Can tree leaves be an alternative source of feed for dairy ruminants?

The importance of agroforestry systems is increasing as they promote sustainable agricultural practices to address climate change and food security. The study aimed to assess the potential of tree species as feed ingredients for dairy ruminants. Leaves from five tree species—Fraxinus excelsior L. (common ash), Morus nigra L. (black mulberry), Robinia pseudoacacia L. (locust tree), Salix babylonica L. (weeping willow) and U. minor Mill. (field elm)—were sampled in three different times in spring–summer season 2023 on a farm in Northern Italy. Proximate composition, analyses along with in vitro analyses, were conducted to determine net energy of lactation (NEL) by gas production and fibre digestibility (NDFD). Results found wide variability among species for chemical and nutritive value. Fibre content (% DM) was highest in U. minor (57.2) and lowest in M. nigra (34.5), whereas crude protein (% DM) was highest in R. pseudoacacia (22.4), followed by S. babylonica and M. nigra (20.3, on average), U. minor (15.1) and F. excelsior (14.0). Morus nigra had the highest NDFD (75.3%) and NEL (5.66 MJ/kg DM). Intermediate NEL values were recorded for F. excelsior and S. babylonica (4.50 MJ/kg DM, on average), the lowest values in U. minor and R. pseudoacacia (3.90 MJ/kg DM, on average). The study indicated that most of the examined tree species can be used as dietary supplements due to their nutritional properties as they maintain their quality throughout the growing season. Morus nigra emerges as the most promising species due to its superior nutritive value.