13 research outputs found
GnRH removal in the 7-11 CO-Synch for timed insemination of beef heifers
The use of artificial insemination can improve genetics, shorten the calving season,
and increase weaning weights by having more
calves born earlier in the breeding season.
Reasons that this technology has not been
used by many producers may include poor
conception rates, time, and cost. Research has been directed at shortening the synchronization time and controlling time of ovulation to eliminate estrous detection using a timed artificial insemination.
Use of a progestin, like the Eazi-Breed
CIDR or melengestrol acetate (MGA), is desirable because they are effective in synchronizing estrus and they can also induce cyclicity in anestrus or prepubertal females. In addition, gonadotropin releasing hormone (GnRH) is commonly included in a synchronization plan because it induces ovulation and synchronizes follicular development. The most common synchronization protocol for beef heifers consists of feeding MGA for 14 days, a prostaglandin injection 17 to 19 days later followed by five days of heat detection for a total duration of 36 to 38 days. Recent research suggests that acceptable conception
rates can be achieved when shortening the
time of MGA to seven days. One example is
the 7-11 CO-Synch which is comprised of
seven days of MGA feeding followed by the
CO-Synch protocol starting on day 11 (see
Figure 1). We have obtained greater then 60%
conception rates using the 7-11 CO-Synch in
previous years. The feeding of MGA not only
synchronizes the estrous cycle but provides
exposure to a progestin that may induce prepubertal heifers to begin cycling. The GnRH injection at day 11 should synchronize the follicular wave which will tighten the timing of ovulation and improve timed insemination conception rates. The disadvantage to this synchronization protocol is that it requires the heifers to go through the chute four times. It
is also believed that heifers are less responsive to GnRH than cows. Thus we tested this protocol with or without the day 11 GnRH injection on conception rates of beef heifers
Ovarian responses and conception rates in response to gNrh, Hcg, and progesterone
We hypothesized that increasing concentrations of progesterone after artificial insemination (AI) would increase fertility. Our objective was to assess changes in ovarian structures, incidence of ovulation, and change in serum progesterone in response to GnRH, human chorionic gonadotropin (hCG), or exogenous progesterone (controlled internal drug release; CIDR insert) treatment, beginning 4 to 9 days after AI (d 0) and again 7 days later (Exp. 1). Blood was collected from 753 cows in 3 herds on days 0 and 7. Ovaries of 162 cows in 1 herd were scanned and mapped to confirm the presence a corpus luteum (CL), and cows were assigned randomly to serve as control (n = 41) or to receive a CIDR insert for 7 days (n = 41), 100 μg of GnRH (n = 40), or 3,300 IU of hCG (n = 40). More cows were induced to ovulate in response to GnRH (60%) and hCG (78%), compared with control (2.4%). Compared with control, cows treated with GnRH or hCG had more induced CL (d 7) and more total CL (d 7), but serum progesterone was increased only in response to hCG. Volume of the original luteal structures was increased by hCG, but tended to be reduced by CIDR and GnRH, compared with luteal volume in control. Total CL volume was increased by hCG, but reduced by CIDR, compared with CL volume of control. In Exp. 2, cows in 5 herds were used to assess conception rates in response to the same treatments described in Exp. 1: control (n = 708), CIDR (n = 711), GnRH (n = 719), and hCG (n = 714). Tendencies for interactions of treatment x herd and treatment x lactation group were detected, but no 3-way interactions were found. Treatment with hCG increased conception rates in second-lactation cows. The CIDR tended to increase, and hCG increased, conception rates in 2 herds, whereas the CIDR decreased conception rates in 1 herd. We concluded that GnRH and hCG effectively induced ovulation, and increased number of CL, but only hCG increased serum progesterone. Further, treatment with the CIDR or hCG increased conception rates, but only in some herds.; Dairy Day, 2006, Kansas State University, Manhattan, KS, 2006
Evaluation of human chorionic gonadotropin as a replacement for GnRH in an ovulation synchronization protocol before fixed-time insemination
