The use of marine plants for growing rabbits

S Rjiba Ktita, A Chermiti and M Mahouachi¹

Institut National de la Recherche Agronomique de Tunisie, Laboratoire de la Production Animale et Fourragère,
Rue Hédi Karray, 2049.Ariana, Tunisie.
soniarjiba@live.fr
¹Ecole Supérieure d’Agriculture du Kef 7119, le Kef, Tunisie

Abstract

This study aimed to introduce marine plants into concentrate mixtures in order to produce rabbit meat. Two species, Ruppia maritima and Chaetomorpha linum were incorporated in concentrate formula (14 and 27%), with barley, wheat bran, straw and soybean meal, the mixtures (R14, R27, C14, C27) were pelleted with specific laboratory instrument and given ad libitum to 30 New-Zealand rabbits divided into 5 equal groups. Commercial pellets were used as control. Feed intake, growth rate and slaughter performances of rabbits were determined by measuring daily refusals, weekly animal weights and carcass quality after slaughtering.

The two marine species studied were very rich on minerals mainly on trace elements as Iron and Manganese. Crude protein and crude fibre contents of control and experimental pellets averaged respectively 19 and 13.5% DM. In the contrast, ash values of the marine plant concentrates were higher than that of the control one. Young rabbits averaged 1264 g of weight at the beginning of the experience and the effect of the diet on the final weights was highly significant. Rabbits fed the experimental diets had lower daily feed intakes than those fed the control one. However, average daily gains were similar between the control and R14 groups but significantly higher than those of C14 and C27. Feed conversion ratio varied from 2.05 with R15 diet to 3.42 with the control one, the difference among all the groups was not significant. Hot carcass weights were highly affected by the diets, the values varied respectively from 1519 g with the control group to 815 with C14. The carcass yield averaged 48.75% between control, R14, R27 and C14 diet, this yield was significantly higher than that released by the animals eating C27 pellets. The species Ruppia maritima gave the best performances, even at an incorporation rate of 27 % into the diet. A particular attention must be taken to the mineral composition of the mixtures mainly those based on the species Chaetomorpha which showed negative results with an incorporation rate of 27% into the diet.

Key Words: Chaetomorpha linum, concentrate, rabbit growth, Ruppia maritima

Introduction

Marine plants represent an important feed resource. All over the world, many species were rejected on the beaches and the lake’s banks causing pollution problems after their decomposition. Studied mainly in human nutrition, the chemical composition of marine plants have shown that these are good sources of minerals, proteins and fibers (Mabeau et Fleurence 1993; Darcy Vrillon 1993; Fleurence et al 1995 and Fleurance 1999), a composition which allowed them to be an important potential that can be used in animal nutrition.

This experience is a preliminarily study to the nutritional value of two species (Chaetomorpha linum and Ruppia maritima) and the possibility to introduce them in concentrate mixtures to growing rabbits. A previous lamb’s growth trial was done with these two species and gives positive results (Rjiba Ktita et al 2010). To the author’s knowledge, it’s the only published reports on the feeding value of these species for animals.

Materials and methods

Marine plants and diets

Two species were used in this experiment: Ruppia maritima and Chaetomorpha linum. After their rejection by the water currents on the offshore of Ghar el Melh lagoon (North-Est of Tunisia), both were manually collected, placed in sieves and washed with fresh water, air-dried and ground. Four concentrate mixtures were formulated on the basis of the ingredient chemical composition (Table 1) and the recommended growing rabbit amounts of crude protein and cellulose (respectively 18 and 13%) (Lebas 2004; Gidenne 2000). Concentrates were pelleted with specific laboratory instrument, air dried and conserved in plastic bags to be distributed to rabbits.

Animals and feed managment

The trial was carried out in the experimental rabbitry at the High Agricultural School of El Kef in the north west of Tunisia. A total of thirty weaned 45-day-old New-Zealand rabbits with a mean weight of 1228 g, were randomly assigned to five groups of 6 and logged in collective cages (2 rabbits/cage).

The experiment consisted of five treatments:

Control (Ctrl): Commercial pellets
R14: Pellets containing 14% of the species Ruppia maritima
R27: Pellets containing 27% of the species Ruppia maritima
C14: Pellets containing 14% of the species Chaetomorpha linum
C27: Pellets containing 27% of the species Chaetomorpha linum

Pellets were given to the animals ad libitum and fresh water was freely available in semi-automatic drinkers.

Measurements and chemical analyses

Ingredients and feed samples taken at the start, middle and end of the experiment were analysed for dry matter (DM), ash, crude protein (CP) and crude fibre (CF) according to the standard methods (AOAC1985), N contents were determined using the Kjeldhal technique and CP was calculated as 6.25 x N. CF were analysed following the procedures cited by Van Soest 1963. Minerals as Ca, Na, Zn, Mn, Fe and Cu were analysed through the atomic absorption spectrophotometer and phosphorus was analysed by the colorimetric method using the molibdo-vanadat reagent (AOAC 1985).

