20 MASS. EXPERIMENT STATION BULLETIN 315 



Striking variations in efficiency were noted, the most efficient lamb requiring 

 6.09 pounds T. D. N. per pound of gain and the least efficient 11.63 pounds 

 T. D. N. per pound of gain, an increase of 90.9 percent in the cost of a pound 

 of gain. 



The above figures indicate an obvious advantage in developing a more efficient 

 strain of sheep. Plans for the continuation of this work include the testing of the 

 efficiency of offspring of the lambs mentioned above, and of future offspring of 

 the dams of the lambs already used, to determine whether or not the ability to 

 utilize feed efficienctly is inherited. 



The Development of the Tunica Dartos Muscle in Rams. (Ralph W. Phillips.) 

 Recent experimental work has demonstrated conclusively that the scrotum has 

 a thermo-regulatory function maintaining the testes at a temperature below that 

 of the body cavity, and that the tunica dartos muscle provides the mechanism 

 for this temperature regulation, functioning very much as a thermostat to main- 

 tain a fairly constant temperature. 



The reaction of isolated strips of the tunica dartos to temperature changes 

 was observed in ram lambs at 3, 6, 9, 12, 15, 18, 21, 24, and 27 weeks of age. 

 The first marked reaction to a temperature change was observed at 12 weeks 

 of age. In lambs castrated before 12 weeks of age the tunica dartos had not 

 developed a sensitivity to temperature changes; and in lambs castrated after this 

 sensitivity developed, there was a tendency for the sensitivity to be lost after 

 a period of time. 



The above results indicate that the development of the temperature sensitivity 

 is dependent upon some substance, probably the testes hormone. The stage of 

 development of testes removed at the time of studying the dartos strips is being 

 studied, and further work is being planned to test the above hypothesis. 



Progeny Performance in Sheep. (Clarence H. Parsons.) A cooperative project 

 with the U. S. D. A. was started in 1932 using the Southdown and Shropshire 

 flocks of sheep in order to determine the inherent capacity of specific families or 

 strains of sheep for the utilization of feed and the production of meat and wool, 

 and to improve them by a study of the manner in which they transmit these 

 characters. 



A specialist from the Bureau of Animal Industry of the U. S. D. A. visits the 

 college each fall to counsel with a committee from the college in grading the 

 type and body characteristics of all lambs born that year. He also visits the 

 college each spring at shearing time to assist in grading and sampling the wool 

 from all the sheep. The carcasses of all sheep slaughtered at the college are graded . 

 The sheep are weighed regularly and accurate feed records kept. 



This work provides a definite and complete record of each sheep which may be 

 used for comparing daughters with their dams, etc., and which is on file after 

 the individual is no longer available for inspection. The contact with a specialist 

 of the Bureau of Animal Industry helps to keep the records uniform and com- 

 parable with similar records at other institutions. The records of this work will 

 be of increasing value as time goes on and more records are available. Already 

 much valuable information has been secured regarding the offspring of a few 

 rams, and the present Southdown ram was secured on the basis of similar records 

 kept on his lambs at the Morgan Horse Farm, Middlebury, Vermont. 



