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Virginia Cooperative Extension - Knowledge for the CommonWealth

Summer "Heat Stress" and heat detection.

Dairy Pipeline: July 2003

Ray L. Nebel
Extension Dairy Scientist,
Reproductive Management
(540) 231-4432

Last summer I had a Master's student (Oscar Peralta) conduct his thesis research on a large commercial dairy located in North Carolina (~1,000 lactating cows) with the primary objective being to evaluate three systems for the detection of estrus. The normal herd personnel conducted visual observations for signs of estrus three times daily at 7:30 a.m., 1:30 p.m. and 11:00 p.m. (during the third milking). Two electronic systems were also used on 266 cows. Between 37 and 45 days in milk cows were fitted with a HeatWatch® (DDx Inc., Denver, CO) pressure sensor that detected mounting activity and an ALPRO® (DeLaval Inc. Kansas City, MO) activity transponder that recorded cow movement. The percent possible heats was calculated similar to the method used by DHI to determine %heats observed (DRMS, Raleigh, NC) so that we could calculate the efficiency of detection for each system. The maximum daily temperature and humidity was used to calculate an index of cow comfort. The months of June, July, and August at this North Carolina dairy were all in the moderate heat stress range with an average maximum temperature for the three months of approximately 96 degrees with a relative humidity of 90%. In combination the three systems detected 72% of the possible heat periods; however, no single system detected greater than 50% of the possible periods of estrus. The conception rate for the 506 inseminations was 19.4% with the 75 cows detected both visually and by the HeatWatch® system having the highest conception rate of 29.3%. The 128 cows detected only in heat visually had the lowest conception rate of 8.6%. Parity influenced conception rates with 26.2% for first lactation, 18% for second and 12% for cows in their third or greater lactation. If the number of pregnant cows resulting from AI is the bottom line for evaluating the performance of the three heat detection systems, studied cows detected by the HeatWatch® system resulted in 11 more pregnancies with 39 fewer inseminations than visual detection. Visual detection resulted in 19 more pregnancies with 50 more inseminations when compared to the activity or pedometer system. The take home message should be that a combination of heat detection methods was superior to any single heat detection system.

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