Performance of dairy cows offered silages produced from grass swards harvested on either three or five occasions during the growing season.

The nutritive value of grass silage can be improved by harvesting herbage at a less mature growth stage, which in practice usually involves more frequent harvests. This study examined the performance of dairy cows offered grass silages produced from perennial ryegrass (Lolium perenne) based swards harvested at 2 different frequencies during the growing season (3-harvest (3H) vs. 5-harvest (5H)). Thirty-four mid-lactation (av. 147 d in milk) dairy cows (30 multiparous, 4 primiparous) were offered either 3H or 5H silages in a continuous design (21 wk) experiment. Within each treatment cows were offered silage from each harvest (in harvest number order) for a pre-determined number of days in proportion to herbage DM yield at each harvest. Silages were offered ad libitum while a common concentrate was offered to all cows at 12.0 kg per cow/d over the first 15 wk of the study, 8.0 kg per cow/d during wk 16 -19 and 6.0 kg cow/d during wk 20 - 21. Total yield of herbage harvested over the season from within 3H and 5H were 12.6 and 11.2 t DM/ha, respectively. Across all harvests the mean ME and CP concentration of silages were 10.9 MJ/kg DM and 131 g/kg DM for 3H, and 11.5 MJ/kg DM and 152 g/kg DM for 5H. Silage DMI was greater for cows offered 5H silages compared with 3H silages (14.1 vs. 11.7 kg/d, respectively). Cows offered 5H silages had a greater daily milk yield (33.5 vs. 31.9 kg) and ECM yield (37.4 vs. 35.6 kg) compared with cows offered 3H silages. Treatment had no effect on milk fat or protein concentration. Cows offered 5H silages produced milk with greater concentrations of CLA and n-3 fatty acids. Treatment had no effect on mean BW or BCS, or on efficiency metrics such as milk yield or ECM yield per kg of DMI. Molar proportions of VFA in ruminal fluid differed between the treatments, with cows offered 3H silages having higher proportion of total butyrate (15.9 vs. 14.4% of total VFA) and lower total valerate (3.2 vs. 3.7% of total VFA) compared with those offered 5H. The acetate: propionate and acetate plus butyrate: propionate ratios were unaffected by treatment. In conclusion, increasing herbage harvesting frequency from 3 to 5 times per year improved the nutritional value of the resulting silages, and this led to higher silage DMI, milk yield and ECM yield. However, overall production efficiency (ECM/DMI) was unaffected by treatment.

Performance of Dairy Cows Offered Grass Silage Produced within Either a Three- or Four-Harvest System When Supplemented with Concentrates on a Feed-to-Yield Basis.

More frequent harvesting of grass swards provides an opportunity to improve the nutritive value of grass silage. This study investigated the effect of offering silages produced within either a three- (3H) or four-harvest (4H) system on dairy cow performance when concentrate supplements were offered according to the individual cow's milk yield (feed-to-yield). Cows (n = 80) were allocated to either 3H or 4H at calving and remained on experiment for 25 weeks. Within both treatments, cows were offered silage from each harvest consecutively in proportion to the dry matter (DM) yield for each harvest. Silage was offered as a mixed ration with concentrate added at a rate of 8 kg/cow/day. Additional concentrates were offered on a feed-to-yield basis. Herbage yields were reduced in the 4H system, but 4H silage contained higher metabolisable energy and crude protein content compared to 3H. Cows offered the 4H silage had greater silage DM intake, milk yield and milk protein content, while milk fat content was greater in cows offered 3H silages. In conclusion, increasing harvesting frequency from three to four harvests per year can improve silage feed value, silage intakes and milk yields when concentrates are offered on a feed-to-yield basis.