Protein and body weight accretion of chicks on diets with widely varying contents of soyabean meal supplemented or unsupplemented with its limiting amino acids

1. Two studies were conducted to evaluate the effects of relative deficiencies of methionine and threonine on the growth performance of 8- to 21-d-old chicks fed on isoenergetic diets containing a wide range of crude protein (CP) concentrations from dehulled soyabean meal (SBM). 2. Chicks fed on graded levels of SBM containing supplemental methionine and threonine (BAL) accreted whole-body protein more efficiently (P < 0.05) than those receiving graded levels of unsupplemented SBM (DEF), and superior (P < 0.05) growth performance was also obtained at lower CP levels when chicks were fed on the BAL diets. 3. Voluntary food intake increased between 30 and 220 g CP/kg in chicks fed on DEF diets, whereas food intake of chicks fed on BAL diets increased only between 30 and 100 g CP/kg, after which it decreased between 100 and 220 g CP/kg. 4. Protein efficiency ratio (g gain per g protein intake) decreased with each incremental increase in CP between 30 and 260 g CP/kg, regardless of whether diets were BAL or DEE 5. These data indicate that maintaining a balanced ratio of amino acids is a preferable approach when poultry producers are interested in employing low CP diets for economic, physiological or environmental reasons.     

Dietary thyroid hormone improves growth and muscle protein accumulation of black-boned chickens

1. The objective of the study was to examine the effect of dietary thyroid hormone on performance and muscle protein accumulation of black-boned chickens. 2. A total of 720 1-d-old birds was housed in 24 pens and assigned to 4 diets containing triiodothyronine (T3) at 0, 0.1, 0.3 or 0.5 mg/kg. 3. The trial was split into starter (0 to 4 weeks) and grower (5 to 8 weeks) phases. At the beginning of the grower phase, each pen was split into two; one subgroup was fed basal diet (T3-) and the other continued with T3-added diet (T3+). 4. Dietary T3 at 0.1 mg/kg improved average daily body weight gain until week 6 but retarded it thereafter. However, T3 at 0.5 mg/kg depressed growth throughout the whole period. During weeks 7 to 8, T3 retarded growth, whereas growth recovered when T3 was withdrawn from the diet. 5. Birds fed the diet containing 0.1 mg/kg during weeks 0 to 4 and those receiving basal diet during weeks 5 to 8 showed the greatest thigh muscle growth, but this growth was depressed when they were fed the 0.5 mg/kg diet during weeks 0 to 8. 6. Serum T3 concentration was increased, while thyroxine (T4) concentration was decreased by dietary T3 treatment at 2 weeks old. At 4 weeks old, T3 and T4 concentrations decreased. At 6 and 8 weeks old, among T3-treated groups the serum T3 concentration of the T3- group was higher than that of the T3+ group. 7. In conclusion, dietary T3 improved weight gain and muscle growth of black-boned chickens before week 6, whereas supplementation depressed growth after 6 weeks. Optimum dietary T3 concentrations showed a carry-over effect on both body weight gain and thigh muscle growth.     

Effects of protein concentration on responses to dietary lysine by chicks

Chicks were fed on diets varying in crude protein (CP) content (140 to 280 g/kg diet) in either 8 steps, experiment 1, or 6 steps, experiment 2. Protein composition was held constant in each experiment. At each protein concentration, 5 (experiment 1) or 6 (experiment 2) concentrations of lysine were tested, ranging from 40 to 60 g/kg CP. Growth rate and efficiency of food utilisation to 21 d of age responded to increasing dietary protein contents up to about 230 g CP/kg. An estimate of lysine requirement at each protein concentration was obtained by fitting a quadratic curve to the response data and calculating the dose of lysine (g/kg CP) needed to maximise either growth rate or gain/food ratio. Although no growth response to dietary protein was obtained between 240 and 280 g CP/kg, the amount of lysine needed to maximise growth and gain/food ratio over this range increased systematically when expressed as g/kg diet, but remained constant if expressed as g/kg CP. The regression of lysine required (g/kg diet) for maximum performance (growth or food efficiency) on CP (g/kg diet) was strictly linear for both responses in both experiments throughout the entire range studied (140 g CP/kg to 280 g CP/kg). The estimated lysine requirement was 0.053 of the CP in experiment 1 and 0.055 of the CP in experiment 2. It is concluded that a fixed ratio of lysine to protein should be specified in practical diet formulation, rather than a minimum dietary concentration of lysine. This would ensure that, if the dietary protein content rises above a prescribed minimum value in least-cost formulation, an appropriate adjustment will automatically be made to the lysine content of the solution.     

