Muscle protein turnover and tenderness in broiler chickens fed cimaterol

To investigate the impact of cimaterol (CIM) on muscle protein turnover, carcass and muscle composition, muscle cathepsin B + L activity and meat tenderness, 21-d-old broiler chickens (n = 88) were assigned to dietary treatments of either 0 or 1 ppm CIM. Fractional synthesis rates (FSR), fractional accretion rates (FAR), proximate composition and collagen content were determined in the breast muscle (BM); pectoralis major) and a group of leg muscles (LM; gastrocnemius and peroneous longus) from groups of six birds per treatment within each of two time periods (age = 38 or 56 d). Whole body composition, serum hydroxyproline content and BM cathepsin B + L activity also were measured. Fractional degradation rates (FDR) were calculated as the difference between FSR and FAR. Feeding CIM increased (P less than .01) whole body protein content. Weights of LM and percentage of body weight as BM and LM were increased (P less than .05) when CIM was included in the diet. Although FSR was not significantly reduced by CIM feeding it decreased (P less than .05) with increasing age. Due to decreases in FAR, FDR thereby was reduced by CIM 31.5% and 11.9% in BM and 38.2% and 37.4% in LM at 38 d and 56 d of age, respectively. Cathepsin B + L activities also were reduced 33.6% (P less than .01) and shear forces were increased by 41% (P less than .05) by CIM feeding. For chickens fed CIM, the correlation between cathepsin B + L activity and shear force was -.63 (P less than .01). Feeding CIM improved carcass leanness and muscling due to reductions in FDR and proteolytic enzyme activity. Feeding CIM also reduced meat tenderness.     

Increased responsiveness to dietary lysine deficiency of pectoralis major muscle protein turnover in broilers selected on breast development

It has been previously established that growth and carcass qualities of chicks are modified by genotype and dietary amino acid supply. In this study, we evaluated the effects of lysine deficiency and genetic selection on muscle protein metabolism. Chicks originating from an experimental line selected for breast development (QL) and its control line (CL) were provided ad libitum access to isoenergetic diets containing 20% crude protein but differing in their lysine content (0.75 or 1.01%). Protein fractional synthesis rates (FSR) were measured in vivo in the pectoralis major and sartorius muscles of 3-wk-old chickens (flooding dose of [3H]phenylalanine). Fractional breakdown rates (FBR) were estimated as the difference between synthesis and deposition. Lysine deficiency reduced (P < 0.001) growth performance and muscle weights and increased (P < 0.05) muscle FSR, capacity for protein synthesis (muscle RNA:Protein, Cs) and FBR. Although QL birds grew faster and had heavier pectoralis major muscles than CL birds (P < 0.05), there was no line difference in sartorius weight (P = 0.15). No difference between the lines was observed in sartorius protein metabolism (P > 0.14). In the pectoralis major muscle, chicks of both lines receiving an adequate lysine intake also exhibited similar protein turnover rates. However, in chicks fed the lysine-deficient (0.75% lysine) diet, FSR and Cs were higher in QL than in CL chicks (P < 0.05), and FBR tended (P = 0.07) to be higher in QL chicks. This increased protein turnover in the QL birds on the lysine-deficient diet suggests that the responsiveness of muscle protein metabolism to amino acid supply is modified by genetic selection for breast development.     

Response time of broiler chickens to cimaterol: meat tenderness, muscle composition fiber size, and carcass characteristics.

The response time to cimaterol (CIM), a beta-adrenergic agonist, by broiler chickens for carcass characteristics, muscle composition, muscle fiber size, catheptic enzyme activity, and tenderness was determined. Two trials were conducted in which chickens were fed a control diet (CON) containing 0 ppm of CIM or a diet containing 1 ppm of CIM. Trial 1 consisted of 55, 31-d-old broiler chickens individually fed for up to 48 h. At 0, 6, 12, 18, 24, and 48 h, five CON and five CIM-fed chickens were killed. Trial 2 consisted of 160, 33-d-old broiler chickens group-fed for up to 14 d. At 2, 4, 6, 8, 10, 12, and 14 d, 10 CON and 10 CIM-fed chickens were killed. The breast muscle (BM) and leg muscle (LM) weight, cathepsin B and L activities, DNA, RNA, and protein concentration, and BM shear force value (SFV) were measured in both trials. Thigh muscle (TM) SFV were measured in Trial 2 only. Fiber size of BM was measured (five birds per treatment) at d 2, 6, 10, and 14. In Trial 1, BM weight and SFV were lower in CIM-fed birds at 6 h (P less than .05). In Trial 2 BM SFV were higher at d 8 (P = .06) and d 10 (P less than .05) in CIM-fed chickens. The SFV of CIM-fed chickens were higher at d 4, 8, 10, 12, and 14 (P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Muscle protein metabolism in finishing pigs fed ractopamine

