High Line Birds Research Articles

Divergent selection on home pen locomotor activity in a chicken model: Selection program, genetic parameters and direct response on activity and body weight.

General locomotor activity (GLA) in poultry has attracted attention, as it negatively influences production costs (energy expenditure and feed consumption) and welfare parameters (bone strength, litter quality, feather pecking and cannibalism). Laying hen lines diverging in the average level of spontaneous locomotor activity in the home pen were developed by genetic selection using the founder New Hampshire line. Activity was recorded using RFID technology at around five weeks of age during four to five days in the home pen. After initial phenotyping, the least active birds were selected for the low activity line and the most active for the high activity line, with no gene transfer between lines. In each of six generations, approximately ten sires were mated to twenty dams producing 158 to 334 offspring per line per generation. The response to selection was rapid and of a considerable magnitude. In sixth generation, the level of GLA was approximately halved in the low and doubled in the high line compared to the control (7.2, 14.9 and 28.7 recordings/h). Estimated heritability of locomotor activity in the low and high line was 0.38 and 0.33, respectively. Males, in general, were more active than females. High line birds were significantly heavier than low line birds. In fourth, fifth, and sixth generation, low as well as high line birds were lighter than control line birds. This selection experiment demonstrates variation in heritability for GLA and, as a result, genetically diverged lines have been developed. These lines can be used as models for further studies of underlying physiological, neural and molecular genetic mechanisms of spontaneous locomotor activity.

Selection for pro-inflammatory mediators produces chickens more resistant to Campylobacter jejuni

Campylobacter spp. are the second leading cause of bacterial-induced foodborne illnesses with an estimated economic burden of nearly $2B USD per year. Most human illness associated with campylobacteriosis is due to infection by C. jejuni and chickens are recognized as a reservoir that could lead to foodborne illness in humans resulting from handling or consuming raw or undercooked chicken. We recently developed a novel breeding strategy based on identification and selection of chickens with an inherently high and low phenotype of pro-inflammatory mediators including IL-6, CXCLi2, and CCLi2, hereafter referred to as the high and low lines, respectively. We have shown the high line chickens are more resistant to the foodborne and poultry pathogens Salmonella enterica serovar Enteritidis, Eimeria tenella, and Clostridium perfringens-induced necrotic enteritis compared to the low line. The objective of this study was to determine whether the same trend of enhanced resistance in the high line birds was observed for C. jejuni. Birds were challenged at 2 d of age by oral gavage (0.5 mL) with 5 × 106 colony forming units (cfu) of C. jejuni/mL, necropsied 4 d post challenge, and cecal content collected to determine if there was a difference in C. jejuni resistance between the high and low line chickens. There were fewer (P = 0.01) chickens from the high line (28/40 = 71.8%) that were colonized by C. jejuni compared to the low line (37/39 = 94.9%). The amount of C. jejuni recovered from the ceca of infected birds was quantified; however, no differences were observed (P = 0.10). Since the high line birds were also more resistant to C. jejuni, it provides additional validation of selection based on pro-inflammatory mediators producing a line of chickens with increased natural resistance against diverse foodborne and poultry pathogens. The poultry industry is moving towards reduced therapeutics and, as such, our breeding strategy would be a viable method to incorporate into traditional poultry breeding programs.

Selection for pro-inflammatory mediators produces chickens more resistant to Clostridium perfringens-induced necrotic enteritis

