Controlled early feed restriction as a potential means of reducing the incidence of ascites in broilers.

Male broiler chicks were grown at cold temperatures to enhance susceptibility to the ascites syndrome. Various feeding regimens were used to determine whether they could influence mortality due to ascites. It was found that a precisely controlled early feed-restriction regimen at the age of 6 to 11 days significantly reduced mortality from all causes and mortality due to ascites, while maintaining optimum body weight and feed conversion at marketing age.

Moderate excess of dietary protein increases breast meat yield of broiler chicks.

Two factorial experiments were carried out to evaluate the effects of dietary protein level, expressed as energy to protein (E:P) ratio, on yields of carcass and breast and on abdominal fat pad weight of male broiler chicks at 43 and 57 d of age. Two diets similar in their energy content and differing markedly in their protein content, in which the E:P ratios were lower and identical to the NRC (1994) recommendations, were used in Experiment 1. Four diets, the combination of two energy and two protein levels, in which the E:P ratios were lower and identical to the recommendations, were used in Experiment 2. There were no differences in feed intake or weight gain until 42 d of age between broilers fed the diets with the low and those fed the recommended E:P ratio. However, feed efficiency of the former was consistently and significantly (P < 0.05) higher. The high-energy diets did not affect feed intake but significantly improved weight gain between 7 and 28 d of age and feed efficiency until 42 d of age. In both experiments, carcass yield was not affected by dietary E:P ratio at 43 d of age; however, at 57 d of age it was increased significantly by the low E:P ratio in Experiment 1 and in birds fed the high energy diet in Experiment 2. On a factorial basis, the effect of the low E:P ratio on increasing yield was significant only in Experiment 1. The high dietary energy level increased carcass yield only at 43 d of age, but on a factorial basis its effect was significant. Carcass yield was significantly (P < 0.001) higher at 57 than at 43 d of age. In both experiments, breast meat yield was negatively correlated with dietary E:P ratio, a significant factorial effect. The difference in this variable between broilers fed the diets containing the low and the recommended E:P ratio was significant, at both ages in Experiment 1, and only at 57 d of age in Experiment 2. Breast meat yield was not affected by dietary energy level, and it was significantly (P < 0.001) higher at 57 than at 43 d of age. Relative abdominal fat pad weight was increased significantly by increasing dietary E:P ratio. Dietary energy level and age did not affect this variable. The relationship between abdominal fat pad weight and breast meat yield within the treatments tended (in most of the cases not significantly) to be negative. However, this negative relationship was significant, at both ages, when the analysis was carried out with the pooled data at each age. It is concluded that the optimal E:P ratio for maximal breast meat yield for broiler chicks, particularly at 57 d of age, may be below the NRC (1994) recommendations.

Research notes: Effect of environmental temperature on broiler chickens subjected to growth restriction at an early age.

An experiment was carried out to evaluate the effect of early growth restriction (EGR) induced by feed restriction on the ability of male broiler chickens to withstand exposure to high environmental temperatures. A 2 x 4 factorial arrangement of treatments was employed to determine whether such an exposure affects the beneficial effect of EGR on performance and carcass quality. Chicks consumed feed ad libitum or were feed-restricted from 6 to 12 d of age (to achieve 60% growth of the ad libitum birds). From 4 to 8 wk of age, the chickens were kept in temperature-controlled chambers at 25, 30, 35 C and a diurnal cyclic temperature of 25:35 C. Weight gain, feed intake, and feed efficiency from 6 to 8 wk of age (after acclimatization to the various temperatures) and BW at 8 wk of age were significantly (P < or = 0.05) depressed by the high temperatures (35 and 25:35 C) compared with values observed at 25 and 30 C. Early growth restriction did not affect these variables. Relative heart, liver, and breast meat weights at 8 wk of age were decreased significantly with increasing temperature. Relative liver weight was also decreased significantly in the EGR chicks, whereas breast yield was increased significantly in these birds. Relative abdominal fat pad size was not affected by increasing the temperature from 25 to 35 C, but it was significantly lower in chickens kept at 25:35 C than in those kept at 25 and 35 C. Early growth restriction significantly reduced the size of abdominal fat. Because no significant interactions between EGR and ambient temperature on the above mentioned variables were observed during 4 to 8 wk of age, it is concluded that EGR can not alleviate the adverse effect of high ambient temperature on performance, nor can high ambient temperature obliterate the beneficial effect of EGR in improving feed efficiency and reducing fattening.

Early feed restriction in chicks: effect of age, duration, and sex.

