Low Weight Line Research Articles

Composition of Eggs from Dwarf and Normal Chickens in Lines Selected for 56-Day Body Weight

Egg weight and egg components were measured at two ages in random samples of 30 nondwarf and 30 dwarf chickens from lines selected for high and low body weight at 56 days of age. Egg, dry shell, dry albumen, total moisture, relative moisture, and dry albumen weights as well as albumen and yolk percentage dry matter were similar at 300 and 360 days of age. Absolute and relative dry yolk weights increased with age, whereas relative shell weight and wet and dry albumen to yolk (A:Y) ratios decreased.Pullets from the high weight line laid larger eggs with more dry yolk, but less relative dry yolk and shell dry matter than those from the low weight line. Nondwarf pullets produced larger eggs with more absolute and relative dry yolk and shell dry matter than dwarf pullets. Line × genotype interactions were present for egg traits other than absolute and relative dry yolk and shell dry matter, providing evidence of differential effects of the dwarfing allele in different genotypic backgrounds.

Divergent Selection for Growth in Japanese Quail Under Split and Complete Nutritional Environments: 3. Influences of Selection for Growth on Heterotic Effects for Body Weight, Feed and Water Intake Patterns, Abdominal Fat, and Carcass Lipid Characteristics

A study was conducted to investigate heterotic effects for body weight, water and feed intake, abdominal fat and carcass lipid levels, and feed efficiency in progeny produced from reciprocal crosses of high (H) and low (L) body weight lines of Japanese quail selected under split diet (SD) and complete diet (CD) environments. Birds under the SD environment could self select feed from high protein and high energy diets. Crossline progeny from the selected lines were evaluated within the respective SD and CD environments in Generation 13.Small egg size of the L dam resulted in a negative maternal effect on the body weight of the HL crossline progeny and the large egg size of the H dam produced a positive maternal influence on the weight of LH crossline progeny. Heterotic effects for water and feed consumption corresponded with the trends for heterosis in body weight. Heterotic effects for abdominal fat and carcass lipid levels were highly negative, and corresponded with trends for heterosis in feed efficiency.

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.

Food Intake Response of Genetically Selected High and Low-Weight Line Cockerels to Plasma Infusions from Fasted Fowl

Two experiments were conducted to determine if food intake of free-feeding chickens could be affected by infusions of plasma from fasted fowl. In the first experiment, chickens from two lines genetically selected for high or low body weight were infused intrahepatically with plasma collected from free-fed and fasted individuals from each line. Food intake of low-weight line birds was increased significantly by infusions of plasma from fasted high-weight line chickens when compared to food intake of low-weight line birds receiving plasma from free-fed low-weight line chickens. Food consumption in high-weight line birds was unaffected by any of the plasma treatments.In the second experiment, plasma from free-fed and fasted high-weight line chickens was infused intrahepatically into Single Comb White Leghorn cockerels. Again the birds receiving the plasma from the fasted fowl consumed significantly more food than those infused with plasma from free-fed fowl. The results of these experiments suggest that some property of plasma from fasted birds stimulates appetite. Selection for increased body weight may have intensified this hunger factor in high weight fowl.

Selection for Body Weight at Eight Weeks of Age.: 19. Influences of Heterozygosity and Dwarfism on Early Egg Production and Associated Traits

Body weight, body components, and reproductive traits were compared during the first 60 days after onset of lay in pullets from lines of White Plymouth Rocks selected for high or low juvenile body weight, their reciprocal F1 crosses, an F2 cross, and dwarfs from the parental lines. Absolute and relative body weight gains were less for dwarf than for nondwarf pullets in the high weight line. In the low weight line, there were differences in absolute but not relative weight gains. Among nondwarfs, both relative and absolute changes in body weight during the first 60 days of lay were similar for crosses and the high weight parental line, and considerably less for the low weight parental line. Numbers of ovulation were the same for the crosses and the high weight parental line, however, more normal eggs were produced by F1 crosses than either parental line. Rate of production was influenced mainly by variation in body weight at onset of lay in the high weight nondwarfs and low weight dwarfs, and by age at first egg in low weight nondwarf pullets. None of the independent variables had a significant association with normal egg production in crosses and high weight dwarf populations.