Two experiments were conducted to evaluate the difference between gonadotropinreleasing
hormone (GnRH) and human chorionic gonadotropin (hCG) given at the beginning
of a timed AI protocol and their effects on fertility. In Experiment 1, beef cows (n =
672) at six different locations were assigned
randomly to treatments based on age, body
condition, and days postpartum. On day −10,
cattle were treated with GnRH or hCG and a
progesterone-releasing controlled internal
drug release (CIDR) insert was placed in the
vagina. An injection of PGF2α was given and
CIDR inserts were removed on day −3. Cows
were inseminated at one fixed timed at 62 hr
(day 0) after CIDR insert removal. Pregnancy
was diagnosed at 33 days (range of 32 to 35)
after insemination to determine pregnancy
rates. For cows that were pregnant after the
first insemination, a second pregnancy diagnosis was conducted 35 days (range of 33 to 37) after the first diagnosis to determine pregnancy survival. Pregnancy rates were reduced by the hCG injection compared with the GnRH injection (39.1 vs. 53.5%). In Experiment 2, cattle were assigned randomly to three treatments, balanced evenly across the two treatments (GnRH vs. hCG) applied in Experiment 1. Cows were injected with GnRH, hCG, or saline seven days before the first pregnancy diagnosis of cows inseminated in Experiment 1. At the time of pregnancy diagnosis,
cattle found not pregnant (n = 328) were given PGF2α and inseminated 56 hours later. A second pregnancy diagnosis was conducted
35 days (range of 33 to 37) after the
second insemination to determine pregnancy
rate at the second AI. Injections of GnRH,
hCG, or saline had no effect on pregnancy
rates of cows already pregnant to the first insemination. Pregnancy rates after second insemination in cows given an injection of hCG or GnRH, however, tended to be reduced. Percentage of cows pregnant after two timed inseminations exceeded 60% without any need
to detect estrus
Genetic relationships of body condition score with carcass traits in Limousin cattle
Field data from the North American Limousin
Federation was used to determine the
heritability and genetic correlations of body
condition score (BCS) with carcass traits.
Carcass traits included carcass weight, ribeye area, fat thickness, intramuscular fat, and % kidney, pelvic, and heart fat, and all were estimated to be lowly to moderately heritable (0.14 to 0.34). Heritability of BCS was 0.19. Favorable correlations existed between ribeye area and carcass weight (0.50), ribeye area and BCS (0.60), and carcass weight and BCS (0.28). Unfavorable correlations existed among ribeye area and intramuscular fat (-0.40), carcass weight and intramuscular fat (-0.23), and intramuscular fat and BCS (-0.64). These results suggest that selection
for BCS should be effective and would result
in some favorable changes in ribeye area and
carcass weight but with unfavorable change in
marbling
Is GnRH necessary at CIDR insertion using a 7-Day CIDR synchronization protocol for beef heifers?
Beef Cattle Research, 2011 is known as Cattlemen’s Day, 2011The EAZI-BREED CIDR is commonly used in estrous synchronization protocols for
both beef heifers and cows. The label calls for insertion of a progesterone-impregnated
controlled internal drug release (CIDR) for 7 consecutive days with an injection of
prostaglandin F2α given a day before CIDR removal. Animals should display estrus 1 to
3 days after CIDR removal. Modifications to this protocol include administration of
gonadotropin-releasing hormone (GnRH) at the time of CIDR insertion and administration
of the prostaglandin injection at the time of CIDR removal on day 7. Use of
GnRH in conjunction with a CIDR may improve estrous synchronization in beef cows
and fertility at fixed-time insemination but may not be necessary when synchronizing
beef heifers. Our objective was to compare heat response and fertility in heifers with or
without GnRH administration at the time of CIDR insertion. Our hypothesis was that
heifer fertility would be similar between treatments
Comparison of CIDR to MGA in a 7-11 cosynch protocol with timed insemination of beef heifers
Previous research has shown that the 7-11
Cosynch protocol using melengestrol acetate
(MGA) is effective in synchronizing beef
heifers. This study compared MGA and a
vaginal insert containing progesterone (CIDR)
in the 7-11 Cosynch protocol on beef heifers.