Several regimens of feed restriction, calculated to support the maintenance of body weight without any allowance for growth, were applied beginning at the ages of 3 to 11 days for periods of 3 to 7 days using male and female broilers. In males, the 7-day feed restriction treatment resulted in improved feed efficiency on an age basis, or on a body weight basis after body weight had reached .7 to 1 kg. Feed restriction also resulted in a reduction in the amount of abdominal fat at the age of 54 to 59 days without any concomitant reduction in body weight. Within the range tested, 3 to 11 days of age, the initiation of the 7-day restriction treatment did not affect response. Similar responses were obtained in females, but with little benefit in feed efficiency when compared with ad libitum-fed birds on a body-weight basis. Also in females, reduction in 56-day body weight and loss of benefits derived from improved feed efficiency and reduced carcass fat could be avoided if the period of restriction was kept at 3 to 5 days.

Severe feed restriction in pullets during the early growing period: performance and relationships among age, body weight, and egg weight at the onset of production.

The performance of egg type (Leghorn x Rhode Island Red) chickens that were feed restricted during the prelaying period was studied in two trials, each conducted with 300 hens. In Trial 1, treatments included 1) an ad libitum-fed control; 2) restriction for close to zero growth between 7 and 28 days of age; 3) the same restriction as (2) but continued by restriction of 50% growth up to 70 days; 4) restriction between 7 and 70 days for 50% growth; and 5) restriction for 50% growth between 7 and 98 days. In Trial 2, birds were restricted severely (close to zero growth) from 7 to 28 days of age, followed by restriction of 50% growth up to 28, 56, 84, and 112 days of age, respectively. In all cases, feed restriction resulted in a delay in the onset of egg production, leading to some increases in egg weight. Egg production rate and cumulative production were not affected, in most cases, by early feed restriction. The BW at the onset and after 20 mo of production was reduced when feed restriction was continued beyond the age of 84 days. Overall feed conversion (grams feed per egg) and feed efficiency (grams feed per gram egg mass) were not affected significantly by feed restriction, although feed efficiency (grams gain per gram feed) was improved during the prelaying period. Within each treatment, BW was positively correlated with age at onset of egg production. Egg weight was a function of both age and BW at the onset of production. The significant correlation between egg weight and BW was maintained even after a year of production.

Effect of dietary protein, energy, and feed pelleting on the response of chicks to early feed restriction.

In three trials, male broiler chicks were subjected to a 6-day feed restriction regimen designed to retard growth severely. In one trial, the amino acid requirements during refeeding were evaluated by testing the adequacy of diets based on model calculations. In two additional trials, the response of feed-restricted birds to increased dietary energy density and to feed pelleting was compared with that of birds fed ad libitum. Results of the first trial showed that weight gain and feed efficiency during the first 2 wk of refeeding were reduced when the diet contained less than the model-calculated protein level for this period. No improvement in performance could be obtained when dietary protein was increased by 1% above model-calculated requirements. An increase in dietary nutrient density resulted in an enhanced growth rate. Feed efficiency was improved by an increase in nutrient density and by early feed restriction with no significant feed restriction x diet density interactions. Pellet-feeding resulted in improved growth without affecting feed efficiency, whereas feed restriction resulted in improved feed efficiency only. Interaction between pelleting and feed restriction was not significant for any of the variables. In all three trials, abdominal fat was reduced by feed restriction without any interaction with energy, protein, or dietary form. The results suggest that the requirements for some amino acid increase after feed restriction and that feed consumption does not limit the accelerated growth response at that time.

Effects of additional vitamins, minerals, or brewer's yeast upon leg weaknesses in broiler chickens.

Leg weaknesses occurring in commercial broiler chickens were studied in three experiments. No significant improvement was obtained by added dietary levels of known anti-perotic factors. Definite improvements in leg weaknesses occurred when the complete, practical diet was supplemented with 2.5 and 5.0% brewer's dried yeast.

The amino acid requirements of chicks: experimental validation of model-calculated requirements.

The amino acid requirements of broiler chicks, on a weekly or biweekly basis, were calculated according to a model presented previously (Hurwitz et al., 1978). Based on the present results, the model has been somewhat modified. The model requirements provided the basis for computer-designed diets which were fed to chicks of different ages and were composed to others computed on the basis of NRC (1971, 1977) requirements. In all cases the model-based diets, which were considerably lower in protein, supported weight gains equivalent to those obtained on NRC-based diets. The relatively poorer feed efficiency observed in the first trial with chicks fed the model-based diets, could be alleviated by equalizing both energy and lipid concentrations in the experimental diets. Thus, equal growth and feed efficiency were obtained with the model and NRC (1971)-based diets, for 2- to 10-week-old chicks. The possible reasons for the slightly higher abdominal fat content of the chicks fed the model-based diets are discussed.

