| Fat depth,eye muscle depth and eye muscle area are three important economic traits of interest for meat sheep breed selection and breeding.The Kazakh sheep is one of the main breeds in Xinjiang sheep breeding industry at present.Improving its obvious defects such as excessive tail fat and low meat production performance,and cultivating new types of Kazakh sheep with good resistance,adaptability to grazing and significantly improved meat performance is the current focus of Kazakh sheep breed resource conservation and utilization.The Txel sheep has fast growth,well-developed muscle and high lean meat rate,and is a common sire in the genetic improvement of sheep meat performance.Therefore,the group has carried out crossbreeding work with Texel sheep as the sire and Kazakh sheep as the dam.In order to compare the selection effect of different crossbreeding combinations and to select the most suitable crossbreeding combinations,this study used four different crossbreeding combinations of Kazakh sheep,Teksel sheep × Teha F1,graded Teha F2 × Teha F1,Teha F1 × graded Teha F2 and graded Teha F2 × Kazakh sheep,obtained by the group from 2020 to 2021,and applied the ultrasound in vivo measurement technique to determine The correlation between the three meat traits and body weight was analyzed,and the regression equation between body weight and each trait was established.The regression equation was then used to analyze the effects of four factors,including birth type,sex,ewe age,and flock category,on the three meat traits of lambs.The aim was to select the best combination from the four combinations by assessing the main meat traits as determined by ultrasound,and to provide a reliable practical and theoretical basis for accelerating the selection and breeding of dominant crossbred populations and improving the efficiency of early selection and evaluation of Teha sheep.The specific research content and the main research results obtained are as follows:(1)Analysis and comparison of three meat traits measured by ultrasound in lambs from different crossbred combinations of Kazakh sheep : In four different crossbred combinations,there were significant differences in lamb body weight and three meat traits measured by ultrasound: fat depth,eye muscle depth and eye muscle area.Among them,body weight,fat depth,ocular muscle depth and ocular muscle area were significantly higher in the F2×F1 combination than in the other three crosses(P<0.05),while fat depth and body weight were lowest in the F1×F2 combination and ocular muscle depth and ocular muscle area were lowest in the F2×Kazakh combination;among the four crosses,body weight had a highly significant positive correlation with the three meat traits,especially ocular muscle depth In the four crossbred combinations,weight was highly positively correlated with all three meat traits,especially eye muscle depth and eye muscle area,and fat depth had low correlation with eye muscle depth and eye muscle area.In contrast,there was no correlation between fat depth and eye muscle area in F1×F2 combination lambs.The one-dimensional linear regression equations of body weight and each trait were established according to the linear regression analysis method.(2)Prediction and comparison of three meat traits in four different growth stages of lambs from different crossbreed combinations of Kazakh sheep:The Gompertz model was used to correct the body weights of lambs from four crossbred combinations to four different growth stages at the same day of age,100 d,150 d,180 d,and 210 d of day of age and to compare between groups.The lambs of the F2×F1 combination had the fastest weight gain and the lambs of the F1×F2 combination had the slowest weight gain.The male lambs of the F2×F1 combination had the highest weight at all growth stages,the male lambs of the F1×F2 combination had the lowest weight at 100 d,150 d and 180 d,and the male lambs of the F2×Kazakh combination had the lowest weight at 210 d.The highest and lowest predicted body weights of male and female lambs were consistent with the measured results.The predicted values of fat depth,eye muscle depth and eye muscle area of the lambs at the same day of age were obtained by substituting the body weights at the same day of age into the prediction equations of body weights and each meat trait of the corresponding crossbreeding combinations.At 100 d of age,sheep from the F2×F1combination exhibited the advantage of fat depth and large eye muscle depth and area.After 150 d of age,the pure Special x F1 combination rams and F2 x F1 combination ewes were the dominant combination.(3)Effect of non-genetic factors on three traits of fat depth,eye muscle depth and eye muscle area:The effects of birth type,sex,ewe age,and herd category on backfat thickness,eye muscle depth,and eye muscle area of 6-month-old lambs were analyzed using the GLM program of SPSS 22.0 for the progressive F2 generation of lambs obtained from crosses between Texel sheep as the sire and Kazakh sheep as the dam.Birth type and sex had highly significant effects(P<0.01)on the fat depth of6-month-old lambs,and the backfat thickness of single-born lambs was significantly higher than that of double-born lambs,and that of male lambs was significantly higher than that of female lambs.There was no significant effect of ewe age and group on the fat depth of 6-month-old lambs(P>0.05);there was a significant effect of sex on the depth of eye muscle of 6-month-old lambs(P<0.05)and a highly significant effect on the area of eye muscle of 6-month-old lambs(P<0.01).The eye muscle depth and eye muscle area of male lambs were significantly higher than those of female lambs.Ewe age had a highly significant effect(P<0.01)on ocular muscle depth and ocular muscle area in 6-month-old lambs,and ocular muscle depth and ocular muscle area in lambs produced by ewes aged 3 years and older were significantly higher than those produced by ewes aged less than 3 years.There was no significant effect of birth type and flock category on oculomotor depth and oculomotor area of lambs at 6 months of age(P>0.05).Through the above study,the three meat traits of fat depth,eye muscle depth and eye muscle area determined by ultrasound in vivo can be used as indicators for selecting meat performance,which can help to screen the optimal crossbreeding combination and obtain lambs with more meat production and good meat quality with moderate backfat thickness,optimal eye muscle depth and eye muscle area,and clarify the F2×F1 and Puret×F1 combination as the superior crossbreeding combination.This study provides an important basis for the selection and genetic evaluation of meat traits in the future crossbreeding improvement of Kazakh sheep. |
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