Herbs, thyme essential oil and condensed tannin extracts as dietary supplements for broilers, and their effects on performance, digestibility, volatile fatty acids and organoleptic properties.

1. Herbs, thyme essential oil (EO) and condensed tannin (CT) extracts were compared for their effects, as dietary supplements, on broiler growth performance, nutrient digestibility and volatile fatty acid (VFA) profiles in the gut. Cooked meat from the birds fed on diets with 4 herbs and an EO extract was compared by a taste panel against those fed on the control treatment, for organoleptic properties in the meat. 2. Female broiler chicks were fed on wheat-soybean meal diets from 0-42 d of age. These chicks were given either the basal diet (control), or the basal diet with one of rosemary, garlic or yarrow herbs, mimosa, cranberry or grapeseed CT's, or thyme EO supplements (8 treatments in total). Body weight (BW) and feed consumption (FC) were measured. 3. The garlic supplement tended to improve growth rate over the first 7 d, while mimosa CT and thyme EO supplements reduced weight gains. The mimosa supplement in diets significantly reduced FC to d 21. Meanwhile, the addition of a cranberry supplement reduced the digestibility of DM, OM and N, compared with the controls. Dietary thyme EO, yarrow, rosemary and garlic supplements modified caecal isovaleric and isobutyric acid proportions (presented as 'Other VFA'; p < 0.05). Dietary herb significantly affected the intensity of meat flavour, and the potential of observing both garlic and abnormal flavours. There were large differences between the consumption of red and white meat samples, while meat temperature affected several flavour attributes. 4. Broiler performance and digestibility for birds given dietary garlic and grapeseed CT supplements were similar to the controls, and these supplements appear suitable for dietary inclusion. Careful choices are necessary when selecting dietary plant extract supplements for broilers, but beneficial effects can be observed.

Overexpression or knockdown of rat tryptophan hyroxylase-2 has opposing effects on anxiety behavior in an estrogen-dependent manner.

Previous studies showed that chronic estrogen treatment increases tryptophan hydroxylase-2 (TpH2) mRNA in the caudal dorsal raphe nucleus (DRN), and this increase was associated with decreased anxiety. The present study explored the interaction of estrogen and targeted, bidirectional manipulation of TpH2 expression in the caudal DRN by knockdown or viral overexpression, to decrease or increase tryptophan hydroxylase expression respectively, on anxiety behavior. Rats were ovariectomized and replaced with empty or estradiol capsules (OVX, OVX/E, respectively). Animals received microinfusions of either antisense TpH2 or control morpholino oligonucleotides into caudal DRN and were later tested in the open field test. A separate group of animals were microinfused with TpH2-GFP or GFP-only herpes simplex viral vectors into caudal DRN and tested in the open field. The bidirectional impact of manipulations on TpH2 expression was confirmed using a combination of quantitative protein and mRNA measurements; TpH2 expression changes were limited to discrete subregions of DRN that were targeted by the manipulations. Estradiol decreased anxiety in all behavioral measures. In the OVX/E group, TpH2 knockdown significantly decreased time spent in the center of the open field, but not in the OVX group, suggesting that TpH2 knockdown reduced the anxiolytic effects of estrogen. Conversely, TpH2 overexpression in the OVX group mimicked the effects of estrogen, as measured by increased time spent in the center of the open field. These results suggest that estrogen and TpH2 in the caudal DRN have a critical interaction in regulating anxiety-like behavior.

The effect of herbs and their associated essential oils on performance, dietary digestibility and gut microflora in chickens from 7 to 28 days of age.

1. The effect of the dietary inclusion of 5 culinary herbs or their essential oils on the growth, digestibility and intestinal microflora status in female broiler chicks was assessed. From 7 to 28 d of age, either a basal control diet without supplement was given or one of 10 others, consisting of the basal diet with either 10 g/kg herb (thyme, oregano, marjoram, rosemary or yarrow) or 1 g/kg of essential oil. 2. Body mass (BM) and feed consumption (AFC) were measured on a weekly basis and used to calculate chick performance. Total viable counts of lactic acid bacteria, coliforms, anaerobes and Clostridium perfringens were determined at 25 d. Apparent nutrient digestibilities were calculated from the measured values for gross energy, nitrogen (N), dry matter (DM) and organic matter, and sialic acid concentration was also measured. 3. Generally, dietary thyme oil or yarrow herb inclusion had the most positive effects on chick performance, while oregano herb and yarrow oil were the poorest supplements. Only thyme and yarrow in these diets had a different effect when used as a herb or oil on weight gain and BM. 4. Dietary treatment had no effect on the intestinal microflora populations, apparent metabolisable energy (AME) or the calculated coefficients of digestibility. Sialic acid concentration was greatest in the birds given dietary thyme oil, compared with all other treatments except those birds receiving marjoram oil, rosemary herb and the controls. However, less sialic acid was excreted in those birds given diets with oregano or rosemary oils, or oregano herb, than in the controls. 5. Plant extracts in diets may therefore affect chick performance, gut health and endogenous secretions, although the chemical composition of the extract appears to be important in obtaining the optimal effects.

