Effect of step-down and step-up protein-energy feeding systems on egg-type pullet growth and laying performance

Effect of energy level of pullet diet and age on laying performance and expression of hypothalamus-pituitary-gonadal related genes in laying hens

Dietary energy density influences feed intake (FI) and development of layer-type pullets. A total of 384 nine-wk-old Hy-Line Brown pullets were randomly assigned to one of 3 dietary treatments: fed a diet with 2,600, 2,750, and 2,900 Kcal metabolizable energy/kg (ME/kg) from 10 to 21 wk of age. The results showed that the 2,900 and 2,600 ME groups had lower feed and ME intake (P < 0.01) from 10 to 21 wk of age. The 2,600 ME pullets had heavier body weight (BW) and longer shank length (P < 0.05) at 21 wk of age than the 2,750 ME group. The eggshell percentage was increased by the 2,600 and 2,900 kcal/kg treatments (P = 0.002). Serum concentration of 17-β-estradiol (E2), follicle-stimulating hormone (FSH), and luteinizing hormone (LH) decreased at 70 wk of age (P < 0.05). Pullet diet and its interaction with age had a significant influence (P < 0.001) on the expression of gonadotropin-releasing hormone 1 (GnRH-1) and gonadotropin-inhibitory hormone (GnIH) in the hypothalamus and of gonadotropin releasing hormone 1 receptor (GnRH-1R) and gonadotropin-inhibitory hormone receptor (GnIHR) in the pituitary. In the hypothalamus, GnRH-1 expression increased from 9 to 40 wk of age and then decreased; however, GnIH expression was highest at 70 wk of age. Follicle-stimulating hormone receptor (FSHR) expression increased (P < 0.001) at wk 40 and decreased at wk 70 compared to wk 21 at various follicular stages. In conclusion, the energy level of pullet diet had no unfavorable influence on feed intake, laying rate, egg mass, and FCR, whereas change egg weight and mortality during the laying period from 21 to 70 wk of age. during the laying period. These results suggest that pullet dietary energy can activate the expression of genes related to reproduction in the hypothalamus, whereas it plays a minor role in the regulation of genes in the pituitary and ovary. Age-induced gene expression in the hypothalamus-pituitary-gonadal (HPG) axis is associated with laying performance in hens.

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.

Effect of dietary protein and energy levels on pullet development

The effects of protein and energy levels in rearing diets and protein levels in layer diets on pullet development and subsequent layer performance were studied using 576 Single Comb White Leghorn pullets of a commercial strain. Twelve groups of 16 1-d-old chicks were assigned to each of three dietary treatments. All chicks were fed a 19% CP starter diet during Week 1. Respective protein levels in diets fed during Weeks 2 through 6, 7 through 14, and 15 through 18 were 13.5, 15.8, and 18.9% for the increasing protein treatment; 15.8, 15.8, and 15.8% for the constant protein treatment; and 18.9, 15.8, and 13.5% for the decreasing protein treatment. During Weeks 15 through 18, half of the groups in each protein treatment were assigned to a high (3.09 Mcal AMEn/kg) or a low (2.78 Mcal AMEn/kg) energy diet. After 18 wk, half of the pullets within each rearing treatment were fed a layer diet containing 16% CP and 0.34% methionine, whereas the other half were fed a layer diet with 19% CP and 0.40% methionine. Increasing the level of protein fed during Weeks 2 through 6 significantly (P < 0.05) increased body weight and feed intake up to 14 wk of age. High dietary energy increased weight gain and decreased feed intake during Weeks 15 through 18. Mortality and days to 50% egg production, as well as egg production, feed intake, feed conversion, and egg weight during the first 16 wk following photostimulation were not affected by rearing dietary treatments. Egg weight, but not other production parameters, was significantly increased by raising CP in the layer diet from 16 to 19%.

Effects of strain and rearing dietary regimens on brown-egg pullet growth and strain, rearing dietary regimens, density, and feeder space effects on subsequent laying performance

The objective of this experiment was to compare the growth and development of two brown-egg strains when grown on three different dietary regimens, i.e., a "normal" step-down protein (SDP) regimen, a step-up protein regimen with a low energy starter (SUPLES), and a step-up protein regimen with a high energy starter (SUPHES). The SUPLES and SUPHES feeding regimens resulted in significantly lower BW and feed conversion, shorter sternum length, and lower tibial breaking strength than the SDP regimen. The weights of the liver, spleen, and fat pad were not different among the three regimens. The high energy starter in the SUPHES regimen significantly reduced FC below that obtained with the SUPLES program. The SUPHES regimen significantly reduced total feed cost compared with the other two feeding regimens. Both step-up protein regimens reduced total protein, energy, Ca, P, lysine, and sulfur amino acid consumption. Because tibial breaking strength was also reduced by the step-up protein regimens, the data suggest that the levels of dietary Ca and P should be increased with these programs to compensate for the reduced consumption associated with them.

Laying hen performance as influenced by protein intake to sixteen weeks of age and body weight at point of lay

White Leghorn chicks were fed corn-soybean meal diets containing 20, 17, 14, and 11% protein, with similar levels of energy, from hatch to 16 wk of age. Body weights at 16 wk were similar for pullets fed the 20 and 17% protein diets, but were reduced by 11 and 27% for birds fed the 14 and 11% protein diets, respectively, as compared with the 20% protein diet. At 16 wk of age, all birds were placed on a common 17% protein laying diet. Pullets fed the 14 and 11% protein laying diets were slightly slower coming into production, however, by 28 wk of age egg production was similar for all four growing treatment groups and remained so until the end of the experiment. Average egg weight was similar for pullets fed the two higher levels of protein during the growing period and significantly lower for those pullets fed the 11% grower diet for all except the 28- and 32-wk periods. Pullets fed the 14% grower diet produced eggs with average weights significantly lower than those for the higher protein diets from 40 to 58 wk of age. Although the results might be interpreted as indicating that higher protein growing diets result in body protein reserves that subsequently enhance egg size, it is more likely that the pullets consuming lower protein diets produce smaller eggs because they have smaller body weights.

