Biomedical subjects

R Pit

Publications and source records attributed to R Pit.

6 recordsLinked to original sources

PubMed2001

Evaluation of between-line variation for within-line selection against ascites in broilers.

Within-line opportunities for selection against ascites were studied in a data set comprising a 10-line comparison. The study attempted to reveal whether contrasts between lines provide reliable candidate traits for within-line selection. Mortality was chosen as the reference trait. As no pedigree information was available, a trait was required that related mortality to the nonmortality data. By principal component analysis, such a trait (ASC_INDIC = ascites indicator) was developed from pathology data. The composite trait ASC_INDIC ranked lines well for their mortality figures (r = 0.96), from which it was concluded that ASC_INDIC represents an underlying continuous ascites trait. Between lines, blood gas traits seemed to be the most promising traits. Within lines, performance traits appeared to be highly correlated to ascites. Comparison of within-line variation to between-line contrasts revealed considerable differences. The high correlation of the blood gas traits with mortality was not present within lines. However, although the magnitude was considerably reduced, the nature of the blood gas traits in their relationship to ascites was similar within and between lines. The study primarily demonstrates that contrasts between lines carry systematic but limited information for within-line coherence. Therefore, line contrasts must be interpreted with care when aiming to study genetic variation and coherence within lines.

Animal Husbandry↗

PubMed2001

Disease-induced variability of genetic correlations: ascites in broilers as a case study.

Breeding against a production disease is complicated by multiple relationships between productivity, disease, and environment. Ascites in broilers is such a disease. The combination of the reasonably well understood etiology (a physiological/pathological cascade due to inadequate oxygen supply) and the practical relevance makes ascites a relevant case for demonstrating and partly revealing these complex relationships. Chickens (n = 2,788) were tested in an ascites-challenging (cold) environment. Genetic analysis of mortality and pathology in combination with performance and physiological traits (especially blood gas traits) revealed ample opportunities for selection against ascites expression. The genetic correlation structure indicated that different mortality traits and pathology traits roughly represent one common characteristic. Direct selection against pathology is more effective than selection on the basis of growth or blood gas traits. The observed negative correlation (-0.26) between productivity and ascites was unexpected. From the etiology of ascites (inadequate supply of oxygen relative to the demand), a positive (unfavorable) correlation was expected. To demonstrate that the actual disease occurrence caused this apparent contradiction, the data from the undiseased subpopulation were reanalyzed. In the undiseased subpopulation, the genetic correlation between productivity and ascites was positive (0.29). This discrepancy was confirmed by comparing regression of ascites expression on actual performance with regression of ascites on independently assessed performance breeding values. The lability of the genetic correlation was explained from complex interactions between productivity, disease susceptibility, and actual occurrence of the disease. The revealed mechanism can be generalized to other production-related diseases and results in systematically lower genetic correlations between disease and productivity. It was inferred that genetic correlations between productivity and such diseases will always be prone to the demonstrated environmental sensitivity, which complicates index selection against production-related diseases.

Animals↗

PubMed2000

Direct experimental evidence of slip in hexadecane: solid interfaces

The boundary condition for the flow velocity of a Newtonian fluid near a solid wall has been probed experimentally with a novel setup using total internal reflection-fluorescence recovery after photobleaching leading to a resolution from the wall of the order of 80 nm. For hexadecane flowing on a hydrocarbon/lyophobic smooth surface, we give what we think to be the first direct experimental evidence of noticeable slip at the wall. We show that the surface roughness and the strength of the fluid-surface interactions both act on wall slip, in antagonist ways.

Journal Article↗

PubMed1988

Fat deposition in a broiler sire strain. 3. Heritability of and genetic correlations among body weight, abdominal fat, and feed conversion.

Body weight, abdominal fat, and feed conversion were measured in ad libitum-fed pedigreed chickens of four lines selected from a broiler sire strain. Lines were selected for four generations for a low amount of abdominal fat (AF), a favorable feed conversion (FC), a high body weight after restricted feeding (GR), and a high body weight after ad libitum feeding (GL). A total of 2,400 pedigreed chickens from three hatches were reared by line in groups on litter and 864 chickens were tested for individual feed conversion in individual cages. The h2 from the sire component for the four lines combined were for body weight, .27 (litter) and .22 (cages); for weight of abdominal fat, .54 (litter) and .40 (cages); for percentage abdominal fat, .53 (litter) and .45 (cages); and for feed conversion, .44 (cages). Analysis within line and sex indicated that, in the relatively fat GR and GL lines, sex-linked inheritance could be involved for abdominal fat. In the leaner AF and FC lines this was not the case. Genetic correlations (sire estimate) for the four lines combined were, between body weight and weight of abdominal fat, .58 (litter) and .55 (cages); between body weight and percentage abdominal fat, .36 (litter) and .47 (cages); between body weight and feed conversion, .16 (cages); between weight of abdominal and feed conversion, .43 (cages); and between percentage abdominal fat and feed conversion, .44 (cages). Genetic correlations did not differ significantly between sexes, but in the AF and FC lines, the genetic correlation between body weight and abdominal fat was higher (AF: .80, FC: .76) than in the GR (.14) and GL (.68) lines.

Abdomen↗

PubMed1988

Fat deposition in a broiler sire strain. 4. Performance of broiler progeny of four differently selected sire lines.

Cocks from four lines selected for a low amount of abdominal fat (AF), a favorable feed conversion ratio (FC), and high body weight after restricted (GR) or ad libitum (GL) feeding were mated to commercial broiler breeder hens. A total of 3,600 broiler progeny in three hatches from these matings was reared by line in litter pens. At 41 days of age GR and GL line progeny had significantly heavier body weights, poorer feed conversion ratio, and higher percentages of abdominal fat than AF and FC line progeny. At comparable body weights (AF, 1,893; FC 1,918; GR, 1,848; and GL, 1,897 g) feed conversion was most favorable for FC line progeny (1.72), AF and GL line progeny did not differ (1.77), and GR line progeny had the poorest feed conversion ratios (1.79). The AF line progeny had the lowest percentage abdominal fat (1.88%), followed by FC line progeny (2.20%), GL line progeny (2.91%), and GR line progeny (3.10%). As in the pure lines, selection for body weight after restricted feeding was not effective in obtaining leaner and more efficient chickens. When compared with differences between pure lines, results of the broiler progeny matings indicate that body weight, feed conversion, and percentage abdominal fat are inherited largely in an additive manner.

Abdomen↗

PubMed1981

Selection for sperm quality in White Plymouth rocks.

A selection for sperm quality was carried out in the White Plymouth Rock population of the Spelderholt institute. The percentage of morphologically abnormal spermatozoa was used as the most important selection criterion. The population was selected in two directions, viz. a line with a low incidence (Ll-line) of abnormal spermatozoa and a line with a high incidence (Hl-line). Cocks were examined and selected at the age of 26 weeks with the help of vital stained sperm smears. The selection response in the Ll-line appeared to be very evident; in the Hl-line the results were more variable. An indirect effect of selection on 8-week bodyweight could be established.

Animals↗