Assessment of Artificial Insemination and Influential Variables of Fertility in Cattle Using Negative Binomial Regression

Abstract

Fertility in cattle is an important trait for the profitability of dairy farms. Some factors affecting fertilization in small and medium-sized dairy farms in Adıyaman and Şanlıurfa provinces located in the Southeastern Anatolia region of Turkey were discussed in this study. The reproductive yield, which is the dependent variable, and the breed of cattle that affect the fertility, and disease were included in the model as categorical variables, while the duration of experience for artificial insemination specialists in the profession and artificial insemination practice were included in the model as continuous variables. The distribution of fertility data was Poisson, however the comparison of mean and variance (μ<σ 2 ) indicated an overdispersion in the data (p<0.05). Therefore, the parameters of the criteria affecting the fertility were estimated using NBR model. The fertility rate was low (55%) in study area and the breed (16%) was an important impact on the fertility. The results revealed that the effects of Holstein and Simmental cattle breeds on fertility was higher compared to the local breeds (46.8% and 50.6%, respectively). The fertility decreased 13.6% in cattle with disease symptoms. The race, disease, working time of the specialist and professional experience in the practice had significant effects on fertility in artificial insemination. In addition, the results revealed that the NBR model can be evaluated effectively and easily with the Stata statistical program in case of overdispersion of categorical data such as conception level.