 aim of this study was therefore to provide standard growth, carcass and meat quality data for two meat breeds that are available in the country, namely the New Zealand White (NZW) and the Phendula. The NZW is a globally recognised meat breed, and has been an essential contributor to the development of many of the hybrid lines used for meat production in other areas of the world (Lebas et al., 1997). In contrast, the Phendula is a local landrace breed that has been developed since 2002, which was recognised officially by the South African Rabbit Judges Council only in 2014. The Phendula was selected with the objective of producing a hardy adaptable breed that is suited to the South African climate, and that incorporated genetics from Chinchilla Giganta, Flemish Giant, New Zealand Red, and New Zealand Black rabbits (recognised breeds in South Africa), as well as those from hardy nondescript rabbits in the area (Gauteng Smallholder, 2014).
Ethical clearance for this study was obtained from Stellenbosch University Animal Care and Use Committee (Ethical clearance number SU-ACUD16-00094).
The growth trial was carried out from April to May 2017 on Mariendahl Experimental Farm, outside Stellenbosch in the Western Cape of South Africa (33° 51' 02.9" S 18° 49' 35.2" E). Eighty New Zealand White (NZW) rabbits and 40 Phendula rabbits of both sexes were used for the trial, with 44 male and 36 female NZW, and 22 male and 18 female Phendula. The rabbits were all weaned on the same day, at 35.6 ± 0.17 days old (variation in age owing to the use of natural mating), and were transferred to cages in a grower house. They were kept in same-sex groups of three, with two NZW and one Phendula per cage, and the sexes were distributed evenly throughout the house. Cages were constructed of welded wire mesh, and were 60 x 60 cm and 50 cm high, standing 1.5 m off the ground. Each cage was provided with a rest mat and piece of dry pear wood to provide environmental enrichment, and wood shavings were spread beneath the cages to absorb urine. A daily lighting period of 10 hours was used, and water and a balanced pelleted diet (Table 1) were available ad libitum.
The recording of live weight started after an adaptation period of one week, with the individually marked rabbits being weighed each week for six weeks. These live weights were used to calculate the ADG for each rabbit per week. The minimum, maximum and average daily temperatures during the trial were 18.3 °C, 23.4 °C and 20.6 °C, respectively.
The rabbits were slaughtered at approximately 11 weeks old (77.6 ± 0.17 days) at a commercial abattoir about 16 km from the experimental farm. Carcass and meat quality data was collected for 10 male rabbits and 10 females of each breed.
The rabbits were fasted for 12 hours prior to slaughter to clear the gastrointestinal tract, with slaughter weights (SW) being recorded prior to fasting. Slaughtering followed national regulations, with electrical stunning prior to exsanguination. After exsanguination, the carcasses were skinned and eviscerated to produce hot carcasses (HC), which included the head and red offal, and were weighed directly after processing. The carcasses were then hung at 2-4 °C for 24 hours to cool and undergo rigor.
After chilling, the chilled carcass (CC) weights were recorded before the carcass was broken down as specified by Blasco & Ouhayoun (1996). The head and red offal (liver, kidney, thymus, trachea, oesophagus, lungs and heart) were removed to produce the reference carcass (RC), and the removed organs and carcasses were weighed. After the removal and weighing of the dissectible fat (interscapular, inguinal and perirenal deposits), the carcasses were divided into the anatomical joints (the fore, intermediate and hind parts) as specified by Blasco & Ouhayoun (1996). This entailed making cuts between the last thoracic and first lumbar vertebra, and between the sixth and seventh lumbar vertebrae. After weighing the portions, the hind legs were removed from the hind part and one hind leg per rabbit was dissected to provide the meat to bone ratio.
The carcass drip loss was calculated as the loss of weight during chilling, expressed as a percentage of the HC weight. The CC weight was expressed as a percentage of the SW to provide the dressing-out percentage, and the RC weight was expressed as a percentage of the CC weight to provide the RC yield. The components of the CC (head and red offal) were expressed as a percentage of the CC weight, whereas the dissectible fat and the portion masses were expressed as percentages of the RC weight.