Forty crossbred barrows (average initial weight, 66.4 kg) were utilized to determine the effects of ractopamine (a phenethanolamine/beta adrenergic agonist) on protein accretion and synthesis, activities of cathepsins B, H, L and calcium-dependent proteinase and nucleic acid content of semitendinosus muscle (ST). All pigs were offered a 16% protein, mineral and vitamin fortified corn-soybean meal diet supplemented with either 0 or 20 ppm ractopamine for 14, 21, 28, 35 or 42 d. Protein synthesis (fractional rates) was studied in pigs at d 21 and 35; ST protease activities, protein and nucleic acid content were measured on d 14, 28 and 42. Ractopamine increased (P less than .01) ST total protein content and maintained RNA muscle concentration and total ST muscle RNA content. DNA content (mg/g ST) declined (P less than .05) upon ractopamine feeding, but total DNA per muscle remained unchanged except for d 42, when the ST muscles were largest. Fractional accretion rates (FAR) were 1.0 and 1.2% for control and ractopamine-fed pigs, respectively. Fractional protein synthesis rate (FSR) was higher (P less than .06) in ractopamine-fed pigs (6.1%/d) than in control pigs (4.4%/d). Fractional protein synthesis rate could account for the observed muscle hypertrophy and increased FAR. Estimated fractional breakdown rates (FBR = FSR - FAR) were 3.4%/d and 4.9%/d for control and ractopamine-fed pigs, respectively. The activities of the catheptic proteases and calcium-dependent proteinase were not affected by the treatments.     

The effect of cimaterol and its withdrawal on carcass composition and meat tenderness of broiler chickens.

To examine the effects of cimaterol (CIM) and its withdrawal on meat tenderness and carcass composition, 21-d-old broiler chickens (n = 288) were randomly assigned to one of nine treatments. For Treatments 1 through 6, birds were fed a control diet or a diet containing 1 ppm CIM until slaughter at 35, 42, or 49 d of age. Treatments 7 and 8 consisted of birds fed the CIM diet for 14 d and then withdrawn from CIM for either 7 or 14 d before slaughter (42 or 49 d of age). In Treatment 9, birds were fed the CIM diet to 42 d of age, then withdrawn from CIM for 7 d. Breast muscle (BM) weight, leg muscle (LM) weight, whole body weight, and BM and LM cathepsin B and L activities were obtained on 12 birds/treatment. Body, LM and BM composition and BM shear values were obtained on 12 additional birds/treatment. Eight birds/treatment were used to balance the number of birds per pen. Leg muscle weight, as a percentage of whole body weight, was elevated in CIM-fed birds at all ages, and BM percentage was greater at 35 d of age (P less than .05). Leg muscle fat percentage was reduced at 35 and 42 d of age (P less than .05), and LM protein was elevated at 42 and 49 d of age (P less than .05) in CIM-fed birds. Percentage of protein in the BM of CIM-fed birds was elevated at 35 and 42 d of age. Protein content of the whole body was also increased at 35 d of age. Shear values were higher in 42- and 49-d-old CIM-fed birds.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of dietary fat type and non-starch-polysaccharide-hydrolysing enzyme addition to rye-based diets on muscle protein turnover in broilers

