IMPROVING NUTRIENT DIGESTIBILITY TO ENHANCE FORAGE UTILIZATION IN LACTATING DAIRY COW FEEDING SYSTEMS
Location: Dairy Forage and Aquaculture Research
Title: Individual animal variability in ruminal bacterial communities and ruminal acidosis in primiparous Holstein cows during the periparturient period
Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 28, 2012
Publication Date: N/A
Interpretive Summary: Cows and other ruminants can digest very fibrous feeds because of bacteria and other microbes that essentially turn the rumen into a large fermentation vat. Past research has shown that the bacterial community composition (type and quantity of the microbes) varies considerably from cow to cow. A cow’s susceptibility to ruminal acidosis (a condition that causes a drop in rumen pH, lower feed intake, and other health problems) also varies from cow to cow. The purpose of this study was to investigate variability among individual cows for their susceptibility to ruminal acidosis both before and after calving, and also to determine whether this variability was related to differences in their ruminal bacterial community composition. Cows that were more susceptible to ruminal acidosis had an increased incidence after calving. Ruminal bacterial community composition differed between pre- and post-calving in some cows; however, cows that demonstrated a greater shift in bacterial community composition were not necessarily those that were more susceptible to ruminal acidosis, and vice versa. The study indicated that shifts in bacterial community composition were only partly associated with differences in severity of ruminal acidosis. This information will be useful to scientists in relating rumen microbial communities to dairy performance.
The purpose of this study was to investigate variability among individual cows for their susceptibility to ruminal acidosis (RA) pre- and postpartum, and determine whether this variability was related to differences in their ruminal bacterial community composition (BCC). Variability in susceptibility to RA among individual cows was characterized based on ruminal fermentation variables. Effects of prepartum dietary treatment on susceptibility of cows to RA were also examined. Fourteen Holstein heifers paired by expected calving date and BCS were allotted to 1 of 2 prepartum dietary treatments: low concentrate (2 diets ranging from forage:concentrate (F:C) = 80:20 to 54:46); or high-concentrate (4 diets ranging from F:C = 68:32 to 46:54). All cows received the same lactation diet postpartum. Microbial DNA extracted from 58 rumen digesta samples collected prepartum (d -50, -31, -14) and postpartum (d +14, +52) and amplified by PCR were subjected to automated ribosomal intergenic spacer analysis (ARISA). Changes in ruminal variables [pH, volatile fatty acids (VFA), and acidosis indicators measured at d -54, -35, -14, -3, +3, +17, +37, +58] were analyzed using principal component analysis (PCA). Based on the shift (defined as the distance of the mean loadings) between the prepartum and postpartum period for each cow, the 14 cows were classified into 3 groups: less acidotic (LA; n=5), more acidotic (MA; n=5), and intermediate (IN; n=4). Cows in the MA group had greater severity of RA (measured as duration of total RA, mild RA, moderate RA and acute RA; area under pH curve for total RA, mild RA, and moderate RA) postpartum than prepartum, and this difference between periods was greater than for the LA cows. The variation in susceptibility to RA was independent of intake, total VFA and individual VFA. However, RA index (total area of pH < 5.8 normalized to intake) showed interaction between susceptibility and period. Production variables (milk yield, fat %, fat yield, FCM, efficiency of milk production) were not influenced by susceptibility to RA. Ruminal BCC was not influenced by dietary treatment or period. However, a shift in BCC occurred across periods for some cows. Based on the magnitude of the shift in BCC (distance between mean ordination values across the periods for each cow), cows were grouped into 3 BCC profile categories: stable (5 cows with lesser shift), unstable (5 cows with greater shift) and intermediate (4 cows with average shift). Cows demonstrating a greater shift in BCC were not necessarily those in the MA group and vice versa. The relationship between the shifts in ruminal fermentation variables (PCA rankings) and the shifts in BCC (ARISA rankings) were not related (n = 14; r2 = 0.00; P = 0.98). It was concluded that not all cows are equally susceptible to RA, and shifts in BCC appear to be independent of differences in the severity of RA postpartum.