Growth performance and carcass characteristics of fattening Awassi lambs fed willow silage

Abstract

Providing at least 20% roughage straw is needed to achieve optimal final body weight and feed efficiency in Awassi lambs but the supply of straw has become unpredictable in Jordan, due to erratic rainfall patterns. In order to determine if wastewater-irrigated willow silage (WS) can replace wheat straw in fattening lambs' diets, Awassi lambs were randomly assigned to three high-concentrate diets that included 0 (W0), 10 (W10), and 20% (WS20) of willow silage, on dry matter basis. Lambs in WS0 were fed wheat straw (S) as sole source of roughage; lambs in WS10 were fed a 1:1 ratio of wheat straw and willow silage while WS20 were fed willow silage as sole roughage. Concentrates were formulated to achieve iso-caloric, iso-nitrogenous diets. Lambs were housed in individual pens and fed high concentrate diets for 90 days, after which, five lambs of each group were slaughtered. Growth performance, carcass characteristics, and meat quality parameters were assessed. Feeding willow silage did not affect DM, CP, NDF, and ADF intakes, average daily gain and the feed to gain ratio. Hot and cold carcass weights, dressing percentages and weight of internal organs, meat pH, cooking losses, and water holding capacity were all unaffected by feeding willow silage. Less (P < 0.01) non-consumable mesenteric and kidney fat but more (P < 0.05) valuable tail fat accumulated in carcasses from lambs fed with willow silage. Feeding willow silage was also associated with decreased shear-force of the meat and improved tenderness score. In contrast, loins were heavier (P < 0.002), and Longissimus dorsi muscles were heavier (P < 0.05) and deeper (P < 0.001) in WS0 lambs, and no significant difference was noted for colour attributes. In conclusion, willow silage can replace wheat straw as source of roughage, encompassing a trade-off between advantages, i.e., improved patterns of fat deposition in the carcass and improved meat tenderness, and drawbacks, i.e., smaller loins and L. dorsi muscles.