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Role of feed restriction programs on enhancing gut health, feed efficiency and meat quality in growing rabbits
Get PDFThe application of feed restriction strategies to meat rabbit production is focused on two main aspects: 1) the improvement of animal health status by reducing mortality and morbidity due to digestive troubles; 2) the increase in the global farm efficiency by enhancing feed conversion and decreasing the costs related to antibiotic treatments. Both of these issues are of great interest in view of guaranteeing an economic sustainability to farmers and meeting the European regulations in terms of food safety. Hence, over the last decades, the effects of feed restriction strategies in growing rabbits have been widely investigated. Most of the studies has carried out feeding restriction during the first three or four weeks after weaning, with the aim to obtain feeding levels ranging from 60% to 90% of ad libitum, and free feeding during the last phase of fattening (from one to three weeks). Quantitative feed restrictions have been obtained directly by reducing the amount of diet supplied or indirectly by limiting the feeding time or the drinking time. Furthermore, qualitative feed restriction has been performed by reducing the energy level in the diets supplied to animals. The choice of restriction method should take into account the rearing facilities and equipment, the environmental conditions, and the impact on animal welfare.
The literature reported that rationing programs could represent a valid tool to reduce the incidence of digestive troubles, to increase diet utilization and to improve feed efficiency in growing rabbits. However, the protective effect of feed rationing on gut health is only limited to the restriction phase, while the incidence of digestive disease could even increase during fattening in rabbits previously restricted. Therefore, the re–feeding technique represents a critical point, but few studies have been focused on this issue. Moreover, the multifactorial origin of ERE makes difficult the interpretation of the variable and sometimes contrasting results among studies. On the other hand, the improvement of feed conversion seems to be a constant effect, but the economic benefits can be limited because of a longer fattening period is often required to achieve the complete recover of the animals in terms of live weight and avoid a substantial decrease in slaughter yield. Indeed, the economic aspects of feed restriction techniques should be carefully evaluated especially in the markets that require high slaughter weights (e.g. Italian market).
The present thesis aimed to define an effective feed restriction program for enhancing feed efficiency and gut health in growing rabbits, without impairing slaughter traits, carcass and meat quality. The goal was pursued by focusing on three specific objectives (i) to evaluate the effect of quantitative feed restriction systems in individually-housed rabbits; ii) to develop an adequate time–based feed restriction program in group–housed rabbits; iii) to optimize the management of the re–feeding phase. These points were developed in four experimental contributions whose working plan and main results are summarized below:
First contribution: Effects of feed restriction system and slaughter age in growing rabbits
The effect of the feeding system (AL: ad libitum vs. D: day–by–day restriction system vs. W: week–by–week restriction system) on digestive efficiency, sanitary status, growth performance, carcass traits, and nitrogen excretion was evaluated on 282 commercial crossbred rabbits kept in individual cages from weaning (36 d of age) to slaughter. The effect of slaughter age (73 vs. 80 d of age) was also assessed. The feed restriction was based on the administration of a restricted amount of the diet which increased from 80% to 100% of AL intake in the first three weeks after weaning according to two feeding curves characterized by either small daily increments (+4 g/d; D group) or large weekly increments (+23 g/week on average; W group). From the beginning of the 4th week, the amount of feed supplied for both restricted groups was increased by 4 g/d for 9 consecutive d in order to prevent high picks in food ingestion, then all rabbits were fed ad libitum until commercial slaughter. No antibiotic treatment was administered during the trial.
The apparent digestibility of the post–weaning diet was measured on 36 rabbits (12 per feeding system) from 49 to 53 d of age (during the restriction phase), while the digestibility of the fattening diet was measured on 36 rabbits (12 per feeding system) from 64 to 68 d of age (during the ad libitum period).
