The response of turkeys to dietary balanced protein during two periods of growth

1. Two experiments were conducted to measure the response of growing turkeys to dietary protein content. In the first, 960 sexed British United Turkey (BUT 6) poults were used to measure the response to balanced protein from 3 to 6 weeks of age. In the second, 1440 sexed BUT and Hybrid Converter poults were raised from 14 to 17 weeks.2. In both experiments, six levels of dietary protein were fed, with feed intake, body and feather weight gain and changes in body composition measured. The levels of protein chosen ranged from 0.53 to 1.2 of the Aviagen requirements for growing turkeys.3. In the first experiment, six poults were sampled from each sex at the start of the experiment for carcass analysis, and four were sampled from each strain and sex in the second. At the end of each experiment, eight poults from each treatment were sampled. Body composition analyses were made on individual defeathered birds.4. Weight gain increased linearly with protein intake in the early period and exponentially in the later period. In both periods, feed intake decreased as protein content reduced.5. In the early period, body lipid content increased from 20.2 to 41.5 g/kg body weight, as dietary protein content decreased, but there was no change in the later period. Efficiency of utilisation of dietary protein declined linearly with an increase in dietary protein content, from 0.87 to 0.46 g/g in the first, and from 0.43 to 0.27 g/g in the later period.6. The inability of the growing turkey to increase feed intake on marginally limiting feeds may have been due to a genetic constraints to store excess energy consumed as body lipid, resulting in the observed decrease in feed intake as dietary protein content is reduced.

Evaluation of a mechanistic model that estimates feed intake, growth and body composition, nutrient requirements, and optimum economic response of broilers

Efficient meat production is crucial in addressing global market demands and sustainability goals. Modeling production systems has gained worldwide attention, offering valuable insights for predicting outcomes and optimizing economic returns. In the poultry industry, researchers have developed mathematical models to predict animal performance and maximize profits. These models incorporate theories to explain real-world processes and enable future event predictions. One such model is the Broiler Growth Model (BGM), which serves as a predictive tool for estimating feed intake, growth, and body composition of broilers. The BGM takes into account the genetic potential of the broilers, the feed they are provided, and several constraining factors that may prevent the animal from achieving their genetic potential. To evaluate the BGM, a series of simulations were performed: (i) model behavior was evaluated by simulating the response of males and females from 22 to 35 d to feeds differing in dietary protein content and nutrient density; (ii) model prediction was evaluated using the results of a protein response trial conducted at UNESP in which six dietary protein levels were fed to male and female broilers over a 56 d period; and (iii) model optimization was used to maximize economic returns in the above trial. The model behaved as expected when feeds differing in protein content were fed, with feed intake per kg of BW increasing as protein level was decreased, resulting in lower gains and higher body lipid contents. Increasing nutrient density resulted in higher feed intake in the second level, followed by a reduction in feed intake in the highest nutrient feed. The simulated response to nutrient density resulted in increasing body lipid deposition as the nutrient density increased. In comparing the simulated and actual results of the protein response trial, the overall error of prediction was up to 15% for feed intake, BW, and body protein. The optimization routine allows the simulation of different economic scenarios, helping in decision-making. The Broiler Growth Model emerges as a valuable tool for the poultry industry, offering predictive capabilities and economic optimization potential. While minor discrepancies between simulated and actual results exist, the BGM holds significant promise for enhancing efficiency and profitability in broiler production, contributing to the broader goals of sustainable broiler meat production.

Review: When worlds collide - poultry modeling in the 'Big Data' era

Within poultry production systems, models have provided vital decision support, opportunity analysis, and performance optimization capabilities to nutritionists and producers for decades. In recent years, due to the advancement of digital and sensor technologies, 'Big Data' streams have emerged, optimally positioned to be analyzed by machine-learning (ML) modeling approaches, with strengths in forecasting and prediction. This review explores the evolution of empirical and mechanistic models in poultry production systems, and how these models may interact with new digital tools and technologies. This review will also examine the emergence of ML and Big Data in the poultry production sector, and the emergence of precision feeding and automation of poultry production systems. There are several promising directions for the field, including: (1) application of Big Data analytics (e.g., sensor-based technologies, precision feeding systems) and ML methodologies (e.g., unsupervised and supervised learning algorithms) to feed more precisely to production targets given a 'known' individual animal, and (2) combination and hybridization of data-driven and mechanistic modeling approaches to bridge decision support with improved forecasting capabilities.

Update and evaluation of the egg production model in laying hens

The egg production model (EPM) described here is a mechanistic and stochastic model that simulates the amino acid and energy requirements of laying hens. It takes into account their potential rate of laying, and egg weight over time, and the composition of the feed provided. The model predicts feed intake based on the assumption that hens will consume enough feed to reach their genetic potential. The environment is assumed to be non-limiting, although feed intake may be constrained by bulk capacity when bulky feeds are offered. The simulation model integrates a least-cost feed formulator, which enables the prediction of a feeding program that maximizes economic returns. A series of simulations were conducted to demonstrate the model behavior, external evaluation, and the economic optimization routine. The model behavior showed that as the energy content in the feed decreased, the simulated feed intake increased to compensate. Consequently, feeds with lower energy concentrations led to an overconsumption of nutrients, resulting in increased egg component weights (yolk and albumen). However, when the balanced protein was reduced while maintaining a constant energy-to-protein ratio, there was no change in egg components, consistent with published literature. The external evaluation indicated that feed intake, egg production, and egg weight were estimated with low error, and there was a similar trend observed between the estimated and observed data. This demonstrates the reliability of the model. Additionally, the paper provides a demonstration of how to use and interpret the results from the egg production model, including the economic optimization routine. The study found that a feed containing 7.8 g/kg of digestible lysine maximized economic returns. This optimization tool can be valuable in making nutritional decisions to optimize economic returns in an egg production system.

