EFFECTS OF SELECTION FOR 365-DAY WEIGHT ON MATERNAL PERFORMANCE OF BEEF COWS

CHANCHARAT LUESAKUL REODECHA, Purdue University

Abstract

Data were derived over a 20-year period on 655 cows. The selection criterion in the herd was increased 365-day weight. Data were grouped into three categories; cow's weight traits from birth to maturity, cow reproductive and maternal performance and cow lifetime productivity traits expressed as number of years a cow was in the herd, number of pregnancies and numbers of calves born and weaned. Genetic, phenotypic and environmental trends were estimated for all cow traits. Data on cows from sires and dams repeated in consecutive years were used to estimate environmental changes. Cow yearling weight increased 5.82 kg/yr (P < .10). Date of the first calving was delayed by 9.80 days/yr (P < .01). Small negative genetic (P > .10) and positive environmental (P < .05) trends were found for dystocia score. Cow reproductive performance was relatively unchanged by selection. Calf weaning weight, which measured cow maternal performance, showed a slight positive genetic trend. Negative genetic trends for cow lifetime productivity traits suggested that selection reduced cow herd-life. When the data were adjusted to a constant cow herd-life, number of calves weaned over a lifetime increased by .25 calves per year (P < .05). Expected genetic changes were calculated as correlated responses to selection for 365-day weight. Expected genetic trends for cow growth traits were strongly positive while first parity calving date was reduced 2.17 days/yr. Expected genetic changes in first parity reproductive performance and cow lifetime productivity traits were negative. Small positive genetic trends were obtained after adjustments to a constant number of years in the herd and were found in both observed and expected trends. The principal effects of selection favoring 365-day weight were reduced herd life, delayed sexual maturity and increased cow size.

Degree

Ph.D.

Subject Area

Genetics

COinS