Selection For Rapid Growth Rate Research Articles

Influence of Ascites Syndrome on Growth Pattern of Chickens Reared at Normal or Cold Ambient Temperature

Abstract Ascites syndrome (AS) is a metabolic disorder usually seen in highly improved meat-type broiler strains. This syndrome causes major financial losses to the poultry industry. Previously it was believed that AS incidence was a side effect of intense selection for rapid growth rate (GR) or higher market weight. If this belief is the case, selection for further increase in GR will not be rational. However, it was later understood that there were significant genetic variations for both GR and susceptibility/resistance to AS; thus selective breeding could be helpful in diminishing the incidence of AS while improving GR. Furthermore, it was hypothesized that genes controlling the GR were not genetically dependent on those genes controlling susceptibility to AS. In the current research, we aimed to study the association of GR traits with AS% in a pure sire line. A total of 1458 1-day-old chicks from 67 sire families were used. The results revealed that ascitic chicks were not significantly superior in early GR traits (i.e. before day 28) than the healthy ones. At later ages, probably due to the commencement of the syndrome, the ascitic chicks were significantly lighter in body weight (BW) than their healthy counterparts. The lack of significant genetic correlations between the GR traits and AS% indicated that there was considerable scope for simultaneous selection of birds for increased BW and GR while controlling susceptibility to AS.

The effects of genetic line (broilers vs. layers) on embryo development

Recent decades were characterized by genetic selection of broiler and layer chickens for enhanced growth rate and meat yield or intensified egg production, respectively. It is to be expected that genetic selection for various traits would also influence embryo development and growth patterns that affect metabolism. The objective of the present study was to examine the effects of broiler (Cobb and Ross) and layer (Lohmann) lines and parent flock age (31 and 38 wk) on embryonic development, heart rate, O2 consumption, and blood parameters. For each line, 2 incubation sets, from flocks aged 31 and 38 wk, with 500 eggs per set, were studied. Development patterns differed between layers and broilers: layers hatched 1 d later and their relative embryonic weight at hatch was significantly lower, probably because of their longer period until hatch, although yolk relative weights were similar. Oxygen consumption of layer embryos was lower than that of broilers, and plasma triiodothyronine concentration, hematocrit, and hemoglobin levels were lower in layers than in broilers. However, layer embryo heart rate was higher from embryonic d (E) 15 onward. Differences were found between the Ross and Cobb lines in embryonic development. Oxygen consumption of Ross embryos was slightly higher than that of Cobb from E16 to E19. Heart rate of Ross embryos was significantly higher than that of Cobb. Furthermore, plasma triiodothyronine concentration of Ross embryos was significantly higher on E14, E16, and hatch. These differences suggest that the genetic selection for rapid growth rate in the 2 broiler lines did not cause differences between their embryonic growth patterns, but it did affect their metabolic rate. Oxygen consumption was higher in embryos from the 38-wk-old flock. The results suggest that genetic selection affected not only production traits but also the developmental pattern of the embryo and its metabolic characteristics.

Hypophagic and dipsogenic effect of the 5‐HT1A receptor agonist 8‐OH‐DPAT in broiler chickens

The effects of the 5-HT(1A) receptor agonist 8-OH-DPAT on food and water intake in male broiler chickens were investigated. The injection of 25 or 50 microg/kg of 8-OH-DPAT 15 min before refeeding in fasted animals produced a decrease in food intake. No effect was observed in drinking. The injection of 25 or 50 microg/kg of the 8-OH-DPAT 60 min after the start of refeeding did not produce any significant modification in food intake. No effect on drinking was recorded. The agonist 8-OH-DPAT injected 15 min before water presentation in water-deprived chickens, produced an increased drinking 60 min after the presentation of water. No effect on food intake was observed. The results show that the effect on food intake of the agonist 8-OH-DPAT in fasted-refed broiler chickens was similar to those observed in mammals and layer-strain chickens. However, the agonist did not alter significantly the food intake when the broilers were fed 60 min before the injection. These results are contrary to the observed effects in mammals and in layer-strain chickens. Probably, the selection for rapid growth rate in broilers causes modifications in the feeding control pattern. The comparison between broilers and layers strain may be a useful tool to elucidate the complex mechanisms involved in food and water intake regulation in chickens.

