Investigating the genetic and phenotypic relationship between biometric traits, body weights and carcass traits measured by ultrasound in Kurdi sheep of North Khorasan

Profitability of sheep in terms of meat production largely depends on growth traits and carcass characteristics. Despite the importance of the quality of sheep meat, few researches have been conducted in this field in the native sheep of the country. Therefore, the importance of examining the characteristics of animal carcasses, especially when they are still alive, is evident. The aim of the present study was to investigate the genetic and phenotypic relationship between biometric traits, body weights and carcass traits measured by ultrasound in Kurdi sheep of North Khorasan. Since the measurement of carcass traits is difficult and expensive, and in order to better design breeding programs to improve carcass traits, if there is a strong genetic relationship, it is possible to replace traits that are easier to measure with carcass traits that are difficult to measure.

The data of 658 Kurdi sheep in the Shirvan Kurdish sheep breeding and breeding station located in North Khorasan province in the northern area of eastern Iran between 57 degrees east longitude and 37.4 degrees north latitude in the spring, summer and autumn seasons of 2021 were used. The information related to pedigree and birth weights (658 records), three months (652 records), six months (638 records) and nine months (419 records) were extracted from the records recorded in the said station. General linear models (GLM) procedure of SAS software was used to investigate fixed effects on traits. To estimate the parameters and the genetic relationship between the mentioned traits, the restricted maximum likelihood (REML) method was used based on single and two traits animal models in WOMBAT software. Multivariate regression was used to obtain the prediction equation of carcass traits based on other studied traits.

Heritability of subcutaneous fat thickness, area, width and depth of ultrasound longissimus muscle were estimated as 0.1±0.06, 0.06±0.06, 0.10±0.03 and 0.08±0.03 respectively. A high positive genetic correlation was observed between subcutaneous fat thickness and longissimus muscle area (0.71±0.31). Ultrasound carcass traits had a high positive genetic correlation with tail traits. A high positive genetic genetic correlation was found between ultrasound carcass traits and height of the withers, height at rump, heart girth, belly circumference, body diagonal length, thigh circumference and rump depth. The model related to longissimus muscle area with the highest coefficient of determination (0.82) is more reliable than other models for prediction.

The low heritability of traits measured by ultrasound technology in Kurdi sheep of Shirvan Kurdi sheep breeding station showed that improving these traits through individual selection is not very effective and other selection methods (family selection or marker-assisted selection) should be used for improvement of these traits. Generally, due to relatively high coefficient of determination, regression models can be used to predict carcass traits in the flock of Shirvan Kurdi sheep station.