We developed a novel selection method based on an inherently high and low phenotype of pro-inflammatory mediators and produced "high" and "low" line chickens. We have shown high line birds are more resistant to Salmonella enterica serovar Enteritidis and Eimeria tenella compared to the low line. Clostridium perfringens is the fourth leading cause of bacterial-induced foodborne illness, and is also an economically important poultry pathogen and known etiologic agent of necrotic enteritis (NE). The objective of this study was to determine if high line birds were also more resistant to NE than low line birds using an established model. Birds were reared in floor pens and challenges were conducted twice (high line = 25/trial, 50 birds total; low line = 26/trial, 52 birds total). Day-old chicks were provided a 55% wheat-corn-based un-medicated starter diet. A bursal disease vaccine was administered at 10× the recommended dose via the ocular route at 14-d-of-age. Birds were challenged daily for 3 d beginning at 16-d-of-age by oral gavage (3 mL) with 10(7) colony forming units (cfu) of C. perfringens/mL then necropsied at 21-d-of-age. All birds had sections of the intestine examined and scored for lesions while the first 10 necropsied also had gut content collected for C. perfringens enumeration. Chickens from the high line were more resistant to C. perfringens-induced NE pathology compared to the low line, as indicated by reduced lesion scores. Ninety percent of the high line birds had lesions of zero or one compared to 67% of the low line birds. Wilcoxon rank sum test showed significantly higher lesion scores in the low line birds compared to the high line (P < 0.0001). There were no differences in the C. perfringens recovered (P = 0.83). These data provide additional validation and support selection based on elevated levels of pro-inflammatory mediators produces chickens with increased resistance against foodborne and poultry pathogens.

Sensitivity of innate and adaptive cellular immune parameters of poultry to minor macro- and micronutrient differences in two nutritionally complete layer feeds

Comparable diets were found to modulate levels of specific and natural humoral immunity in different manners over two generations of genetically selected hens for a high or low Ab response. These diets were based on ingredients that were grown organically (diet A) or conventionally (diet B). Here we report the effects of these diets on cellular immune parameters such as monocyte reactivity measured by NO production, proliferation of whole blood leucocytes and PBMC with the T- and B-cell mitogens, ConA and LPS respectively. Furthermore we measured the in vitro modulatory effects of water soluble extracts of the two diets on T-cell proliferation of whole blood cultures. In both generations a feed change enhanced monocyte reactivity in all birds with the high line birds being most sensitive. Whole blood assays showed the most pronounced diet effects on T-cell reactivity. The low line birds of the first generation showed the greatest effect, but in the second generation all lines were affected by the diets. In the PBMC the greatest effects were found in the control values, with the effects differing in each generation. The present results together with the results found in the whole blood cultures, suggest dietary effects on the intrinsic reactivity of peripheral lymphocytes as well as in vivo effects, the first with quickly measurable effects and the last activity reflected in our later measurements. These results suggest that a feed change with only minor nutritional differences will induce immunomodulatory effects, and each diet has a unique effect on cellular parameters of innate and adaptive immunity.

Total Cholesterol, Total Triglycerides, and Cholesterol Distribution Among Lipoproteins as Predictors of Atherosclerosis in Selected Lines of Japanese Quail

The proportions of plasma high and low density lipoprotein cholesterol have been linked to inherited tendency for atherosclerosis in humans. Studies were conducted with Japanese quail males from lines genetically selected for high and low TC and a randombred (unselected) control line that were fed 0.0 or 0.5% cholesterol for 12 weeks. Atherosclerotic plaques were more severe in the high than in the low line quail and in those fed cholesterol compared to non-cholesterol-fed quail. Serum TG, TC, VLDLC, LDLC, and HDLC were also higher in the high than in the low line quail and in cholesterol-fed vs. non-cholesterol-fed quail. Significant interactions indicated that TC and LDLC concentrations were more affected by dietary cholesterol in the high line than in the low line. The low line quail maintained higher HDLC and lower LDLC than the high line. Regression and correlation analyses revealed that although VLDLC, LDLC, and TC were significant predictors of atherosclerosis in the high line birds, the TC/HDLC ratio was a better predictor in the low line. The Japanese quail lines used herein represent useful experimental models for studies of genetic differences in atherosclerosis in humans.

