Enhancing comprehensive growth through increasing skeletal growth in the dry season

Summary

​This project investigated the effect of diet energy and protein on skeletal elongation rate (SER) in cattle and sheep undergoing periods of nutritional restriction and re-alimentation. One of the major aims of this project was to determine if it is possible to "un-couple" growth in skeletal height with liveweight  (LW) gain in growing steers and drive additional frame size in cattle in the dry season to enhance compensatory LW gain in the wet season. Gene expression of growth plate tissue and plasma hormone analysis indicates that insulin like growth factor-1 (IGF-1)  is central to the cellular pathways responsible for controlling changes in skeletal elongation in response to nutrition. When growing steers were fed diets resulting in minimal LWG, metabolisable energy (ME) was the primary nutritional component that controlled growth, skeletal elongation, bone formation and hormonal and growth plate gene expression response to the diet. These low ME diets also led to reduced bone volume and rib cortical thinning because of reduced bone formation. Adding crude protein  or exogenous bovine somatatropin (bST) to a low ME diet was not able to drive additional hip height (HH) gain or compensatory LWG. However, the LW:HH relationship appears to be central to growth and strategies to create growth paths where animals diverge further from the normal LW:HH are likely to yield more effective compensatory LWG.