Milk fatty acid profile and nitrogen utilization of dairy cows fed ryegrass-red clover silage containing plantain (Plantago lanceolata L.)

The effect of plantain (Plantago lanceolata L.) ensiled with ryegrass and red clover (GCP) on the milk fatty acid (FA) profile and nitrogen utilization of dairy cows was tested. Diet GCP was compared to diets based on ryegrass (G), ryegrass and red-clover silage (GC) and total mixed rations (TMR) composed of maize silage, soybean meal and hay (760, 150 and 90 g/kg dry matter (DM), respectively). Cows fed grass-silage diets were supplemented with 3 kg/day of wheat resulting in forage-to-concentrate ratios (DM basis) of 79:21, 85:15 and 86:14 for G, GC and GCP diets, respectively. On average per kg DM, diet G was composed of 790 g ryegrass, diet GC of 577 g ryegrass, 12.3 g blue grass, 218 g red clover, 37.4 g white clover and 5.54 g other species. Diet GCP contained 352 g ryegrass, 127 g red clover, 22.8 g white clover, 7.31 g dandelion and 351 g plantain per kg DM. In a completely randomized design, 24 multiparous dairy cows were fed one of the experimental diets during 13 days of adaptation and 7 days of sampling. The yields of energy-corrected milk (ECM) (27.1 kg/day) and milk protein (910 g/day) of cows fed diet GCP were higher than those of cows fed diet G (20.2 kg ECM/day, 680 g milk protein/day), but did not differ from those of cows fed diet GC or TMR. Urinary nitrogen (N) excretion relative to N intake and relative to total manure N did not differ between treatments. Utilization of dietary N for milk N formation (g/kg) was lowest for diets GCP (251) and GC (257), highest for diet G (357) and intermediate for diet TMR (313). The proportion of polyunsaturated FA in milk fat was highest for cows fed GCP followed by GC, G and TMR. The ratio of n-6 to n-3 FA was lower for diet GCP (1.5:1) compared to G (2.5:1) and TMR (5.7:1). Compared to G, GC and TMR, the cows fed GCP had a higher secretion of 18:1 trans-11 and 18:2 cis-9, trans-11 in the milk relative to dietary 18:3 n-3+18:2 n-6 consumed. In conclusion, increasing botanical diversity in the diet by adding plant species from another functional group, as done when switching from diet G to GC to GCP, did not improve N utilization but did lead to distinctly different milk FA profiles, especially when compared to a maize-silage based diet.