Two-Way Selection for Threshold Body Weight at First Egg in Broiler Strain Females.: 3. Reproductive Performance Under Various Levels of Feed Restriction

Two-way selection was carried out for high and low threshold body weight at onset of lay (ThrWtLay). The present study determined the effect of this selection on reproductive performance under conditions of quantitative feed intake restriction. Female chicks of the two lines were raised under a commercial feed restriction program until 22 wk of age (target weight 2,200 g). At this time they were divided into five treatment groups, one of which had free access to feed, the others receiving 120, 130, 140, and 150 g/day of a commercial layer mash, respectively. The experiment was carried out in two independent replicates, in consecutive years. In all treatments, low-line birds entered lay at a significantly lower body weight and earlier age than the high-line birds. During the prepeak laying period, the early entry into lay of the low-line birds resulted in significantly greater egg numbers as compared with the high-line birds (P < .01). This difference was maintained in the postpeak laying period (34 to 58 wk). When averaged over all treatments and both replicates, the low-line birds produced 70% more eggs than the high-line birds in the prepeak period, 14% more during the postpeak period, and 25% more overall. Over all treatments and both replicates, egg weight of the high-line birds averaged 2.7 g greater than that of the low-line birds. At each feeding level, low-line birds at the end of lay had lower carcass weight and breast weight, and shorter shank length, but a greater absolute weight of abdominal fat than high-line birds. Thus, low-line birds were characterized by increased adiposity. It is hypothesized that the selection implemented in these lines acted primarily to decrease photoperiodic drive of the high-line relative to the low-line birds. This resulted in an increase in the number of days of light stimulation required for initiation and completion of ovum maturation and ovulation by the high-line as compared to the low-line birds. A similar decrease in photoperiodic drive may be at the root of current broiler breeder reproductive problems. If so, selection for low ThrWtLay may be a means of ameliorating these difficulties.

Selection for High and Low Threshold Body Weight at First Egg in Broiler Strain Females.: 1. Direct Response to Selection and Correlated Effects on Juvenile Growth Rate and Age at First Egg

A selection program for high and low threshold body weight at first egg was carried out in a broiler line. Selection was on the basis of weight at first egg, following gradual release from feed restriction at a relatively advanced age. After six generations of selection, the lines differed by 862 g in the trait under selection. In addition, 6-wk body weight of high-line (HL) birds was 91 g greater, and age at first egg was 32 days greater than in low-line (LL) birds. When raised under an ad libitum feeding regimen from hatch, HL birds entered lay 20 days later than LL birds. When onset of lay was markedly delayed by maintaining feed restriction until 29 wk of age, body weight at first egg of HL birds was greater by 645 g than that of LL birds. Similarly, when birds of the two lines were subjected to forced molt and brought to a body weight well below that of initial body weight at first egg, and then allowed to gain weight and reenter lay, body weight difference at first egg of HL and LL birds following rehabilitation was similar to that found on original entry into lay. It is proposed that the results may most plausibly be explained as resulting from a primary effect of the selection procedure on the time required to first egg from onset of sexual competence, defined as onset of responsiveness to lay-inducing factors such as light. Alternative explanations involve effects of the selection procedure on threshold weight or threshold age requirements for sexual competence.

Studies of the Relationship Between Fear-Related Responses and Production Traits in Japanese Quail (Cotumix coturnix japonica) Bidirectionally Selected for Dustbathing Activity

In three experiments, female Japanese quail originating from lines selected for low or high dustbathing activity and the randombred control were studied. Fearfulness was measured as latencies to emerge from a box and to recover from induced tonic immobility (TI), and the influence of social disturbance by repeated placement in male cages during the breeding season, and the effect of repeated frightening by exposure to unfamiliar objects on egg quality traits was examined. Eggs (a total of 790) were collected over a 5-day period, weighed, and examined; body weight at 12 wk was recorded for all birds.Low line females had longer latencies to emerge than high line birds. It is suggested that selection for dustbathing activity had resulted in correlated changes in the susceptibility to fear. These genetic differences in fearfulness, however, may be only detectable at lower levels of induced fear.The social disturbance and frightening treatments did not affect egg production or the incidence of shell-less eggs. Repeated disturbances caused a significantly lower degree of egg shell calcium coating on the posttreatment day, suggesting that eggs were laid prematurely. As only 12.8% of all eggs examined were classified as uncoated, it is concluded that coatings are part of the normal egg shell pigmentation in the quail lines studied. There was no apparent correlation between emergence test and TI. The association between fear-related responses and production traits was of low magnitude.

