No abstract

Total agglutinin antibody titers, 2-mercapto ethanol (2-ME) sensitive and 2-ME resistant antibody titers were determined in 598 White Leghorn chicks after intramuscular injection with sheep red blood cells. Antibody titers were determined on day 0 and on days 3, 7, 10, 13 postinjection. Mean total tier (5.2, log2 value) was highest on day 7. Females showed a significantly higher response to injection with sheep red blood cells than males. Also, significant hatch effects were noted. Heritability estimates generally varied from 0 to .5 for all parameters. In the earlier stages of the immune response the sire estimate of heritability for total and 2-ME sensitive antibody titer was higher than the dam estimate. Additive genetic correlations between 2-ME sensitive (days 3 to 13) and resistant (days 7 to 13) antibody titers were negative, varying from -.30 to -.93. The response to selection for total antibody titer is, therefore, not easily predicted.

Variability in body composition was examined weekly from 3 to 10 weeks of age in chickens from a broiler sire strain. Genetic aspects of body weight, quantity of abdominal fat, and feed conversion were examined in pedigree birds of the same strain at 6 weeks of age.Variability in abdominal fat relative to body weight (RAF), total percentage of carcass fat, and body weight (BW) was not influenced by sex or age. The phenotypic correlation (rp) between RAF and BW was generally positive, but low (between .20 and .68); that between RAF and total percentage of carcass fat was invariably positive and higher.The heritability estimated from sib analyses for body weight after ad libitum feeding was 0 (h 2 s ; res ) and 1 (h 2 d arns ), for RAF .41 (h 2^^) and 1 (h^ams). for feed conversion .39 (h 2 s i res ) and .53 (h 2 d ams ), and for body weight after restricted feeding .31 (h 2 s { res ) and .57 (h 2

The theory that net muscle growth is, at least partly, regulated by catabolic factors has been tested in order to set up an animal model to study meat aging and post-mortem tenderization. Male and female chickens of a layer strain (White Leghorn), a commercial broiler strain (Ross), and two experimental broiler lines (designated GL and FC) were used to estimate differences in proteolytic enzyme activities in the breast muscles. The GL and the FC lines were selected for high body weight gain and high feed efficiency, respectively. At 6 wk of age the birds were slaughtered and the activities of endogenous proteinases and their specific inhibitors in breast muscles measured. The Leghorns showed significant differences in all traits compared with the three broiler genotypes. Within the broiler types, FC birds tended in the direction of the Leghorns and GL birds in the opposite direction. Ross birds were intermediate between FC and GL birds. All types and sexes differed significantly in slaughtering weight. Feed conversion ratio and protein conversion ratio were highest for Leghorns. The FC birds showed the lowest feed conversion. Ross and GL birds showed intermediate values. The Leghorns showed higher calpain activities and lower calpastatin activity than the three broiler genotypes. The FC broilers showed intermediate calpain and calpastatin activities but higher cathepsin H and total cystatin values. The GL broilers showed lower cathepsin B, D, and H activities. In all cases the Ross broilers showed intermediate values. From these figures it is concluded that the strains of birds used in this study can be used as a natural source of variability to study the mechanisms involved in post-mortem proteolytic degradation and thus in the study of muscle tenderization and meat aging. It is also concluded that it could be very interesting to study the behavior of the different proteolytic systems more carefully in relation to muscular growth characteristics and compare them to anabolic factors involved in muscle growth.

1. The concentrations of growth hormone (GH), insulin-like growth factor I (IGF-I), thyroxine (T4), triiodothyronine (T3), reverse-triiodothyronine (rT3), triglycerides (Tri), free fatty acids (FFA) and glucose (Glu) were determined at 2, 4 and 6 weeks of age in blood plasma of male and female chickens of broiler lines selected for body weight (GL) or food conversion (FC). 2. Plasma concentrations measured in the same animal over a 24 h or a 2 week interval were not significantly correlated with each other. For different traits measured in the same plasma sample only the correlation between T4 and rT3 differed significantly from zero. 3. All traits were dependent on age. Line and sex effects were significant (P less than 0.05) for GH, T4, Tri, FFA and Glu. Additionally, line significantly influenced the plasma T3/T4 ratio and sex influenced plasma rT3. Interactions between line, sex and/or age were seldom significant. 4. Within line and sex, GH (at 6 weeks of age) and T3 (at 4 weeks of age) were negatively, and IGF-I and Tri (both at 6 weeks of age) positively correlated with the amount of abdominal fat at 6 weeks of age. No significant correlation between body weight at 2, 4 or 6 weeks of age and any of the plasma traits was found.