92 



THE EEPOET OF THE 



No. 36 



The following table shows the lots of cows, sprayed and imsprayed, with 

 the milk production of each cow for the last ten days of the period and the total 

 milk production of the lot for the same time. 



Table of Milk Production, 



July 17th— July 31st. 



Lot. 



Cow. 



Milk. 



Total 

 Milk. 



Aug. 1st— Aug. 12th. 



Lot. 



Cow. 



Milk. 



Total 

 Milk. 



Aug. 13th— Aug. 25th. 



Lot. 



Cow. 



Milk. 



Total 

 Milk. 



Lbs. 



It must be borne in mind in examining these figures that there is a normal 

 loss in milk production from the middle of July to the end of August irrespective 

 of fly attacks. This loss is due of course to drying up of pastures and was 

 especially evident in 1917. Under normal conditions this loss is gradual, so that 

 in three periods such as used in this experiment the middle Avould represent 

 practically an average of the first and last. 



An examination of the table of milk production shows us that such an 

 average production during the middle period was not evidenced W'here the cattle 

 had heen sprayed for part of the time. 



Lot A during the first period of ten days, sprayed, gave 1,012.8 lbs. of milk, 

 and in the third period of ten days, also sprayed, gave 880 lbs. of milk. During 

 the second, or unsprayed period, the lot, however, gave 911.5 lbs. of milk, which 

 is 35 lbs. or approximately 4 per cent, less than the average of the two sprayed 

 periods. 



Lot B during the first period, when unsprayed, gave 972.9 lbs. of milk and 

 in the third period, also unsprayed, gave 788.2 lbs. During the second, or 

 sprayed, period this lot gave 911.-8 lbs. of milk, which is 31 lbs., or approximately 

 3% per cent, more than the average of the two unsprayed periods. 



A comparison of the production of the two lots serves " more strikingly to 

 point out the benefit derived from spraying. Lot A containing 5 cows in the 

 first ten days when sprayed produced 40 lbs. more than lot B containing 4 cows 

 unsprayed. In the third period lot A of 5 cows sprayed produced 92 lbs. more 

 than lot B of 4 cows unsprayed. In the second period, however, lot B of 4 cows 

 sprayed produced a fraction of a pound more than lot A of 5 cows unsprayed. 



This comparison of the two lots also shows the advantage of morning spraying. 

 Lot A in the first period when sprayed in the afternoon gave only 40 lbs. more 

 than lot B unsprayed, whereas the same cows in the third period, when sprayed 

 in the morning, gave 92 lbs. more than the unsprayed lot. The afternoon spray- 

 ing was less than 50 per cent, efficient as compared with the morning spraying. 



