This research communication was designed to evaluate the effects of different levels of diet restriction on the composition and ethanol stability (MES) of raw bovine milk. This research was carried out using three electronic databases: Scopus, Pubmed and Web of Science. The main inclusion criteria were: (i) original research, (ii) use of alcohol (ethanol) test as a method to assess milk stability, (iii) measure different levels of feed restriction and (iv) allow access to the raw data of articles. Of the nine publications that addressed the subject filtered by the systematic review, seven fitted the selection criteria and were selected to perform the meta-analysis. Feed restriction (reduction of 20, 30, 40 and 50% of the dietary dry matter offered) decreased (P < 0.01) milk yield (−18%), ethanol stability (−5%), acidity (−4%), protein (−3%) and lactose (−2%) concentrations, but did not affect the values of pH, density, fat and total solids concentrations, nor somatic cell count. The correlation between milk yield and MES was low but positive and numerically higher in the control group compared with the restriction group. The milk of cows fed the control diet presented greater ethanol stability (76.5%) compared with milk of cows fed the restrictive diet (72.8%). This decrease by up to 4 percentage units due to restriction levels ranging from 20 to 50% of diet intake may cause limitations in milk processing at the dairy industry, increasing milk rejection.

The objective of the present study was to investigate the relationship between rooting behaviour and foraging in growing pigs. In study 1, forty-eight 11-week-old pigs were housed in eight groups of six with access to a rooting substrate in the form of spent mushroom compost. In half of the groups the rooting substrate contained food rewards, and in the other half of the groups it did not. All pigs had ad libitum access to feed. In study 2, one hundred and ninety-two 11-week-old pigs were housed in thirty-two groups of six, all with access to spent mushroom compost, and eight groups were each fed to 70, 80, 90 or 100% appetite. Treatments were applied over a two-week period in both studies. The number of pigs involved in active rooting (rooting in substrate while standing), inactive rooting (rooting in substrate while sitting or lying) or non-rooting activity (standing in substrate area and involved in any activity except rooting) was recorded by scan sampling. These behaviours tended to reach a peak in the morning and again in the afternoon. Inactive rooting was not significantly affected by treatments in study 1 or study 2. Food rewards in the rooting substrate led to a significant reduction in active rooting behaviour and in non-rooting activity during peak periods of the day (P < 0.05). It is suggested that learned associations between rooting behaviour and acquisition of food caused the pigs to stop rooting when all the food rewards had been consumed. The fact that rooting was performed in the absence of nutritive feedback suggests that this behaviour is performed independently of its appetitive foraging function. Restricting feed levels to 70 or 80% of appetite led to a significant increase in active rooting and in non-rooting activity during peak periods (P < 0.05). The relationship between feed restriction and active rooting behaviour tended to be linear (P < 0.08). This suggests that levels of rooting behaviour are flexible in response to nutritional needs.

Broiler breeder chickens are commonly reared under strict feed-restriction regimes to reduce obesity-induced health and fertility problems during adult life, and are assumed to experience a reduced welfare due to the resulting hunger. In these conditions, feed competition could influence the growth rate, so that the individuals falling behind in growth would experience more stress and hunger. We hypothesised that these chickens are poor competitors due to a reactive coping style and experience a further reduced welfare situation before size-sorting (‘grading’) at four weeks of age. Our results from open field, tonic immobility and home pen activity monitoring show signs of lower fear and higher home-pen activity levels in smaller hens and do not support the idea of reactive coping. H/L ratios of smaller hens were also found to be lower, indicating less stress in these birds. Dissections of smaller and larger four-week breeder hens may offer an explanation in the form of a relatively larger gastrointestinal tract in smaller birds. We argue that this is a form of habituation to restricted feeding, offering these birds a physiological stress coping mechanism, and that low early growth rate may not always be a sign of poorer welfare in broiler breeders.

