The present study was carried out at the KUATE farm located in Bandjoun in the Western region of Cameroon characterized by an equatorial climate of the Guinean and Cameroonian mountain type with two seasons: a dry season lasting 4 months (mid-November to mid-March) and a rainy season lasting 8 months (mid-March to mid-November).

To carry out this work, 36 weaned rabbits (24 males and 12 females) of local breed aged on average 53 days and having an average weight of 1337 ± 119 g were used. The animals were housed in a building containing bamboo and wire hutches, arranged in a battery like structure and divided into boxes each containing a semi-automatic feeder and a pipette connected to a trough containing drinking water. The rabbits were identified with a marker by alphabetical letters and numbers written inside the left ear.

The plant material consisted of pineapple press residue as the main source of fiber. These residues were collected fresh, dried ( Figure 1 ), and then crushed before being incorporated into feed.

From the dry residue of crushed pineapple presses and other ingredients purchased commercially, three rations were formulated and then granulated. The basic ration or control ration did not contain pineapple press residues (0%). The other two rations were formulated with increasing levels of inclusion of pineapple press residues (20% and 40%). Table 1 presents the bromatological composition of the rations used.

DM: dry matter; T0: control ration without dry pineapple press residue; T1: ration containing 20% of dry pineapple press residue; T2 ration containing 40% dry pineapple press residue. Belgo Fos 23: Calcium + Phosphorus, Pork concentrate 10% Belgo Cam: proteins + fats + minerals.

The formulated rations were:

Once the fresh pineapple press residues were collected, three samples of 500 g were taken to the Animal Production and Nutrition Research Unit of the University of Dschang where they were dried at 50°C to constant weight in a ventilated oven of Gallenkamp brand and preserved for various analyses. The determination of the dry matter, organic matter, ash, crude protein and fat content were done following the AOAC method [15] . Crude fiber was determined by the Scharrer method meanwhile Neutral Detergent Fiber (NDF), Acid Detergent Fiber (ADF) and Acid Detergent Lignin (ADL) contents were determined according to the method of Van Soest [16] . The phosphorus content was determined by UV-visible spectrophotometry according to protocol ISO/TC 34/ SC6 N371 (1991) and that of other minerals by flame atomic absorption spectrophotometry after dry incineration, according to official analysis methods AOAC [17] and Jorhem [18] .

The weaned rabbits (24 males and 12 females) were randomly distributed into three batches or treatments (T0, T1 and T2), each treatment had 3 repetitions of 4 animals each (12 animals per treatment). The rabbits in each treatment received the formulated feed for 49 days. The animals were fed ad libitum and the quantities served as well as refusals were weighed every day, which made it possible to evaluate feed intake. At the start of the trial, the rabbits were weighed, and then, every 7 days, their weights were recorded in a database. This made it possible to evaluate weight gain. Weighing was done using an electronic scale with a maximum capacity of 10 kg and accuracy of 1 g.

On the last day of the test (49th day), 3 rabbits were randomly selected from each treatment, fasted for 24 hours then sacrificed for the evaluation of carcass characteristics. The emphasis was placed on the liver, the caecum, the kidneys, the classic carcass yield and the commercial carcass yield.

It consisted of determining the price per kg of each experimental ration based on the local prices of raw materials, and for each treatment, feed cost of production per kilogram of live weight of rabbit based on the price per kg of feed and feed convention ratio.

$FI(Kg)=\text{Quantity of feed distributed}-\text{quantity refused}$

$WG(g)=\frac{\text{Total weight of young rabbits weighed}}{\text{number of subjects weighed}}$

$ADWG(g)=\frac{\text{Weight obtained after one week}}{7}$

where 7: Number of days per week.

$FCR=\frac{\text{amount of feed consumed per week}\text{(g)}}{\text{weight gain per week}\text{(g)}}$

$CY(\%)=\frac{\text{carcass weight}\text{(g)}}{\text{live weight of the animal before sacrifice}\text{(g)}}\times 100$

$RWO(\%)=\frac{\text{weight}\text{of}\text{the}\text{organ}\text{(g)}}{\text{live}\text{weight}\text{of}\text{the}\text{animal}\text{before}\text{sacrifice}\text{(g)}}\times 100$

$FCPofKgofrabbit\left(FCFA\right)=\text{Price of Kg of feed}\left(\text{FCFA}\right)\times \text{FCR}$

Data on all studied parameters were submitted to one-way analysis of variance (ANOVA) (food intake) and the Duncan test was used at the 5% significance level, to compare the means when it existed. Significant differences.

The chemical composition of pineapple press residues is summarized in Table 2 . It reveals that pineapple press residues are rich in cellulose, and have a significant energy value, but have a low crude protein content.

