Effects of ad libitum feeding on performance of different strains of broiler breeders

(1) Tolerance to ad libitum feeding was compared in three genotypes of broiler breeder hens: a standard broiler breeder fed ad libitum (SA) or restricted (SR), a slow growing 'label' broiler breeder (L) and an experimental dwarf heavy broiler breeder (E). Two similar experiments were conducted in two distinct research centres. (2) Feed intake and body weight were measured every 3 weeks from hatch to 40 to 49 weeks of age. Egg production and egg abnormalities were recorded. The number of yellow follicles in ovaries was counted at the age of 32 weeks. (3) Body weight was stabilised at 2.2, 3.7 and 5.4 kg after 24 weeks of age in L, E and SA hens, respectively. Growth of the SR hens was similar to that of L up to 20 weeks and stabilised at a similar level to that of E hens after 30 weeks of age. (4) Sexual maturity was delayed by 6 weeks in restricted breeders compared to ad libitum fed hens that started to lay at 20 weeks. SA hens had low egg production and a high proportion of defective eggs, which was largely compensated for by feed restriction. However, productivity of SR hens remained lower than that of L breeders. (5) Compared to the low viability and reproductive fitness observed with SA hens, the E dwarf broiler breeder tolerated ad libitum feeding and had better egg production, fewer egg abnormalities and yellow follicles per ovary and a higher egg production. However, laying rate was still lower than that of the SR and L groups. Energy conversion (kJ/g egg) from 32 to 40 weeks of age was much higher in the SA group than in the other three groups. 6. The feasibility of feeding a dwarf broiler breeder ad libitum calls for further research on implications of specific IGF and GH-receptor expression at the level of the ovary in dw chickens.     

Withdrawal of zinc oxide-containing diets from mature, female domestic fowl: effects on laying performance and the weights of selected tissues

1. Two hundred and sixteen laying hens of two strains were given diets containing ZnO to provide 0, 0.5, 0.75, 1.00, 1.25, 1.50, 2.00, 3.00 or 4.00 g added Zn/kg. These diets were given ad libitum for 5 consecutive 28-d periods. All hens subsequently received the control diet with no added ZnO for 5 weeks. 2. Four hens from each treatment were killed 0, 1 and 5 weeks after substitution of the ZnO-supplemented diets by the control diet. 3. The adverse effects of the ZnO-containing diets on body weight, food intake, egg production, pancreas, gizzard, oviduct and ovary weights/kg body weight were reversed by removal of the ZnO from the diets. 4. Five weeks after withdrawal egg production of the group which had received the diet with the highest concentration of added ZnO was only 50% of that of the control birds. 5. The beneficial effect of the added ZnO on internal egg quality was not maintained after withdrawal of the ZnO-containing diets.     

饲粮代谢能水平对汶上芦花产蛋鸡生产性能、血清生化指标和蛋品质的影响

本试验旨在研究饲粮代谢能(ME)水平对产蛋期汶上芦花鸡生产性能、血清生化指标和蛋品质的影响,并建立代谢能需要量析因模型,确定产蛋期汶上芦花鸡的饲粮代谢能需要量。试验采用单因素完全随机设计,选取40周龄、体重相近的健康汶上芦花鸡360只,随机分为5个组,每组6个重复,每个重复12只鸡。各组分别饲喂代谢能水平为10.68、10.89、11.10、11.30和11.51MJ/kg的试验饲粮,其他主要营养水平保持一致。预试期7d,试验期35d。结果表明:1)饲粮代谢能水平对产蛋期汶上芦花鸡的平均日采食量(ADFI)、平均日代谢能摄入量(ADMEI)、平均体重、代谢体重(BW0.75)、产蛋数、产蛋率和平均日产蛋量(ADEM)均有显著影响(P0.05)。随饲粮代谢能水平的升高,ADFI、ADMEI、产蛋数、产蛋率和ADEM呈增加趋势,但当代谢能水平为11.51 MJ/kg时降低。随饲粮代谢能水平的升高,料蛋比呈降低趋势,但当代谢能水平为11.51 MJ/kg时增加。饲粮代谢能水平为11.51和11.30 MJ/kg时的平均体重和BW0.75显著高于代谢能水平为11.10 MJ/kg时(P0.05)。2)随饲粮代谢能水平的升高,产蛋期汶上芦花鸡的血清葡萄糖(GLU)、甘油三酯(TG)和总胆固醇(TCHO)含量均呈增加趋势。3)饲粮代谢能水平对产蛋期汶上芦花鸡的蛋白高度、蛋黄颜色、哈氏单位和蛋黄比率有显著影响(P0.05)。低能组(代谢能水平为10.68、10.89和11.10 MJ/kg)的蛋白高度和哈氏单位显著高于高能组(代谢能水平为11.30和11.51 MJ/kg)(P0.05)。随饲粮代谢能水平的升高,蛋黄颜色和蛋黄比率呈增加趋势,其中代谢能水平为11.51 MJ/kg时的蛋黄颜色和蛋黄比率显著高于其他各代谢能水平时(P0.05)。4)以ADMEI为因变量,以平均日增重(ADG)、ADEM和BW0.75为自变量,拟合41~45周龄汶上芦花鸡饲粮代谢能需要量的析因模型为:ADMEI=0.88 ADG+10.63 ADEM+476.40 BW0.75(R2=0.982 5,P0.05)。满足41~45周龄汶上芦花鸡最佳生产性能的适宜饲粮代谢能需要量为11.29 MJ/kg。     