Replacement beef heifers (n=179) from three
herds were assigned to MGA or CIDR treatments. Beginning on day 1, heifers on the MGA treatment were fed to consume 0.5 mg
daily of MGA for 7 days. On day 7, the last
day of MGA feeding, the MGA heifers received
an injection of Lutalyse (PGF). Heifers on the CIDR treatment received a CIDR on day 3; on day 9 the CIDR was removed, and heifers received an injection of Lutalyse. On day 11, all heifers received an injection of OvaCyst (gonadotrophin-releasing hormone; GnRH), followed by another injection of Lutalyse® 7 days later (day 18). At 48 hours after the final Lutalyse injection, all heifers were time inseminated and received an injection of OvaCyst. Pregnancy status was determined 33 days after breeding by ultrasonography. No difference in pregnancy
rate was observed between the CIDR (46%) and MGA (47%) treatments
Short-term progestin estrus synchronization with timed insemination for beef heifers: CIDR vs. MGA
Recently, a new product, Eazi-Breed CIDR (a vaginal insert containing progesterone), was approved for estrus synchronization in beef heifers. In previous studies the CIDR
has produced excellent estrus synchrony, but it is more costly than the commonly used progestin, melengestrol acetate (MGA). Therefore, the objective of this study was to compare the CIDR to MGA in a shorter-term
timed breeding program. Seventy-seven commercial beef replacement heifers were assigned to one of two treatments, CIDR (n=38) or MGA (n=39). Each heifer in the CIDR
treatment group received a CIDR on day 1,
which was removed on day 7. The MGA treatment group received MGA in the feed
each day from day 1 to day 6. All heifers in
both treatment groups received an injection of prostaglandin F2α (PGF) on day 7. Forty-eight hours after the PGF injection (day 9), all heifers received an injection of gonadotropin hormone-releasing hormone (GnRH) and were artificially inseminated. Pregnancy status was determined by ultrasonography 29 days post-breeding.
A greater percentage (P=0.05) of heifers were pregnant in the CIDR treatment (55%) than in the MGA treatment (33%)
Relationships between live animal ultrasound predicted intramuscular fat and shear force in fed cattle
Approximately 280 Simmental- and Hereford-
sired feedlot steers were ultrasonically
evaluated for intramuscular fat deposition using CPEC and Critical Vision, Inc. (CVI) ultrasound systems. Warner-Bratzler shear force measurements were taken on steaks from the 13th rib region. Differences between CPEC
and CVI ultrasound and actual marbling
measurements were corrected for bias and
identified as CPEC deviation and CVI deviation. Correlation coefficients and linear models were used to determine if shear force values were associated with amount of intramuscular fat predicted by the ultrasound systems. Correlation coefficients of CPEC deviation and CVI deviation with shear force were 0.18 and 0.15, respectively. This indicates that animals overestimated for marbling by ultrasonic
measures had a tendency to have higher shear force values. However, when the data were evaluated with linear models, which take
many variables into account, we found that
animals with ultrasound marbling predictions
higher than the actual carcass marbling score
were not associated with higher shear force
values. Thus, animals with a higher marbling
prediction are not associated with an unfavorable increase in shear force values. Selecting animals for increased marbling through ultrasound evaluation should have neither a favorable nor unfavorable effect on tenderness
Timed artificial insemination in yearling beef heifers: 7-11 Cosynch VS. Cosynch
Previous research demonstrated that an estrus-synchronization program using a short
period of melengestrol acetate (MGA) feeding
in conjunction with a Cosynch protocol was
effective in synchronizing estrus in postpartum beef cows. The objective of our study was to test this synchronization protocol (7-11 Cosynch) in yearling beef heifers in comparison to a Cosynch protocol. Fifty-eight commercial beef replacement heifers were assigned randomly to two protocols: Cosynch (n=29) and 7-11 Cosynch (n=29). Beginning on day 1, heifers in the 7-11 Cosynch protocol were fed MGA (0.5 mg/heifer daily) for 7 days. On day 7, the last day of MGA feeding, the heifers on the 7-11 Cosynch protocol received an injection of PGF2α. On day 11 all 58 heifers received an injection of GnRH (100 μg). On day 18, all 58 heifers were injected with PGF2α. On day 20, all of the heifers received a 100 μg dose of GnRH by injection and were artificially inseminated. Ultrasonography was used to determine pregnancy status 29 days after breeding. A greater percentage
(P<0.01) of heifers were pregnant after the 7-11 Cosynch treatment (67%) than after the Cosynch treatment (31%). This study demonstrates the potential of achieving
acceptable pregnancy rates using timed artificial insemination in yearling beef heifers
Heifer synchronization using 7-11 synch or 7-11 synch + CIDR
Two aims of heifer estrus synchronization protocols are to induce prepubertal heifers
to start cycling by the beginning of the breeding season and to shorten time spent in estrous detection. Use of progestins such as melengestrol acetate (MGA) and intravaginal
progesterone-releasing devices (CIDR) can induce prepubertal heifers to begin cycling
as well as synchronize estrus in cycling heifers. In past years, a timed artificial insemination protocol (7-11 COSynch) has been tested with varying results. Pregnancy rates using 7-11 COSynch have typically ranged from 40 to 60%. The objective of the current trial was to determine the effect of a similar heat-detection protocol (7-11 Synch) with or without a CIDR. We compared heat response, interval to estrus, and conception rates in beef heifers