The response of broiler chickens and turkey poults to steam-pelleted diets supplemented with fat or carbohydrates.

The responses of growth and feed efficiency to pelleted feed was investigated in 4- to 7-wk-old broiler chickens, and in 8- to 12- and 16- to 20-wk-old turkeys. In all cases, the growth and feed efficiency responses were linear within the ranges of dietary energy tested. When energy was added by carbohydrate supplementation, weight gain and feed efficiency responses were parallel for both mash and pellets, but due to the growth response to pellets, the elevation was higher for pellets than for mash. When energy was added by fat, the growth response to pellets also resulted in an increase in function elevation but the slope of the response was lower than in mash feeding, possibly due to a decline in pellet quality as dietary fat increased. Grinding of pellets completely abolished the growth and feed efficiency responses observed when the physical form was preserved. In chickens, comparisons of ground pellets to mash suggested some decline in nutritional quality due to the process of pelleting when either carbohydrates or fat were increased in the diets. In both chickens and turkeys, the feeding of pelleted diets resulted in an increase in abdominal fat.

Characterization of growth and development of male British United turkeys.

Body weight and the size of various organs (tibia, pectoral muscle, leg muscle, liver, spleen, and testes) were monitored in growing male turkeys (British United Turkeys) in an effort to characterize their growth pattern. The results were fitted with either a single- or a double-component Gompertz equation, describing single and diphasic growth patterns, respectively, using an iterative nonlinear estimation algorithm. The diphasic model with an early and a late growth component provided a better description of the body weight function than the single-phase model. The start of sexual maturation, evidenced by testicular development, marked the transition age between the early and the late phases of growth. A single-component Gompertz equation was sufficient to describe growth of various individual organs. Growth of bone and liver appeared to follow the early growth component, whereas the path of muscle development appeared to be closer to the later growth component. The results suggest that the diphasic growth behavior of male turkeys is caused by a differential growth rate of various organs, rather than by a periodicity in the overall growth rate.

The effect of dietary protein level on the lysine and arginine requirements of growing chickens.

Comparisons were made of the growth and carcass fat responses to dietary lysine and of the lysine requirements of 1-wk-old broiler chickens receiving diets containing either 18, 20, 23 or 25% protein. Similar comparisons were made of the responses elicited by dietary arginine in diets containing 18 or 23% dietary protein. The responses to lysine supplementation and the lysine requirements of chicks receiving 23 or 25% protein diets were similar. In comparing the 18 or 20% to the 23% protein diet, the initial responses of growth and feed efficiency to dietary lysine were augmented, but the maximal weight gain diminished as dietary protein decreased, leading to a decrease in the lysine requirements. The amounts of extractable carcass fat or abdominal fat pad increased as dietary protein was lowered and, in general, were reduced either by lysine or arginine supplementation. Percentage of pectoral muscle increased slightly with dietary arginine and protein supplementation. The results suggest that when total dietary amino acid level is reduced, the requirements for the individual amino acid decrease due to growth retardation resulting from single or multiple amino acid deficiencies. Single amino acid supplementation of low protein diet is more effective in improving the amino acid balance than supplementation of high protein diets, resulting in a further decrease in the requirements.

Blood system response of chickens to changes in environmental temperature.

Hemodynamic changes were studied in broiler chickens during exposure to constant temperatures (10 to 35 C) or diurnal temperature cycles (10:30 C and 15:35 C), and during acute heat or cold. Packed cell volume (PCV) was significantly high at low constant temperatures (10 and 15 C), whereas at high temperatures (30 and 35 C) plasma volume (PV) was significantly high. A linear relationship between hematocrit and heart weight was observed and indicates an adaptation of heart mass to changes in cardiac output and hematocrit to meet the demands of increased basal metabolic rate. Only during the diurnal temperature cycle of 15:35 C did a significant increase in PV occur when ambient temperature (Ta) was raised form 15 to 35 C. Acute exposure of chickens to high temperature did not affect PV or PCV, but resulted in hyperthermia (44.7 +/- 0.4 C). Changes in PCV are probably related to modulation of the supply of oxygen to accommodate changes in heat production. The significant hypervolemia observed at high temperatures could occur to provide the fluid needed for heat dissipation by panting. The lack of response of the blood system to acute temperature changes may be at least partially responsible for the chickens' failure to control body temperature.