Dietary energy:protein ratio influences the efficiency of utilisation of dietary protein by growing turkeys

1. The following experiment was designed to confirm that the efficiency of dietary protein utilisation (ep) can be reduced when the AMEn to digestible crude protein (DCP) ratio of the feed falls below a critical level. In addition, whether the efficiency would be improved at high DCP contents through the addition of oil or starch was determined.2. A 14d trial (starting at 21 d of age), using BUT 6 turkeys, was designed to measure the effects on ep of four feeds (12.1 MJ AMEn/kg) with AMEn:DCP ratios ranging from 45 to 72 MJ AMEn/kg, and two additional feeds with the same DCP as the highest protein feed, one with an AMEn:DCP ratio of 59, through the addition of canola oil, and the other with a ratio of 51 MJ/kg supplemented with both starch and oil. Twenty birds constituted each experimental unit, with two replications of each sex being used per dietary treatment.3. Ten birds per sex were sampled at the start of the trial and a further five per pen at the end for carcass analysis. Each carcass including feathers was ground and subsampled for water, protein and lipid determination.4. A split-line regression described ep on the four feeds unsupplemented with additional energy (R² = 0.81) with breakpoint at 60.6 MJ AME/kg DCP, maximum ep at 0.736 g/g, and a slope of 0.017. No improvement in ep resulted from supplementing the high protein feed with oil or a mixture of oil and starch, but feed intake and protein and lipid retention increased significantly (P < 0.05).5. The argument that insufficient energy is available to enable high protein feeds to be utilised efficiently was not corroborated by the evidence from this trial.

Composition of feathers and pulp of two broiler genotypes

1. Cobb and Ross broilers (200 of each sex and breed) were fed four phases of diets ad libitum formulated with balanced protein to match their amino acid requirements throughout growth. Ten birds per genotype were sampled and euthanised at two-weekly intervals from 14 to 112 d of age. All feathers were dry-plucked from each of the seven tracts (specific skin areas) and pulp (the centre of the feather filament) was removed from primary and secondary remiges.2. Daily losses of feathers were collected from an additional 20 individually-caged broilers of each breed. These feathers were separated into natal down, contour feathers, remiges and rectrices and then pooled by type, sex and genotype to quantify water and protein contents. Only those feathers collected from male Cobb 500 MX broilers were analysed for amino acid content.3. Amino acid contents of feathers from the seven tracts were measured only in Cobb males on days 1, 28 and 70; for pulp on days 28 and 70; and for the four types of moulted feathers.4. Protein content on a dry matter basis remained relatively constant over all ages and tracts during growth. Water content decreased with age in both sexes and genotype. Lysine and methionine content in feathers decreased with age while cystine, valine, leucine and serine increased. Lysine, methionine and histidine levels were higher in pulp than in mature feathers whereas cystine and valine were higher in mature feathers than in pulp.5. These results, together with information about moulting patterns in broilers, enabled the effects of age of the bird and of the type of feather, to be taken into account when determining the rate of deposition of amino acids in feathers.

Gut capacity of broiler breeder hens

1. Broiler breeders are subjected to qualitative or quantitative feed restrictions to prevent obesity, which causes major health and welfare problems. Diluting their feed by adding inert or low nutrient, bulky materials can reduce obesity, but the capacity of the gut needs to be determined to apply this strategy successfully. Two trials were conducted to measure the bulk capacity of Ross 308 broiler breeders prior to and after the onset of lay. The trial was completely randomised, with nine individually-caged breeders, with each cage as a replicate, totalling 189 birds per trial2. Birds were given ad libitum access to one of 21 maize-soyabean based feeds, an undiluted control or progressive dilution (10, 20, 30 and 40%) with either cellulose fibre, rice husk, sand, vermiculite or sawdust. Feeds were analysed for density, crude-, acid detergent- and neutral detergent-fibre, water-holding capacity (WHC), cation-exchange capacity and oil-holding capacity.2. In general, feed intake (scaled to body weight^0.67) increased and then declined as the proportion of each diluent increased. Intake increased linearly when rice hulls and sand were used as diluents.3. Water holding capacity was the most appropriate measure to define the gut capacity of broiler breeders.4. The trial data was used to estimate the maximum-scaled feed intake (SFI_max) in broiler breeders, which was 240-56.1WHC + 4.34WHC² g/kg^0.67/d.

The response of reproducing Japanese quail to dietary valine

1. A feeding trial was conducted to measure the responses of Japanese quail to dietary valine. In total, 280 Japanese quail were randomly assigned to eight treatments giving seven replicates (cage - 35 cm length, 35 cm width × 15 cm high). Experimental diets were formulated using a dilution technique to give a range dietary Val concentration (1.97 to 9.85 g/kg).2. Feed intake was maximised at 6.66 g Val/kg and above, but declined linearly below this level. Body weight reached a maximum of 170 g on 6.66 g Val/kg. Egg output peaked at 9.5 ± 0.3 g/bird/d with an egg weight of 11 g for the 6.66 g Val/kg diet. Rate of laying for the group that received the feed with the lowest Val content was close to zero (1.40%), but egg weight on this treatment was 70% of the maximum egg weight. Valine required per gram of egg output was estimated as 10.6 mg/g, whereas the maintenance requirement was 159 mg/kg body weight. Val required for maximum egg output was estimated in 154 mg/d.3. The marginal cost of Val in Brazil currently is negative below a level of 8.0 g/kg feed, which is above that required for maximum egg output. Consequently, Val cannot be regarded as a limiting amino acid currently, as the optimum economic intake exceeds the requirements of all the individuals in the population. The price of a quail egg weighing 11 g in Brazil at the time of the experiment was R$ 0.021. Even if the marginal revenue for these eggs was doubled to 0.4 c/g, there would be no reason to increase the intake of Val.