The effect of rapeseed meal on the energy metabolism of laying hens

1. The effect of 100 g rapeseed meal (RSM)/kg diet on the energy metabolism of hybrid laying hens was examined by indirect calorimetry. Thyroid hormone concentrations, thyroid weight, liver weight and body weight, egg production and food intake were also measured. 2. Fasting heat production was significantly lower in hens receiving RSM than in controls, but this difference disappeared when the birds were fed. 3. Thyroid hormone concentrations decreased, while thyroid and liver weights increased slightly; none of these effects was significant. Body weight, egg production and food intake were unaffected and no liver haemorrhages were noted. 4. The maintenance metabolisable energy (ME) requirement of control and treated birds, estimated from short-term energy balance measurements, was 474 kJ/kg0.75 d; net availability of ME in both treatments was 0.85.     

Effects of low dietary protein and different allocations of food during rearing and restricted feeding after peak rate of lay on egg production,fertility and hatchability in female broiler breeders

1. A 3x2x2 factorial experiment was conducted with boiler breeder females to determine the effects of body weight gain (three levels) and conventional or lower crude protein concentrations in the rations during rearing, and restricted or ad libitum feeding after the peak rate of lay on egg production, fertility, hatchability, mortality and food consumption. 2. Compared with ad libitum feeding, conventional food restriction resulted in a decrease in average daily food consumption of 0.6 during rearing, 0.2 during early lay and an increase of 0.4 after the peak rate of egg production. Mortality was decreased by more than half. 3. Restricted birds had higher total and settable egg production, fewer defective or damaged eggshells and higher fertility and hatchability than those fed ad libitum. The modified (more generous) rearing programme resulted in lower rates of egg production and higher rates of mortality compared with the conventional food restriction programme. 4. Low-protein rearing rations were associated with higher rates of food intake, higher mortalities and lower rates of egg production than the conventional protein rations. There were no differences in the fertility or hatchability of eggs between birds fed on the two concentrations of dietary crude protein. 5. Ad libitum feeding post-peak was associated with higher rates of mortality to 60 weeks of age. Post-peak feeding had little effect on the rate of lay or egg weight in conventionally restricted birds fed high protein rations or in birds fed ad libitum. Restricted feeding post-peak decreased the rate of lay and egg weight in birds on the modified restriction programme and in conventionally restricted birds fed on the low protein rations. There was no effect of post-peak feeding on fertility or hatchability of eggs. 6. The total numbers of saleable chicks per kg food consumed were 1.83, 1.72 and 0.52 for conventional, modified and ad libitum feeding during rearing; 1.56 and 1.15 for restricted and ad libitum feeding post-peak: there were no differences associated with protein concentrations of rations fed during rearing.     