Chronic low dose ovine corticotropin releasing factor or urocortin II into the rostral dorsal raphe alters exploratory behavior and serotonergic gene expression in specific subregions of the dorsal raphe.

Corticotropin releasing factor (CRF) family peptides play key roles in integrating neural responses to stress. Both major CRF receptors have been pharmacologically identified in the dorsal raphe nucleus (DRN), a stress sensitive and internally heterogeneous nucleus supplying many forebrain regions with serotonergic input. Despite the involvement of chronic stress and serotonergic dysfunction in human mood and anxiety disorders, little is known about the effects of chronic CRF receptor activation on the DRN. We infused ovine CRF (1 ng/h), urocortin II (UCNII, 1 ng/h), or vehicle alone into rat DRN over 6 days. During infusion, animals were allowed to freely explore an open field for 15 min on each of 2 days, with the addition of a novel object on the second day. Following behavioral testing, 5-HT1A, 5-HT1B, 5-HT transporter (SERT), and tryptophan hydroxylase-2 (Tph2) expression was examined through the DRN by in situ hybridization. Ovine CRF infusion resulted in significantly decreased novel object touches, climbs, as well as increased latency to first novel object contact. UCNII had a similar but less dramatic effect, decreasing only climbing behavior. Both ovine CRF and UCNII blunted the decrease in corner time expected on re-exposure to the open field. Both peptides also produced regionally specific changes in gene expression: 5-HT1A expression was increased 30% in the mid-rostral ventromedial DRN, while SERT was decreased by 30% in the mid-caudal shell dorsomedial DRN. There also appeared to be a shift in the relative level of Tph2 expression between the ventromedial and core dorsomedial DRN at the mid-rostral level. Changes in 5-HT1A, SERT, and relative Tph2 mRNA abundance were correlated with novel object exploration. These findings suggest chronic intra-DRN administration of CRF agonists decreases exploratory behavior, while producing subregionally limited changes in serotonergic gene expression. These studies may be relevant to mechanisms underlying behavioral changes after chronic stress.

Bone breaking strength and apparent metabolisability of calcium and phosphorus in selected and unselected broiler chicken genotypes.

1. The present study examined the bone strength and apparent mineral metabolisability of a selected broiler chicken compared with those of a relatively unselected genotype. 2. Selected (SB) and unselected genotypes (UB) were reared under standard conditions and were fed on either a high quality (HQ) or a low quality (LQ) diet. Tibiotarsi samples were collected at 42 d from SB and compared to tibiotarsi from UB of the same age and the same body mass (BM). 3. Bones were assessed for: bone breaking strength (BBS), morphology (weight and length), and both organic (OM) and inorganic content (ASH). Apparent dry matter digestibility and the coefficient of apparent metabolisability of calcium and phosphorus were determined at the same BM. 4. The BBS of SB (214 +/- 9 N) was greater than that of same-age UB (119 +/- 8 N) but the same as that of same-BM UB (218 +/- 10 N). At the same age, the SB had stronger, heavier bones with more ash and organic matter per unit length of tibiotarsus than UB. At the same BM, the tibiotarsi of the SB were shorter and lighter, with a higher ash and a similar organic content than the bones of the UB. At the same BM, BBS was about 15% lower in both genotypes fed on the LQ compared to the HQ diet. 5. The coefficients of apparent metabolisability of calcium and phosphorus were the same in both genotypes when fed on the HQ diet, but were lower in the SB than in the UB genotype when the birds were given the LQ diet. 6. The tibiotarsi of the selected broilers were stronger, or at least as strong, as those of the unselected broiler genotype, which may be due to similar levels of apparent calcium metabolisability of the selected chickens.

