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Heat Detection in High Producing Cows
By JOSEPH C DALTON November 6, 2020
Well-trained personnel can accurately identify cows in heat using once-daily tail paint application and subsequent identification of ruffled tailhead hair or lost paint. This system works because the primary sign of heat is when a cow stands to allow a herdmate to mount. Consequently, when an animal stands to be mounted, the mounting animal’s brisket rubs the paint off the tailhead of the animal being mounted. Unfortunately, reading tail paint is not an “all paint present” or “no paint present” proposition, as there are many factors that influence mounting and standing activity, including milk production, lameness, facilities (dry lot, pasture, free stall), and heat stress. The focus here is on milk production.
Researchers at University of Wisconsin-Madison used HeatWatch to investigate the behavioral characteristics of heat in high producing dairy cattle. The HeatWatch estrus detection system includes a transmitter (contained in a patch that is glued to the tailhead), a receiver and supporting software. When activated for a minimum of 2 seconds, the transmitter emits a radio wave that includes transmitter ID number, date, time, and duration of activation. The system works 24 hours a day 7 days a week.
Approximately 300 Holstein cows were divided into low and high milk production groups (average production per cow was 74 and 102 lb. per day, respectively). Milk yield affected the average duration of heat as high producing cows exhibited a shorter heat period than low producers (6.2 vs. 10.9 hours, respectively).
The average number of standing events were fewer for high compared with low producing cows (6.3 vs. 8.8, respectively). Further, nearly 54% of heat periods for high producing cows, as compared to 32% for low producers, were classified as short duration, low intensity.
The mechanism by which high milk production alters the expression of heat is not completely understood. Other Wisconsin researchers reported the plane of nutrition necessary for high milk production increases liver blood flow and metabolic clearance of steroid hormones. Estradiol, a steroid produced by the preovulatory follicle, plays an important role in reproduction, as it acts on the brain to induce behavioral heat. Lower circulating concentrations of estradiol have been reported in high producing cows. Apparently, increased metabolic clearance of estradiol may contribute to the altered expression of heat in high producing cows, resulting in increased difficulty in identifying these cows in heat.
Certainly, as high producing cows exhibit fewer overall standing events, coupled with a high proportion of heat periods classified as short duration, low intensity, it makes sense that many high producing cows will exhibit a “partial rub” or “half rub” where only a portion of the paint applied to the tailhead in a once daily tail paint system would be removed. Herein lies the value of an appropriate decision-making process, using secondary signs such as increased activity, clear mucous discharge from the vulva, swelling and redness of the vulva, in addition to accurate records describing days since last AI or last heat, to aid in the determination of whether such a cow is in heat. The facts are high milk producing cows do come into heat; however, the signs based on standing behavior are more subtle than those from lower producing cows.