The effect of including plantain (Plantago lanceolata L.) in perennial ryegrass and white clover pastures on milk production and nitrogen excretion of dairy cows throughout the grazing season.

The objective of this study was to investigate the effect of including plantain (Plantago lanceolata L.; PL) in a perennial ryegrass (Lolium perenne L.; PRG) and white clover (Trifolium repens L.; WC) pasture mixture grazed by dairy cows on DMI, milk production and composition, and N excretion throughout the grazing season. Twenty-six (6 primiparous and 20 multiparous) Holstein-Friesian dairy cows were blocked on parity and assigned to 1 of 2 dietary treatments, balanced for economic breeding index, calving date, BW and BCS at calving, and milk production. Treatments were PRG and WC pasture and PRG, WC, and PL pasture (GCP), supplemented with concentrate feed at milking (daily at 0730 and 1500 h). Cows grazed their allocated pasture from d 4 postpartum until the end of the grazing season (34-wk study). Nitrogen excretion was quantified during 2 N partitioning studies; conducted when cows were in early (61 ± 11 DIM; wk 10) and late (214 ± 11 DIM; wk 32) lactation. Cows offered GCP had a 6% lower daily milk solids yield in early lactation (EL) but a 9% greater daily milk yield in late lactation (LL). Milk fat concentration was significantly lower from cows offered GCP in EL and LL. Treatment did not significantly affect cumulative milk, milk fat, or milk protein yield per cow, however, cows offered GCP had a numerically lower cumulative milk solids yield (433 kg/cow vs. 451 kg/cow). Estimated pasture DMI was greater for cows grazing GCP in the EL (+10%) and LL (+16%) N partitioning studies. Dietary PL content was 33% and 32% of GCP cows' total DMI in the early and LL N partitioning studies, respectively. Nitrogen utilization efficiency was 12% lower for cows grazing GCP in the EL N partitioning study (27.5% vs. 31.2%) but 13% greater in the LL N partitioning study (22.3% vs. 19.7%). Estimated total urine volume was greater in both N partitioning studies for cows grazing GCP, and urinary N excretion (-30%) and concentration (-39%) were only lower in the LL N partitioning study for cows on the GCP treatment.