Growth-Associated Traits in Parental and F1 Populations of Chickens Under Different Feeding Programs: 1. Ad Libitum Feeding

Two experiments were conducted to compare body composition, plasma concentrations of glucose, lipid and protein, gastrointestinal tract (GIT) morphology, and digestive enzyme activities among populations of chickens exhibiting wide differences in growth. In the first experiment, males from a high weight (HW) line, a low weight (LW) line, and crosses between the lines (HL) were examined. In the second experiment, the same high weight (HW′) line, a White Leghorn (LEG) line and their crosses (HLEG) were compared. In both experiments, comparisons were made at both 25 and 61 days of age.The HW chicks were heavier and had larger breasts and longer shanks than the LW or LEG chicks. Although the crosses (HL, HLEG) exhibited values for these traits intermediate to those of the parental lines, HLEG chicks tended to resemble one of the parental lines more closely than did the HL chicks. Differences among all mating combinations were significant for body fat, but the crosses (HLEG, HL) tended to more closely resemble their HW parental line. The HW chicks had significantly higher concentrations of glucose, lipid, and protein in plasma at 25 but not 61 days of age. No differences in glucose, lipid, or protein concentrations in plasma were observed in the second experiment. When expressed as a percentage of body weight, LW and LEG chicks tended to have larger GIT than HW chicks, whereas crosses more closely resembled the HW line. Although significant differences in digestive enzyme activities were obtained, these differences were generally associated with differences in body weight. It was concluded that genetic variation in the traits examined was dependent on both population and age.

Realized genetic parameters from an antagonistic selection index in Tribolium castaneum

Simultaneous selection of two highly correlated traits was practiced in Tribolium castaneum in a replicated experiment for six generations. Two lines were selected in each of three replicates: P+A− for an antagonistic selection index to increase pupal weight at 21 days and decrease adult weight at 31 days, and P−A+ for an antagonistic selection index to decrease pupal weight and increase adult weight. Genetic correlation between pupal and adult weights estimated in the base population was 0.95. Estimates of realized heritabilities and genetic correlation were obtained and compared with full-sib estimates. For the aggregate genotype, the P+A− line had a significant positive selection response, while the P−A+ line showed a significant negative response as would be expected. The response to divergent selection was asymmetrical, being less for the low pupal weight and high adult weight line than vice versa. Less asymmetry was found for the realized heritability, which agreed very well with the index heritability estimated in the base population. Both individual traits changed in the same direction, increasing for the P+A− line and decreasing for P−A+ line, even though a significant response was found only for pupal weight in the P+A− line. Therefore, the response to antagonistic selection for each individual trait seems to be heavily controlled by the strength of the genetic correlation between them. The realized genetic correlation between pupal weight and adult weight obtained from antagonistic selection index was in excellent agreement with full-sib estimates. Realized heritabilities for each trait were overestimated, especially for adult weight, even though there were essentially no differences between realized and estimated values.Key words: selection (artificial), antagonistic index, parameters (realized), Tribolium.

Selection for growth alters the feeding response to injections of biogenic amines

Two experiments were conducted to determine if selection for growth altered the response to intracerebroventricular (ICV) injections of methoxamine and 5-hydroxytryptamine (5-HT). Lines of chickens divergently selected over 25 generations for 8-week body weight were used. The ICV injection of methoxamine into fully fed birds significantly increased food intake in the high-weight line but had no effect on food intake in the low-weight line. Conversely, the ICV injection of 5-HT had no effect in fully fed birds but significantly decreased food intake in 24-hr fasted birds in both weight-lines. Food intake was affected by 5-HT for a much longer period in the high-weight line than in the low-weight line. These results suggest that selection for growth alters the brain response to biogenic amines.

The Influence of Staining Techniques and Examiners on Evaluation of the Morphology of Fowl Spermatozoa

A total of 53 dwarf Single Comb White Leghorn males from the relaxed selection mating of low and high body weight lines and a randombred control line were used to determine the influence of technique (eosin-nigrosin smears or collection of spermatozoa on membrane filters) and examiner on the assessment of sperm morphology. There were significant (P less than .05) line, technique, examiner, and technique X examiner interactions for sperm abnormalities. Total abnormal spermatozoa were higher in the high line than in the other two lines, and this was associated with increased midpiece defects and twisted spermatozoa. Eosin-nigrosin smears showed almost twice the percentage of abnormal spermatozoa compared to stained membrane filters.

Lipogenesis and Lipolysis in Fed and Fasted Chicks from High and Low Body Weight Lines

Lipogenic and lipolytic capacities were examined in fasted and nonfasted 28-day-old chicks from high-weight (HW) and low-weight (LW) selected lines. Lipogenesis was assessed in liver and bone (sternum) tissues through the activities of malic enzyme (EC 1.1.1.40), citrate cleavage enzyme (EC 4.1.3.8), and acetyl coenzyme A carboxylase (EC 6.4.1.2), as well as through the in vitro incorporation of acetate-1-14C into liver and bone lipid fractions. Lipolysis was estimated through the in vitro release of free fatty acids (FFA) from abdominal adipose tissue and through plasma FFA.Fasting depressed lipogenesis and increased lipolysis. Regardless of the feeding state, LW chicks exhibited higher lipogenic and lipolytic capacities than their HW counterparts, suggesting that lipid degradation may be relatively more important than synthesis in determining net fat deposition. In addition, the incorporation of radioactive acetate into bone lipid was associated with detectable activity of lipogenic enzymes, providing further evidence that the skeleton is an important site of lipogenesis in the chicken.