Prediction of maximum scaled feed intake in broiler chickens based on physical properties of bulky feeds

1. A trial was conducted to investigate the capacity of broiler chickens to consume bulky feeds during three stages of growth. These phases were from 1 to 15 d, 16 to 30 d and from 31 to 45 d. 2. A basal feed was serially diluted (0%, 2.5%, 5.0%, 10% or 15%) with one of five diluents (cellulose fibre, sawdust, rice husk, sand or vermiculite) to produce 25 feeds which were supplied on an ad libitum basis to the birds in each phase. Cobb 500® strain chicks were used, and, within each phase, each feed was given to nine individually-caged birds, 225 in total, distributed in a completely randomised design. 3. Intake increased initially, and then declined, as the proportion of each diluent increased. The consumption of feeds that limited intake were directly proportional to metabolic body weight and so a scaled feed intake, expressed as g/BW^0.67 per day, was calculated. There were large effects of feed type on intake, in the short term, with consumption of a bulky feed leading to higher intakes. 4. It was concluded the Water Holding Capacity (WHC) content of the feeds could be appropriate measurement of 'bulk' responsible for limiting intake and could be used to predict maximum feed intake capacities of broiler chickens fed bulky diets.

A description of the growth and moulting of feathers in commercial broilers

1. Changes in feather length and weight and daily losses of down, contour feathers, remiges and retrices were studied in two commercial broiler strains to determine feather growth and moult in broilers up to 112 d of age. 2. Ten pens of 20 chicks for each sex x strain were fed adequate amounts of dietary protein in a four-phase feeding programme. Ten birds were sampled per genotype at 14, 28, 42, 56, 70, 84, 98 and 112 d. Feather loss was determined for individual birds caged within a nylon net. 3. All feathers were dry-plucked from each of seven tracts, with representative feathers from the capital-cervical, dorsopelvic and interscapular, pectoral and femoral tracts being randomly selected. Three rectrices of the dorsocaudal tract and three primaries and secondaries of the humeral-alar tract of the right wing were evaluated. 4. The length of the selected feathers was measured, and the feathers from each tract and from the whole bird were weighed. 5. A wide range of rates of maturing (0.0250-0.0907/d) and mature weights (9.62-52.9 g) were evident between sampled tracts. 6. Feather weight failed to predict some moults which were detected by the measurement of feather losses. From the weight data, moulting was evident only in the humeral-alar and dorsocaudal tracts, whereas, when daily losses were measured, contour feathers accounted for over 0.7 proportion of feather losses. Logistic equations adequately described the cumulative losses of down, contour feathers and remiges. 7. Feather loss needs to be considered when feather growth is determined from feather weight at different ages. 8. The rate of maturing (B) of feathers was numerically higher in Ross males and females than in the Cobb strain. In females, B was higher than in males (0.0483 vs. 0335/d) but the mature weight was lower (162 vs. 230 g).

The growth of turkeys 1. Growth of the body and feathers and the chemical composition of growth

1. The potential growth of modern turkey genotypes was measured using male and female BUT 6 (BUT) and Hybrid Converter (HYB) strains. At one-day-old, 720 male and 960 female poults were randomly allocated to 48 littered pens in two houses with 30 males or 40 females of each strain per pen. Five feeds of decreasing protein content were fed to both sexes during the growing period. 2. Birds were weighed at 1, 7, 14, 21, 35, 56, 77, 119 d (males only), 126 d (females only) and 140 d (males only) and, on each occasion, six birds were selected and removed for carcass analysis. 3. Growth was similar in both strains, but the growth rate of females appeared to decline relative to the earlier trajectory after 70 d, and this tendency being greater in HYB females. 4. HYB birds of both sexes had more feathers than BUT to 77 d, but thereafter these differences were non-significant. A single allometry between feather and body protein weight was observed over all genotypes with no differences apparent between sexes within strains. The Gompertz curve adequately described the growth of body protein, water and ash. 5. Body lipid (g/100g bodyweight) declined in the early stages of growth. This might reflect an energy deficiency in the diet or might indicate that the present description of lipid growth does not apply in turkeys as it does in other species. 6. Whereas the description of body growth, feather growth and the chemical components of growth given in this paper may not fully reflect the true potential of the genotypes used, nevertheless they provide useful information regarding the latest genotypes available in the turkey industry. Some of the observations suggested that current performance might be improved if further research is conducted regarding dietary energy transactions.

The growth of turkeys 2. Body components and allometric relationships

1. The relationships between the main components of the body and body protein among males and females of BUT 6 (BUT) and Hybrid Converter (HYB) turkey strains were examined. 2. The weights of breast meat, breast skin, drumstick meat, drumstick skin, thigh meat, thigh skin and wing-plus-skin as well as the head, neck, feet, blood, heart, liver and gizzard were measured at different stages of growth after which all components of each bird were minced together in order to determine the feather-free body protein weight of each bird sampled. Using the weights of the components and the protein content of each bird the allometric relationships between the components and body protein were determined and then compared for each strain x sex combination. 3. By excluding the breast weights at day-old and at 7 d, the remaining points produced an acceptable allometric relationship (R² = 0.992). Thigh weight could be predicted for all strain x sex combinations using one allometric equation, as could drumstick skin weight. Breast and thigh skin weights differed between males and females. Females of the HYB strain exhibited heavier drumstick and wing-plus-skin weights at a given body protein weight than the other three strain x sex combinations. These differences in both the constant term and regression coefficient in the allometric equations between genotypes are probably due to differences in the amount of lipid that is deposited in these tissues. 4. Sexes differed in the allometric relationships for head, feet, heart and liver, while breeds differed in gizzard weight. A common relationship between the four genotypes could be used to predict the weight of blood in the carcass. 5. The allometric equations fitted to the data in this trial enable the accurate prediction of the weights of the different physical components given the weight of body protein.