Aflatoxin Effects in White Leghorn Chickens Selected for Response to Sheep Erythrocyte Antigen: 1. Body Weight, Feed Conversion, and Temperature Responses

Chickens from lines selectively bred for high and low antibody response to sheep red blood cell antigen and reciprocal crosses between them were fed diets containing 0, 1, 2, 3, and 6 μg of total aflatoxin/g diet from 2 to 42 days of age. Low-line birds, although larger, did not differ from the high-line birds in feed consumption, feed conversion, surface, or cloacal temperatures. Differences between crosses and parental lines varied according to the particular trait. Responses to dietary aflatoxin were similar regardless of population. Aflatoxin depressed body weight, feed consumption, and feed conversion at 14 days and subsequent ages with the effect on body weight and feed consumption occurring at lower levels than that noted for feed conversion. Although aflatoxin did not alter cloacal temperatures, there were progressive decreases in surface temperatures at 2μg/g and higher.

Amino acid transport and intracellular Na + and K + content of chicken erythrocytes genetically selected for high and low leucine transport activity

1. 1. Amino acid transport and intracellular Na + and K + content have been studied in two lines of chickens, one high and the other low uptake, selected for their ability to transport leucine into erythrocytes. 2. 2. Low line birds were less effective in absorbing glycine into erythrocytes than were high line birds, the difference in transport being due to a difference in maximal flux ( V max), but not in apparent affinity for transport sites ( k t ). 3. 3. In contrast to glycine uptake, the greater ability of the high line to absorb lysine was found to be due to a difference in both V max and K t . 4. 4. High line erythrocytes were also observed to contain slightly more K + (about 5%) and about 20% less Na + than low line erythrocytes. 5. 5. These results are discussed in terms of the ion dependency of amino acid transport.

Activity of Certain Liver Enzymes in Fast- and Slow-Growing Lines of Chickens

The relationship between growth rate and the metabolic activity of certain liver enzymes was studied using two strains of White Plymouth Rock chickens which had been selected in divergent directions for eight-week body weight. The activities of hexokinase, glucokinase, phosphofructokinase, glucose-6-phosphate dehydrogenase, citrate synthase, glycogen synthetase, glutamate dehydrogenase and aspartate transaminase were measured at 4, 8 and 20 weeks of age.The mean percentage rate of growth of the birds selected for high eight-week body weight exceeded that of the birds selected for low eight-week body weight only during the early growth period. Thereafter, and until sexual maturity, the low-line birds grew at a faster rate, relative to body size. The mature body weight of the high-line birds exceeded that of the low-line birds by a factor of approximately 1.5.A close similarity was noted between the metabolic activity of certain liver enzymes and the growth rate (relative to body size) of the birds studied. At four and eight weeks of age, the faster-growing birds (whether high- or low-line) generally exhibited a greater capacity for glucose phosphorylation and glycolysis, but a poorer capacity for glycogen synthesis, than the slower-growing birds. At twenty weeks, growth rate and metabolic activity were similar in both strains.

Relationship of Heat Tolerance and Oxygen Consumption in Chickens

Chicks from lines genetically selected for high or low heat tolerance were compared to lines selected for high or low oxygen consumption. Oxygen consumption, survival time, respiration rate, lung capacity and body weight were determined.Selection for high oxygen consumption and high heat tolerance resulted in birds with similar characteristics. The high line birds for both heat tolerance and oxygen consumption had greater oxygen consumption, survival time and lung capacity but lower body weight.