Comparison of three lines of broiler breeders differing in ascites susceptibility or growth rate. 1. Relationship between acoustic resonance data and embryonic or hatching parameters

Ascites is a prevalent cardiovascular disease among modern broilers with negative impacts on production and animal welfare. The peak of mortality due to ascites occurs at the end of the growing period, but the etiology of this problem may start during embryonic development. A few recent reports have demonstrated that the signs of ascites susceptibility are manifested during the late stages of incubation. In the current study, we used a nondestructive method based on egg acoustic resonance parameters [resonant frequency (RF) and damping] to establish a relationship between embryo physiological events during early development in broiler eggs and susceptibility to ascites. The hatching eggs of 3 broiler lines differing in ascites susceptibility were used for this study: ascites-resistant dam line (DAR), ascites-sensitive dam line (DAS), and ascites-sensitive sire line (SASL). These lines were selected on the basis of fast growth, high breast meat yield, and ascites induction at low temperatures such that the order of ascites susceptibility in terms of mortality was SASL >> DAS > DAR. Eggs were incubated under standard conditions in forced-draft incubators. We measured egg weights at setting, albumen pH, Haugh units (HU) at setting, and embryo weights at d 11 and 18, at internal pipping (IP), and at hatch. The durations of IP, external pipping (EP), and hatching were also determined. At 2 hourly periods during incubation, egg RF and damping were also measured. There were differences in egg weights between DAR and SASL vs. DAS, but albumen HU, albumen pH, and the ratio of yolk weight to egg weight were similar. There were differences in RF, damping, embryonic growth rates, and hatching events. Changes in resonant frequency and damping, which certainly suggest eggshell differences among lines, were not totally related to variations in physiological events during early and late embryonic development. A comparison between DAR and DAS, between DAS and SASL, or DAR and SASL indicates that sensitivity to ascites and selection for rapid growth rate in ascites-sensitive lines have different effects on embryonic parameters. We concluded that the sensitivity of broiler breeders to ascites does not influence egg internal quality, but the occurrence of ascites sensitivity in broilers could not be reliably predicted by early in ovo acoustic resonance parameters and hatching events.

Genomic mapping of direct and correlated responses to long-term selection for rapid growth rate in mice.

Understanding the genetic architecture of traits such as growth, body composition, and energy balance has become a primary focus for biomedical and agricultural research. The objective of this study was to map QTL in a large F(2) (n = 1181) population resulting from an intercross between the M16 and ICR lines of mice. The M16 line, developed by long-term selection for 3- to 6-week weight gain, is larger, heavier, fatter, hyperphagic, and diabetic relative to its randomly selected control line of ICR origin. The F(2) population was phenotyped for growth and energy intake at weekly intervals from 4 to 8 weeks of age and for body composition and plasma levels of insulin, leptin, TNFalpha, IL6, and glucose at 8 weeks and was genotyped for 80 microsatellite markers. Since the F(2) was a cross between a selection line and its unselected control, the QTL identified likely represent genes that contributed to direct and correlated responses to long-term selection for rapid growth rate. Across all traits measured, 95 QTL were identified, likely representing 19 unique regions on 13 chromosomes. Four chromosomes (2, 6, 11, and 17) harbored loci contributing disproportionately to selection response. Several QTL demonstrating differential regulation of regional adipose deposition and age-dependent regulation of growth and energy consumption were identified.

Agonistic behavior and growth in newly emerged brown trout (Salmo trutta L) of sea‐ranched and wild origin

AbstractSelection experiments and game theory models have revealed that the changes in agonistic behavior following selection for rapid growth rate of fish depend on the access of food. If food is spatially restricted and in excess of demand, the intensity of agonistic behaviors will decrease. This prediction was tested in an experiment on wild and sea‐ranched brown trout (Salmo trutta L.) fry originating from a common stock. Agonistic behavior, activity, and specific growth rate were studied in tanks (56 × 56 cm) at high (159.4 fry/m2) and low (9.6 fry/m2) stocking densities given either a large or small food ration (3.0% and 1.5%, respectively, food per total body weight and day). Observations were done during 4 days in each trial. Generally, fry of sea‐ranched origin had a higher growth rate. No differences in activity were found. Intensity of agonistic behavior was higher among wild groups. There was a tendency for interaction between density and strain, e.g., wild fish were relatively more aggressive at higher densities. Food ration had no effect on level of agonistic behavior. These results indicate that the selection for rapid growth in hatcheries may indirectly select for reduced aggressiveness. Genetic integrity and diversity of wild populations may be threatened when interbreeding occurs between wild and hatchery fish. Aggr. Behav. 28:145–153, 2002. © 2002 Wiley‐Liss, Inc.