Energy partitioning at low temperatures in broiler breeders

The objective of the present study was to investigate how broiler breeder hens partition dietary metabolisable energy (ME) at low temperatures. Performance of caged broiler breeders fed equal quantities of essential nutrients (other than energy) was measured in six environmental chambers, with the temperature in each chamber being kept constant at 10°C, 12.5°C, 15°C (two chambers), 17.5°C or 20°C for two 6-week periods. Throughout these two trial periods, birds were fed 160 g/day of one of four diets containing 12.9, 11.9, 10.5 or 9.7 MJ apparent ME/kg, so that daily energy allocations ranged from 1552 to 2964 kJ/bird. Irrespective of the environmental temperature to which they were subjected, broiler breeders consumed virtually all of the feed allocated to them each day. Mean rate of lay and egg output in the final 3 weeks of each period of hens on the highest apparent ME feed was unaffected by the decrease in temperature from 19.5°C to 9.9°C, but equally depressed on the three lower energy levels. Both weight gain and egg weight increased marginally, but significantly, as the temperature decreased. As a function of body protein weight (BP, kg), egg output (EO, g/day) and growth (ΔW, g/day), the ME consumed (kJ/day) by broiler breeders over all treatments was partitioned as follows: 2423 (±30.3) BP + 7.04 (±0.41) EO + 13.5 (±1.10) ΔW. An ME intake of 1900 kJ/bird.day would appear to be adequate for broiler breeders over the range of temperatures used in the trial.

Modelling the egg components and internal cycle length of laying hens

A model that can estimate the changes that occur to the composition of egg components over time is an important tool for the nutritionists, since it can provide information about the nutrients required by a laying hen to achieve her potential egg output. In this context, the present study was aimed to model the potential egg production of laying hens during the egg-production period. One hundred and twenty Hy-Line W36 and ISA-Brown layers were used from 18 to 60 weeks of age, with each bird being an experimental unit. The birds were housed in individual cages during the experimental period. Egg production (%), egg weight (g) and the weight of egg components were recorded for each bird. The data were used to calculate the parameters of equations for predicting the weights of yolk, albumen and shell, and for predicting internal cycle length. The predicted results were evaluated by regressing residual (observed minus predicted) values of the predicted values centred of their average value. The equations for predicting mean yolk weight with age are for Hy-Line W36 (y1) and ISA-Brown (y2) respectively. Albumen and shell weights for Hy-Line W36 were described by the equations 15.07 × (yolk weight)0.37 and 0.70 × (yolk + albumen weight)0.50 respectively, and for ISA-Brown, 21.99 × (yolk weight)0.24 and 1.60 × (yolk + albumen weight)0.34 respectively. The average internal cycle length over time for Hy-Line W36 (ICL1) is described by the model 22.95 + 5.24 × (0.962t) + 0.02 × t and for ISA-Brown by 24.01 + 10.29 × (0.94t) + 0.004 × t, where t is the age at first egg (days). The assessment of the results indicated that the equations for predicting egg weight were more accurate for Hy-Line W36 but less precise for both strains, whereas the equation models for predicting the internal cycle lengths were more accurate and precise for ISA-Browns. The models could predict the potential weight of egg components and the rate of laying associated with the internal cycle lengths, and, on the basis of this information, it is possible to improve the nutrient requirement estimated.

The effect of dietary energy:protein ratio, protein quality and food allocation on the efficiency of utilisation of protein by broiler chickens

1. Various theories have been proposed to explain the reduced performance of broilers when given feeds excessively high in protein, but a satisfactory solution to this problem had, up to now, not been found. Three experiments were conducted to test the hypothesis that the efficiency of utilisation of protein (e_p) is a linear-plateau function of the ratio between the feed apparent metabolisable energy and digestible crude protein contents (AMEn:DCP) and that dietary protein quality, feed allocation and sex do not influence this relationship. 2. A 'linear-plateau' model successfully described the efficiency of protein utilisation (e_p) as a function of AMEn:DCP in all three experiments. In Experiment 1, with both sexes being both ad libitum and control fed, the breakpoint was at 58.6 MJ AMEn/kg DCP. In Experiment 2, both sexes were fed balanced and unbalanced protein series, and at different rates, the slopes of the ascending part of the linear-plateau relationships for the different treatments were the same for all treatments (0.0204), and the inflection point was at 71 MJ AMEn/kg DCP. Using similar treatments in Experiment 3, the breakpoint for the balanced protein was 72 MJ/kg and for the unbalanced, 64, with a combined slope of 68 MJ AMEn/kg DCP. 3. The three experiments provide adequate evidence that e_p is a linear-plateau function of the dietary AMEn:DCP ratio with a breakpoint of around 66.2 ± 1.98 MJ AMEn/kg DCP. Below this critical ratio, food intake declines as does protein and lipid retention. 4. That broilers, like pigs, exhibit an energy-dependent phase when high-protein feeds are offered is of practical importance when formulating pre-starter feeds for broilers and starter feeds for turkey poults as the e_p of such feeds may well fall below the maximum due to the lack of dietary energy required to process the high dietary protein contained in such feeds resulting in poorer performance than expected.

The response of weaned piglets to dietary valine and leucine

Valine (Val) is considered to be the fifth-limiting amino acid in a maize-soyabean meal diet for pigs. Excess leucine (Leu) levels often occur in commercial diets, which may attenuate the effect of Val deficiency because of an increased oxidation of Val. The objective of the present experiment was to determine the effect of increasing concentrations of Leu on the response of young piglets to dietary Val. In all, 75 Large White×Landrace entire male pigs, 44 days of age and with a mean starting weight of 13.5 kg, were used. Three of these were sacrificed at the start to determine their mean initial chemical composition. A summit feed first limiting in Val was serially diluted with a non-protein diluent to produce a series of five digestible Val concentrations of 11.9, 10.1, 8.3, 6.6 and 4.8 g/kg, with a sixth treatment being added to test that the feeds were limiting in Val. Three identical Val series, each with six levels of Val, were supplemented with increasing amounts of Leu (23, 45 and 67 g/kg), thus 18 treatments in total. All pigs were killed at the end of the trial after 18 days for analysis of water, protein, lipid and ash in the carcass. The levels of Val and Leu and their interaction significantly influenced all the measurements taken in the trial. Daily gain in liveweight, water and protein, and feed conversion efficiency all increased with dietary Val content, whereas feed intake decreased as both Val and Leu contents increased. The deleterious effect of increased Leu on feed intake and growth was more marked at lower levels of Val. Supplementing the feed with the lowest Val content with additional Val largely overcame the effect of excess Leu. The efficiency of utilisation of Val for protein growth was unaffected by the level of Leu in the feed, the primary response to excess Leu being a reduction in feed intake. An intake of around 9 g Val/day yielded maximal protein growth during the period from 44 to 62 days of age in pigs of the genotype used in this trial.

