Does feed restriction and re-alimentation differently affect lipid content and metabolism according to muscle type in pigs (Sus scrofa)?

This study aimed to investigate whether feed restriction and re-alimentation differently affect lipid content and activities of lipogenic or catabolic enzymes according to muscle types in pigs. At around 28 kg body mass (BW), sixty pigs (n=30 per group) were allocated to either ad libitum (AL) or restricted/re-feeding (RA) regimens. After feed restriction (80 kg BW), lipid content was reduced (P<0.01) in the oxidative rhomboideus (RH) as in the glycolytic biceps femoris (BF) muscles of RA pigs compared with AL pigs. Lower activities (P<0.05) of the lipogenic enzymes fatty acid synthase (FAS) and malic enzyme (ME) were observed in the RH but not in the BF of RA vs. AL pigs. After re-feeding (110 kg BW), lipid content was restored in the RH, but was still 12% lower (P<0.05) in the BF of RA compared with AL pigs. In the RH, the trend for an enhanced FAS activity and for a smaller weight-related decrease of ME activity in RA pigs than AL pigs during re-feeding, may have contributed to the muscle fat recovery observed in the RA pigs. In the BF, higher oxidative enzyme activities (P<0.10) in RA pigs compared to AL pigs might explain the incomplete lipid recovery observed after re-feeding in the former animals. In conclusion, metabolic activities in response to restriction and re-feeding differed according to muscle metabolic type.     

Nutrition-induced differences in body composition, compensatory growth and endocrine status in growing pigs

In this experiment, we assessed the effect of amino acid (AA) intake restriction in entire male Yorkshire pigs between 15 and 38 kg BW (restriction phase) on BW gain, body composition and plasma levels of blood urea nitrogen (BUN), cortisol, insulin-like growth factor I (IGF-I), growth hormone (GH) and leptin during the subsequent re-alimentation phase. During the restriction phase, 36 pigs were allotted to one of two dietary treatments: adequate AA intake (control) or AA-limiting diets (AA-30%). Thereafter, pigs were fed common non-limiting diets up to 110 kg BW. Throughout the experiment, pigs were scale-fed at 90% of the estimated voluntary daily digestible energy intake. At the end of the restriction phase, pigs on AA-30% had lesser BW gain (650 v. 784 g/day; P < 0.001), loin area (LA; 12.2 v. 14.2 cm2; P < 0.001), BUN (4.6 v. 6.3 mg/dl; P < 0.02), lesser plasma levels of IGF-I (440 v. 640 ng/m; P < 0.001) and cortisol (8.2 v. 19.2 μg/dl; P < 0.001), greater backfat thickness (BF; 7.56 v. 6.56 mm; P < 0.02), and greater plasma levels of leptin (2.7 v. 1.8 ng/ml; P = 0.027) and GH (3.3 v. 2.0 ng/ml; P = 0.05) than pigs on control. During the re-alimentation phase, previously restricted pigs showed full compensatory growth (CG) in terms of BW gain (1170 v. 1077 g/day; P < 0.002), whole-body protein deposition (Pd) (179 v. 163 g/day; P < 0.001) as well as physical and chemical body composition (whole-body lipid to body protein mass ratio, LB/PB; 1.14 v. 1.15; P > 0.10). Besides GH at 45 kg BW (4.2 v. 2.4 ng/ml; P = 0.066), there were no effects of previous AA intake restriction on leptin, IGF-I and BUN during the re-alimentation phase (P > 0.10). Plasma cortisol and IGF-I levels may act as an indicator of AA-induced restriction in Pd in growing pigs. Plasma BUN level does not appear as a sensitive indicator for compensatory Pd. Plasma leptin and GH levels allow for the involvement of the brain in controlling chemical body composition. Full CG was observed during the energy-dependent phase of Pd in growing pigs and might be driven by a target LB/PB, possibly mediated via plasma leptin, IGF-I and GH levels.     

Impact of feed restriction on health,digestion and faecal microbiota of growing pigs housed in good or poor hygiene conditions

