Effect Of Early Feed Restriction Research Articles

The effect of early feed restriction on the commercial pieces of two broiler chicken strains

The aim of this research to evaluate the effect of feed restriction (FR) on starter periods of two different broiler strains on commercial meat pieces. The study was conducted on 120 day old chicks with an average body weight of Lohman strain of 44.16 ± 3.72 g and Cobb strain of 45.79 ± 3.95 g. The method was a completely randomized design (CRD) factorial 2x4 with 3 replications. The factor A1 was Lohman, and A2 was Cobb. Factor B was the start of the application of FR as much as 20% for 8 days, namely B0 = without FR, B1 = on day 8, B2 = on day 11, and B3 = on day 14. Feed was given ad libitum before and after FR until day 35. The interaction between treatment affect the carcass (%) and brisket (%). Final body weight (FBW), carcass (%), breasts (%), and wings were affected by strains. FBW, carcass (%) and breast (%) of Lohman strain were higher than Cobb. The wings (%) and brisket (%) of Cobb were higher than Lohman's. The application of FR on the Lohman at starter period was better than Cobb in terms of the percentage of commercial pieces.

Feed efficiency and the liver proteome of fattening lambs are modified by feed restriction during the suckling period

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.

Effect of early feed restriction on body weight and compensatory growth in Label Rouge broiler chickens

This research was conducted to assess the compensatory gain in birds that have suffered severe food restriction and a reduced growth in its initial phase. A total of 144 birds were used in the Label Rouge lineage with average initial weight 239.90 ± 76.80 g, from 28 to 49 days. The experimental design used was a completely randomized design, where the birds were distributed in 18 boxes, containing 3 treatments and 6 replicates of 8 birds per cage. The treatments were as follows: birds with body weight of 150.73 ± 12.62 g, between weighing from 239.79 ± 13.14 g and heavy weight of 329.17 ± 24.89 g in different periods, from 28 to 35, 35 to 42 and 42 to 49 days of age, respectively. In relation to weight gain, the heavy birds, obtained better results when compared to the other. The feed consumption has changed in the three periods and, in the period of 42 to 49 days, the treatments did not differ among themselves. Feed conversion rates (p = 0.127) and feasibility (p = 0.6163) of birds do not differ in different periods.

Programming Merino lambs by early feed restriction reduces growth rates and increases fat accretion during the fattening period with no effect on meat quality traits

The objective of the study was to determine the effect of early feed restriction on carcass and meat quality traits in Merino lambs. Twenty-four male Merino lambs (4.81±0.256kg) were assigned to two groups (12 animals in each group). The first group (ad libitum, ADL) was kept permanently with the dams. The second group (restricted, RES) was milk-restricted. After weaning (15kg), daily feed intake of all lambs was identical, but a lower gain: feed ratio was recorded in the RES group (0.320 vs. 0.261; P<0.001). After animals were slaughtered (27kg), lower ultimate pH and reduced yellow colouration of subcutaneous fat was recorded in meat from the RES lambs when compared to ADL group, whereas a trend towards a significant increment of intramuscular fat content and no effect on meat quality traits was observed in the RES lambs. Early feed restriction may be useful to increase intramuscular fat accretion in Merino lambs during the fattening period.

The Effects of Early Feed Restriction on Growth Performance, Internal Organs and Blood Biochemical Indicators of Broilers

The growth rate of broiler chickens has increased greatly due to enhancement in genetics, nutrition and management. However, the high growth rate of broilers has caused many health problems, To avoid those problems, feed restriction was used as a management strategy to prevent excessive growth during early period. This study accessed the effects of early feed restricted on growth performance, internal organs and blood biochemical indicators of broilers. A total of 180 male Arbor Acres broilers were obtained and randomly assigned to 2 treatment groups. The treatments included control group (basal diet and feed restricted group (dietary energy and protein levels were diluted by 10%). At 14 d, two birds of each replicate were randomly chosen, wing vein blood samples were taken for blood biochemical indicators determination, then slaughtered to measure internal organs. The result showed that birds fed diluted feed had lower ( P ) body weight at 14 days. There was no significant difference in body weight between restricted and control groups at 42 days. No changes were observed in feed intake and feed conversion ratio between groups. Feed restriction also had no significant effects on internal organs, intestine and serum biochemical indicators. Taken together, this study suggested that dietary protein and energy diluted by 10% from 8 to 14 d is a suitable feeding program.