Animals were adapted to the experimental diets for 7 days, the amounts of pellets distributed to each cage and the corresponding refusals were controlled daily. Rabbits were weighed at the beginning and weekly through the experimental period (63 days).

At the end of the experiment, three animals from each group were slaughtered and measurements concerning the slaughter performance as the weights of hot carcass, digestive tract, liver, kidney, fat and the content of stomach, small and large intestines were recorded. Carcass quality was evaluated through two parameters, the carcass yield and the total fat.

Statistical analyses

Data were analysed as a completely randomised design using the diet as the main source of variation and the GLM procedure of SAS software (SAS 1987). Treatment effects on intake, growth and slaughter parameters were compared using the LSD means.

Results and discussion

Chemical composition of marine plants and diets

Chemical composition of ingredients and concentrate mixtures are presented in tables 1 and 2.

Marine plants are rich in ash, 37.7 % DM with Ruppia m. and 43% DM with Chaetomorpha l., these amounts are higher than those of raw materials usually used in animal nutrition where they do not exceed 15% of DM (Sauvant et al 2002). Incorporated at two levels (14 and 27%) into the concentrate mixtures these species increased the ash amount from 9.5 % DM in the control pellets to 20% DM in those containing 27% of Chaetomorpha l. (Table 2).

Experimental concentrates were formulated to have similar CP content than the commercial one (19% DM,on average), a limited quantity of straw (90g/kg) was added to each mixture in order to increase the CF level to13% DM. These amounts were recommended to growing rabbits (Lebas et Perez 1989; Lebas 2004).

Ruppia m. and Chaetomorpha l. were very rich in minerals mainly in trace elements, in fact the first species contains 607 and 348 mg/kg DM respectively of Iron and Manganese (Table 2). The recorded amounts of these elements into Ruppia mixtures were respectively 332 and 370 mg/kg DM with R14 and 121 and 151 mg/kg DM with R27. Chaetomorpha pellets (14 and 27%) were also very rich in Iron (317 and 347 mg/kg respectively) and in Manganese (332 and 372 mg/kg respectively). All these amounts are higher than those recommended for rabbits (Lebas1989), but still lower than the limit of toxicity (Lebas 2004; Gidenne 2010).

Growth performances

Young rabbits averaged 1264 g of weight at the beginning of the experience, the diet’s effect on final weights is highly significant (Table3). Indeed, after 63 days of growth, the obtained weights are 3079 g with R27 and 2012 g with C14.

The growth curves of the rabbits with the different diets are linear (Figure 1). The patterns show similar growth rate between the rabbits eating control diet of commercial pellets and those eating the Ruppia’s. By contrast, as the trial progressed the difference became progressively pronounced between the two last diets and those based on Chaetomorpha l., which showed the lowest growth rates.

Figure 1. Growth curves of the rabbits fed experimental pellets

Average daily intakes and gains were presented in Table 3. Rabbits fed the experimental diets had lower daily feed intakes than those fed the control one. Average daily gains were similar between the control group and R14 but higher than those of C14 and C27. In the contrast, feed conversion rations similar between all the feeds. The growth depression noted with the animals of the two groups C14 and C27 could be attributed to the reduced intake of the pellets which decreased when the introduction level of the species Chaetomorpha l. increased into the mixture.

No mortality was observed in the control and R27 groups, by contrast 3 cases were observed with the diet containing 27 % of Chaetomorpha l., one in thegroup C14 and one in the group eating R15. Two hypotheses can be advanced to explain these mortalities, noted mainly with animals eating C27, the first one is unbalanced mineral composition of these pellets and the second is the biochemical composition of the species Chaetomorpha l. New investigations are necessary to confirm or not these hypotheses.

Slaughter performances

Slaughter results are summarized in Table 4. The diet’s effect on hot carcass weights and carcass yields was highly significant. The values varied respectively from 815 g (C27) to 1519 g (ctrl) and from 38% (C27) to 51% (R14 and R27). The carcass yield averaged 48.75% between control, R14, R27 and C14 diet, it was higher than that released by the animals eating C27 pellets.

After slaughter, no difference was observed on the content weights of stomach, large and small intestines. These averages are in line with the cited bibliographic values (Gidenne et Lebas 2005). Nevertheless, animals eating C27 pellets presented the higher content weights of the digestive tract (stomach and intestines). We could advanced that this diet and especially the species Chaetomorpha l., which overload the stomach was poorly digested.

Conclusions

• The species Ruppia maritima gives good performances, even at an incorporation rate of 27 % into the diet, in the contrast to the second species Chaetomorpha linum, which need other studies with lower incorporated levels. A particular attention must be taken to the mineral composition of the formulated pellets and especially to the mineral and vitamin premixes. Another trial studying digestibility, nitrogen and mineral balance of the diets based on these marine resources could better explain these results and gives conclusive deductions.

Acknowlegement

Authors thank Dr.Jamel Ksouri (INSTM Tunis), for his help to collect and identify the marine plant species.

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Received 1 August 2014; Accepted 14 September 2014; Published 3 November 2014

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