Abstract:

The research aimed to reveal the content and distribution rules of energy and protein in different body tissues for 20-35 kg Dorper and Thin-tailed Han crossbred ram lambs fed with different diet levels, and to establish some mathematical models to predict body composition and chemical composition by means of live weight in crossbred sheep. Twenty-one lambs were randomly assigned to three groups，one group fed ad libitum (AL), and the other two groups fed either 70% (IR70) or 40%(IR40) of ad libitum. Each group contained seven sheep and every sheep was a replicate. A slaughter trial was performed when the lambs in AL group reached 35 kg of live weight. Dry matter, crude protein, fat as well as gross energy content were measured in different tissues including bone, muscle, fat, blood+viscera, hide and fleece. In body composition, AL group lambs had the highest proportion of fat to moisture and showed significant difference to IR40 group (P<0.05), while the proportion of protein/fat was higher in IR40 group than that in AL group (P<0.05). No significant difference was found in the ratio of the muscle, blood+viscera or hide weight to fleece-free empty body weight (P>0.05), but the ratio of bone to fleece-free empty body weight was significant difference (P<0.05) among three treatments. Energy content (MJ·kg^-1) and protein content(%) in the tissues showed no significant difference (P>0.05) among three feeding levels. The ratio of dry matter or protein to fleece-free empty body weight showed no significant difference between the three groups (P>0.05), however, IR40 group lambs had a higher ratio in moisture and ash than that of AL and IR70 group lambs(P<0.05) . The feeding level significantly affected the proportion of crude protein, fat and moisture in Dorper and Thin-Tailed Han crossbred ram lambs between 20 to 35 kg of live weight, and a highly negative correlationship was found between fat and moisture. The parameters of E/GE and CP/GCP in different tissues were affected by the feeding levels but the impact was not consistent. The protein content was relatively stable while the fat content was easily affected by age and the feeding levels. There was a strong correlationship between empty body weight and different tissues and organs, and a strong correlationship was also found between fleece-free empty body weight and the main chemical composition in body.