Effects of supplementing broiler breeder diets with organoselenium compounds and polyunsaturated fatty acids on hatchability.

The effects of supplementing broiler breeder diets with polyunsaturated fatty acids (PUFA) and organoselenium compounds on fertility, hatchability, and the weight of 1-d-old chicks was assessed. Prepeak (23 wk) and peak (27 wk) production breeders were fed 1 of 4 diets: a wheat-based commercial breeder diet with 55 g/kg of either soybean oil (SO) or fish oil (FO), but no added Se (only that originating from feed ingredients), and each diet with added Se as Sel-Plex (SO + Se, FO + Se). The diets were designed to contain <0.1 mg/kg of Se and about 0.5 mg/kg of Se for the nonsupplemented (no added Se) and the supplemented diets, respectively. The Se concentration of the eggshell of the hatching egg was measured. The concentration of Se, PUFA, and total lipid content of the brain and liver of the 1-d-old chick was determined. The number of fertile eggs increased, embryonic mortality decreased, and hatchability increased as hen age increased from 23 to 27 wk. The Se concentration in the eggshell and the brain and liver of 1-d-old chicks was higher in the high-Se treatments com pared with the concentration in the low-Se treatments. Fish oil inclusion in the breeder diet increased embryonic mortality in wk 3 of incubation and reduced both hatchability and 1-d-old chick weight in hens of both ages. The addition of Se to the FO diets ameliorated some of these adverse effects, because chicks hatched from eggs laid by 23-wk-old breeders of the FO + Se treatment were heavier than those receiving the FO treatment. The Se concentration in the brain and liver of chicks from the FO hens was higher than that in chicks from the SO hens. The concentration of docosahexaenoic fatty acid was higher in the liver of chicks from the SO + Se treatment compared with that of chicks from the SO treatment, indicating possible protective effects of Se. Hatchability was decreased by increased PUFA and was higher in 27-wk-old compared with 23-wk-old breeders.

Maternal organo-selenium compounds and polyunsaturated fatty acids affect progeny performance and levels of selenium and docosahexaenoic acid in the chick tissues.

The effects of supplementing broiler breeder diets with polyunsaturated fatty acids (PUFA) and organo-Se compounds on the levels of Se and PUFA in chick tissues and on chick performance were assessed. Prepeak (23 wk) and peak (27 wk) production broiler breeders were fed 1 of 4 diets: a wheat-based commercial diet with soybean oil or fish oil but no added Se, and each diet with added Se as Sel-Plex (soybean oil + Se, fish oil + Se; Alltech Inc, Nicholasville, KY). The diets were designed to contain less than 0.1 mg of Se/kg and about 0.5 mg/kg for the nonsupplemented and the supplemented diets, respectively. As-hatched chicks from the 4 parental treatments were fed a nutritionally high quality diet (ME = 12.57 MJ/kg; CP = 228.7 g/kg) or a low quality diet (ME = 10.28 MJ/kg; CP = 182.8 g/kg), resulting in 8 dietary treatments. Performance was better and mortality lower in chicks from 27-wk-old breeders compared with those from 23-wk-old breeders. Fish oil in the maternal diet increased progeny mortality and reduced chick body mass at hatch. Body mass at 7 and 14 d posthatch was lower in chicks fed the low quality diet compared with chicks fed the high quality diet. At hatch, and for up to 14 d posthatch, chicks from hens fed diets high in PUFA had higher concentrations of docosahexaenoic acid (DHA) in the brain and liver compared with chicks hatched from hens fed diets low in PUFA. The DHA content of the tissues of chicks from breeders fed diets supplemented with Se was higher than that in chicks from breeders fed unsupplemented diets. Even after 14 d of being fed a diet with identical levels of Se, chicks hatched from parents fed diets high in Se had higher tissue Se concentrations than those hatched from parents fed diets low in Se. Supplementation of the maternal diet of chicks with organo-Se appears to enhance the DHA concentration of the chick brain, which may improve brain function.

A house dust mite allergen homologue from poultry red mite Dermanyssus gallinae (De Geer).