Effect of rearing regimens on pullet growth and subsequent laying performance

Treatments consisted of eight pullet dietary regimens: high protein with low, medium, or high ME; low protein with high ME, step-up protein, and diets with gradually decreasing protein levels and increasing ME levels with deficient methionine and TSAA levels, recommended methionine levels (TSAA-deficient), or recommended methionine and TSAA levels. Two additional regimens were introduced at 20 wk by selecting light and heavy birds, from caged birds maintained under high protein, medium ME conditions. Laying performance was measured from 20 to 64 wk. During the rearing period, birds fed the low energy and the methionine-deficient regimens consumed less energy (P less than .05). Body weight at 8 wk was affected by initial protein levels (P less than .05), but such effect was not seen after 16 wk of age. Birds on the step-up protein regimen consumed less feed during the laying period but also produced less egg mass (P less than .05). Birds with heavier body weights at 20 wk had better laying performance than birds with lighter body weights (P less than .05). A rearing regimen (0 to 20 wk) that resulted in a total protein intake of 1,140 g and a total ME intake of 20.0 Mcal was shown to control final pullet body weight and maximize laying performance; although at higher ME intake (21.5 Mcal) no detrimental effect was seen.

Use of sunflower seeds in grower diets for pullets and subsequent performance as affected by aureomycin and pelleting

In two experiments the effects of unhulled sunflower seeds (USFS) were evaluated at levels of 19 and 38% in corn-based diets for pullets between 10 and 19 wk of age. As an additional treatment a .09%-lysine monohydrochloride supplement was added to the 38% USFS-containing diet in Experiment 2. Isonitrogenous grower diets made up of corn and soybean meal or largely oats served as control diets. During the productive phase, layers were fed a high oats diet as mash (both experiments) or in pelleted form (Experiment 2). One half of the hens in each study were fed layer diets containing Aureomycin at 100 g per ton for 1 wk during each 28-day period to monitor the effect on egg production. Treatments during the laying phase were superimposed on the previous growing phase treatments. Pullets fed the 38% USFS diet in Experiment 1 were significantly lighter (P less than .01) at 19 wk of age and reached 50% egg production 2 days later than those on the control corn-soy diet. However, subsequent overall laying performance for 14 28-day periods was not significantly affected by the growing treatments. Neither growth nor laying performance was influenced by the treatments imposed during the rearing period of the second experiment. The two supplies of USFS varied considerably in crude fiber (14.6 vs 25.8%) and ether extract components (42.4 vs. 29.0%, respectively). The discrepancy in growth response to USFS of the two experiments was possibly related to the difference in the ether extract portions of the oil seeds. Egg production rate was significantly increased by Aureomycin only when the diet was pelleted.

Rearing early maturing pullets

A number of experiments were undertaken using White Leghorn pullets to determine the effect of diet and growing treatment on 16-wk body weight and carcass composition. Irrespective of the level of dietary energy, body weight gain and carcass composition appeared to be closely correlated with energy intake of the pullets. Diets as low as 15% protein with and without methionine supplementation resulted in 16-wk body weights similar to those of animals fed diets containing 21% protein, suggesting that protein is not a critical nutrient influencing weight gain of pullets. Pullets fed ad libitum every other day from 12 to 16 wk of age were significantly lighter at 16 wk than pullets full fed a regular grower diet or the regular diet diluted with 20% oat hulls. Pullets must achieve a certain body weight and carcass composition in order to trigger the onset of production. Dietary energy, not protein, appears to be the critical nutrient involved.

Modified step-up protein feeding regimens for egg-type chickens. 1. Growth and production performance

Effects of sequential changes in dietary protein on growth from 0 to 20 weeks of age and on egg production from 20 to 72 weeks of age were evaluated with White Leghorn chickens. Four dietary treatments were compared. They consisted of three dietary regimens wherein an 18% crude protein (CP) diet was fed to 1, 2, or 3 weeks of age (Treatments 1, 2, and 3, respectively) and then common 12, 15, and 18% CP diets to 8, 14, and 20 weeks, respectively. These three regimens were compared with a control regimen (Treatment 4) that consisted of feeding 18, 15, and 12% CP diets to 6, 14, and 20 weeks of age, respectively. At 20 weeks of age, 144 birds from each treatment were moved into laying cages for the subsequent 52 weeks of egg production. In comparison with birds on the control feeding regimen, those reared under Treatments 1, 2, and 3 consumed significantly less feed during the 20-week growing period. Birds of Treatments 2 and 3 consumed significantly more protein than those of Treatments 1 and 4. By feeding a 12% CP diet from 1, 2, and 3 to 8 weeks of age, body weights were significantly lower than the average body weight of the control birds, approximately 20, 17, and 13%, respectively, by 6 weeks of age, but only 2 to 4% at 16 weeks of age, and by nonsignificant amounts at 28 weeks of age. Treatment 1 birds consumed 1.8% (significantly) less feed per unit body weight and were 2.6% (significantly) lighter at 20 weeks of age compared with the control birds.(ABSTRACT TRUNCATED AT 250 WORDS)