Feed intake and weight gain of growing goats fed diets of various energy and protein levels

Growing goats, 45 Alpine and 45 Nubian, were used in a 3 x 3 factorial arrangement to quantify the influence of dietary energy and protein levels on daily DM intake and nutrient utilization for growth. Goats had ad libitum access to complete mixed diets containing either 2.46, 2.77 or 3.05 Mcal/kg ME plus 11.2, 12.7 or 15.1% CP for 16 wk. Dry matter intake decreased curvilinearly as dietary ME density increased (P less than .001). Dry matter intake increased linearly (P less than .05) as dietary CP level increased during all growth intervals except wk 25 to 28 of age. Average daily gain was 115, 113 and 99 g/d for goats fed diets containing 2.46, 2.77 and 3.05 Mcal/kg ME, respectively. Average daily gain was 104, 106 and 117 g/d for goats fed diets with 11.2, 12.7 and 15.1% CP, respectively. Dry matter intake was higher (P less than .01) for Alpine than for Nubian goats, whereas ADG was similar between breeds. Intake of ME was 248, 260 and 198 kcal/(kg.75.d) for goats fed the low- medium- and high-energy diets, respectively. Intake of CP was 9.1, 10.7 and 13.2 g/(kg.75.d) for goats fed low-, medium- and high-protein diets, respectively. Average requirements for growth derived from regression analysis of all data points were 4.6 kcal ME and .26 g CP/g ADG. The prediction equation for intake of growing goats of 4 to 8 mo of age was: DMI, g/d = 1,749 - 496 DE, kcal/g + 18 live weight, kg + 3 ADG, g/d; r2 = .73 (Sy.x = 127, P less than .0001, n = 90). The requirement of ME for growth was 33% lower than the value recommended in 1981 by the National Research Council.     

Effect of dietary protein content on episodic growth hormone secretion and on heat production of male broiler chickens.

1. The effect of the crude protein content (200 and 150 g/kg) of isoenergetic diets on episodic growth hormone (GH) release and on heat production was investigated in male broiler chickens. 2. Decreasing the crude protein content of isoenergetic diets from 200 g/kg (HP diet) to 150 g/kg (LP diet) resulted in depressed body weight gain, impaired food conversion efficiency and increased abdominal fat deposition. 3. The pattern of growth hormone secretion was markedly affected by dietary treatment. Broiler chickens fed on the LP diet had higher overall mean, amplitude, baseline and peak frequency than the HP chickens. 4. The LP chickens produced more heat per unit of metabolic body weight than the HP chickens. 5. The hypothesis relating the pattern of GH secretion to protein conversion efficiency was corroborated.     

Effects of dietary threonine and crude protein on growth performance, carcase and meat composition of broiler chickens

