VTechWorks Repository :: Browsing by Author "Dunnington, E. Ann"

Browsing by Author "Dunnington, E. Ann"

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Bilateral Asymmetry in Chickens of Different Genetic backgrounds
Yang, Aiming (Virginia Tech, 1998-05-04)
The dissertation consists of a series of experiments conducted to study developmental stability of various genetic stocks at different stages in the life cycle. The primary measures of stability were type and degree of asymmetry of bilateral traits and heterosis. Higher relative asymmetry (RA), which was defined as (|L-R| / [(L+R)/2]) x 100, was observed in lines of White Leghorns selected 23 generations for high or low antibody response to sheep red blood cells than in their F1 crosses. The bilateral traits were 39-day shank length and length and weight of the first primary wing feather. Shank length was again measured on day 49 while body, heart, shank, and lung weights and ceca lengths were obtained on day 56. Heterosis was positive for organ sizes and negative for degree of RA. Shank length and diameter, weight and length of the first primary wing feather, and distance between the junction of maxilla and mandibles and auditory canal (face length) were used to classify bilateral types and measure RA in six genetic stocks. The stocks were the S23 generation of White Leghorn lines selected for high or low antibody response to SRBC, sublines where selection had been relaxed for eight generations, and reciprocal crosses of the selected lines. Differences were found among all stocks for the traits measured. Rankings among traits for RA in descending order were face length, shank diameter, feather weight, and shank and feather lengths. The RA of shank and feather lengths did not differ from each other. The mean RA of the five traits was higher for the two selected lines than the crosses between them. The RAs of the two lines where selection had been relaxed was similar to that of selected lines. In a line of White Rocks selected 39 generations for low eight-week body weight, bilateral traits measured were shank length and diameter, face length, and weight and length of the first primary wing feather of females at 240 days of age. The RAs of individuals that had not commenced egg production by 245 days of age were similar to those that had entered lay. In both cases, these RAs were higher than those of a subline in which selection had been relaxed for four generations. Broiler sire lines had higher RA than dam lines for lung weight at hatch. Heterosis of RAs suggested superior homeostasis in F1 crosses than in the sire lines. Based on populations studied, it may be concluded that RAs were trait specific with the RA of shank length being lower (0 < RA < 2%) than lung weight which was 10% or higher regardless of genetic background. The types of bilateral asymmetry exhibited although less consistent, still had consistency such that feather weight and ceca weight exhibited antisymmetry across different stocks. Length and width of shank and weight of lung, were generally of fluctuating asymmetry. Heart:lung ratios differed among genetic stocks. In White Leghorns, lungs from late embryonic development to 25 days after hatch were heavier in a line which had heavier juvenile body weight than in one with lower juvenile body weight. In commercial broilers, heart:lung ratios at hatch were lower and thus inferior in parental lines than in their F1 crosses.
Dietary Protein Moderates Acid-Base Responses to Repeated Sprints in Exercising Horses
Graham-Thiers, Patricia M. (Virginia Tech, 1998-11-30)
Restricting dietary protein may reduce endogenous acid load. Horses were fed diets with 10% supplemental corn oil in experiment one and either 0% or 10% supplemental corn oil in experiment two. Also, low protein (7.5% crude protein, LP) fortified with .5% lysine and .3% threonine or high protein (14.5% crude protein, HP) was fed. Horses underwent similar interval training and standard exercise tests. In experiment two, horses performed an SET prior to conditioning. The SET consisted of warm ups at the walk and trot followed by six repeated sprints and concluding with a 30 minute recovery at the walk. All sprints were at 10 m/s except the SET prior to conditioning in experiment two, which were at 7 m/s. Blood samples were taken every two weeks and as part of SETs. Samples were analyzed for pH, pCO₂, pO2, Na⁺, K⁺, Cl⁻, lactate, total protein (TP), albumin, creatinine and plasma urea-N (PUN). Bicarbonate, strong ion difference (SID) and total weak acids (Atot) were calculated. Plasma urea-N concentrations were higher in the HP group. Plasma creatinine was not different in experiment one but was higher in the LPHF group in experiment two. Also, the LPHF group had a low body condition score and the same weight therefore had a higher lean body mass. Plasma albumin was not different in either experiment and TP was not different in experiment one. Total protein was higher in the HF groups in experiment two. Protein moderated acid-base responses to SETs in both experiments. The LP group had higher pH and bicarbonate levels as well as a tendency for a higher SID in experiment one and in the SET prior to conditioning for experiment two. Lower lactate levels were observed in the LP group in experiment one. Following conditioning in experiment two, the LP group had higher pH and bicarbonate levels but only combined with HF. Restricting dietary protein can increase pH and bicarbonate levels and high fat has been shown to improve fatty acid oxidation and spare muscle glycogen. Therefore, restricting dietary protein especially in combination with high fat may be beneficial for the exercising horse.