Feed restriction could be a relevant strategy to preserve gut health, reduce systemic inflammatory response and finally limit antibiotic use. This study assessed the effect of feed restriction on growing pigs submitted to a moderate inflammatory challenge induced by the degradation of the environmental hygiene that is known to alter growth rate. The experiment was run on 80 pigs selected at 7 weeks of age according to a 2×2 factorial design: two feeding levels, ad libitum (AL) and feed restricted (FR) at 60% of AL, and two conditions of environmental hygiene, clean and dirty. Pigs were housed individually throughout the experiment. From 61 to 68 days of age (day 0 to 7), pigs were housed in a post weaning unit and feed restriction was applied to half of the pigs from day 0 to day 29. At 68 days of age (day 7 of the experiment), pigs were transferred in a growing unit where half of FR and half of AL pigs were housed in a dirty environment (poor hygiene) and the other half in a clean environment (good hygiene) until day 42. Growth performance was recorded weekly. Blood and faeces samples were collected to measure indicators of inflammation, nutrient digestibility and microbiota composition. Faecal consistency was monitored daily to detect diarrhoeas. Feed restriction decreased daily weight gain (−35% to −50%, P<0.001), increased the feed conversion ratio (+15%, P<0.001) and CP digestibility (+3%, P<0.05) and reduced the occurrence of diarrhoeas irrespective of hygiene conditions. Poor hygiene conditions decreased growth performance (−20%, P<0.05) and total tract digestibility of all nutrients (P<0.001). Haptoglobin (+50%) concentrations and lymphocyte (+10%) and granulocyte (+40%) numbers were higher in poor hygiene conditions (P<0.05), confirming that the model was effective to induce a systemic inflammatory response. Both feed restriction and hygiene modified the profile of the faecal microbiota. In this study, feed restriction did not reduce the systemic inflammatory response caused by poor hygiene conditions despite the limitation of the occurrence of digestive disorders. However, our study opens discussions regarding the impact of hygiene and feed restriction on gut microbial communities and digestive health.     

Evolution of the fatty acid profile of subcutaneous back-fat adipose tissue in growing Iberian and Landrace × Large White pigs

The lipid content and fatty acid (FA) profile in pig tissues are strongly influenced by genotype and nutrient supply, with implications in meat quality. The de novo lipid synthesis and pattern of FA unsaturation could be an important cause of variation in the overall efficiency of energy utilization among breeds. To test the effects of pig genotype and CP supply on the evolution of back-fat tissue FA profile throughout the growing and finishing stages, 32 Iberian (IB) and Landrace × Large White (LR × LW) barrows were offered one of two diets differing in CP content (13% or 17% as fed). A pair-fed procedure (0.8 × ad libitum intake of IB pigs) was used. Subcutaneous fat samples were taken at the dorso-lumbar region at ∼38, 50, 65, 90 and 115 kg BW. Higher proportions of total monounsaturated FA (MUFA; P < 0.01) and lower proportions of total saturated FA (SFA; P < 0.01 to 0.05) were found in the outer back-fat layer of pigs both at 50 and 115 kg BW. Pig genotype affected the FA composition of both subcutaneous back-fat layers. The proportions of C18:0 and SFA in fat tissue were higher in IB than in LR × LW pigs from 38 to 65 kg BW, especially in the outer layer. In addition, MUFA contents were higher in IB pigs at 115 kg BW in both layers (+5% on average; P < 0.01). Increased proportions of C18:2 n-6 and polyunsaturated FA (PUFA) were found in LR × LW pigs, irrespective of the stage of growth and back-fat layer (P⩽0.02). At 50 kg BW, pigs receiving the high-protein diet presented the highest C18:2 n-6, C18:3 n-3, C20:5 n-3 and PUFA contents. A significant genotype × CP content interaction was observed for C18:3 n-3 because of the increased concentration of this FA in LR × LW pigs when offered the 17% CP diet (P < 0.05). Higher C16:0 and SFA contents (+5%; P = 0.03) were found in pigs offered the 13% CP diet and slaughtered at 115 kg BW. There was a genotype × CP interaction for MUFA concentration because of the higher MUFA content observed in IB pigs offered the highest protein content diet (P = 0.03). Our results suggest that genetic variation in de novo lipid synthesis and pattern of FA unsaturation might contribute to explain differences in back-fat FA profile of IB and LR × LW pigs under identical nutritional management. They could be also relevant to explain the low efficiency of nutrient and energy utilization in the IB pig.     

The effect of 1-week feed restriction on performance,digestibility of nutrients and digestive system development in the growing rabbit

A 3 to 4 week feed restriction of about 20% to 25% of the free intake is widely applied in rabbit breeding systems to reduce post-weaning digestive disorders. However, a short intensive feed restriction is described in few studies and can be beneficial for growing rabbits due to a longer re-alimentation period. The aim of this study was to evaluate the effect of ad libitum (AL) and two restriction levels of feeding (50 and 65 g/rabbit per day) applied for 1 week on performance, gastrointestinal morphology and physiological parameters during the restriction and during the re-alimentation period. Rabbits were divided into three experimental groups: AL rabbits were fed AL, R1 rabbits were restricted from 42 to 49 days of age and received 50 g daily (29% of AL) and R2 rabbits were restricted at the same age and were fed 65 g of feed daily (37% of AL). In the 1^st week after weaning and in the weeks after restriction, all the groups were fed AL. During the restriction period, daily weight gain (DWG) in R1 significantly dropped to 11% (experiment 1) and 5% (experiment 2) compared with rabbits in the AL group, although they were fed 29% of AL, whereas in the R2 group it decreased to 20% (experiment 1) and 10% (experiment 2). In the week following feed restriction, DWG in the restricted groups increased (P<0.001) to 166% and 148% in R1 and to 128% and 145% in R2. Restricted rabbits in both the experiments reached up to 90% to 93% of the final live weight (70 days) of the AL group. Over the entire experimental period, feed restriction significantly decreased feed intake to 85% to 88% of the AL group; however, the feed conversion ratio was lower (P<0.05) only in experiment 1 (−6% in R1 and −4% in R2). Digestibilities of CP and fat were not significantly higher during the restriction period and during the 1^st week of re-alimentation compared with the AL group. Significant interactions between feeding regime and age revealed the shortest large intestine in the AL group at 49 days of age and the longest at 70 days in the AL and R1 groups. Small intestinal villi were significantly higher and the crypts were significantly deeper in the restricted groups. It could be concluded that short intensive feed restriction increased digestible area in the small and large intestines, including the height of villi and depth of crypts, which might be involved in the compensatory growth and defence mechanism.     