1. Muscle protein turnover was measured in broilers fed on rye-based diets containing either beef tallow (T) or soybean oil (S) at an inclusion rate of 100 g/kg. Each of these diet types was tested either in the absence (S[-], T[-]) or presence (S[+], T[+]) of a xylanase-containing enzyme preparation. Protein turnover was measured in gastrocnemius muscle (GM) and pectoralis major muscle (PM). 2. Fractional rate of protein synthesis (FSR) was measured by the large dose technique using [15N]-labelled phenylalanine whereas fractional protein growth rate (FGR) was estimated by regressing tissue protein content over time. Fractional breakdown rates (FBR) were calculated by the difference between FSR and FGR. 3. In PM, FSR (%/d) was 22.1, 23.4, 21.5 and 24.4 in groups S[-], S[+], T[-] and T[+], respectively, and FBR (%/d) was 8.3, 9.8, 4.5 and 10.8 with the xylanase effect being significant. The FGR of 17.0%/d calculated for the broilers fed on the T[-] diet tended to be higher than for the other groups (13.6 to 13.8%/d). No significant effects were detected for these parameters in the GM. 4. The absolute amounts of protein which were synthesised daily and accreted in both muscles were significantly higher with xylanase supplementation in both fat type diets but at a significantly higher level when soybean oil was the dietary fat type. 5. The observed effects on protein turnover have to be seen in the context of an overall adverse effect of dietary soluble pentosans from rye in combination with tallow on physico-chemical chyme conditions, digestion and absorption of energy and nutrients and tissue-specific metabolic changes.     

Effect of a major gene for growth on protein synthesis in mice

Rates of protein synthesis of mice with a major gene (hg) for rapid postweaning gain (line Ch) and their normal counterparts (line CH) were determined at 21, 31 and 42 d of age with an intraperitoneal injection of a flooding dose of 14C-leucine. A preliminary experiment demonstrated that the relationship between the specific activities of leucine in acid-soluble supernatants and carcass protein corresponded to the theoretical precursor-product relationship, indicating that the method is valid for estimating protein synthesis rates. Using this method at 21, 31 and 42 d of age, whole-body protein fractional synthesis rates (FSR) were 43.7, 32.7 and 29.1%/d and 41.9, 32.6 and 33.1%/d for lines CH and Ch, respectively. Although differences between lines were not significant, FSR decreased with age. Absolute synthesis rate (ASR), where ASR = (FSR) X (whole body protein), was greater (P less than .001) at 21, 31 and 42 d of age in line Ch as compared with CH, and increased (P less than .001) with age. The relative contributions of liver, gastrointestinal tract, heart-kidney-lung and remaining carcass to whole body protein ASR were not affected by line, but did change (P less than .05) with age. Whole body protein fractional breakdown rate (FBR), calculated as FSR minus whole body protein fractional growth, indicates that differences between lines CH and Ch whole-body FSR and(or) FBR exist only between 24 and 33 d of age, and that the maximum value of this difference probably does not exceed 10%.     

Myofibrillar protein turnover in feed-restricted and realimented beef cattle

The objective of this study was to determine the effect of feed restriction and repletion on myofibrillar protein turnover in cattle. Crossbred steer calves (n = 12) about 310 d of age were assigned randomly to a diet of corn and silage that was 1) provided ad libitum for 146 d (ALC) or 2) restricted so steers gained .2 kg/d for 80 d but received ad libitum access to feed thereafter for 66 d (RFC). At 27, 55, 97, 118 and 146 d a 24-h urine sample and a blood sample were obtained. Urine was analyzed for N tau-methylhistidine (N tau-MH), creatinine (C), urea nitrogen (UN) and total nitrogen (TN). Serum samples were analyzed for hydroxyproline (HYP), C and albumin (A). Body weights were lower (P less than .05) in RFC at 55, 97, 118 and 146 d. Excretion of N tau-MH was lower (P less than .05) in the RFC at 27 and 55 d but higher at 118 d. Urinary C excretion was higher in ALC at the last four sample times. Urinary UN and TN excretion were lower (P less than .05) in RFC at 55, 97 and 118 d; urinary UN also was lower (P less than .05) at d 146. Serum A was higher (P less than .05) in ALC at 55 and 118 d, respectively. Serum HYP was higher (P less than .05) in RFC at 27 and 55 d. Calculated myofibrillar protein breakdown rates (FBR) and fractional synthesis rates (FSR) were higher (P less than .05) in RFC at the last two sampling periods; FSR was lower for the RFC at the first sampling period.(ABSTRACT TRUNCATED AT 250 WORDS)     

Skeletal muscle protein synthesis and growth hormone secretion in young lambs treated with clenbuterol