Effect of early feed restriction on physiological responses, performance and ascites incidence in broiler chickens raised in normal or cold environment

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.

Effects of Early Feed Restriction on Some Welfare Indices and Economic Efficiency of White Pekin and Mule Ducks

Two hundred ducklings represent two different genotypes White Pekin and Mule ducks (a sterile hybrid from the interspecific cross of a Pekin duck and Muscovy drake) were used in this study to determine influence of breed of ducks (White Pekin vs. Mule), feeding regime (early feed restriction regime by Skip-a-day program vs. free feeding) on Behaviors, Productive performance, Immune response, corticosterone, fear response and economic parameters of the Mule and Pekin ducks. The obtained results showed that Rearing Mule ducks under skip-a-day program for 7 days led to increase of wall exploratory behavior and decrease of aggressive behavior. Moreover, it had a higher body weight from 3rd to 7th weeks of age in addition a higher weight gain from 4th to 6th weeks of age compared to White Pekin ducks. Induction of feed restriction regime improved walking behavior, wing and leg stretch, wall and floor explorations. Moreover, it motivated occurrence of catch-up growth and improved immunity, but it increased aggressive behavior of ducks. The economic analysis showed that total costs of the ducks fed ad-libitum were greater than those fed on restriction regime. In addition, total veterinary management costs were not statistically significant among Mule and Pekin breed and either ad-libitum or restricted feed regime ducks. With reference to the profitability measures, the results obtained showed that the Pekin ducks achieved higher net return than the Mule ducks. Furthermore, the benefit-cost analysis revealed that the restricted regime ducks data were lower than the ad-libitum duck groups.

Effects of wet feeding and early feed restriction on blood parameters and growth performance of broiler chickens.

The aim of the study was to investigate the effects of early feed restriction (FR) with wet feeding on size of small intestine, blood lipids and performance parameters in broilers from d 1 to 42. A total of 160 one-day-old male broiler chickens were randomly allocated to 4 treatments with 4 pens per treatment and 10 chickens per pen, in a fully randomized 2 × 2 factorial arrangement, two feeding arrangement; providing feed ad libitum (Full Fed) or FR by 50% between days 6 to 12, and feed in either wet or dry form (wet form, 1.2 g water per 1 g dry feed). Body weight and feed intake of broiler chickens were determined at d 0, 21, and 42, and feed conversion ratio (FCR) was calculated. At d 42, two birds per replicate were euthanised for determination of carcass weight, organ weight and length, and also for blood parameters, which included high density lipoprotein (HDL), low density lipoprotein (LDL), total cholesterol and triglycerides (TG). The broilers fed wet form irrespective of FR throughout had superior body weight gain and carcass weight compared with birds fed dry diets at d 22 and 42 (P < 0.05). The wet form with FR significantly showed lower FCR compared with the wet form and ad libitum at d 1 to 21 (P < 0.05). The broilers fed wet form had significantly increased HDL, LDL, and total cholesterol and decreased TG (P < 0.05). In conclusion, wet form can improve performance growth and blood parameters, and the FR birds were able to attain normal market body weight at d 42, which suggests that growth compensation occurred.