Coupling body weight and its composition: a quantitative genetic analysis in rainbow trout

We examined whether selection for rapid growth rate in rainbow trout, Oncorhynchus mykiss, will potentially lead to correlated genetic responses in body composition. The potential for correlated responses was evaluated by estimating heritabilities and genetic correlations for body weight and traits characterising body composition (condition factor, wasted biomass, fillet weight, three measures of fat, flesh redness, percent fillet protein, ash and water) at the age of 3 years in a half/full-sib mating design. Percent abdominal fat from body weight, percent fillet protein, ash and water were the only traits to display heritabilities close to zero ( h 2=0.02–0.06). The other body composition traits and body weight displayed moderate levels of genetic variation ( h 2=0.11–0.45), making direct and correlated genetic responses to selection possible. Genetic correlations of body weight with percent fillet fat, protein, ash and water and flesh redness were low ( r A=−0.12–0.36), indicating that the quality of fillets is not strongly changed by the selection for rapid growth rate. In contrast, the weight of abdominal fat and waste will be increased as a correlated response, because due to a part–whole relationship, the traits showed strong positive genetic correlations with the body weight ( r A=0.63–0.98). Moreover, we found large differences between sexes especially in the traits that are closely related to body size (i.e., condition factor, weight of waste and abdominal fat) and, to a lesser extent, in the traits related to fillet quality. However, the differences between sexes in body composition could be mainly explained by the difference between sexes in body size. In conclusion, the genetic properties of body weight and body composition traits of the rainbow trout population studied do not impose strong constraints on the progress of the breeding programme.

Evaluation of Black Bengal goats and their cross with the Jamunapari breed for carcass characteristics

Carcass quality of Jamunapari×Black Bengal (JBB), Black Bengal selected for growth (SBB) and random-bred (RBB) wethers of 1 year of age was studied. There was no significant difference between JBB and SBB in pre-slaughter traits and carcass characteristics, except height at wither and dressing percentage which were significantly higher in JBB than in SBB, and muscle fiber diameter which was significantly smaller in JBB than in SBB. Performance of RBB was significantly lower than JBB and SBB. When hot carcass, non-carcass, variety meat, prime cuts, fat deposition and total saleable portion were expressed as % of empty live weight and compared among genetic groups, JBB ranked first. Selection for rapid growth rate within Black Bengal goat increased its live weight and improved meat production. Increased live weight showed a positive relationship with increased fat deposition. Relationships between ‘eye muscle’ area and hot carcass yield, empty live weight and gut fat and perinephric fat and gut fat were positive and significant.

The effects of genetic selection for increased growth rate on mucosal and muscle weights in the different regions of the small intestine of the domestic fowl ( Gallus domesticus)

1. The total organ weights and the constituent weights of mucosal and muscle tissues have been determined in the small intestines of three lines of domestic fowls subjected to different degrees of artificial genetic selection for rapid growth rates. 2. Effects of selection have been examined on the basis of wet and dry tissue weights in duodenum, jejunum and ileum from each line of birds. 3. Effects of selection have been compared on both absolute tissue weights and relative weights (i.e. expressed per kilogram body weight). 4. Selection for rapid growth rate is associated with increases in absolute weight and length of small intestine but marked reductions in relative weight and length. 5. In the fastest growing group of birds the major effect is a decrease in the relative mass of mucosa which is most pronounced in the more proximal regions of the small intestine. 6. These findings are discussed in relation to possible enhancement of intestinal digestive and absorptive efficiency in birds selected for improved growth rate and feed conversion. 7. The differences in tissue composition of the small intestine between lines and between regions of the intestine in the same line emphasise the difficulty in selecting an anatomical parameter upon which to base the in vitro and in vivo measurements of nutrient absorption in a number of established preparations.

