Estimation of Pregnancy Probability After the First Insemination in Holstein Cows Using Logistic Statistical Analysis

To evaluate the effects of some environmental factors on the probability of being pregnant after only one insemination in Iranian Holstein cows, a total of 38074 records obtained from 10726 cows at different parities and inseminated during years 1985 to 2009 were utilized. All records were collected from a very large dairy herd which comprised of two units. A generalized statistical linear model was applied to analyze the data. Logistic regression model was applied as the statistical model. In the model, fixed effects of period and month of insemination, inseminator, parity and herd unit were included. The statistical model was run using GLIMMIX procedure of SAS software. Odds ratio estimation for period 1 (years 1985 to 1990) in comparison to periods 2 (years 1991 to 2000) and 3 (years 2001 to 2009) was 1.106, 1.133 respectively, which means chance of being pregnant after first insemination in year period 1 in comparison to periods 2 and 3 were respectively 10.6%, 13.3% higher. Average insemination per conception in unit one and two was 2.22 and 2.38 respectively, and the difference was statistically significant. Odds ratio estimation for herd unit showed that chance of being pregnant after the first insemination in unit 1 was 15.4% higher than unit 2. Results indicate the influence of environmental and management factors on number of services needed for a cow to be conceived which by improving them reproductive efficiency will increase and pregnancy cost will decrease.