GROWTH IN SIZE AND BODY PROPORTIONS IN FARM ANIMALS 



329 



Figure 8. The priorities of various tissues in taking nutrients from the blood 

 stream ( denoted by arrows ) . The uptake depends on the metabohe rates of 

 the respective tissues. When the level of nutrition is reduced moderately 

 (one arrow taken from each tissue) the growth of fat ceases but the brain, 

 bone, and muscle tissues continue to grow,^ though at a slower rate. During 

 early pregnancy, the placenta and fetus have high priorities. (Hammond, 

 1944.) 



general, the evolution of the species (Hammond, 1952). In horses, 

 cattle, and sheep, whose young are born at an advanced stage of de- 

 velopment and have to follow their dam, the maximum proportions of 

 leg length occur at birth, while in rabbits, which are born at a less 

 advanced stage of development, this does not occur until later. In 

 general, the head and the legs form a high proportion of the body 

 weight at birth. With development, the body first lengthens and later 

 deepens. The growth gradients start at the extremities and pass inward 

 to the loin, while the lower parts of the ribs are the latest to develop. 

 When growth is limited by a low level of nutrition, the earlier 

 developing parts and tissues have priority of supply ( Hammond, 1944 ) . 

 The priorities are indicated in Figure 8. When the level of nutrition 

 is high, all the tissues are equally served according to their needs, but 

 when nutrition is lowered (take away one arrow from each tissue in 

 Figure 8 ) , fat ceases to grow, while the other tissues continue to grow 

 but at a slower rate. When nutrition is still further lowered (take away 

 two arrows from each), nerve and bone continue to grow at a slower 

 rate, muscle growth ceases, but fat is removed into the bloodstream 

 ( arrow reversed ) to assist in the growth of brain and bone. Pomeroy 

 ( 1941 ) has shown that if young pigs of 300 pounds are made to lose 

 weight by low-level nutrition, the bones and brain continue to grow at 

 the expense of the later-developing parts, such as muscle and fat. 



