Research has concluded that your chances of success for detecting heat in high-producing cows are just over half the rate for average milking animals. If you routinely check for heat only once or twice per day, your success rate drops even more.
High-producing cows are in estrus for a shorter period of time than lower producing herd mates. A regular, frequent heat detection routine could detect standing heats more successfully.
Reduced heat detection success tends to be blamed on increased herd sizes and more cows per person, as well as higher milk production per cow.
Higher milk production is related to negative energy balance, which occurs when cows simply can't eat enough to replace body weight used to produce milk.
Researchers have generally attributed delayed first ovulation and smaller follicle size-factors contributing to reduced fertility rates-to negative energy balance.
There was a negative correlation between milk production and estrus duration. The high group had more intense mounting activity, with more mounts during the shorter time period. Still, the lower production group averaged 8.8 mounts versus 6.3 for the high-producing group.
Some interesting and challenging information about estrus events revealed by this study included:
- 15 percent of recorded estruses consisted of only one standing event;
- estruses with recorded standing events-two or more-were detected on average 93 days after calving, with a range of 50 days when heat detection didn't start until 165 days;
- the average duration was 8.7 hours, with an average of 7.6 standing events;
- Standing events lasted only 25 seconds per estrus on average.
Estradiol affects how well a cow shows heat signs. Circulating progesterone levels tend to be low in high-producing cows as well, although their ovaries tend to have higher-than-average amounts of progesterone-producing luteal tissue.
Modeling done as part of this research showed high-producing cows metabolize more estradiol and progesterone through their livers. Since this removes reproductive hormones from circulation more quickly, they are less available to do their job. It could explain the reduced estrus activity.