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Effect of Warm Weather on Grazing Performance of Milking Cows

Dairy Research Department, Louisiana Agricultural Experiment Station

ABSTRACT

Observations on 3 Jersey and 3 Holstein milking cows during the summer of 1945 at Baton Rouge, Louisiana, gave the following results:

1. Cows showed a progressive rise in body temperature throughout the day. When they left the milking barn at 5: 45 A.M. it averaged 101.7° F.; upon entering the shade of trees at 9 :20 A.M. it was 102.4° F.; after a period of one hour in the shade, 102.6° F.; at 2 :00 P.M., 103.3° F.; and upon entering milking barn at 3 : 00 P.M. it was highest, 103.5° F. During these same respective periods respiration rates were 63, 64, 71, 78, and 79 per minute. Atmospheric temperatures during these periods increased from 73.0° F. at 5:45 A.M. to a high of 86.7° F. at 2:00 P.M.
   
2. Observations of 24-hour grazing periods showed that during two relatively warm days cows grazed less than two hours, 1.9 and 1.8 hours during daytime (between A.M. and P.M. milking periods) but grazed three times as much, 5.7 and 5.5 hours, at night (between P.M. and A.M. milking). Data on two cool days showed daytime grazing 2.4 times as great as for warm days, and 24-hour grazing totals more than one hour longer than for warm days.
   
3. The number of grazing periods averaged 1.4 for daytime and 2.7 for night. Cows seldom had but one important grazing period during the daytime. Three grazing periods were the most common at night and the time spent grazing averaged 5.5 hours, while 3.5 hours were spent lying down and 0.7 hours standing without grazing.
   
4. Results of the study suggest the need for good pasture at night and, especially on warm days, an excellent daytime pasture. There appears to be a need for experimental trials to test the best method of providing supplemental feed to cows during their long periods in shade during warm summer days, and to determine the best methods for making them more comfortable during this same period.
   

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