Chemical composition, rumen degradability, protein utilization and lactation response to selected tree leaves as substitute of cottonseed cake in the diet of dairy goats

The aim of this study was to investigate the potential of leaves from Grewia oppositifolia (G. oppositifolia) and Ziziphus mauritiana (Z. mauritiana) as a crude protein (CP) supplements to low quality diets of goats in Pakistan. Chemical composition and CP degradability of the tree leaves were compared with cottonseed cake (CSC). The CP content of the supplements ranged from 141 to 269 g/kg dry matter (DM). Contents of total phenols and condensed tannins (CT) were higher (P<0.01) in Z. mauritiana than G. oppositifolia 49, 33 and 20, 0.6 g/kg DM, respectively. Leaves from G. oppositifolia were higher (P<0.05) in Ca (35 g/kg DM). The rate of degradation and effective degradability of CP at rumen outflow rates of 0.04 and 0.06/h were consistently higher (P<0.05) in CSC than in the leaves. Tree leaves did not vary from each other in N disappearance characteristics. A balance trial in a 4 × 4 Latin square design was conducted with four dry Beetal goats (35 ± 2.3 kg body weight (BW)). The goats were fed on range grass hay as a sole diet or supplemented with CSC, G. oppositifolia or Z. mauritiana on an iso-N basis. Addition of the supplements to the diets increased DM intake and N retention (P<0.05) without affecting DM digestibility. N retention in goats varied (P<0.05) due to diet composition and was highest (6.2 g) with Z. mauritiana. Lactation responses were examined with 16 Beetal goats (44.6 ± 4.20 kg BW; days in milk 44 ± 2.4), assigned randomly to a supplement of CSC, G. oppositifolia, Z. mauritiana or mixture of both. All goats received a basal diet of maize silage ad libitum and were daily grazed on natural pasture for about 4 h. Yield of milk differed among the supplements and was highest (P<0.05) for Z. mauritiana. Among the supplements, a high (P<0.05) milk fat content of 56 g/kg milk was recorded with CSC and G. oppositifolia. Total solids, protein and solids not fat concentrations in the milk did not respond to supplementation. We conclude that Z. mauritiana and G. oppositifolia leaves can replace CSC as a supplement in low quality diets of dairy goats.