Description of a model to optimise the feeding of amino acids to growing pullets

1. A nutrition model is described that may be used to optimise the amino acid nutrition of laying-type pullets prior to the onset of lay. It is not a method of optimising lifetime laying performance. 2. The potential growth and composition of the body, feathers, ovary and oviduct are described from hatching to the age at which sexual maturity is attained, from which the daily amino acid and energy requirements for the average individual in the population can be calculated. 3. There are two parts to the approach used, the first being a description of the model itself and the second being a description of how the required information was gathered. A number of assumptions made in developing the model are discussed. 4. The rates of maturing of the body, feather-free body and body protein of the DeKalb pullets used were shown to be constant at 0.017/d and those of feathers at 0.02/d. These are considerably slower than those of the oviduct and ovary (0.139 and 0.084/d respectively). The ovary attained a higher mature weight (78.4 vs. 58.7 g) than the oviduct. 5. The age at which the growth of the reproductive organs is initiated in the model is defined by the user. The daily amount of threonine required to meet the requirements for maintenance and potential growth of the developing tissues and organs is calculated for each day of the growing period from hatching to the age at which the first egg is laid. A method of calculating the required daily concentration of threonine in the feed is described, from which a feeding programme may be derived. 6. For the model to produce an optimum economic feeding programme for a population of laying-type pullets, more information than is available from this study is required. These issues are discussed in the paper.

The reproductive response of female ostriches to dietary protein

A study was conducted with breeding ostriches over two consecutive breeding seasons to determine their response to different concentrations of a well-balanced dietary protein. Five concentrations of protein were fed to both females and males at an intake of 2.5 kg/bird d. The respective diets contained 75, 91, 108, 123 and 140 g protein/kg feed with energy held constant at 9.2 MJ metabolisable energy/kg feed. Egg production (mean ± SE, 39.1 ± 3.6 eggs/female/season) was unaffected by dietary protein concentration. Similarly, no significant trends were found for the number of unfertilised eggs (9.1 ± 1.8), dead-in-shell chicks (8.2 ± 1.3), the number of chicks hatched (19.5 ± 2.5) and change in the mass of females (-16.3 ± 10.2 kg). Egg weight decreased linearly as dietary protein content increased. Age of the ostrich female had a highly significant effect on the number of eggs laid, the number of chicks hatched, the number of dead-in-shell and infertile eggs produced per hen, as well as the mass change of female breeding birds, but did not affect the response of any of these variables to dietary protein content. It was concluded that ostriches do not benefit from dietary protein contents greater than about 75 g/kg when this is fed at a daily total feed intake rate of 2.5 kg/bird during the breeding season.

Changes in the feather-free body of broiler breeder hens after sexual maturity

Changes in the feather-free body (water, lipid and protein) of broiler breeder hens was measured at intervals between 15 and 60 weeks of age to provide information that could be used as the basis for predicting their maintenance requirements. The mean weight of feather-free body protein varied between 348 and 379 g at 15–20 weeks, increasing to 648 g by 40 weeks and then remaining relatively constant for the rest of the laying period. Mean body lipid content increased from 160 g at 15 weeks to 711 g at 60 weeks. The initial increase in feather-free body protein weight can be ascribed to increases in ovary and oviduct weights as the birds become sexually mature, and to the variation in ages at which this development takes place. Our conclusion is that changes in bodyweight in broiler breeders after sexual maturity are mainly in body lipid content, this being a consequence of the way in which the birds are fed, and that any gain in body and feather protein occurs only in hens that are out of lay. We suggest that it should not be necessary to assume that protein and lipid growth is obligatory when determining nutrient requirements of broiler breeder hens.

Predicted optimum ambient temperatures for broiler chickens to dissipate metabolic heat do not affect performance or improve breast muscle quality

An experiment was conducted to test the hypothesis that muscle damage in fast-growing broiler chickens is associated with an ambient temperature that does not permit the birds to lose metabolic heat resulting in physiological heat stress and a reduction in meat quality.

The experiment was performed in 4 climate chambers and was repeated in 2 trials using a total of 200 male broiler chickens. Two treatments compared the recommended temperature profile and a cool regimen. The cool regimen was defined by a theoretical model that determined the environmental temperature that would enable heat generated by the bird to be lost to the environment.

There were no differences in growth rate or feed intake between the two treatments. Breast muscles from birds on the recommended temperature regimen were lighter, less red and more yellow than those from the cool temperature regimen. There were no differences in moisture loss or shear strength but stiffness was greater in breast muscle from birds housed in the cool compared to the recommended regimen.

Histopathological changes in the breast muscle were similar in both treatments and were characterised by mild to severe myofibre degeneration and necrosis with regeneration, fibrosis and adipocyte infiltration. There was no difference in plasma creatine kinase activity, a measure of muscle cell damage, between the two treatments consistent with the absence of differences in muscle pathology.

It was concluded that breast muscle damage in fast-growing broiler chickens was not the result of an inability to lose metabolic heat at recommended ambient temperatures. The results suggest that muscle cell damage and breast meat quality concerns in modern broiler chickens are related to genetic selection for muscle yields and that genetic selection to address breast muscle integrity in a balanced breeding programme is imperative.

