Performance characteristics of rabbit
The two breeds of rabbit utilized their feeds identically with no statistical difference in the total weight gain at the close of the trial implying the acceptance of the FCPHM-based diets by the rabbits. It was also observed that beyond 12.5% inclusion of FCPHM in the diets, the final body weight (FBW), TWG and FCR declined implying that effective utilization of the FCPHM by the two breeds of rabbit can only be achieved at 12.5% inclusion level. This negates the reports of Ozung et al. (2017) who asserted that rabbits fed 12.5% CPH meal-based diet had lower FBW, total feed intake (TFI), TWG and FCR. However, the current findings are supported by Adeyeye et al. (2019b) who reported non-negative effect of the growth parameters in rabbits fed rumen liquor fermented ash cocoa pod husk.
Total feed intake (TFI) was seen to be higher in CHL breed, but with lower TWG and FCR which suggests breed differences in the utilization of FCPHM-based diet at 8th week of the trial. The daily intake of the rabbits was however higher than the range reported by Isika et al. (2012) who reported the average daily feed intake (ADFI) to range between 60.46 and 70.46 g/rabbit/day for rabbits fed diets in which groundnut cake was replaced with cocoa bean meal. Ozung et al. (2017) emphasized that differences in ADFI values could be attributed to differences in feed materials, environmental influences and concluded that cocoa pod husk meal should be fermented prior to its inclusion in rabbits’ diets. At 5th–8th weeks, the NZW rabbit breeds consumed lesser than CHL breeds with a numerical improvement of 33 units in total weight gain (TWG). It was also observed that inclusion of the FCPHM beyond 12.5% led to a decline in the TWG and FCR of the rabbits, respectively. However, the interaction between the breed and dietary effect was not significant implying that they were independent of these factors.
Carcass characteristics and relative organ weights
The present study suggested that the live weights (grams), eviscerated weight (%) and dressed weights (%), except Head + skin + limbs (%) (HSL) were influenced by the inclusion of FCPHM in the diets, but not significantly influenced by the breed effects. In line with the earlier report by Ozung et al. (2017), rabbits fed diet containing 12.5% FCPHM consistently had the highest live weight, eviscerated weight, dressed weight and HSL and beyond this inclusion level there was decline in values which further confirms the optimum inclusion level of FCPHM to be 12.5%. The current results as regard the breed effect confirm the report of Nasr et al. (2017) that New Zealand crossbreeds dressed higher than Chinchilla crossbreeds.
Of the relative organ weights measured, only the relative weight of liver was significantly affected by the breed effect which is in consonance with Papadomichelakis et al. (2012), while only the relative weight of the heart was significantly affected by the levels of inclusion of FCPHM in the diets. These organs declined in values as level of FCPHM in the diet of rabbits increased beyond 12.5%, further confirming this level as the safe level of inclusion that will not lead to atrophy of the heart and liver in the rabbits. However, the weights of all organs measured in this study fell within the normal range as reported by Nasr et al. (2017). Generally, the relative weights recorded in this study indicated that there was no visceral damage due to consumption of FCPHM and all internal systems were functionally normal. The weights of liver and kidney of the rabbit’s showed that FCPHM did not have any metabolic disease or distress effect. Sani et al. (2017) reported that, if a feed contains anti-nutritional element, abnormalities in weights of liver and kidney would be observed. The abnormalities will arise due to increased metabolic rate of the organs in an attempt to reduce the toxic elements or to convert the anti-nutritional agents to non-toxic metabolites.
According to Oloruntola et al. (2016), blood examination is an effective means of detecting the influence of nutrition physiological and pathological status of animals. In this study, it was observed that all haematological parameters measured were not statistically affected by the breeds and dietary treatments, but there was a numerical decrease in red blood cell (RBC) and granulocytes (GRAN) counts as the dietary inclusion levels of FCPHM increased. Although the values fell within the normal range earlier reported by Etim et al. (2014), these decreasing trends in RBC and GRAN could imply that the animals may become anaemic at higher levels of FCPHM inclusion and become more susceptible to infections. This current result agreed partly with the report of Adeyeye et al. (2019a) who indicated that all haematological parameters were not significantly influenced by processed cocoa pod husk, except for the haemoglobin (Hb), RBC and mean cell volume (MCV). The mean corpuscular haemoglobin concentration (MCHC) values obtained in this study were not affected by dietary treatments and were within the normal range for healthy rabbits. The white blood cell differentials, namely lymphocytes, neutrophils, monocytes, basophils and eosinophils, stabilized within dietary treatments. The stability of these haematological indices has been adduced to nutritional adequacy and support of the diet’s composition for normal haematopoiesis in the animals (Ogunsipe et al. 2017; Adeyeye et al. 2019a). Osaiyuwu et al. (2017) also reported that differences in the responses of some blood proteins (haemoglobin, albumin, transferrin and carbonic anhydrase) of New Zealand × Chinchilla crossbred rabbits could be underscored by genetic variability and hence biochemical polymorphism of crossbreed.
