Poljoprivreda (Jun 2015)
PREDICTION OF SERVICE PERIOD DURATION OF COWS ACCORDING TO MILK YIELD AND COMPOSITION IN EARLY LACTATION
Abstract
The objectives of this research were to determine significant effects on the duration of the period from calving to conception (service period), the relationship between the duration of the service periods and the traits recorded during the milk recording and develop a system of predicting the duration of service period based on the milk recording results in early lactation (the first two controls) in Holstein and Simmental cows population, which would consequently increase competitiveness and financial performance of the farm. Statistical analysis using survival analysis and logistic regression method included 14,864 Holstein cows with a total of 29,278 milk recording records and 18,708 Simmental cows with a total of 37,416 milk recording records. Correlation coefficient values were within the range ±0.00 to ±0.20 indicating a negligible correlation between the service periods duration and the traits recorded during the milk recording. Higher conception probability at all classes of service periods duration in the Simmental compared to the Holstein breed was determined using the analysis of movement survival curves for service period duration. Based on the results of logistic regression two statistical models were created. Model 1 includes traits recorded during the milk recording separately for each breed and each test day. Model 2, besides traits from model 1, also included effects of region, season of recording, herd size classes, season of conception and calving season. The power testing of the models for prediction of incident was shown using the concordance index representing the compliance agreement of recorded and predicted data within each model. The increase of the concordance index value was determined for each model with a higher number in comparison to the initial model. Additionally, the increase of the concordance index value was determined for control day 2 compared to the control day 1 for both analysed breeds.
Keywords