Choice tests may aid determining whether qualitative dietary restriction improves the welfare of feed-restricted broiler breeder chickens (Gallus gallus domesticus). However, hunger-stress may reduce competency to choose by impairing learning. The effect of chronic feed restriction on the ability of broiler breeders to learn a hunger-relevant discrimination task was investigated using a Y-maze paradigm. The task was to associate black and white arms with large and small quantities of feed. Birds were reared to three growth curves by means of severe (n = 12), moderate (n = 12) or very mild feed restriction (n = 12). Learning the task and selecting the larger food option allowed birds to increase their feed intake. Time taken to traverse the Y-maze was also measured. Birds from all treatment groups traversed the Y-maze more quickly over time, indicating that they had learnt that running down the Y-maze arms was associated with a rewarding outcome (food). However, feed restriction significantly reduced their ability to associate the black and white cues with differences in food quantity. Consequently, average pay-offs in terms of daily feed increments disproportionately accrued to the less feed-restricted treatment groups. It is concluded that feed restriction affected the performance of broiler breeders in this task, perhaps by narrowing their attention such that they ignore potentially hunger-relevant contextual cues. However, low overall group success rates demonstrate that this task was difficult to learn even for less severely feed-restricted birds. Therefore, Y-maze choice tests may not be the most appropriate method for determining hungry broiler breeder dietary preferences.

Due to genetic selection for fast growth and high breast meat yield, commercial strains of broiler chickens and broiler breeders are predisposed to high feed intake; however, feeding broiler breeders ad libitum impairs their health and reproductive performance. Broiler breeders are feed-restricted throughout rearing to maintain health and performance, yet feed restriction results in hunger, feeding frustration and lack of satiety. The objective of this study was to examine the effect of alternative feeding strategies, including feed additives (separately or combined) and a fixed non-daily feeding schedule, on the feeding motivation and welfare of broiler breeders during rearing. At 3 weeks of age, 180 Ross 308 breeder pullets were allocated to 90 cages and fed with one of five isocaloric treatments: (1) daily control diet (control), (2) daily calcium propionate diet (CaP), (3) daily soybean hull diet (SBH), (4) daily alternative diet (alternative: CaP + SBH) and (5) 4/3 control diet (four on-feed days and three non-consecutive off-feed days per week). The CaP diet included calcium propionate at 1.4% from 3 to 6 weeks of age, and at 3.2% from 7 to 12 weeks of age, and the SBH diet contained soybean hulls included at 40%. The alternative diet included both soybean hulls and calcium propionate at the same inclusion rate as the SBH and CaP diets, respectively. Pullets were weighed and scored for feather coverage every week. A feed intake test was conducted at 3, 4, 8, 10 and 11 weeks of age for 10 min during on- and off-feed days. At 12 weeks of age, feather samples were analysed for fault bars. Data were analysed using linear mixed regression models, with cage nested in the models and age as a repeated measure. At 4 weeks of age, pullets fed soybean hull-enriched diets (SBH and alternative diets) and those on the 4/3 schedule had lower feed intake than control pullets (P = 0.02). Feathers from pullets fed the SBH diet had fewer fault bars than those fed the CaP diet (P = 0.04). The results indicated that the inclusion of soybean hulls (alone or combined with calcium propionate) and a 4/3 feeding schedule can reduce feeding motivation of broiler breeders during early rearing.

