Genetic Trends in Milk Production and Days Open in the First Three Lactations of Swedish Dairy Cattle

Abstract

Best Linear Unbiased Prediction transmitting abilities (ETA) of AI sires were used to estimate genetic change in production (kg 4% milk, FCM) and days open period (DO) for the first three lactations in Swedish Red and White (SRB) and Swedish Friesian (SLB) breeds over a 10-year period. Trends were calculated for the populations of sires and first-calf heifers. The latter trend, calculated as the regression of the weighted average of sires' ETAs (weighted by number of daughters first freshening in this year) for each year on year, were for FCM 17.6, 11.2, 10.7 kg for the three lactations respectively for SRB and 7.7, 2.5, 5.4 kg respectively for SLB for the period 1973–80. The corresponding trend for the period 1980–1983 was substantially higher: 41.0, 27.8, 41.3 kg respectively for SRB and 25.2, 32.2, 42.2 kg respectively for SLB. The genetic trends in DO for the population of first-calf heifers for the whole period were: -0.14, -0.06, 0.13 days for the three lactations respectively for SRB and -0.26, -0.15, -0.21 days respectively for SLB. In conclusion, selection based mainly on first lactation production gave high correlated responses in second and third lactation production but no undesirable correlated changes in days open periods.

Key Words:

• milk yield
• calving interval
• selection response