At the moment of the first digestibility trial, the feed ingestion of the restricted group was equal to 95% of AL group and therefore only the digestibility of crude protein was increased (P<0.001). During the second period, no residual effect of the previous restriction treatment was observed on diet digestibility. In the whole trial, mortality, morbidity and sanitary risk reached respectively 12.7%, 11.3% and 24.0% on average. Mortality and sanitary risk were significantly (P<0.05) reduced in restricted rabbits compared to those fed ad libitum ( 12.0 percentage points), in particular when a day–by–day restriction curve was applied ( 14.2 percentage points). In the first three weeks the feed restriction level was equal to 91% in D group and 93% in W group; daily growth decreased in both restricted groups ( 7.5% with respect to AL) whereas feed conversion did not differ among groups. In the second period only W rabbits showed higher feed intake (+4.2%) and weight gain (+14.5%), and a better feed conversion ( 3.2%) compared to AL rabbits. Final live weight (on average 2748 g), feed conversion ratio (3.07), cold dressing percentage (59.8%) and other carcass traits were not affected by the feeding treatment. The daily nitrogen excretion was reduced ( 0.08 g/d per rabbit; P<0.05) in the D group respect to AL group. The increase of slaughter age from 73 to 80 d significantly increased final live weight (+7.5% g; P<0.001) and feed intake (+4 g/d, P<0.05), reduced daily weight gain ( 3.1 g/d; P<0.001) and impaired feed conversion (2.92 vs. 3.22; P<0.001). All carcass traits were greatly (P<0.01) modified by delaying slaughter age; carcass weight increased (1563 g to 1705 g) as well as dressing percentage (59.3% to 60.5%), carcass fatness and muscularity, whereas the incidence of full gut decreased ( 0.7 percentage points). Nitrogen excretion was also increased (+0.21 g/d per rabbit) in older rabbits.
In conclusion, feed restriction improved rabbit health status without impairing growth performance and carcass traits. The day–by–day restriction curve reflected better the feeding behaviour of growing rabbits compared to the week–by–week curve, allowing to obtain a feeding level similar to that expected. However, the application of this type of restriction appears difficult in commercial farms because it is time and labour consuming if automatic feeding systems are not available and could not to be adequate with group–housed rabbits. The delay of slaughter increased dressing percentage, but impaired feed conversion and increased environmental nitrogen excretion.
Second contribution: Time–based feed restriction and group composition for gender: effects on growth performance, feeding behaviour and meat quality of growing rabbits
The effect of the feeding system (AL: ad libitum vs. R: feed restriction) and the sex–based group composition (X: only females vs. Y: only males vs. Z: mixed sexes) on growth performance, feeding behaviour, slaughter traits and meat quality was evaluated on 288 crossbred rabbits (144 females and 144 males), housed from weaning (33 d of age) to slaughter (75 d of age) in 18 collective pens (1 m2; 16 animals per pen). A time–based feed restriction was realized by increasing the access time to the feeders (allowed mainly during the hours of darkness) step–by–step (+1 h every 3–4 d) from 10 h/d to 16 h/d in the first three weeks. After that, feeding time increased gradually (+1 h/d) until reaching the free access to the feeders. During the first three weeks, an average restriction level equal to 95% of ad libitum was obtained. During the first three weeks, feed intake decreased (128 vs. 122 g/d; P<0.01) and feed conversion improved (2.42 vs. 2.29; P<0.001) in restricted rabbits in comparison with rabbits fed ad libitum. In the second trial period, the previously restricted rabbits showed a worse feed conversion (2.70 vs. 2.83; P<0.001) compared to rabbits always fed ad libitum. In the whole trial, growth performance were not affected by the feeding system. The feed restriction greatly modified the feeding behaviour of R rabbits, which showed a higher hourly feed consumption compared to AL ones throughout the time of access to the feeders. Once fed freely, R rabbits showed an intake pattern similar to that of AL rabbits within two days. The feed restriction did not affect slaughter weight (on average 2860 g), dressing percentage (61.0%) or meat quality.