1. The aim of the study was to investigate the effects of dietary threonine (Thr) and crude protein (CP) in maize-soybean meal based diets on the growth performance, carcase traits and meat composition of broiler chickens and to determine the dietary Thr requirement for optimum performance (weight gain and feed conversion efficiency (FCE)) at 0 to 3 weeks and 3 to 6 weeks of age. 2. Two basal diets that differed in CP (191.3 or 179.7 and 176.7 or 165.4 g/kg at 0 to 3 and 3 to 6 weeks, respectively) were formulated to have identical contents of Thr (6.0 and 5.4 g/kg), energy (12.97 and 13.39 MJ ME/kg) and other essential amino acids except for Gly + Ser. Basal diets were supplemented with L-Thr from 0.6 to 1.8 g/kg in 0.6 g/kg increments. Broiler chicks (540) were randomly allocated to 9 dietary treatments with 6 replicates of 10 (5 female, 5 male) chicks. 3. A significant interaction between dietary CP and Thr was found for feed intake, body weight (BW) gain and FCE. Increasing Thr supplementation improved feed intake, BW gain and FCE, especially in high CP diets in both feeding periods. 4. Incremental increases in dietary Thr increased breast yield at both CP levels and drumstick yield only on high CP diets. The proportion of thigh decreased with Thr concentration. Liver weight was significantly reduced by Thr supplementation; abdominal fat was not affected. 5. Estimated Thr requirements for FCE increased as dietary CP increased according to an exponential model. This model indicated higher Thr requirements than those of broken-line models for growth performance.     

Increasing dietary crude protein does not increase the methionine requirement in kittens

The objective of this study was to determine if the methionine (met) requirement of kittens is correlated with the concentration of dietary crude protein (CP). The study used 48 male kittens in two replications of six 4 x 4 Latin squares, each representing one concentration of met (1.5, 2.5, 3.5, 4.5, 6.0 or 9.0 g/kg diet) with four CP concentrations (150, 200, 300 and 500 g/kg diet) in 2-week periods. Cystine was present in the lowest CP diet at 5.3 g/kg diet and increased as dietary CP increased. Body weight gain, food intake, nitrogen balance and plasma amino acids, glucose, insulin, cortisol, somatomedin C, T(3) and T(4) concentrations on day 12 were measured. From breakpoint analysis of the nitrogen retention curves, the met requirement of kittens was found to be 3.1, 3.8, 3.1 and 2.4 g met/kg for the 150, 200, 300 and 500 g CP/kg diets, respectively. When met was limiting (1.5 or 2.5 g/kg diet), increasing dietary CP did not decrease, but rather increased food intake, body weight gain and nitrogen retention. Plasma met concentrations increased as dietary met increased and at 2.5-3.5 g met/kg diet were not different among kittens fed the various CP diets. Total plasma T(3) and T(4) increased significantly as dietary CP increased in kittens given the 2.5 and 4.5 g met/kg diets. Results indicate that food intake and possibly altered hormonal secretion play a role in this growth response. In conclusion, the met requirement of growing kittens, unlike omnivores and herbivores studied, was not positively correlated with the concentration of dietary CP.     

Effects of sex and protein and energy levels in the diet on the blood parameters of the chukar partridge (Alectoris chukar)

1. The effects of sex and dietary composition were investigated in 48 male and 48 female 16-week old chukar partridges. 2. Sixteen starter and 16 grower diets were arranged in a 4 x 4 factorial design with 4 concentration of crude protein (CP) and 4 concentration of metabolizable energy (ME). 3. Blood samples were collected at 16 weeks of age and analysed for total protein, triglycerides, uric acid, total cholesterol, glucose, calcium, phosphorus, sodium, potassium and chlorine. 4. There were no significant effects of sex on the measured parameters. 5. Serum total protein was highest in partridges fed on a diet containing 200/175 g CP/kg (starter grower). Serum cholesterol concentrations of partridge fed the diet with 240/200 or 280/225 g CP/kg were significantly higher than that for partridge fed diets containing a lower gCP/kg. 6. Serum total protein and glucose levels significantly decreased as dietary energy level was increased. Serum triglycerides and calcium were highest in partridge fed on the diets containing 13.39/13.81 and 11.71/12.55 ME MJ/kg, respectively. Serum phosphorus and chloride levels were highest in partridges given the diet containing 10.88/11.92 ME MJ/kg. 7. There were significant interactions between the effects of CP and ME on serum triglycerides, sodium and potassium levels. 8 The results of this study suggested that dietary CP, and especially ME concentration, significantly affect blood parameters in chukar partridge.     