Tropomyosin is an allergenic, actin-binding protein and a proposed vaccine candidate from several species of parasite. Tropomyosin cDNA, obtained by polymerase chain reaction (PCR) amplification from Dermanyssus gallinae RNA, encoded a predicted protein with 89% and 88% identity to tropomyosins from the ticks Boophilus microplus and Haemaphysalis longicornis, respectively, and 85% identity to the house dust mite (HDM) tropomyosin Der p 10. Mouse antibodies raised against HDM tropomyosin reacted with a band of 38 kDa on Western blots of D. gallinae extract, consistent with the molecular masses of acarine tropomyosins and the putative product of the cDNA encoding D. gallinae tropomyosin. When the same preparation of D. gallinae proteins was used in Western blots with serum from infested hens, the IgY component of the serum bound to a number of mite proteins, but not to tropomyosin, indicating that hens are not directly exposed to this allergen during a natural infestation. Immunolocalization of tropomyosin in mites indicated a ubiquitous distribution of the molecule in mite tissues. Immunolocalization and Western blotting also indicated that poultry red mites ingest host IgY.

Ability of a proteinase inhibitor mixture to kill poultry red mite, Dermanyssus gallinae in an in vitro feeding system.

The development of a reliable in vitro feeding system has enabled the rapid testing of presumptive anti-mite factors, a mixture of protease inhibitors (PI), by incorporating these into the blood feed. Mites were collected from a caged-hen facility and underwent a regime of starvation under varying conditions of temperature and darkness to determine the optimum conditions that encouraged mites to feed in the in vitro system. The efficacy of two anti-coagulants, heparin (HS) and acid citrate glucose (ACD), on mite feeding rates and mortality was evaluated. The ability of a mixture of PI to kill mites was also evaluated. The rate of feeding was greater in mites that were starved and cooled for between 7 and 30 days compared with mites that were not starved or cooled. The percentage of mites that fed when presented with HS treated blood (70%) was greater when compared with ACD treated blood (48%). The mortality of mites fed blood treated with HS + PI increased to 45% compared with a mortality level of 5% in mites fed on blood treated with HS alone. A reliable in vitro method for feeding D. gallinae which has the potential to be used to rapidly screen blood-borne products for their efficacy in reducing mite numbers has been developed.

Effects of supplementing broiler breeder diets with organic selenium and polyunsaturated fatty acids on egg quality during storage.

We assessed the effects of supplementation of broiler breeder diets with polyunsaturated fatty acids (PUFA) and organic Se on hatching egg quality during storage. Broiler breeders (n = 352) were fed 1 of 4 diets: SO (soybean oil with no added Se), SO with Se (SO+Se), fish oil (FO), or FO and Se (FO+Se). Eggs from prepeak (23 wk) and peak production (27 wk) breeders were stored for 14 d under typical (15 degrees C, 78% RH) conditions. Eggs were analyzed for albumen Haugh units (HU) and pH, shell characteristics, egg component weight, Se content, and fatty acid (FA) profile. The efficiency of transfer of Se into the egg was greater in low Se treatments compared with in high Se treatments. The majority of Se from the low Se treatments was deposited in the yolk, whereas in high Se treatments, the Se was deposited evenly in the yolk and albumen. In the low Se treatments, the Se content of yolk and albumen was lower than in the high Se treatments and decreased as age increased. Albumen HU decreased with increased storage, although high Se treatments had greater HU compared with low Se treatments. Eggs from the FO treatment were smaller with thinner eggshells compared with the SO treatment, but addition of Se to the FO diets ameliorated some of these effects. The egg yolk FA profile from the SO+Se treatment was altered compared with that from the SO treatment, perhaps due to interactions between dietary PUFA and Se-dependent enzyme systems. Hatching egg quality during storage was affected by dietary PUFA and Se content, as well as broiler breeder age.

Genetic and phenotypic relationships between and within support and demand tissues in a single line of broiler chicken.

1. With commercial selection for increased broiler performance there has been a correlated increase in the incidence of several metabolic disorders. A study was undertaken to investigate the balance between the unselected support tissues (including the heart, liver, spleen and the components of the gastrointestinal tract (GIT)) which drive growth in the selected demand tissues (eviscerated body mass) by assessing the genetic correlations between these traits. 2. Data were collected on 483 broiler birds taken from a commercial male broiler line with pedigree information. 3. Genetic parameters were estimated by restricted maximum likelihood with an individual animal model. Heritability estimates for the production traits ranged between h2 = 0.48 and 0.59 for leg and breast mass, respectively. The support tissues were generally associated with low to moderate heritabilities ranging between h2 = 0.19 for proventriculus to h2 = 0.38 for duodenum mass, although moderately high heritability estimates (h2 = 0.51 to 0.54) were associated with the spleen and gizzard. 4. The genetic correlations between production traits and support organs were generally low, however, heart mass was positively correlated with all carcase components of the lean tissue mass; the genetic correlations ranged between r(g) = 0.55 with breast mass to r(g) = 0.64 with eviscerated body mass. 5. In general, there were strong positive genetic correlations between the different components of the GIT. Organs that have been implicated in the development of metabolic disorders such as ascites (for example, the heart) could theoretically be used in commercial selection indices due to moderate heritabilities (heart: h2 = 0.30) and favourable correlations with commercially important traits.