Responses of laying hens to forced molt procedures of variable length with or without light restriction.

The importance of the length of the rest period and of photoperiod as components of the forced molt procedures was evaluated in 650- and 560-d-old Lohman hens. The procedure included an 8-d feed withdrawal phase and rest periods varying from 0 to 35 d, during which the birds were fed for maintenance only. In the first trial, forced molt was applied with or without omission of artificial illumination. The rest period varied between 2 and 20 d. In the second trial, all treatments included omission of artificial illumination, and a variable rest period between 0 and 35 d. Egg production ceased, after 4 to 5 d of feed withdrawal and resumed 8 to 15 d after the end of the rest period, without any consistent response to its length. Forced molt stimulated egg production rate and diminished its age-dependent rate of decline, reduced the proportion of broken and shell-less eggs, and improved shell quality. Following wide oscillations proportional to the length of the rest period, egg weight stabilized at levels similar to that of the unmolted controls. Feed intake was stimulated by forced molt to levels exceeding those of the control hens. Body weight increased during the postmolt period to levels slightly exceeding those of unmolted controls. Results of one trial show that omission of artificial illumination was essential for the full expression of the molt responses. In the other trial, production rate and shell quality were improved and the percentage of broken eggs was reduced when the length of the rest period was increased. Maximal improvements appears to have been reached with rests period of 14 to 21 d.

Response of growing turkeys to dietary fat.

Growth, feed efficiency, and carcass fat were evaluated in turkeys fed diets in which added fat varied, holding energy or the calories:protein ratio constant. In the 1 to 3-wk-old turkey, growth and feed efficiency increased with dietary energy, but did not change significantly when fat was added isocalorically. The 12 to 14-wk-old turkey responded with improved growth and feed efficiency when dietary fat was added either isocalorically or with increasing energy density. However, the response to the isocaloric fat addition was smaller in magnitude than the response when fat was added without calorie adjustment. No difference could be detected in 12 to 15-wk-old turkeys in the performance response to tallow and soybean oil. Carcass fat deposition generally increased with dietary fat supplementation, regardless of the caloric change. The results suggest that in the midterm of development of the growing turkey, dietary fat per se affects growth, feed efficiency, and carcass fat. Growth and feed efficiency responses to nutrient density occur in both young and older birds.

The response of broiler chickens and turkey poults to dietary energy supplied either by fat or carbohydrates.

The efficacy of fat and carbohydrates as energy sources was compared in 1- to 4- and 4- to 7-wk-old broiler chickens and in 16- to 19-wk-old turkeys. An increase in dietary energy by carbohydrate was made by a graded replacement of wheat bran by wheat. Energy was increased by fat through a graded replacement of soybean hulls with refined soybean oil. In the experiments with broiler chickens, the feed efficiency responses to added energy were observed within the entire range of dietary energy tested, with no significant differences between the responses to carbohydrate and fat as energy supplements. The growth response to energy from either source appeared to be characterized by diminishing returns in the chicken. In the 16- to 19-wk-old turkeys, the growth and feed efficiency responses were linear within the range from 2,650 to 3,250 kcal/kg. In chickens and in turkeys, the growth and feed efficiency responses to energy supplied by fat were indistinguishable from those of carbohydrates. In chickens, the fractions of abdominal fat and pectoral muscle were not affected significantly by the energy density and source.

The response of laying hens to induced molt as affected by strain and age.

Molt was induced in 502-d-old Lohmann, Hy-Line W-77, Yafa, and Yarkon strains of laying hens (Experiment 1), and at different ages during the 1st yr of production in the Lohmann strain (Experiment 2). The induced molt treatment included an 8-d feed withdrawal period followed by a 22-d rest period during which the birds received 60 or 70 g/d of a low-nutrient maintenance diet, in both experiments, respectively, and a reduced duration of daylight. In both experiments, induced molt resulted in an increase in postmolt egg production rate and a diminution of the rate of decline of production with age. The first eggs during the postmolt period were smaller than those of the unmolted birds but egg size increased rapidly to control levels. Egg breakage was markedly reduced by induced molt and its rate of increase with age was diminished. Postmolt feed intake was higher than that of the unmolted birds and body weights reached values higher than those of the controls. Those responses were not different among strains but the ranking among the strains in the molted group was similar to that of the unmolted controls, for all production traits. The postmolt rate of production approached that of first cycle peak and was not affected by treatment age. Shell quality as reflected by the percentage of breakage during the postmolt period was similar to that of the unmolted controls approximately 3 to 4 mo earlier.

