40 Pork Production 



nancy advances, therefore, an increasing proportion of 

 the rations is needed to nourish the developing pigs. 



The kind of food materials which will satisfy main- 

 tenance is likewise different from that required to meet 

 the needs of embryonic growth. The demands for 

 maintenance are met by food materials which will supply 

 the heat and energy to run the body machine and make 

 good the repair of body waste. To meet the needs of the 

 growing pigs in embryo there is demanded, in addition, 

 material which will produce bone and muscle. The 

 first is largely met by the carbohydrates of the ration, 

 while the latter can only be derived from the supply of 

 protein and mineral matter. A ration which will satisfy 

 both these demands in proportion is, therefore, a balanced 

 one. 



Young sows and gilts carrying their first litters must 

 be fed with reference, also, to a third demand, for 

 their own growth and development. The first need of 

 the immature sow is food for maintenance, then for the 

 growth of her pigs in embryo. If any food remains after 

 these demands are satisfied, .it may be used for the in- 

 creased growth of her own body. If the supply of feed 

 is insufficient to supply all three requirements, the last 

 is the one to suffer. The maternal instinct of the sow is 

 so strong as to cause her to sacrifice, in the absence of suffi- 

 cient nourishment, her own energy and body tissue that 

 the foetal litter may have the substance for growth. 



Corn alone as a feed for pregnant sows. 



In the corn-belt the central question is to what extent 

 it is safe or advisable to make use of corn in the ration 

 of the pregnant sows. Outside the corn-belt, likewise, 

 the question is to what extent the home-grown grains 



