Randombred Control Line Research Articles

Responses to various selection protocols for lamb production in Rambouillet, Targhee, Columbia, and Polypay sheep.

To investigate the effectiveness of four selection protocols for improving reproduction in sheep, we evaluated nine selection lines and two random-bred control lines for lamb and wool production. Results were based on 25,026 dam and 30,628 lamb records from Rambouillet (R), Targhee (T), Columbia (C), and Polypay (P) sheep collected from 1976 through 1988. Phenotypic trends over years were positive (P < .01) for most reproductive traits, body weight, wool grade (coarser grades), and lamb weaning weight in nearly all selected lines. Small positive trends for both random-bred control lines indicated there were improvements in management and(or) environment during the period. Small but significant phenotypic declines in fleece weights occurred in most lines, including controls. Substantial genetic gains (P < .01) in litter weight weaned (120 d), net reproductive rate (lambs weaned divided by ewes mated), prolificacy, body weight, and weaning weight were made in nearly all selected lines. There were also small but significant improvements in milk score in most lines. There were significant genetic declines and improvements in fleece weights; however, the average genetic change in fleece weight for lines selected for litter weight weaned was negligible. Genetic improvement in litter weight weaned was attributed approximately 37% to prolificacy, 27% to percentage of lambs weaned, 17% to lamb weaning weight, 12% to fertility, and 7% to ewe viability from breeding to lambing. On average, selection based on independent culling levels (litter weight weaned plus yearling body weight), yearling body weight, or early puberty was only 85, 67, or 59%, respectively, as effective as that based solely on litter weight weaned for improving litter weight weaned. The net value of the average (over all breeds) annual increase in production per ewe resulting from selection for litter weight weaned accumulated over 12 yr to an estimated $11.40 and $21.51 annually for genetic and phenotypic increases, respectively.

Jejunal glucose uptake and oxygen consumption in turkey poults selected for rapid growth

Two lines of turkey poults, one selected for rapid growth at 16 wk of age (F line) and the other a randombred control line (RBC2) were used to investigate the effect of selection for rapid growth on jejunal O2 consumption and glucose transport as well as whole-body O2 consumption. All trials used unsexed poults and were designed as a randomized complete block with day and line as independent variables. In Trial 1, 120 turkey poults, fed a standard starter ration (25.5% CP), were used to examine the effect of selection on feed intake, body weight gain, and efficiency from hatching (Day 0) to 13 d of age. At Day 14, 36 of 60 birds from each line were killed to measure intestinal length and weight and jejunal O2 consumption after 18 h of feed deprivation. Compared with the RBC2 line, the F line had relatively shorter but heavier small intestinal segments when adjusted by 18 h feed-deprived body weight (FBW; P < 0.001). The F line consumed more O2 over the entire jejunum adjusted to FBW than RBC2 line (43.8 vs 34.6 nmol O2/min.g FBW; P < 0.001). Jejunal ouabain- and cycloheximide-sensitive O2 consumption were greater (P < 0.05) in the F line. In Trial 2, 16 14-d-old poults from each line were used to measure in vitro jejunal glucose transport rate. There was no difference in glucose transport of the jejunum (nanomoles per minute per gram of FBW) between the lines. In Trial 3, 20 poults from each line were used to measure whole-body O2 consumption at 7 to 10 d of age. The F and RBC2 lines had similar whole-body O2 consumption rate per gram of FBW. These data suggest that selection of turkeys for rapid growth at 16 wk of age did not increase efficiency of jejunal glucose uptake in 14-d-old turkey poults.

Ornithine decarboxylase activity in muscle, liver, and intestinal tissue of turkeys during a short-term feed withdrawal and following refeeding