The response to dietary threonine in laying-type pullets during growth

1. This study aimed to provide information on the response of laying-type pullets to dietary threonine (THR) during three periods of growth prior to the onset of lay. Different batches of Dekalb White pullets were used in three separate trial periods (from 4 to 6, 8 to 11 and 13 to 16 weeks of age) using 8 dietary THR concentrations in each period, using a completely randomised design, and with each treatment being replicated 6 times, using 15 birds per replication in period 1 and 8 birds in periods 2 and 3. In period 1 the THR content (THRc) ranged from 2.3 to 7.6 mg/g, in period 2 from 1.7 to 5.5 mg/g, and in period 3 from 1.4 to 4.7 mg THR/g feed. 2. Body weight gain, food intake and the deposition of protein and lipid in the feather-free body and in the feathers were measured in each period. Linear regressions were fitted to all data falling below the break point defined by the broken stick regression, to estimate the efficiency of utilisation of THR. The maximum protein growth rate was 4.0 ± 0.2, 5.3 ± 0.4 and 3.5 ± 0.5 g/d in periods 1, 2 and 3, respectively. 3. The efficiency of utilisation of dietary THR for THR deposition in each period was the same, at 0.85 ± 0.1 mg/mg. As dietary THRc decreased, the amount of body lipid deposition increased. 4. With this information, it is possible to determine the daily requirement for THR for the potential growth of body and feather protein in growing pullets.

Modelling changes in the components of eggs from broiler breeders over time

1. Because the components of the egg differ in nutrient content, and the proportions of these components change over time, the daily intake of nutrients required to produce an egg will also change with time. Information on these relationships is essential when attempting to determine the nutrient requirements of a broiler breeder hen at different stages of lay, and in predicting performance when the hen is supplied with a given amount of food with a given nutrient composition. 2. Yolk weight is related to hen age and may be predicted using a linear-by-linear function, the coefficients of which are the same for Cobb and Ross breeders. Allometric functions may be used to predict albumen weight from yolk weight, and shell weight from the weight of the egg contents. Egg weight is given by the sum of the three components. 3. The proportion of yolk increased with advancing age whilst the proportions of albumen and shell decreased. However, at a given age, larger eggs contain proportionally more albumen. Eggs from Cobb hens had proportionately more albumen than Ross eggs towards the end of lay. 4. A stochastic population model verified that these functions accurately reflect the proportional changes in the egg components with advancing hen age and at a given age, over a range of egg weights.

Interaction of hen production type, age, and temperature on laying pattern and egg quality

The effect of production type (layer vs. broiler breeder), age (onset and end of laying cycle), and temperature (20 and 28°C) on various aspects of the egg production process and quality was evaluated. Highly significant differences were detected between laying hens and broiler breeders (P ≤ 0.001) in all production parameters. Similarly, age significantly affected rate of lay (P ≤ 0.001; 75.4% for young vs. 62.6% for old), mean sequence length (P ≤ 0.001; 7.7 d for young vs. 2.6 d for old), and time of oviposition (P ≤ 0.001). However, there was no effect of temperature on rate of lay, sequence length, or feed intake. Significant interactions between hen type and age were apparent in rate of lay (P ≤ 0.001), sequence length (P ≤ 0.001), and time of oviposition (P ≤ 0.001). A significant interaction between production type and age (P ≤ 0.015) was evident in egg weight, but egg component proportions were dependent only on hen type. Egg shape index was significantly affected by age (P ≤ 0.004), by temperature (P ≤ 0.028), and an interaction between type and age (P ≤ 0.001). Specific gravity declined with age (P ≤ 0.035) and increasing temperature (P ≤ 0.013).

A mechanistic, stochastic, population model of egg production

1. A mechanistic, stochastic egg production model is presented. Mean age at first egg may be predicted from the lighting programme applied during rearing, using the Bristol-Reading model (Lewis et al., 2002). 2. Rate of ovulation is determined by an amended version of the mathematical model of the ovulatory cycle, originally proposed by Etches and Schoch (1984). 3. Oviposition times are estimated from ovulation times. 4. Yolk, albumen and shell weights are calculated using allometric functions. 5. The model predicts egg production of a theoretical flock of laying hens for a full laying year, including random occurrences of double-yolked and soft-shelled eggs and internal ovulations.

A comparison of the effects of feeding treatments and lighting on age at first egg and subsequent laying performance and carcase composition of broiler breeder hens

The effects of the growth curve from 15 to 20 weeks, age at photostimulation and pattern of photostimulus on sexual maturity, egg production and egg weight were evaluated in two trials with broiler breeder females to 56 and 34 weeks of age (housed in litter pens and individually caged, respectively). Carcase composition and reproductive morphology of hens varying in laying efficiency were measured in the second trial. Trial 1: Four growth curves were applied from 15 to 20 weeks to pullets housed in litter pens. Birds were transferred from 8- to 10-h photoperiods at 20 or 24 weeks of age, followed by weekly increments of one hour to reach a 16-h final photoperiod. Lower-than-recommended body weights at 20 weeks significantly delayed sexual maturity, reduced peak rate of lay, total eggs and mean egg weight. However, double-yolked egg production was lower, resulting in non-significant differences in settable egg numbers between body weight treatments. Birds reared to the heaviest body weight exhibited a significantly advanced sexual maturity, but total egg numbers, peak rate of lay and mean egg weight were not significantly affected. However, the laying of more double-yolked eggs resulted in a decrease in the number of settable eggs. Delaying photostimulation to 24 weeks significantly retarded sexual maturity, reduced total and settable egg numbers, and increased mean egg weight. A tendency for fewer double-yolked eggs was observed. Trial 2: At 19 weeks, birds were selected from the 4 body weight categories in Trial 1 and moved to individual cages in 8 rooms. Five lighting programmes were applied. The pattern of photostimulation applied did not affect any of the production traits measured. At 34 weeks, 24 birds were selected for the analysis of reproductive morphology, presence of internal or multiple ovulations, and carcase composition. Eight hens showing an early age at first egg and regular egg production records, 8 birds showing erratic laying performance and 8 non-layers were killed for this purpose. There were no differences in carcase composition or reproductive morphology between these groups. No internal ovulations or double or multiple ovarian hierarchies were observed. The results presented confirm that broiler breeders do not require a lighting stimulus in order to initiate ovarian activity and that, where no lighting stimulus is given, body weight or feeding level plays a critical role in stimulating the birds to attain sexual maturity. However, when a lighting stimulus is given, factors such as body weight and body composition become relatively less important in regulating the age at sexual maturity.