In the first trial period growth performance did not change according to the sex of the animals, while in the second period the pens with only females or with mixed sexes showed higher daily growths compared to those with only males (47.0 g/d vs. 43.8 g/d vs. 46.1 g/d for X, Y and Z groups, respectively; P<0.01). At the same time, the feed conversion ratio decreased in pens X and Z in comparison to Y ones (3.66 vs. 3.91 vs. 3.72; P<0.01). Considering the whole rearing period, daily weight gain, feed intake and feed conversion did not change according to the group composition and the animals reached similar live weights at the end of trial. Transport losses were higher in X pens compared to Y ones (3.00% vs. 2.45% vs. 2.80%; P<0.01), while the cold dressing percentage (60.2% vs. 61.8% vs. 61.0%; P<0.001) and the head proportion on carcass (7.41% vs. 7.65% vs. 7.60%; P<0.05) were higher in males. Meat pH, thawing losses and shear force of l. lumborum were significantly (0.05<P<0.01) lower in Y and Z rabbits compared to X ones. The frequency of injuries increased in pens Y, with only males, and Z, mixed–sexes (5.2% vs. 18.3% and 13.3%; P<0.05). In conclusion, growth performance and meat quality were not significantly affected by the feeding system. The progressive increase of the access time to the feeders from 10 to 16 h/d in the first three weeks did not allow to control accurately the feed restriction level because rabbits adjusted very quickly their ingestion capability. Growth performance, slaughter traits and meat quality were not affected by the sex–group composition. Housing animals in groups of only males increased the risks of aggressiveness.
Third contribution. Effect of the feeding program and group size on growth performance, health status and meat quality in growing rabbits
The effect of the feeding program (AL: ad libitum vs. R: feed restriction) and the group size (8, 16 or 32 rabbits per pen) on growth performance, health status, carcass traits and meat quality was evaluated on 320 crossbred rabbits (160 females and 160 males) reared from weaning (31 d of age) to slaughter (73 d) in 20 open–top pens with different group size (8, 16 or 32 animals) at the same stocking density (16 animals/m2).
Feed restriction provided a progressive decrease of the access time to the feeders during the first week (from 14 h/d to 8 h/d), a stable time of 8 h/d in the second week and a progressive increase (+1 h/d) during the third and fourth week (re–feeding phase), thus achieving a restriction level equal to 85% of ad libitum. Throughout the last two weeks, all rabbits had free access to the feeders.
Feed restriction significantly (P<0.001) reduced feed intake ( 15%) and feed conversion ( 12%) in the first three–week period. During the last three–week period, the previously restricted rabbits showed higher daily growth rate compared to the AL ones (47.2 g/d vs. 48.8 g/d; P<0.05), whereas feed intake and feed conversion did not differ between groups. In the whole period, feed conversion was significantly lower in R group compared to AL group (3.05 vs. 2.93; P<0.001). Digestive troubles appeared before in AL rabbits, but morbidity soon raised in R group during the re–feeding phase. At the end of the trial, mortality rate tended to be higher in the restricted rabbits (6.3% vs. 11.9%; P<0.10). Slaughter weight (2734 g), dressing percentage (61.3%), carcass traits and meat quality were not affected by the feeding program.
No significant difference in growth performance, slaughter results and meat quality was observed according to the group size. Nevertheless, rabbits housed in larger groups were subjected to increased sanitary risk (6.3% vs. 14.8% and 18.0% for groups with 8, 16 and 32 rabbits/pen, respectively; P<0.05).
In conclusion, the application of a feed restriction program characterized by a progressive reduction of the access time to the feed during the first week, a constant phase in the second week, and a progressive increase during the third and fourth week allowed to obtain the expected restriction level in the first trial period (85% of ad libitum). Feed restriction significantly improved feed conversion without affecting final live weight, slaughter traits and meat quality. However, even if a progressive re–feeding phase was performed, morbidity and mortality rate increased in the previously restricted rabbits during the second trial period. Housing animals in large groups impaired sanitary conditions.
Fourth contribution. Effect of different rationing and re–feeding programs on growth performance, digestive physiology, health status, slaughter traits and meat quality in group–housed rabbits
The effects of feeding system (ad libitum vs. restriction) and restriction method (diurnal vs. nocturnal access to feed) were evaluated on growth performance, digestive physiology, health status, slaughter traits and meat quality of 400 growing rabbits housed from weaning (28 d of age) to slaughter (70 d) in collective pens of 8 animals (stocking density of 16 animals/m2). Moreover, the effects of re–feeding speed (fast: +4 h/d vs. slow: +1/+2 h/d of access to feed) and re–feeding level (complete: up to 24 h/d vs. incomplete: up to 12 h/d of access to feed) were also assessed. The following groups were formed: ad libitum (AL); diurnal rationing with fast and complete re–feeding (DF); nocturnal rationing with fast and complete re–feeding (NF); nocturnal rationing with slow and complete re–feeding (NS) and nocturnal rationing with very slow and incomplete re–feeding (NI).