The activity of ornithine decarboxylase (ODC), an enzyme associated with cellular growth and protein synthesis, was examined in breast muscle, liver, and intestinal tissues of turkeys during a short-term period of feed withdrawal (FW) and following refeeding. Turkeys from a randombred control line were reared under standard management practices to 3 wk of age in battery brooders. Feed was then withdrawn from FW birds for a 48-h period, after which feed was consumed ad libitum. Control birds consumed feed ad libitum throughout the test period. Tissues were collected from 12 birds per treatment following 24 and 48 h of FW and at 6, 12, 24, and 48 h following refeeding for later determination of tissue ODC activity. Activity of ODC was greater in tissue from the small intestine than in liver tissue and both had greater activity than that exhibited by breast muscle. Short-term FW and refeeding produced differential responses in ODC activity of the three tissues examined. Feed withdrawal resulted in a reduction of ODC activity in intestinal tissue, whereas activity was unaffected for liver or breast muscle tissues. Compensatory increases in ODC activity were observed in liver and intestinal tissues; however, the increase was both more rapid and transitory in small intestine than in liver tissue. The ODC activity in breast muscle was largely unaffected by short-term FW and refeeding. Patterns of ODC activity in liver during FW and refeeding closely resembled patterns observed for absolute and relative liver weight. Thus, the results of the present experiment demonstrate that short-term FW and refeeding influence underlying growth mechanisms of supply organs, such as hepatic and intestinal tissue, in addition to affecting overall growth and muscle development.

Dietary unsaturated fatty acids affect antibody responses and growth of chickens divergently selected for humoral responses to sheep red blood cells

The effect of linoleic and linolenic acid on antibody (Ab) responses to SRBC and BSA and on growth performance were studied in pullets of three genetically different laying lines. Pullets were fed one of three diets: a control diet, a linoleic acid-enriched diet, or a linolenic acid enriched-diet. The linoleic and linolenic acid enriched-diets were the control diet enriched with either sunflower oil or linseed oil. Two chicken lines divergently selected for high (H) and low (L) Ab responses to SRBC, and a randombred control (C) line were used. Total Ab responses to SRBC were not affected by diet, but in the H line a tendency for higher IgG titers to SRBC after primary immunization were found when birds were fed the linoleic diet. The humoral response to BSA was significantly affected by a line by immunization by diet interaction. In the H line birds, the linoleic diet significantly enhanced Ab titers to BSA as compared to the normal diet and linolenic acid-enriched diet. The linolenic acid-enriched diet significantly decreased Ab titers to BSA in the C line birds. No dietary effects on the titer to BSA were found in the L line birds. During the first 3 wk of life, the linolenic acid-enriched diet resulted in reduced BW gain of H line birds. After that period, no effects of diet on BW gain was found. It is concluded that modulation of Ab responses of poultry to T cell-dependent antigens by essential fatty acids is affected by genotype. The relationship between magnitude of Ab responsiveness, BW, and essential fatty acids is discussed.

Effect of the genetic selection of turkeys for increased body weight and egg production on immune and physiological responses

Selection of poultry for fast growth rate is often accompanied by a reduction in specific immune responses or increased disease susceptibility. In this study, 17-wk-old male turkeys from each of four closed genetic lines, a randombred control (RBC) line and its subline (F) selected for increased 16-wk BW, and another RBC and its subline (E) selected for increased egg production, were tested for in vivo response to toe web inoculation with phytohemagglutinin-P (PHA-P), in vitro response of lymphocytes in whole blood to PHA-P and concanavalin A (Con A), hemolytic complement activity, differential white blood cell counts, hematology, and serum chemistry values. Fifteen male turkeys from each of two commercial lines, Com A and Com B, were also tested. The large-bodied F line birds had a lower toe web response to PHA-P, lower lymphocyte counts, and lower relative spleen weights than their smaller parent line. Body weights, total erythrocyte counts, blood urea nitrogen (BUN) levels, and in vitro mitogenic response to PHA-P and Con A were higher in the F line birds. Line E had lower hemolytic complement levels, lower relative spleen and relative bursal weights, and a higher in vitro mitogenic response to PHA-P than its parent line. The Com B line had a lower toe web response to PHA-P, and lower serum levels of gamma-glutamyltransferase and bilirubin than Com A. Line Com B had higher total RBC counts and higher levels of alanine aminotransferase (ALT) than Com A. These results support the concept that some changes in the cell-mediated immune response, as well as other physiological changes that may potentially affect immune response, appear to accompany selection for faster growth.

