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Evaluation of nutritional quality of tropical and temperate forages
Komey, Agnes Josylyn
Background: Grasses (Poaceae) and herbaceous legumes (Fabaceae) are the usual forages used in animal production. They can be categorised into temperate (C3/cool-season) and tropical (C4/warm-season). Forage crops with C3 photosynthetic pathways (temperate forages) are more nutritious than those with C4 (tropical forages). Aim: To evaluate the nutritional quality of tropical and temperate forages. Design and methods: Data were gathered for four (4) tropical forage crops (legumes; Stylosanthes guianensis and Centosema pascuorum versus grasses; Biachiara decumbens and Pennisetum purpureum) from 11 scientific publications. To be added, the publication had to contain at least data on crude protein, neutral detergent fibre, acid detergent fibre and dry matter. Forage samples were analysed using methods proposed by AOAC (1990 and 2011), Goering and Van Soes (1970), Silva and Queiroz (2002), Van-Soest et al. (1991). For temperate forage, the method was as follow: The study was done at the Research Station of Fodder Crops in Vatin (49o31'N, 15o58'E, 560 m.a.s.1) located in the Czech Republic. Medicago sativa (alfalfa) and Trifolium pratense (meadow /red clover) were the legume forages used. The grass species were Lolium perenne (perennial ryegrass) and Dactylis glomerata (cock's foot). The legumes were harvested before flowering (butonization), and the grasses were harvested at the boot stage. Samples of each forage species were analysed for crude protein (CP), neutral detergent fibre (NDF), acid detergent fibre (ADF) and dry matter (DM). SPSS (version 20) was used to analyze the data gathered, as well as analysis of variance (ANOVA). The differences in the nutritive values between crop types within the same group (tropical grass/legume and temperate grass/legume) were analysed using independent sample t-tests (SPSS). The differences in nutrients between temperate and tropical forages were analysed using ANOVA and Tukey's pairwise comparison test. For all analyses, the statistical significance threshold was fixed at P 0.05. Results: There were significant differences observed in the nutrients among the forage legumes. The CP content for Centro (C.pascuorum) was significantly more than that of stylo (S.guianensis); 14.83a ± 0.84 vs 11.32b±0.84 respectively (P-value= 0.02 from Tukey's pairwise comparison). Also, significant differences were observed among the forage grasses. The ADF content for signal grass was significantly more (40.68a ± 1.06) compared to cock's foot grass (32.39b ± 2.25) (P-value=0.011 from Tukey's pairwise comparison). Conclusion: The study resulted in temperature forages having better nutritional quality than tropical forages.
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