The effects of dietary protein independent of essential amino acids on growth and body composition in genetically lean and fat chickens

1. Growth performance between 28 and 49 d of age and carcase composition at 49 d in genetically lean (LL) and fat (FL) broilers fed on diets varying in non-essential amino acid (NEAA) concentrations were compared in 2 experiments. In experiment 1, 3 crude protein (CP) contents (133, 155, and 178 g/kg) were compared. In experiment 2, 4 CP levels (131, 150, 170 and 189 g/kg) were compared. All diets were supplemented with synthetic amino acids to cover the EAA requirement of the LL birds. 2. Weight gains of FL chickens were not affected by dietary treatments, while those of LL increased when CP level increased. 3. Reducing CP content always increased body lipids, abdominal fat and food conversion ratio in both lines in both experiments; however, the effect on abdominal fat was more pronounced in the FL birds. 4. Reducing CP concentration always decreased breast muscle proportion in both lines in both experiments, even when growth rate was not affected by CP. 5. It is concluded that LL chickens require diets more concentrated in NEAA than fat chickens and that there seems to be an effect of NEAA on breast muscle development.     

Histological alterations of the intestinal villi and epithelial cells in chickens fed dietary sugar cane extract

1. Sugar cane extract (SCE) is the residue after removing glucose, fructose and sucrose from sugar cane juice. To investigate the effects of dietary SCE on growth performance and alterations to intestinal histology, 36 male Sanuki Cochin chickens were divided into three groups: a control group was fed a commercial diet (180 g/kg CP, 13.59 MJ/kg ME) and the treatment groups were fed the commercial diet supplemented with 0.5 or 10 g/kg SCE ad libitum for 35 d. 2. Feed intake and weight gain tended to be higher in the 0.5 and 10 g/kg SCE groups than in the control group. No specific gross morphological alterations were observed in the visceral organs of chickens in any of the groups. However, intestinal villus height, villus area, epithelial cell area and cell mitosis in each intestinal segment had higher values in the SCE groups than in the control group. In the 0.5 and 10 g/kg SCE groups, but not in the control group, the cells on the villus apical surface protuberated and had larger cell clusters and some areas with cells with no microvilli. 3. The observed alterations to intestinal histology in chickens fed dietary SCE diets demonstrate that the function of villi and cells on the villus tip might be activated in all the intestinal segments and that cell turnover is also accelerated. These activated intestinal functions appear to promote growth and immuno-stimulation in chickens fed SCE diets, especially in the 0.5 g/kg group.     

Effects of dietary protein and energy concentrations on performance and carcase characteristics of chukar partridge (Alectoris chukar) raised in captivity

1. This study was conducted to determine the effects of starter and grower diets with differing crude protein (CP) and metabolisable energy (ME) concentrations on the body weight (BW), live weight gain (LWG), feed consumption (FC), feed conversion ratio (FCR), and carcase, breast+back, rump, wing, neck and abdominal fat weights of chukar partridge raised in captivity. 2. Chukar partridges were fed on starter diets containing 4 concentrations of CP (160, 200, 240, 280 g/kg) and 4 concentrations of ME (10.9, 11.7, 12.6, 13.4 MJ/kg) from hatch to 8 weeks of age; they were fed on grower diets containing 4 concentrations of CP (150, 175, 200, 225 g/kg) and 4 concentrations of ME (11.9, 12.6, 13.2, 13.8 MJ/kg) from 9 to 16 weeks of age. All diets contained at least 5.5 g/kg methionine, 15 g/kg lysine and 10 g/kg methionine+cystine. Sixteen starter and 16 grower diets were arranged in a 4 x 4 factorial design with 4 levels of CP and 4 levels of ME. Each treatment was replicated three times with each replicate consisting of 5 males and 5 females. 3. Partridges fed on a starter diet containing 160 g CP/kg were significantly lighter at 8 weeks of age than those in groups given diets containing a higher CP. However, at 16 weeks of age, the differences in BW among treatments had disappeared. Throughout, there were no significant effects of ME concentration on BW and LWG. 4. The daily mean FC for the 0 to 8 week and 0 to 16 week periods was not affected by dietary CP concentration. For the 9 to 16 week period, the partridges fed on a grower diet containing 225 g CP/kg consumed more feed than those given a diet containing 175 g CP/kg. 5. The highest FCR for the 0 to 8 week period was in partridges fed on a starter diet containing 160 g CP/kg. For the 9 to 16 week period, the lowest FCR was in partridges fed on a grower diet containing 150 g CP/kg. For the 0 to 16 week period, there was not a significant effect of dietary CP concentration on FCR. The daily mean FC and the FCR for the 0 to 8, 9 to 16 and 0 to 16 week periods decreased when the ME concentration of the starter and grower diets increased. 6. The carcase, rump and breast+back weights of the male partridges increased when the ME content of the diets increased. Weights of all carcase components of the male partridges were significantly greater than those of the carcase components of the females. 7. There were no significant interactions between CP and ME concentrations on BW, LWG, FC, FCR and carcase characteristics. 8. We conclude that the starter diet for chukar partridges raised for meat production should contain at least 200 g CP/kg, 11.7 MJ ME/kg, and the grower diet should contain 150 g CP/kg, 12.6 MJ ME/kg.     

