Abstract

The objective of this study was to determine the effect of including forage rape, chicory, or irrigated pasture in the diet of mid-lactation dairy cows on performance, rumen metabolism and microbiome, milk quality, CH4 emissions and N excretion. Twelve multiparous lactating dairy cows (527 +/- 40 kg BW; 24.8 +/- 2.5 kg /d milk production and 140 +/- 20 DIM at the beginning of the study; mean +/- SD) were randomly allocated to three dietary treatments in a replicated 3 x 3 Latin square design. The treatments were diets based on grass silage and concentrate plus irrigated pasture (IP), chicory (Ch), and forage rape (Fr). The IP diet was composed of 500 g/kg grass silage, 300 g/kg fresh perennial ryegrass irrigated pasture and 200 g/kg commercial grain-based concentrate; the Ch diet was composed of 500 g/kg grass silage, 300 g/kg fresh chicory and 200 g/kg commercial grain-based concentrate; and FR diet composed of 500 g/kg grass silage, 300 g/kg fresh forage rape, 150 g/kg commercial grain-based concentrate and 50 g/kg of soybean meal. Cows fed diets containing forage rape and chicory had greater dry matter intake than those fed diet with irrigated pasture (P < 0.001). There were no differences in time spent eating among the treatments (P > 0.05), but cows fed the diet containing chicory spent less time ruminating. Milk protein production was greater for the forage rape diet (P = 0.047), compared to the chicory diet. Treatments did not affect the ammonia (NH3) concentration in the rumen. Cows on the forage rape diet had a greater concentration of ruminal total VFA compared to the chicory diet (P = 0.036) and greater valerate concentration compared with cows fed the irrigated pastures diet (P = 0.029). Succinivibrionaceae UCG-001 was more prevalent in cows fed the irrigated pasture diet (all FDR < 0.05). Cows fed diets containing irrigated pasture or forage rape excreted more fecal N compared to cows fed diets containing chicory (P = 0.003), whereas cows fed the chicory diet excreted less N (urinary plus fecal), than cows fed forage rape diets (P = 0.004). No differences (P > 0.05) were observed between treatments for total methane (CH4) production (g/day), nor for the intensity (CH4/kg milk), but CH4 yield was lower in cows fed diets with forage rape and chicory. Overall, using chicory and forage rape in the diet may be a viable option to maintain productivity on dairy farms during the summer. Inclusion of either chicory or forage rape in the diet reduced CH4 yield; however, considering the lower nitrogen excretions of cows fed chicory, the environmental impact due to ammonia, nitrate losses, and N2O emissions might be lower compared with cows fed forage rape.