Effects of feeding forage rape or chicory in a grass silage and concentrate-based diet as supplementary crops to replace irrigated pasture on performance, rumen metabolism and microbiome

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 × 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.