Divergent Antibody Responses to Vaccines and Divergent Body Weights of Chicken Lines Selected for High and Low Humoral Responsiveness to Sheep Red Blood Cells

Primary and secondary antibody responses to intramuscularly administered proteins of Eschericia coli (F11), Newcastle disease virus (NCD), infectious bronchitis virus (IB), and infectious bursal disease virus (IBD), respectively, were measured at weekly intervals in two chicken lines. The latter had been divergently selected for high and low antibody responses to sheep red blood cells (SRBC), and in a random-bred control line. An oil-based adjuvant was required to induce primary and secondary antibody responses to NCD, IB, and IBD. With respect to F11, elevated antibody responses were found in birds sensitized and boosted to F11 with and without adjuvant. The humoral response to F11 and to all viral antigens was significantly higher in the high (H) line than in the low (L) line, whereas the control (C) line showed intermediate titers. At 5 and 17 weeks of age, L line birds were significantly heavier than birds of the H and the C lines. A negative phenotypic correlation within lines between body weight at 17 weeks of age and antibody titers at 1 week after sensitization was found, but no further correlations between humoral responses and body weight or growth could be established. The present results suggest that selection for enhanced humoral responsiveness to SRBC resulted in enhanced responsiveness to components of several vaccines. Mechanisms underlying the relationship between divergent selection for immune responsiveness and body weight are discussed.

Divergent Selection for Body Weight and Yolk Precursor in Coturnix coturnix japonica.: 11. Correlated Responses Over Thirty Generations

Japanese quail lines were divergently selected for 4-wk BW (HW and LW lines) and plasma yolk precursor [total plasma phosphorus (TPP); HP and LP lines] for 30 generations. The base population was a randombred control line (R1) that was maintained along with the selected lines. Sublines were established from the ninth selected generation of HW by continuing to select males for increased 4-wk BW and selecting females for increased (HW-HP line) or decreased (HW-LP line) TPP. Correlated responses over the entire selection period were measured.Egg production of HW, LW, HP, and HW-HP declined over generations. There was a positive quadratic component to the change in HW indicating that the change in egg production over generations was decreasing. There was no significant change in egg production of LP. Number of ovarian follicles in rapid development increased in LP and decreased in LW and HP, Total follicular weight increased in HW and LP and decreased in LW. Production of abnormal eggs increased over generations in HW and HW-HP.Body weight at the beginning and end of the laying period increased in HW, HW-HP, HW-LP, and LP and decreased in LW. Egg weight increased in HW and HW-HP and decreased in LW and LP. The increase in egg weight of HW was due to a disproportionate increase in shell and yolk. Wet weight of the liver increased in HW and decreased in LW and HP. Dry liver weight decreased in LW, HP, and LP. Mortality to 4 wk of age increased in LW, HP, and LP.

Divergent Selection for Body Weight and Yolk Precursor in Coturnix coturnix japonica.: 10. Response to Selection Over Thirty Generations

Japanese quail lines were divergently selected for 30 generations for 4-wk BW (HW, LW) or plasma yolk precursor (HP, LP) as measured by total plasma phosphorus (TPP) at the beginning of lay. The HW, LW, HP, and LP lines were initiated from a randombred control line (R1). In the ninth generation of selection in the HW line, sublines were developed by continuing to select males for increased 4-wk BW whereas females were selected for increased (HW-HP line) or decreased (HW-LP) TPP. Individual selection was used in the HW, LW, HW-HP, and HW-LP lines. In the HP and LP lines, females were individually selected whereas males were selected on their full-sisters’ performance.Realized heritabilities (h2), based on the linear regression of selection responses (corrected for environmental changes) on accumulated selection differentials (weighted for the number of offspring produced) over generations, declined with selection in the HW, LW, HP, and LP lines. The h2 of 4-wk BW in the HW line was 0.42 during the first 10 generations of selection and then declined to 0.30 during the next 20 generations of selection. In the LW line, realized h2 of 4-wk BW was 0.40, 0.16, and −0.12 in Generations 1 through 10, 11 through 20, and 21 through 30, respectively. The respective h2 for TPP in the HP line were 0.29, 0.17, and 0.14. The h2 of TPP in the LP line was 0.35 during the first 10 generations and essentially zero during the next 20 generations.Four-week BW and TPP were negatively associated in the HW, HP, and LP lines. There was no significant relationship between these two traits in the LW line.

