Study of non-genetic and inbreeding effects on some production traits of Sarabi cattle breed

Introduction: About 6 million heads of cows in Iran are native cattle, but their characteristics and production potential remains unknown. Inbreeding is one of the important factors which must be considered in the herd and can be of considerable economic loss to producers. In this research, we tried to investigate the occurrence of inbreeding and its effects on the production traits of Serabi native cattle in a breeding center related to agricultural ministry located in Sarab. The aim of this study was to evaluate inbreeding effects on milk yield, fat percentage, protein percentage, and birth weight of Sarabi dairy cattle. In this research, the effects of inbreeding and environmental factors on production traits and birth weight of Sarabi cows have been studied.
Material and methods: The data were collected from 1250 Sarabi cows during 1992- 2012 years by Sarabi Breed Center in East Azerbaijan province. In the present study, a pedigree file containing 1250 head (764 females and 486 males) of dairy cows was used, including data about the registration number of the livestock, date of birth, gender, father's registration number, and registration number of the mother, date of birth, parity, and production records. After the removal of animals with unknown and unregistered parents in the flock, the pedigree was arranged using pedigree software. Pedigree software was used to calculate the inbreeding coefficient for each animal. The principles of this software in the calculation of inbreeding coefficient is based on the formation of a kinship matrix among the individuals. The inbreeding coefficients of animals were considered as a discrete trait in 4 groups.
Results and discussion: In this herd, inbreeding coefficient was estimated between 0- 0.28. Average inbreeding coefficients of all cows and inbred cows are 0.0109 and 0.0574, respectively. Totally, 19% of all animals were inbred. In this study, inbreeding coefficient has been included in the model either as a continuous variable or as a classification variable. When inbreeding factor considered as continuous variable in the model, its effect on milk yield, fat and protein percentage, and birth weight was significant (p < 0.01). When inbreeding considered as a continuous trait, 1% increase in inbreeding coefficient had an effect equal to -2.69 kg, 1.59%, and +18.1% on milk yield, fat, and protein percentage, respectively. Miglior et al. (1995a) reported a 1% increase in inbreeding coefficient in Holstein cows reduced calf weaning by 0.44 kg and reduced milk production by 25 kg. Mohammadkarim (2006) using a univariate model reported for 1% increase in inbreeding coefficient, changes in milk yield, fat yield, open days and length of first lactation equal to -14.02, -0.349 kg, + 0.4839 and + 0.148 days, respectively. Inbreeding has a negative effect on production traits and birth weight. Results showed that the effects of year-season of calving and parity on production traits and birth weight were significant (p < 0.01). The regression coefficient of milk, fat and protein percentages and birth weight on inbreeding, when inbreeding considered as a discrete variable, were -0.129kg, +0.093%, +0.072% and -0.564 kg, respectively. In this study, when inbreeding traits considered as a continuous variable, did not show any linear or nonlinear relation with birth weight trait of Sarabi cows. It can be concluded that in order to maintain the genetic reserves of Sarabi cattle breed, it is necessary to carefully monitor the reproduction breedings in this native cattle population. In the case of endangered breeds, such as Sarabi breed, these breeds have beneficial properties, particularly in relation to resistance to diseases, and tolerance to stressful environments. These desirable traits can be transferred to future genetic composition cattle breeds. Preserving the genetic resources of the country's livestock and pay attention to similar breeds of Sarabi should be taken into consideration by decision makers at livestock breeding centers. In Holstein cows it has been found that high milk production is associated with a genetic susceptibility to disease (Khaleghi & Rafat 2018), so the desirable characteristics of the Sarabi breed should be studied in this regard of susceptibility to diseases. The existence of a complete family tree in computer registrations is the first step in controlling inbreeding. The existence of this pedigree will help breeders to avoid breeding between close-up animals, like a brother-sister and a father -daughter, which will increase the incidence of inbreeding in the population. For this purpose, it is recommended to use optimal mixing softwares that controls inbreeding. There are programs for managing the breeding to identify animals as soon as possible and calculate their relativeness in the herd. By this method, it is possible to prevent the occurrence of high inbreeding in the herd and produce calves with high profitability. The prospect of this research is to carry out further research on the issue of inbreeding and effective population size on local breeds of dairy cattle to prevent the replacement of these breeds with Holstein.
Conclusion: It is imperative to prevent the replacement of the foreigner breeds (Holstein generally) instead of Sarabi breed and its extinction as much as possible.