De novo lipogenesis during controlled overfeeding with sucrose or glucose in lean and obese women.

BACKGROUND: The results of previous studies suggest that de novo lipogenesis may play an important role in the etiology of obesity, particularly during overconsumption of different carbohydrates. OBJECTIVE: We hypothesized that de novo lipogenesis would increase during overfeeding, would vary depending on the type of carbohydrate consumed, and would be greater in obese than in lean women. DESIGN: De novo lipogenesis was measured during 96 h of overfeeding by 50% with either sucrose or glucose and during an energy balance treatment (control) in 8 lean and 5 obese women. De novo lipogenesis was determined by measuring the amount of deuterium incorporation into plasma triacylglycerols. Fat and carbohydrate balance were measured simultaneously by continuous whole-body calorimetry. RESULTS: De novo lipogenesis did not differ significantly between lean and obese subjects, except with the control treatment, for which de novo lipogenesis was greater in the obese subjects. De novo lipogenesis was 2- to 3-fold higher after overfeeding by 50% than after the control treatment in all subjects. The type of carbohydrate overfeeding (sucrose or glucose) had no significant effect on de novo lipogenesis in either subject group. Estimated amounts of absolute VLDL production ranged from a minimum of 2 g/d (control) to a maximum of 10 g/d after overfeeding. This compares with a mean fat balance of approximately 275 g after 96 h of overfeeding. Individual subjects showed characteristic amounts of de novo lipogenesis, suggesting constitutive (possibly genetic) differences. CONCLUSION: De novo lipogenesis increases after overfeeding with glucose and sucrose to the same extent in lean and obese women but does not contribute greatly to total fat balance.

Can betaine partially replace or enhance the effect of methionine by improving broiler growth and carcase characteristics?

1. Growth rates and carcase characteristics were measured in male broiler chickens fed on a control diet deficient in methionine (c. 2.8 g/kg methionine) or a series of diets containing graded levels of betaine or DL-methionine or both additives. 2. We aimed to answer 2 main questions. First, can betaine replace part of the methionine in a broiler ration? Secondly is there a synergism between methionine and betaine? 3. Birds given the control diet or that supplemented only with betaine ate less, grew more slowly, had higher food convension ratio (FCR) and varied more in mass at 42 d than birds fed diets with DL-methionine. Adding 1.2 g/kg DL-methionine to the control ration produced the heaviest birds at 42 d (2500 g) with the 2nd heaviest breast muscle (366 g). 4. After correcting for treatment differences in body mass (analysis of convariance), birds fed on the control diet and the diet supplemented with betaine only, had relatively lighter breast muscles but relatively heavier abdominal fat pads than those of birds given diets supplemented with DL-methionine. However, adding betaine to diets containing added methionine further improved the relative breast muscle yield. 5. After correcting for differences in body mass between treatments, birds fed on diets containing most methionine had lighter viscera than birds fed diets deficient in methionine. This demonstrated gut plasticity, suggesting that the viscera enlarged to sequester methionine from low-methionine diets. 6. Our data refute the hypothesis that betaine can substitute for methionine in broilers fed diets that are marginally deficient in methionine plus cystine. However, betaine may improve carcase composition, especially breast meat yield.

Comparison of recoveries in breath carbon dioxide of H13CO-3 and H14CO-3 administered simultaneously by single 6 h constant unprimed intravenous infusion.

