Nitrogen excretion of lactating dairy cows fed an alfalfa hay- or birdsfoot trefoil hay-based high-forage diet

摘要

Extensive research has been conducted to decrease the environmental impacts of dairy farming by using forages containing condensed tannins (CT). In this study, it was hypothesized that feeding CT-containing birdsfoot trefoil (Lotus corniculatus, BFT) to lactating dairy cows would result in a decrease in N degradation in the rumen, causing a shift in N partitioning into milk and manure outputs, compared with alfalfa hay. Urine N is more volatile and harmful to the environment compared with fecal N. By reducing urine N, overall N utilization efficiency can improve. It was our goal to verify how the changes in N partitioning would affect the overall N utilization efficiency by dairy cows fed BFT hay-based high-forage diet. The results in this report showed that feeding BFThay diet reduced protein degradation in the rumen, decreased N excreted to milk and urine, and increased N excretion into feces, resulting in decreased urinary-N:fecal-N ratio due to feeding BFT-hay diet. However, the change in the N excretion routes was not associated with N utilization efficiency, which may have resulted from poor nutritive quality of BFT hay. Although the BFT hay fed in the current study was in a very mature condition and was of poor quality, DM intake and milk yield were similar in both treatments. Therefore, it is implied that BFT hay can replace alfalfa hay in dairy rations, because even poor quality BFT hay compared with alfalfa hay led to similar lactational performance and a beneficial shift in N excretion into environment.