average duration was 8.7 hours, with an average of 7.6 standing events; standing events lasted only 25 seconds per estrus on average. On the first ovulation 50 days after calving, the HeatWatch system detected no standing activity among 41 per cent of the cows, and only one standing event among 52.6 per cent. Cows that showed no standing activity had higher production. Many theories have been put forward to explain why high-producing cows have poorer fertility. Wiltbank's study provides another one. He and his team measured circulating levels of reproductive hormones in the cows and found that high-producing animals tended to have lower levels of estradiol and progesterone. 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. Modelling 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. Wiltbank used the data from this study to predict the probability of successfully detecting standing heat in a cow on her milk production. With four-times-per-day heat detection, the probability of success is about 90 per cent for cows producing about 35 kilograms of milk per day. For cows producing 45 kg per day, the success rate drops to 50 per cent probability, and results are even poorer when heat detection is carried out just once or twice a day. It is also interesting to note in this study that cows exhibited recordable standing behaviour at 93 to 95 days after calving on average. This suggests your breeding program may be more successful if you intensify heat detection and breeding between 95 and 120 days. Recent CanWestDHI data indicate this practice doesn't harm overall profit. An important consideration in managing lactation and calving intervals is to maintain the dry interval at 40 to 70 days. A dry period longer than 70 days has been shown to reduce overall production. Other considerations for successful heat detection include:
average duration was 8.7 hours, with an average of 7.6 standing events; standing events lasted only 25 seconds per estrus on average. On the first ovulation 50 days after calving, the HeatWatch system detected no standing activity among 41 per cent of the cows, and only one standing event among 52.6 per cent. Cows that showed no standing activity had higher production. Many theories have been put forward to explain why high-producing cows have poorer fertility. Wiltbank's study provides another one. He and his team measured circulating levels of reproductive hormones in the cows and found that high-producing animals tended to have lower levels of estradiol and progesterone. 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. Modelling 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. Wiltbank used the data from this study to predict the probability of successfully detecting standing heat in a cow on her milk production. With four-times-per-day heat detection, the probability of success is about 90 per cent for cows producing about 35 kilograms of milk per day. For cows producing 45 kg per day, the success rate drops to 50 per cent probability, and results are even poorer when heat detection is carried out just once or twice a day. It is also interesting to note in this study that cows exhibited recordable standing behaviour at 93 to 95 days after calving on average. This suggests your breeding program may be more successful if you intensify heat detection and breeding between 95 and 120 days. Recent CanWestDHI data indicate this practice doesn't harm overall profit. An important consideration in managing lactation and calving intervals is to maintain the dry interval at 40 to 70 days. A dry period longer than 70 days has been shown to reduce overall production. Other considerations for successful heat detection include:
57904676-Heat-Detection.docx