Genetisk variation i brunststyrka hos svenska mjölkkor

Abstract: When cows in Sweden are inseminated the heat strength is reported to the Swedish milk-recording scheme and AI scheme. Cows that show strong signs of estrus are desirable and the trait is included in the Swedish breeding goal. A strong heat makes it easier to inseminate at the right time and to avoid long and expensive days open. Since ten years the heat strength is scored from one to five by the farmer and reported to the milk-recording scheme and AI scheme. Earlier the score was from one to three and the decision was made by the AI technician. The genetic parameters for heat intensity have been estimated from data collected before the scoring was changed, but parameters have not been estimated for the new system. The aim of this study was to estimate genetic parameters for heat intensity for possible use in the genetic evaluation. Data collected in the Swedish milk-recording scheme and AI scheme during the years 1997 to 2003 was used in the study which included both Swedish Holstein and Swedish red and white dairy cattle. The results showed that the heritability of the heat intensity is low in dairy cattle; the heritability was around one percent both in the heifer period and in lactation one to three in both breeds. About one fourth of the herds had a standard deviation in the herd of zero for the trait. This indicates that it is common that the scale for scoring the heat intensity is not used in a proper way when judging the cows' heat intensity. The correlation between lactations for heat intensity was high while it was lower between the heifer period and first lactation.