This work was carried out at the Research and Production Station located in El-Emam Malik Village, El-Bostan, West of Nubaria, and at the laboratories of Animal Production and Parasitology and Animal Diseases Departments, National Research Centre, 33 El Bohouth Street, Dokki, Cairo, Egypt.
Animals and feeds
Forty-five New Zealand White (NZW) rabbits aged 5–6 weeks with an average body weight of 730 ± 23 g were randomly divided into five equal experimental groups (9 rabbits in each group).
Three replicates of each treatments composed of three rabbits were housed together in galvanized wire cages (50 × 50 × 45 cm) and provided with stainless steel nipples for drinking and feeders allowing recording feed intake during the feeding trial that lasted for 72 days.
All experimental group rabbits were kept under the same managerial conditions and rations were offered, which were pellets with a diameter of 4 mm.
Five experimental pelleted rations were formulated to cover the nutrient requirements for rabbits according to NRC (1977).
The first ration was considered control (R1) and contained no apricot seed kernel (0% ASK). The 2nd, 3rd, 4th, and 5th experimental rations contained levels of ASK 0.75, 1.5, 3, and 4.5% respectively. Rations and water were offered ad libitum.
Digestibility trials
At the last 2 weeks of the experimental period, all rabbits were used in digestibility trials over period of 7 days to determine the nutrient digestibility and nutritive values of the tested rations. Feces were daily collected quantitatively. Feed intake of experimental rations and weight of feces were daily recorded. Representative samples were dried at 60 °C for 48 h, ground, and stored for later chemical analysis. The nutritive values expressed as total digestible nutrients (TDN) and digestible crude protein (DCP) of experimental rations that calculated using classic method as described by Abou-Raya (1967).
Carcass traits
At the end of the experimental period, three representative rabbits from each treatment were randomly chosen and fasted for 12 h before slaughtering according to Blasco et al. (1993) to determine the carcass measurements. Edible offal per gram (heart, liver, testes, kidneys, lungs, and spleen) and head were weighed and added to warm carcass weight. The 9th, 10th, and 11th ribs were frozen in polyethylene bags for later chemical analysis. The ribs of samples were dried at 60 °C for 48 h.
Analytical procedures
Chemical analysis of ASK, experimental rations, and feces were analyzed as described by AOAC (2005) methods. on the other hand, the air-dried samples of best 9th, 10th, and 11th ribs were analyzed for DM, EE, and ash according to the AOAC (2005) methods, while crude protein (CP) percentage was calculated by difference as recommended by (O’Mary et al. 1979) according to the following equation: CP content on DM basis = 100 − (Ether extract + ash).
Blood parameters
Two blood samples were collected from ear vein puncture from five rabbits from each group. The first blood sample was collected into an EDTA and was used for hematological evaluations. The second blood sample was centrifuged and the serum separation. Serum samples were stored at − 20 °C until further biochemical analyses.
Hematological investigations
Hemogram of collected blood samples was described by Weiss and Wardrop (2010). It included the red blood cell count (RBCs), packed cell volume (PCV), hemoglobin (Hb) concentration according to (Bunn 2011; Elghetany and Banki 2011), and calculated red blood indices [mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC), total leukocyte counts (TLC), and differential leukocyte counts].
Serum biochemical studies
It was earlier mentioned that the blood samples were collected through vein puncture; blood sample was placed in a plain centrifuge tube for serum separation. Serum samples were stored at − 20 °C until further biochemical analyses of total proteins (Henary et al. 1974), albumin (Doumas et al. 1971), total cholesterol (Allain et al. 1974), triglycerides (Fossati and Prencipe 1982), activities of aminotransferases (AST and ALT) (Reitman and Frankel 1957), urea according to (Patton and Crouch 1977), and creatinine according to (Husdan 1968). Serum globulins were determined by subtracting the value of serum albumin from the value of serum total proteins, also A/G ratio was calculated. Commercial diagnostic kits from Biomerieux, France, and Quimica Clinica Aplicada (QCA), Amposta, Spain, were used for assay of serum biochemical parameters.
Statistical analysis
Data on feed intake, live body weight, feed conversion, nutrient digestibility, carcass data, and blood constituents were subjected to one-way analysis of variance using to SPSS (2008). Duncan’s multiple range test (Duncan 1955) was used to separate means when the dietary treatment effect was significant according to the following model:
$$ {\mathrm{Y}}_{\mathrm{i}\mathrm{j}}=\upmu +{\mathrm{T}}_{\mathrm{i}}+{\mathrm{e}}_{\mathrm{i}\mathrm{j}}\kern0.6em \mathrm{Where}:\kern0.36em {\mathrm{Y}}_{\mathrm{i}\mathrm{j}}=\mathrm{observation}.\kern0.48em \upmu =\mathrm{overall}\kern0.17em \mathrm{mean}. $$
Ti = effect of experimental rations for i = 1–5; 1 = control ration contained 0% ASK, 2 = ration contained 0.75% ASK, 3 = ration contained 1.50% ASK, 4 = ration contained 3.00% ASK, and 5 = ration contained 4.50% ASK.
eij = the experimental error.