Selection Experiment on Growth and Litter Size in Rabbits

Abstract An experiment was carried out with New Zealand White rabbits to study the effect of four generations of selection on body weight at an age of 112 days. The response given as deviation of body weight at 112 days from control line and expressed as a regression (b) ± standard deviation was respectively 46.2 grams ± 9.6 and -80.4 grams ± 7.2 per generation for upward and downward selection. The realized heritability for upward selection in the high body weight line (HBW) was 0.11 ± 0.02 and for downward selection in the low body weight line (LBW) was 0.31 ± 0.02. The realized heritability from a regression of cumulative response on cumulative selection differential as a divergence between HBW and LBW was 0.19 ± 0.001. The heritability for body weight at 112 days estimated from paternal half-sib correlation was 0.46 ± 0.25.

Selection for Body Weight at Eight Weeks of Age. 17. Overfeeding

Female chicks from lines selected for high and low body weight and their reciprocal F1 crosses were overfed via force feeding to crop capacity from hatching to 21 days of age. Low-weight line chicks could be overfed at an earlier age toa greater extent than those from the high-weight line and F1 progeny. The degree of overfeeding appeared to be associated with the relative size of certain gastrointestinal components. Differences among lines in their capacity to be overfed were reflected in concomitant changes in body weight and carcass fat. Relationships among feed consumption and growth are discussed within the context of selection for body weight and heterosis under various feeding regimens.

Genetic selection for growth rate alters hypothalamic satiety mechanisms in chickens.

The relationship between genetic and hypothalamic obesity was investigated by comparing the response to electrolytic lesioning of the ventromedial hypothalamus in chickens from lines developed through divergent selection for high and low body weight. The high-weight line exhibits obesity, while the low-weight line is relatively lean. Lesioned adult chickens from the low-weight line exhibited the expected obesity syndrome, while lesioned high-weight-line chickens exhibited neither increased feed consumption nor increased body weight. The results suggested that artificial selection for increased body weight resulted in a diminution of hypothalamic satiety mechanisms.

Effect of amphetamine and cocaine on seizure in lead treated mice

Mice, genetically selected for differences in brain weight were employed. Lead administration (0.5% lead acetate) from conception increased the proportion of 21 day old mice exhibiting seizures; total duration of observed seizures was also increased. Mice from the low brain weight line more frequently exhibited seizures than either mice from the high brain weight line or the Binghamton heterogenous stock. Although genome and lead administration alter bodyweight, the inability of bodyweight to predict seizure occurence and/or total duration of seizure within conditions also ws noted. Lead administration from conception through testing increased the probability and duration of transcorneally induced electroconvulsive seizures of 21 day old mice within all three genotypes, and both cocaine and amphetamine injections 15 min prior to ECS reduced the number of animals exhibiting seizures as well as the duration of seizures in both lead treated and control mice.

Jejunal Glucose Absorption in Selected High and Low Weight Lines of Domestic Fowl

Intestinal glucose uptake was measured in normal and dwarf chickens from lines selected for high and low body weight. Jejunal tissue rings were excised from 9-week-old chicks and incubated in a medium containing .002 m glucose. Significantly more glucose (micromoles per gram dry tissue weight) was absorbed by tissues from the low weight line when compared to tissues from the high weight line. The dwarf gene, dw, had no effect on glucose Uptake.glucose absorption small intestine

Cocaine and seizure protection in mice of varying brain weights

The effects of cocaine administration on seizure duration and proportion of animals that seized were examined in mice genetically selected for differential brain weight. In the two experiments reported, mice of the Fuller brain weight lines and of the Binghamton Heterogeneous stock were used. In Experiment 1, 21 day old male and female mice were administered either 0, 5, 10 or 20 mg/kg of cocaine hydrochloride. Fifteen minutes after each mouse was injected, a transcorneal shock was administered to that animal. Type and duration of seizure were measured. Low brain weight mice were more susceptible to seizures and showed more severe seizures that the medium and high brain weight mice or the Heterogeneous stock. Cocaine hydrochloride provided a degree of protection against seizures in a dose dependent fashion, particularly in the medium brain weight and Heterogenous stock mice. Experiment 2 examined whether repeated daily doses of cocaine (15–21 days of age) would alter the pattern of susceptibility described above. In this experiment mice were given either 0 mg/kg or 10 mg/kg of cocaine hydrochloride. At 21 days of age, 15 minutes after injection, mice were subjected to transcorneal shock and the subsequent nature and duration of seizures observed. Mice of the low brain weight line were again seen to have more seizures than those from the high brain weight line. Cocaine decreased the severity of transcorneal induced seizures.

