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1. An experiment was conducted to investigate if broilers can improve their performances and N-retention using choice feeding (CF). 2. Treatment 1 consisted of a standard three-phase feeding regime (SF). Treatments 2-7 were CF treatments with a high (HP) and a low protein (LP) feed offered simultaneously to the birds. Choice feeding started at day 1 or 8 and feeds were offered in mash form or as pellets. 3. When choice feeding was started at day 1 and the HP diet was mash, growth rates were increased (+4.2%) compared to SF, whereas all other CF treatments showed similar or significantly lower final body weights compared to SF. Feed conversion was increased for all CF strategies. 4. Highest yield and breast meat percentages were obtained if the low protein diet was pelleted. The amount of N excreted was increased for most choice feeding treatments as a result of the increased N-intakes and the less efficient growth. 5. Broilers were able to make a choice between two feeds differing in protein/amino acid contents starting as early as day 1, but choices were influenced by feed form. The results confirmed that very high protein/amino acid concentrations in the starter period are desirable to improve growth rates in fast-growing chickens.

The objective of the research reported here was to control the growth trajectory of broiler chickens during the production process based on an adaptive compact dynamic process model. More specifically, the daily feed supply was calculated, based on a model-based control algorithm, with the aim of following a previously defined target growth trajectory as close as possible. For the modeling of the dynamic growth response of broiler chickens to the control input, feed supply, an online parameter estimation was used. The developed control algorithm was able to grow the birds according to different target trajectories ranging from restricted (final BW of 1,800 g and 1,945 g in experiments 1 and 3, respectively) to compensatory growth trajectories (final BW of 2,400 g and 2,100 g in experiments 2 and 4, respectively). The mean relative error (MRE) between the different predefined target growth trajectories and the realized growth trajectories ranged from 3.7% to 6.0%. With a few exceptions, the numerical values of feed conversion ratio and mortality after wk 1 were lower and the values of uniformity index were higher in the controlled groups compared with animals fed ad libitum. As a conclusion, it can be stated that integration of dynamic data-based modeling approaches with new hardware and sensing techniques to measure information from the animals should make it possible to control broiler growth trajectories.

1. In previous studies it was found that automatic broiler weighing systems can have accuracy problems. Researchers reported poor agreement between automatic and manual mean weighing used as a reference. The difference was observed especially after 4 to 5 weeks and this was explained by assuming that heavier birds visited the weighing system less at the end of the growing period. 2. Our study tested this hypothesis under practical production conditions. 3. In total, 193,536 digital images of broilers on and in the neighbourhood of the platforms were collected over three growing periods of 6 weeks. The area (upper view) of the broilers was calculated using image analysis techniques. 4. The hypothesis that the weighing system was used less frequently by heavier animals was confirmed. More specifically, statistical differences between the area of broilers on and in the neighbourhood of the weighing system could be demonstrated for week 5.

The objective of this study was to explore whether time-variant parameter estimation procedures allow modeling and predicting the dynamic growth response of broiler chickens to feed intake in real time. A recursive linear model was used that estimated the model parameters every 24 h based on a fixed number of actual and past measurements (i.e., time window). Based on 48 datasets, it was concluded that the mean relative prediction error (MRPE) of the recursive linear modeling approach had a minimum for a window size of 5 d. Weight of the birds could be predicted during the growth process 3 to 7 d ahead with a mean relative prediction error of 5% or less. In comparison with the prediction results of three static empirical growth models (one linear and two nonlinear models), the recursive modeling technique had a similar accuracy to the nonlinear empirical models (MRPE of 1.4% to 2.3% vs. 1.1% to 2.8%), but it was less accurate for larger prediction horizons (2 to 7 d). The compact recursive linear model was more accurate than the static linear growth model for prediction horizons of one up to 4 d, depending on the feeding strategy. Since such recursive modeling approach allows the prediction of broiler growth without any prior knowledge of the system and takes into account the time-variant (nonlinear) nature of the growth process based on only a small window of measured information, it is suitable for real-time integration in process management.