Range and Confinement Rearing of Four Genetic Lines of Turkeys.: 2. Effects on Behavior and Tonic Immobility

An experiment was conducted to determine the effect of range and confinement rearing on behavior and tonic immobility of four genetic lines of turkeys. Lines of turkeys utilized were selected for increased body weight, or increased shank diameter, or were randombred control lines developed in 1966 and 1986. Birds from the four lines were brooded lines and sexes intermingled to 8 wk of age in confinement. At that time, half the birds from each full-sib family were moved to a large range pen and the remaining birds were moved to a large confinement pen. Selection for increased body weight has resulted in an increased number of eating bouts, decreased duration of walking bouts, and greater fear response (as measured by tonic immobility inductions and duration). Rearing environment affected drinking, eating, and resting behavior. Range-reared birds had fewer drinking bouts of increased duration, and longer eating and resting bouts than did their confinement-reared contemporaries. There were no line by environment interactions, indicating that the four lines responded similarly in both rearing environments.

Range and Confinement Rearing of Four Genetic Lines of Turkeys. 1. Effects on Growth, Mortality, and Walking Ability

Line by environment interactions complicate interpretation of results from long-term selection experiments. To investigate the potential effects of such interactions, a study was conducted in which birds from four genetic lines were reared in two environments. Birds from four turkey lines were brooded in confinement housing. At 8 wk of age, half of the birds from each full-sib family were moved to a large range pen and the remainder were placed in a large confinement pen. Significant line by environment interactions were present only for walking ability scores of males. A general lack of significant line by environment interactions indicates that rearing environment of these lines may be altered without affecting interpretation of results from a selection experiment. In addition, the current randombred control lines continue to adequately serve as control populations for a long-term selection experiment.

The Influence of Major Histocompatibility Complex Genotypes on Resistance to Pasteurella multocida and Newcastle Disease Virus in Turkeys

Sublines homozygous for each of four MHC haplotypes were developed from randombred control populations of turkeys and challenged with Pasteurella multocida (capsular serogroup a, somatic serotype 3, 4) at 6 wk of age or Newcastle disease virus (NDV; Texas GB strain) at 4 wk of age. In addition, individuals from a randombred control line (RBC2) and a subline (F) of RBC2 long-term selected for increased 16-wk BW were included in most of the challenge trials. The duration of the challenge trials was 2 wk for both organisms.Mortality following challenge with P. multocida or NDV was higher in the F line than in its randombred control. The MHC genotypes differed in mortality following exposure to both organisms but the rankings of the genotypes were not the same for P. multocida and NDV. The increased susceptibility of the F line to both organisms could not be explained by known changes in the frequency of the MHC haplotypes.

Differences in distribution of lymphocyte antigens in chicken lines divergently selected for antibody responses to sheep red blood cells

The proportion of cells showing differentiation antigens specific for T cells, B cells and leukocytes was studied at various ages in peripheral blood, and at 14 weeks of age in the bursa of Fabricius, spleen and thymus of two lines of chicken that had been selected over 13 generations for either high (H) or low (L) antibody responses to sheep red blood cells (SRBC), and also in a randombred control (C) line. Flow cytometry showed no consistently significant differences between the three lines in numbers of circulating lymphocytes and other leukocytes after hatching. However, higher percentages of CD4 + cells and B cells were present in the spleen and thymus from the H line compared with the L line. However, the L line was characterized by a higher proportion of splenic CD8 + cells and spleen cells expressing gamma-delta T-cell receptors. Immunization with sheep red blood cells had no effect on the distribution of CD4 + or CD8 + cells in the various tissues at 2 and 7 days after immunization. These results suggest that previously reported differences in in vivo immune responses between these chicken lines may be related to the differences in resident T-lymphocyte subpopulations in the lymphoid tissues. The involvement of T-cell subsets and non-antigen-specific mechanisms in divergent selection on humoral immune responses in chickens is discussed.

