No. 6. DEPARTMENT OF AGRICULTURE. 237 



seventh month of the period of pregnancy. Seven months calves 

 are said to be more liable to live than those dropped at the eighth 

 month and usuall}' thrive better. Aborted calves are, as a rule, 

 bailers, thrive badly and die or should be destroyed as worthless. 



In order to detect infected individuals in a herd, laboratory 

 methods are useful. Many different plans have been tried, but up 

 to the present the best results have been obtained by an examination 

 of the blood or what is known as the complement fixation test. It 

 has been possible with this test, to detect practically all of the 

 infected animals in a herd. To do this work properly it is necessary 

 to have a laboratory well equipped and a man especially trained in 

 bacteriology. Our State is fortunate in being provided with the 

 necessary equipment for studying this disease and many others that 

 are dillicult-to diagnose. In large breeding herds where the owner 

 desires to eliminate contagious abortion, this test is practically the 

 only alternative. By its use infected animals can be segregated from 

 those that have recovered or that have not yet become infected. 



It is possible to establish a diagnosis of the disease in a herd 

 from a post-mortem and laboratory examination of the foetus, foetal 

 membranes, etc. In formation obtained in this way is too late to 

 be of practical service. 



In order to control the disease it is necessary to consider the 

 various ways in which it has been spread. There are several im- 

 portant factors. It should be remembered that the bacillus of Bang 

 is the only cause of the disease in cattle; that it lives, thrives and 

 multiplies in the foetus, the fetal envelopes and uterus, and that 

 it lives but a short time outside of the pregnant animal. This is 

 one important reason for not breeding infected animals for about 

 three months from the time abortion occurs. The most usual form 

 of introducing the disease in a herd is in the purchase of new cows. 

 It is possible, however, to get the disease from the male. It is 

 spread in a herd principally by feed that is contaminated with the 

 infected foetus, fetal envelopes or vaginal discharge. Professor Bang 

 was the first to discover the fact that the disease is spread by the 

 food. The surest way in which it can be transmitted is by intra- 

 venous injections. In this way it has been possible to discover 

 important facts in reference to the period of incubation. The time 

 from which virulent material was injected into the blood to the 

 time of abortion has varied from thirty-three, to two hundred and 

 eighty-one days. The average in ten cases was one hundred and 

 twenty-six days. Artificial infection is believed to produce the dis- 

 ease more quickly than where it is contracted under natural con- 

 dition. An infected animal may abort before she is placed in a herd 

 and still carry the disease to the new herd, or she may be infected 

 at the time of purchase and carry the foetus for several months 

 and then abort, other animals in the herd may then follow in from 

 six to eight months. When the disease is once introduced into 

 a herd it will remain for years unless necessary measures are adopted 

 for its extermination. There is no doubt but that a certain degree 

 of immunity is carried; it is unusual for animals to abort the sec- 

 ond time and still more so the third. Where nothing is done to 

 check the disease the old members of the herd cease to abort and 

 it is confined principally to the heifers and will continue in them 

 from year to year. 



