Effects of perennial ryegrass, perennial ryegrass-white clover, and perennial ryegrass-white clover-plantain swards on the milk production, intake, digestibility, nitrogen excretion, and urination characteristics of dairy cows in late-lactation.

The objective of this experiment was to investigate the effects of sward type on the milk production, intake, digestibility, N excretion and urination characteristics of late-lactation dairy cows offered freshly harvested herbage indoors in a cut-and-carry feeding system during autumn. Nine ruminally cannulated multiparous Holstein Friesian cows averaging (mean ± SD); 181 ± 12 DIM and 526 ± 37 kg liveweight were randomly assigned to 1 of 3 dietary treatments (DT) in a replicated 3 × 3 Latin square experimental design. The experiment included 3 29-d periods, with each period consisting of 21-d of dietary adaptation before an 8-d measurement period. The 3 DT were: 1) tetraploid perennial ryegrass receiving 50 kg of synthetic N/ha/cut (GO); 2) tetraploid perennial ryegrass-white clover receiving 25 kg of synthetic N/ha/cut (GC); and 3) tetraploid perennial ryegrass-white clover-plantain, containing 50% plantain, receiving 25 kg of synthetic N/ha/cut (GCP). All cows were also supplemented daily with 0.89 kg DM/d of a standard concentrate. There was no effect of DT on the majority of milk production outcomes; however, cows fed GCP had lower milk fat yield and tended to have lower milk fat concentration when compared with cows fed GO and GC. There was no effect of DT on DM or OM intake. Cows fed GCP had lower apparent DM, OM and N digestibility when compared with cows fed GO and GC. Urinary N concentration was lower for cows fed GCP (0.36 g/100 g) when compared with cows fed GO and GC (0.63 and 0.58 g/100 g, respectively). Urinary N excretion was greatest for cows fed GO (355 g/d), intermediate for cows fed GC (323 g/d), and lowest for cows fed GCP (267 g/d). Cows fed GCP had greater fecal N output when compared with cows fed GO and GC. Cows fed GCP had lower urinary N output as a proportion of N intake when compared with cows fed GO and GC, whereas cows fed GCP had greater fecal N output as a proportion of N intake when compared with cows fed GO and GC. There was no effect of DT on the concentration of N in milk or milk N output. Cows fed GCP had greater urine output and greater herbage water intake when compared with cows fed GO and GC. Lastly, when compared with cows fed GO and GC, cows fed GCP had a greater number of urinations per day (15.1, 14.9 and 19.3 events/d, respectively) and greater urine event volume (3.7, 3.7 and 4.2 L/event, respectively). Overall, these results support the inclusion of plantain in perennial ryegrass-white clover swards as a practical and effective strategy to reduce urinary N excretion in pasture-based dairy systems.