Quantitative analysis of the feeding behavior of four populations of chickens

Comparisons were made among male chickens from four populations for traits associated with feeding behavior during the period from 21 to 71 days of age. The populations were obtained from two lines of chickens, divergently selected for juvenile body weight, into which the sex-linked gene for dwarfism was introduced. Differences among populations in body weight paralleled those for feed consumption, which appeared to be related to meal number rather than meal size. Males from the high-weight line, while spending significantly less time in feeding activity, consumed more feed than those from the low-weight line. Normal chicks exhibited a more pronounced periodicity in feeding rhythms than did the dwarf chicks. Positive correlations of meal size with premeal and with postmeal intervals support the hypothesis that both meal activation and termination mechanisms contribute to appetite control. Differences in the cross-correlation function of meal size with meal intervals between normal and dwarf birds suggested that meal termination mechanisms were of greater importance to appetite control in normal than in dwarf chickens.

Antibody Production and Escherichia coli Resistance in Socially Stable Flocks of Dwarf and Nondwarf Chickens

Dwarf and normal pullets from lines that had undergone selection for divergence in juvenile body weight were maintained in cages as socially stable flocks. Antibody titers were measured at 6 and 14 weeks of age and an Escherichia coli challenge was administered at 16 weeks of age. There was a significant line by dwarf genotype interaction with dwarfs having lower antibody titers than normal pullets in the low weight line and higher antibody titers in the high weight line. The mortality of dwarfs from the low weight line to an Escherichia coli challenge was much higher than that of any other group. These results were consistent with those from previous experiments where the Escherichia coli challenge was given to hens in single cages.

Selection for Body Weight at Eight Weeks of Age: 15. Feed Passage and Intestinal Size of Normal and Dwarf Chicks

Comparisons were made of feed passage rates and size of the gastrointestinal tract components among populations of chickens exhibiting wide differences in growth rate. The populations consisted of White Plymouth Rock stocks selected bidirectionally for high and low juvenile body weight. Comparisons included males heterozygous for the sex-linked gene for dwarfism, as well as normal and dwarf males and females.The indigestible marker, ferric oxide, appeared earlier and disappeared later in the excreta of males from the low-weight line than in those from the high-weight line. Results with female chicks were similar, except that line differences in the time to the first appearance in the excreta were not significant. There were no significant differences in feed passage rates due to the dwarf gene.The weights of the crop, gizzard, duodenum, and the total gastrointestinal tract were, when expressed as a percentage of body weight, significantly heavier for male chicks from the low-weight than for those from the high-weight line. Duodenum weights of female chicks from the low-weight line were also significantly larger than those from the high-weight line. Effects of the dwarfing gene on various components of the gastrointestinal tract, when expressed as percentage weights, were not significant with one exception. Dwarf females from the high-weight line had lower duodenum weights than normals while the reverse was true in the low weight line. In general, the proportionately larger intestinal weights appeared to correspond with a slower clearance of feed through the gastrointestinal tract and may be indicative of altered digestive or absorptive functions resulting from selection for growth.

Dwarfism in Diverse Genetic Backgrounds: Diet-Egg Production Relationships

The effect of diet on phenotypic expressions of the sex-linked dwarf gene, dw, was studied in lines of chickens selected for high and for low juvenile body weight. The relative reduction of body weight and shank length due to dw was consistently greater in the low-weight than in the high-weight line regardless of diet. The hen-day egg production of high-weight dwarf pullets was greater than that of their normal siblings while the opposite relationship was found in the low-weight line. Feeding a diet containing increased levels of protein, calcium, phosphorus, and metabolizable energy increased the egg production of dwarf pullets, regardless of their background genome, but did not significantly affect the egg production of normal pullets. This diet also partially prevented the reduction in shell thickness associated with dwarfism in the low-weight line. In addition, the tendency of dw to reduce the incidence of defective eggs in the high-weight line and to increase the incidence of the low-weight line varied with diet. Dwarf pullets of both rapid and slow growing populations require different diets for the maximum realization of their genetic potential.