Effect of Selection for High or Low Incidence of Tibial Dyschondroplasia for Seven Generations on Live Performance

An experiment was conducted to determine the effect of divergent selection for tibial dyschondroplasia (TD) on live performance of broilers. Broilers used in the experiment were produced from the parental lines selected for high (H) and low (L) incidence of TD and a randombred control (C) line. Diallel crosses were made between H and L lines. The offspring produced were HH, HL, LH, LL, and CQ where the first letter refers to sire line and the second letter refers to dam line. Body weights, average daily body weight gains, and exponential growth rates were determined at weekly intervals. The incidence of TD was recorded at 4 and 7 wk of age.There was no difference among body weights of lines up to 5 wk of age. Sire lines influenced body weights of birds from 5 to 7 wk of age. A significant interaction between sire and dam lines for body weight was the result of decreased body weights of birds in the HH line from 5 to 6 wk of age. There was a similar interaction for body weight gain, which resulted in a slower growth rate of birds in the HH line from 3 to 5 wk of age. Tibial dyschondroplasia incidence was 84.1 and 92.0% in the HH line, 5.6 and 5.4% in the LL line, and 7.0 and 13.2% in the CC line at 4 and 7 wk of age, respectively. It was suggested that genetic predisposition for TD was independent of body weight.

Random Amplified Polymorphic DNA Comparisons Among Broiler Lines Selected for Incidence of Tibial Dyschondroplasia

Lines selected for high (H) and low (L) incidence of tibial dyschondroplasia (TD) for eight generations and a randombred control (C) line of broiler chickens were fingerprinted by random amplification of genomic DNA mixed from 20 individuals of each line with 20 oligonucleotide primers. Among these 20 primers, 15 could distinguish the H from the L line, 14 the H from the C line, and 13 the L from the C line. Band sharing (BS), on the average over 20 primers, was .7 for the H vs L comparison and .8 for both H vs C and L vs C comparisons. The levels of BS calculated from individuals was .6 between the H and L line, .7 between the H and C line, and .7 between the L and C line. The ranking of BS values obtained from individual DNA samples was consistent with that obtained from the mixed mixed DNA samples. Genomic distance between divergently selected lines (H vs L) was larger than that between the divergently selected lines and randombred line (H vs C and L vs C). Individual variation within lines was detected in spite of eight generations of selection. Results showed that eight generations of divergent selection for TD incidence in broiler chickens had resulted in genetic variation among lines. The procedure of random amplified polymorphic DNA assay using mixed DNA samples could be used to evaluate genetic distance among lines of chickens.

The Stability of Three Randombred Control Lines of Turkeys

A survey of growth and reproduction traits over eight and seven generations, respectively, is presented for three randombred control (RBC) lines of turkeys. Of the 26 traits measured, regression coefficients for the three RBC lines differed for only 8-wk body weight of females and egg weight, although the difference was in magnitude and not direction of the slopes. A common environmental trend was suggested for 8-wk male and female body weight and for 16-wk shank width of males. There was little evidence of genetic drift in these three RBC lines of turkeys.

Survey of Major Histocompatibility Complex Class II Haplotypes in Four Turkey Lines Using Restriction Fragment Length Polymorphism Analysis with Nonradioactive DNA Detection

Four turkey lines were typed for MHC Class II haplotypes with restriction fragment length polymorphism (RFLP) analysis using a nonradioactive probe made from a chicken genomic clone of MHC Class II genes. The RFLP analysis detected 18 new patterns in the populations. There were three new haplotypes that had a frequency of about 10% or more in a population, whereas the rest appeared only once. The haplotype frequencies were significantly different in the E line, selected only for increased egg production, and the F line, selected only for increased body weight, compared with their respective randombred control lines. The shift of haplotype frequencies in the two selected lines seemed to be in opposite directions. One, but not the same, haplotype predominated in the selected lines, with about 50% of total haplotypes. Fewer haplotypes were frequent in the selected lines, whereas the frequencies in the control lines were relatively widely distributed, with the most frequent haplotype being below 35%. The frequency of homozygotes of the Class II haplotypes was the highest in the F line.

Genetic Correlations of Tibial Dyschondroplasia Incidence with Carcass Traits in Broilers

Relationships among the incidence of tibial dyschondroplasia (TD) with 7-wk live BW, carcass component weights (CCW), and abdominal fat weight (AFW) were assessed using high and low incidence of TD lines developed by a seven-generation divergent selection experiment, along with a randombred control line. The incidence of TD exhibited negative genetic correlations with both BW (−.65 and −.46 estimated from sire’s and dam’s components of variance and covariance, respectively) and with CCW (<−.28). The incidence of TD and AFW was not correlated based on sire’s components of variance and covariance. The correlation of TD incidence with AFW was not as high as with the other traits under consideration based on dam’s components of variance and covariance. Correlations of AFW with CCW were negative based on sire’s components of variance and covariance, but positive based on dam’s components of variance and covariance. Heritabilities of TD, BW, AFW, and CCW estimated by sire’s variance components were lower than those estimated by dam’s variance component. Dams might have a greater influence on TD incidence than sires. Selection for decreasing TD incidence should be feasible while simultaneously increasing BW and CCW in broilers.

