Month of Harvest and Leaf Age Impact the Bromatological Composition and Polyphenol Content of Gymnopodium floribundum Rolfe Leaves

In the present study, the effects of macro- and microclimatic conditions, month of harvest, and leaf age at harvest on the bromatological composition and polyphenol content of Gymnopodium floribundum leaves were evaluated. Leaves were harvested in December 2017 and 2018 and March, June, and September 2018. At each harvest, three composite samples of mixed-age leaves were collected from 12 trees (four trees for each sample), and the sampling was repeated on day 90 post-harvest to collect 90-day-old leaves. Fresh and dry matter, crude protein, acid and neutral detergent fibers (ADF and NDF, respectively), lignin, total tannins, condensed tannins (CT), total phenols, in vitro dry matter (IVDMD) and organic matter (IVOMD) digestibility, and metabolizable energy (ME) were estimated. Rainfall, relative humidity, and microhumidity were associated with chemical composition. IVDMD, IVOMD, and ME were highest in leaves sampled in March regardless of age ( p < 0.001). Water content, ADF, NDF, and lignin were highest in the leaves sampled in September, regardless of age ( p < 0.05), suggesting that leaves require more structural support in the rainy season. CT content was highest in September in the mixed-age leaves and in September and December in the 90-day-old leaves ( p < 0.05). A high fiber and CT content during the period of rapid leaf growth could deter herbivory.