The effects of dietary forage, social hierarchy, and stocking density on stress in lactating cows during relocation
Pence, Kristen Jean (Virginia Tech, 2005-06-16)
The objective of these studies was to determine the effects of forage fiber, social hierarchy, and stocking density on stress in lactating cows during relocation to new dairy facilities. In experiment one, 23 lactating cows were fed a basal ration, or the basal ration plus grass or alfalfa hay at 10% of DM offered from 3 wk pre-move to 9 wk post-move. In experiment two, 17 lactating cows were housed together before and after relocation and evaluated for dominance rank. In experiment three, 44 cows were housed together before relocation, then in pens of varying stocking density (0.67, 0.83, 1.0, or 1.17 cows per stall) post-move. In these studies, the effects of treatment on MY, lameness, behaviors, plasma cortisol, cow cleanliness, and DMI were monitored. In experiment one, cows fed grass or alfalfa hay diets had higher plasma cortisol concentrations on the day of relocation than cows fed TMR, but there were no differences in DMI or MY. Cows fed alfalfa hay or TMR had increased lameness scores following relocation; cows fed grass hay did not have increased lameness scores. In experiment two, there were no differences in plasma cortisol or lameness scores between dominant and subordinate cows. Subordinate cows had lower MY following relocation compared to dominant cows. In experiment three, cows housed at a stocking rate of 1.17 had higher plasma cortisol than cows housed at a stocking rate of 0.67. All cows had higher lameness scores following relocation, but cows housed at a stocking rate of 0.67 tended to have higher lameness scores than cows housed at stocking rates of 0.83, 1.0, and 1.17. In summary, some management practices may decrease the negative effects of stress on lactating cows during relocation.
Fecal Kinetics and Digestibilities of Hays and Supplements Estimated by Marker Methods in the Horse
Hargreaves, Belinda Jane (Virginia Tech, 1998-11-20)
A marker model of fecal kinetics using chromic oxide (Cr) or ytterbium chloride (Yb) is being developed for grazing horses. The model consists of removal of feces at a constant rate from a single compartment, the prefecal mass. It was tested in experiments on stall-fed horses in the context of digestion balance trials. Following the preliminary work of Holland et al., (1998), three improvements in experimental design were tested. First, the rate constants were determined from both the administration and post-administration curve of the one-compartment model. Second, markers were administered three times a day to reduce diurnal variation in fecal marker concentration. Third, yttrium (Y) and Yb were tested were tested as internal markers, for the estimation of digestibility of hay and supplements, respectively. Eight horses were fed Diet 1 (orchardgrass/alfalfa mixed, OG) or Diet 2 (tall fescue/alfalfa mixed, TF) in Exp.1, and Diet 3 (OG plus fat-and-fiber supplement, OGFF) or Diet 4 (OG plus sugar-and-starch supplement, OGSS) in Exp.2. Balance-marker experiments were conducted for 17 and 20 d, with 7 and 10 d of dietary accommodation in Exp.1 and 2, respectively. Chromic oxide and Yb were administered orally and fecal samples were collected every 8 h for 8 d. Dry matter, Cr, Yb and Y were measured in feeds and feces. In balance experiments, estimates of DMD (D_E) using Y, were determined precisely (SE 1 to 3 %) for hay and hay and supplement diets. Linear relationships, correlations and calibration curves were determined, validating Y as a marker. Mean daily fecal Cr data (C_t) at time t (days) including a delay (d) were fitted to a single exponential, with one rate constant (k), rising to an asymptote (C_a): C_t = C_a - C_a·e^-k(t-d) Diets 1 and 2 had two sets of C_tdata, total collection (a) and fecal grab data (b), and each set was used in model development. Diets 3 and 4 had two sets of C_t data (both using fecal grab data), Cr marker dilution (3Cr and 4Cr) and Yb marker dilution (3Yb and 4Yb). For pooled data, delays of 3 to 6 h (Diets 1a, 1b, 2a and 2b) and delays of 5 to 7 h (Diets 3Cr, 4Cr, 3Yb and 4Yb) gave best fits (highest estimates of R²). The delays introduced to the Cr model for both 3Cr and 4Cr diets did not correspond to the preliminary study (Holland et al., 1998), where a 2 h delay gave the best fit in the model for horses fed hay and supplement. The present estimates may more realistically relate to mouth-to-cecum transport times, because the marker was administered three times a day instead of once, and the initial part of the tracer curve was more precisely defined. The results showed that fecal Cr kinetics could be calibrated precisely (SE 1 to 3 %) to predict fecal DM output of horses fed Diets 1b, 2b, 3a but not 4a. Similarly, fecal Yb kinetics could be calibrated to predict fecal DM output of horses fed Diet 3b but not 4b. The rate constants yielded turnover times (TT) that were longer with hay and supplement diets, than with hay alone, and which contrast with previous findings in the horse. However, the longer TT were similar to slower rates of marker excretion in sheep fed concentrates instead of all-roughage diets, suggesting that the lower fiber content retarded the rate of propulsion of digesta through the digestive tract. For two of the eight models of fecal kinetics, the rate constants of the post-administration curve were not well determined by the data, and rate constants from the administration curve were used. In future experiments, more frequent fecal sample collection during the post-administration period may improve rate constant determination. Improvements in diurnal variation of fecal marker concentration were obtained by dosing three times a day. But discrepancies between Cr and Yb concentration means of diurnal samples and combined samples showed incomplete mixing, the major source of tracer error. Therefore more frequent marker administration and fecal samples should be tested in future experiments to achieve more thorough mixing in the prefecal mass for modeling fecal kinetics, and in the small intestine for estimating digestibility.
