Morphological adaptation of rumen papillae during the dry period and early lactation as affected by rate of increase of concentrate allowance

Knowledge of the morphological adaptation of rumen papilla, which plays an important role in volatile fatty acid absorption, in dry and early lactation dairy cattle is limited. Therefore, macro- and microscopic changes in papilla morphology during the dry period and lactation and the effect of rate of increase of concentrate allowance were studied. Samples were collected from 12 rumen-cannulated Holstein Friesian dairy cows during a pretreatment period, 50, 30, and 10 d antepartum (the dry period) and 3 d postpartum (pp), and a treatment period, 9, 16, 30, 44, 60, and 80 d pp. Cows had free access to either a dry period ration [27% grass silage, 27% corn silage, 35% wheat straw, and 11% soybean meal on a dry matter (DM) basis] or a basal lactation ration (42% grass silage, 41% corn silage, and 17% soybean meal on a DM basis, and 0.9 kg of DM/d concentrate). Treatment consisted of either a rapid (1.0 kg of DM/d; RAP; n = 6) or gradual (0.25 kg of DM/d; GRAD; n = 6) increase of concentrate allowance (up to 10.9 kg of DM/d), starting at d 4 pp, aimed at creating a contrast in rumen-fermentable organic matter (FOM) intake. Papillae were collected from the ventral, ventral blind, and dorsal blind rumen sacs and measured digitally. Intake of DM (11.9 kg/d) and FOM (5.7 kg/d) did not change during the pretreatment period, but increased during the treatment period to 24.5 and 15.0 kg/d at 80 d pp, respectively. Concentrate treatment and sampling day interacted for FOM intake, which was 22% greater in RAP at 16 d pp compared with GRAD. Papilla surface area decreased during the pretreatment period by 19% to 28.0 mm2 at 3 d pp, thereafter increasing to 63.0 mm2 at 80 d pp. Concentrate treatment and sampling day interacted for surface area, which was greater in RAP compared with GRAD at 16 (46.0 vs. 33.2 mm2), 30 (55.4 vs. 41.2 mm2), and 44 (60.5 vs. 49.7 mm2) days pp, showing that papillae can respond to a rapid rate of increase of FOM intake by increasing growth rate. Microscopic morphology was affected by sampling day, but neither by concentrate treatment nor by their interaction, with a decrease in papilla and epithelium thickness during the lactation. In conclusion, the rumen papillae respond to changes in FOM intake and the magnitude of this response depends on the rate of increase of FOM intake. This response in surface area of the rumen papillae potentially facilitates the absorption of the volatile fatty acids