generate succinate which is converted to propionate. Relative abundance of OTU-S3004 showed a positive Spearman correlation with propionate (ρ = 0.41, P = <0.01) but not acetate in the liquid rumen fraction.