Self-selection of dietary protein and energy by turkey breeder hens

1. An experiment was conducted to determine the effects of self-selection of dietary protein and energy by turkey hens on reproductive performance in a warm environment. 2. Dietary self-selection had no significant effect on egg production, egg weight, or body weight of turkey hens. 3. Fertility and hatchability of eggs produced by self-selecting hens were significantly reduced compared to eggs from control hens fed on a complete diet. 4. Protein intake was significantly reduced among self-selecting hens when compared to control hens fed on a complete diet (P less than or equal to 0.001). 5. Food and energy intake decreased as the ambient temperature increased. Nevertheless, protein intake of self-selecting hens increased over the course of egg production despite decreasing food intake. Therefore, self-selecting hens preferred a diet with a greater protein content (g protein/kg diet) in the last 10 weeks of egg production than during the first 10 weeks of egg production.     

Reproductive performance of dwarf broiler breeders given different allowances of food during the rearing and breeding periods and two lighting patterns

1. Dwarf broiler breeders were either fed ad libitum or restricted to allow growth to mean body weights of 1.4 or 1.8 kg at 20 weeks of age. During the breeding period these birds were fed ad libitum, or food was restricted to different degrees and the birds subjected to two different incremental lighting patterns. 2. Egg production of birds fed ad libitum during the breeding period increased with the degree of food restriction during rearing. 3. Food restriction during the breeding period increased the egg production of birds weighing 1.8 kg at 20 weeks but decreased that of birds weighing only 1.4 kg. 4. Fertility was relatively low and inversely related to body fatness of females. 5. The differences in lighting pattern did not influence performance. 6. For optimum reproductive performance during the rearing period dwarfs should not be restricted so severely as conventional breeders. Best chick production was obtained from birds with a bodyweight of 1.8 kg at 20 weeks of age, which were subjected to a 10% restriction of food during the breeding period.     

Modelling energy utilisation in broiler breeder hens

1. The objective of this study was to determine a metabolisable energy (ME) requirement model for broiler breeder hens. The influence of temperature on ME requirements for maintenance was determined in experiments conducted in three environmental rooms with temperatures kept constant at 13, 21 and 30 degrees C using a comparative slaughter technique. The energy requirements for weight gain were determined based upon body energy content and efficiency of energy utilisation for weight gain. The energy requirements for egg production were determined on the basis of egg energy content and efficiency of energy deposition in the eggs. 2. The following model was developed using these results: ME = kgW0.75(806.53-26.45T + 0.50T2) + 31.90G + 10.04EM, where kgW0.75 is body weight (kg) raised to the power 0.75, T is temperature ( degrees C), G is weight gain (g) and EM is egg mass (g). 3. A feeding trial was conducted using 400 Hubbard Hi-Yield broiler breeder hens and 40 Peterson males from 31 to 46 weeks of age in order to compare use of the model with a recommended feeding programme for this strain of bird. The application of the model in breeder hens provided good productive and reproductive performance and better results in feed and energy conversion than in hens fed according to strain recommendation. In conclusion, the model evaluated predicted an ME intake which matched breeder hens' requirements.     

Production responses of layer strain hens to food restriction during rearing

Production responses of laying hens to food restriction during rearing were measured in two trials. Food was restricted by two methods: time restriction (TR, food continuously available for 24 to 30 h each 72 h) and proportion restriction (PR, daily allocations of about 60 to 70% of that consumed by ad libitum fed birds (F]. The rearing treatments were applied from 42 to 162 d and from 56 to 168 d of age in experiments 1 and 2 respectively. All birds were fed ad libitum in the laying period to 437 d and 476 d of age in experiments 1 and 2 respectively. Body weight was reduced significantly in both experiments by both methods of restriction, but more so by TR. Marked compensatory growth accompanied the high food intake following the end of food restriction. There was a significant increase in average egg weight concommitant with a change in the relationship between egg weight and age. Possibly this is due to an altered pattern of food intake at onset of lay.     

