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Virginia Cooperative Extension -
 Knowledge for the CommonWealth

Detection of Early Heats Is Important

Dairy Pipeline: September 1997

by Ray L. Nebel
Extension Dairy Scientist, Reproduction
Virginia Tech

Knowing if cows are cycling and establishing a heat expectancy chart that includes early heats will assist in lowering days to first service and days open. Recently, we monitored 24 cows with the electronic heat detection system HeatWatch( to determine when the first standing heat occurs. Cows were fitted with a transmitter 10 days after calving and were monitored continuously to determine when the first heat occurred and the intensity of that heat compared to later heat periods. Days to first heat averaged 42 days with the earliest heat occurring at 25 days. The last cow to exhibit heat was detected at 71 days. Only 20% of the cows were not detected by 50 days in milk. The intensity of the first heat was approximate half the subsequent heat period with the first heat having an average of 6 standing events (being mounted by herdmate), whereas the second heat period averaged 11 standing events. All but 4 cows (83%) exhibited their second heat period 17 to 24 days following the first detected heat. Thus, detecting the first heat will allow for accurate prediction or anticipation of the next heat, which will usually be after the voluntary waiting period and thus the heat of first service.

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