The objective of this study was to explore the metabolic profiles of pregnancy malnutrition induced by feed restriction (FR) and the counteracting effects of glycerol and rumen-protected choline chloride supplementation. Two feeding trials were conducted. In the first experiment, twenty pregnant Hu sheep carrying multiple fetuses with a gestation period of 108 d were randomly divided into two groups. The ewes in the control (CON) group were offered 100 % of their nutritional requirements as recommended by the National Research Council (NRC), while the FR group was offered 30 % of feed intake of CON for 15 d. In the second experiment, eighteen pregnant Hu sheep were offered a feed intake comprising 30 % of the NRC-recommended nutritional requirements twice daily. The sheep were randomly divided into three groups: the FR group in the second experiment (FR2), with no supplementation, the glycerol (GLY) group, which received 40 ml of glycerol per d, and the rumen-protected choline chloride (RPC) group, which received 10 g of rumen-protected choline chloride per d for 9 d. In the first experiment, the urine metabolome of sixteen ewes showed significant difference between the CON group and FR group. Compared with the CON group, FR decreased the level of d-glucose, lactic acid, levoglucosan, α-ketoglutarate, phosphohydroxypyruvic acid, glucose 6-phosphate and the methyl donors, while increasing the level of pyruvate, fumaric acid and carnitines in urine. Both the GLY and RPC treatments counteracted some of these changes and modulated the urine metabolome in advanced pregnant ewes suffering from malnutrition.

The present study was designed to describe the effects of early feed restriction of Merino lambs on feed efficiency during the fattening period by examining ruminal microbiota and fermentation parameters, gastrointestinal morphology, digestibility or liver proteome. In total, 24 male Merino lambs were randomly assigned to two experimental treatments (n=12 per treatment). Lambs of the first group (ad libitum (ADL)) were kept permanently with the dams, whereas the other 12 lambs (restricted (RES)) were milk restricted. When lambs reached a live BW (LBW) of 15 kg, all the animals were offered the same complete pelleted diet (35 g dry matter/kg LBW per day) until slaughter at a LBW of 27 kg. The RES lambs showed poorer feed efficiency during the fattening period when compared with the ADL group (feed to gain ratio, 3.69 v. 3.05, P<0.001). No differences were observed in ruminal microbiota, fermentation parameters or apparent digestibility. However, the proportion of the small intestine and the length of ileal villi were reduced in the RES lambs. In total, 26 spots/proteins were identified in the liver proteomic profile, with significant differences (P<0.05) between experimental treatments, suggesting a higher catabolism of proteins and a reduction in β-oxidation of fatty acids in RES lambs when compared with the ADL animals. In conclusion, early feed restriction of Merino lambs during the suckling period promotes long-term effects on the small intestine and the proteomic profile of the liver, which may influence the metabolic use of nutrients, thus negatively affecting feed efficiency during the fattening phase.

Domesticated horses are increasingly kept under semi-natural housing conditions, whereas their adaptation capacity is not fully investigated. In all, 10 Shetland pony mares were held under semi-extensive conditions for 1 year. In winter animals were allocated into two feeding groups (60% and 100% of maintenance energy requirement, respectively). Triiodothyronine, thyroxine, non-esterified fatty acids (NEFA), total bilirubin, total protein, triglyceride, glucose, insulin and hair length were measured at monthly intervals, whereas BW, body condition score, cresty neck score and resting heart rate were recorded every 2 weeks. From summer to winter all Ponies showed a reduction in resting heart rate (P<0.001) and triiodothyronine (P<0.001) but an increase in NEFA (P<0.001), thyroxine (P<0.001) and triglyceride (P<0.001) concentrations. Feed restriction led to a reduced resting heart rate (P=0.009), increased NEFA (P<0.001) and total bilirubin (P=0.008) concentrations. Thyroid hormones did not differ between feeding groups (P>0.05). Refeeding of restrictively fed ponies resulted in a rapid increase in resting heart rate and BW and a return of blood parameters to reference values. Adequately supplied animals adapted without difficulty to varying environmental conditions, whereas feed restriction in ponies during winter resulted in reduced resting heart rates suggesting a reduced basal metabolic rate. The energy restriction was compensated by mobilizing body fat reserves which led to changes in blood parameters. Refeeding in feed restricted animals revealed a remarkably quick recovery of physiological and blood parameters to reference values. We therefore suggest that year round-outdoor housing can be a suitable housing system for robust horse breeds provided that an adequate food supply is available.

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.