Evaluation of feeding spray-dried bovine plasma protein on production performance of laying hens exposed to high ambient temperatures

The purpose of this study was to evaluate feeding 2 levels of spray-dried bovine plasma protein (SDP) on production performance of laying hens subjected to high ambient temperatures. Two groups of 96 Hy-Line W-98 hens (38 wk of age) were housed in each of 2 environmentally controlled chambers. At 40 wk of age, all hens were fed 3 diet treatments consisting of (1) a control diet (0% SDP); (2) the control diet supplemented with 0.75% SDP; and (3) the control diet supplemented with 1.50% SDP. Hens in each chamber (8 cages of 4 hens per cage) were ad libitum fed 1 of each diet for 5 wk. The heat stress (HS) chamber was maintained at 21°C (wk 1), 29°C (wk 2), and 35°C (wk 3 to 5). The thermoneutral chamber was maintained at 21°C during wk 1 to 5. A significant main effect of week was observed for hens maintained in the HS chamber for egg production, egg weight, egg mass, and feed consumption, which resulted in acute heat stress causing a reduction in these parameters. Hens fed the 1.50% SDP diet in the HS chamber produced greater (P < 0.05) egg mass on average than hens fed the control or 0.75% SDP diet (wk 1 to 5). During the second week of acute HS (wk 4), hens fed the control and 1.50% SDP diets had greater (P < 0.05) egg production than those fed the 0.75% SDP diet. During wk 5, hens in the HS chamber that were fed the 1.50% SDP diet produced more (P < 0.05) eggs than those fed the control diet. Therefore, based on the results of this study, acute HS negatively affected short-term production performance. In addition, feeding hens an SDP-supplemented diet may have a slight positive effect on production performance when maintained in acute HS conditions.     

Effects of photostimulation at 18, 24 and 30 weeks of age on the productivity of female turkeys fed ad libitum or restricted until point of lay.

1. Turkey females were fed ad libitum or restricted from 6 weeks of age to achieve mean body weights of 0.6 of ad libitum fed birds on photostimulation at 18, 24 or 30 weeks of age. Body weight, food intake, egg production and hatchability were recorded to 54 weeks of age. 2. Restricted turkeys were fed ad libitum after first egg or 36 weeks of age. Food intake after 30 weeks of age averaged 170 g/bird/d and was similar for all treatments. At 54 weeks of age, restricted turkeys photostimulated at 24 and 30 weeks were not as heavy as turkeys photostimulated at 18 weeks and ad libitum fed turkeys. 3. A large proportion of restricted turkeys photostimulated at 18 weeks of age did not commence lay until 30 to 40 weeks and a significant number of restricted birds photostimulated at 24 weeks had short laying cycles. Restricted birds photostimulated at 30 weeks came into lay and showed similar persistency of lay to ad libitum fed turkeys. 4. Ad libitum fed turkeys laid 115.0, 122.0 and 101.0 and restricted turkeys 92.4, 99.5 and 103.4 eggs when photostimulated at 18, 24 and 30 weeks, respectively. The number of non-settable eggs was lower in restricted compared with ad libitum fed turkeys and declined with age at photostimulation. 5. Egg size at the end of the experiment was similar for ad libitum fed turkeys and restricted birds photostimulated at 18 weeks but was 2.3 g lower for restricted birds photostimulated at 24 and 30 weeks of age. 6. Hatchability was higher, and the proportion of second quality poults was lower with eggs from restricted turkeys. The mean numbers of poults hatched were 59.9, 75.1 and 66.0 for ad libitum fed and 71.7, 65.7 and 79.4 for restricted turkeys photostimulated at 18, 24 and 30 weeks of age.     

The effect of T. vivax infection in West African Dwarf goats on energy and nitrogen metabolism

Summary

To investigate how T. vivax affects metabolism in dwarf goats, nine wethers (infection group) given alfalfa pellets ad libitum were infected intravenously and food intake was recorded up to 49 days after infection in the infection group and in the control group (n=9). Controls received the same diet, ad libitum before infection and in restricted amounts after infection in order to obtain similar intakes in the two groups. Digestible organic matter intake (DOMI) and nitrogen balance (NB) were determined during four balance trials. All animals were bled regularly to measure parasitaemia, packed cell volume (PCV) and a number of serum metabolites.

All infected animals showed symptoms typical for T. vivax infection as judged by parasitaemia, PCV and rectal temperature. Infection had a non‐uniform negative effect on food intake. Compared with controls at equal DOMI, NB was lower in infected animals, the difference being significant 4 weeks after infection. This was caused by a gradual increase in NB at equal DOMI of the control group. The NB of the ad libitum fed infected animals 2 and 4 weeks after infection was comparable to values normally found in healthy ad libitum fed dwarf goats with an equal DOMI.