Further investigations on protein requirement of genetically lean and fat chickens

1. Genetically lean (LL) or fat (FL) chickens were fed from 28 to 42 d of age on one of 6 diets with different protein contents (from 73 to 208 g/kg). In order to keep a constant amino acid balance the experimental diets were made by diluting a well-balanced protein-rich diet with a protein-free diet. 2. Dietary protein influenced the growth rate of both genotypes similarly. However, maximum weight gain was reached in LL at a lower protein intake than in FL. 3. Regression between total protein gain (body protein + feather protein) or body protein gain and protein intake exhibited significantly different slopes, that of LL being superior to that of FL. 4. At a given protein intake, feather protein gain was also superior in LL to FL. Moreover feather protein, as a percentage of total protein gain, was superior in LL to FL. When the dietary protein fell below 126 g/kg, feather protein represented a higher proportion of total protein gain. 5. Multiple linear regressions of protein intake (as the dependent variable), and body weight and protein gain or weight gain (as the independent variables) suggest that the maintenance requirement for protein is similar in both lines but that the protein efficiency for growth is significantly superior in LL. 6. In a second experiment both genotypes were offered either a single high protein diet (232 g/kg) or a single medium protein diet (186 g/kg) or had free-choice between a high (269 g/kg) and a low protein (145 g/kg) diet. In free-choice feeding, FL chickens selected an overall dietary protein content which was significantly lower (179 v. 200 g/kg) to that of LL. In both genotypes, free-choice feeding led to fatter and less efficient chickens than predicted by the linear regression between adiposity or food conversion and protein content.     

Influence of dietary protein level, amino acid supplementation, and dietary energy levels on growing-finishing pig performance and carcass composition