Effects of temporary intensive feed restriction on performance,nutrient digestibility and carcass criteria of growing male Californian rabbits

The aim of the study was to evaluate the effect of a temporary quantitative feed restriction on growth performance, nutrient digestibility and carcass criteria of rabbits. A total of 80 weaned male Californian rabbits (30 d of age) were randomly assigned to four treatments of 20 rabbits each. The Control group was fed ad libitum during the whole experimental period (days 30–72 of age). For the three restricted fed groups the feed intake was reduced by 15%, 30% and 45% compared to the Control group, respectively. The feed restriction was applied after weaning and lasted for 21 d. Thereafter, at 51 d of age, in all treatments the feed supply returned to ad libitum intake till 72 d of age (AL period). The feed restriction decreased the body weight gain of rabbits (during the restriction period and the whole experimental period, p < 0.001) and improved feed conversion ratio during all tested periods (p < 0.001). In the AL period, the daily body weight gain of all groups was similar. After the AL period, the digestibility of all measured nutrients was significantly higher for animals fed restrictively. Furthermore, feed restrictions significantly decreased the proportion of perirenal and scapular fat and increased relative weight and length of the gastrointestinal tract. Therefore, it can be concluded that the applied feed restriction improved feed conversion, nutrient digestibility and reduced fat at the slaughter age of Californian rabbits, but the reduced body weight gain could not be compensated by a subsequent ad libitum feeding for 3 weeks.     

Re-alimentation strategy to manoeuvre body condition and carcass characteristics in cull ewes

Improvement in body condition and carcass traits through nutritional intervention was studied in cull ewes. Sixty-eight adult non-productive Malpura ewes (average body weight 26.7 ± 0.33 kg) were randomly divided into four equal groups: G0 maintained on free grazing for 8 h on protected natural rangeland with ad libitum guar (Cyamopsis tetragonoloba) straw (GS) after grazing; G1, G2 and G3 fed with supplemental concentrate at the rate of 250 g, 2.5% of live weight (LW) and ad libitum, respectively. The experiment was continued for 90 days and daily feed intake, weekly LW and body condition score (BCS) were recorded. Intake and digestibility of nutrients were assessed by indicator method. Rumen fermentation attributes and blood biochemical profile were studied to assess the dietary effects and animals were slaughtered at the end of experiment for evaluation of carcass characteristics. Higher dry matter (DM) intake and improvement in plane of nutrition was observed in G2 and G3 with a higher LW gain (LWG) and improvement in BCS than in G0. The digestibility of DM, organic matter, CP, ADF and cellulose was higher (P < 0.05) in G2 and G3 than in G0. A lower ruminal pH and ammonia N but higher total N and trichloroacetic acid-precipitable N, an increase in holotrichs, spirotrichs and total protozoa population, increase in haemoglobin but decrease in serum total cholesterol and non-esterified fatty acids were observed in high-concentrate-fed groups. Carcass attributes revealed increase (P < 0.05) in empty LW, dressing yield, eye muscle area, subcutaneous and intramuscular fat, decrease in shear force value and higher (P < 0.05) protein content in Longissimus dorsi muscle in test groups than in the control. Above all, the G2 animals had better rumen environment and blood biochemical attributes and consumed more feed with enhanced digestibility that supported higher LWG at better feed conversion efficiency, improvement in BCS and carcass quality. Thus, re-alimentation of cull ewes with challenged feeding of concentrate at 2.5% of LW on a basal roughage diet for a period of 3 months may have promise for better economic return to the farmers with possibly meeting quality mutton for human consumption.     

