Abstract
Despite the possible influence of tannins on the nutritional value of the forages from Caatinga vegetation, there are few studies that evaluated their tannin concentration. This study was conducted to characterize condensed tannins present in the legumes species Mimosa hostilis (Jurema Preta), Mimosa caesalpinifolia (Sabiá) and Bauhinia cheilantha (Mororó), at three stages of their phenological cycle. The concentration of soluble tannin (ST), bound tannin (BT) and total tannin (TT) were determined using the butanol-HCL method; astringency was by the radial diffusion method, and the monomeric composition of purified tannins by a high-performance liquid chromatograph with delphinidin, cyanidin and pelargonidin as standards. Concentration and astringency of purified condensed tannins, as well as their monomeric composition varied between species, and in some cases among phenological cycles. The values observed were always above the limits considered beneficial for ruminal digestion (i.e. 5%). Jurema Preta presented the highest values (30.98% TT and 22% astringency at full growth stage), and Mororó the lowest (10.38% TT and 14% astringency during fructification). Jurema Preta presented a mean relationship prodelfinidin (PD): procyanidin (PC) of 97:3, which did not vary during the phenological cycle, showing the high astringent capacity of these tannins. Sabiá presented a relationship of 90:20 during full growth and flowering stages, decreasing to 40:50 at fructification. In Mororó the PD:PC relationship was more equilibrated, around 40:50 during full growth and flowering stages, decreasing to 35:60 During fructification. Propelargonidin was not detected or was present at low concentration in the three species.
Highlights
Due to its abundance and resistance to drought, semi-arid native vegetation has been historically used for raising livestock, constituting frequently the only protein and energy source for the local ruminants
Tannins might be associated with adverse effects as anti-nutritional factors, causing lower dry matter intake and reduced digestion of protein and fiber
The effects depend on tannin concentration in the plant and other factors, such as type of tannin, animal species, physiological status and diet composition (Schofield et al, 2001; Makkar, 2003)
Summary
Due to its abundance and resistance to drought, semi-arid native vegetation has been historically used for raising livestock, constituting frequently the only protein and energy source for the local ruminants. Around seventy percent of woody species from some ecological sites contribute significantly to bovine, ovine and goat diets (Araújo Filho et al, 1993). These plants are constantly submitted to several stressing agents such as, high temperature, water shortage, intense solar radiation, and nutrient deficiencies, which modify their morphology and development rates, limiting their production and altering their nutritional quality (Buxton & Fales, 1994). Condensed tannins are polyphenols present in the majority of tropical legumes. They are associated to a reduction in voluntary intake and in the digestibility of dry matter, organic matter, protein and fiber. Climatic conditions and soil fertility influence the concentration of tannins, but their monomeric composition and molecular weight as well (Lascano et al, 2001), characteristics that may determine the effect of these phenols on the nutritional quality of the plants
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