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Biomedical subjects

J V Craig

Publications and source records attributed to J V Craig.

53 records · Page 3Linked to original sources
PubMed1975

Reproductive performance of three strains of chickens in colony-cage and floor-pen environments.

Genetic strains, ages, and housing environments were studied for their effects of egg production, gains in weight and fertility over an eight-week interval. Rate of egg production in small floor pens was clearly superior to that in high-density, commercial type colony cages. Fertility was influenced by all major variables and by interactions among some of them. One genetic stock was clearly superior to two others. Differences between strains were more clearly evident in the rigorous colony-cage environment than in floor pens. Fertility in colony cages was lower than in floor pens over the eight-week test, but the difference decreased with time. Young males had higher fertility than older ones.

Age Factors↗
PubMed1975

Changes in relative aggressiveness and social dominance associated with selection for early egg production in chickens.

We tested the hypothesis that artificial selection for early reproductive performance of chickens kept under competitive conditions increases aggressiveness and social dominance. Two populations subjected to long-term selection for number of eggs laid before 40 weeks of age and the unselected control population from which they derived were used. Results generally supported the hypothesis but indicated that increased aggressiveness associated with such selection may characterize the adolescent period only. For one of the selected strains, rank for aggressiveness and social dominance between adolescence and full maturity was reversed, relative to the control population. Associations between increased aggressiveness (and social dominance) and decreased age at sexual maturity are discussed, along with implications as to the role of social status and reproductive performance when different genetic strains compete within flocks.

Aggression↗