Dietary self-selection and use of reverse-protein diets for developing broiler breeder 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%.

Metabolic and behavioral adaptation of light-bodied chicks to meal feeding

1. Two-week-old male chicks of a light-bodied strain were fed one (1M) or two (2M) 2-h meals per day. An additional group was pair-fed (P1M) the amount consumed by the 1M group on the previous day. 2. After 21 days, final body weight of the 1M and 2M chicks attained 65% and 80%, respectively, of that of the control group fed ad libitum. The weight gain of the P1M chicks was equal to that of the 1M chicks. 3. Food consumption of chicks adapted to meals was not even throughout the feeding period. On day 16 of the experiment, the 1M birds consumed 65% of the meal during the first 30 min. P1M chicks behaved similarly to the 1M ones. The intake of the 2M chicks during each meal was exactly half of their daily consumption, despite the uneven time period between meals. 4. The time during which food remained in the gastrointestinal tract (GIT) was longer under the meal feeding regimes than in the ad libitum-fed groups. 5. Although neither body composition nor metabolisable energy was affected by meal regime, food utilisation was poorer in the 1M and P1M than in the ad libitum and 2M-fed chicks.

Self-selection of dietary protein and energy by turkey breeder hens

1. An experiment was conducted to determine the effects of self-selection of dietary protein and energy by turkey hens on reproductive performance in a warm environment. 2. Dietary self-selection had no significant effect on egg production, egg weight, or body weight of turkey hens. 3. Fertility and hatchability of eggs produced by self-selecting hens were significantly reduced compared to eggs from control hens fed on a complete diet. 4. Protein intake was significantly reduced among self-selecting hens when compared to control hens fed on a complete diet (P less than or equal to 0.001). 5. Food and energy intake decreased as the ambient temperature increased. Nevertheless, protein intake of self-selecting hens increased over the course of egg production despite decreasing food intake. Therefore, self-selecting hens preferred a diet with a greater protein content (g protein/kg diet) in the last 10 weeks of egg production than during the first 10 weeks of egg production.

Divergent selection for growth in Japanese quail under split and complete nutritional environments. 4. Genetic and correlated responses from generations 12 to 20

Divergent selection during Generations 12 to 20 for high (H) and low (L) 4-wk BW under split-(SD) and complete-(CD) diet environments resulted in continued progress in both upward and downward directions. Following 20 generations of selection, there were 4.8- and 3.6-fold differences between BW of H and L lines in the SD and CD environments, respectively. Regression coefficients of mean 4-wk BW on generation of 1.88 and 1.58 g in the H lines and -1.50 and -1.37 g in the L lines indicated symmetrical selection responses. Realized heritabilities for 4-wk BW ranged from .2 to .4; selection differentials were significantly (P less than .01) larger in the H lines than in the L lines. Directional changes in 2-wk and adult BW and in egg weight across generations were similar to that of the selection trait (4-wk BW). Selection resulted in decreased hatchability and egg production and an increase in the age of sexual maturity. However, these changes were smaller than corresponding changes observed in earlier generations (0 to 11). Egg size of lines selected in the SD environment continued to be larger than egg size of corresponding lines in the CD environment. Considerable genetic variation for BW remains under both SD and CD environments following 20 generations of divergent selection. Smaller gains resulting from lower heritabilities agree with theoretical expectations of decreasing responses accompanying continuous selection.

Protein and energy self-selection by turkey hens: reproductive performance

1. The influence of protein and energy self-selection on the reproductive performance of turkey hens was investigated. Large White turkey hens were fed on either a complete diet (185 g CP/kg, 11.30 MJ ME/kg) or were provided with a choice between a high protein-low energy diet (348 g CP/kg, 7.74 MJ ME/kg) and a high energy-low protein diet (81 g CP/kg, 13.39 MJ ME/kg). 2. Egg production, egg weight, and the fertility and hatchability of eggs produced were not significantly affected by the dietary treatments (P greater than 0.05). 3. While energy intake was not significantly different between groups, protein consumption decreased by approximately 40% (P less than or equal to 0.001) among self-selecting hens compared to hens fed on the complete diet. This resulted in a 10% (P less than or equal to 0.05) reduction in the food intake in the self-selecting birds.