The amino acid requirements of growing turkeys. 2. Experimental validation of model-calculated requirements for sulfur amino acids and lysine.

The response to protein and the requirements for sulfur amino acids and lysine have been evaluated in male turkeys throughout the growth period as an experimental validation of model-calculated requirements (Hurwitz et al., 1983). The sulfur amino acid requirements were 3.4 and 3.1 mg/kcal for 1- and 5-week-old turkeys, respectively. The requirements for lysine were 4.8, 2.7, and 2.2 mg/kcal for 1-, 12-, and 16-week-old turkeys, respectively, which were in close agreement with the model predictions. Dietary protein in diets calculated on the basis of the model was sufficient to maintain maximal growth and feed efficiency. The results were the basis for accepting the general validity of the model-calculated requirements (Hurwitz et al., 1983).

Increased skin tearing in broilers and reduced collagen synthesis in skin in vivo and in vitro in response to the coccidiostat halofuginone.

In vivo and in vitro experiments were conducted in an effort to elucidate the mechanism of suppression by halofuginone of skin strength in broilers. In the in vivo study, halofuginone was included at concentrations of 0, 1.5, 3, and 6 mg/kg of diet, corresponding to 0, 50, 100, and 200%, respectively, of the amount recommended for use as a coccidiostat. Each dietary treatment was given to 260 female broiler day-old chickens. Skin tearing was evaluated at the processing plant. Skin collagen and Kjeldahl-nitrogen were determined chemically. At the age of 7 wk, BW and feed efficiency were affected only in birds consuming the diet containing the highest concentration of the drug. Skin tearing increased but skin collagen concentration decreased in a dose-dependent manner. Fibroblasts were obtained by collagenase digestion from chicken skin and cultured. The cultured cells were incubated with various concentrations of halofuginone, monensin, and nicarbazin, and [3H]proline incorporation was evaluated in collagenase-digestible (representing mostly collagen) and nondigestible proteins exported by the cells into the medium. Halofuginone, at a concentration as low as 10(-11) M, inhibited incorporation of [3H]proline into collagenase-digestible proteins, but did not affect incorporation of [3H]proline into collagenase-nondigestible proteins. Even at concentrations as high as 10(-9) M, neither monensin nor nicarbazin affected collagenase-digestible proteins. The in vitro results suggest that halofuginone specifically inhibits collagen synthesis by skin fibroblasts. Results of both in vivo and in vitro trials suggest that the increase of skin tearing during processing, induced by halofuginone, is caused by direct suppression of skin collagen synthesis.

Skin tearing in broilers in relation to skin collagen: effect of sex, strain, and diet.

The relationship between skin tearing and collagen in broilers was investigated in two trials in which strain and sex, and strain and diet served as factorial-arranged variables, respectively. In the first trial, males and females of three strains were examined. Both skin tearing and skin collagen were significantly influenced by strain and sex without any significant strain by sex interaction. Skin collagen, expressed as a fraction of fresh skin protein (N x 6.25) was lower and skin tearing was higher in females than in males, particularly in the most susceptible strain. In the second trial, the effects of supplementary protein or methionine and of a low-density diet were tested in females of two strains that differed in their susceptibility to skin tearing. High dietary protein reduced skin tearing and increased skin collagen. The significant diet by strain interaction resulted from the more pronounced response of the susceptible strain. Neither supplementary methionine nor feeding of low-dietary-density diet significantly affected skin tearing or skin collagen.

Differential responses to dietary carbohydrates and fat of turkeys kept at various environmental temperatures.

Interactions between environmental temperature and dietary energy sources were evaluated in 6 to 9-wk and 9 to 12-wk-old turkeys using weight gain, feed efficiency, and carcass fat as response criteria. The dietary variables (soybean oil or glucose) were added in five or six increments at the expense of each other or of the fiber supplements, keeping the minima for protein and amino acid/energy constant. The resulting diets were fed to birds kept at 10 and 27 C. Duplicate experiments were conducted for each mode of dietary variable addition. Parallel increases in body weight gain and feed efficiency were obtained at the two temperatures when fat replaced carbohydrates or fiber, thereby raising dietary energy density. Some responses of weight gain and feed efficiency at the two temperatures were obtained also with a graded isocaloric addition of fat but the response was significant only at 27 C and not at 10 C. A greater response of gain and feed efficiency to energy supplied by dietary glucose was obtained at 10 C as compared with 27 C. Dietary fat supplementation resulted in increased deposition of carcass fat when given together with energy or isocalorically regardless of environmental temperature. Carcass fat was increased by glucose-energy at the low temperature only.