Feed restriction strategy in the growing rabbit. 1. Impact on digestion, rate of passage and microbial activity

The effects of a quantitative feed restriction on the digestive physiology of the young rabbit remain largely unclear. Several digestive functions were thus analysed in the rabbit after weaning, using a monofactorial design that produces a linear reduction of the intake, from ad libitum (AL group) to 80%, 70% and 60% of AL (I80, I70 and I60). The restriction programme was applied by giving a daily meal during 21 days after weaning (34 days), and then a 4-day transition period was managed where the feed intake was fixed at 80% of the AL group, before to be fed ad libitum till 69 days of age. The young rabbit quickly adapted to the restriction programme, since within 4 days after weaning they ate totally their ration within 6-7 h after the feed distribution at 8:00, while AL animals consumed 75% of their feed between 15:00 and 8:00. From 55 to 59 days old, rabbits of I70 and I60 groups reached the intake of the I80 group within 1 day, and then the feed intake of restricted animals increased progressively without over-eating. From 54 to 69 days old, the intake of the four groups did not differ and averaged 143.7 g/day per rabbit. During restriction, the live weight and the weight gain decreased linearly with the restriction level. From 55 to 69 days, the weight gain increased linearly according to the restriction level previously applied, but the final weight of restricted rabbits remained lower than AL ones (-3%, -5% and -7%, respectively, for I80, I70 and I60). After 7 days of restriction, the digestibility was not significantly affected by the restriction level, except for crude protein that presented a slightly higher (+1.5 unit, P = 0.05) coefficient in I70 and I60 groups. The mean retention time (MRT) of particles increased by 50% for restricted animals (mean: 26.2 h for I80 and I60) compared to the AL ones, while that of the liquid phase (three times longer than the particles) was linearly and moderately increased with restriction (+20% between AL and I60). In restricted groups, the caecal pH was lower (-0.3 unit, P < 0.05) and could be related to their higher volatile fatty acid (VFA) concentration (+16 mmol/l compared to AL, P < 0.05). The fermentation pattern, ammonia concentration and the caecal bacterial fibrolytic activity remained similar among treatments, although the butyrate proportion tended to be higher in restricted animals. Impact of feed restriction on performances and digestive health is reported in the second part of this study.     

Effect or ractopamine on growth and body composition of pigs during compensatory growth

The purpose of this study was to measure the growth and body composition of pigs during normal or compensatory growth from 60 to 100 kg, without (cont) or with ractopamine (rac) supplementation (20 mg/kg of diet). Thirty-four pigs were scanned by dual X-ray absorptiometry (DXA) for body composition analysis at a starting weight of 61.4 ± 0.3 kg and at a final weight of 100.4 ± 0.5 kg. Half the pigs were fed ad libitum throughout (8 cont and 9 rac). The other half were fed at maintenance for 8 weeks and then scanned again by DXA. Following the maintenance feeding, the pigs were fed ad libitum (9 cont and 8 rac) to the final weight. Compensatory growth resulted in a 30% increase in the rate of weight gain (1.23 v. 0.94 kg/day, P < 0.05), including a 44% increase in the rate of lean tissue deposition (0.90 v. 0.62 kg/day, P < 0.05), but no change in the rate of fat deposition (0.31 v. 0.30 kg/day, P > 0.05). Feeding rac resulted in a 13% increase in the rate of weight gain (1.15 v. 1.02 kg/day, P < 0.05), consisting of a 29% increase in the rate of lean tissue deposition (0.86 v. 0.67 kg/day, P < 0.05) and an 18% reduction in the rate of fat deposition (0.27 v. 0.33 kg/day, P < 0.05). The effects of ractopamine on the rates of fat and lean tissue deposition were similar for pigs continuously fed ad libitum and those experiencing compensatory growth. Both compensatory growth and the addition of ractopamine to the diet resulted in an improvement in efficiency of protein deposition; however, ractopamine also resulted in a reduction in the efficiency of energy deposition. For both growth rate and lean tissue deposition, there was an additive effect for ractopamine and compensatory growth. Thus, feeding ractopamine will enhance the growth and body composition during compensatory growth in swine.     

Effect of feed restriction on the performance and behaviour of pigs immunologically castrated with Improvac®

For centuries, entire male pigs have been castrated to reduce the risk of boar taint. However, physical castration of pig is increasingly being questioned with regard to animal welfare considerations. Immunization against gonadotrophin releasing hormone (GnRH) provides an alternative to physical castration. Using the currently available commercial product (Improvac®; Pfizer Animal Health), a two-dose regimen of a GnRH vaccine is administered. After the second vaccination, a substantial increase in feed consumption has been reported, which may be associated with increased body fatness and decreased feed efficiency when compared with unvaccinated entire male pigs. The aim of the present study was to investigate the effect of a feed restriction on these traits and on the behaviour of 120 group-housed entire males (five pigs/pen) vaccinated against GnRH. The first vaccination was performed at 62 days of age and the second (V2) at 130 days of age. Pigs were slaughtered in two batches 4 to 5 weeks after V2. They were either offered feed ad libitum over the 22 to 114 kg BW range (AL treatment) or ad libitum up to a maximum of 2.50 (R2.50 treatment) or 2.75 kg/day per pig (R2.75 treatment). Behavioural observations and skin lesion scoring were conducted 1 week before V2, and 1 and 3 weeks after V2. At slaughter, the volumetric lean meat content was measured using an X-ray computed tomography scanner. Between V2 and slaughter, the average feed intakes for the R2.75 and R2.50 treatments were 15% and 22% lower than the average AL feed intake (3.20 kg/day), respectively. Feed restriction was associated with a reduced average daily gain after V2 (846, 932 and 1061 g/day in the R2.50, R2.75 and AL groups, P < 0.01) but had no effect on the feed conversion ratio (3.00 kg feed/kg BW gain on average, P = 0.62). No difference was observed in the lean meat content (71.8%, 70.7% and 70.4% in the R2.50, R2.75 and AL groups, P = 0.14), despite a reduced backfat thickness measured in restrictively fed pigs (12.0, 13.0 and 13.6 mm in the R2.50, R2.75 and AL groups, P < 0.01). Higher skin lesion scores were observed 3 weeks after V2 in R2.50 and R2.75 pigs than in the AL ones (scores 33.4, 27.7 and 25.5, respectively, P = 0.04). These results, combined with an unimproved feed efficiency and no marked change in carcass characteristics, suggest that immunologically castrated pigs should not be restrictively fed during the late finishing period.     