Limiting the post-weaning intake of the young rabbit is known to improve its resistance to digestive disorders, whereas a degradation of its housing hygiene is assumed to have a negative impact on its health. This study aims at providing insights into the mechanism of digestive health preservation regarding both host (growth and immune response) and its symbiotic digestive microbiota. A 2×2 factorial design from weaning (day 28) to day 64 was set up: ad libitum intake or restricted intake at 70% of ad libitum, and high v. low hygiene of housing (n=105 per group). At day 36 and day 45, 15 animals/group were subcutaneously immunized with ovalbumin (OVA) to assess their specific immune response. Blood was sampled at 36, 45, 57 and 64 days of age to determine total and anti-OVA immunoglobulin type G (IgG) and haptoglobin levels. The cecal bacterial community was explored (18 per group) by 454 pyrosequencing of genes coding for the 16S ribosomal RNA, whereas cecal pH, NH3 and volatile fatty acid (VFA) concentrations were measured to characterize fermentative activity. A 30% reduction in feed intake reduced the growth by only 17% (P<0.001), and improved the feed conversion ratio by 15% (P<0.001), whereas the degradation of hygiene conditions slightly decreased the feed intake in ad libitum fed rabbits (−3.5%, P<0.02). As poor hygiene conditions did not affect weight gain, feed conversion was improved from day 42 (P<0.05). Restricted feeding led to a lower mortality between day 28 and day 40 (P=0.047), whereas degraded hygiene conditions decreased overall morbidity (7.8% v. 16.6%; P<0.01). Both a reduced intake and low hygiene conditions of housing affected microbiota composition and especially dominant genera belonging to the Ruminococcaceae family (P<0.01). Moreover, low hygiene was associated with a higher Ruminococcaceae/Lachnospiraceae ratio (3.7 v. 2.4; P<0.05). Cecal total VFA and pH were increased (+19%; P<0.001) and decreased (−0.1 pH unit; P<0.05), respectively, in feed-restricted rabbits. Neither specific anti-OVA IgG nor haptoglobin was affected by treatments. Total IgG concentrations were the highest in animals raised in poor hygiene conditions after 8 days of restriction, but decreased after 19 days of restriction in high hygiene conditions (−2.15%; P<0.05). In conclusion, the degradation of hygiene conditions failed to induce a systematic specific and inflammatory response in rabbit, but reduced morbidity instead. Our results suggest that the microbiota composition would be a helpful source of biomarkers of digestive health.

Intensive selection of broilers for faster growth and better feed efficiency resulted in greater susceptibility to metabolic disorders such as ascites syndrome, which is one of the major causes of mortality and economic loss in broiler industry. Whereas cool temperature is one of the primary triggers for ascites, early feed restriction (FDR) significantly alleviates its incidence and mortality. However, little is known about effects of FDR, cold environmental temperature and their interaction on physiological responses in broiler chickens. For this purpose, 320 one-day-old male broilers were divided into two treatment groups of Ad libitum (Ad) and feed restricted (FR) with eight pen replicates each. Chickens in FR group underwent feed access limitation from days 7 to 14 of age. On day 21 half of the birds (four pens) in each group exposed to the cold temperature (CT) and the other half (four pens) continued at normal temperature (NT). Average daily feed intake, average daily weight gain and feed conversion ratio (FCR) were measured at days 7, 14, 21, 28 and 42. At 39 and 46 days of age two chicks with a BW around the pen average were selected from each pen and slaughtered after collecting blood samples. Then, relative weight of internal organs and right ventricle weight per total ventricle weight (RV : TV) ratio were calculated. Compared with NT group, CT birds had higher daily feed intake and FCR (P<0.05) from day 28 to 42. Cumulative ascites mortality in CT chickens was higher (P<0.001) than NT chicks. Within the CT group, ascites mortality in FR chickens was reduced (P<0.001) to 1.25% compared with 8.75% in Ad chicks. Birds in CT group had significantly (P<0.05) thicker right ventricle and greater relative weight of heart, hematocrit and triiodothyronine concentration. However, none of these parameters were affected by FDR. Under cold stress conditions, FDR reduced activity of alanine aminotransferase and aspartate aminotransferase (P<0.05). Serum triglyceride, cholesterol, high-density lipoprotein and total protein were not influenced by either temperature or feeding regimen. In conclusion, these findings suggest that FDR reduces ascites incidence mainly by allowing better development of internal organs, which helps them to cope with the high metabolic pressure and suffer less damage.

