Effect of particle size of silage of rehydrated corn on grazing dairy cows

Abstract

The particle size (PS) of rehydrated and ensiled corn (REC) can affect grinding rate on farm and starch digestibility. We evaluated the effect of PS of REC on dry matter (DM) intake (DMI), lactation performance, total tract digestibility, and ruminal fermentation profile of grazing dairy cows. The treatments were corn (68% vitreous) finely ground (GC) and coarsely ground (CO) or finely ground (FI) ensiled in buckets (200 L; 63.2% DM) for 39.9 ± 2.3 d. The mean geometric particle size was 366, 1364 and 1694 µm for GC, FI and CO respectively. 21 paddocks of Urochloabrizantha cv. Marandu (54.8 kg DM/cow/d of forage allowance; 11.1 ± 1.1 cows/ha) grazed for 1 d. Eighteen cows (21.3 ± 4.3 kg/d; 563 ± 62 kg; 190 ± 112 d in milk) formed 6 squares in a 3×3 Latin square design (3 periods of 21 d, 14 adaptation), grouped by level production: High (26.1 ± 2.6 kg/d), Medium (20.9 ± 2.0 kg/d) and Low (16.9 ± 1.0 kg/d), being a square of the level High formed by 3 rumen cannulated cows. The NRC (2001), model estimated DMI, predicting intake of 1.1% of body weight for forage neutral detergent fiber (NDF). Individual supplementation was carried out at 0500, 1000 and 1400 h, with whole plant corn silage (2.7 kg DM/d), soybean meal and treatments, milking was at 0600 and 1600 h. Undegraded NDF from feces and diet, incubated in situ for 240 h and fecal excretion using Cr2O3, were used for estimated pasture consumption. Ruminal fluid and blood, collected at 0, 5 and 9 h after morning feed, were analyzed as repeated measures, by model containing the effect of period, group, cow (group), treatment and the interaction between group and treatment (P≥0.12). The ingredients and nutrients of the diets were (%DM): 39.6 ± 2.7% pasture; 15.5 ± 1.7% corn silage; 13.2 ± 1.1% soybean meal; 29.6 ± 1.4% corn; 13.5 ± 0.4% crude protein; 32.2 ± 0.6% NDF; 22.6 ± 1.1% starch. The FI treatment resulted in lower DMI (16.7 vs. 18.1 kg/d) and digestible organic matter (DOMI; 9.6 vs. 10.6 kg/d) than GC (P≤0.05), both without differing from CO (17.7 and 9.9 kg/d, respectively). Treatments not affect milk production (P≥0.17; 19.2 kg/d) and energy corrected milk (ECM; 16.8 kg/d) which showed low fat content (2.99%; P = 0.33). Cows fed FI had the highest Milk/CMS ratios (1.18 vs. 1.05) and ECM/DOMI (1.86 vs. 1.64; P≤0.05). The D of DM, OM and starch were low (86.3 vs. 92.3% of intake) and the concentration of fecal starch was high (7.0 vs. 4.0% of DM) for the CO treatment (P≤0 .05). The D of the NDF was lower in the treatment GC than FI (45.6 vs. 48.9% of intake; P≤0.05). Plasma glucose was higher for FI and CO treatments (75.0 mg/dL) than GC (70.8 mg/dL; P≤0.05). The FI treatment increased feed efficiency and CO reduced starch D.