The aim of this study was to assess the bioequivalence of H13CO-3 and H14CO-3, by administering both labels simultaneously by single infusion and comparing their recovery in breath CO2 and urinary urea. Six healthy male subjects (age range 24-41 years; weight 76.7 (sd, 18.6) kg; height 1.79 (sd 0.05) m) were infused with unprimed solutions of HCO3- (110.0 mmol/kg) labelled with 13C (0.76 mmol 13C/h) and 14C (48 Bq/h) at a constant rate for 6 h, in a whole-body calorimeter (1400 litres) for measurement of CO2 production. Samples of breath were collected hourly in a Douglas bag and all urine was collected into two batches (0-4 h and 4-6 h) for estimating recovery of infused label by measurement of enrichment or specific activity. Recovery in breath CO2 of both labels increased from about 25 % for the first hour to 88 % and above for hours 3-4 onwards. Mean recovery of 13C in breath CO2 was slightly higher than that of 14C for all periods (mean difference always less than 1 % of infused label) but was significant only for the first 3 h (P < 0.05). Recovery of 14C in urea was significantly higher (P < 0.01) than 13C, but was confounded by substantial variability and uncertainties concerning 13CO2 background enrichments. These results suggest that there is no compelling need to alter factors currently used for recovery of 14C in breath when using 13C instead, and vice versa.

Macronutrient disposal during controlled overfeeding with glucose, fructose, sucrose, or fat in lean and obese women.

BACKGROUND: Previous short-term studies (< or =6 h) showed differences in energy expenditure (EE) and macronutrient oxidation in response to overfeeding with different types of dietary carbohydrate. This finding could have implications for obesity. OBJECTIVE: We used 96-h continuous whole-body calorimetry in 8 lean and 5 obese women to assess metabolic disposal (energy dissipation and glycogen or fat storage) of a controlled excess of dietary energy supplied as different carbohydrate sources or as fat. DESIGN: Five dietary treatments were applied in random order: energy balance (control) and overfeeding by 50% of energy requirements with fat (O(fat)) or predominantly with glucose, fructose, or sucrose (O(cho)). Macronutrient oxidation rates were assessed from nonprotein gaseous exchanges. Net macronutrient balances were calculated as cumulative differences between intake and oxidation. RESULTS: Increased EE in response to overfeeding dissipated 7.9% of the energy excess with a variation in EE of <1.7% across overfeeding treatments (NS). EE during the O(fat) treatment significantly exceeded that during the control treatment in the lean but not in the obese women. There were no significant differences between lean and obese women in macronutrient oxidation or balances, so data were pooled. O(cho) induced glycogen storage on day 1 ( approximately 100 g) but thereafter progressively stimulated carbohydrate oxidation so that balance was reached on days 3 and 4. Fat oxidation was proportionately suppressed. Of the excess carbohydrate, 74% was oxidized; there were no significant differences between the various O(cho) treatments. O(fat) stimulated fat oxidation by 18% and suppressed carbohydrate oxidation. On average, 12% of the excess energy was stored as glycogen and 88% as fat; there was no significant difference between overfeeding treatments. CONCLUSION: There was no significant difference in fat balance during controlled overfeeding with fat, fructose, glucose, or sucrose.

Metabolic and organ mass responses to selection for high growth rates in the domestic chicken (Gallus domesticus).

Evolutionary hypotheses suggest that higher rates of postembryonic development in birds should either lower the resting metabolic rate (RMR) in a trade-off between the costs of growth and maintenance or increase RMR because of a buildup of metabolic machinery. Furthermore, some suggest that higher rates of postembryonic development in birds should reduce peak metabolic rate (PMR) through delayed tissue maturation and/or an increased energy allocation to organ growth. We studied this by comparing metabolic rates and organ sizes of fast-growing meat-type chickens (broilers) with those of birds from a laying strain, which grow much slower. During the first week of life, despite growing six times faster, the RMR of the broiler chickens was lower than that of birds of the laying strain. The difference between strains in RMR disappeared thereafter, even though broilers continued to grow twice as fast as layers. The differences between strains in growth rate during the first week after hatching were not reflected in similar differences in the relative masses of the heart, liver, and small intestine. However, broilers had heavier intestines once they reached a body mass of 80 g. In contrast, broilers had relatively smaller brains than did layers. There was a positive correlation, over both strains, between RMR and the masses of leg muscles, intestine, and liver. Furthermore, despite delayed maturation of muscle tissue, broilers exhibited significantly higher PMR. We hypothesize that a balance between the larger relative muscle mass but lower muscle maturation level explains this high PMR. Another correlation, between leg muscle mass and PMR, partly explained the positive correlation between RMR and PMR.