To determine effects of clenbuterol (CB) on muscle protein turnover and growth hormone (GH) secretion, 16 crossbred wether lambs (14.4 kg) were randomized into two groups designated to receive daily oral boluses of gelatin capsules containing corn starch with either 0 (control, CTL) or 1.87 mg/kg body weight CB for either 14 (n = 8) or 28 d (n = 8). This calculates to be approximately 40 mg CB/kg diet. Lambs had ad libitum access to a 16% crude protein corn-soy diet and feed consumption (FC) was measured. After 14 and 28 d, lambs were slaughtered and semitendinosus (ST), longissimus (LD) and brachialis (BR) muscles were exercised, weighed and analyzed for protein (TP) content. For 6 h prior to slaughter of 28-d lambs, 2.5 microCi L-[U-14C]tyrosine/kg was infused intravenously, blood was sampled and plasma was analyzed for specific radioactivity of tyrosine. Plasma GH concentrations were assessed by radioimmunoassay. No differences due to treatment were found in FC, rate of gain or GH concentrations. Semitendinosus and BR weights of control lambs at 14 d did not differ between treatments. At 28 d, ST and BR weights of control lambs (58.8 and 18.5 g, respectively) were less (P less than .10) than those of lambs treated with CB (74.3 and 23.1 g, respectively). The TP per ST and BR at 28 d for control lambs was 71.5 and 85.1% (P less than .10) that of muscles of lambs treated with CB. Fractional protein synthesis rates (FSR) of the BR (9.4 vs 6.1%/d) and total protein synthesized in ST muscle per day (1.4 vs .8 g) were elevated (P less than .10) in lambs treated with CB compared to controls. These data suggest that the increased fractional accretion rate observed in lambs treated with CB for 28 d was caused by increased FSR.     

Ubiquitin gene expression and ubiquitin conjugation in chicken muscle do not reflect differences in growth rate between broiler and layer birds.

Previous work has shown that chicken strains selected for growth (broilers) degrade muscle proteins less rapidly than those selected for egg laying. They also have decreased calpain and increased calpastatin content in breast muscle. This study aimed to test the hypothesis that these differences correlate with changes in the ATP- and ubiquitin-dependent proteolytic system. Chickens of a broiler strain (Ross 1) and a layer strain (ISABrown) were reared to the age of 4 wk under identical conditions with ad libitum access to feed and water. Mean fractional growth rates were 10.4%/d for broilers and 7.4%/d for layers. Feed intake measured in the last week of the trial was slightly greater in layer birds (.11 and .12 g x g body weight(-1) x d(-1) for broilers and layers respectively; P < .006). Polyubiquitin (UbI) messenger RNA was abundant in the muscles of these well-fed birds, but it showed little difference between strains. Muscle did not significantly express the UbII polyubiquitin gene. The ATP-dependent system conjugating ubiquitin to endogenous proteins had greatest activity in the gastrocnemius muscle of broiler birds but was not significantly different between breeds. Proteins cross-reactive with antisera to recombinant human proteasome regulatory subunits MSS1 (multicopy suppressor of SUG 1; S7) and TBP1 (tat binding protein 1; S6') were present in muscle homogenates from both strains of bird. The chick equivalent of TBP1 was more abundant in breast muscle of broiler birds than in leg muscle, or in either muscle of layers. Antiserum to recombinant yeast subunit mts2 (mitosis temperature sensitive gene 2; S4) did not react with any protein of the expected size but detected a 30-kDa peptide that was not associated with the 26S proteasome; this was found only in muscle from the layer strain. Hence, during normal growth of chickens, rates of protein degradation are not controlled by the expression of ubiquitin mRNA or the conjugation of ubiquitin. However, the composition of the 26S proteasome may be a regulatory factor.     

Effects of dietary energy levels on Pectoralis major mixed muscle protein turnover and body composition in two broiler lines housed in different grow-out environments