NEFA values in serum were significantly elevated after infection. Except for two infected animals with an extremely low food intake towards the end of the experiment, no rise in serum ketone bodies was evident. After infection, serum protein increased, differences with controls being significant 4 and 7 weeks after infection.

It is concluded that T. vivax infection results in a decrease in energy intake and a decrease in NB up to at least 4 weeks after infection. At equal DOMI, NB of infected animals was not lower than expected for ad libitum fed healthy animals but was lower than in healthy controls on a restricted diet, probably as a result of a decrease in maintenance requirements of the latter. The data on NB and serum NEFA concentrations suggest that non‐protein energy sources are used to supply the increased energy demand as a result of infection.     

Energy and protein requirements for maintenance and growth of Boer crossbred kids

Meat production by goats has become an important livestock enterprise in several parts of the world. Nonetheless, energy and protein requirements of meat goats have not been defined thoroughly. The objective of this study was to determine the energy and protein requirements for maintenance and growth of 34 (3/4) Boer x (1/4) Saanen crossbred, intact male kids (20.5 +/- 0.24 kg of initial BW). The baseline group was 7 randomly selected kids, averaging 21.2 +/- 0.36 kg of BW. An intermediate group consisted of 6 randomly selected kids, fed for ad libitum intake, that were slaughtered when they reached an average BW of 28.2 +/- 0.39 kg. The remaining kids (n = 21) were allocated randomly on d 0 to 3 levels of DMI (treatments were ad libitum or restricted to 70 or 40% of the ad libitum intake) within 7 slaughter groups. A slaughter group contained 1 kid from each treatment, and kids were slaughtered when the ad libitum treatment kid reached 35 kg of BW. Individual body components (head plus feet, hide, internal organs plus blood, and carcass) were weighed, ground, mixed, and subsampled for chemical analyses. Initial body composition was determined using equations developed from the composition of the baseline kids. The calculated daily maintenance requirement for NE was 77.3 +/- 1.05 kcal/kg(0.75) of empty BW (EBW) or 67.4 +/- 1.04 kcal/kg(0.75) of shrunk BW. The daily ME requirement for maintenance (118.1 kcal/kg(0.75) of EBW or 103.0 kcal/kg(0.75) of shrunk BW) was calculated by iteration, assuming that the heat produced was equal to the ME intake at maintenance. The partial efficiency of use of ME for NE below maintenance was 0.65. A value of 2.44 +/- 0.4 g of net protein/kg(0.75) of EBW for daily maintenance was determined. Net energy requirements for growth ranged from 2.55 to 3.0 Mcal/kg of EBW gain at 20 and 35 kg of BW, and net protein requirements for growth ranged from 178.8 to 185.2 g/kg of EBW gain. These results suggest that NE and net protein requirements for growing meat goats exceed the requirements previously published for dairy goats. Moreover, results from this study suggest that the N requirement for maintenance for growing goats is greater than the established recommendations.     

Effect of protein quality on energy requirements for maintenance in growing rats

Forty 3-week old male Wistar rats (initial weight 45-50 g) were used. After weaning they were fed ad libitum for four weeks (I to IV) on 6 isocaloric and isonitrogenous semisynthetic diets based on soya bean meal (diet SBM) or on ground lupin seed (diet LS) alone or autoclaved (A) or not at 120 degrees C and supplemented with DL-methionine (diets ALSm or LSm, respectively) or with DL-methionine + L-lysine (diets ALSm + l or LSm + l). The diets differ in their protein quality and were formulated in order to provide the adequate experimental conditions to determine the biological value (10% crude protein). Then over the fifth and sixth weeks (V and VI) the rats were fed on the same diets but restricted to 60% of the voluntary feed intake. In a parallel experiment, a group of eight rats previously fed ad libitum on diet SBM for four weeks was fasted for 72 h and then fed on the same diet at a level of intake slightly below maintenance. After a 24 h adaptation period, irrespective of the level of intake and type of diet, a series of 24 h gas-exchanges measurements were carried out in open-circuit respiration chambers. Measurements of energy balance were used to calculate ME for maintenance (MEm) and the efficiency of utilization of ME, using a linear regression of energy retention (RE) on ME. The estimates for MEm derived from energy balances of rats fed above maintenance ranged from 564 to 621 kJ/kgW0.75 per d. No significant differences between diets were observed. From pooled data MEm was found to be 599 kJ/kgW0.75 per d, a value not significantly different from that calculated from measurements at fasting and below maintenance levels (598 kJ/kgW0.75 per d). The efficiency of utilization of ME for maintenance was 81.1% and the efficiencies of utilization of ME for RE ranged from 36.6 to 59.9%. It is concluded that no variations in MEm requirements in growing rats attributable to variations in dietary protein quality have been found. Nevertheless, these results should be taken with caution because of limitations inherent of statistical modelling approaches of partitioning ME.     