The left Longissimus thoracis et íumborum (LTL) muscle was used to measure the pH and L*a*b* colour values, and to determine the cooking loss and Warner-Bratzler shear force (WBSF). The pH of the muscle was measured using a Crison PH25 portable pH meter (Lasec SA, Cape Town, South Africa). Meat colour was measured at three locations along the dorsal surface of the left LTL from the intermediate part, with a colour-guide 45°/0° colorimeter (11 mm aperture, illuminant/observer of D65/10°; catalogue number 6801; BYK-Gardner, Geretsried, Germany). Results were reported as L* (lightness), a* (redness), and b* (yellowness) values.
Once the pH and colour had been measured, the left LTL was vacuum packed and cooked for one hour at 80 °C in a water bath, after which it was chilled at 2-4 °C overnight. After chilling, the cooked meat portions were patted dry and weighed to determine the cooking loss (Honikel, 1998). The cooked LTL muscles were used to determine the WBSF (Honikel, 1998). This entailed cutting the cooked muscle into 2-cm thick steaks, from which 1 x 1 x 2 cm rectangular blocks were cut, with the length of the block being parallel to the muscle fibres. These blocks were then sheared perpendicularly to their long axis, with the maximum shear force required being measured with an Instron 3343 (serial number J8415, Advanced Lab Solutions, Randburg, South Africa) fitted with a 1-mm thick Warner-Bratzler blade with a semi-circular cutting edge (radius 0.508 mm). The Instron had a load cell of 5 kN and crosshead speed of 200 mm/min. The maximum load in Newton (N) was reported, with the average of the values for all blocks (five to six) being reported as the WBSF of the sample.
The right LTL that was excised from the fore part was used to determine the drip loss. It was weighed and suspended inside an inflated plastic bag at 2-4 °C for 24 hours, with care being taken that the muscle did not touch the inside of the bag. At the end of the 24-hour period the muscle was removed from the bag, blotted dry and weighed, with the drip loss being calculated as the difference between the weight before and after hanging, as a percentage of the starting weight.
The right LTL, which was excised from the intermediate part, was vacuum packed and frozen at -20 °C to determine proximate composition. Prior to analysis, the muscle was thawed at 2-4 °C for 24 hours and homogenized in order to remove the effects of any variation within the muscle. The moisture, ash and protein contents were quantified according to Association of Official Analytical Chemists (AOAC, 2002), methods 934.01, 942.05 and 992.15, respectively. The fat content was determined using the rapid solvent extraction method as described by Lee et al. (1996), with a 1:2 chloroform/methanol solution being used owing to the low fat content of rabbit loin muscle (Dalle Zotte & Szendrö, 2011).
The growth trial was structured as a three-factor factorial experiment in a completely randomized design, with the main effects being breed, sex and age. Only the first two main effects were relevant for the carcass and meat quality data. The individual rabbits served as the experimental units, with the number of replicates varying among the treatment groups.
Statistical analysis was performed using Statistica version 13 software. Normality was tested using normal probability plots and, where necessary, outliers were removed and the Box-Cox transformation was used to normalize the data prior to statistical analysis. This was necessary only for the hindleg meat to bone ratio data. Statistica's variance, estimation, precision and comparison (VEPAC) mixed-model function was used to determine the significance of the main effects and second- and third-order interactions for the live performance data, and the R lm package was used for the carcass and meat quality data. Initial weight (live weight at six weeks old) was used as a covariate for the analyses. Fisher's LSD test was used to identify differences between the treatment combinations, with the adjusted least squares means being used for post hoc calculations.
Main effects and interactions with P <0.05 were considered significant, and values are reported as least squares means ± standard error (SE).
Only the sex-age interaction was significant for the live performance data (Figure 1), with females having greater live weights than males at 11 weeks old (P <0.001).