Early feed restriction in broilers. II: Body composition and nutrient gain

Two experiments were performed, in male and female broilers separately, to evaluate the effect of early feed restriction on the composition, gain, and efficiency of nutrients retention by comparative slaughter. Treatments were applied from 8 to 16 d age as follows: without feed restriction [standard feed (SF) ad libitum]; quantity restriction (80% ad libitum consumption of SF); time restriction (SF offered throughout 8 h/d); and quality restriction (SF diluted with 10% kaolin and 10% rice hulls containing 80% of the limiting nutrients). The broilers were raised in pens and 6 replications/treatments were used. The composition and body gain of DM, CP, and EE, and efficiency of protein and energy retention were evaluated. Time restriction was considered the most severe, mainly in males that showed less protein gain at 42 d age. Proportional body gain of EE was higher than that of CP in the refeeding period in the quantity and time restricted broilers and no improvement in the protein retention efficiency was observed in those birds previously restricted. The possibility that feed restriction decreases carcass fat was not observed.

Effects of Early Feed Restriction on Some Performance and Reproductive Parameters in Japanese Quail (Coturnix coturnix japonica)

Effects of Early Feed Restriction on Some Performance and Reproductive Parameters in Japanese Quail (Coturnix coturnix japonica)

Early feed restriction in broilers. I–Performance, body fraction weights, and meat quality

SUMMARY Two experiments were performed, with male and female broilers separately, to evaluate the effect of early feed restriction on performance, carcass, organs, breast, legs, and back weights, and breast meat quality. Treatments were applied from 8 to 16 d of age as follows: without feed restriction [T1; standard feed (SF) ad libitum]; quantity restriction (T2; 80% ad libitum consumption of SF); time restriction (T3; SF offered throughout 8 h/d); and quality restriction (T4; SF with 80% of the limiting nutrients). Birds from both sexes submitted to T2 or T3 had lower BW at the end of the restriction period, however, they were able to reach the same BW at 42 d when compared to T1. Quality restriction did not reduce initial growth because birds compensated for the dilution by increasing feed intake. Organ weights recovered more quickly than the other fractions. Females on T3 recovered BW earlier than males. Quantity restriction allowed the full recovery of breast weight at 35 d, whereas T3 only achieved that at 42 d. Restriction programs did not have any effect on weight loss due to thawing, cooking, shear force, or lipid oxidation on the breast meat. Early restriction programs either by T2 or T3 can be used as a method for controlling growth rate in broilers without any damage to performance and meat quality at 42 d of age.

Effect of Early Feed Restriction with or without Enzyme Supplementation on Performance, Nutrients Digestibility and Blood Biochemical Parameters of Broiler Chickens

Effect of Early Feed Restriction with or without Enzyme Supplementation on Performance, Nutrients Digestibility and Blood Biochemical Parameters of Broiler Chickens

The Effects of Early Feed Restriction on Broiler Performance

Summary This experiment was conducted to investigate the effects of feed restriction on broiler chickens performance. A total of 280 day-old commercial male broiler chicks from Ross-308 line were used in the experiment. The experiment was held with a randomly allocated control group and three treatment groups and five replicates. The birds were fed ad-libitum in the control group while the feed availability were restricted for 8, 16 and 24 hours per day in 1st, 2nd and 3rd treatments, respectively during 15th and 22th days of age. Average live body weight, body weight gain, feed consumption, livabilitiy and performance index did not differ between treatments (P>0.01), Cumulative feed conversion ratios to 49 d were significantly different among treatments (P<0.05).

Effect of early feed restriction on performance and health status in growing rabbits slaughtered at 2 kg live-weight