Effect of nutrient density on production performance, egg quality and humoral immune response of brown laying (Dahlem Red) hens in the tropics

A study was conducted to evaluate the effect of various concentrations of metabolizable energy (ME) with graded incremental levels of crude protein (CP) and essential amino acids (lysine and methionine) on production performance, egg quality and humoral immune response of Dahlem Red laying hens. Four experimental diets based on maize–soybean meal-deoiled rice bran were prepared. Diet 1 was fed as a control diet containing 2,600 kcal ME/kg, 15% CP, 0.75% Lys and 0.36% Met, and in the other three diets (D2, D3 and D4), concentrations of the above nutrients were increased by 2.5%, 5.0% and 7.5%, respectively. The levels of Ca (3.5%) and available P (0.32) were constant in all the diets. Each diet was offered ad libitum from 28 to 40 weeks of age to eight replicates containing six birds in each replicate. The egg production, egg weight and egg mass (in grams of egg per hen per day) were not affected by increasing the nutrient density up to 7.5% (2,795 kcal ME/kg diet) compared to the control group (2,600 ME/kg diet). However, feed consumption and feed efficiency (in grams of egg per gram of feed) were influenced by the variation in the nutrient density of diets. As the nutrient density increased by 5% (2,730 ME/kg diet), birds consumed significantly (P < 0.001) less feed. The birds in the 7.5% higher density group produced significantly (P < 0.05) higher egg mass per unit feed consumption compared to the control diet. Increasing nutrient density up to 7.5% had no effect on relative weight of albumen, yolk or shell. The Haugh unit, yolk colour and shell thickness were also not affected due to variation in the nutrient density. The humoral immune response measured at 34 and 40 weeks was progressively improved by increasing the nutrient density up to 5%. Increasing the nutrient density beyond 5% in the diet had no further influence on the humoral immune response. Based on the results of the present study, it can be concluded that Dahlem Red laying hens required 2,795 kcal/kg ME, 16% CP, 0.8% lysine and 0.4% methionine for eliciting optimum performance and immune response during 28 to 40 weeks of age.     

Effects of ambient temperature on heat increment of feeding and energy retention in growing broilers maintained at different food intakes

Zero-activity heat production (HP), body temperature (Tb) and energy retention were measured in growing broilers maintained at 5 ambient temperatures (Ta) (14 degrees , 17 degrees , 22 degrees , 27 degrees and 32 degrees C) and at 5 feeding rates (ad libitum intake and 75%, 50%, 25% and 0% (fasting) of ad libitum). Zero-activity HP increased with decreasing Ta and increasing food intake. However, at 14 degrees C, zero-activity HP in birds fed ad libitum and 75% did not show further increase, but those in birds fed less than 75% of ad libitum increased rapidly. Results of the regression of zero-activity HP on Ta ranging from 32 degrees to 17 degrees C indicated that the slope was affected little by food intake, but the intercept decreased with decreasing food intake. Tb increased significantly with increasing food intake. There was little variation with Ta but, at and above 27 degrees C, a slightly increased Tb was observed only in birds fed ad libitum. Overall effects of Ta and food intake on HIF (% TME intake) were not found, but HIF tended to increase with decreasing food intake at 14 degrees C. Total energy retention and energy retention as fat decreased with decreasing Ta and food intake, although energy retention as protein decreased only with decreasing food intake. Results obtained here suggest that availability of TME is affected little by Ta ranging from 32 degrees to 17 degrees C and that HIF is utilised, in part, to maintain Tb at any Ta.     