The rationing programs previewed a first week of decreasing access time to feed until 9 h/d; a second week of stable daily access time (8 h/day) and a re–feeding period starting from the beginning of the third week.
The diurnal access to the feed led to an initial restriction level more severe than that obtained with the nocturnal rationing programs, but after one week of adaptation DF group reached the feed intake of nocturnal restricted groups (N groups). Feeding time reduction (until 8 h/d) in the first two weeks decreased feed intake ( 24% of ad libitum) and weight gain ( 7% with respect to the AL group) of restricted rabbits leading to a significantly lower live weight at the end of the third week (1761 g vs. 1671 g for AL and restricted rabbits, respectively; P<0.001). However, restricted rabbits showed a feed conversion significantly lower compared to that of ad libitum ones (2.11 vs. 1.95; P<0.001) in the first period. Indeed, during the second week, the feed restriction significantly (0.01<P<0.001) enhanced the digestibility of dry matter (+3.5%) and most of nutrients compared to the ad libitum system, irrespective of the feed restriction method. At 43 d of age, the pH of the caecal content was lower in DF and NF rabbits compared to AL ones (5.46 vs. 5.34 on average; P<0.01). Accordingly, the total production of volatile fatty acids (VFA) increased in DF and NF groups with respect to AL group (+15% on average), while the N–ammonia decreased in restricted groups ( 29% on average). In the second rearing period, with the re–feeding phase, the weight gain was higher (P<0.001) in previously restricted rabbits compared to AL ones (47.1 g/d vs. 51.1 g/d) because of the increase (P<0.001) in feed intake (157 g/d vs.165 g/d). The NI group, characterized by an incomplete re–feeding, showed higher feed efficiency with respect to the groups submitted to complete re–feeding curves (P<0.05). Indeed, at the end of re–feeding (51 d of age), the digestibility of gross energy and crude protein of fattening diet was higher in NI group compared to the fast re–fed groups (0.05<P<0.01). At the same age, the total VFA production was still higher in the restricted groups compared to AL one (+19% on average; P<0.001) and increased with the decrease of re–feeding speed (P<0.01).
Animal health status was not affected either by the feeding system (ad libitum or feed restriction) or by the rationing method (diurnal or nocturnal) or by the re–feeding program (fast, slow or incomplete).
Slaughter weight (2607 g on average), dressing percentage (60.2% on average), carcass traits and meat quality did not change according to the feeding program.
In conclusion, a nocturnal rationing program performed by decreasing gradually the access time to feed in the first week of post–weaning and increasing slowly the feeding time up to 12 h/d at the fourth week onwards represented the best strategy to optimize feed efficiency in growing rabbits without impairing health status, growth performance, slaughter traits and carcass and meat quality.
The restriction levels applied in our trials (85–90% of ad libitum during the first three weeks after weaning) have been set to find a balance between the positive effects on gut health and the negative impact on the growth performance of rabbits. Generally, a more severe feed restriction (≤80% of ad libitum) applied during post–weaning allows to obtain a relevant enhancement of animal health status, but it may compromise the overall productive performance of rabbits by decreasing final live weight, slaughter yield and impairing carcass traits. In the first contribution, with rabbits housed individually, the total mortality rate was significantly reduced by applying a moderate restriction level (90% of ad libitum) during post–weaning especially when a progressive and gradual feed restriction curve was adopted. In this regards, a slight feed restriction may exert a protective effect on gut health in conditions of limited contacts among animals. Nonetheless, in the third contribution, a strict rationing program preserved the digestive health of rabbits housed collectively in the first two weeks, but its positive effect disappeared when the animals started the re–feeding phase. Feed restriction can lead to a relevant increase of mortality in previously restricted rabbits during the last weeks of fattening, thus increasing the economic impact of animal losses. Indeed, in the fourth contribution neither the application of a very slow and even incomplete (12 h/d) re–feeding programs was effective in reducing the incidence of digestive troubles once an antibiotic-free diet was supplied.
