Fertility after synchronization of estrus in dairy heifers using Fertility after synchronization of estrus in dairy heifers using GnRH, PGF2 α , and Progesterone (CIDR) GnRH, PGF2 , and Progesterone (CIDR)

Our objective was to determine fertility of heifers after synchronization of estrus using PGF 2 (cid:34) , preceded by progesterone, GnRH, or both. Dairy heifers (n = 246) were assigned randomly to three treatments: 1) 50 (cid:58) g of GnRH given 6 d before 25 mg of PGF 2 (d –1) plus a used intravaginal progesterone-releasing insert (CIDR-B; d –7 to 0; CIDR+GnRH); 2) same as CIDR+GnRH without the GnRH (CIDR); and 3) same as CIDR+GnRH without the used CIDR (GnRH). All heifers were fitted with Heat-Watch® patches and characteristics of estrus examined before AI included duration of estrus, number of standing events, and total duration of standing events. In addition, all heifers were observed visually twice daily for estrus. Rates of conception and pregnancy differed among treatments. All of the estrus-synchronization treatments produced acceptable estrus detection and pregnancy rates but the CIDR+PGF 2 (cid:34) treatment was most effective for improving conception and pregnancy rates.


Introduction
The importance of dairy heifers as future replacements has been overlooked, especially in terms of their high fertilit y and excellent expression of estrus rela tive to the ir lactat ing herd mates.Estr us can be synchronized either by shortening the luteal phase with PGF 2" or by artificially extending t he luteal phase with progest ins.I ntr oduced in the early 1980 's, the CIDR-B (Co ntrolled Internal Drug Release; InterAg, Hamilto n, NZ) is an intravaginal insert that provides contr olled release of exog enous progesterone to cattle.The CIDR increases plasma concentrations of pro gesterone in ovariectomized cows.Signs of behavioral estrus and ovulation are suppressed dur ing treatment with progesterone.Short-term treatment with the CIDR produced tight synchrony of estrus, but co nception rates were variable and related to treatment duration.Pregnancy rates have been reported to range from 50 to 82%.The objectives o f the present study were to determine estrual characteristics and fertility of heifers after synchronization of estrus using PGF 2" preceded by progesterone, GnRH, o r bot h.

Procedures
Holste in heifers (n = 246) averaged 13 ± 0.1 months of age (12 to 20 mont hs) and weighed 8 86 ± 4 lb (754 to 1236 lb) prior to treatment.Sixteen replications of the treatments (ranging from 6 to 29 heifers per replicat ion) were conducted between November 1998 andAugust 2001.The dairy heifers were maintained in dry lots with concrete feed aprons and fed a total mixed diet of chopped prairie or alfalfa hay, corn or milo gr ain, soybean me al, and minerals and vitamins to exceed NRC (1989) guidelines for growing heifer s by 15 % for all nutrients.Heifers were assigned randomly to three treatments (Figure 1): 1) 50 :g of GnRH (Cystorelin, Merial, Iselin, NJ) was injected i.m. (d !7), 6 d before 25 mg of PGF 2" (Lutalyse, Pharmacia Animal Health, Kalamazoo, MI) was injected i.m. on d -1, plus a used intravaginal progesterone-releasing insert (CIDR-B, InterAg, Hamilton, NZ) (d -7 t o 0; CIDR + GnRH + PG F); 2 ) same as CIDR + GnRH + P GF witho ut t he GnRH (CIDR + PGF); and 3) same as CIDR + GnRH + PGF without the used CIDR (GnRH + PGF).A HeatWatch® (DDX, Inc., Denver, CO) patch was attached to the rump of each heifer prior to d !7 and maintained in place unt il pregnancy was diagnosed.All dairy heifers also were observed visually twice daily for signs of estrus beginning on d !1.The following measurements were calculated from the HeatWatch® system: number and duration of total standing time and of each individual standing event, duration of estrus (interval between first and last st anding events), and interval from the PGF 2" injection to estrus.
Interval from first standing event after PGF 2" until insemination was known in over 92% o f the dairy heifers; of which over 66% were inseminated between 6 and 16 h after onset of estrus.Two technicians performed inseminations.Pregnancy was diagnosed by transrectal ultrasonography in all heifers once between 27 and 34 d after insemination.
Rates of estrus detection (number of heifers detected in estrus during 7 d after PGF 2" ), conception (number of pregnant heifers divided by number of heifers inseminated), and pregnancy (number of pregnant heifers after synchronized insemination divided by the number of heifers treated) were calculated.Intervals from injection of PGF 2" to visual observation or HeatWatch detection of first standing event were determined.Measures of estrus-detection rate, conception rate, pregnancy rate, interval from PGF 2" to estrus, and concentrations of progesterone wer e ana lyzed using a st atistical model consisting of treatment , season, and their interaction.

Results and Discussion
Distribution of estrus after PGF 2" based on continual surveillance of the HeatWatch system for the dair y heifer s is illus trated in Figure 2.More (P<0.01)than 60% o f the heifers in the CIDR + PGF (67%) and CIDR + GnRH + PGF (75 %) treat ments came into estrus in the 48-to 72-h interval after PGF 2" than in the GnRH + PGF treatment (41%).However, more (P<0.05)heifers in the GnRH + PGF treatment came into estrus during the 24-to 48-h interval (44%) tha n in the other treatments (<8%).
A delayed interval to estrus after CIDR remo val was explained by changes in serum concentrations of progesterone.A CIDR effect (P<0.001) was detected on the day of CIDR removal (day 0) where only 29% of the dairy heifers in the GnRH + PGF treatment had elevated ($1 ng/mL) concentrations of progesterone compared to 77% of the dairy heifers in the two treatments with CIDR.
Table 1 summarizes reproductive traits of heifers in response to treatments.The estrusdetection rates varied from 73 t o 85% and were not different among treatments.Conception rates varied little, from 47 to 69%, but were greater (P<0.05) in the CIDR+PGF treatment compared to the GnRH + PGF treatment.Likewise, pregnancy rates were greater (P<0.05) for heifers in the CIDR+PGF treatment.
Table 2 summarizes the estrual characteristics of the dairy heifers in each treatment.Interval from PGF 2" to estrus and the total number of standing events were affected differently by the CIDR.Interval from PGF2" to estrus was prolonged (P<0.001) by 18-19 hr in the two CIDR treatments compared to that for the GnRH + PGF treatment.In contrast, the pre-estrual supplementation of progesterone via the CIDR tended (P = 0.11) to reduce the number of standing events per estrus by 20%.Duration of standing estrus and total or individual duration of standing events were not altered by treatment.
Seasonal effects were detected for the number of standing events and duration of total and individual standing events.Total standing time was 69 to 81% greater (P<0.05) during spring (100 ± 16 sec) and fall (107 ± 8 sec) than during summer (59 ± 11 sec) and 51% greater (P<0.05) during winter (89 ± 10 sec) than summer.These data provide evidence that administration of progesterone for 7 d before PGF2" produced superior conception and pregnancy rates.The administration of progesterone via a CIDR as described in this study has not been approved by the United States Food and Drug Administration.It is anticipated to be available within the next calendar year.

Figure 2 .
Figure 2. Percentage Distribution of Estrus after PGF2a Injection