DM: dry matter; NDF: neutral detergent fiber; ADF: acid detergent fiber; ADL: acid detergent lignin.

The growth parameters studied ( Table 3 ) were significantly influenced by the presence of pineapple press residues in the rations. The highest values of feed intake were obtained respectively from rations containing 40% (968.07 ± 18.04 g) and 20% (995.14 ± 28.55 g) of pineapple press residues meanwhile the lowest (p < 0.05) feed intake was with the animals fed the control ration (928.46 ± 57.13 g). The significantly (p < 0.05) lower total weight gain (178.65 ± 18.50 g) and average daily weight gain (25.52 ± 2.64 g) were obtained from rabbits fed 40% pineapple press residues and the highest, respectively, with rations at 20% and 0% pineapple press residues. The lowest feed conversion ratio was respectively obtained from the 0% (4.39 ± 0.32) and 20% (4.63 ± 0.73) rations meanwhile the highest (p < 0.05) from the 40% pineapple press residue (5.42 ± 0.56).

a, b: means bearing identical letters are not significantly different (p > 0.05) for the same characteristics. T0: control ration without pineapple press residue; T1: ration incorporated with 20% pineapple press residue; T2 ration incorporated with 40% pineapple press residue; p: probability.

The animals’ feed intake ( Figure 2 ) showed an increasing level throughout the trial, regardless of the ration. However, feed intake of ration containing 20% pineapple press residue (T1) was regularly higher than that of the other rations.

Figure 3 shows that throughout the trial, the curves showing the changes in the live weight of the animals according to the different rations presented the same trend and pattern. However, the curve materializing the weights of animals from batch T1 (20% pineapple press residue) tends to be above and that of animals from batch T2 (40% pineapple press residue) below the other curves. Indeed, from the first week after birth, the weights of animals who received 20% pineapple press residue in their ration (T1) were highest, followed by those of animals having received 0% (T0) and 40% (T2) respectively.

The weekly evolution of weight gain shown in Figure 4 revealed that they fell with age, whatever the ratio. However, the best weight gain was regularly obtained from animals having received 20% pineapple residue in their ration (batch T1) and the lowest from those having received 40% (batch T2).

Figure 5 shows that the feed conversion ratio of all rabbits evolved in a jagged pattern. However, those of the animals which did not receive pineapple press residues in their ration (T0) had a downward trend throughout the trial, followed by animals in treatments T2 and T1 respectively.

Carcass yields and relative weight of organs were significantly (p < 0.05) influenced by the presence of pineapple press residues in the animals’ rations ( Table 4 ). Indeed, the analysis of variance showed that the yields of commercial (53.07% ± 0.13%) and classic (76.15% ± 0.17%) carcasses of animals fed with the ration containing 20% pineapple press residues were significantly (p < 0.05) higher than those of the other animals. Furthermore, the yield of the classic carcass (73.17% ± 0.05%) of animals fed with the ration containing 40% pineapple press residue was significantly (p < 0.05) higher than that of animals from the control group (72.69% ± 0.21%).

Table 4 shows that the relative weight of the liver significantly (p < 0.05) increased with the level of pineapple press residues in the ration. The highest value (2.81% ± 0.03%) was obtained from animals that received 40% pineapple press residues (T2) and the lowest (2.38% ± 0.04%) from those in the control (T0). The relative weights of the kidneys of the animals fed press residues were comparable (p > 0.05) between them (0.55% ± 0.04% and 0.53% ± 0.03% respectively for batches T2 and T1) but significantly (p < 0.05) higher than that of the animals in control (0.45% ± 0.02%) group. As for the caecum, the significantly highest relative weight (p < 0.05) was obtained from animals in the control group (6.07% ± 0.18%) followed respectively by those of the animals from the T2 (4.40% ± 0.08%) and T1 (3.50% ± 0.19%) groups.

a, b and c: means bearing identical letters are not significantly different (p > 0.05) for the same characteristics. T0: control ration without pineapple press residue; T1: ration incorporated with 20% pineapple press residue; T2: ration incorporated with 40% pineapple press residue; p: probability.

The incorporation of pineapple press residues reduced the cost of rations ( Table 5 ). Indeed, the price per kg of the T1 ration (318.00 FCFA) was the least expensive, followed by that of the T2 ration (334.50 FCFA), the cost per kg of the T0 ration (341.50 FCFA) being the most expensive. In addition, the ration incorporated with 20% pineapple press residue (T1) presented the lowest feed cost of production of a Kg body weight of rabbit and that incorporated with 40% pineapple press residue (T2) had the highest cost.

T0: control ration without pineapple press residue; T1: ration incorporated with 20% pineapple press residue; T2 ration incorporated with 40% pineapple press residue; FPC: feed production cost; FCFA: franc of the African financial community.