Two experiments were conducted to determine the effects of feeding reduced-CP, AA-supplemented diets at two ambient temperatures (Exp. 1) or three levels of dietary NE (Exp. 2) on pig performance and carcass composition. In Exp. 1, 240 mixed-sex pigs were used to test whether projected differences in heat increment associated with diet composition affect pig performance. There were 10 replications of each treatment with four pigs per pen. For the 28-d trial, average initial and final BW were 28.7 kg and 47.5 kg, respectively. Pigs were maintained in a thermoneutral (23 degrees C) or heat-stressed (33 degrees C) environment and fed a 16% CP diet, a 12% CP diet, or a 12% CP diet supplemented with crystalline Lys, Trp, and Thr (on an as-fed basis). Pigs gained at similar rates when fed the 16% CP diet or the 12% CP diet supplemented with Lys, Trp, and Thr (P > 0.10). Pigs fed the 12% CP, AA-supplemented diet had a gain:feed similar to pigs fed the 16% CP diet when housed in the 23 degrees C environment but had a lower gain:feed in the 33 degrees C environment (diet x temperature, P < 0.01). In Exp. 2, 702 gilts were allotted to six treatments with nine replicates per treatment. Average initial and final BW were 25.3 and 109.7 kg, respectively. Gilts were fed two levels of CP (high CP with minimal crystalline AA supplementation or low CP with supplementation of Lys, Trp, Thr, and Met) and three levels of NE (high, medium, or low) in a 2 x 3 factorial arrangement. A four-phase feeding program was used, with diets containing apparent digestible Lys levels of 0.96, 0.75, 0.60, and 0.48% switched at a pig BW of 41.0, 58.8, and 82.3 kg, respectively. Pigs fed the low-CP, AA-supplemented diets had rates of growth and feed intake similar to pigs fed the high-CP diets. Dietary NE interacted with CP level for gain:feed (P < 0.06). A decrease in dietary NE from the highest NE level decreased gain:feed in pigs fed the high-CP diet; however, gain:feed declined in pigs fed the low-CP, AA-supplemented diet only when dietary NE was decreased to the lowest level. There was a slight reduction in longissimus area in pigs fed the low-CP diets (P < 0.08), but other estimates of carcass muscle did not differ (P > 0.10). These data suggest that pigs fed low-CP, AA-supplemented diets have performance and carcass characteristics similar to pigs fed higher levels of CP and that alterations in dietary NE do not have a discernible effect on pig performance or carcass composition.     

Nitrogen utilization by ruminants during restricted intake of high-concentrate diets

A series of experiments was conducted to determine the effects of limit-feeding high-concentrate (LFHC) diets on dietary CP requirements of steer calves. When steer calves were fed 80% concentrate diets at 78 g/kg of BW.75, increasing dietary CP resulted in increased ADG (P less than .001). Average daily gain was increased in steers as daily monensin dosage increased from 120 to 180 mg (P less than .05). Increasing the daily monensin dosage to 240 mg did not increase ADG further. There were no (P greater than .10) CP X monensin interactions, suggesting that the monensin response was caused by improved energy utilization and not be the possible protein-sparing effects of ionophores. Steer calves in the second feedyard experiment expressed similar ADG when provided equal NEg as limit-fed, high-moisture ear corn (HMEC) or when given ad libitum access to corn silage. The basal diet did not affect the steers' daily N requirement for growth. Gain per unit of protein intake declined quadratically (P less than .05) with increasing CP intake, indicating that CP requirements were near NRC estimates on both diets. The corn silage-based diet was less digestible (70.3 vs 77.4%; P less than .01) than the HMEC diet when fed to lambs. Fecal output differed (P less than .10) substantially (342 g/d of corn silage vs 205 g/d of HMEC), whereas fecal N output was only slightly higher (6.97 vs 6.34 g/d, respectively; P less than .10). Limited feeding of higher-concentrate diets to steer calves seemed to be an effective management procedure and did not cause acute digestion upset.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of the ratio of essential to non essential amino acids on performance and carcase composition of the broiler chick

Male broilers were fed on isocaloric diets containing 140, 180 or 220 g/kg crude protein from 1 to 3 weeks of age. Four diets were formulated for each protein concentration so that essential amino acids (EAA), all balanced in proportion to requirement, supplied 350, 450, 550 or 650 g/kg crude protein. Weight gain, efficiency of food utilisation and total carcase protein reached plateaux at 550 g EAA/kg protein irrespective of the dietary protein content, whereas the proportion of carcase fat decreased and that of carcase protein increased as the proportion of EAA in the dietary protein increased. All EAA in the diet containing 550 g EAA/kg protein were supplied at 125% of requirement, suggesting that the amino acid requirements as reported are inaccurate. Weight gain and carcase protein were shown to be significantly (P less than 0.001) dependent on total intake of EAA rather than on the proportion of EAA in the diet per se. In order to supply sufficient EAA for maximum gains, the diet had to contain more than 140 g crude protein/kg and 450 g EAA/kg protein.     