A total of 50 mixed parity sows of a high-prolificacy genetic line were used to evaluate the impact of feed restriction during lactation on their production and reproductive performance and their performance in the subsequent lactation. From day 7 of lactation, sows were distributed according to a completely randomized experimental design into two treatments. In treatment 1, sows were fed 8.0 kg feed/day (control) and in treatment 2, sows were fed 4.0 kg/day. The same suckling pressure was maintained until weaning on day 28 of lactation. Average minimum and maximum temperatures measured during the experimental period were 32.1°C and 16.5°C, respectively. Control sows presented significantly higher feed intake (P<0.001) compared with the restricted sows (6.43 v. 4.14 kg/day, respectively). Treatments influenced BW and backfat thickness losses (P<0.001). Control sows lost less BW than the restricted-fed sows (7.8 v. 28.2 kg). Restricted-fed sows lost more backfat thickness than those in the control group (3.97 v. 2.07 mm; P<0.01). Restricted-fed sows tended (P<0.10) to be lighter at weaning compared with the control sows (211 v. 227 kg). The composition of BW loss was influenced by the treatments (P<0.001), as the restricted-fed sows lost more body protein, lipids and energy compared with the control sows (3.90 v. 0.98 kg, 11.78 v. 4.83 kg and 584 v. 224 MJ, respectively). Litter weight gain was greater (P<0.05) in control sows than in restricted-fed sows (2.70 v. 2.43 kg/day). Daily milk production was 19% higher (P<0.01) in the control sows compared with the restricted-fed sows (8.33 v. 6.99 kg/day). However, restricted-fed sows presented a higher (P<0.05) lactation efficiency than the sows of the control group (82.30% v. 72.93%). No differences were detected (P>0.10) in weaning-to-estrus interval and averaged 4.3 days. No effect of the treatment (P>0.10) was observed on any of the studied performance traits in the subsequent lactation, except for litter size at birth that tended (15.2 v. 14.1; P<0.10) to be lower for the restricted sows. In conclusion, the present study demonstrated that feed restriction during lactation leads to intense catabolism of the body tissues of sows, negatively affecting their milk production, and the litter weight gain and possibly number of piglets born in the next litter. On the other hand, restricted-fed sows are more efficient, producing more milk per amount of feed intake.

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 1st 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 1st 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.

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.

To ensure health and reproductive performance, broiler breeders are feed restricted during the rearing period and, to a lesser extent, during the production period. Although restricted feeding improves health and bird welfare, on the other hand the birds are chronically hungry and suffer from frustration of feeding motivation, which has a negative effect on bird welfare. The aim of the current paper is to give an overview of the role of feed (nutritional aspects as well as feeding management) as a possible tool to improve broiler breeder welfare. Possible strategies discussed are 1) dietary dilution, by reducing the energy content and/or increasing the NSP content, by adding soluble or insoluble fibres to the diet; 2) adding appetite suppressants (e.g. calcium propionate) to the diet; 3) changing feeding management (e.g., scattering feed in the litter). Some of these strategies, i.e. dietary dilution or adding appetite suppressants, positively affect behavioural patterns of the birds, by reducing stereotypic pecking and eating motivation, and increasing the time spent sitting. Appetite suppressants have however been criticised for causing birds to feel ill. These behavioural changes, however, can only be considered as indirect parameters of improved bird welfare and there is still a need for a reliable indicator of hunger. It is clear that nutritional strategies can be helpful in reducing hunger stress in broiler breeders. Nutrition, however, cannot fully solve the broiler breeder paradox. The main reason for this paradox is related to breeding goals that are focussed on improving feed conversion and increasing breast meat percentage. Future genetic selection should aim at uncoupling the link between (re)production and welfare or reducing the conflict between these outcomes.