Attenuation of bleomycin-induced Hprt mutant frequency in female and male rats by calorie restriction

Calorie restriction modulates spontaneous and chemically induced tumors and increases maximal life span in experimental animals; however, the mechanism by which calorie restriction exerts its ameliorating effects is not fully elucidated, although reduced levels of reactive oxygen species (ROS) by calorie restriction has generated much interest. In the present study, we have determined whether or not calorie restriction would affect the mutagenic response in rats treated with bleomycin (BLM) a radiomimetic drug that is associated with DNA damage by a free radical mechanism. Fourteen weeks after weaning, the rats were divided into two groups; ad libitum (AL)-fed and 40% calorie restriction. Both AL and calorie-restricted animals were injected with 2.5, 5.0 and 10.0 mg BLM/kg, or with phosphate-buffered saline (PBS), and they were killed 4 weeks post drug treatment. Lymphocytes from the spleens were seeded in 96-well microtiter plates to determine mutant frequency in the hypoxantine guanine phosphoribosyl transferase (Hprt) gene. The mutant frequency in the BLM-treated rats was higher in AL males (P=0.001), and AL females (P=0.0174) than in their calorie-restricted counterparts. The difference in mutagenic response relative to AL males and AL females appeared unrelated to a low percent cloning efficiency seen in the males, since the mean absolute number of Hprt mutant clones was higher in the AL males compared to the females. A reduction in animal weight by calorie restriction was significant in both sexes (P<0.001), but the dose effect appeared non-significant. The results indicate that calorie intake of 60% reduced the mutagenic response of BLM, a compound known to induce oxidative DNA damage, and suggest a possible decrease in ROS as a function of calorie restriction.     

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

Feed restriction after weaning is widely used in meat rabbit farms to promote health and reduce mortality, but this practice impacts negatively on rabbit growth and slaughter performance. This study compared a 3-week post-weaning feed restriction with ad libitum medicated feeding, evaluating effects on feed intake, growth, health, carcass and meat quality of rabbits of two genotypes: Italian White pure breed and Hycole hybrid×Italian White crossbred. A total of 512 rabbits at 36 days of age, of both sexes and two genotypes, were divided into four homogeneous groups assigned, from 36 to 57 days of age, to different feeding programmes (FP): restricted non-medicated (R-N), ad libitum non-medicated (L-N), restricted medicated (R-M) and ad libitum medicated (L-M). The diets were medicated with oxytetracycline (1540 mg/kg) and colistin sulphate (240 mg/kg). The restriction, performed by giving 70, 80 and 90 g/day of feed for the 1st, 2nd and 3rd week, was followed by ad libitum feeding in the successive 5 weeks, up to slaughter at 92 days of age. Restricted feeds were ingested at a level of 64% of the feed intake recorded in the ad libitum fed rabbits; it was significantly associated, regardless of medication and rabbit genotype, with a lower feed intake (−22 to −24 g dry matter/day) during the entire experiment, compensatory growth and a lower feed conversion ratio in the ad libitum period, and a lower final live weight (−150 g) than ad libitum feeding (P<0.001). During restriction, mortality was lower in the restricted rabbits (6.25%, 5.47% v. 12.5%, 14.8% for R-N, R-M, L-N and L-M; P<0.05), whereas in the ad libitum period mortality did not differ among the groups (9.23%, 9.90%, 11.0% and 4.59% for R-N, R-M, L-N and L-M). Dressing out percentage was not affected by FP or genotype; heavier carcasses were produced by rabbits fed ad libitum (+100 g; P<0.001) and crossbred rabbits (+122 g; P<0.001). Restriction did not alter meat quality, except for a tendency towards a higher cooking loss and less fat; crossbred meat was higher in L* (+1.3; P<0.01) and b* (+0.51; P<0.05) colour indexes and tenderness (−0.14 kg/cm²; P<0.05) than pure breed meat. Under the conditions of this study, a 3-week restricted feeding after weaning resulted to be a suitable alternative, also for high growth potential genotypes, to the antibiotics to preserve rabbit health. The production of lighter carcasses could be compensated partly by the lower feed conversion ratio showed by restricted rabbits.     