Gene action involved with reproduction and growth of brain and muscle in weight-selected lines of chickens
Anthony, Nicholas B. (Virginia Polytechnic Institute and State University, 1988)
Genetic Variation influencing reproduction and growth of White Rock chickens was studied. The populations used were lines high (HH) and low (LL) selected for 56-day body weight, reciprocal F₁ crosses (HL and LH), F₂ crosses of the F₁ and dwarf populations (HD and LD) originating from lines HH and LL. Inheritance of egg production and egg composition was examined (Experiment 1). Although reciprocal effects were generally unimportant, nonadditive genetic variation was evident for reproductive traits and egg component measures of shell and yolk. Comparisons in Experiment 2 involved dwarf and normal chickens from lines HH and LL. Yolk weight increased while the ratio of albumen to yolk decreased with age. Line and genotype differences were evident for egg shell and yolk traits while line by genotype interactions showed that genetic background influenced expression of dw. Embryo growth of dwarfs was similar to that of nondwarfs at all ages (Experiment 3). Reduced egg size of dwarf pullets did not reduce embryonic weights. Embryo length and weight and yolk sac weight were greater for line HH than LL. In Experiment 4, allometric growth and cellular content of brains were measured in normal and dwarf chickens from lines HH and LL and reciprocal F₁ crosses from hatch to maturity. Allometric slopes were similar for lines HH and LL with significant heterosis. Within an age, DNA, RNA and protein content (mg/g) were similar for all populations. Brain weight differences were due to equal filling of a greater number cells for line HH than LL. Final brain size was influenced more by embryonic hyperplasia than postembryonic hypertrophy. The final experiment measured growth and cellular content of pectoralis and gastrocnemius muscles in populations HH, LL and F₁ from hatch to day 273. HH chicks had a smaller DNA unit size and a greater unit number than LL chicks at hatch. During rapid muscle growth, cell size was larger for HH than LL chickens. Pectoralis muscle grew at a faster rate than gastrocnemius muscle. Also cellular filling as measured by the DNA unit size was higher for pectoralis than gastrocnemius muscle through day 4. By day 10 the pattern reversed with values greater for gastrocnemius than pectoralis muscle.
Genetics, humoral immunoresponsiveness, and disease resistance in chickens
Boa-Amponsem, Kwame Jr. (Virginia Tech, 1998-06-11)
Lines of White Leghorn chickens selected > 20 generations for (HA) and against (LA) antibody response to SRBC injected i.v. from 41 to 51 days of age, are now known to have diverged in primary antibody response to SRBC. Experiments described in this dissertation were designed to further evaluate the immune competence of these lines as influenced by age, diet, and a disease agent. A crossing experiment was also conducted to further describe the mode of inheritance of such competence. Humoral immunocompetence was evaluated by primary, memory, and maternal antibody responses to SRBC. Primary antibody response, measured 5, 10, and 20 days after inoculation with SRBC was greater in HA than LA chicks inoculated at 14, 21, and 28 days of age. In chicks injected at 7 days of age, a higher frequency of responders was observed for HA than LA chicks suggesting an earlier onset of immunocompetence in the high than low antibody line. Immunological memory antibody responses (secondary and tertiary) was studied in parallel experiments on two groups of chicks hatched at a 14-day interval. Chicks in both hatches were from the same matings of parental Lines HA and LA. Memory responses were evident in chicks at 14 days of age. Antibody responses to a second and third inoculation with SRBC were similar for both lines suggesting that genetic factors that influence primary and memory responses are not the same. The responses of LA chicks to repeat inoculations with SRBC were anamnestic whereas those of HA chicks initially inoculated at 28 days of age were not anamnestic. This study did not establish any major influence of nutrient density on either primary or memory immune responses even though the higher nutrient density diet improved growth performance. Assays in chicks indicated that maternal antibodies were transferred earlier into eggs laid by HA hens than in those of LA hens ( 7 to 9 days vs 10 to 12 days after inoculation) regardless of dosage administered. Response patterns whether assessed in terms of frequency of detection or magnitude of response showed divergence between the lines. Chicks of parental, reciprocal F , F , and backcrosses of 1 2 mating combinations of Lines HA and LA were injected with SRBC at 36 days of age. Contrasts between parental lines for antibody titers measured 5 and 12 days later showed higher antibody titers in HA than LA chicks. Sex-linked effects were evident because reciprocal contrasts for F crosses, individual heterosis, and 1 maternal heterosis were sex dependent. Response to marble spleen disease virus ( MSDV) measured 6 days after inoculation of chicks from parental, reciprocal F1, F2, and backcross matings of the lines, indicated that the mode of inheritance of spleen weight differed after infection. In the infected chicks, parental contrasts for absolute and relative spleen weights showed greater resistance to MSDV in LA than HA chicks. No other genetic effect was consistently important after infection.
