MORTALITY STUDIES IN RHODE ISLAND REDSi 



By F. A. Hays 

 Research Professor of Poultry Husbandry 



INTRODUCTION 



The problem of mortality is of vital concern to all poultrymen. Although 

 great strides have been made in the prevention and control of diseases, losses 

 from a wide range of diseases and disorders are still very heavy. It is estimated 

 by the Bureau of Agriculture Economics that the annual loss of chickens in the 

 United States in cash value is over 130 million dollars. About 40 percent of 

 these losses are probably due to the avian leukosis complex. It is a common 

 belief that selective breeding can do much to reduce the mortality rate. Frateur 

 (1924) was one of the first to attempt to breed chickens for resistance to a specific 

 bacillus. By inoculating with fowl diphtheria in the mucous membrane of the 

 mouth he discovered resistant and susceptible birds. Matings were made to 

 produce an Fi generation which was tested by direct inoculation. An F2 gen- 

 eration was also secured and tested as well as some back-crosses. Results of these 

 studies led to the conclusion that resistance was due to a single dominant gene. 



Significant progress has been made in breeding chickens for resistance to pul- 

 lorum disease. Roberts and Card (1935) carried a strain of chickens through a 

 nine-year period that showed an average survival of 71 percent to lethal doses 

 of 5. pullonun, while control chicks showed an average survival over the same 

 period of 28.1 percent. Crosses between resistant and susceptible strains in- 

 dicated a dominance of resistance. Resistant chicks had a high erythrocyte 

 count while susceptible strains had a high leukocyte count. There was no 

 evidence of acquired immunity in the different lines. Lambert (1932) selectively 

 bred chickens for high resistance to lethal doses of fowl typhoid bacterium, 

 5. gallinarum. In five generations the resistant strain had a mortality rate of 

 only 9.4 percent, while the control stock had a mortality rate above 85 percent 

 during the same period. A difference was also observed between breeds: Rhode 

 Island Reds were the least resistant, and White Plymouth Rocks the most re- 

 sistant of four breeds tested. Lambert states that the evidence points to in- 

 herited resistance and that passive transfer of immunity was not great. By 

 selective breeding of mice, Hetzer (1937) reduced the mortality rate from injec- 

 tions of S. aertrycke from 98 to as low as 7 percent. He points out that resistance 

 to this organism is inherited on a multiple factor basis. Gowen and Calhoun 

 (1943) studied the blood cells of six strains of mice and found a pronounced cor- 

 relation between resistance to mouse typhoid, 5. Typhimurium, injections and 

 numbers of leukocytes. 



Experimental data on the mode of inheritance of resistance and susceptibilit}- 

 to virus diseases are very meager. This is due in no small degree to the diffi- 

 culties in isolating viruses. The causative agents of the avian leukosis complex 

 have been but partially' identified. 



Asmundson and Biely (1932) and Biely, Palmer and Asmundson (1932) made 

 the first attempts to study the mode of inheritance of resistance to fowl paralysis. 

 These workers noted a difference in susceptibility among the seven breeds tested. 



' These studies have been made possible by the constant interest and cooperation of the De- 

 partment of Veterinary Science. 