Photoperiod and oviposition time in broiler breeders

1. Oviposition times were recorded for broiler breeder hens under 8-, 10-, 11-, 12-, 13-, 14- and 16-h photoperiods. 2. Mean oviposition time (MOT) was delayed relative to dawn by approximately 0.5 h for each 1-h increase in photoperiod up to 14 h, but was similar for 14- and 16-h photoperiods. However, the 0.5 h/h regression for the time when half the eggs were laid continued through to 16 h. 3. The rate of change in MOT for each 1-h increase in < or = 14-h photoperiod was similar to that reported for early and modern egg-type hybrids, but, compared with modern genotypes, time of lay itself was 1 h later than white-egg and 2.5 h later than brown-egg hybrids. 4. At photoperiods < or = 12.25 h, the number of eggs laid before dawn increased by 4-5% for each 1-h reduction in daylength.

Constant photoperiods and sexual maturity in broiler breeder pullets

1. Broiler breeder pullets were maintained on 10-, 11-, 12-, 13-, 14- or 16-h photoperiods to determine the effect of constant photoperiods on sexual development in broiler breeders. The birds were fed to achieve a 2100 g body weight at approximately 17 or 20 weeks to see if the photosexual response was modified by rate of growth. 2. In both body weight groups, pullets maintained on 10h were the first to reach sexual maturity (50 eggs/100 bird-d), and these and the 11-h pullets matured significantly earlier than any of the other photoperiod groups. Pullets maintained on 13 or 14 h matured latest, at about 3 weeks after the 10-h pullets, though both were only marginally later than the 12- or 16-h birds. These differences in maturation probably reflect the different rates at which photorefractoriness is dissipated in broiler breeders reared on photoperiods that vary in their degree of stimulatory competence. 3. There were no significant interactions among the photoperiods and the ages at 2100 g; faster-growing birds consistently matured about 10 d earlier than conventionally grown pullets.

Effects of body weight at, and lighting regimen and growth curve to, 20 weeks on laying performance in broiler breeders

1. A total of 4000 Ross broiler breeders were reared to a 20-week target body weight of 1.55, 2.16 (standard), 2.50 or 2.84 kg, using either a convex or concave growth curve. Each treatment group was either exposed to a conventional broiler breeder lighting regimen, with a series of weekly one-hour increments in photoperiod from 8h at 19 weeks to a 16-h maximum, or maintained from 4d on a 17-h photoperiod. 2. Each 100 g increment in body weight at 20 weeks was associated with a significant increase of 0.55 kg in cumulative food intake, and a 1.5-d advance in sexual maturity. However, leaner body weights at 20 weeks resulted in smaller body weight gains between 20 and 60 weeks (-2.4 g/d/kg body weight at 20 weeks), and an increased production of double-yolked eggs. Neither egg production nor mean egg weight was affected by 20-week body weight. 3. Birds fed to produce more rapid early growth had higher feed intakes to 20 weeks, but reached sexual maturity 7 d later than birds permitted accelerated growth from 15 weeks. Growth curve did not influence body weight gain in lay, egg production or mean egg weight. 4. Birds maintained on 17-h photoperiods reached sexual maturity 27 d later, produced 7 fewer eggs to 60 weeks, and had a mean egg weight 1.2 g heavier than birds photostimulated at 19 weeks. Lighting treatment did not affect food intake to 20 weeks, the proportion of double-yolked eggs or body weight gain between 20 and 60 weeks. 5. Birds fed to have a faster growth early in the rearing phase and maintained on 17-h photoperiods produced 11 fewer eggs than those fed to have accelerated growth at the end of the rearing phase, yet there was only one egg difference between the growth-curve groups for the conventionally lighted birds, which was not significant. 6. The earlier sexual maturity of the conventionally lighted birds compared with those maintained on 17-h photoperiods either indicates that broiler breeders require an increment in photoperiod to stimulate rapid gonadal development or that broiler breeders exhibit juvenile photorefractoriness that takes longer to be dissipated when birds are not given a period of short days. 7. The findings suggest that a nutritional stimulus late in rearing is only necessary for satisfactory egg production if birds have not received a concurrent increment in photoperiod.

Temporary exposure of prepubertal, somatically-mature broiler breeder females to stimulatory photoperiods

1. Individually-caged Ross 308 broiler breeders were transferred temporarily at 147 d from 8 to 14-h photoperiods and back to 8 h at 5-d intervals from 5 to 25 d and at 32 d. Control birds were maintained on 8 h or transferred permanently to 14 h. 2. Five long days had minimal effect on age at first egg, between 10 and 25 long days progressively accelerated sexual development, and maximum advance was achieved by 32 long days. However, a model involving the ogive of a normal distribution with a mean of 14 long days and an SD of 5.3 indicated that 28 long days would be sufficient to maximise sexual development. 3. The similarity of this model for broiler breeders with one previously produced for egg-type pullets suggested a common physiological mechanism for photosexual responses to two opposing changes in photoperiod.

Photoperiodic responses of broilers. III. Tibial breaking strength and ash content

1. A total of 7960 Cobb and Ross broiler males were reared on various photoperiods or continuous illumination in two trials to 35 or 40 d. Tibial breaking strength was measured in both, and tibial ash content determined in the first of the two trials. 2. Tibial breaking strength was significantly affected by photoperiod, body weight, testicular weight, and genotype. Although peak bone strength occurred at about 7 h for Ross and at 12 h for Cobb, with reductions in strength for both shorter and longer photoperiods than these peaks, the removal of body weight effects showed that tibial breaking strength was negatively correlated with photoperiod per se. However, after removal of photoperiodic influences, breaking strength was positively correlated with both body weight and testicular weight. 3. Ross birds had greater tibial breaking strengths than Cobb, irrespective of whether the comparisons were made at the same photoperiod, the same body weight, or the same ash content. 4. Ash content increased according to the logarithm of photoperiod, but was unrelated to body weight. Tibial breaking strength increased with ash content. Ash contents were similar for Ross and Cobb birds. 5. Despite the significant differences in breaking strength and ash content, there were no broken bones or signs of leg abnormality in any of the 300 birds sampled. Tibial breaking strength data may therefore be of limited value in assessing the benefits of photoperiod to welfare in modern broilers.