Evaluation of standardized ileal digestible lysine requirement for 8–20 kg pigs fed low crude protein diets

Two experiments were conducted to determine the standardized ileal digestible lysine (SID Lys) requirement for weaned pigs fed with low crude protein (CP) diet. In Experiment 1, 144 pigs were fed a normal CP (20%) diet with 12.3 g/kg SID Lys and five low CP (18.5%) diets providing SID Lys levels of 9.8, 11.1, 12.3, 13.5, and 14.8 g/kg, respectively, for 28 days. Reducing dietary CP from 20% to 18.5% enhanced (p < 0.05) the growth performance. The average daily gain (ADG) and gain to feed ratio (G:F) increased (linear and quadratic; p < 0.05), serum urea nitrogen (SUN) decreased (linear and quadratic; p < 0.05) as SID Lys increased. The SID Lys levels required to maximize ADG and optimize G:F were 12.8 and 13.1 g/kg using a curvilinear plateau model, and to minimize SUN was 13.4 g/kg using a two‐slope broken‐line model, which averaged 13.1 g/kg SID Lys. In Experiment 2, 18 pigs were used in a 12‐day N balance trial and received the same diets of Experiment 1. Total N excretion was decreased when dietary CP reduced and further decreased when SID Lys increased. Collectively, 1.5% dietary CP reduction improved the growth performance and decreased the N excretion; the optimal SID Lys requirement was at 13.1 g/kg of 8–20 kg pigs fed with 18.5% CP diet.     

Blood proteins and amino acids of female breeder turkeys fed on maize-soybean diets supplemented with methionine

Two hundred and six female breeder turkeys were fed on maize-soybean diets of equal energy content, containing 100, 120 or 140 g crude protein (CP)/kg to which DL-methionine was added at 0, 1, 2 or 3 g/kg diet in a factorial design. Serum albumin concentrations were found to be more sensitive measures of dietary protein adequacy than were total serum protein concentrations. Albumin concentrations at peak egg production were highest among birds fed on 120 and 140 g CP/kg diets. Four weeks later, they were highest only for those on the 140 g CP/kg diet. The elevated concentrations of blood threonine and lysine and the decreased concentration of glycine with increased dietary protein were in agreement with the data on egg production. These data suggested that a sub-optimal balance of dietary amino acids may have occurred.     

Responses to an estrogenic growth promoter in beef steers fed varying nutritional regimens

We investigated the influence of DM and(or) energy intake and dietary CP levels on the performance and nitrogen (N) retention of beef steers with and without growth promoter implants. In Exp. 1, four implanted (Synovex-S, 200 mg of progesterone plus 20 mg of estradiol benzoate) Angus steers and four Angus steers that were not implanted were assigned to concurrent 4 x 4 Latin squares. Initial BW averaged 296 kg. Each square consisted of moderate and moderately high DM intake treatments (4 and 6 kg/d) and low and adequate CP intake treatments (450 and 600 g/d) in a 2 x 2 factorial arrangement. Periods were 2 wk of adaptation, 5 wk of growth, and 1 wk of balance collection. Experiment 2 consisted of two replicates of 32 Hereford steers each (initial BW 324 kg). Each replicate was a 4 x 2 factorial in which steers were individually fed for 63 d. All steers had ad libitum access to a 60% corn-based concentrate diet containing either 7.9, 10.0, 12.1, or 14.6% CP (DM basis), and steers were either implanted or not implanted with Synovex-S. Experiment 3 was similar to Exp. 2 except that all steers (initial BW 315 kg) received a low-protein diet (7.6% CP) with calculated energy densities of either 1.86, 2.04, 2.22, or 2.42 Mcal ME/kg DM, and steers were limited to an equalized DM intake of 9.5 kg daily. In Exp. 1, gains for the low CP, moderate and moderately high DM intakes and the adequate CP, moderate and moderately high DM intakes were 240, 555, 208, and 730 g/d, respectively, for steers not implanted and 333, 643, 488, and 988 g/d, respectively, for implanted steers (SEM = 102 g/d). Respective values for retained N were .13, .18, .16, and .26 g/kg BW.75 and .13, .15, .22, and .29 g/kg BW.75 (SEM = .04 g/kg BW.75). Implant response was greater (CP x implant, P < .01) for both gain and retained N when adequate CP compared to low CP diets were fed. For Exp. 2, the lowest CP diet reduced ADG (.97 vs 1.27 kg/d) and efficiency of gain (100 vs 120 g gain/kg DM). Synovex-S was less effective in improving efficiency for the lowest protein diet than for the other diets (11.7 vs 20.2%). During Exp. 3, neither Synovex-S nor dietary energy influenced gain and efficiency. We concluded that adequate dietary protein is necessary to optimize the response to estrogenic growth promoters and that the low response under inadequate protein and energy intake is not improved by increasing the energy density of the diet.     

