J.A. Cartmill

Conception rates of dairy cows following early not-pregnant diagnosis by ultrasonography and subsequent treatments with shortened Ovsynch protocol

Our objective was to determine the feasibility of prompt reinsemination of dairy cows when diagnosed not pregnant 27-29 days after first-service timed AI (TAI). We assumed that a first-wave dominant follicle was present at that time that would ovulate in response to GnRH once precocious luteal regression was induced after administration of PGF(2alpha). Cows that had not been detected in estrus and reinseminated by Days 27-29 after a first-service TAI were diagnosed not pregnant by ultrasonography. Nonpregnant cows from three herds were assigned randomly to receive either no further treatment until reinsemination (controls; n=189); 25mg i.m. of PGF(2alpha) and then reinsemination according to detected estrus (81 of 108) or at 72-80h after PGF(2alpha) treatment (PGF) in the absence of estrus (27 of 108); or 25mg i.m. of PGF(2alpha) followed by 100 microg i.m. of GnRH 48h later (PGF+GnRH) and then reinsemination after detection of estrus (9 of 160) or at 16-20h after GnRH (151 of 160). Blood samples were collected at the time of the not-pregnant diagnosis and again 48h later. Concentrations of progesterone before treatment with PGF(2alpha) were elevated (<1ng/ml) in 61% of the cows when PGF(2alpha) was administered and 81% of the cows given PGF(2alpha) had low (<1ng/ml) concentrations of progesterone 48h after PGF(2alpha). Treated cows were re-inseminated earlier (P<0.01; 31+/-1days) after first-service TAI than controls (55+/-1days). Conception rates after treatment were not different among treatments: PGF (22%), PGF+GnRH (23%), and control (23%). Average intervals from calving to conception were 22-23 days less (P<0.001) in treated cows than in controls. We concluded that treating nonpregnant cows with PGF(2alpha) on Days 27-29 after insemination produced acceptable conception rates when inseminations were made after detected estrus or when TAI was used after GnRH treatment. Further, both treatments reduced days between first-service TAI and second inseminations, and days from calving to conception.

Effectiveness of Select Synch (Gonadotropin-Releasing Hormone and Prostaglandin F2α) for Synchronizing Estrus in Replacement Beef Heifers1

Our objective was to determine if a 7-d, gonadotropin-releasing hormone (GnRH) + prostaglandin F2α (PGF2α) protocol (Select Synch) was effective for synchronizing estrus in replacement beef heifers compared with two traditionally used programs. Heifers (n = 637) consisting of Angus, Hereford, Simmental, and Hereford × Angus breeding at three Kansas locations were assigned randomly to each of three treatments: 1) melengestrol acetate (MGA●; 0.5 mg/d per heifer for 14 d) starting on d –31 plus 25 mg of PGF2α administered 17 d later (d 0; MGA + PGF2α; n = 301); 2) two 25-mg injections of PGF2α given 14 d apart (d –14 and 0; 2 × PGF2α; n = 176); or 3) injection of 100 mg of GnRH (d –7) followed by 25 mg of PGF2α (d 0; Select Synch; n = 160). Twice daily observations for estrus began on d –5 and continued until at least d 10. Inseminations were performed 10 to 14 h after first detected estrus. Pregnancy was diagnosed by transrectal ultrasonography between 33 and 37 d after insemination. A greater (P<0.05) percentage of heifers on the MGA + PGF2α (83%) treatment than on the Select Synch (73%) or 2 × PGF2α (71%) treatment were detected in estrus during the target breeding week. Average interval to estrus from the second or only injection of PGF2α was greater (P<0.001) after MGA + PGF2α (72.1 ± 2.5 h) and 2 × PGF2α (71.3 ± 2.5 h) treatments than after the Select Synch (54.3 ± 2.4 h) treatment. Overall conception and pregnancy were not different. There were treatment × location interactions for conception and pregnancy rates. All three programs synchronized estrus, but overall, because more heifers in the MGA + PGF2α treatment were detected in estrus during the target breeding week, this protocol tended to be most effective.