Photoperiodic responses of broilers. II. Ocular development

1. Poultry are naturally long-sighted when they hatch, becoming emmetropic by 6 weeks of age. However, Cobb and Ross broilers exposed to <or=12-h photoperiods rapidly learn to eat in the dark, a behaviour which could adversely affect the establishment of emmetropia. And so, in the current study, eyes were enucleated, post mortem, at 40 and 54 d from broilers given various photoperiods between 2 and 24 h, and eye weight determined to indirectly assess the extent to which photoperiod might affect ocular development. 2. In both genotypes, there was an inverse linear relationship between absolute eye weight and photoperiod up to 21 h, but continuously illuminated birds consistently had heavier eyes. When expressed relative to body weight, eye weight for <or=21-h birds was inversely related to the logarithm of photoperiod. 3. The slope of the regression of relative eye weight on <or=21-h photoperiod log values was significantly less at 54 d than at 40 d in both genotypes, but constantly illuminated birds continued to have above average eye weights. 4. Cobb birds invariably had heavier eyes than Ross, both in absolute and relative (to body weight) terms. 5. The results support previous work suggesting that there is a minimum period of daily darkness required to maintain chicken eye growth within the normal range and show that very short photoperiods, as well as ultra-long photoperiods and continuous illumination, adversely affect ocular development, with potential welfare implications.

Photoperiodic responses of broilers. I. Growth, feeding behaviour, breast meat yield, and testicular growth

1. A total of 7960 Cobb and Ross broiler males were reared in two trials to 35 d on various photoperiods between 2 and 21 h or under continuous illumination; a total of 444 birds were randomly selected at 35 d and retained for subsequent determination of breast meat yield and testicular weight at 40 or 54 d of age. 2. In both strains, feed intake and growth were positively correlated with photoperiod during the first 21 d, but afterwards feed intake was not significantly affected by photoperiods longer than 6 h and growth was negatively correlated with photoperiod beyond 12 h. Overall, to 35 d, there were no significant photoperiodic influences on either feed intake or growth for >or=6-h photoperiods, but significant depressions in feed intake and growth for photoperiods shorter than 6 h. Feed conversion efficiency was maximised by 12-h photoperiods, with decreases in efficiency above and below 12 h. Mortality was unaffected by photoperiod <12 h, but increased proportionately with photoperiod >12 h. The incidence of Sudden Death Syndrome (SDS) had an inverse relationship with photoperiod <or=10 h, but was positively correlated with photoperiod >10 h. The European Efficiency Factor was curvilinearly related to photoperiod, with the highest efficiency occurring at 12 h. Ross birds had significantly greater feed intakes but poorer feed conversion efficiencies than Cobb; differences in growth, overall mortality and the incidence of SDS between the strains were not significantly different. 3. By 5 d, birds given <or=15 h illumination had learned to eat in the dark, with the amount of feed consumed being inversely proportional to photoperiod; further increases in the amount of nocturnal feeding occurred between 5 and 20 d for <or=12-h photoperiods. The mean hourly rate of nocturnal feeding was consistently lower than diurnal feeding, irrespective of photoperiod. Nocturnal feeding patterns were similar for both genotypes. 4. Breast meat yield at 40 d was unaffected by photoperiod in Cobb birds, but significantly higher in continuously illuminated Ross birds than <or=21 h. At 54 d, breast meat yield was significantly higher in both genotypes given 21 h or continuous illumination and, overall, higher than at 40 d. 5. Testicular weights at 40 and 54 d of age increased with photoperiod in both genotypes to 12 or 15 h. Thereafter, weights plateaued for Cobb but decreased for Ross as the photoperiod was further extended to continuous illumination. 6. New EU welfare regulations come into effect on 30 June 2010 and these state that meat-chickens must have at least 6 h of darkness in each 24-h period, i.e. a maximum photoperiod of 18 h; compliance with the regulations should have no adverse effect on either performance or profitability.

Photoperiods for broiler breeder females during the laying period

Ross 308 broiler breeder females, maintained in litter-floor pens, were reared from 2 d of age on 8-h photoperiods and transferred abruptly to an 11-, 12-, 13-, or 14-h photoperiod at 20 wk of age and at a mean BW of 2.09 kg. Four qualitative dietary treatments were superimposed upon each photoperiodic treatment, but, in the absence of any significant interactions of photoperiod with diet, only photoperiodic means are reported. Age at 50% egg production (ASM) was progressively advanced as photoperiod increased from 11 to 13 h but was similar for 13-h and 14-h birds. Egg production was significantly related to ASM, with peak egg numbers being stimulated by a transfer to 13-h photoperiods. Rate of lay after 48 wk of age declined more rapidly in the 14-h birds than in any of the other groups, suggestive of an earlier onset of adult photorefractoriness. More eggs were laid outside the nest box and more cracked and dirty eggs were produced by birds on 11- and 12-h photoperiods than on 13- or 14-h photoperiods. Mean egg weight was positively correlated with ASM but negatively related to photoperiod; the number of eggs thought to be double-yolked was not significantly affected by photoperiod. Total egg mass output was not significantly affected by photoperiod. Birds exposed to 11-h and 12-h photoperiods were heavier at 60 wk than birds transferred to 13- or 14-h photoperiods. These findings show that a transfer from 8 to 13 h at 20 wk optimizes egg-laying performance in broiler breeder females, especially when they are kept beyond 60 wk of age.