The effect of feed restriction on gene expression of regulatory enzymes of intermediary metabolism was studied in two sheep breeds (Australian Merino and Dorper) subjected to two nutritional treatments: feed restriction (85% of daily maintenance requirements) and control (ad libitum feeding), during 42 days. The experimental animals (ram lambs) were divided into four groups, n = 5 (Australian Merino control (MC), Australian Merino Restriction (MR), Dorper control (DC) and Dorper Restriction (DR)). After the trial, animals were sacrificed and samples were taken from liver tissue to quantify glucose levels and gene expression of relevant intermediary metabolism enzymes (phosphofructokinase (PFK), pyruvate kinase (PK), phosphoenolpyruvate carboxykinase, fructose 1,6-bisphosphatase, glucose-6-phosphatase, glycogen synthase (GS), fatty acid synthase (FAS), glutamate dehydrogenase (GDH) and carbamoyl phosphate synthase (CPS)) through real-time PCR. During the experimental period, the MR animals lost 12.6% in BW compared with 5.3% lost by the Dorper lambs. MC and DC rams gained, respectively, 8.8% and 14% during the same period. Within the Dorper breed, restricted feed animals revealed a significant decrease over controls in the transcription of PFK (1.95-fold) and PK (2.26-fold), both glycolytic enzymes. The gluconeogenesis showed no change in the feed restricted animals of both breeds. DR feed group presented a significant decrease over the homologous Merino sheep group on GS. In both experimental breeds, FAS mRNA expression was decreased in restricted feed groups. GDH expression was decreased only in the DR animals (1.84-fold) indicating a reduced catabolism of amino acids in these animals. Finally, CPS was significantly (P < 0.05) higher in the Dorper sheep, indicating a facilitated urea synthesis in this breed. These results indicate a better adaptation of metabolic intermediate regulatory enzymes and hepatic glucose production of Dorper sheep to feed restriction concurring with the BW results in the experimental groups.

Dietary restriction for the weight-loss management of obese horses limits the natural trickle-feeding behaviour. During feed restriction, wood shavings are often advised as bedding to prevent dietary supplementation from non-feed sources. Data from twelve overweight/obese horses and ponies of mixed breed and sex, bedded on wood shavings during 16 weeks of feed restriction, were retrospectively evaluated. DM intake (DMI) was restricted to 1·25 % of body mass (BM) daily. Animals were randomly assigned to one of two diets (hay/chaff, n 6; hay/balancer meal, n 6). BM was recorded weekly. Feeding behaviour was recorded by continual observation over 24 h during week 15. The apparent digestibility (gross energy (GE), acid-detergent fibre (ADF) and DM) of feed was determined for all animals by total faecal collection (72 h, week 16). Rates of weight loss were independent of diet type, DM (R2 0·15), GE (R2 0·20) and ADF digestibilities (R2 0·18). Despite similar DMI, faecal DM ranged between 0·52 and 1·16 % of BM daily and was associated with wide ranges in apparent digestibility (GE − 11·34 to 53·08 %; ADF − 50·37 to 42·83 % and DM 2·14 to 57·32 %), which were improbably low for some animals. Apparent digestibilities were associated with DM output (GE R2 0·96; ADF R2 0·99 and DM R2 0·99) and time spent feeding (GE R2 0·62; DM R2 0·61 and ADF R2 0·59), indicating that feed intake was supplemented with wood shavings in at least five of the twelve animals. Quantities of wood shavings ingested (negligible to >3·0 kg/d) were back-calculated from predicted feed digestibilities. All animals remained healthy. Implications of ‘feed-bulking/energy dilution’ for feed-restricted animals need further consideration.

