A 3-week feed restriction after weaning as an alternative to a medicated diet: effects on growth, health, carcass and meat traits of rabbits of two genotypes

Physiological and immunological aspects of feed restriction and its beneficial impacts in fattening rabbits' productivity-an updated review

Two feed restriction (FR) regimens are utilized with weaned rabbits including a quantitative FR (amount-limited feed or time-restricted admission to feed) and a qualitative FR (modulation of diet content especially protein and energy). The use of post-weaning FR may help in preventing post-weaning digestive disorders, stimulating compensating growth, improving feed efficiency, and decreasing carcass fat content. Interestingly, FR may contribute to changing meat's chemical composition and its physical quality attributes by regulating the morphological and biochemical characteristics of muscle fibers. Also, FR could enhance the gastrointestinal tract development, its histomorphology, and improve feed digestibility and absorption. Furthermore, FR regimens are involved in establishing gut microbial balance and enhancing the host immunological response. It might be concluded that post-weaning FR is involved in influencing the physiological and immunological aspects of growing rabbits. It might be documented that light to mild FR (i.e., 80-90% AL), early (i.e., at the first 2 weeks post-weaning), and relatively short in duration (i.e., for 2-3 weeks) had no negative effects on live body weight, while severing FR reduced live body weight in comparison with ad libitum rabbits.

Effect of feed restriction on growth performance, carcass traits, and some hematological and blood biochemical parameters in growing rabbits

Sixty-four male New Zealand White rabbits, 4 weeks old, were used to study the effects of feed restriction (FR) on growth performance, carcass traits, and some blood parameters. Rabbits were randomly allotted to 4 equal groups. The first group was fed ad libitum (control group). The second, third, and fourth groups were restricted from 4 to 8 (R4-8), 8 to 12 (R8-12), and 4 to 12 (R4-12) weeks of age, respectively. Restricted groups were fed 85% of the control. Means of live body weights (LBW), average daily gain weights (ADGW), relative growth rate (RGR) were calculated. Carcass traits and blood parameters were measured. Results showed that, FR reduced LBW, ADGW and RGR in R4-8 and R4-12 groups. However, FR did not impair the previous traits in R8-12 group. Carcass weight was not impaired in R8-12 group. However, FR reduced kidney fat in all restricted groups. Feed restriction reduced hemoglobin, red blood cell (RBC) and platelet levels in R4-8 and/or R4-12 groups. However, RBC and platelet levels were not altered in R8-12 group. Conclusively, FR impaired growth performance, carcass weight and blood parameters in R4-8 and R4-12 groups, however, the previous traits were not impaired in R8-12 group.

Effects of feeding methods on growth and slaughter performance, blood biochemical indices, and intestinal morphology in Minxinan black rabbits (Oryctolagus cuniculus)

Feed restriction after weaning is a common strategy used in commercial rabbit farms to improve feed efficiency, promote health, and reduce mortality. However, few studies have investigated the feed restrictions of Minxinan black rabbits (Oryctolagus cuniculus). Thus, the effects of feed restriction on growth and slaughter performance, intestinal morphology, and blood biochemical indices of Minxinan black rabbits were evaluated in this study. Rabbits in group A (control group) had ad libitum intake, while those in feed restriction groups (groups B, C, and D) were restricted to 80% of the average daily feed intake (ADFI) of group A the day before. The rabbits in group B were fed once per day at 8:00 am. Rabbits in groups C and D were fed twice per day at 8:00 am (50%) and 4:00 pm (50%) and 8:00 am (30%) and 4:00 pm (70%), respectively. The experimental period lasted for 8 weeks. Compared to that in group A, the diarrhea rate of group C was significantly decreased (P < 0.05), and the ADFI, feed conversion ratio, abdominal fat weight, abdominal fat rate, total protein, albumin, globulin, alanine aminotransferase (ALT), low-density lipoprotein, and intestinal crypt depth of all feed restriction groups were significantly reduced (P < 0.01). Feed conversion ratio in group D was significantly better than that in groups B and C (P < 0.05). The efficiency index (EI) of groups C and D was higher than that of groups A and B (P < 0.01). Triglyceride levels in groups C and D were significantly lower than those in group A. The villus length to crypt depth of the duodenum and jejunum in group D was significantly higher than that in group A (P < 0.01). In conclusion, the following parameters can be improved by feed restriction: feed conversion ratio, diarrhea rate, abdominal fat rate, serum ALT, lipid indices and intestinal health of Minxinan black rabbits, and the EI of the farm. Feeding twice per day, 30% at 8:00 am and 70% at 4:00 pm, had the best comprehensive effects.

