7. Water spinach as a feed resource for growing rabbits
Authors: Pok Samkol, 2005.
Summary : There were three experiments: (i) performance traits of growing rabbits given graded levels of broken rice and water spinach ( Ipomoea aquatica ) ad libitum, (ii) digestibility indices and N balance in growing rabbits fed a basal diet of water spinach supplemented with broken rice and (iii) effect of increasing offer level of water spinach on intake, growth and digestibility coefficients of rabbits. All the experiments were conducted in the ecological farm of CelAgrid in Prah Theat village, Rolous commune, Kandal Stung district, Kandal province, about 26 km from Phnom Penh City, Cambodia.
Experiment1 : Four local male rabbits (1.77 ± 0.10 kg live weight) and four New Zealand White males (1.74 ± 0.10 kg) were allocated to 4 experimental treatments according to a duplicate 4*4 Latin square arrangement. The treatments were: Br0: water spinach ad libitum , Br4: same as Br0 but with 4 g/day of broken rice, Br8: same as Br0 but with 8 g/day of broken rice and Br12: same as Br0 but with 12 g/day of broken rice. The rabbits were housed in metabolism cages during the trial. The metabolism cages (50 x 55cm) were built to allow the quantitative collection of hard faeces and urine and were installed in an open floor. Each experimental period consisted of five preliminary days when the rabbits were adapted to the diets followed by another five days for collection of faeces, urine and feed refusals. The rabbits were weighed at the beginning of the trial and at the end of each period. The whole plant (combined stems and leaves) of water spinach was offered as bunches hanging from the side of the cage. The level offered was approximately 50% greater than the recorded intake. Fresh water spinach was offered three times per day: in the morning at 7.30 am, at the middle of the day at 12:00 am and in the afternoon at 4:00 pm. On the basis of previous observations, additional water was not provided as the fresh plant contains almost 90% water thus providing a ratio of moisture to dry matter of close to 9:1. Rice bran was offered in a metal bowl anchored by wire to the side of the cage to avoid spillage. The broken rice was offered two times per day, in the morning at 7: 30 am and in the afternoon at 4:00 pm, in order to decrease the speed of eating by the rabbits. Feed refusals and faeces were collected every day and were kept frozen in plastic bags until analysis. At the end of each period, feed refusals and faeces were mixed thoroughly by hand and a representative sample homogenized in a coffee grinder, for analysis of pH, NH3, Short Chain Fatty Acids (SCFA), DM, N, crude fiber and ash content. Organic matter concentration was calculated as 100 minus % ash in dry basis. Urine was collected in a plastic bucket to which 40% (w/v) sulphuric acid was added to maintain the pH below 4.0. At the end of each period the volume was measured and a sample analysed for N.
Experiment 2: Sixteen crossbreed (Local x New Zealand White) rabbits with average live weight of 961 ± 145 g were allocated to four treatments according to a randomized block arrangement to study the effect of supplementary broken rice (0, 4, 8 and 12 g/day) in rations of water spinach given ad libitum. The rabbits were housed in individual cages constructed from wood and wire mesh. The dimensions of the cages were width 0.5 m, length 0.7 m and height 0.5 m. Feed and feeding was the same experiment 1.The rabbits were weighed at two-week intervals. Feed intake was recorded daily from weight of fresh materials offered minus residue in the next morning. Feed conversion ratio was calculated from individual daily DM intake and live weight gain. Feed samples were taken weekly for DM, ash, organic matter and N analysis.
Experiment 3: Twelve New Zealand White rabbits with average live weight of 897 ± 95.2 g were used in this experiment. The animals were weighed every five days. The purpose of this studied was observation of different level of water spinach from 8, 10, 12, 4, 16 and 18% of body weight (DM basis). The water spinach (combined stems and leaves) was offered as bunches hanging from the side of the cage. It was fed to the rabbits three times per day in the morning at 8:00 am, middle day at 12:00 m and in the afternoon at 4:00 pm. Water was not supplied as earlier observations indicated that rabbits have the ability to consume water from the feed to their needs as water spinach has a moisture content of almost 90%. The fresh biomass yield of the water spinach was determined by weighing the fresh foliage at each of two harvests. Samples were separated into leaves and stems and these portions analysed for DM, N and organic matter. The acid insoluble ash content of feeds and faeces was estimated according to Van Keulen and Young (1977) in the days 30 and 60 of the feeding trial. Faeces were obtained in the morning before distribution of the feed. Feed refusals were collected every day and kept frozen in plastic bags until analysis. After thawing the samples, they were mixed thoroughly by hand and pooled, ground in a coffee grinder in the fresh state and, thereafter, representative samples were used for chemical analysis.
Experiment 1: There was a significant decrease in faecal pH with increasing levels of broken rice. However, there was no significant effect among treatments on the DM, NH3 and SCFA concentrations in the faeces. Faecal DM content was higher for local than for NZ White rabbits. There were no significant differences in digestibility indices between levels of broken rice. There was a trend (P<0.10) for DM and organic matter digestibility indices to be higher in the local than in the NZ genotype. This trend was significant (P<0.05) in N digestibility favouring the local breed. There was no significant effect on N retention due to genotype or the level of broken rice. It is concluded that fresh water spinach has a high nutritive value for rabbits. There were no nutritional advantages from providing additional digestible energy in the form of broken rice. Water spinach appears to be a complete diet for rabbits providing water as well as all required nutrients.
Experiment 2: As the level of broken rice increased, the effective offer level of the water spinach also increased with the result that the rabbits selected more of the leaves than the stems at least until the 8 g/day level of broken rice was reached after which the consumed ratio of leaf to stem decreased. There was no effect of the level of broken rice on the growth rate or the feed conversion. On un-supplemented water spinach the growth rate was 18.1 g/day during the first 6 weeks of the trial, falling to 9.3 g/day from 7 to 12 weeks, the overall growth rate being 14 g/day. The use of water spinach as the basis of rabbit production systems could be an appropriate low-cost technology for small-holder farmers.
Experiment 3: Increasing the offer level of water spinach from 8 to 18% of live weight (DM basis) increased the proportion of leaf consumed, the intake of crude protein and the digestibility of the DM and the crude protein. Digestibility of crude fiber decreased with increase in the proportion of leaves consumed. Live weight gain was depressed with increasing offer level apparently because of a decrease in the crude fiber content of the diet, as with increasing offer level, the rabbits selected “low-fiber” leaves rather than “high-fiber” stems. It is concluded that fresh water spinach as the sole feed of rabbits can support acceptable growth rates of 14 to 20g/day with DM feed conversion between 3.83 and 5.18. The crude fiber level in water spinach appears to be too low to support maximum performance and better results may be achieved by providing supplementary feed sources that are high in fiber.