VIGOR IN PRODUCTION-BRED FLOCKS ITl 



Table 11 c-onfir^iis Harris's (1927 loc. cit.) observations that pullets whicli 

 die during tiieir laying year show a greater variability in egg production 

 previous to death than is shown for the same period by pullets which survive 

 the year. This fact is illustrated by the greater magnitude of the probable 

 error in mean winter production for the group dying after March 1. 



These data do not indicate, however, that mean egg production from first 

 egg to March first is lower in the group of birds that subsequently die before 

 the end of the pullet laying year. Neither do the data indicate that heavy 

 winter laying is responsible for later mortality, because the group which died 

 and the group which lived have almost identical mean winter production rec- 

 ords. Mean winter records for the two groups for the five year period are 

 62.44it2 67 eggs for the group dying after March 1, and 64.16±2.08 eggs for 

 the group surviving the year. These means are statistically identical and 

 point to no relation between winter egg production and subsequent mortality 

 rate in this strain of birds. High winter egg record cannot therefore be used 

 as a measure of vigor and it cannot be held responsible for high mortality in 

 the laying houses during the summer months. 



13. General Chusnification of Cavses of Mortality in Laying Houses. 



Many difficulties are encountered in attempting to discover causes of death 

 in domestic fowl. Even when careful post-mortem examinations are made on 

 every fowl, there are many S)pecimen,s which show no specific cause. In the 

 stock of the Massachusetts Agricultural Experiment Station post-mortem 

 examinations have only been possible in a limited way and the majority of 

 recorded causes of death are based on external observations only. These 

 records are thus presented not for their scientific value but to gi%'e a general 

 insight into the relative frequency of types of disorders encoimtered during 

 the experiment. 



Table 12 indicates no significant differences in the percentage of deaths in 

 the laying houses between the daughters of pullet mothers and hen mothers. 

 The percentage of losses from the same causes varies from year to year. For 

 example, cannibalism made its greatest inroads in 1922 and 1923. Since those 

 years losses from cannibalism have decreased, reaching an insignificant figure 

 in 1926. The general depleted condition, "going light", characterized by ex- 

 cessive loss of weight and strength has increased during the five-year period 

 causing 42 per cent of all losses in 1926. Paralysis has not been a very im- 

 portant cause of losses in the flocks. The heaviest losses from this disease 

 occurred in 1926. Roup of the diphtheritic type caused heavy losses in 1924 

 and 192.5. This disease has not materially affected losses on the other three 

 years. Miscellaneous unclassified causes of death have been important each 

 year. Such losses have not varied greatly from 3.5 per cent of the total. 

 These causes are not of epidemic nature and might be credited to low vitality. 



The general simimary for the entire period shows cannibalism as responsible 

 for slightly more than 20 per cent of the losses. This habit has been correct- 

 ed by methods of management and is no longer an important cause of losses. 

 The depleted condition, "going light," has not been attributed to any specific 

 diseases or to internal or external parasites. It is apparently due to faulty 

 metabolism and other obscure causes. This disorder shows an upward tend- 

 ency, and no method of control is known. Paralysis appears to depend 

 largely upon sanitation for control, and requires careful watching because it 

 seems to be increasing slightly. Roup is a very serious epidemic disease and 