Effect of compensatory growth on performance, carcass composition and plasma IGF-1 in grower finisher pigs

A total of 48 female pigs (Large White × Landrace × Duroc cross) were used to determine whether a compensatory feed regime influenced performance, carcass composition and the level of plasma IGF-1. Pigs of initial age 73 days were fed a commercial diet at 0.70 of ad libitum (R) for 40 days followed by a return to ad libitum feeding for a further 42 days. The control group was fed ad libitum (A) throughout. Groups of animals on R and A feed regimes were slaughtered at the end of restriction period (SL1), 2 days after refeeding ad libitum (SL2) to establish the more immediate effects of refeeding on IGF levels, and after 42 days refeeding (SL3; n = 8 for each group). As expected, during the restriction period, average daily live weight gain in all the slaughter groups of R pigs was significantly lower than A pigs (P < 0.01); there was no significant difference in feed conversion ratios. In the re-alimentation period of SL3, R pigs grew 12.9% faster (P = 0.033), indicating compensatory growth. At SL1, there was a trend for carcass weight (P = 0.108) of A pigs to be higher than R pigs, but at SL2 live weight and carcass weight of A pigs were significantly heavier than R pigs (P < 0.05), but not at SL3. For killing-out percentage, there was no difference in SL1. After refeeding for 2 days (SL2) and 42 days (SL3), R pigs had significantly lower killing-out percentage than A pigs (P < 0.05). As a proportion of live weight, R pigs had smaller heart, kidney and liver (P < 0.05) than A pigs at SL1. At SL2, only the kidney was smaller in the restricted group (P < 0.05) and there were no significant differences in SL3. As a proportion of carcass weight, Longissimus dorsi was heavier in the R pigs at SL1 (P = 0.108) and SL2 (P < 0.05), but not at SL3. At SL1, there was a trend for intramuscular fat of A pigs to be higher than R pigs. The plasma IGF-1 level was lower in R pigs than A pigs (P = 0.010) at SL1, and slightly lower at SL2 (P = 0.110), with no significant differences at SL3. Dietary restriction period influenced plasma IGF-1 levels, which returned to the ad libitum group levels when animals were refed, as did live weight and carcass weight. It appears that the internal organs and possibly fat, but not muscles, underwent a compensatory response when animals were refed.     

Feed restriction strategy in the growing rabbit. 2. Impact on digestive health, growth and carcass characteristics

A field enquiry mentioned the potential positive impact of a feed restriction on the health of young rabbits, but no objective information relates the intake to digestive health. The effects of a post-weaning feed restriction strategy were thus studied on digestive health and growth and carcass parameters of the growing rabbit, using a monofactorial design that produces a quantitative linear reduction of the intake, from ad libitum (AL group) to 80%, 70% and 60% of AL. The study was performed simultaneously in six experimental sites, on 1984 growing rabbits (496 per treatment) collectively caged from weaning (34 to 38 days of age, depending on the site) to slaughter (68 to 72 days). The feeding programme was applied as followed: restriction during 21 days after weaning, and then ad libitum till slaughter. During the feed restriction period the growth rate was linearly reduced with the restriction level, by 0.5 g/day for each percent of intake reduction. When returning to ad libitum intake (after 54 days old) a compensatory growth and a higher feed efficiency occurred. Therefore, the impact of the feeding programme on the slaughter weight (SW) was significant (-4.5 g/% of restriction), but relatively moderate: the weight loss of the more-restricted rabbits (60%) reached 7.7% (-200 g) compared to the AL group. Over the whole fattening period, the feed restriction reduced linearly and significantly the feed conversion (FC) (-0.0077 unit/% of restriction). Carcass traits were little affected by the feeding programme, except for a slightly lower decrease of the dressing percentage (mean: 1.2 units between AL and the three restricted groups). On the six experimental sites, mortality and morbidity were always caused by acute digestive disorders, namely diarrhoea and/or caecal impaction. Independent of the treatment, the mortality rate strongly varied according to the site (between 7% and 18% from weaning to 54 days and for the AL group). During feed restriction, the mortality was significantly lower from a restriction threshold of 80% (meanly: -9% compared to AL). The morbidity was also significantly reduced (-6%) for the two most restricted groups (70% and 60%). The favourable effect of a lower intake on health did not persist after returning to ad libitum intake (54 days to slaughter), since mortality and morbidity were not significantly different among the treatments. Such a feeding strategy thus represents a double benefit in terms of feed costs and lower losses of young rabbits.     