1. Two experiments were conducted to investigate the influence of compensatory growth, induced by early quantitative food restrictions, on the efficiency of nitrogen-retention in two lines of Ross broilers. 2. Birds were restricted to 80% of the ad libitum intake of the previous 24 h of the control group from d 4 to d 7. After the period of restrictions all birds were fed ad libitum. 3. In both trials, the final body weight of the restricted Ross 208(308) birds was similar or even higher than that of the control group. For the Ross 508 line, compensatory growth was substantial in the first trial, but non-existent in the second trial. In all cases, the mortality of restricted birds was lower than in control birds. 4. Not only environmental factors, but mainly chick quality, seemed to have a major influence on the capacity of the chickens to establish compensatory growth. 5. As compensatory growth was established, some improvement in N retention was induced. Although differences were not significant, they may be environmentally important. 6. It is concluded that a retardation of the early growth of fast growing broiler chickens can, in certain circumstances, reduce mortality and increase performance and N retention.

1. An experiment was conducted with male broiler chickens to investigate the effect of different early food restriction programmes on proportional weights and allometric growth coefficients of carcase parts and on pulsatile growth hormone secretion. 2. At 4 d of age the animals were restricted to 80% or 90% of the ad libitum intake for 4 d or 80% for 8 d. When the restriction was finished, all birds received ad libitum food again. 3. On d 1, 8, 11, 14, 21, 28, 35 and 42, from each group 8 birds were weighed, stunned and killed and the weights of the stomachs, liver, heart, sternum, right thigh, right drumstick, breast and abdominal fat pad were determined. On d 29, 30, 31, 32 serial blood samples of 2 birds from each group were taken to determine the plasma growth hormone (GH) content. 4. Only the most severe restriction resulted in a tendency for the stomachs to mature earlier and the thighs to mature later. No other significant effect on the allometric coefficients could be observed. 5. It is concluded that during the restriction the birds give priority to the development of the supply organs such as the stomach, which are more important during early development at the expense of the demand tissues like breast and thigh. 6. No significant differences concerning the GH secretory parameters could be observed.

1. An experiment was conducted with broiler chickens to determine the effects of different early food restrictions, strain (Ross 508 and Hybro G) and sex on performance, mortality carcase composition and meat characteristics. 2. Birds were restricted to 80% or 90% of ad libitum intake for 4 d (80%-4 d-group and 90%-4 d-group, respectively) or 80% for 8 d (80%-8 d-group). All restrictions started on d 4. After the periods of restriction, all birds were fed ad libitum. 3. Only the 90%-4 d-group reached a final body weight not significantly different from, but lower than, the ad libitum group. The other restrictions were too severe to allow a sufficient 'catch-up'. 4. No significant differences in food conversion and total carcase fat content between groups were observed. Abdominal fat showed a tendency to increase due to the restrictions induced. 5. There was a slight trend towards a reduced mortality and of 'sudden death syndrome' but no clear effect of food restriction on number of chickens removed with leg problems. There was no significant decrease in uniformity of the flocks due to restriction. 6. The group 80%-8 d had a significant lower yield percentage. Cut-up parts and meat quality were not changed by restriction. Ross birds had a significantly higher proportion of breast meat than Hybro chickens. Meat of female chickens seemed to be paler than that of males, possibly because of the higher proportion of carcase fat. 7. Food restriction did not always give good results. However, a mild restriction (90% for 4 d) may offer some economic advantages over an ad libitum feeding regimen, mainly by reducing mortality.

1. The aim of the study was to determine the ideal ratio of the essential amino acids lysine (Lys), methionine (Met), threonine (Thr), tryptophan (Trp), arginine (Arg), valine (Val) and isoleucine (Ile) and to assess the required dietary lysine concentration for optimum performance in broiler chickens of 2 commercial strains from 20 to 40 d of age. 2. An identical basal diet was used throughout all experiments. It consisted mainly of maize and soyabean meal and contained 172 g crude protein and 13.2 MJ AME(N) per kg. For each experiment, the basal diet was adequately supplemented with all essential amino acids except the one to be tested, which was supplemented in 6 graded concentrations in exchange for maize starch. One (Met, Trp, Arg, Val, Ile) or 2 (Lys, Thr) growth trials were conducted per amino acid tested and the response in weight gain, food: gain ratio, breast meat yield and abdominal fat were examined. 3. The ideal amino acid ratio relative to Lys (expressed as a percentage) was calculated to be 75% Met+Cys, 63% Thr, 19% Trp, 112% Arg, 71% Ile and 81% Val on a true faecal digestible basis when the data were subjected to broken-line regression analysis. From both lysine studies the concentration for optimum food: gain ratio was calculated, by exponential regression analysis, to be 11.5 g true faecal digestible lys per kg diet.