Abstract #538

# 538
Lactation performance of dairy cows fed rehydrated and ensiled corn grain differing in particle size and concentration in the diet.
L. P. Castro1, J. D. L. Dias1, D. V. D. Lage1, E. F. Barbosa1, R. P. Melo1, K. Ferreira1, J. T. R. Carvalho1, F. F. Cardoso1, R. A. N. Pereira3,2, M. N. Pereira*1,2, 1Universidade Federal de Lavras, Lavras, MG, Brazil, 2Better Nature Research Center, Ijaci, MG, Brazil, 3Empresa de Pesquisa Agropecuaria de Minas Gerais, Lavras, MG, Brazil.

Rehydrated and ensiled ground corn (REC) has high ruminal starch digestibility, but particle size (PS) and dietary starch concentration (S) can affect starch digestion. An 84% vitreousness hybrid was ground to geometric mean particle sizes (GMPS) of 1,591 (Fine) and 2,185 (Coarse) µm for rehydration (60% DM) and ensiling in 200 L buckets for at least 205 d. The rate of grinding (ton/h) was 3.9 for Fine and 11.7 for Coarse (P < 0.01). Ensiling increased (P < 0.01) ruminal in situ DM degradation (63.7 vs 34.1%), regardless of particle size. Sixteen Holsteins (152 ± 96 DIM) in 4 × 4 Latin squares (21-d periods) were individually fed a 2 × 2 factorial combination of low or high starch with Fine or Coarse. Variation in the concentration of starch in the diet (29.2 vs 23.5% of DM) was achieved by partial replacement of REC for citrus pulp. Milk yield (31.0 kg/d) and solids secretion did not differ (P ≥ 0.19). Fine REC tended to reduce DMI and to increase feed efficiency only with the high starch diet (P ≤ 0.10 for the interaction of S and PS). Total-tract starch digestibility tended (P = 0.06) to be reduced by Coarse (96.4 vs 97.2% of intake) and the daily secretion of urinary allantoin tended to be increased (P = 0.09). The molar proportions of acetate and butyrate in ruminal fluid were reduced and propionate and isoacids were increased by high starch (P < 0.01). Coarse reduced plasma d-lactate concentration when fed in the high starch diet (P < 0.08 for the interaction of S and PS). High starch reduced the proportion of daily intake from 1900 to 0700 h (P = 0.02) and induced preferential intake of feed particles <8 mm (P = 0.06) and greater refusal of particles >19 mm (P = 0.01) in the morning. The preferential intake of <8 mm particles tended (P = 0.06) to be increased by Fine in the morning. Coarse grinding of REC ensiled for more than 200 d had no effect on lactation performance and intake when starch in the diet was 23.5% of DM. When dietary starch was increased to 29.2%, fine grinding induced short-term intake depression, gain in feed efficiency, and increased plasma d-lactate concentration, suggestive of ruminal acidosis. Funded by FAPEMIG/CNPq.

Key Words: starch digestibility, corn grain particle size, corn grain silage