Genetics, immunoresponsiveness, and disease resistance in chickens
Martin, Alison (Virginia Polytechnic Institute and State University, 1989)
The experiments reported in this dissertation explored the effects of selection for antibody response on other immunological measures and on production traits. The role of thyroid hormones in antibody response was also studied. Selection for high (HA) and low (LA) antibody response to sheep erythrocytes altered subclasses of antibodies in different ways. In line LA antibody response was primarily mercaptoethanol-susceptible (IgM), while the line HA response was primarily mercaptoethanol-resistant antibody (IgG). Sublines of HA and LA were developed with all possible combinations of major histocompatibility complex haplotypes B¹³ and B²¹. An experiment was conducted to test Marek’s disease resistance of these haplotypes in line LA. Mortality from a natural exposure was high for all three groups, and there was no difference among haplotypes. Correlated responses of growth and reproductive traits in lines HA and LA were due to genetic correlations with antibody response. These genetic correlations were generally negative and are suggestive of differential allocation of resources. Phenotypic correlations were generally very small. Changes in allelic frequencies at alloantigen systems were also observed in response to selection. Experiments designed to study the role of thyroid hormones on antibody responses showed no direct relationship. Chickens from lines HA and LA fed thiouracil exhibited hypothyroidism but did not differ from controls in antibody response. Differences in thyroid hormone concentrations between lines of dwarf and non-dwarf White Rocks selected for high and low juvenile body weight bore no relationship to differences in antibody responses.
Genotype by feeding regimen interactions in growth selected chickens
O'Sullivan, Neil P. (Virginia Tech, 1991)
Growth, reproduction, and immunocompetence were measured in lines of chickens maintained under different feeding regimens. Populations included a commercial broiler breeder parent line segregating at a sex-linked feathering locus (K, k⁺) and 4 experimental lines of which 2 had undergone 32 generations of divergent selection for 56-day body weight and 2 were their sublines in which selection has been relaxed for 5 generations. Mild feed restriction of the broiler line from 7 to 27 days of age reduced carcass fat and heterophil:lymphocyte ratios, and increased immune organ weight, antibody titer to sheep red blood cell (SRBC) antigen and livability than ad libitum fed birds. Body weights were similar by 56 days of age, and there was sexual dimorphism for rate of accelerated growth. Long term obesity, but not short term weight gain, was detrimental to reproductive performance, feed utilization, response to SRBC, and resistance to Escherichia coli, lymphoid leukosis and livability of broiler breeder dams. Poorer quality crumbles also reduced reproductive performance. An association between an endogenous viral gene encoding for avian leukosis virus (ev21) and the sex-linked K allele of the Z chromosome was confirmed in the broiler genome. Reproductive performance and feed utilization were inferior for K/- than k⁺/-, notwithstanding a pleiotropic effect of K associated with heavier egg and embryo weights. Variation in residual feed consumption was influenced by feathering genotypes and management practices. Increases in hatchability for the initial period after onset of lay were due to a reduction in early embryo deaths. Egg and 18-day embryo weights, ratios of embryo:egg and yolk:albumen, and proficiency of lipid transfer also increased but the latter was not associated with higher hatchability. Selection for 56-day body weight resulted in a divergence between lines at 21 days of age of 404% for body weight, 279% for feed intake and 138% for feed conversion ratio. Genotype by feeding regimen interactions were observed for growth and appetite development. Early posthatch growth of small intestine was highly correlated with subsequent growth of demand organs. Selection had also resulted in correlated changes in cell size of muscles, but not liver or small intestine which increased in size due to cell hyperplasia. Correlated changes in feed intake mediated synthesis and secretion of digestive enzymes.
