Changes in ruminal volatile fatty acid production and absorption rate during the dry period and early lactation as affected by rate of increase of concentrate allowance

Abstract

The aim of the present experiment was to study changes in volatile fatty acid (VFA) production using an isotope dilution technique, and changes in VFA fractional absorption rate (kaVFA) using a buffer incubation technique (BIT) during the dry period and early lactation, as affected by the postpartum (pp) rate of increase of concentrate allowance. The current results are complementary to previously reported changes on rumen papillae morphology from the same experiment. From 50 d antepartum to 80 d pp, VFA production rate was measured 5 times and kaVFA was measured 10 times in 12 rumen-cannulated Holstein Friesian cows. Cows had free access to a mixed ration, consisting of grass and corn silage, soybean meal, and (dry period only) chopped straw. Treatment consisted of either a rapid (RAP; 1.0 kg of DM/d; n=6) or gradual (GRAD; 0.25 kg of DM/d; n=6) increase of concentrate allowance (up to 10.9 kg of DM/d), starting at 4 d pp, aimed at creating a contrast in rumen-fermentable organic matter intake. For the BIT, rumen contents were evacuated, the rumen washed, and a standardized buffer fluid introduced [120 mM VFA, 60% acetic (Ac), 25% propionic (Pr), and 15% butyric (Bu) acid; pH 5.9 and Co-EDTA as fluid passage marker]. For the isotope dilution technique, a pulse-dose of (13)C-labeled Ac, Pr, and Bu and Co-EDTA as fluid passage marker was infused. The rate of total VFA production was similar between treatments and was 2 times higher during the lactation (114 mol/d) than the dry period (53 mol/d). Although papillae surface area at 16, 30, and 44 d pp was greater in RAP than GRAD, Bu and Ac production at these days did not differ between RAP and GRAD, whereas at 16 d pp RAP produced more Pr than GRAD. These results provide little support for the particular proliferative effects of Bu on papillae surface area. Similar to developments in papillae surface area in the dry period and early lactation, the kaVFA (per hour), measured using the BIT, decreased from 0.45 (Ac), 0.53 (Pr) and 0.56 (Bu) at 50 d antepartum to 0.28 (Ac), 0.34 (Pr) and 0.38 (Bu) at 3 d pp. Thereafter, kaVFA (/h) rapidly increased up to 0.67 (Ac), 0.79 (Pr), and 0.79 (Bu) at 80 d pp. Although papillae surface area was greater at 16, 30, and 44 d pp in RAP than GRAD, no differences in kaVFA between RAP and GRAD were observed during these days showing papillae surface area is not the limiting factor for kaVFA during early pp adaptation.

Aspects of rumen adaptation in dairy cattle : morphological, functional, and gene expression changes of the rumen papillae and changes of the rumen microbiota during the transition period

“…The k a Ac, k a Pr, and k a Bu from the dry period and 3 d pp in the present study largely agree with those reported earlier by Dieho et al (2016b) for similar sampling days using an identical incubation technique and buffer composition. The k a Ac, k a Pr, and k a Bu observed in the present study from 17 d pp onward are lower than those reported by Dieho et al (2016b), but both our current and previous studies show a clear increase in k a VFA early postpartum.…”

“…In our previous experiment (Dieho et al, 2016b) in early lactation, we observed a similar lack of increase in k a VFA with a temporary increase in rumen papillae surface area in response to a more rapid increase of the rate of increase of concentrate allowance.…”

“…Errors e ijkl were assumed to be auto-correlated for repeated observations on the same cow and site, using a spatial power covariance structure over sampling days . All other data for which sampling site within the rumen was not applicable were analyzed with a reduced model by removing S k and D(C) jl and with repeated measurements on the same cow (Dieho et al, 2016b). Where appropriate, D l was replaced by Week l .…”

“…The BIT procedure, buffer fluid composition, sample processing, and analysis was described in detail in Dieho et al (2016b). Briefly, 50.0 L of standardized buffer fluid at 39°C and pH 5.9, containing 120 mM VFA [60% acetic (Ac), 25% propionic (Pr), and 15% butyric (Bu) acid] and 0.17 mM Co-EDTA as fluid passage marker (Udén et al, 1980), was prepared immediately before use.…”

“…For determination of pH and VFA concentrations, buffer fluid was sampled immediately before introduction into the rumen and after 60 min of incubation in the rumen. Concentration of VFA in rumen and buffer fluid was determined by GC using hydrogen as carrier gas, and the concentration of Co in the buffer fluid was determined by atomic-absorption spectrophotometry (Dieho et al, 2016b). The fractional absorption rate (k a , /h) of Ac (k a Ac), Pr (k a Pr), and Bu (k a Bu), and the fractional fluid passage rate (k l , /h) were calculated as described by .…”