Integrated farming system of Azolla-Aigamo duck meat-rice production in paddy fields, 3: Seasonal nutritive value of aquatic fern Azolla

Four Azolla strains namely, A. caroliniana 3004 (CA3004) , A. microphylla 4138 (MI4138) , Hybrid 4087 (HY4087) .A. Japonica (JP) were analyzed for seasonal nutritive value. The strains were cultivated in plastic boxes individually, but mixed those Azolla in paddy field. Sample were collected monthly from June to September. Feeding trials using Aigamo duck (crossbred of wild and domestic ducks) in paddy fields were conducted to clear the effect of reducing formula with Azolla and using rice screenings instead of formula. Formula feed was supplied daily in the level of 100, 75 and 50% per duck. Azolla in paddy field were cultivated and supplemented from another paddy field during experiments. Azolla contained water as much as 95% in fresh water during growing season. The four Azolla strains varied in their composition considerably in June. On a dry matter basis in July, August and September, the values obtained ranged from 19.3 to 33.4% crude protein, 3.7 to 51% crude fat, 4.7 to 10.3% crude fiber, 13.9 to 24.6% crude ash. When compared with those strains, the ranking of seasonal nutritive values showed to tend as follows: HY4087 > MI4138 > CA3004 NE JP in crude protein, Ca3004 > JP > MI4138 NE HY4087 in crude ash, JP > CA3004 NE HY4087 NE HI4138 in crude fiber. Seasonal changes of nutritive values of the mixed Azolla strains in paddy field were very small when compared with four Azolla strains cultivated in plastic boxes. But crude protein content in the dry matter was slightly low and crude ash content was high in July, August and September. Azolla contained water as much as 95% in fresh water, which frequently made it difficult to use those strains as feeding materials. Average body weight gain of Aigamo ducks were significantly (P < 0.05%) affected with reducing formula feed. Aigamo ducks almost died when reducing formula feed by 50%. On the other hand, average body weight gain of their consistently increased with rice screenings instead of formula feed. These results indicated that, when Azolla was introduced to the Aigamo duck-rice farming, Azolla strains were played only a supplemental role as feedstuffs.