In the first two trials, no differences in terms of feed efficiency and growth performance were detected among restricted and ad libitum groups. On the other hand, in the third and fourth contributions, with the implementation of more severe feed restrictions, daily growth decreased in the first period, but restricted rabbits reached live weights similar to those of AL ones at the end of trial, thanks to the occurrence of a compensatory growth during the re–feeding period. Moreover, a significant reduction of feed conversion was detected in restricted groups especially when an incomplete re–feeding was used. The rationing programs did not affected slaughter results, carcass traits and meat quality: the restriction levels tested and the length of re–feeding phase could explain these results. The improvement of feed efficiency in restricted rabbits could be related to the increase in diet digestibility. However, this effect occurred only during the restriction phase. Indeed, an incomplete re–feeding until the end of trial allowed to maintain a higher diet digestibility compared to the complete re–feeding techniques.
The feeding behaviour of rabbits greatly changed when the animals were subjected to limited access time to the feeders. However, in our conditions, the rabbits adopted a feeding behaviour similar to that of rabbits always fed ad libitum within few days after reaching the free access to the feed. In the fourth contribution, a diurnal access to the feed involved a deeper change in the feeding behaviour of rabbits, which need approximately one week to reach the intake level of rabbits fed during the night.
In conclusion, our results confirm the possibility to apply feed restriction programs in the Italian production system with the main objective of enhance feed efficiency. The control of digestive diseases still appear difficult to be achieved and the relationship between feed restriction and gut health needs further investigations. A time–based feed restriction, characterized by a feeding time shorter than 10 h/d during the first three weeks after weaning and followed by an incomplete re–feeding (up to 12 h/d) could be the most suitable technique to be used in field conditions and in group–housed rabbits. Further investigations may be also carried out to prove a possible synergistic effect by combining feed restriction programs with different diet compositions
Effect of sex and slaughter age on carcass and meat quality of brown hares (L. europaeus)
No full textThe present study aimed at evaluating slaughter results, carcass traits and meat quality in 48 farmed brown hares (L. europaeus) of both sexes slaughtered at two ages (sub-adult hares, on average 73 d of age, vs. adult reproducing hares, on average 17 months) in a commercial slaughterhouse and then dissected following standardized procedures for rabbits. At slaughter, the females were heavier than the males (2783 vs. 2629 g; P<0.05), showed higher full gut incidence (13.7 vs. 12.9%; P<0.05), lower skin and feet incidence (13.3 vs. 14.0%; P<0.01), and lower dressing percentage (66.7 vs. 67.6%; P=0.06). The carcasses of females had lower dissectible fat (1.34 vs. 2.17%; P<0.05) and higher proportion of both l. lumborum (14.3 vs. 13.8%; P<0.05) and hind legs (37.2 vs. 36.4%; P=0.06). When age increased, slaughter live weight (2022 to 3391 g) and carcass weight increased (P<0.001), but dressing percentage did not vary (67.2% on average); the full gut incidence decreased (14.5 to 12.1%; P<0.001), whereas skin and feet proportion increased (12.9 to 14.5%; P<0.001). When age increased, head, liver and thoracic organs proportions decreased (P<0.001); dissectible fat (1.34 to 2.17%; P<0.05) and l. lumborum (13.5 to 14.5%; P<0.001) increased; moreover, hind legs proportion decreased (37.3 to 36.3%; P=0.01) but the muscle to bone ratio of hind legs increased (5.11 to 6.23; P<0.001). Meat quality did not vary with gender, whereas sub-adult animals significantly differed (P<0.001) from adults, showing lower meat pH, higher lightness index, higher redness index for l. lumborum (3.03 to 1.46) and lower redness index for b. femoris (4.07 to 5.76); besides they had higher meat thawing losses and lower shear force measured on the hind leg (2.97 to 4.02 kg/g; P<0.001). In conclusions, hare slaughter and carcass traits differed according to both sex and age, whereas meat quality was affected only by age
