ANALYSIS OF FERTILITY IN SWISS SIMMENTAL CATTLE - GENETIC AND ENVIRONMENTAL-EFFECTS ON FEMALE FERTILITY

Genetic and environmental effects on female fertility were analysed using the 90-day non return (NR) rate and the interval from first to last insemination (IFL). First insemination records from 706 040 cows and 345 775 heifers of the Swiss Simmental breed gathered over a 6-year period were used. Variance components for sire of females were estimated using a restricted maximum likelihood (REML) procedure. Estimated heritabilities ranged from 1.1% (90-day NR rate, heifer) to 3.8% (IFL, cow) and genetic coefficients of variation from 6.5% (90-day NR rate,heifer) to 30.2% (lFL, cow). An approximate approach was applied to derive estimates of genetic correlations among traits using estimated breeding values. The following results were found: (1) 90-day NR rate and IFL are genetically highly correlated (r(g) approximate to -0.9); (2) the genetic correlation among male and female fertility is close to zero; (3) the genetic correlation between cow and virgin heifer fertility is 0.4; and (4) female fertility and milk yield have antagonistic genetic correlations ( r(g) approximate to 0.6). Based on genetic variability of fertility traits and their high economic importance, it is concluded that fertility should be considered in the selection scheme for Swiss Simmental cattle.