Genotype by nutrition interactions for immunoresponsiveness and disease resistance in chickens
Praharaj, Naba Krushna (Virginia Tech, 1996)
This dissertation involved a series of in vivo experiments to measure growth, immunoresponsiveness, and disease resistance in several genetic stocks maintained under different nutritional regimens. Genetic stocks included (1) a commercial layer line, (2) commercial broiler lines, (3) a White Rock line selected for high juvenile body weight, (4) a White Leghorn line selected for low antibody response to sheep erythrocytes, (5) a fast growing White Rock dwarf line, (6) a slow growing White Rock dwarf line, (7) a cross of 3 X 4, and (8) reciprocal crosses of 5 X 6. The nutritional regimens were either alternate-day (AD) and ad libitum (AL) feeding or high (E) and low (A) nutrient density. As expected, within a feeding regimen males were heavier than females and within a sex, AL chicks were heavier than AD chicks. Also, chicks fed Diet E were heavier than those fed Diet A. For traits associated with body weight there were significant feeding regimen by sire family interactions which was due to differences among sires in the magnitude of AD:AL relationship. Heterosis for body weight was consistently higher in males than females regardless of feeding regimens and higher for AD than AL chicks suggesting that the degree of heterosis was age and environment dependent. Immunocompetence as measured by production of antibody against sheep erythrocytes (SRBC) was higher for chicks fed AD than AL. In one experiment there was a significant diet by stock interaction for SRBC antibody titers. The interaction was because the commercial broilers fed Diet A had higher SRBC antibody titers than those fed Diet E, while the pattern for diets reversed in commercial layers. This suggested that the allocation of nutritional resources towards growth and immune response was not independent of the previous selection history of the population. Also, influence of genetic factors on antibody production was evident as there were differences among sire families in antibody titers to SRBC. In addition, heterotic effects for SRBC antibody were evident as titers were higher for the 3 X 4 crosses than lines 3 and 4 and titers were higher for the 5 X 6 crosses than lines 5 and 6. In faster growing genetic stocks responses to E. coli inoculation as measured by mortality and severity of cardiac and air sac lesions were greater for chicks fed AL than AD. For chicks fed AD lesion scores were lower for those without access to feed for the 24-h period immediately after challenge. When AD chicks were released to ad libitum feeding for several days and then inoculated, lesions were more severe than for AL and AD chicks. This result demonstrated that chicks from lines selected for rapid growth tended to allocate a greater proportion of resources to growth which reduced their ability to adjust rapidly to a disease challenge. Genetic factors influencing the response to E. coli inoculation were also evident as lesions were less severe for cross chicks than for their parental lines.
Glycemic Response in Thoroughbred Mares
Williams, Carey Ann (Virginia Tech, 2000-08-09)
The objective of this study is to determine if fat as an energy source, and fiber in a pasture supplement will be beneficial when compared to a concentrate high in sugar and starch. In the first experiment, 12 pregnant and lactating mares were used in three different glycemic response tests to determine the effect of feeds on pregnant mares. The mares were fed a pelleted concentrate (PC) three months before foaling; after foaling they were divided into two groups and fed a feed high in sugar and starch (SS), or a feed high in fat and fiber (FF). The second experiment, used the same 12 mares (R mares) and 10 barren mares (B mares) in three different tests to determine the effects of the feeds, season and reproductive stage. A series of blood samples was collected via a jugular catheter from 0 to 390 min after consuming a meal. Glucose and insulin baseline and peak values, increments and areas under curves (AUC) were compared by ANOVA. For the first experiment, responses to PC did not differ between the two groups. Peak plasma glucose and insulin concentrations were higher in SS group than in FF during both early and late lactation. Glucose and insulin AUCs were higher in SS than in FF during both early and late lactation. In the second experiment, peak glucose increments had differences for the main effects feed, pregnancy and season, and interactions feed by pregnancy and feed by season. The glucose AUC values showed similar differences for the main effects and the interaction feed by pregnancy. Peak insulin increments had a difference for feed and pregnancy, but not the interactions. Insulin AUCs also revealed a difference between feed and pregnancy, and also for season, and the interaction feed by pregnancy. These results indicate that metabolic fluctuations are moderated by the replacement of sugar and starch with fat and fiber. This replacement may reduce the risk of certain digestive and metabolic disorders.