Effect of increasing soluble fibre and starch and reducing acid detergent fibre in diets at different protein level for growing rabbits
No full textFrom weaning (at 36 d of age) until slaughter (at 79 d), 282 commercial crossbred rabbits (951±31 g) were assigned to six experimental groups and fed ad libitum six diets formulated according to a bi-factorial arrangement with three (soluble fibre+starch)-to-ADF ratios (0.6, 1.2 and 2.0) and two protein levels (15.0% and 17.0%). The dietary soluble fibre (5.0%, 7.0% to 9.0%) and starch (10.0%, 14.0% to 18.0%) levels jointly increased at the expense of acid detergent fibre (ADF) (22.0%, 18.0% to 14.0%). The growth performance, and the in vivo nutritive value of diets were recorded. The caecal fermentation traits were measured on 36 rabbits slaughtered at 45 d of age. When the (soluble fibre+starch) to ADF ratio raised, daily growth linearly increased (P=0.05) and feed intake decreased (P<0.001) and, thus, feed conversion improved (P<0.001); the digestibility of dry matter (50.8 to 71.5%), gross energy (50.3 to 70.7%) and fibre fractions linearly increased (P<0.001); at caecum, the concentration of total volatile fatty acids (VFA) raised (63.0 to 78.5 mmol/L; P=0.02), whereas the proportion of propionate decreased (4.0 to 3.5 mol/100 mol VFA; P=0.04). When the dietary protein increased, feed conversion improved (3.47 to 3.37; P<0.001) and the digestibility of dry matter increased; (60.3% to 61.6%; P<0.001) at caecum, the N ammonia level tended to decrease (P=0.07), whereas total VFA production and VFA molar proportions were not affected. The increase of the (soluble fibre+starch) to ADF ratio reduced the mortality rate (15.8%, 4.5% and 4.9%; P=0.02), whereas the dietary protein level did not affect rabbit health. In conclusion, the contemporary increase of dietary soluble fibre and starch at the expense of ADF increased digestive feed utilization and growth performance, and enhanced fermentation activity at caecum and health status. The increase of dietary protein moderately improved productive results and did not affect health status
Optimizing feed efficiency and nitrogen excretion in growing rabbits by increasing dietary energy with high-starch, high-soluble fibre, low-insoluble fibre supply at low protein levels
No full textA total of 282 crossbred rabbits of both genders were divided into six experimental groups and fed ad libitum six diets formulated in a 2 x 3 factorial arrangement according to a bifactorial arrangement based on three dietary energy levels (low, approximately 8.45 MJ/kg; medium, 9.9 MJ/kg: and high, 11.5 MJ/kg) and two protein levels (15% and 17%). The increase of dietary energy was obtained by a simultaneous increase of dietary starch (9.1%, 13.7%, and 17.9%) and soluble fibre (4.8%, 7.1%, and 9.4%) at the expense of acid detergent fibre (23.0%, 18.0%, and 13.5%). Growth performance and nitrogen excretion from weaning until slaughter, and digestive traits were monitored. The increase of dietary energy enhanced the apparent digestibility of dry matter (50.8%, 60.5%, and 71.5%; P < 0.001), gross energy (50.3%, 59.7%, and 70.7%; P < 0.001), soluble fibre (73.1%, 77.8%, and 82.9%; P < 0.10), and neutral detergent fibre (16.1%, 29.0%, and 48.1%; P < 0.001). In the caecum, the total volatile fatty acid (VFA) content increased (63.0, 79.2, and 78.5 mmol/L; P <0.05), and the propionate rate decreased (4.0%, 4.2%, and 3.5% mol VFA; P <0.05); in the jejunum, the villi to crypt ratio tended to decrease (4.18, 3.89, and 3.57; P < 0.10). The increase of dietary energy supply decreased feed intake (181 g/d, 157 g/d, and 135 g/d; P < 0.001), which improved feed conversion ratios (3.98, 3.40, and 2.87; P < 0.001), and decreased nitrogen excretion (3.15 g/d, 2.56 g/d, and 1.93 g/d; P < 0.001). The increase of dietary energy significantly decreased mortality (15.8%, 4.9%, and 4.9%; P <0.05). When dietary crude protein increased from 15% to 17%, apparent digestibility increased for dry matter, crude protein, total dietary fibre, and gross energy (P<0.01). Growth performance during the trial was not affected, but nitrogen excretion decreased significantly (2.73 g/d vs. 2.37 g/d; P < 0.001). In conclusion, the increase of dietary energy by the simultaneous increase of dietary starch and soluble fibre to replace insoluble fibre optimized feed efficiency and controlled nitrogen excretion in growing rabbits with positive effects on digestive traits and health. The reduction in dietary protein level was determined to be an useful strategy to reduce farm nitrogen excretion
