Intake, digestion, and nitrogen balance of sheep fed shrub foliage and medic pods as a supplement to wheat straw

Abstract

Low animal performance in arid and semi-arid areas of Morocco is mainly due to protein and energy deficiencies of available forages. A metabolism trial was conducted to evaluate the influence of supplementation with shrub foliage and medic (Medicago sp.) pods on nitrogen (N) utilization by sheep fed low-quality roughage. Diets were wheat (Triticum aestivum L.) straw (WS), WS plus alfalfa (Medicago sativa L.) hay (AH), WS plus oldman saltbush (Atriplex nummularia Lindl.) foliage (AN), WS plus blue wattle (Acacia cyanophylla Lindl.) foliage (AC), and WS plus medic pods (MP). Alfalfa feeding level was set to provide a crude protein (CP) concentration of 90 g kg−1 dry matter (DM) in the diet. Shrub foliage and medic pods were offered ad libitum. Average intake levels for AN, AC, and MP were 37.2, 32.4, and 47.2% DM, respectively. Chemical composition and in vitro dry matter disappearance (IVDMD) were measured. Digestible dry matter intake (DDMI) was greatest (P < 0.05) for saltbush diet (36.3 g kg−0.75), followed by the alfalfa diet (30.0 g kg−0.75). Unsupplemented wheat straw and blue wattle diets had the lowest DDMI (21.3 g kg−0.75). The daily N balance for the supplemented diets was greatest (P < 0.001) for alfalfa and saltbush diets with +6.7 g and least for the blue wattle diet (+ 3.0 g). Feeding the unsupplemented wheat straw diet resulted in the lowest N retention (+ 0.6 g day−1). A degradability trial was then conducted to investigate the rate and extent of DM and CP digestion of the same forages in the rumen. Forage samples were incubated for 0, 2, 4, 8, 12, 24, 48, and 72 h. Rate and extent of DM digestion were highest (P < 0.05) for saltbush foliage. Rate of CP degradation was fastest (P < 0.05) for alfalfa hay (0.151 h−1). Extent of CP degradation was greatest (P < 0.05) for saltbush foliage (74.4%), followed by MP (69.0%), AH (63.9%), and BW (6.8%). Inclusion of saltbush foliage, and to some extent medic pods, with low-quality forage diet was comparable to inclusion of alfalfa hay. These results indicated that improving degraded rangelands by planting palatable shrubs, and managing medic pastures to produce enough pods to be grazed in the summer should reduce the need to supply sheep with costly protein-rich supplements during periods of feed shortage.