Tips for Trimming Your Interservice Interval

One of the keys to getting cows and heifers bred efficiently is minimizing the time between their first insemination and subsequent ones, if needed. The "interservice" interval also is sometimes called the "interbreeding interval" or "reinsemination interval."

Regardless of how it is labeled, it is simply the number of days between services—the time from one AI event to the next. While the interval can be measured on an individual-cow basis, it is most useful to look at an average for the entire herd.

It is common for herds to have interservice intervals of more than 40 days. But achieving a tighter interval will help to increase a herd's pregnancy rate, decrease average days open and shorten calving intervals.

To shorten your interservice interval, heat detection three weeks after insemination is useful, even in a herd relying primarily on timed AI. Heat detection can be improved by focusing on employee training, maintaining good animal identification (including easy-to-read ear tags) and keeping accurate records. There are now handy cell-phone apps that can make it easy for employees to record observed heats.

Activity monitoring systems are another option for efficiently and accurately capturing heat activity at all hours of the day, lessening reliance on personnel to observe and record heats.

There's a decent chance cows that have not displayed heat signs by 24 days post-insemination are pregnant. But it is important to identify those that are actually open as soon as possible. Pregnancy diagnosis options are becoming more diverse. Among them are:


Rectal palpation, traditionally performed at 35 to 45 days post-insemination;


Ultrasound, which often is done in the 28- to 35-day window, potentially shaving about a week off the interservice interval; and


Pregnancy-associated glycoprotein (PAG) testing, which can be done by analyzing milk or blood around 28 to 32 days.

PAG testing can be advantageous because it can be performed on-farm on a more frequent basis than tests that require a veterinarian or technician to come to the farm. One disadvantage of this very early method of pregnancy diagnosis is that some cows may lose their pregnancies after early testing due to early embryonic death.

There are many rebreeding strategies to return open cows to service. A week can be gained in resynchronization by administering a dose of GnRH one week before the intended date of pregnancy diagnosis. GnRH has no detrimental effects on pregnancy but may be the chosen first step toward resynchrony and timed AI. If the animal is found open a week later, a prostaglandin shot can be administered, possibly followed a few days later by timely AI.

Overall, interservice intervals can be shortened by improving heat-detection strategies, focusing on strategic and timely pregnancy/open-cow diagnosis and expedient resynchronization of animals that otherwise would go too long before reinsemination.