Effect of feed restriction level and period on performance and health of growing rabbits
No full textThe present study aimed to evaluate the effect of the level (100%, 90% and 80% of ad libitum) and period (2 and 3 weeks) of post-weaning feed restriction on growth performance and health status of 246 growing rabbits controlled from weaning until commercial slaughter (33-75 d of age). Despite significant effects of restriction program during the restriction period itself and soon after, the differences in final live weights of non-restricted and restricted rabbits were not significant, whereas rabbits submitted to the strongest restriction (80%) still tended to be lighter compared to R90 rabbits (P=0.06). Therefore, daily weight gain from 33 to 75 d of age was lower in R80 compared to R90 rabbits (P=0.04); feed intake was lower in restricted vs. not restricted rabbits and in R80 vs. R90 rabbits. Feed conversion was lower (P=0.04) in restricted rabbits without differences between the two restriction levels (R90 vs. R80). The restriction program, level and period did not affect rabbit health in the entire trial
Effect of feeding programme on performance and health of growing rabbits
Get PDFThe effects of two feeding systems (L, ad libitum vs. R, feed restriction) combined with three diets (HH, a high digestible energy diet, 11.1 MJ DE/kg, during the whole trial vs. MM, a moderate DE diet, 10.7 MJ/kg, during the whole trial vs. MH, a moderate DE diet during the first three weeks and a high DE diet during the last two weeks) were evaluated in 252 commercial crossbred rabbits kept individually from weaning to slaughter (34 to 70 d of age). The restricted rabbits were fed from 85% of the theoretical ad libitum intake at the beginning of the trial to 100% of the ad libitum level at the end of the 3th week. During the first week, growth rate was impaired by feed restriction (53.6 and 46.8 g/d in L and R rabbits, P0.10) and lower growth rate compared to R rabbits (48.2 vs. 51.3 g/d, P=0.05). During the fourth and fifth weeks, neither growth rate nor feed intake differed between the two groups. In the whole trial only feed conversion was improved by feed restriction (2.96 vs. 2.89 in L and R rabbits; P<0.01) and by the high-DE program (2.89 vs. 2.93 and 2.97, for HH, MH and MM groups, respectively; P<0.05). Morbidity was lower in the restricted group (5.5% vs. 2.4% in L and R rabbits; P<0.001) and in HH and MM groups compared to MH group (3.6% and 2.4% vs. 5.9% respectively; P<0.001). In conclusion, feed restriction improved feed efficiency and health, whereas the change from a moderate to a high energy diet during the growing period could impair rabbit health
Feed restriction programs and slaughter age in growing rabbits
No full textThe present study aimed at evaluating the effects of the feeding system (AL: ad libitum vs. D: day-by-day restriction vs. W: week-by-week restriction) and the slaughter age (73 vs. 80 d) on health status, growth performance, carcass and meat quality, and material balance of growing rabbits. A total of 300 commercial crossbred rabbits were housed in individual cages from weaning (36 d of age) to slaughter. The feed restriction was based on the administration of a restricted amount of the diet varying from 80% of the ad libitum intake at the beginning of the trial to 100% of the ad libitum intake at the beginning of the 4th week. The restriction level (about 90% on average) was obtained by two restriction curves: a day-by-day curve with small daily increments (+4 g/d; D group) and a week-by-week intake curve with large weekly increments (+23 g/week on average; W group). Mortality was significantly higher in the AL group compared to the daily and weekly restricted groups (20.7% vs. 11.0% and 6.5%; P<0.05). Final live weight (on average 2749 g), feed conversion (3.07), cold dressing percentage (59.9%) and other carcass and meat quality traits were not affected by the feeding system. However, the restricted rabbits evidenced increased empty body fat and energy gains (P<0.01) as a consequence of the compensatory growth during the second half of the trial. The delay of slaughter from 73 to 80 d of age significantly increased final live weight (2,647 vs. 2,847 g; P<0.001), reduced daily weight gain (47.3 vs. 44.3 g/d; P<0.001), increased feed intake, and impaired feed conversion (2.92 vs. 3.22; P<0.001). Besides, lipid and energy body content raised in the older rabbits (P<0.001). No substantial interaction between feeding regime and slaughter age was found. In conclusion, feed restriction improved rabbit health status and did not affect either growth performance or carcass and meat quality, whereas increased the body fat and energy deposition compared to the ad libitum feeding. A progressive day-by-day restriction curve appeared to be less risky and more respectful of the feeding behaviour of growing rabbits in comparison with a discontinuous week-by-week increment of feed administration and permitted to obtain a restriction level nearer to what expected (91% in D group vs. 93% in W group). The increase of slaughter age was much more effective in modifying growth and slaughter performance as well as body composition of rabbits than the feeding system
Effects of water salinity in an aquaponic system with rainbow trout (Oncorhynchus mykiss), black bullhead catfish (Ameiurus melas), Swiss chard (Beta vulgaris), and cherry tomato (Solanum lycopersicum)
Get PDFThis study evaluated the role of increasing salinity in brackish-water aquaponics, also defined as haloponics, during an 8-month cycle characterized by two fish monoculture phases in autumn and spring and a polyculture phase in winter. The effects of three water salinity levels (low: 0.5‰; medium: 3.0‰; high: 6.0‰) were assessed on the health, growth performance and carcass traits of black bullhead catfish (Ameiurus melas) and rainbow trout (Oncorhynchus mykiss), and the concurrent production of Swiss chard (Beta vulgaris, ssp. vulgaris) and cherry tomato (Solanum lycopersicum). During 268 days, from September to June, a total of 261 catfish (initial weight 147 ± 22 g) were distributed in the nine units of an experimental aquaponic system (three units per treatment; initial stocking density 8.50 kg/m3). In December, 150 trout (initial weight 153 ± 22 g) were added to the system (initial stocking density 5.06 kg/m3) and reared for 103 days with catfish. During the trial, two growing cycles of Swiss chard and one of cherry tomato were carried out. Water microbiota communities were dominated by the phyla of Proteobacteria (60%) and Bacteroidota (19%), followed by Actinobacteriota, Cyanobacteria, Fusobacteriota, Patescibacteria, and Firmicutes. The Shannon entropy index for alpha-diversity decreased when the water salinity increased, where low and high salinities groups significantly differed. As for the 20 most abundant genera, differences according to water salinities were found on their relative abundance. Water salinity did not affect the final weight (348 g, on average), eviscerated carcass yield (87.5%) and fillet (52.0%) yields of trout, as well as the final weight (193 g), eviscerated carcass yield (84.1%) and fillet yield (48.3%) of catfish. Water salinity did not affect the fillet chemical composition in both species. At low salinity, the fillet fatty acid profile of catfish showed lower (-6.5%; P < 0.05) MUFA and higher PUFA (+6.8%; P < 0.05) and n-6 (+5.9%; P < 0.05) proportions compared with high salinity. At high and medium salinity, Swiss chard showed higher total yield (+61%; P < 0.01) in the first production cycle and higher total (+28%; P < 0.01) and marketable (+32%; P < 0.001) yield in the second production cycle compared with low salinity, whereas cherry tomato truss weight was lower (-32%: P < 0.001) at high compared with medium and low salinity. The use of brackish water until 6‰ proved to be a viable alternative to reduce freshwater consumption, without impairing fish and leafy vegetable growth or the overall balance of the aquaponic system
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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