Phenotypic evaluation of fertility traits and their association with milk production of Italian Friesian cattle.

The effect of environmental factors on first service conception rate, days from calving to first service, weeks from calving to conception, days from first to second service, and number of services per conception and the relationship of production with reproductive performance were estimated using 1.42 million records. The production trait was 305-d mature equivalent milk production. Season and age affected fertility: reproductive performance was lowest for lactations initiated during warm months (May to July) and decreased with parity. The association of production and fertility was antagonistic. High producing cows had 12 d more from calving to first service, .15 lower first service conception rate, .32 more services per conception, and 4.8 wk more from calving to conception than low producing cows in the same herd. The negative effect of production on fertility was reduced by superior herd management associated with high production. The difference in reproductive performance of cows in high and low producing herds represented only about 35% of the difference in the performance of high and low producing cows within herds for all fertility traits. The negative effect of production on fertility for interval between first and second service was totally compensated for by better management.