Line characterization and evaluation of genetic parameters of serum cholesterol levels, activity, feed intake, growth and body moisture in selected and unselected lines of laboratory mice
Dunnington, E. Ann (Virginia Tech, 1975-05-05)
Feed intake, growth, efficiency, and serum cholesterol levels (SCL) were recorded for 102 male mice, and voluntary physical activity and SCL were recorded for 113 male mice from lines selected for 22 generations for maximum 21- to 42-day gain (H), minimum 21- to 42-day gain (L), and a random-bred control (C). Heritability (h²), phenotypic and genetic correlations of SCL, activity, growth, and body moisture content were estimated for 466 sire-son pairs of mice from an unselected line. Blood samples were obtained by sinus orbital bleeding at 35 and 70 days of age in the line characterization study and at 62 days of age in the genetic parameters study and were analyzed for SCL by gas chromatography. Voluntary physical activity was recorded as revolutions of an exercise wheel every sixth day from 21 to 70 days of age in the line characterization study and at 28, 49, and 70 days of age in the genetic parameters study. Feed intake (of an 11% fat, 9% fat, and 4-1/2% fat diet) was recorded for several days each week and extrapolated to obtain weekly intake data. A least-squares analysis of variance from a model including lines, diets, and line x diet interactions indicated highly significant differences in the main effects but few significant interactions. Total SCL, growth, and efficiency were higher, and intake lower in mice on the higher fat diet. SCL (mg/100 ml) at 10 weeks of age was 220.3, 178.1, and 180.4 for animals fed an 11% fat diet and 143.3, 124.1, and 132.2 for animals fed a 4.5% fat diet. Activity scores (revolutions) for the H, C, and L lines were 79234, 107987, and 124409. Activity generally increased in all lines from 21 to 56 days of age, then declined slightly. Heritability estimates of SCL and body moisture 2 content were .31 ± .07 and .20 ± .11, and h² estimates for activity ranged from .27 ± .14 to .54 ± .12. Negative genetic correlations occurred between body moisture content and SCL and between body moisture content and weight gains.
Pasture Intake, Digestibility and Fecal Kinetics in Grazing Horses
Holland, Janice Lee (Virginia Tech, 1998-11-18)
Pasture intake of grazing livestock needs to be estimated to allow determination of energy and nutrient intakes. It is commonly estimated by difference, subtracting intakes of other feeds from estimated needs for dry matter or energy. However, these estimates are often erroneous, because they do not take individual animal variation for growth, reproductive status or activity level into account. One method that has had success in grazing ruminants has been the use of markers, or tracers, to estimate fecal output and nutrient digestibility. External markers are dosed to the animal and can be used to determine fecal output. Internal markers are an inherent part of the diet in question and can be used to determine dry matter and nutrient digestibilities. These estimates can then be used to give estimates of intake. These studies were conducted to evaluate the effectiveness of traditional marker methods in determining fecal output, digestibility, and thus intake in grazing horses. The first trial was conducted on 8 mature mares and geldings, housed in stalls, to determine if a common external marker, Cr, could be used to determine fecal output. Horses were dosed once daily with a molasses, Cr, and hay mixture for 12 d. Feces were collected throughout the day into individual tubs so that total fecal output (TC) could be measured. Daily fecal Cr excretion values (Ct, mg/kg DM) were fit to a monoexponential equation with one rate constant (k), rising to an asymptote (Ca): Ct = Ca - Ca.e-kt. Superior fits were found when a delay (d) was incorporated into the equation, estimating the time required for Cr to enter the prefecal pool: Ct = Ca - Ca.e-k(t-d). Estimates of fecal output (FO) were calculated using the equation: FO = Cr dose-d / Ca and provided good estimates when compared to TC values. Subsequent trials evaluated to use of internal markers and more frequent dosing of Cr to improve estimates of intake. Eight mature geldings were housed in stalls and were fed 2 hays in a replicated Latin Square design. The monoexponential equation with the delay continued to fit the data well. Thrice daily dosing of Cr improved the predictions of FO, when dosing was every 8 h. The internal marker, yttrium (Y) consistently overestimated digestibility (D). The internal markers, n-alkanes, gave a better estimate of digestibility. When the digestibility estimates were combined with the FO estimates to estimate dry matter intake (DMI, kg/d): DMI = [FO / (1-D)]*100, the combination including n-alkanes gave better estimates. Further studies found that dosing Cr for 12 d did not improve the fit of the monoexponential equation compared to dosing for only 8 d. Marker methods that had been developed in stalls were applied to grazing horses, and results continued to be promising.
