On-farm examination of sainfoin supplementation effects in dairy cows in a roughage-based feeding system: Indicators of protein utilisation

A case study was conducted with the objective to determine the effects of the tanniferous legume sainfoin (Onobrychis viciifolia) on protein utilisation of dairy cows, which were exposed to excessive dietary crude protein during autumn pasture grazing in a zero-concentrate feeding system. The study was conducted under practical conditions, deliberately accepting a certain lack of controllable variables. In order to assess a system applicable in practice, relatively small amounts of sainfoin were offered, and graded supply levels were compared by varying the duration of offer instead of dietary concentration. Within one dairy herd of 60 Swiss Fleckvieh cows, 30 individuals were chosen and randomly allocated to three groups balanced for milk yield, milk urea concentration, days in milk and parity. Over a period of 5 weeks, 2 kg per cow and day of sainfoin pellets were provided either intermittently, for 2 × 5 days (SST) in weeks 3 and 5 of the experiment or continuously over 35 days (SLT). A control group (CON) received 2 kg per cow and day of ryegrass pellets during the 5 weeks. The entire herd grazed on a protein-rich natural sward and was kept overnight in an open-space barn receiving fresh grass and hay ad libitum. Experimental pellets were offered individually twice per day in buckets. Feed, milk, faeces and urine samples were collected in weeks 0 (baseline), 3 and 5. Milk was analysed for fat, protein and urea, urine for purine derivatives, creatinine and nitrogen, and faeces for protein, fibre and particle fractions. During three sampling weeks, chewing activity was recorded by sensor halters. Treatment SST increased rumination time in the first half of the day, which was the only treatment effect on intake and rumination behaviour. Milk fat and protein yields were greater in SST compared to CON, but no treatment effect on concentration and yield of milk urea was found. The proportion of particle fractions in faeces was smaller in both sainfoin treatments compared to CON. In urine, the ratio of purine derivatives to creatinine tended to be higher in SST than in CON, and total urinary nitrogen excretion was lower, indicating a slightly better protein efficiency in SST. In summary, the study revealed small positive effects on protein metabolism and yield when sainfoin was applied short-term over two short periods, whereas long-term application had no effect