Feeding behaviour of the growing rabbit fed freely or restricted, and impact on performances and digestive organs

This study aimed to determine how rabbits’ feeding and drinking behaviour was influenced by a feed restriction programme, and how performance and the morphometry of the digestive tract and lymphoid organs were influenced. At weaning (28 d old), 432 rabbits were housed in cages of 6, and allotted to 2 groups according to feed intake level: ad libitum feeding (AL group) from 28 to 72 d old, and feed intake (R group) restricted to 70% of AL intake from 28 till 49 d old, followed by ad libitum feeding from 50 till 72 d old. During the restriction, the R group intake was 36% lower than that of the AL group. When returning to an ad libitum feeding, the R group intake increased by 270%, thus exceeding the AL intake by 26% (P=0.03). The daily weight gain was reduced by 28% for R group during the restriction (40.0 vs. 55.7 g/d; P<0.001), whereas the feed conversion was improved (−11%, 1.86 vs. 2.09; P<0.001). The restriction led to a shorter intestine (−15%, 202 vs. 233; P<0.05) and lighter spleen (−15%, 4.8 vs. 5.9; P<0.05), whereas the number of Peyer patches was not influenced. Most of the growth delays of lymphoid tissues observed at the end of the restriction period in the R rabbits remained until the end of the experiment. The feeding activity of AL rabbits mainly occurred during the dark period (19:00-09:00), with 16% of rabbits eating. The R group strongly and massively started their feeding activity at feed distribution time (8:30-09:00), with 65% of rabbit eating at the start, then 35% still eating half an hour later. Feeding activity of R group remained high for 8 h after the feed distribution, with 28% of rabbits having a feeding activity between 9:30 and 17:00. R group had a higher number of meals (+30%) and drinks (+28%), and a longer meal duration (+30%) compared to AL group. R group consumed 63% of the intake within 6-7 h compared to ad libitum fed rabbits, which spread their intake over 15 h. No changes in social behaviour (access to feed or drinking, resting, aggressiveness) were detected, suggesting that this restriction programme did not impair welfare compared to that of ad libitum fed animals.

Maximum levels of cross-contamination for 24 antimicrobial active substances in non-target feed. Part 9: Polymyxins: colistin

The specific concentrations of colistin in non-target feed for food-producing animals, below which there would not be an effect on the emergence of, and/or selection for, resistance in bacteria relevant for human and animal health, as well as the specific antimicrobial concentrations in feed which have an effect in terms of growth promotion/increased yield were assessed by EFSA in collaboration with EMA. Details of the methodology used for this assessment, associated data gaps and uncertainties, are presented in a separate document. To address antimicrobial resistance, the Feed Antimicrobial Resistance Selection Concentration (FARSC) model developed specifically for the assessment was applied. However, due to the lack of data on the parameters required to calculate the FARSC, it was not possible to conclude the assessment until further experimental data become available. To address growth promotion, data from scientific publications obtained from an extensive literature review were used. Levels of colistin in feed that showed to have an effect on growth promotion/increased yield were reported. It was recommended to carry out studies to generate the data that are required to fill the gaps which prevented the calculation of the FARSC for these antimicrobials.

The effect of feed restriction, sex and age on the carcass composition and meat quality of nutrias (Myocastor coypus)

The objective of the study was to evaluate the effect of quantitative feed restriction on the carcass composition and physical, chemical, histochemical and sensory properties of meat from male and female nutria at the end of the feed restriction and fattening period. In the experiment, from two to eight months of age, males and females were divided into two groups: one group was fed ad libitum throughout the experiment, and the second group was restricted to two weeks (from 11 to 12 weeks of age). The restricted nutrias received 75% ad libitum feeding. The significant interaction among feed restriction, sex and age was revealed only in the cross-sectional area of all muscle fiber types. Age was the main factor affecting carcass composition and meat quality characteristics. Sex-related differences in carcass composition and some sensory attributes and feed restriction-related differences in carcass composition were observed.

Impact of feed restriction and fragmented feed distribution on performance, intake behaviour and digestion of the growing rabbit

Postweaning feed restriction preserves rabbit digestive health after weaning, but the underlying physiological mechanisms are not yet understood. To elucidate whether the feeding intake pattern modification related to feed restriction might be involved, we studied the effects of both feed intake quantity and intake frequency. Animals were allotted at weaning (28 d old) in a 2 × 2 factorial design: feed intake quantity (AL = ad libitum vs R = 75% of AL) and fragmented feed distribution (FFD) (1 vs 13 distributions), thus forming four groups (AL1, AL13, R1 and R13). New Zealand White growing rabbits were used from weaning to slaughter (70 d old), to analyse mortality, morbidity, performance, intake behaviour, digestion and microbial activity. Seven days after starting feed restriction (35 d old, group R1), rabbits consumed 44% of the feed within 2 h, 65% in 4 h and in 7 h over 95%. Over the 28-70 d period, mortality was low (5.3%) while morbidity averaged 18.5% and neither was affected by treatment. However, FFD tended to decrease the morbidity rate during the first 14 days after weaning (P = 0.06). Feed conversion (28-70 d) was improved by restriction (+15%, P < 0.001) and by FFD (+5%, P < 0.001). Nutrient digestibility was improved by restriction (+10% for energy, P < 0.01), but not by FFD. Fragmented feed distribution led to a lower stomachal pH, in the antrum (1.48 vs 2.13, P < 0.001) and in the fundus (1.52 vs 2.63, P < 0.001), while a higher pH was found in the caecum (6.07 vs 5.86, P < 0.001). Butyrate proportion in the caecum was reduced by four units for restricted groups. Fragmented feed distribution reduced the caecal VFA concentration by 23% within restricted rabbit groups only. A similar interaction between intake level and FFD was observed for fibrolytic activity (cellulase and xylanase). The diversity of caecal bacterial community was not modified by either of the two factors studied. Globally, fragmented meals have no major impacts on the caecal microbial activity, diversity, and thus would not be implicated in the better resistance of restricted rabbit to digestive troubles.