Divergent selection for growth in Japanese quail under split and complete nutritional environments. 2. Water and feed intake patterns and abdominal fat and carcass lipid characteristics

A study was conducted to investigate water and feed intake patterns, abdominal fat and carcass lipid levels, feed efficiency and growth in high (H) and low (L) body weight lines of Japanese quail divergently selected under complete diet (CD) or split diet (SD) environments. Birds under the SD environment could self-select from high-protein low-energy or low-protein high-energy diets. Progeny from both the selected and control (C) lines were evaluated under the SD environment in Generations 6 and 10, and under the CD environment in Generation 10. Under the SD environment, body weights of the H lines were similar as were body weights of the L lines; however, under the CD environment, there were significant differences between H lines and between L lines. Body weights were higher under the CD than under the SD environment. Differences between H and L lines in body weights and 1-wk relative growth rates within SD and CD environments were attributed to differences in water and feed consumption and feed efficiency. Water consumption was greater in the SD than CD environments. Feed consumption was greater in the SD than CD environment from 0 to 2 wk of age; thereafter, feed consumption was higher in the CD environment. Abdominal fat and carcass lipid levels were greater in H than L lines, with the magnitude of the difference greater in the SD environment, indicating that the SD may be a better environment than the CD environment for the study of abdominal fat and carcass lipids in Japanese quail.

Divergent selection for growth in Japanese quail under split and complete nutritional environments. 1. Genetic and correlated responses to selection

Japanese quail were divergently selected for 4-wk body weight under two different nutritional environments. In one environment quail were divergently selected for high and low body weight (H and L) under a split diet (SD) with quail having the opportunity to self-select feed from high protein and high energy diets. In the other environment, quail were similarly selected (H and L) under a normal (28% protein) complete diet (CD). After 11 generations of selection, H-SD and H-CD lines were 48.9 and 49.7% higher in 4-wk body weight than controls. Quail from L-SD and L-CD lines were 46.5 and 45.4% lower in 4-wk body weight than controls. Realized heritabilities for 4-wk body weight were .36 +/- .03, .30 +/- .03, .52 +/- .02, and .47 +/- .03 for H-SD, L-SD, H-CD, and L-CD lines, respectively. Selection differentials were significantly higher in the SD than in the CD environment. Changes in 2-wk, adult body, and egg weight across generations paralleled that of the trait under selection (4-wk body weight). Selection also resulted in decreased hatchability and egg production with increased age to sexual maturity in both environments. The SD environment was determined to be a stress environment because of birds' inferior growth there compared with growth in the CD environment. Rate of growth, however, to reach adult body size was superior for L-SD quail once the stress environment was removed. There was also evidence that eggs were larger for quail in the SD than the CD environment.

Effects of modified conventional and reverse-protein rearing dietary regimens on the performance of Leghorn hens

Two commercial Leghorn genotypes were used to study the effects of rearing dietary treatments on juvenile mortality, growth, and adult performance. One control, two modified conventional, and three reverse-protein juvenile dietary regimens were compared. The two genotypes differed in egg production, age at 50% egg production, egg weight, egg specific gravity. Haugh units, and monetary returns. There was no evidence of any genotype X dietary treatment interaction. Juvenile dietary treatments had a significant (P less than .05) effect on body weights at 21 days of age that continued through the juvenile and adult periods to 490 days. Age at 50% egg production, feed efficiency, and initial egg weights were also affected. Although hens reared on one of the modified conventional and two of the reverse-protein regimens returned $.53 per bird more than the remaining three rearing dietary regimens, this difference was not significant (P greater than .05). Evidence is provided that reverse-protein juvenile dietary regimens may support adult performance that equal or surpass the performance of birds reared on conventional dietary programs.

