D.R. Eborn

Effect of postweaning diet on ovarian development and fertility in replacement beef heifers.

Programs for developing replacement heifers are designed for heifers to calve at 2 yr of age and to extend their stayability in the herd and minimize feed cost. The experimental objective was to determine whether developing prepubertal heifers on less dietary energy and to a BW of 55% rather than 65% of mature BW at 14 mo of age would compromise ovarian development and reduce fertility. In a 3-yr study, 8-mo-old Angus (n = 60/yr) and composite MARC II (n = 60/yr) heifers were assigned equally by age, BW, and breed to receive either a low (LG) or high (HG) BW gain diet fed to achieve an ADG of either 0.45 or 0.8 kg/d from 8 to 15 mo of age, including the first 21 d of breeding, and then transferred to pasture. At 14 mo, heifers were housed with fertile bulls for 47 d. Estrus was monitored for 21 d. Within 12 h after detection of estrus, ovarian length and height, preovulatory follicle diam., and antral follicle count (AFC) were measured by transrectal ultrasonography. Corpus luteum (CL) volume and plasma progesterone concentration were measured 5 to 15 d after estrus. Data were analyzed by ANOVA with treatment, breed, and year and their 2-way interactions as independent variables. At breeding, HG heifers were heavier than LG heifers (419.9 vs. 361.8 ± 7.5 kg; P < 0.01); ADG for the treatment period was 0.79 vs. 0.47 ± 0.04 kg/d (P < 0.01), respectively. In 2010 and 2011, 97.2% of heifers were cyclic by 21 d of breeding. Size of the ovary, preovulatory follicle, CL, and AFC did not differ between HG and LG, but preovulatory follicle diam. and ovarian length were greater (P ≤ 0.05) for MARC II vs. Angus heifers. Progesterone concentrations were less for LG vs. HG heifers (P ≤ 0.02), whereas CL volume was not affected by treatment or breed but was correlated positively with preovulatory follicle size (P < 0.01). Total AFC ranged from 5 to 49 and was correlated positively with ovarian volume but was not associated with fertility. A greater proportion of HG vs. LG heifers conceived within the first 21 d of the breeding period (64.4% vs. 49.2% ± 3.8%, respectively; P < 0.01), but overall pregnancy rate was not affected by treatment (83.0% vs. 77.7% ± 3.1%, respectively; P > 0.10). Pregnancy rate was 10% less (P < 0.01) for Angus vs. MARC II heifers. Developing beef heifers at a lesser ADG to a lighter BW (55% vs. 64% of mature BW) at breeding did not influence postweaning ovarian development or AFC or compromise pregnancy rate during the 47-d breeding period.

Is GnRH necessary at CIDR insertion usinga 7-Day CIDR synchronization protocolfor beef heifers?

Introduction The 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.

Heifer synchronization using 7-11 synch or7-11 synch + CIDR

Introduction 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.

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.

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 (PGF2α). 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 (gonadotrophinreleasing 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 postbreeding. A greater percentage (P=0.05) of heifers were pregnant in the CIDR treatment (55%) than in the MGA treatment (33%).

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.

Timed-insemination of beef heifers using Cosynch with one or two initial injections of GnRH

Our purpose was to determine if giving an additional injection of GnRH to beef heifers synchronized with the Cosynch protocol would increase pregnancy rate to timed A.I. Eighty yearling beef heifers received an injection of GnRH, 7 days before receiving an injection of PGF (Cosynch). One half of the heifers were also given an injection of GnRH 14 days prior to the PGF injection (2×GnRH-Cosynch). All heifers were given a GnRH injection 2 days after PGF and inseminated at that time. Pregnancy rate for the 2×GnRH-Cosynch group (40%) was not different than that for the Cosynch group (50%) and was actually numerically lower. This trial suggested that an additional injection of GnRH 1 week prior to the Cosynch protocol was not beneficial in increasing the pregnancy rate of heifers to timed A.I.