The haematological values obtained in this study though not significant were all numerically higher for the New Zealand White breed than in the Chinchilla breed except for haemoglobin concentration, lymphocytes, mean cell haemoglobin and mean cell volume that showed otherwise.
Serum biochemical indices
To assess the metabolic state of an animal, the serum metabolites levels are an important indicator to check (Neufingerl et al. 2013). In this study, only the total protein was significantly influenced by the dietary treatments of the entire metabolites examined. This negates the reports of Adeyeye et al. (2019a) which elaborated that the total protein, cholesterol, high-density lipoprotein (HDL) and low-density lipoprotein (LDL) were significantly influenced by the dietary inclusion of ash-treated cocoa pod husk meal in rabbit diets. They indicated that there were numerical increases in the values of the HDL and total protein up to 20% inclusion level of processed cocoa pod husk meal, but beyond which there were decline in values. On the other hand, the ALT, total protein and globulin concentrations in this study were significantly influenced by the breed effects. However, unlike haematological parameters, the serum metabolite values were numerically higher for Chinchilla than for the New Zealand Whites breed, except for HDL and triglycerides.
The albumin (ALB) and triglycerides (TRIG) were not significantly different, but fell within the normal range of values for rabbits as reported by Etim et al. (2014). Albumin and TRIG are important blood parameters that are indicative of nutritional status of an animal. The ALB levels indicate the level of protein in the blood, while the TRIG levels provide information on the overall nutrients metabolism (Meineri et al. 2017). The optimum ALB (34.33 g/l) and TRIG (1.03 mmol/l) concentrations obtained in this current study could therefore imply that the nutrient requirements of the rabbits were met in the diets provided. Although ALB concentration in serum is predicated on other factors that are independent of nutrition such as infections, trauma, hydration status, liver function and kidney disease (Sekine et al. 2013), the result of this study clearly shows that none of these extra-nutritional factors had considerable effects on the animals as indicated in the serum antioxidant status of the animals.
The AST and ALT did not show any significant differences across the dietary treatment and breed effects. These serum enzymes are largely functional in the liver and responsible for transamination in the metabolism of specific amino acids. Globulin (GLOB) concentrations, an important blood protein which when present in very low concentration could result in high rate of mortality (Adegbenro et al. 2016), were within the normal physiological range and significantly indifferent in this study.
Serum antioxidative status
The present study clearly revealed that all serum antioxidant indices, except lipid peroxidation (LPO), were not statistically different. The rabbits fed 25% FCPHM containing diet had the highest serum MDA concentration, while the Chinchilla rabbits were more susceptible to oxidative stress than the New Zealand White rabbits. MDA is a lipid peroxidation index which is predictive of oxidative stress (Shehu et al. 2018). This implies that the higher MDA concentration values recorded for the rabbits fed diet containing 25% FCPHM had greater free radicals-mediated cell damage and oxidative stress than the rabbits fed other diets. The statistically higher MDA concentration in the Chinchilla rabbit and diet containing 25% FCPHM group could be adduced to genetic intolerance and the high dietary inclusion of FCPHM, respectively. It is noteworthy that the rabbits fed diet containing 12.5% FCPHM had the lowest MDA concentration values and hence were least predisposed to free radicals-mediated cell damage and oxidative stress. The results obtained in this study for lipid peroxidation are supported by the reports of Meineri et al. (2017) and Shehu et al. (2018) who indicated that rabbits raised in cages were predisposed to oxidative stress than other group raised in pens due to psycho-emotional stress induced by immobilization in cages. The glutathione peroxidase (GPx), a seleno-enzyme that reduces phospholipid hydroperoxides by glutathione (GSH), was found to be similar across treatments and the values found to be within normal range of 0.05–0.15 µmmol/mg/protein reported by Reshma et al. (2015). Superoxide dismutase and catalase were not significantly influenced by the breed and dietary treatment.