Responses to Long-Term Divergent Selection for Eight-Week Body Weight in Chickens

Thirty-six generations of divergent selection for body weight at 8 wk of age resulted in approximately an eightfold difference between the high (HWS) and low (LWS) lines for this trait. In both White Plymouth Rock lines, selection intensities declined over generations, with responses about five times greater during the first 18 than the last 18 generations of selection in Line HWS and about two times greater in Line LWS. Also, responses to selection were more irregular in the later than in earlier generations. Sexual dimorphism of body weight (male:female) was greater for Line LWS than HWS. A randombred control line (AC) maintained concurrently with the selected lines did not exhibit environmental trends across generations. Relaxed lines, established at different generations of selection, were used to evaluate effectiveness of selection and monitor environmental changes over short periods.

Changes in Functional Qualities of Turkey Eggshells in Strains Selected for Increased Egg Production or Growth ,

Much past research has been devoted to physical eggshell qualities, i.e., weight, deformation, or egg density, but little research has investigated the functional eggshell qualities when expressed in terms of eggshell conductance to gases. Conductance is a measure of the ease with which gases diffuse across the pores of the shell and is (by Fick’s law) determined by the number and geometry of the individual pores. The objective of the present study was to determine changes that have occurred in functional eggshell characteristics (eggshell conductance) following selection for egg production or growth over nearly 30 generations. Major changes have occurred in the physical dimensions of eggs from selected lines of turkeys compared with their respective randombred controls. Egg weights increased 11% due to selection for growth and decreased 14% due to selection for egg production. Other measurements such as length and width increased allometrically with egg weights. Selection for egg production has decreased the physical dimensions (egg weight, volume, or surface area) of eggs, and selection for growth has increased the same measurements, but adjustments have not been made by selected hens to increase or decrease the functional characteristic (conductance) allometrically (conductance constants). An interaction was observed in eggshell conductance constants as the hens aged, suggesting that genetic selection may affect functional characteristics. This suggests that the energetics of embryonic development may be different in eggs from turkey hens of various ages. Energetics may result in poor hatchability and poult quality. It can be concluded that as the hens aged the conductance and conductance constants did not change allometrically with increasing egg weight. This may suggest a reason for increased embryonic mortality seen in the selected lines compared with their randombred control lines.

Histomorphology, oLH and hCG receptors, and testosterone secretion in vitro in Rambouillet rams from lines in which females had been selected for low or high reproductive rate.

The objective of this study was to determine whether gross or histomorphological components of the testes, capacity and dissociation constants (Kd) of testicular oLH and hCG receptors, and gonadotrophin-stimulated testosterone secretion in vitro differed among Rambouillet rams from lines selected for low or high female reproductive rate and from rams of a random-bred control line. Lines had been selected for approximately 20 years. Data were collected from 22-month-old rams during the late breeding season. Rams among lines did not differ (P > 0.05) in gross testicular characteristics or most histomorphological characteristics. However, the percentage volume of interstitial vascular tissue was greater (P < 0.05) for rams from lines selected for low female reproductive rate than for rams from lines selected for high female reproductive rate. Receptor sites per Leydig cell and binding capacities of oLH and hCG receptors per testis, per gram of parenchyma, and per milligram of membrane protein did not differ (P > 0.05) among lines. The Kd values for oLH and hCG receptors did not differ (P > 0.05) among lines; however, receptor sites per Leydig cell, capacities of testicular parenchyma to bind gonadotrophin and Kd values were higher (P < 0.05) for oLH than for hCG receptors. Total oLH- and hCG-stimulated testosterone secretion in vitro did not differ (P < 0.05) among lines. In conclusion, selection for or against reproductive rate in Rambouillet ewes has not altered gross or most histomorphometric characteristics of the testes of male offspring, with the exception that selection against reproductive rate increased the proportion of testicular volume occupied by vascular tissue within the interstitium.(ABSTRACT TRUNCATED AT 250 WORDS)