Adding one more prostaglandin shot boosts pregnancies

No one likely relishes the thought of giving an additional prostaglandin shot in the Double-Ovsynch protocol for first timed artificial insemination (A.I.) that already calls for four GnRH and two prostaglandin treatments in just 27 days.

But doing so can dramatically increase pregnancy rates. Some herds which have adopted the program have upward of 90% cows pregnant after three inseminations. "You don't have to have an aggressive synchronization program to increase pregnancies, but it does help," says Paul Fricke, a University of Wisconsin dairy reproductive specialist.

Fourteen studies involving thousands of cows suggest about 15% to 20% of cows have progesterone levels that are not low enough at the time of breeding. "Based on these data, a major problem with the current timed A.I. protocols is that a subset of cows fails to fully regress their corpus luteum resulting in low progesterone levels that limit fertility," he says.

"This likely happens because an Ovsynch protocol sets up some cows to have a seven-day-old corpus luteum at the time of the prostaglandin treatment which is only just beginning to acquire luteolytic activity," Fricke says. But a University of Wisconsin study published last year suggests the second prostaglandin shot can boost pregnancies.

The second shot of prostaglandin is given the week of breeding. In the traditional Double-Ovsynch protocol, a prostaglandin shot is given on Monday, a GnRH shot is given Wednesday and timed A.I. is done on Thursday. Under the revised protocol, an additional prostaglandin shot is also given on Tuesday, 24 hours after the first.

The biggest effect seems to be in second-calf and older cows, a 23% increase in pregnancies with a second prostaglandin shot. First-calf heifer pregnancies climbed 4.6% with the second shot, so the overall herd improvement was 13%. Note: The differences weren't statistically significant because of the relatively low number of cattle, 373, in the trial.

Resynchronization is also critical

Resynchronization after the first breeding is also critical to getting open cows rebred. Here, too, a second prostaglandin shot is warranted.

For these second and subsequent timed A.I.s, Fricke recommends giving a GnRH shot 25 to 32 days after the timed A.I., then doing an ultrasound seven days later. If the cow is open and has a corpus luteum greater than 15 mm, she should be given a prostaglandin shot immediately, a second prostaglandin shot 24 hours later and a GnRH shot eight hours after that. Timed A.I. should occur 12 hours later.

If the cow is open and lacks a corpus luteum or has a corpus luteum less than 15 mm, she should receive a CIDR insert, which is left in for seven days. Then, the same prostaglandin-prostaglandin-GnRH-timed A.I. schedule should be followed.

"Inclusion of a CIDR insert for the 10% to 15% of cows lacking a corpus luteum at this time is a critical aspect for maximizing fertility when using this resynch strategy," Fricke explains.

Increase wait period

Fricke is also urging farmers to increase their voluntary wait periods (VWP) before cows are bred the first time to allow the uterus to more fully recover from calving. In a well-managed herd he worked with, the pregnancy rate with a 50-day VWP was a respectable 25%. But when the herd pushed the VWP out to 76 days, the pregnancy rate jumped to 33%.

"Overall, fertility to first timed A.I. averaged 56%, fertility to second timed A.I. was 50% and fertility to third timed A.I. was 45%," he says. "The first three timed A.I.s occurred from 77 to 180 days in milk, and 90% of the cows became pregnant."

Fricke also emphasizes none of these results are possible without good nutrition, adequate body condition score, low rates of mastitis and good uterine health.

To reduce their use of reproductive hormones, some farms are using electronic activity monitors to find cows in heat and time A.I. But studies show an average of 25% of cows are not cycling by 60 to 70 days in milk. Some form of synchronization can ensure these cows are inseminated before they are too far along in lactation, Fricke says.