Differences in productive robustness in rabbits selected for reproductive longevity or litter size

The aim of this work was to evaluate the ability of a line selected for reproductive longevity (LP) to confront productive challenges compared to a line selected during 31 generations for litter size at weaning (V). A total of 133 reproductive rabbit does were used (72 and 61 from LP and V lines, respectively). Within each line, three groups with different levels of productive effort were planned: PP9, inseminated at day 4 after the first partum and with nine kits during the second partum, and inseminated after first weaning (30 days) and with nine (PW9) or five kits (PW5) during the second partum. The reproductive performance, body condition (perirrenal fat thickness (PFT)) and lipolytic response were controlled. LP does showed greater mean live weight (LW; +128 g; P < 0.05), PFT (+0.47 mm; P < 0.05) and estimated body energy (EBE; +0.29 MJ/kg; P < 0.01) than V does at second partum. However, LP does that mated at first post partum did not significantly differ in EBE relative to V does at second partum. During the first week of lactation, dry matter (DM) intake was similar for both lines (94 and 95 g DM/kg LW0.75 day for V and LP does, respectively). There was a significant difference in milk yield between both lines during the first week when litter size was nine (60 v. 54 g of milk/kg LW0.75 day for LP and V does, respectively; P < 0.01), but no difference when litter size was five. Consequently, when litter size was nine, LP does showed a lower recovery of PFT (0.6 mm less; P < 0.05) than V does during the first 10 days of lactation. However, when litter size was five, LP does showed a higher LW (+210 g; P < 0.05) than V does at 10 days of lactation and a similar recovery of PFT. During the last 3 weeks of the lactation, LP does showed a higher feed intake (+6 g DM/kg LW0.75 day; P < 0.05) and milk yield (+27 g/day; P < 0.001) than V does when litter size was nine, resulting in no significant differences in LW at 30 days of lactation. However, when litter size was five, both lines showed similar feed intake and milk yield, maintaining their differences in LW at 30 days of lactation (+206 g for LP does; P < 0.05). These results show that the rabbit line selected for reproductive longevity is more robust with respect to coping with productive challenges, than a line selected for reproductive intensity.     

Effect of dam factors on milk intake and performance of Belgian Blue suckling calves

Milk intake data were collected at 4-week intervals from Belgian Blue double-muscled (BBDM) suckling calves up to 16 weeks after birth. Dams were fed at 100%, 90%, 80% or 70% of their energy requirements during a 140-day indoor period from the beginning of December to the end of April (restriction period). Afterwards, cows were turned out on pasture (re-alimentation period). Mean calving date was 3 June, but parturitions were spread over the year. A total of 521 individual milk intake (IMI) and 120 average daily milk intake (AMI, mean of IMI) records were collected. IMI amounted to 7.0 ± 2.2 kg/day and was not affected by energy level during the indoor period. It was highest in May and June. Calves born out of multiparous cows consumed more milk than those born out of primiparous cows (7.4 v. 6.2 kg per day; P = 0.001), while intake tended to be higher in female than in male calves (7.2 v. 6.8 kg per day; P = 0.044). Dam age at calving, parity, post partum weight and body condition were only weakly correlated with AMI (r 0.4). AMI was correlated with pre-weaning live-weight gain (r = 0.807) and weaning weight (r = 0.783), with a slightly higher correlation for male than for female calves. Daily live-weight gain during the suckling period was increased by 79 g per extra kg daily milk intake on average, and by 86 and 74 g, respectively, for male and female calves. Calf solid feed intake was low, even when milk intake was low. In terms of net energy intake, milk was only substituted for solid feed by 29%. It can be concluded from the calf intake that milk production in BBDM cows is comparable with that of cows from other beef breeds, but its variation is considerable, complicating an accurate estimation.     

Effects of water restriction on growth performance,feed nutrient digestibility,carcass and meat traits of rabbits

The study investigates the effects of a post-weaning water restriction on performance, nutrient digestibility, carcass traits and meat quality of 84-day-old rabbits. A total of 1388 weaned rabbits (35 days) were randomly divided into two groups on the basis of BW and sex. The two groups were fed the same diets ad libitum both in the post-weaning (35 to 60 days) and fattening (61 to 84 days) periods. In the post-weaning period, one group (AL) also received drinking water ad libitum, whereas the other (WR) had a water restriction from 35 to 41 days 2 h/day; from 42 to 48 days 2.5 h/day; from 49 to 55 days 3 h/day; and from 56 to 60 days 4 h/day. During the fattening period, both groups had water-free access. Individual live weights and feed intake per cage were recorded weekly for 32 cages randomly chosen per group (64 rabbits) to calculate the BW gain, feed intake and feed conversion ratio (FCR). The apparent digestibility values of nutrients were measured using acid-insoluble ash. Carcass data were collected from 16 rabbits (8 males and 8 females) per group selected for similar final BW in both groups. Mortality from 35 to 60 days was higher in the AL group (10.1% v. 5.2%, for AL and WR, respectively, P < 0.0001). BW gain was higher for the AL group during both the post-weaning (+22.4%, P < 0.01) and the entire period (+7.5%, P < 0.05). Water restriction reduced feed intake both in the post-weaning (−17.4%, P < 0.0001) and in the entire period (−9.9%, P < 0.05). During the fattening period, FCR was lower for the WR group (5.15 v. 5.75 g/g, for WR and AL, respectively, P < 0.05). The apparent digestibilities of dry matter, organic matter, NDF, ADF and cellulose were greater in the restricted rabbits (+4.7%, +4.5%, +10.2%, +18.8% and +12.8%, P < 0.01, P < 0.01, P < 0.05, P < 0.01, P < 0.05, respectively). Perirenal and scapular fat percentages were higher in the AL rabbits (+30.7% and +116.6%, P < 0.01 and P < 0.001, respectively). Water restriction increased saturated fatty acids (C16:0, +12.9%, P < 0.05), lauroleic acid (C12:1, +75.0%, P < 0.01), n-3 polyunsaturated fatty acids (C20:5, +50.0%, P < 0.01 and C22:5, +16.6%, P < 0.05) and the n-3/n-6 ratio (+28.6%, P < 0.05). The applied water restriction between 35 and 60 days executed during the winter months improved the digestive health of rabbits, with no negative effects on carcass traits, or physical and chemical meat characteristics. However, from the animal welfare point of view, a water restriction can be criticized as a method to restrict feed intake.     