Excessive specialisation and production requirements place high demands on the metabolism of the broiler chicken. A number of metabolic problems, such as ascites, arise in chickens due to intensive selection to manifest their genetic potential for rapid growth. Ascites syndrome (Pulmonary Hypertension Syndrome) is one of the major causes of mortality and morbidity in modern broiler production today. Genetics, the environment, and management all seem to interact to produce a cascade of events that culminate in ascites syndrome. It is generally accepted that the high metabolic rate of current broiler lines causes an increased demand for oxygen, especially in cold environments or when birds are fed high nutrient density diets. In such situations, the relatively underdeveloped cardio-respiratory system of modern broilers fails to fulfil the required oxygen demand, which leads to hypoxemia, resulting in the development of pulmonary hypertension and subsequently ascites. Many nutritional, medicinal and management strategies have been proposed to alleviate the ascites. Higher levels of dietary vitamin C and E along with selenium might be beneficial, as they decrease the free radicals that are generated in birds with ascites. As the high metabolic rate (fast growth) is a major factor contributing to the susceptibility of broilers to ascites, appropriate selection strategies or feed restriction or light restriction in order to slow down the growth rate seem practically viable methods, since final body weight is not compromised. Optimisation of the house temperature and ventilation in cold weather seem helpful practices to decrease the incidence of ascites.

Under current practices, broiler parent stock (broiler breeders) encounter several welfare problems, such as feed restriction and injury during mating. Intensive selection for production traits, especially growth rate, is associated with increased nutritious requirement and thus feed consumption, but also reproductive dysfunctions and decreased sexual activity in broiler breeders. A resulting serious welfare problem is the subsequent severe feed restriction which is applied during rearing, in order to prevent health problems and to achieve better egg production. This severe feed restriction has negative effects on bird welfare as it causes chronic stress resulting from hunger. Recent research has focused on management practices to alleviate the negative effect of this feed restriction. Using both a more fibrous feed and an appetite suppressant seems most successful. There are welfare concerns involved in the mating of broiler breeders. In many countries mutilations (beak trimming, despurring and toe clipping) are carried out in male broiler breeders as a standard procedure to prevent excessive damage to the hens during mating. It has been reported that broiler breeder males show low libido but, at the same time, may be aggressive and show rough behaviour during mating, which can cause severe injuries to the hens, although some injuries may be caused by over-mating hens. Current studies aim to develop management practices to reduce hen injury due to over-mating and improve the sexual behaviour in both males and females. In the last part of the review, an examination of how breeding companies are taking welfare into consideration in their commercial selection scheme is made. In practice, although for example reduced mortality and some health criteria are included in selection programs and some alternative breeds as used, other welfare issues remain, such as feed restriction during rearing.

This work aims at the identification of relevant intermediate metabolism enzymes contributing to improved meat production due to genetic selection. A wild rabbit (WR) breed and a highly meat selected breed (New Zealand (NZ) rabbit) were used. Food restriction was used as an experimental condition so as to enhance differences within the metabolic pathways under study. During a period of 30 days, NZ and WR experimental breeds were subjected to, respectively, 40% and 60% ad libitum food restriction leading to 17.7% and 21.1% initial weight. Hepatic glycolytic, lipidic and protein regulatory enzyme activity, transcriptional and metabolite levels were determined. Insulin-like growth factor (IGF-1), triiodothyronine, and cortisol were also evaluated. In the glycolytic pathways, the NZ control rabbits presented a higher phosphofructokinase and pyruvate kinase activity level when compared to the WR, while the latter group showed a higher expression of glycogen synthase, although with less glycogen content. In the nitrogen metabolism, our results showed a lower activity level of glutamate dehydrogenase in WR when subjected to food restriction. Within the lipid metabolism, results showed that although WR had a significantly higher mRNA hepatic lipase, non-esterified fatty acid levels were similar between the experimental groups. NZ rabbits presented a better glycemia control and greater energy substrate availability leading to enhanced productivities in which triiodothyronine and IGF-1 played a relevant role.