Eighteen days after the AI, a bull was introduced to the
herd in order to serve cows that returned to oestrus. Pregnancy
examinations were performed by palpation per rectum
six to eight weeks after the AI, when it was easy to
detect pregnancies conducted from AI. All examinations
were made by one and the same experienced veterinarian.
Data were analysed using the SPSS 13.0 for Windows software.
To study the effect of season, suckling, parity and
interval between calving and entering the program among
cows on the rejections and pregnancy rates, the data were
analysed using logistic regression for binomially distributed
data. Before analyses, parity was classified to three
groups, first parity cows, middle-aged cows (parity 2-5)
and old cows (parity 6-), and interval between calving and
entering the program to three groups, short (50-70 days),
medium (71-100 days) and long (101-days) interval. For
parity and interval, the last and first category, respectively,
served as a reference category. Initially, all the variables
were included in the analysis. In the backward stepwise
analysis procedure, non-significant variables were omitted.
Chi-square test was used to analyse the differences in
rejections and pregnancy rates between cows and heifers.
P-values less than 0.05 were considered significant.