Resource allocation in chickens: genetic and nongenetic influences on development, growth and reproduction
Katanbaf, Manouchehr N. (Virginia Polytechnic Institute and State University, 1988)
Genetic and nongenetic influences on organ development in chickens were studied. Populations included lines divergently selected for juvenile body weight, reciprocal F₁ crosses between them, and a commercial broiler-breeder parent line segregating for early and late feathering alleles. Nongenetic influences included restricted and ad libitum (AL) feeding regimes. Positive correlated responses to selection for body weight included proportionally larger breast, legs, fat depots and small intestine. Negative responses included fecundity, feather and gizzard weights. The degree of non-additive genetic variation differed among traits but reciprocal effects were negligible. Weights and lengths of organs at specific ages did not necessarily reflect the situation at common body weights suggesting differences in resource allocations among populations. In commercial meat-type chickens, AL feed consumption was near gut capacity and increased rapidly to approximately 140 days of age. Concomitantly, body weights increased to approximately 130 days and then plateaued. Influences of early and late feathering alleles were minor except for weights of feathers. Alternate-day feeding prior to sexual maturity reduced weights of fat depots, feathers and muscles and increased size of the gastrointestinal tract. Effects of every day, skip-one-day and skip-two-day restrictions of feed were generally similar. Chickens adapted quickly to restricted feeding but, when released to AL feeding allocated resources into growth. This reallocation reduced their resistance to an Escherichia colichallenge. Prior to sexual maturity, relative weights and lengths of the gastrointestinal tract decreased with age and relative sizes of fat depots and muscle increased with age. Thereafter relationships of most organs to body weight remained stable. Restricted chickens adapted to fasts by maintaining exogenous energy stores (gastrointestinal tract contents) for longer periods. Unlike those fed AL, they did not became obese and their livability and fecundity were greatly enhanced.
The Role of Nutrition and Administration of Estrogen in Holstein Calf Growth, Development, and Adenogenesis
MacGhee, Meghan Elizabeth (Virginia Tech, 2015-05-07)
Raising replacement heifers consumes a large portion of dairy and beef producers' income. An ultimate goal of producers is to decrease inputs and maximize outputs to produce fertile replacement heifers. Manipulating early postnatal growth and development through diet enables this practice to be successful. Puberty is greatly influenced by body weight (BW). Once heifers reach puberty, they become fertile and can achieve their reproductive potential. Growth can easily be influenced during the preweaning phase of development. Offering calves a higher plane of nutrition through milk diets prior to weaning hastens development and can lead to an earlier age at the onset of puberty. The objective of the first study was to understand how plane of nutrition influences BW, bone mineralization, and organ growth during the preweaning phase of development in Holstein calves. Calves offered a higher plane of nutrition experienced greater BW gains, increased bone mineralization, and accelerated organ growth. The second study evaluated plane of nutrition on reproductive development, specifically adenogenesis in Holstein heifer calves. Adenogenesis, or the development of uterine glands, is initiated in the early postnatal period. It involves rapid endometrial epithelial cell proliferation, germinal bud formation, invasion into the stroma, and extensive branching and coiling. Little is known about how nutrition impacts adenogenesis in ungulates, however, this study provided validation that it does drive gland formation. Additionally, this study assessed the influence of exogenous estradiol on reproductive development and adenogenesis when given after the completion of adenogenesis. We can confirm that exogenous estradiol given after the completion of adenogenesis does not alter the outcomes of gland formation. The beneficial effects of feeding a higher plane of nutrition to calves prior to weaning on bone mineral density, organ growth, and adenogenesis may provide new possibilities for understanding the impacts of early nutrition on calf immune responses and productive lifespan of the cow. Collectively, these studies emphasize the importance of nutrition during preweaning growth and development of Holstein calves.
Selection for serum cholesterol, voluntary physical activity, 56- day body weight and feed intake in albino mice
Dunnington, E. Ann (Virginia Tech, 1978-01-15)
A short-term selection experiment was conducted with ICR albino mice produced by the reciprocal crossing of two lines of unselected animals which had been random-bred for 28 generations. Lines were developed by selecting for maximum and minimum serum cholesterol (SC) (lines CH and CL), voluntary physical activity (lines AH and AL), 56-day body weight (lines WH and WL) and feed intake (lines IH and IL). An unselected, random-bred control line was maintained with each pair of divergent selected lines (CC, AC, NC and IC, respectively). In the lines selected for SC, physical activity and 56-day body weight, selection was based on individual performance. Twenty-five paired matings plus five extra paired matings were used to perpetuate the lines each generation for five generations. The feed intake lines were perpetuated by within-sex, full-sib family selection with 30 paired matings per generation for five generations.
