Associations Between Service Interval, Interval from First Service to Conception, Number of Services per Conception, and Level of Butterfat Production

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Abstract
The interval from 1st service to conception decreases as the interval from calving to 1st service, service interval, increases from 0 to 127 days at which it reaches a minimum. After a service interval of 127 days, the interval from 1st service to conception increases slightly as the service interval increases. The length of the service interval accounts for only 1.4% of the variance of the interval from 1st service to conception; thus even though its effect on the interval from 1st service to conception is significant its effect is small and thus of little importance. Service interval does not significantly affect the number of services per conception and accounts for only 0.3% of the variance of services per conception. The partial regression of the number of services per conception on butterfat production for a constant service interval and constant interval from 1st service to conception is -0.00004 [plus or minus] 0.0007 and is not significant. It is concluded that there is no real biological relationship between services per conception and level of butterfat production. The interval from calving to conception increases at an increasing rate as service interval increases to approximately 50 days. After a serivce interval of 50 days the interval from calving to conception increases almost linearly and in an approximate 1 to 1 ration as the service interval increases. Calving interval has approximately the same relationship to service interval as does the interval from 1st service to conception. With the present data the average service interval must be from 36 to 49 days to maintain an average calving interval of approximately 365 days. If the conception rate was increased to 60%, the average service interval allowed could be increased approximately 11.5 days and a calving interval of approximately 365 days could still be maintained.