Effect of ambient temperature on the productive and carcass traits of growing rabbits divergently selected for body fat content.

Rabbits are particularly sensitive to heat stress which can affect productive performance, with rabbit breed/line possibly playing a role on the response to this condition. The study aimed at evaluating the effect of different ambient temperatures on the live performance and carcass traits of growing rabbits divergently selected for total body fat content. The two genetic lines (Lean and Fat) were selected based on the total body fat content estimated by computer tomography during five generations. From birth to slaughter (13 weeks of age), the rabbits were housed in two rooms where the temperature was controlled with air conditioners: in the control room the average ambient temperature was 20 °C and in the high temperature room it was 28 °C. After weaning (35 d), 60 Lean and 60 Fat rabbits/room were housed by two in wire-mesh cages and fed ad libitum with commercial pellets. The BW and feed intake (FI) were measured at 5, 7, 9, 11 and 13 weeks of age to calculate the daily weight gain (DWG) and feed conversion ratio (FCR). Mortality was recorded daily. At the end of the experiment, rabbits were slaughtered and carcass traits were measured. Mortality was independent of temperature and line. The temperature significantly influenced the FI, DWG, BW and the fat deposits: they were lower at higher ambient temperature. The effect of temperature differed according to the rabbits' total body fat content. At control temperature, the FI (165 vs 155 g/day; P < 0.05) and FCR (4.67 vs 4.31; P < 0.05) were higher in Fat rabbits, which also had more perirenal (36.2 vs 23.1 g; P < 0.05) and scapular fat (10.8 vs 7.1 g; P < 0.05). At high temperature, no differences in fat depots (14.5 vs 9.8 g; 5.3 vs 3.5 g) were found between the two lines. It can be concluded that temperature × genetic line interaction had an important role in productive and carcass traits, as the effect of temperature differs between Lean and Fat rabbits.

The use of near-infrared reflectance spectroscopy in the prediction of the chemical composition of goose fatty liver.

The use of near-infrared reflectance spectroscopy (NIRS) on a meat product is described in this report. The aim of the study was to develop calibration equations to predict the chemical composition of goose fatty liver (foie gras) with lipid contents greater than 40% of the fresh pate. Spectra of 52 foie gras samples were collected in the visible and NIR region (400 to 2,498 nm). Calibration equations were computed for DM, CP, lipids and fatty acids using modified partial least-squares regression. R2 values were high for the total lipid content (0.805) and DM (0.908) but were low for ash (0.151) and relatively low for protein content (0.255). For the major fatty acids, R2 ranged from 0.886 for palmitic acid to 0.988 for oleic acid. Oleic acid, the main fatty acid of the liver, and the stearic acid had higher R2 values than the less represented fatty acids. This study suggests that the NIRS technique can be used to predict lipid content and the fatty acid composition of goose fatty livers, but calibration must be built on a larger number of samples to generate accurate predictions.

Effect of age, diet and sex on muscle energy metabolism and on related physicochemical traits in the rabbit.

Muscle energy metabolism and related physicochemical traits of the meat were studied in 84 Provisal hybrid rabbits of both sexes. From weaning (30 days) to 55 days of age, the rabbits were divided into 4 groups which were given ad libitum one of the following diets: H diet with high digestible energy (DE) level, L diet with low DE level, F diet with high DE level, obtained by supplementing with animal fats, and W diet with moderate DE level. The H, L and F diet were suitable for lactating does and weaning rabbits; the W diet for weaned young rabbits. From 55 days to slaughter age, the rabbits were given a G diet suitable for growing and fattening. The rabbits were slaughtered at 55 days (23 rabbits), 80 days (31 rabbits) or 87 days (30 rabbits) of age. The activity of a representative enzyme of the glycolytic (fructose-1,6-diP aldolase) and oxidative (NADP-isocitrate dehydrogenase: ICDH) energy metabolism pathways and two related physicochemical traits, namely lightness (L (∗)) and ultimate pH (pH(u)), were determined in the biceps femoris (BF) and longissimus lumborum (LL) muscles. The chemical composition of whole longissimus dorsi (LD) and total hindleg (HL) muscles was also determined. In BF and LL muscles, the activity of the glycolytic energy metabolism increased during the fattening period, as a result of metabolic differentiation. The increase stopped earlier in BF than in LL muscle. Variations in pH(u) values followed the same trend. The dietary effect on biochemical and physicochemical traits was moderate. A slight decrease in muscle pH(u) was observed under the less energetic diets. Aldolase activity was significantly higher in females. The significant correlations between metabolic and physicochemical traits confirmed that as glycolytic energy metabolism increases, the protein content increases, whereas pH(u) decreases. Slaughter weight was positively correlated to glycolytic energy metabolism.

Rabbit growth, feed efficiency and body composition: Effects of recombinant porcine somatotropin.

The effects of recombinant porcine somatotropin (rpST) were studied on rabbits from INRA 1077 strain, between the ages of 70 and 90 days. Ten rabbits received a daily intramuscular rpST injection (100 mg per day per kg of live weight) and were compared with ten control rabbits. Growth rate and feed efficiency were not affected by treatment. Perirenal fat deposits were smaller in rpST-treated than in the control rabbits (2·01 vs 2·72%) as were reference carcass lipid content (9·4 vs 10·8) and energy value (0·84 vs 0·88 MJ /100 g). The ratio between polyunsaturated fatty acids (FA) and saturated and monounsaturated FA was higher (0·32 vs 0·28). Reference carcass protein content was increased (20·5 vs 19·9%), as was the percentage of skin in slaughter weight (14·3 vs 13·4%). Muscular ultimate pH (24 h post mortem) was lower in the semimembranosus accessorius (5·67 vs 5·78) and in the biceps femmoris (5·65 vs 5·74) of treated rabbits. In conclusion, rpST, as a heterologous hormone, develops protein-rich tissues whilst lowering fat content and appears to affect the balance of muscular energy metabolism.