Stress response and habituation as influenced by nutritional and thermal factors in dwarf and normal chickens
Idrus, Zulkifli (Virginia Tech, 1994-09-05)
Experiments were conducted to explore physiological, pathological, and immunological aspects of stress in chickens. Mechanisms of habituation and their association with adrenal steroids were also studied. Degree of stress experienced during perinatal and neonatal stages was evaluated. In both stages, heterophilia and lymphopenia were noted and post-hatching heterophil to lymphocyte (H/L) ratios declined in a quadratic manner with age. Feed restriction elicited a similar stress response, as indicated by H/L ratios in dwarfs and normals with the effect of adapting to fasting having dissipated between 12 to 16 days. Resistance to Eimeria tenella infection was greater in normals than dwarfs, and for fasted than ad libitum fed chicks. Neither genotype nor feeding regimen had an effect on antibody response to SRBC. Frustration induced by thwarting of feeding resulted in a dramatic elevation in HIL ratios and conspicuous behavioral responses, suggesting responses to fasting may be physiologically and psychologically modulated. Provision of sand during feed withdrawal attenuated physiological responses, possibly via alteration of psychogenic components. An experiment was designed to evaluate the impact of mild feed restriction at several ages on heat tolerance. Normal chicks feed-deprived during the neonatal stage had lower H/L ratios, improved resistance to marble spleen disease and growth during heat treatment than those fed ad libitum or fasted at older ages. A companion experiment examined habituation and concomitantly the role of glucocorticoids in stress response. Neonatal fasting-induced stress responses without concurrent increases in adrenal steroidogenesis did not enhance ability of normal chicks to withstand high ambient temperatures. The hypothesis regarding modulatory roles of corticosteroids in neonatally-elicited adaptation was affirmed in a subsequent study. Feed withdrawal for 8 or 24 h at 36 days of age did not induce either H/L or plasma corticosterone response of chicks stressed early in life. In contrast, neither criterion provided evidence for adaptation to feed deprivation by neonates treated with an adrenal steroidogenesis blocker during the fast. corticosterone mediated inhibitory feedback regulation of the hypothalamic - pituitary - adrenal axis which down-regulates ACTH response was also evident.
Utilization of Yolk as a Feed Source in Newly Hatched Chicks With and Without Vitellin
Baker, Kori S. (Virginia Tech, 2000-05-25)
Increasing feed efficiency and early body weight gain has always been a top priority in the poultry industry. This experiment was designed to study the effects of feed sources differing in energy and protein levels as well as yolk removal on behavior, feed efficiency, energy intake, body weight and GIT growth in newly hatched chicks. Chicks in Experiment 1, Trial 1, were White Plymouth Rock chicks from the 40th generation of a line selected for high body weight, fed either freeze dried unincubated yolk (Diet Y) or mash (Diet M-A) from day 0 to day 5, after which all chicks were fed Diet M-A. Chicks in Experiment 1, Trial 2 were males from a commercial layer stock fed either a choice of residual yolk (yolk harvested from newly hatched chicks) and unincubated yolk (Diet Y), or mash (Diet M-A) alone from day 0 to day 6, after which all chicks were fed Diet M-A. In these experiments where chicks were offered yolk as a feed source for a period of time, body weight gain was significantly reduced and mortality increased. There was evidence that Diet Y chicks, consuming a high-lipid feed, experienced decreased appetite. There were no differences in body weight between the two diet groups in Trial 1 or Trial 2 on day 0, but during the days in which yolk was fed, Diet M-A chicks maintained a weight advantage over Diet Y chicks. Chicks used in Experiment 2 were males from a commercial layer stock. Yolk sacs were surgically removed (Trt YR) from half of the chicks while the other half remained yolk-intact (Trt YI). From day 0 to day 6, all chicks were offered a choice of residual yolk (Diet Y) or mash (Diet M-A) and beginning on day 6, all chicks were fed Diet M-A. Throughout the experiment, the Trt YI chicks maintained their body weight advantage over the Trt YR chicks, but by day 13, the Trt YR chicks gained proportionately more body weight. Because of wastage, feed efficiency and energy intake values were not reported. The only difference in GIT data was the amount of chyme; its value was higher in the Trt YI chicks than in Trt YR chicks. Behavior results showed that Trt YI chicks stood more while Trt YR chicks rested more throughout the experiment. Chicks used in Experiment 3 were males from a commercial layer stock. This experiment consisted of 4 groups: Trt YI chicks fed Diet M-E (mash feed high in energy and protein), Trt YI chicks fed Diet M-A (mash feed lower in energy and protein), Trt YR chicks fed Diet M-E and Trt YR chicks fed Diet M-A. Serial dissections on days 6, 13 and 20 allowed for better understanding of effects of diet and/or treatment on the growth of selected parts of the GIT. On days 13 and 20, there were no differences due to diet or treatment for GIT data except for the consistent difference due to diet for relative weight of the gizzard, whose value was higher in the Diet M-A chicks. Similar to results from Experiment 2, on day 13, Trt YR chicks fed Diet M-A gained more body weight than the Trt YI chicks fed the same diet. Also consistent with Experiment 2, of chicks fed Diet M-A, the Trt YI chicks stood more than the Trt YR chicks. Due to unusually large feed consumption values, feed efficiency and energy intake data were not reported.

Browsing by Author "Dunnington, E. Ann"

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