SU MMARYThe model described simulates the response of a population of broiler breeders to a daily allowance of a feed of specified composition for up to 280 days from sexual maturity. The population is generated using normally distributed values for initial bodyweight, initial body lipid and protein weight, age at first egg, yolk weight constant and 'aggressiveness ', the latter producing different feed intakes around the controlled mean. Age at sexual maturity for each bird is predicted from bodyweight and from information about rearing lighting programmes. Egg production, clutch patterns, yolk weights, egg component weights, double-yolked eggs, internal laying and soft-shelled eggs are predicted. Body protein growth, including feathers, is assumed to cease at sexual maturity, thus bodyweight changes after maturity are due entirely to accumulation or utilization of lipid.Energy transactions are expressed in units of effective energy. Protein required for egg production is calculated from the composition of the next egg to be laid and an assumed fixed chemical composition. Assumptions for protein partition rules are that maintenance has highest priority, yolk protein deposition second and albumen protein third. Provided that sufficient energy and nutrients are available, yolk protein deposition is assumed to occur continuously to meet the predicted growth rate, unless inter-clutch intervals exceed 2 days (user defined), when yolk growth ceases. Energy and nutrients (amino acids) for albumen production accumulate in a pool which has some controlling influence over ovulation. If the energy and nutrients in the albumen pool will support the predicted development of the next egg then ovulation will occur, otherwise ovulation is delayed until sufficient energy and nutrients are available. All events are timed within a 24 h day assuming that feeding is at one time in the morning.The desired feed intake is calculated each day according to the supply of the first limiting energy or nutrient (invariably an amino acid) in relation to potential need. Actual feed intake is either the desired intake or the feed allowance, whichever is the lower. The additional energy required for thermogenesis is taken into account, but not the constraining effects of high temperature or the bulkiness of the food as a constraint to voluntary food intake.Some shortcomings of the current model are discussed, these being areas suitable for further research on broiler breeder nutrition. INTRODUCTIONThe requirement of a broiler breeder hen during the laying period for energy and for each of the essential nutrients is a function of the potential reproductive performance of the bird, of its state, and of the environment in which the bird is kept. These requirements will differ among the birds in a flock, as will their daily food intakes. Consequently, the task of designing feeds and calculating daily feed allocations that will maximize profit over the laying cycle is extremely difficult. The scientific literature on the subject is not entirely helpf...
This study was conducted to examine the response of broiler breeder hens to feeds supplemented with synthetic lysine and methionine when fed once or twice daily during peak production. Replacing intact protein with increasing amounts of free lysine and methionine, up to 2.3 g/kg feed, had no effect on feed intake, bodyweight gain, egg weight or efficiency of lysine utilisation, but reduced the crude protein content in the diet up to 3.3 percentage units and improved the efficiency of protein utilisation by 22.3%. However, for each extra gram of dietary free amino acid content/kg diet, the rate of lay and egg output decreased by 3.0% and 2.5 g per day, respectively, and the efficiency of methionine utilisation decreased by 4.3%. There was no interaction between frequency of feeding and amino acid supplementation. These results suggest that free amino acids are not utilised by broiler breeders.
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.
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.
________________________________________________________________________________ AbstractThe study was conducted to determine the extent to which broiler breeder hens could make use of excess body lipid reserves as a means of maintaining laying performance. The experiment was divided into two phases. In the first phase, the birds aged 37 weeks were allocated one of four daily allowances: 160, 175, 190 or 205 g of a commercial broiler breeder feed for a period of four weeks in order to achieve four levels of fatness in the hens. During the second phase, also lasting four weeks, the birds were given a high protein, low energy feed at three rates of allocation (120, 100 or 80 g/hen d). Performance was higher over the final two weeks of Phase 2 when birds were fed 120 g/d in this period, with production tending to decrease as allocations increased in Phase 1, although this was not significant. The same pattern of response was seen in birds given 100 g/d in the second phase of the trial, i.e. excessive lipid reserves tended to be detrimental to performance in these two treatments. However, where 80 g was allocated daily in Phase 2 this was clearly insufficient to sustain performance, but in this case egg production was considerably higher in birds that had been given larger amounts of food in Phase 1, and which could therefore draw on body lipid reserves as a source of energy. Rate of lay increased by 3.5% and egg output by 4.0 g/d for every additional 10 g of food given in Phase 1, as a result of lipid reserves having been utilised when daily food intake was severely depressed. Egg weight was not affected by any of the feed allocations until the last two weeks of the trial when birds fed 80 g/d started laying smaller eggs. Broiler breeders are capable of maintaining their egg production for short periods at an energy intake that is much lower than is recommended and this has implications when modelling the effect of food composition on performance of broiler breeder hens. ________________________________________________________________________________
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