Growth and development of broiler breeders. 1. Effect of early plane of nutrition and growth rate

In two experiments, male and female broiler breeders were reared on two different planes of growth as a result of early nutritional treatment. The starter treatment(s) consisted of a 19.5% crude protein, (CP), 2970 kcal diet from 0 to 14 days and 15.5% CP, 2750 kcal ration from 2 to 10 weeks. The birds in the grower treatment were fed the latter diet from 0 to 10 weeks. Both treatments were ad libitum fed from 0 to 3 weeks and then restricted to meet the breeder's recommended body weight targets. In Experiment 1, the starter treatment resulted in significantly heavier body weights at 3 weeks of age but not at later ages. The initiation of feed restriction was necessarily more severe for those chicks fed the starter diet. This restriction resulted in a significantly smaller liver at 10 weeks of age in breeder cockerels and dwarf breeder females. Vaccination titers [Newcastle, Infectious Bursal Disease (IBD),] and response to sheep red blood cells (SRBC) brachial vein injection were not affected by treatment. In a second experiment, there were no differences in bursa, spleen, or thymus weights between starter and grower treatments at 10 weeks of age, and the liver weights were again significantly larger in the grower treatment. One treatment of dwarf and normal pullets was overly restricted from 3 to 10 weeks (Grower-R), and lighter body weights were obtained at all ages. Only the spleen in the normal breeders was significantly smaller at 10 weeks of age in this treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Dietary self-selection of laying hens inadequate to overcome the effects of high environmental temperature

Two environmental temperatures, 21 and 30 C, were used during a 28-day experimental period. There were two groups of hens in each temperature treatment. The control groups (C) were given a conventional balanced diet and each dietary self-selection group (S-S) was provided, on an individual hen basis, three diets each one being high in energy, protein, or calcium. The S-S groups had significantly reduced egg production, which probably resulted from the significantly reduced protein intake. Egg weight and energy intake were reduced in the S-S group at 21 C while calcium intake and egg shell strength at 30 C were higher as compared to the corresponding C group. Dietary self-selection did not enable hens to regulate nutrient intake for comparable performance to hens provided one balanced diet. Also, the detrimental effects of high environmental temperature were not overcome by dietary self-selection.

Influence of nutritional modification on skeletal size of Leghorn and broiler breeder pullets

Two trials were undertaken to study the effect of nutrient intake on skeletal size in growing pullets. Leghorn chicks at 28 days were smaller in weight and shank and keel length when fed 16% as compared to 22% crude protein. Increasing the energy or mineral-vitamin concentration of the diet had no effect on skeletal parameters. Increased skeletal size of pullets in response to increased diet protein was associated with reduced (P less than .01) tibial ash content. In a subsequent trial, broiler breeder pullets were fed, ad libitum, starter diets (0 to 21 days) containing graded levels of protein from 20 to 13%. Reducing protein level had a consistent negative effect on body weight, shank length, and keel length at 21 days. When birds were subsequently fed restricted quantities of a common grower diet, no differences in body weight and skeletal parameters were evident at maturity. It is concluded that although early body weight and skeletal size can be markedly influenced by diet protein level, such effects are subsequently nullified by conventional restricted feeding programs.

Effect of intermittent feeding on blood plasma growth hormone and prolactin in chickens of a heavy breed

1. Variations in plasma growth hormone (GH) and prolactin concentrations were determined during growth (at 20, 33, 56 and 83 d of age) in ad libitum (control) and intermittently (alternate days) fed chicks. 2. In each group of birds the concentration of plasma GH was inversely related to age. The mean prolactin concentration was highest in the youngest (20-d-old) birds. 3. The concentration of plasma GH in the intermittently-fed birds deprived of food for 24 h (depleted birds) was significantly higher than that in the controls at 33, 56 and 83 d of age. The mean GH concentration in the intermittently-fed birds 24 h after refeeding (repleted birds) was less than that in the depleted ones. 4. The overall mean concentration of plasma prolactin in the depleted birds was significantly less than that in the control and repleted birds. 5. These results are consistent with the effects of fasting on GH and prolactin secretion and demonstrate that growth retardation in the intermittently-fed birds was not due to impaired GH secretion.