Protective effect of clenbuterol on duodenal epithelium during food restriction in rats

The aim of the study was to examine the effect of the beta2-adrenoceptor, clenbuterol, on the duodenal epithelium of food-restricted rats. Clenbuterol was administered as a dietary admixture (4 mg/kg diet) to three groups of male Wistar rats (n = 8) housed individually in metabolic cages and fed ad libitum for 15 days at 110% and 160% of the estimated requirement for energy maintenance. Untreated groups at each energy intake level were also included. Samples of the duodenum were examined by light microscopy. Compared with control animals, clenbuterol treatment significantly increased body mass in all diet groups, although it induced no changes in mean food intake. Gastrointestinal (GIT) dry mass was increased by clenbuterol only in the most severely-restricted-diet group. In this group, clenbuterol treatment increased GIT tissue nitrogen (23%), more than it did in the ad libitum group (13%). In all treated groups, clenbuterol induced significant hypertrophy of duodenal enterocytes and circular muscle layers, and the diameter of lymphatic vessels increased. In the clenbuterol-treated, restricted-diet groups the height of the brush borders of enterocytes increased. It is concluded that clenbuterol has a protective effect on the intestinal structure in rats on restricted as well as ad libitum diets.     

低蛋白质补充合成氨基酸日粮对9～16周龄宁都三黄鸡生长性能和胴体品质的影响

本研究旨在探讨蛋能比保持一定的情况下,低蛋白质补充前3种限制性氨基酸日粮对9～16周龄宁都三黄鸡生长性能和胴体品质的影响。试验选用160羽体重为(573.1±11.0)g的9周龄健康宁都三黄母鸡,随机分为4个处理,每个处理4重复,每个重复10羽鸡。处理Ⅰ组(对照组)为玉米-豆粕型日粮,按照我国黄羽肉鸡饲养标准(2004)进行配制,其中代谢能为13.3 MJ/kg、蛋白质含量为16.5%(蛋白质/代谢能=12.3 g/MJ)。处理Ⅱ、Ⅲ、Ⅳ组(试验组)日粮蛋能比与处理Ⅰ组一致,代谢能分别为12.6、11.8、11.0 MJ/kg,蛋白质含量分别为15.5%、14.5%、13.5%。4组日粮均补充了蛋氨酸、赖氨酸和苏氨酸以满足三黄鸡对其需要。结果表明:(1)日粮蛋白质水平由16.5%降至14.5%,9～16周龄宁都三黄鸡日采食量、日增重和料重比无显著影响(P>0.05);当蛋白质降幅达3个百分点时,尽管补充了蛋氨酸、赖氨酸和苏氨酸,但宁都三黄鸡的生长性能受到显著影响(P<0.05);(2)日粮蛋白质水平降低3个百分点,宁都三黄鸡全净膛率显著升高(P<0.05),但对屠宰率、半净膛率、胸肌率及腿肌率影响不显著(P>0.05);(3)日粮蛋白质水平降低2个百分点及以上同时补充蛋氨酸、赖氨酸和苏氨酸时,宁都三黄鸡的腹脂率显著降低(P<0.05)。综合生长性能和胴体品质指标,在补充前3种限制性氨基酸的情况下,宁都三黄鸡日粮蛋白质降低的幅度不应超过2个百分点。