Synchronization of estrus and ovulation in dairy heifers using norgestomet, GnRH, and PGF2α

Two experiments were performed using the same treatments. All heifers received two injections of PGF2α 14 days apart. Controls then were inseminated after detected estrus. Heifers assigned to the two treatments also received 6 mg of norgestomet for 8 days beginning 7 days before the second of two PGF2α injections. The heifers in the last treatment also received GnRH 48 hr after the second PGF2α injection to induce ovulation in any heifer not observed in estrus before a fixed-time insemination at 72 hr after PGF2α. In Experiment 1, any control heifer or herifer in the two treatments not detected in estrus by 72 hr after PGF2α received a fixedtime insemination at 72 hr. Heifers receiving GnRH tended to have fewer standing events and a shorter duration of estrus. Fixed-time inseminations reduced conception compared to those after detected estrus. In Experiment 2, when inseminations were performed only after detected estrus, all measures of fertility were unaffected by treatments. These results indicated that addition of norgestomet and(or) GnRH did not improve measures of estrus synchronization or fertility of dairy heifers.; Dairy Day, 1997, Kansas State University, Manhattan, KS, 1997;

We thank two corresponding dairy producers for their assistance with this study:George plus one ear implant containing 6 mg of of 1996.Dairy heifer replacements (n = 287) norgestomet (Syncro-Mate-B implant; Rhone-were treated as in Figure 1.A total of six sires Merieux, Inc., Athens GA) 7 days before the was used between the two dairy farms.All insecond PGF injection; the implant was re-seminations were performed after detected 2" moved 24 hr after PGF .In addition, 100 µg of estrus, and in one herd, a second insemination 2" GnRH (Cystorelin®, Rhone-Merieux, Inc., was given if the heifer was in estrus at the next Athens, GA) was administered 48 after the heat check period.Clean-up bulls were used second injection of PGF (2×PGF +N+G).
after three unsuccessful inseminations.Preg-2" 2" Inseminations were made after detected estrus or nancy was diagnosed by calving date, assuming remaining heifers received one fixed-time insem-that a normal distribution of gestation for Holination 18 hr after GnRH or 72 hr after PGF .
stein heifers was 280 ± 14 days (266 to 294 2" Inseminations were made by one technician days).Any heifer not calving during this period using semen from one sire.Pregnancy was after the treatment insemination became pregdiagnosed by palpation of the uterus and its nant to a repeat insemination or to the clean-up contents between 38 and 52 days after insemina-bull.Estrus-detection, conception, pregnancy, tion.
and calving rates were calculated as in Experi-From 10 control heifers and from five heifers in each of the two treatments, daily blood sam-Results and Discussion ples were collected beginning at the first injection of PGF and continuing until 48 hr after the Experiment 1  1.Interval to the onset of estrus radioimmunoassays.Hormonal concentrations was in the 55-to 67-hr range and not different were plotted for each heifer and normalized to among treatments; however, the estrus-detection the peak in estradiol-17$ that occurred near the rate tended to be greatest in the heifers given onset of estrus after the second PGF injection.
norgestomet without the subsequent GnRH

2"
The estrus-detection rate was calculated as estrus was reduced (P<.05) when GnRH was the proportion of heifers detected in estrus by given at 48 hr after PGF .Similarly, the duravisual observation (twice daily) or by the tion of estrus tended to be less for that same HeatWatch device during the first 96 hr after the treatment, whereas duration of individual standsecond PGF injection.Conception rate was the ing events was not different.Conception, preg-2" proportion of heifers detected and inseminated nancy, and calving rates were similar, but each that became pregnant.Pregnancy rate was the measure tended to be less in the last treatment proportion of heifers that became pregnant of the with GnRH.Heifers that received the fixed-time total treated.Calving rate was the proportion of insemination had lower (P<.01)conception rates heifers that calved of the total treated.The than those inseminated after a detected estrus 2" ment 1.
Profiles of estradiol-17 and progesterone in blood serum were not different between the controls and those additionally treated with norgestomet (Figure 2).
These results indicate that administration of GnRH following the removal of the norgestomet implant may have suppressed estrual behaviors such as standing activity and duration of estrus, despite similar peak concentrations of estradiol-17 near the onset of estrus.

Experiment 2
Results of the second experiment are summarized in Table 2.In this experiment, inseminations were performed only after detected estrus.Es&us-detection, conception, pregnancy, and calving rates were unaffected by treatments.Herd and sire effects were detected for conception and pregnancy rates.Interval to inseminations after PGF, was 1 day later in one herd than in the other herd.In 22.8% of the heifers, double inseminations were made at estrus, and a tendency (P=.13) for improved conception was detected (73.8 vs 60.9%).These results indicate that the addition of norgestomet and(or) GnRH did not improve either estrus synchrony or any measure of fertility.

Figure 1 .
Figure 1.Treatment Protocol for Experiments 1 and 2. Inseminations were performed after detected estrus or at 72 hr after the second PGF,, injection in the absence of estrus in Experiment 1. Inseminations were made only after detected estrus in Experiment 2.= 6-mg norgestomet implant.

Figure 2 .
Figure 2. Daily Concentrations of Estradiol-17 and Progesterone in Blood Serum of Dairy Heifers during 14 Days before and 2 Days after the Second of Two PGF,, Injections (Arrows) in Controls (0; n = 10) or Norgestomet-Treated Heifers (0; n = 10).Concentrations were normalized to the peak of estradiol-17 that occurred near the onset of estrus after the second PGF,, injection.-= norgestomet treatment during 8 days.

1
Segura (Big Sky Dairy) and Joe Segura (Valley View Dairy).Department of Animal Sciences, New Mexico State University, Las Cruces.one fixed-time insemination at 72 hr.A interval from PGF to the onset of estrus, durasecond group of heifers also received two injec-tion and number of standing events per heifer in tions of PGF 14 days apart plus one ear implant estrus, and duration of standing heat were calcu- received