The effect of a time-limited access to the feeders (8 h per d from 9:30 to 17:30) on fattening performance and health status was studied in rabbits reared until 2 kg live-weight as typical in the Spanish market. For this purpose, the same diet (10.5 MJ digestible energy/kg, 38.9% neutral detergent fibre and 18.4% crude protein on dry matter basis) was used over two consecutive trials. A total of 192 growing rabbits (96 in each trial) were weaned at 35 d and assigned to 2 different feeding treatments (continuously fed ad libitum or restricted from 35 until 49 d). In the first trial, feed restriction reduced daily feed intake (94.3 vs. 74.2 g; P&lt;0.001), daily weight gain (43.6 vs. 27.1 g; P&lt;0.001) and impaired feed conversion rate (FCR) (2.28 vs. 2.92, P&lt;0.001) in the first 14 d after weaning. Later on, no feed restriction was applied and a compensatory growth was observed in previously restricted rabbits (44.8 vs. 54.8 g/d; P&lt;0.001). Early restricted rabbits did not reach the Spanish commercial weight (2 kg) at 63 d of age and weighed less than full-fed rabbits (1989 vs. 1888 g; P=0.001). Moreover, feed restriction did not improve FCR in the whole fattening period (2.56 on average). The second trial was extended until 70 d to permit restricted rabbits to attain market weight. However, at that age, live weight of restricted rabbits was also lower than that of rabbits always fed ad libitum (2285 vs. 2101 g; P=0.001). In the first trial, no health problem was recorded (average mortality 1.04%) whereas in the second trial feed restriction allowed both mortality (25.6 vs. 6.34%, P=0.017) and morbidity (41.4 vs. 12.7%, P=0.004) to decrease. The higher number of losses in the second trial made economic FCR differ from scientific FCR (3.63 vs. 2.89, on average) in the 35–70 d period. Moreover, morbidity increased heterogeneity of fattening performance. In conclusion, the interest of feed restriction in Spanish fattening rabbit farms is mitigated by the conventional market weight. Nevertheless, in a context with high rates of digestive troubles, a time-limited access to the feeder enhances health status on the farm and could justify the short delay necessary to reach slaughter weight.

Effect of early feed restriction on hepatic lipid metabolism and expression of lipogenic genes in broiler chickens

The study was conducted to investigate the effect of early feed restriction (ER) on lipid metabolism and mitochondrial function in the liver of broiler chickens. Newly hatched broiler chickens were randomly allocated into control and ER group which was subjected to feed restriction with feed provided on alternate days from hatch to 14 days of age (14 d), followed by ad libitum feeding until the end of the experiment on 63 d. ER group exhibited significantly lower body weight throughout the experiment. Serum concentrations of total cholesterol (TC) and high density lipoprotein cholesterol (HDLC) were significantly higher in ER group at 14 d ( P < 0.05), and the higher serum TC level in ER group was also observed at 63 d. In contrast, the contents of triglyceride (TG), TC and lipoprotein lipase (LPL) activity in liver were significantly lower in ER group at 14 d ( P < 0.05). At 14 d no significant difference was detected for the mRNA expression of the acetyl-CoA carboxylase-α (ACC-α), carnitine palmitoyltransferase I (CPT-I), sterol regulatory element binding protein-1c (SREBP-1c) or peroxisome proliferator-activated receptors α (PPAR-α) between control and ER group. At 63 d ACC-α mRNA expression was significantly down-regulated accompanied with a significantly up-regulated CPT-ImRNA and a decreased tendency of SREBP-1c mRNA expression in ER group ( P = 0.09). Swollen mitochondria with fragmented and reduced cristae were observed in liver of ER group at 14 d. Meanwhile the inner mitochondria membrane viscidity increased and hepatic mitochondrial superoxide dismutase (SOD) activity decreased at 14 d. The results suggest that feed restriction at early postnatal stage may produce long-term effect on lipid metabolism of broiler chicken, probably through, at least in part, alterations in mitochondria morphology and function.

