Nutritive evaluations of some browse tree foliages during the dry season: Secondary compounds, feed intake and in vivo digestibility in sheep and goats

Four browse tree foliages (Cassia fistula, Schinus molle, Chorisia speciosa and Eucalyptus camaldulensis), native to the semi-arid region of north Egypt, were harvested during the dry season and evaluated for nutritional quality by determination of levels of nutrient and secondary compounds, as well as feed intake and apparent digestibility in sheep and goats. The study consisted of four experiments conducted in sequential 28-day periods that were the same in all respects, except that a different foliage was evaluated in each experiment which used six adult male Rhmani sheep (35 ± 2.3 kg body weight (BW) at the start of the study) and six crossbred goats (30 ± 1.56 kg BW). Sheep and goats were randomly divided into two groups of three and offered foliage at a level equal to 1.3 of the previous days voluntary intake of fresh matter and a commercial concentrate, with or without 10 g/animal/d of PEG, at 10 g/kg of BW to meet 0.7 of maintenance metabolizable energy requirements. Foliage crude protein (CP) content ranged from 124 (S. molle) and 128 (C. speciosa) to 185 g/kg DM (C. fistula). Ether extract was highest (97 g/kg) in S. molle. C. fistula had the lowest neutral detergent fiber (NDFom), acid detergent fiber (ADFom) and acid detergent lignin (lignin(sa)), while E. camaldulensis had the highest values. Total phenolics (TP), condensed tannins (CT), saponins (SAP), alkaloids (ALKA), the aqueous fraction (AF) of lectins, polypeptides and starch, and essential oils (EO) were lowest in C. speciosa (29, 21, 3, 0, 4 g/kg DM and 0.40 ml/kg DM, respectively) and highest in E. camaldulensis (102, 68, 15, 5, 3 g/kg DM and 15 ml/kg DM, respectively). Levels of TP, CT, SAP, ALKA and EO were highly positively intercorrelated among foliages, although AF was weakly negatively correlated to all others. Goats consumed 3.9% more foliage dry matter (DM) than sheep per kg BW0.75, and their digestibility was about 8% higher, probably reflecting their better capacity to detoxify secondary compounds in the rumen than sheep. Levels of CT (and due to its correlations, also TP, SAP, ALKA and EO) was a strong predictor of DM intake of PEG unsupplemented foliages within both sheep and goats. PEG increased (P<0.05) intake of DM and its components in sheep and goats. Digestion of DM and NDFom were not affected by feeding PEG, although digestion of OM, EE and CP were higher (P<0.05). TP in tree foliages (and due to its correlations, also CT, SAP, ALKA and EO) was not a predictor of the proportional increase in DM with PEG feeding, which was best predicted by level of CP within foliage. Overall, C. speciosa, had the highest nutrient value for both sheep and goats, both without and with PEG feeding, S. molle and C. fistula were intermediate and E. camaldulensis had the lowest nutritive value.