Effect of dietary fat or starch supply during gestation and/or lactation on the performance of sows, piglets' survival and on the performance of progeny after weaning

Two trials were carried out to compare the effects of fat or starch inclusion in sow's diet on sow and litter performance. In each trial, sows were assigned to one of two treatments. In trial 1, the sows were fed diets containing either soybean oil (5%, treatment GL5) or cornstarch (11.3%, GL0) from day 35 of gestation to weaning. Daily net energy and nutrient allowance were equalised during gestation. In trial 2, the same treatments were applied only after farrowing (treatments L5 and L0, respectively). Within each trial, a batch of piglets was studied until slaughter. In trial 1, adipose cell development and total lipid content were determined on some pigs at weaning (n = 6/treatment) and at slaughter in dorsal subcutaneous adipose tissue (n = 13/group at least) and in muscle (n = 46/group at least). Piglets' birth weight was not affected by treatment in trial 1. Survival rates at birth and after 24 h of life were higher in treatment GL5 (4.0% v. 7.5% stillborn piglets in GL0 treatment, P < 0.05; 8.7% v. 12.6% of piglets alive at 24 h of age died in treatment GL0, P = 0.06). Subsequently, overall survival rate until weaning was higher in treatment GL5 (81.4% v. 75.7% of total born piglets, P = 0.03), but litter size at weaning was not significantly affected (11.3). Litter growth rate before weaning was increased when a fat-enriched diet was provided during gestation and lactation (+140 g/day per litter; P < 0.01) and to a lower extent when provided only after farrowing (+90 g/day; P < 0.05). Energy supply through fat did not decrease the mobilisation of the sow's body reserve and backfat thickness loss was even higher with treatment GL5 (P < 0.05). After weaning, pigs' average daily gain, feed : gain ratio and carcass lean content were not affected by the energy source supplied before and/or after farrowing. At weaning, the number of adipose cells in the dorsal subcutaneous adipose tissue and in the Longissimus dorsi muscle was higher in the GL5 pigs. Muscle lipid content at weaning did not differ between treatments, but it was higher at slaughter, around 110 kg, in the GL5 pigs (3.46% v. 2.58%, P < 0.001).     

Influence of dietary fibre level and pelleting on the digestibility of energy and nutrients in growing pigs and adult sows

Two experiments were carried out to investigate the effect of pelleting on the apparent total tract digestibility (ATTD) of energy and nutrients according to the dietary fibre (DF) level in growing pigs (experiment 1) and in adult sows (experiment 2). Four diets based on wheat, barley, maize and soybean meal and supplemented with increased contents of a mixture of wheat bran, maize bran, soybean hulls and sugar beet pulp (116, 192, 268 and 344 g NDF/kg dry matter (DM) in diets 1 to 4) were tested. In experiment 1, 32 growing pigs (62 kg average BW), in two replicates and according to a factorial design, were fed one of the four diets, either as mash or as pellets. The digestibility of energy, organic matter (OM) and all nutrients decreased with DF increasing for both feed forms; the reduction was about 1% for each 1% NDF increase in the diet (P < 0.001). Pelleting improved moderately the digestibility of energy and OM (+1.5% and +1.0%, respectively; P < 0.05) in connection with greater DF (+5%; P < 0.05) and fat digestibility (+25%). Thus, pelleting improved the digestible energy content of diets on average by 0.3 MJ/kg of feed DM (P < 0.01). In experiment 2, four adult dry sows (235 kg average BW) were used in a 4 × 4 Latin square design and fed the four diets used in experiment 1 as pellets. The digestibility of energy, OM and macronutrients also decreased with DF increase (P < 0.001; -0.4% per 1% increase of dietary NDF for energy) while the digestibility of DF (i.e. crude fibre (CF) or ADF) increased (P < 0.001) or remained at a high level. In conclusion, increasing DF in diets decreases the digestibility of nutrients and energy in pigs and in sows. Although positive, the pelleting impact is minor on the energy and nutrients digestibility of fibre-rich diets in growing pigs, even in high-DF diets.