This study determined the Pectoralis (P) major mixed muscle protein turnover (PT) in two meat broiler lines, Line A and Line B, during the finishing grow-out feeding period (21–42 days) as affected by the dietary metabolizable energy (ME) levels and ambient temperatures. Experimental finishing diets consisted of 80, 90, 100, 110 and 120% ME of recommended nutrient guidelines for energy level. Fractional synthesis rates (FSR) or fractional degradation rates (FDR) were measured in P. major at day 36 and 42. Protein and fat mass gain were measured, and respective energy retention efficiencies as protein and fat (EREp and EREf) were determined. Metabolic heat production (HP) was also reported. Experimental feeding studies were conducted in cool season (24 hr mean: 69.91˚F and 63.98% RH) and in hot season (24 hr mean: 77.55˚F and 86.04% RH). Results showed that FSR or FDR values were not affected by dietary ME levels at day 36, whereas reduced FSR (p < .05) were observed at day 42 fed diets with reduced ME levels (≤100% ME) which could have resulted from greater maintenance energy requirement of maturing broilers at that age. Broilers fed reduced ME diets (≤100% ME) maintained protein mass (equivalent to broilers fed ≥100%–120% ME) by reduced FDR and increased feed intake. Grow-out ambient temperature did not affect FSR or FDR values across ME levels. Line B retained higher protein mass, lower fat mass and greater HP compared to Line A. This was followed by higher feed intake in Line B. Further, Line B exhibited higher EREp and lower EREf across dietary ME levels. In summary, PT homeostasis and body composition changes in broiler lines studied seemed to be regulated by the birds’ intent to normalize energy intake as per physiological need by controlling feed intake.     

Relative responses of protein turnover in three different skeletal muscles to dietary lysine deficiency in chicks 1

1. The effect of lysine deficiency was analysed on muscle protein turnover in 2‐, 3‐ and 4‐week‐old growing broilers. Protein fractional synthesis rates (FSR, in %/d) were measured by a reliable in vivo technique (flooding dose of L‐[4‐³H] phenylalanine) in the Pectoralis major (PM), the Anterior latissimus dorsi (ALD) and the Sartorius (SART) muscles. Protein fractional breakdown rates (FBR, in %/d) were estimated as the difference between the synthesis rates and the growth rates of tissue protein.

2. Lysine deficiency resulted in significant increases in muscle FSR and FBR. When expressed in absolute rates (g/d), tissue protein deposition was reduced whatever the tissue. This phenomenon was accompanied by decreased protein synthesis (ASR).

3. The protein turnover responsiveness to the lysine deficiency appeared to depend on the studied muscle, since the PM muscle was the most sensitive whereas the SART and ALD muscles presented a lower sensitivity.     

Growth, food intake and energy balance of layer and broiler chickens offered glucose in the drinking water and the effect of dietary protein content

1. Four experiments were carried out to study the effect of offering a 91.5 g/l solution of glucose, compared to tap water, on fluid intake, food intake and growth of individually-caged immature chickens of both layer and broiler strains. 2. Male chicks of an egg-laying strain were offered glucose solution or tap water from 27 to 62 d after hatching. There was no effect of glucose on fluid intake but it depressed food intake (P less than 0.01) to give equal total energy intakes for each treatment. Body weight gain was reduced (P less than 0.001) and carcase fat content increased (P less than 0.001) by the glucose to yield no difference to total carcase energy. 3. When birds were placed in a respiration chamber for two 23-h periods there was no effect of treatment on outputs of energy as faeces + urine or as heat. 4. Male broilers were offered glucose solution or tap water with diets containing either 150 or 195 g protein/kg from 20 to 55 d after hatching. With the low-protein diet glucose depressed food intake (P less than 0.01) but total energy intake and carcase energy were not significantly affected. With the high-protein diet glucose did not depress food intake but increased total energy intake and total body fat. 5. Layer and broiler chicks were offered either a choice of the low- and high-protein diets or a single diet intermediate in protein content, with glucose solution or tap water. With broilers total food intake was depressed by glucose, mainly by a reduced intake of the low-protein diet. Intake of neither diet by the layer chicks was significantly affected by glucose. 6. It is concluded that provision of extra energy in glucose solution depresses food intake when the resultant energy:protein ratio becomes limiting. With a higher protein diet, or with birds having lower protein requirements, glucose solution does not depress food intake and increased fat deposition occurs.     

