Effect of low protein diets for growing Leghorn pullets upon subsequent laying performance

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.

Onset of lay related to multiphasic growth and body composition in White Leghorn pullets provided ad libitum and restricted diets

Growth of the body as a whole and of parts of the reproductive tract of White Leghorn pullets that ate ad libitum and restricted diets were analyzed by a multiphasic growth function. Parameter estimates were related to onset of lay. Chemical body compositions at defined stages of pubertal growth were related to the development of the reproductive organs. Data of pullets that had been restricted in one of two rearing periods (0 to 6 and 7 to 18 wk of age) were used. In each period, pullets were fed a low-lysine diet or a daily restricted amount of feed, on a pair-gain basis. In all mathematical fits, a well distinguishable "pubertal body growth spurt" at around 19 wk of age was found. About 40 to 70% of total growth within this phase consisted of growth of the reproductive tract (the ovary covered 19 to 35%, the oviduct 15 to 23%, and the uterus 7 to 11% of total growth). Age at maximum gain of the pubertal body growth spurt was 20.1 wk for lysine-restricted pullets and 19.6 wk for feed-restricted pullets. This difference reflected differences in onset of lay (50% rate of lay) between lysine- and feed-restricted birds (22.3 and 21.6 wk, respectively). An interval of 14 to 15 d existed between maximum gain of the pubertal body growth spurt and onset of lay. It was suggested that the occurrence of the pubertal body growth spurt can serve as a predictor for subsequent onset of lay. Body composition at defined moments during the pubertal body growth spurt was calculated by interpolation from chemical analyses of Weeks 15, 18, 20, 22, and 24. Crude fat content in the body at start of the pubertal body growth spurt varied considerably between the feeding regimens (112 to 179 g). The fat-free body (consisting of CP, ash, and water) showed less variation between the treatments at this stage (807 to 870 g). It is concluded that a particular amount of fat-free tissue is critical in pullet development and may be required before sexual organ development starts.

Effect of method and phase of nutrient restriction during rearing on productive performance of light hybrid pullets and hens

1. An experiment was conducted to study the effect of method (low-lysine or quantity of food) and phase (starter or grower) of restriction during rearing on growth and laying performance in Leghorn hybrids. 2. A reduction in body weight gain was achieved by feeding pullets a low-lysine diet in either the starter phase (0-6 weeks of age: 4.0 g/kg digestible lysine) or the grower phase (7-18 weeks of age: 3.0 g/kg digestible lysine). 3. In each phase, the lysine restriction was compared with a daily food restriction, in which pullets received a quantity of food sufficient to pair-gain with their lysine-restricted counterparts. 4. The delay in onset of production was greatest in the lysine-restricted birds, for both phases of restriction. 5. Hens restricted during the grower phase laid heavier eggs than those restricted during the starter phase, despite having similar body weights at end of rearing. This effect was not influenced by the restriction method. 6. Production traits varied between pullets reared on different feeding strategies up to similar body weights at 18 weeks and onwards. It is concluded that body weight is not the only factor determining laying performance.