Effects of early feed restriction on live performance, carcass characteristics, meat and liver composition, some blood parameters, heterophil-lymphocyte ratio, antibody production and tonic immobility duration

The aim of this study was to determine the effects of early feed restriction on performance, carcass characteristics, meat and liver composition, some blood parameters, H-L ratio, antibody titers against SRBC and tonic immobility duration in broilers. One hundred ninety male chicks (Ross 308) were randomly allocated into two treatment groups each of 95 chicks. Broilers in one treatment fed ad libitum until 42 day of age, however in other treatment, broilers were deprived of feed for 4 h per day from 7 to 21 day. Body weight, feed consumption, feed to gain ratio, carcass characteristics and the percentage of examined organs except heart were not statistically significant in groups. Percentage of heart was higher (p < 0.05) in broilers fed ad libitum. At 41 d of age, H-L ratio (p < 0.05) and TI duration (p = 0.001) were higher, serum glucose (p < 0.05) and triglyceride (p < 0.001) levels were lower in broilers fed ad libitum. Chemical composition of breast and thigh and also fat and ash of liver were not affected by early feed restriction. Moisture of liver (p = 0.001) was lower and protein of liver (p < 0.01) was higher in broilers fed ad libitum.

Effect of Qualitative and Quantitative Feed Restriction on Growth Performance and Immune Function in Broiler Chickens

The current study was conducted to investigate the effect of early feed restriction (FR, 8 to 14 d of age) on growth performance and immune function in broiler chickens. Birds were fed corresponding diets from 3 to 35 d of age, which consisted of three phases: starter (3 to 7 d of age), FR (8 to 14 d of age) and re-alimentation (15 to 35 d of age) phases. During the FR period, each group of birds was fed the basal diet ad libitum (CON), 85% (EN85) and 70% (EN70) of lower calorie diet ad libitum (qualitative FR), and 85% (FI85) and 70% (FI70) of voluntary intake on a daily basis (quantitative FR). As a result, there was no statistical difference in weight gain, feed intake and feed conversion ratio between the CON and quantitative or qualitative FR groups during the entire (3 to 35 d) periods. In particular, the EN85 group resulted in a significant (p<0.05) increase in weight gain compared with the EN70, FI85 and FI70 groups. Plasma total protein and albumin at 14 d of age (during FR) were significantly (p<0.05) lower in the quantitative and qualitative FR groups, but these parameters at 35 d of age (after re-alimentation) were higher (p<0.05) in the EN85 and EN70 groups than in the CON group. Plasma IgG level was unaffected by dietary FR procedure. In cytokines, there was no significant difference in the expression of lymphocytic IL-4 and IFN-y at 14 d of age between the FR and the CON groups, whereas lymphocytic IL-6 and iNOS expression were significantly (p<0.05) lower in FI85 and FI70 groups. Moreover, lymphocytic iNOS was also significantly (p<0.05) lower in birds fed qualitative and quantitative diets compared with those fed ad libitum. In the thymus, IL-4 expression was higher (p<0.05) in FI85 and FI70 groups, whereas IL-6 expression was lower (p<0.05) in the FI85 and FI70 groups than in the CON group. Thymic iNOS was significantly (p<0.05) lower in birds fed qualitatively and quantitatively restricted diets compared with those fed ad libitum. At 35 d of age, there was no difference in the expression of IL-4, IL-6 and IFN-y of lymphocytes and thymus between the FR and CON groups. In conclusion, 85% of quantitative and qualitative FR would have a beneficial effect on the expression of some cytokines including IL-4 and iNOS without change in growth performance of birds.

Asymmetry measures and allometric growth parameter estimates for investigate effect of early feed restriction on deviation from bilateral symmetry in broiler chickens