Composition and Muscle Cellularity of Japanese Quail After Selection for High Body Weight Under an Optimal or Suboptimal Nutritional Environment

The purpose of this study was to determine if the compositional and cellularity changes associated with selection for rapid growth rate in an optimal and suboptimal nutritional environment were similar. The P-line Japanese quail had undergone long-term selection for high 4-week body weight and received a 28% protein diet. The unselected C-line quail received the same diet. T-line quail were selected by the same criteria as P-line quail but received a 20% protein diet containing .2% thiouracil. Body weights and muscle weights of P- and T-line quail were similar at 10 days of age. At 56 days T-line body weight and muscle weights were intermediate between C-and P-line quail, but whole body composition of P- and T-line quail was similar. The P- and T-line quail possessed a greater apparent number of muscle fibers than C line quail. Total muscle DNA content was lower in T-line muscles compared to P-line muscles at 56 days of age. No differences within age were observed among lines for myofiber diameter, fiber type composition, for concentrations of DNA, RNA and protein, or for protein/DNA and RNA/DNA. At 10 days the weight, length, and diameter of the humerus and femur bones were greatest in T-line quail; these same parameters were intermediate between C- and P-line quail at 28 and 56 days of age. It was concluded that selection for rapid growth rate per se caused apparent fiber number and fiber length to increase while the effect of suboptimal nutritional environment was not evident until after 10 days of age. Selection under suboptimal conditions as exercised in this study prevented expression of the maximum number of muscle DNA units.

The Influence of Growth Rate on the Development of Marek’s Disease in Chickens

The response of chickens to the JM strain of Marek’s disease virus was studied following directional selection for body growth rate. Comparisons were made for four pairs of selection lines, two pairs resulting from long term selection for growth rate and two pairs following a single generation of selection. In all cases, it was observed that the faster growing lines were more susceptible to the development of Marek’s disease than their corresponding lines exhibiting a slower growth rate. These observations suggest that selection for rapid growth rate would result in increased susceptibility, while reverse selection would result in decreased susceptibility. This correlated response can, however, be influenced by the residual genotype present.The results of IHA tests showed that the injected group had a significantly higher JM-antigen titer and incidence of Marek’s disease compared with the naturally exposed groups, indicating the parallel relationship between the virus level and the incidence of tumor formation. The accompanying higher titer of antibody did not provide protection against neoplasia. It appeared to be produced in response to the antigen level, since antigen and antibody titers were found to be positively correlated.

DNA and Weight Determinations on 12 to 14 Day Embryonic Muscle Tissue of Fast and Slow Growing Crossbreds

SELECTION for rapid growth rate or large size could be made more efficient by the use of supplemental measurements to predict growth of individuals. Larger body size has been found to be positively correlated with increased numbers of muscle cells (Smith, 1962; Lepore et al., 1965) and higher levels of glutathione (Charkey et al., 1965).A critical age for obtaining efficient indicators of potential growth may be embryos that are about two-thirds developed. At this stage, the numbers of muscle fibers are established during a gradual cessation of proliferation of the embryonic myoblast cells in mammalian (Bardeen, 1900; Joubert, 1956) and in chick embryos (Kitiyakara, 1959). The growth curve of chick embryos described by Lerner (1939) from 7 to 20 days showed a “sharp acceleration” in growth at 13 days, reaching a maximum rate at 14 days. Genetic effects for rate of embryonic growth have been reported as maximal at …

Selection for Rapid Growth Rate in Chickens

SINCE the advent of the broiler industry more than 20 years ago, poultry breeders have been selecting for rapid growth rate in broiler-strain chickens. They have made much progress. However, it has been difficult to separate genetic progress from that resulting from advances in nutrition for improvement of growth rate. Jaap, Smith and Goodman (1962) used a randombred control population to measure the genetic change which occurred in eight-week body weight of broilers produced commercially between 1955 and 1959. During this period the breeders were estimated to have increased the eight-week weight of broilers by approximately ½ lb. This ½ lb. was almost a 20 percent gain achieved in four generations. Naturally, poultry breeders are wondering whether they may be approaching the upper limits for rapid creases in growth rate in present day populations.The implications of genetical theory (Lerner, 1958; Falconer, 1960) are not clear. Therefore, several additionals election…