Supplemental progestin increases pregnancyrates in suckled beef cows

In two experiments, combining a source of progestin with the ovulation synchronization protocol using gonadotropin-releasing hormone plus prostaglandin F2α (GnRH + PGF2α) tended to increase or statistically increase pregnancy rates in suckled cows compared to GnRH + PGF2α alone. These improvements were accomplished without any detected estrus when cows were inseminated and received a second injection of GnRH at 48 hr after PGF2α.

Presynchronization of estrous cycles in dairy cows before ovsynch + CIDR and resynchronization of repeat estrus using the CIDR

Postpartum anestrus is one of the major limitations to achieving acceptable pregnancy rates. The Ovsynch protocol is an excellent tool to improve reproductive efficiency of dairy cows because it can induce estrous cycles in anestrous cows. In the first experiment, administering two PGF2 injections to lactating dairy cows 14 days apart with the second injection given 12 days before the Ovsynch protocol increased (P<0.05) pregnancy rate by 10 percentage points in cycling and noncycling cows. Inserting a progesterone-releasing insert (CIDR) for 7 days during the Ovsynch protocol did not further increase pregnancy rates. In a second experiment, a resynchronization treatment consisting of a used CIDR inserted for 7 days from days 13 to 20 after insemination increased (P<0.05) embryo survival from day 30 to 58 by 11 percentage points but failed to increase overall rate of return to estrus and conception rate at the second AI (first eligible estrus after first AI).; Dairy Day, 2001, Kansas State University, Manhattan, KS, 2001;

Anestrus in lactating dairy cows before ovulation synchronization

The incidence of anestrus in dairy cattle prior to first inseminations carried out after a minimum of 60 days postpartum ranged from 4 to 58% in first-lactation cows and 14 to 50% in older cows. Dairy cows with more days in milk, older than 2 years, and in better body condition (probably reflective of greater postpartum dry matter intakes) were more likely to cycle than thinner cows. Cows that were not cycling before the first week of insemination conceived at lower rates and took longer to become pregnant.

Synchronizing estrus in replacement beefheifers using select synch, MGA, AND PGF2

The Select Synch protocol (GnRH at day 7, PGF2 at day 0, AI at detected heat) was compared to protocols using either MGA + prostaglandin (Colorado system) or two injections of prostaglandin to synchronize estrus in replacement heifers at three locations. Percentage of heifers detected in heat before, during, or after the target breeding week was not different among treatments but varied in percentages among locations. Overall conception rates ranged from 64 to 69%. Pregnancy rates varied from 46 to 56% and tended to be greatest in the MGA + PGF2 treatment. Costs of these treatments ranged from

Pregnancy rates in dairy cattle after three different, timed, breeding protocols

3.50 to

Fixed-time inseminaton of suckled beef cows. 2. Cosynch and progesterone

8 and were lowest for the MGA + PGF2 protocol.

Increasing pregnancy rates at first service in dairy cows exposed to high ambient temperatures before and after calving

Synchronizing ovulation enables dairy producers to inseminate cows by appointment rather than after detected estrus. Three different, timed artificial insemination protocols using different combinations of prostaglandin F2α and gonadotropin-releasing hormone were used to synchronize ovulation in 702 lactating Holstein cows. Cyclicity, pregnancy rate, and embryonic survival rate from each treatment were compared. Our results indicate that all three treatments produced acceptable pregnancy rates in first lactation cows. However, for cows in their second or greater lactation, the treatment using prostaglandin F2α 12 days before the Ovsynch protocol improved pregnancy rates more than the other two.

Supplemental progesterone increases pregnancy rates and embryo survival in lactating dairy cows

Recent studies have identified the effectiveness of using GnRH + PGF2 to synchronize estrus and ovulation in beef cattle (1998 Cattlemen’s Day Report; pp 34-36). This protocol (known as Select Synch) requires an injection of GnRH 7 days before PGF2, which is given on the first day of the breeding season. Cows then are observed for estrus and inseminated. This protocol requires three separate handlings through the working chute (two for hormone injections and one for AI). The handling depends on when heat occurs. Pregnancy rates (number of pregnant cows/number of cows treated) have exceeded 50% using this protocol in other studies.