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Beware of being 'average'
The optimum age at first calving has repeatedly been shown to range from 22 to 24 months of age. However, Paul Fricke, reproduction specialist at the University of Wisconsin-Madison, cautions against using average age at first calving as a benchmark because the “average” can be deceiving. Instead, Fricke recommends that 24 months of age be considered a maximum.
Consider two herds that both have an average age of 14 months at first breeding. The first herd only detects and breeds 50 percent of the heifers that are in heat and has a conception rate of 40 percent. The average age at first calving is 25.7 months, which appears to be close to the goal of 24 months. However, a closer look reveals that, by 15 months of age, only about 40 percent of the heifers are bred and will calve by 24 months of age. By 21 months of age, nearly 10 percent of the heifers in this herd are still open, meaning they will calve at 30 months or even older.
The second herd finds and breeds 80 percent of the heifers that are in heat and has an excellent conception rate of 70 percent. In this herd, 80 percent of the heifers are bred by 15 months of age, and the average age at first calving is 24 months.
In order to calve by 24 months of age, heifers need to become pregnant at 14 to 15 months of age. Fricke recommends Holstein heifers enter the breeding group at 13 months of age, 875 pounds and 50 inches at the withers.
Source: Dairy Calf and Heifer Association
Economics of sexed semen
In a recent issue of the Journal of Dairy Science, researchers from the University of Minnesota published the results of a study investigating the effects of using sexed semen in heifers on reproduction, health and production during their first lactation. They studied 1,371 heifers on two California dairies. All heifers received prostaglandin when they entered the breeding group and were bred when estrus was detected based on removal of tail paint. Heifers that did not show estrus continued to receive prostaglandin every 14 days until estrus was detected. For the first insemination, heifers were either bred with sexed or conventional semen. Heifers that displayed estrus after first insemination were re-bred up to 11 times with conventional semen.
In one herd, heifers bred with sexed semen entered the breeding group 21 days earlier than those bred with conventional semen. As a result, heifers bred with sexed semen were bred for the first time at a slightly younger age than those bred with conventional semen (13.1 versus 13.8 months of age). There was no difference in age at first service for heifers in the other herd (13.0 months). Over half (52 percent) of the heifers bred with conventional semen became pregnant after their first service, compared to approximately 40 percent of heifers bred with sexed semen. Semen type did not affect pregnancy loss after first service, but the two herds had different rates of early loss. Seventy percent of heifers that began the study calved in the study herds. Most heifers removed from the study were sold as replacements; heifers that conceived to their first breeding were more likely to be sold as replacements. Among these, heifers bred to sexed semen were more likely to be sold than those bred to conventional semen.
Looking at heifers that were only bred once, sexed semen resulted in 86 percent female calves, compared to 48 percent female calves born from conventional semen. There were no differences between semen types in gestation length, calving difficulty or incidence of retained placenta or metritis. However, heifers bred with sexed semen were more likely to deliver a dead calf than those bred with conventional semen (8 percent of female and 15 percent of male calves from sexed semen were born dead; 1 percent of female and 5 percent of male calves from conventional semen died). Even though heifers bred with sexed semen had more calves born dead, 79 percent of the heifers bred with sexed semen delivered live, female calves compared to 47 percent of the heifers bred with conventional semen.
When all heifers were included in the analysis, there was a longer interval between first breeding and first calving for heifers initially bred to sexed semen (10.2 versus 9.9 months) due to greater pregnancy loss after first service in heifers bred with sexed semen. Of all the heifers initially bred with sexed semen, 61 percent delivered live, female calves compared to 50 percent of heifers bred with conventional semen.
Semen type did not affect overall risk of culling, first lactation milk yield or heifers’ ability to breed back after their first calving. Although the rearing costs were greater for heifers bred to sexed semen, the costs to produce a female calf were lower ($809 versus $1,250) with sexed semen than with conventional. Overall, economic return was negative for all heifers at the end of the first lactation. However, in this study heifers bred to sexed semen had recovered more of their rearing costs than those bred to conventional semen (overall return of -$84 versus -$175) by producing more heifer calves and through sale of sexed semen-bred replacement heifers before calving.
Source: Dairy Calf and Heifer Association
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