Efficacy evaluation of lasalocid plus roxarsone combination medication with different geographic field strains of Eimeria acervulina

Performance of broiler chickens medicated with lasalocid alone (at 125 ppm) or in combination with roxarsone (at 50 ppm) was evaluated in battery and floorpen trials after challenge with geographically different field strains of coccidia containing predominately the upper intestinal species Eimeria acervulina. No significant difference in bird performance measured at 6 days postinfection (PI) was observed between lasalocid plus roxarsone-medicated (L+RM) or lasalocid-medicated (LM) birds challenged in separate battery trials with mixed-species inocula from Alabama or Georgia containing 92% or 88% E. acervulina, respectively. In contrast, L+RM birds challenged in another battery trial with a Louisiana mixed-species inoculum containing 92% E. acervulina showed significant reduction in average weight gain at 6 days PI compared with LM-challenged birds. A floorpen trial done with the same Louisiana inoculum showed significant reduction in average bird weight gain at 27 and 35 days of age (6 and 14 days PI) for L+RM-challenged birds compared with both unmedicated-nonchallenged (UMNC) control and LM-challenged birds. The LM+R groups were significantly lower in average bird weight at 27 days of age than the unmedicated-challenged controls. Feed conversions (FCs) for L+RM birds were significantly higher than those for the UMNC control birds during time of challenge (21-27 days of age) and for the 1-to-27-day-of-age time period. No significant difference in FC was seen between the UMNC and LM groups. Results of this study showed that performance of broiler birds medicated with lasalocid plus roxarsone could vary for geographically different mixed-species challenge inocula that contained predominately E. acervulina.     

Variant serotypes of infectious bronchitis virus isolated from commercial layer and broiler chickens.

Twenty infectious bronchitis virus (IBV) field isolates obtained from commercial layer and broiler chickens in 1987 and 1988 were serotyped using the virus-neutralization (VN) test. Six different previously unrecognized variant serotypes were identified from a total of seven isolates from layer chickens. Only two isolates, both from Maine, were the same variant serotype. Variant serotypes also were recovered from layer flocks in Illinois and Washington and the province of Ontario, Canada. Two different variants were isolated from the same multi-age layer complex in Connecticut. Only one of 13 broiler chicken isolates was found to be a new variant serotype, that being from birds reared in Delaware. Cross-protection studies in specific-pathogen-free chickens indicated that vaccines containing the Holland, L-1, or Connaught strains of Massachusetts (Mass) combined with Arkansas produced a broader spectrum of immunity against challenge with the layer variants than Mass (Holland) alone or Mass (L-1) + Connecticut. All vaccines tested produced solid immunity (greater than or equal to 80% protection) against the broiler variant virus.     

Comparative efficacy of enrofloxacin, oxytetracycline, and sulfadimethoxine for the control of morbidity and mortality caused by Escherichia coli in broiler chickens

The purpose of the present study was to compare the ability of enrofloxacin, oxytetracycline, and sulfadimethoxine to reduce morbidity and mortality caused by Escherichia coli (colibacillosis) in broiler chickens. The chickens were raised in 80 pens (20 birds per pen) with 20 pens representing each treatment group under simulated commercial conditions that produced a colibacillosis challenge scenario. Each group of 20 randomized pens (replicates) was given one of four water treatments. Chickens that received enrofloxacin had significantly less mortality (P < 0.01), lower average gross pathology (colibacillosis) scores (P < 0.01), and better feed-conversion ratios (P < 0.05) than did chickens that received either oxytetracycline or no medication. Chickens that received enrofloxacin had significantly less mortality and lower pathology scores than those that received sulfadimethoxine and numerically lower feed conversion than the sulfadimethoxine group. Results from the present study show that enrofloxacin is superior to oxytetracycline and sulfadimethoxine for the control of morbidity and mortality caused by E. coli in broiler chickens. Our findings will help veterinarians choose and prescribe the most efficacious antimicrobial when treating colibacillosis.     

IGF-I receptors in embryonic skeletal muscle of three strains of chickens selected for differences in growth capacity.

IGF-I receptors in embryonic skeletal muscle from three strains of chickens have been characterized. Specific receptors for IGF-I were present in breast and thigh skeletal muscle of 13 d chicken embryos. Dissociation rate constants (Kd) for breast muscle of a slow growing layer strain (Leghorn), an intermediate growth strain (Synthetic Whiterock), and a fast growing broiler strain (Cornish) were 3.24, 3.04, and 2.68 nM, respectively. Kd for the thigh muscle of the slow, intermediate and fast growing strains were 3.30, 2.90 and 3.29 nM, respectively. Kd values were not significantly different between strains or between tissues (p greater than .05). Receptor concentration (Bmax) in breast muscle of slow, intermediate and fast growing strains were 1.22, 1.08 and 0.92 pM/mg protein, respectively. Receptor concentration in thigh muscle of the slow, intermediate and fast growing strains were 0.95, 0.76, and 0.79 pM/mg protein, respectively. Bmax values were significantly different (p less than .05) between breast muscle (1.08 +/- .05 pM/mg protein) and thigh muscle (.84 +/- .05 pM/mg protein). IGF-I receptor number for breast muscle although not statistically significant (p greater than .05), indicated a trend towards differences between the slow growing Leghorn strain and the faster growing Cornish strain. The results suggest that strains of birds with different growth capacity may have different densities of IGF-I receptors in breast skeletal muscle plasma membranes.     

