Abstract #M303

# M303
The effects of varying undigested NDF and physically effective NDF content of fresh cow rations on metabolism in multiparous Holstein cows.
S. E. LaCount*1, B. M. Leno1, C. M. Ryan1, T. R. Overton1, 1Department of Animal Science, Cornell University, Ithaca, NY.

The objective of this study was to determine the effect of varying undigested NDF at 240 h (uNDF240) and physically effective NDF (peNDF) content of fresh cow rations on metabolism. Multiparous Holstein cows (n = 56) were fed a common prepartum ration beginning 28 d before expected parturition and assigned randomly at calving to 1 of 2 postpartum diets differing in content of uNDF240 and peNDF. High fiber (HF; 35.3% NDF, 12.1% uNDF240, 25.0% peNDF; n = 27) and low fiber (LF; 32.8% NDF, 9.5% uNDF240, 21.4% peNDF; n = 29) treatment diets were formulated for equivalent metabolizable protein (110 g/kg DM) and starch (24.8% DM), with higher fiber levels achieved through the addition of straw. At 29 DIM, cows fed HF were switched to the LF diet and all cows were fed the LF diet through 42 DIM. Blood samples were collected 2×/wk prepartum, daily from d 0 through 7 DIM, 3×/wk through 21 DIM and 2×/wk to 42 DIM. Liver biopsies were obtained from a subset of 40 cows on d 7 ± 1.1 (mean ± SD) and 14 ± 1.0 postpartum and incubated in an in vitro system to determine liver capacity to convert [1-14C] propionate and [1-14C] palmitic acid to end products. Data were analyzed by repeated measures ANOVA with the random effect of cow within treatment and fixed effects of treatment, time, and treatment × time. A treatment × time effect was observed for plasma NEFA and was higher for cows fed HF particularly from 21 to 31 DIM (P = 0.01), plasma β-hydroxybutyrate was higher for cows fed HF from 12 to 31 DIM (P < 0.01), and plasma glucose was lower for cows fed HF from 9 to 27 DIM (P < 0.01) compared with cows fed LF. Cows fed LF tended to have greater liver oxidation of palmitate to CO2 (12.23 nmol/(g·h) vs. 10.94 nmol/(g·h); P = 0.15) and lower conversion to esterified products (226.9 nmol/(g·h) vs. 248.2 nmol/(g·h); P = 0.10) than cows fed HF. Conversion of palmitate to acid soluble products was not different between treatments and no effects on in vitro liver propionate metabolism were observed. Changes in plasma metabolites and liver fatty acid metabolism were consistent with lower dry matter intake of cows fed the HF diet.

Key Words: transition cow, fiber, metabolism