MANAGEMENT AND ECONOMICS OF NATURAL SERVICE BULLS IN DAIRY HERDS

In many dairies, natural service bulls are used to improve the efficie ncy of estrus detection. The primary task of such bulls is to get cows pregnant as soon as possible after they become available. The inabili ty to detect estrus efficiently and accurately in dairy herds is a maj or limitation to the attainment of maximum reproductive efficiency wit h artificial insemination. Efficiency of estrus detection is assessed as the percentage of the herd detected in estrus during a stipulated p eriod; accuracy gauges the percentage of the herd in which there is tr ue estrus. Inefficient or inaccurate estrus detection leads to an incr ease in the interval from calving to conception; the results are a red uction in milk production, an increase in the required number of repla cement heifers, and a consequent reduction in farm income. Many dairie s use natural service (NS) bulls because of the perception that NS res ults in higher pregnancy rates due to improved estrus detection effici ency and accuracy. In other words, NS avoids human errors in estrus de tection. The use of NS on a farm becomes a valid option if the effecti ve pregnancy rate is below 25%. This option is of maximum benefit only if the bulls used are able and willing to impregnate cows in estrus. For NS to be effective, the selection, management, and evaluation of b ulls must be considered vital components of the dairy herd health prog ram. Sound reproductive management depends an adequate record-keeping and proper analysis and interpretation of records.