Pathogenesis of rotavirus infection in various age groups of chickens and turkeys: clinical signs and virology

Age-related susceptibility patterns of turkeys, broilers, and specific pathogen-free (SPF) White Leghorn chickens to experimentally induced infection with turkey or chicken rotavirus isolates were compared. The following determinants were evaluated: clinical signs, onset and duration of virus production, viral titers, involvement of intestinal villi in the replication of the virus, and the development of antibodies against the virus. Older turkeys and chickens were more susceptible than were their younger counterparts, turkeys were more susceptible than were broiler and White Leghorn chickens (regardless of age), and broiler chickens were slightly more susceptible than were age-matched White Leghorn chickens. Turkeys developed diarrhea, accompanied by high viral titers within 1 day after inoculation with virus. Viral antigen was found in the epithelial cells of the intestinal villi throughout the intestinal tract and some cells of the cecal tonsils. Antibodies could be detected as early as 4 to 5 days after inoculation. These findings were more pronounced in turkeys inoculated at 112 days of age than in birds inoculated at a younger age. Age-related susceptibility patterns were similar in White Leghorn and broiler chickens. Infection was subclinical in birds less than 56 days old, whereas older birds developed soft feces. Egg production in the White Leghorn chickens decreased after being inoculated with virus at 350 days of age.     

L．fermentum1．2029对坏死性肠炎肉鸡回肠上皮紧密连接蛋白表达的影响

将240只AA肉鸡随机分为3个处理组：对照组、坏死性肠炎（Necrotic enteritis,NE）模型组及乳酸杆菌处理组。28日龄,每组屠宰24只鸡,对各组肉鸡肠道损伤进行肉眼评分,并采集回肠黏膜样本分别用于电镜下形态观察和Real—timePCR检测紧密连接蛋白claudin-1和occludin的表达。结果显示,乳酸杆菌处理组降低了炎症的损伤程度（P〈0．05）;电子显微镜观察显示,乳酸杆菌处理组鸡回肠上皮微绒毛较NE模型组有改善;real—timePCR分析显示,乳酸杆菌处理组claudin-1和occludin的表达显著高于NE模型组（P〈0．05）,但与对照组没有差异。该试验结果表明,L．fermentum1．2029可降低NE的损伤程度,并能有效上调NE条件下claudin-1和occludin的表达,显示其具有保护肠道屏障功能的作用。     

Postmortem proteolysis in longissimus muscle from beef, lamb and pork carcasses

Postmortem proteolysis in skeletal muscle and factors affecting this process were examined in pork, lamb and beef longissimus muscles (LM) to determine the cause of differences in meat tenderness among these species. Fat thickness differed among species in the following order: pork greater than beef greater than lamb. The following patterns were observed for rate of temperature and pH decline: lamb greater than pork greater than beef and pork greater than beef greater than lamb, respectively. At 1 d postmortem, pork was the most tender, followed by beef and lamb, respectively. Between 1 and 14 d of postmortem storage, lamb LM was the most improved in tenderness, followed by beef and pork, respectively. Species did not differ (P greater than .05) in LM collagen solubility. Pork LM from fed pigs had the highest (P less than .05) level of cathepsins B + L and cystatin(s) activities, whereas no differences (P greater than .05) were observed among the species for cathepsin B activity. The lowest (P less than .01) Ca2(+)-dependent protease (CDP)-II and CDP inhibitor activities were observed in pork LM. Beef LM had the highest CDP inhibitor activity (P less than .05) but was intermediate in CDP-II activity. No differences were observed among species for CDP-I activity. The sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of myofibrils isolated at 0, 1 and 14 d postmortem indicated that by d 1, desmin hydrolysis was most extensive in pork muscle, followed by lamb and beef.(ABSTRACT TRUNCATED AT 250 WORDS)