Nutritional composition of lentil straw, vetch hay, olive leaves, and saltbush leaves and their digestibility as measured in fat-tailed sheep

Abstract

Several less researched forages from various Mediterranean plants may be superior, or at least equivalent, in forage value to barley (Hordeum vulgare) straw. These include lentil (Lens culinaris) straw, vetch (Vicia sativa) hay, dried olive (Olea europea L.) leaves, and saltbush (Atriplex halimus). Using in vitro, in sacco and in vivo methods, we tested (i) the nutritional composition, (ii) digestibility and metabolizable energy, and (iii) intake and nitrogen balance in fat-tailed Awassi lambs of these feeds or diets prepared with these feeds. In vivo, the forages were fed in proportions of about 3/4 of the total diet to 30 animals allocated to five groups in a randomized complete block design. Diets, balanced for nitrogen, included concentrate (280g/kg) and were offered at 1.1kg dry matter (DM)/day with ad libitum access to water. Test forages had large differences in content (g/kg DM) of organic matter (OM; 690–916, Atriplex leaves vs. barley straw), crude protein (CP; 43–169, barley straw vs. vetch hay) and neutral detergent fiber (258–672, Atriplex leaves vs. barley straw). Olive leaves contained the highest phenol and ether extract levels (63 and 32g/kg DM, respectively). Atriplex leaves were particularly rich in Na (94g/kg) and K (39g/kg). Atriplex leaf OM had the highest digestibility (0.68), but its low level reduced the metabolizable energy (ME; 6–7MJ/kg DM) to that of barley straw. Its limited palatability caused significant refusals as well. Vetch hay, olive leaves, and lentil straw had superior OM digestibility to that of barley straw (the latter not significant). Olive leaf CP had limited ruminal degradability and total tract digestibility. None of the forages significantly affected body N retention, while olive leaves significantly reduced rumen microbial efficiency. The different models used to estimate ME ranked vetch hay first (9MJ/kg DM), followed by olive leaves and lentil straw (6.5–8MJ/kg DM). Overall, vetch hay was the most valuable forage in terms of energy and protein supply. Lentil straw and olive leaves were similar or slightly superior to barley straw, although they presented a different ruminal degradation pattern. Atriplex leaves, if fed restrictedly, could be used to replace barley straw when access to water is ad libitum.