Nguyen Thi Kim Kang et al., 2004. Livest. Res. Rural Dev., 16 (8): article 57

Eighty local (Tau Vang) laying hens at 19 weeks of age were allocated to 5 dietary treatments and 3 replicates. The control diet was a mixture of broken rice and roasted soya beans (SB100) with no duckweed For the other four diets duckweed was available ad libitum, giving 5 treatments with roasted soya beans at levels of 0, 25, 50, 75 and 100% (SB0DW, SB25DW, SB50DW, SB75DW and SB100 respectively). Intakes of feed DM and concentrate DM were not different among treatments. Intake of duckweed increased as the roasted soya beans content of the concentrate diet was reduced, contributing up to 29% of the total dietary protein on the zero soya bean basal feed. The crude protein content of the total diet declined linearly (from 16.8 to 12.5% in DM) as the roasted soya beans protein contribution was reduced from 100 to 0%. Age at first egg decreased in a curvilinear response to the proportion of dietary protein contributed as duckweed, with optimum values around the 75% replacement level. Eggs produced per layer in the 56 day period were linearly related with percent protein from duckweed. There was no consistent trend for feed conversion into eggs. Average egg weight and the proportion of total eggs weighing over 38 g tended to show a curvilinear response to the proportion of protein derived from duckweed with optimum values at around 20% as duckweed protein. Both fertility of incubated eggs and hatchability of fertile eggs showed curvilinear relationships with proportion of protein derived from duckweed, with optimum values at around 15% and 25% as duckweed protein for fertility and hatchability, respectively. The yolk pigmentation of the eggs increased in response to protein derived from duckweed. The yolk index of eggs from hens on the SB100 diet was slightly lower (0.38) than the recommended standard of 0.4. Highest production and better fertility and hatchability of eggs from hens consuming the SB25DW diet resulted in highest numbers of chicks hatched and the highest gross income and margin over feed costs. It is concluded that egg production, egg quality, feed conversion and net profit are highest when fresh duckweed replaces 75% of the protein from roasted soya beans in a diet based on broken rice. Even at 100% of roasted soya beans replacement by duckweed, the egg production and margin of income over feed costs were better than on the control diet in which the supplementary protein came only from roasted soya beans.