تجزیه و تحلی ل صفت ماندگاری در برههای گوسفند نژاد ماکویی مبتنی بر توابع خطر نسبی.

Introduction: An animal's ability to survive in the breeding season is called its survival trait. One of the most important features of survival analysis are unfinished (censored) observations. In other words, the event under study does not necessarily occur at the time the observations were recorded. As such, survival observations and data are generally incomplete, and some people experience events while others have no observations for that event. In general, nonparametric regression methods (Kaplan-Meier estimator, Cox hazard ratio model) and parametric methods are more commonly used than other methods for this type of analysis. Survival and longevity analysis are performed using linear function, threshold function, and hazard ratio function methods. Linear models are easier to use, but due to the non-linearity of the survival trait, they are biased and heritability estimates using this method are low, close to zero. Threshold models are more accurate and provide higher genetic estimates. When analyzing the hazard ratio method, the accuracy is higher than previous models due to the use of more information (use of censored data), but it is more time-consuming and has a higher computational burden. Therefore, the aim of the present study was to estimate the genetic parameters and the effect of fixed factors on the survival of Makuie lambs up to one and two years of age using the proportional hazards function under the Weibull distribution. Material and methods: This study used 2332 records of Makuie lambs collected at the Makuie Sheep Center between 1986 and 2010. In the first step, fixed factors were identified that influence longevity (gender, birth type, year of birth, month of birth, birth weight, weaning weight, weaning age). and maternal) were identified. Age) were analyzed using the LIFEREG method of the SAS statistical software version 9.4 under Weibull distribution. Subsequently, significant effects were used in the survival analysis using the proportional hazard model. Survival to 1 and 2 years of age was analyzed using the Weibull hazard model of SURVIVAL KIT software version 6.12. The SURVIVAL KIT software is able to provide components of genetic variance and estimate breeding values for animals using mixed models. Post-weaning survival up to one year (for analysis up to one year of age) and two years (for analysis up to two years of age) was assessed daily. Results and discussions: In the analysis of survival from weaning to one year of age, 38.12% of observations and in the study of survival to two years of age 13.68% of observations were censored. According to the study, year of birth had a significant impact on lamb survival. The year of birth influences the amount of precipitation and ultimately the availability of food resources by affecting grazing and thus changing the quality and quantity of food. Lambs born in 2004 and turning two years old in 1994 had the lowest risk of loss. Lambs born in 2010 had the highest risk of shedding. When examining the effect of month of birth on lamb survival, it was found that lambs born in April had a higher risk of being discarded considering they had reached one year of life. However, lambs born in May and reaching two years of age had the highest risk of shedding, and the risk was 1.96 in May compared to March. Lambs born in May reach autumn young and are in a period of rapid growth. As the herd studied is kept semi-dense, access to feed for these lambs is limited and they are removed from the herd due to their low weight and insufficient growth rate. Birth weight is one of the most important survival factors and has a direct impact on the elimination rate. Threshold weights have the highest elimination risk ratio and the weight of 3.54.7 kg has the lowest elimination risk ratio for survival at one to two years of age. There is a curved relationship between risk of excretion and birth weight, i. H. with increasing birth weight up to mean weight (3.54.5 kg), the risk ratio decreases and then increases. Low birthweight mortality is due to an inability to control body temperature and high birthweight mortality is due to infertility. Weaning weight is an important factor affecting post-weaning survival. Similar to birth weight, weaning weight also has a curved relationship with survival. With an increase in weaning weight from 10 kg to 19 kg, the risk of shedding for survival at one and two years of age decreases from 1.8 to 0.97 and 0.93, respectively, and with an increase in weaning weight the risk ratio increases then 2.53 and 2.38 respectively. Lack of growth-induced production favors the elimination of low-weight weaned lambs. Therefore, the elimination risk ratio is high at low weights. However, as weaning weight increases, the desire to maintain it for later periods increases and the pressure to wean decreases. The average weaning weight in the herd is 19.01 kg. The results also show that the lowest elimination risk ratio and hence the highest survival rate is at weaning weight at 18-20 kg. Therefore, to increase the survival rate and reduce the elimination risk ratio, management and correction programs to select the optimal weaning weight can be developed. For surviving to one to two years of age, the risk of shedding was higher in male lambs than in females. From weaning to one year of age, the elimination risk ratio for male lambs was 2.17 compared to female lambs and for survival to two years of age the elimination risk ratio was 2.61 for male lambs compared to female lambs. This difference in molting rate can be attributed to sex-related factors, possibly unrecognized sex characteristics, systemic diseases, different management practices in males and females, and a high molting rate in males due to overfeeding. There are three types of Makuie birth (single, twin, and triplets). Lambs born with twins and triplets have lower birth and weaning weights than single lambs. Due to the above issues, low birth weight and low weaning weight reduce survival and increase the risk of excretion. Another reason for the reduced survival rate in multiple births is reduced breast milk production, which may be due to poor maternal genetics or inadequate nutritional intake. The heritability of survival to one and two years of age for Makuie lambs was 0.062 and 0.079 according to censor rates of 38.12% and 13.68%, respectively. Conclusions: Because heritability is estimated to be at a low level, control of environmental factors and management will play an important role in improving Makuie lamb survival. [ABSTRACT FROM AUTHOR]