Effects of food intake regulation on the energy metabolism of laying hens

1. The effects of dietary energy restriction on the energy metabolism of post‐peak‐of‐lay hens of two hybrid layer strains were studied by indirect calorimetry.

2. Starving and resting rates of heat production (SHP and RHP) were measured, over 1‐d periods, at intervals during a 25‐week period in which the experimental birds were individually restricted to 80% of their previous energy intake ad libitum.

3. In both strains mean RHP per bird was about 7% lower in the restricted birds than in controls fed ad libitum, but when RHP was expressed in terms of metabolic body size (kg^0.75) the two groups did not differ.

4. Mean SHP per bird was about 18% lower in the restricted birds of both strains than in the corresponding controls; the decrease in SHP per kg^0.75 was 12%.

5. Heat increment of feeding and calculated maintenance energy were higher, and net availability of metabolisable energy for maintenance and production was lower, in the restricted than in the control groups.

6. Gross efficiencies of egg production, in terms of both mass and energy, increased in the restricted birds.

7. Live‐weight and total carcass energy after 25 weeks of restriction were respectively about 15% and 30% lower in the restricted groups of both strains than in the groups fed ad libitum.     

Comparative Study on Nitrogen Metabolism and the Nitrogen Maintenance Requirement in Lohmann Brown Roosters and Layers

The objective of this study was to investigate the effect of dietary protein level on nitrogen retention and compare nitrogen metabolism in Lohmann Brown adult roosters and layers. The nitrogen maintenance requirement ( Nm ) was determined based on the nitrogen balance. Thirty Lohmann Brown adult roosters and 30 laying hens at 27 weeks of age were randomly divided into five groups of six birds per group. The birds were fed with one of five diets containing 10.46%, 11.77%, 13.79%, 16.77% or 18.29%of crude protein. Nitrogen intake, nitrogen retention and nitrogen retention efficiency were higher in roosters than in laying hens, and the average nitrogen retention rate for groups fed with CP level of 11.77%,13.79%, 16.77% and 18. 29% was improved by 9.14%. The nitrogen maintenance requirement for Lohmann Brown roosters and laying hens at 27 weeks of age were 0.4245 g/d and 0.5059 g/d, respectively,and Nm based on average body weight (BW) and metabolic body weight ( BW0.75 ) was 0.2364 g/kg BW and 0.2739 g/kg BW0.75 for laying hens and 0.2754 g/kg BW and 0.3208 g/kg BW0.75 for roosters, respectively. The regression equations for daily N gain ( NB, protein accretion) vs. daily N intake ( NI )for Lohmann Brown layers and roosters were NB =0.3743NI -0. 1589(R2 =0.79) and NB =0.6228NI -0.3151 (R2 =0.85),respectively. The results of this study indicate that nitrogen intake and nitrogen retention at the same dietary CP level were higher in roosters than in laying hens.     

Nitrogen retention and performance of brown laying hens on diets with different protein content and constant concentration of amino acids and energy.

1. The aim of this study was to determine the nitrogen balance and the performance of laying hens fed on diets with a protein content lower than the diets currently used in commercial practice but with adequate concentrations of lysine, sulphur amino acids, tryptophan and threonine. 2. Ninety-six Hy-Line Brown hens, 24 weeks old, were divided into 3 groups of 8 replicates and received, for 16 weeks, diets formulated to have 3 different protein concentrations: 170 (control), 150 and 130 g/kg CP and the same energy content. For each protein concentration, the contents of lysine, methionine, methionine+cystine, tryptophan and threonine were maintained at minimum requirement concentrations by supplying synthetic amino acids. 3. In the first half of the trial, egg production and egg weight were similar in all groups. From the 9th week onwards group 150 CP laid heavier eggs and had a slightly lower egg deposition and total mass. Food conversion ratio was best in the control group. 4. Nitrogen intake was related to the protein concentration of the diet, the food intake being almost the same in the 3 experimental groups. Faecal nitrogen content significantly and linearly decreased with reduction in dietary protein content and was about 50% of the intake. Considering the nitrogen faecal/intake ratio, the 150 CP group showed better nitrogen utilisation at each sampling time.