You can use both leaves and branches (cut into smaller pieces by a chopper) as mulch around the base of the plants.
As feed, long term usage of Mango leaves may be problematic according to feedopedia. Selected sections excerpted below.
Mangiferin poisoning
Mango leaves contain high levels (7% DM) of mangiferin, a phenolic compound. Mangiferin may cause poisoning of cattle if mango leaves are fed at high levels. In India, cows used to be fed mango leaves because mangiferin is degraded into euxanthic acid, a rich yellow pigment used in paints that was excreted in urine and collected. However, because continuous intake of the leaves could be fatal to cows, the practice was outlawed in 1908. Sporadic cases of lethality caused by mango leaves have been reported (Orwa et al., 2009; Lowry et al., 1992; Morton, 1987).
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Ruminants
Mango leaves are palatable and acceptable to ruminants. Recent heamatological investigations on goats fed on mango leaves revealed that they were safe and could not be detrimental to goats (Ajayi et al., 2005). This is not fully consistent with the negative effects of mangiferin described by Lowry (Lowry et al., 1992).
Used as sole feed
While mango leaves compare favorably with young cockspur grass (Echinochloa crusgalli) when they are offered as sole roughage to goats (Akbar et al., 1991), comparisons with other plant species are generally less positive. Mango leaves can sustain 6.4 g daily weight gain in goats when Leuceana leucocephala results in 54 g daily weight gain (Kibria et al., 1994). Apparent digestibility and N retention observed for mango leaves are also lower than for other plant species (Kongmanila et al., 2009; Ikhimioya et al., 2007). When growing goats are given the choice, mango foliage has the lowest DM intake (0.3% BW) compared to shrubs and fodder trees such as Erythrina variegata (0.9% BW), Ficus racemosa, jack tree (Artocarpus heterophyllus), jujube (Ziziphus mauritiana), kapok (Ceiba pentandra) or bamboo (Bambusa vulgaris) (Kongmanila et al., 2009). Since goat selectivity is thought to be correlated with feed nutritive value, mango leaves should be considered as a low quality feed, which may be due to the presence of stems in mango foliage (Kongmanila et al., 2008).
Used in combination with other feeds
Mango leaves are better used when associated to other forages. Supplementing mango foliage with water spinach (Ipomoea aquatica) increases DM and CP intake, apparent digestibility and N retention in goats (Kongmanila et al., 2009). Mango foliage may also be profitably used as supplement in forage based diets: it enhances goats total DM intake and overall animal performances when offered as a supplement in a Guinea grass/concentrate-based diet (Ajayi et al., 2005). It compares favourably with Gliricidia sepium or Ficus thonningii in such diets (Ajayi et al., 2005).