Abstract. The purpose of this study is to investigate the effect of different feeding programs such as ad libitum feeding (AD), 20 % feed restriction based on ad libitum group (FR1) and not fed between 9 a.m. and 3 p.m. (FR2) on deviation from bilateral symmetry or developmental stability in broiler chickens by means of two different approaches namely asymmetry measures and allometric growth model parameters. The weekly left and right sides of shank length, shank width, wing length and face width of chickens were collected from 7 days of age to 42 days of age. Results of this study showed that the deviations from the bilateral symmetry were mostly in fluctuating asymmetry (FA) in the FR1 group birds. On the other hand, the deviations from the bilateral symmetry in the birds in group AD and FR2 were mostly in the form of anti-symmetry (AS) and directional asymmetry (DA) respectively. In this study, the deviation from the bilateral symmetry was mostly in FA type for the measured morphological characters for the FR1 group, and the FA level was usually lower indicating higher welfare level and lower developmental instability for these animals than that of the AD and FR2 groups. Allometric growth coefficients for evaluating the effects of the feeding programs on the developmental stability were a little bit different from the findings obtained by the asymmetry measures‘ being taken into account. Allometric growth parameters, therefore, should be taken into consideration, along with asymmetry measures when investigating effect of rearing conditions or environmental conditions on developmental stability. As a conclusion, intensive feeding (AD) and long-term feed restriction (FR2) can be said as an important environmental factor affecting developmental stability and dependently the animal welfare and performance.

Reduced PKCα expression in pulmonary arterioles of broiler chickens is associated with early feed restriction

Objective The present study was conducted to investigate the effect of early feed restriction on protein kinase Cα (PKCα) expression in pulmonary arterioles, which has been revealed to promote pulmonary vascular remodeling in pulmonary hypertensive broilers. Methods A total of 270 day-old mixed sex commercial broilers were randomly distributed to a normal temperature control group (NT), a low temperature control group (LT) and a low temperature plus feed restriction group (LR). The PHS incidence, the right/total ventricular weight ratio (RV/TV), the vessel wall area/vessel total area ratio (WA/TA), the mean media thickness in pulmonary arterioles (mMTPA) and the expression of PKCα in the pulmonary arterioles were measured weekly. Results Low temperature treatment significantly increased the PHS mortality. The RV/TV, WA/TA and mMTPA values of group LT were significantly elevated compared with those of group NT on d 35 and 42. The LT chickens had increased PKCα expression compared with their NT counterparts on d 28 and afterwards. Feed restriction reduced the PHS mortality, RV/TV, WA/TA and mMTPA in cold-exposed broilers. The LR chickens had much lower PKCα expression in pulmonary arterioles than the LT chickens. Conclusion Early time feed restriction inhibited pulmonary vascular remodeling in broilers, which might be partly attributed to reduced PKCα expression in pulmonary arterioles.

Effect of early feed restriction on myofibre types and expression of growth-related genes in the gastrocnemius muscle of crossbred broiler chickens

The purpose of this study was to investigate the immediate and long-term effects of early feed restriction (ER) on morphology and gene expression of lateral gastrocnemius muscle. Newly hatched crossbred broiler chickens were allocated into control and ER groups, the latter being free-fed on alternate days from hatch to 14 days of age (14 d), followed by ad libitum feeding as the control group until 63 d. The lateral gastrocnemius muscle was taken at 14 and 63 d, respectively for myofibre typing by both myosin ATPase staining and relative quantification of myosin heavy chain (MyHC) mRNA for slow-twitch (SM), red fast-twitch (FRM) and white fast-twitch (FWM) myofibres. The body weight and lateral gastrocnemius weight were significantly lower in the ER group, accompanied by significantly reduced serum triiodothyronine. The ER group exhibited significantly higher SM and FRM MyHC expression at 14 d, but lower SM expression at 63 d. Myosin ATPase staining revealed a similar pattern. The percentage of SM was higher at 14 d while lower at 63 d in the ER group. These morphological changes were accompanied by changes of mRNA expression for growth-related genes. The ER group expressed lower insulin-like growth factor I (IGF-I) and higher IGF-I receptor (IGF-IR) at 14 d, yet significantly increased growth hormone receptor and IGF-IR mRNA at 63 d. These results indicate that ER may delay the slow to fast myofibre conversion as an immediate effect, but would result in a lower percentage of slow fibres owing to compensatory growth in the long term, which involves changes of mRNA expression for the growth-related genes in the muscle.