Abstract
Two experiments were conducted to evaluate the effects of a high concentrate, s.c. PGF2α compared with a conventionally concentrated, i.m. PGF2α in estrus synchronization protocols for heifers. In Exp. 1, 869 Angus-based beef heifers were enrolled at 8 locations. All heifers were exposed to the 7-d CO-Synch + controlled internal drug release (CIDR) estrus synchronization protocol. On day 7 of the protocol heifers received 100 µg of GnRH i.m., and a CIDR insert for 7 d. On day 0, at CIDR removal, estrous detection patches were applied to heifers and, within location, heifers randomly received 1 of 2 PGF2α treatments: 5 mL of Lutalyse i.m. (CONTROL; n = 434) or a 2 mL of Lutalyse HighCon s.c. (HiCON; n = 435). A second GnRH injection was administered at 54 ± 2 h and heifers were fixed-time AI (TAI). Heifers were evaluated for estrous activity at TAI by determining the activation of estrous detection patches. Pregnancy rates to AI (PR/AI) were diagnosed by transrectal ultrasonography between 35 and 55 d after TAI. The percentage of heifers exhibiting estrus between day 0 and TAI did not differ (P = 0.68) between CONTROL and HiCON treatments (47 vs. 46 ± 4%, respectively). Additionally, PR/AI were similar (P = 0.65) between CONTROL and HiCON treatments (46 vs. 45 ± 3%). In Exp. 2, 190 Angus-based beef heifers were enrolled at 2 locations. Heifers were exposed to the melengestrol acetate (MGA)—PGF2α protocol where they were offered 0.5 mg MGA per day from days 1 to 14. On day 33, heifers were randomly assigned to receive CONTROL (n = 95) or HiCON (n = 95) treatment, and estrous detection aids were applied. Heifers were exposed to AI 12 h after detection of estrus. Heifers not detected in estrus at location 1 received a second PGF2α injection 6 d after the initial PGF2α injection and were placed with fertile bulls. Heifers at location 2 that did not express estrus were administered 100 µg of GnRH i.m. and exposed to TAI 96 h after the initial PGF2α injection. Transrectal ultrasonography was used to diagnose PR/AI between 51 and 57 d after the initial PGF2α injection. The percentage of heifers exhibiting estrus during the estrus detection period was similar (P = 0.40) between CONTROL and HiCON treatments (82 vs. 87 ± 4%). Furthermore, PR/AI were similar (P = 0.62) between CONTROL and HiCON treatments (60 vs. 65 ± 5%). In summary, the 2 concentrations and corresponding routes of administration of PGF2α were similar in efficacy at synchronizing estrus in beef heifers.
Keywords: beef heifer, estrus synchronization, prostaglandin F2α
INTRODUCTION
Exogenous hormones and their analogues are used to manipulate the bovine estrous cycle to reduce the amount of labor and time expended on estrus detection. Prostaglandin F2α is a fatty acid hormone commonly administered to cows and heifers as part of estrus synchronization protocols. Administration of PGF2α results in regression of a functional corpus luteum between days 5 and 16 of the estrous cycle (Rowson et al., 1972), and estrus within approximately 3 d (Tervit et al., 1973).
Numerous studies have evaluated the effectiveness of various PGF2α products. No differences were reported between the ability of different PGF2α products to decrease progesterone concentrations (Schams and Karg, 1982; Guay et al., 1988) or induce an estrus response (Plata et al., 1990; Martineau, 2003), and have shown no differences in pregnancy rates (Salverson et al., 2002; Stevenson & Phatak, 2010). The route of PGF2α administration also had no effect on the decline in progesterone concentration, nor on the proportion of cows undergoing luteal regression (Chebel et al., 2007). In addition, heifers treated with PGF2α i.m. or s.c. showed similar intervals from administration to estrus (Edqvist et al., 1975; Colazo et al., 2002) and had similar rates of ovulation (Colazo et al., 2002).
A high concentrate PGF2α product, Lutalyse HighCon (12.5 mg of dinoprost tromethamine/mL; Zoetis Animal Health), was recently been approved for use by the U.S. Food and Drug Administration. According to label directions, Lutalyse HighCon may be administered by i.m. or s.c. injection in bovine females. Subcutaneous administration may reduce the occurrence of blemishes on beef carcasses (Powell, 2013), improve tenderness (Griffin et al., 1998), and reduce the income lost per head at slaughter (Hilton, 2004). To date, no research has been conducted to determine the effectiveness of this product in estrus synchronization protocols for beef heifers.
Therefore, this study was performed to evaluate the efficacy of the high concentrate PGF2α product, Lutalyse HighCon, by determining its effectiveness in estrus response and pregnancy rates in beef heifers. We hypothesized that an s.c. injection of a high concentrate PGF2α would not alter estrus response or pregnancy rates when compared with the administration of a conventional concentrate PGF2α in estrus synchronization protocols for beef heifers.
MATERIALS AND METHODS
All heifers were handled in accordance with procedures approved by each collaborating university’s Animal Care and Use Committee.
Experiment 1
Angus-based crossbred, yearling heifers (n = 869; 406 ± 2 kg BW) were enrolled at 8 locations in 2 states (South Dakota and North Dakota). Herd size ranged from 50 to 220 heifers. Within location, heifers were exposed to the 7-d CO-Synch + controlled internal drug release (CIDR) protocol. On day 7, heifers received a 2-mL i.m. injection of GnRH (Factrel; 100-μg gonadorelin hydrochloride; Zoetis Animal Health, Parsippany, NJ) and a CIDR (EAZI-BREED CIDR; 1.38-g progesterone; Zoetis Animal Health) insert. Heifer BW was recorded at 5 of the 8 locations (SD-1, SD-3, SD-4, SD-7, and ND). On day 0, at CIDR removal, estrous detection patches (Estrotect; Rockway Inc., Spring Valley, WI) were applied, and heifers were randomly assigned to receive 1 of 2 PGF2α treatments (Figure 1). Heifers assigned to the CONTROL treatment (n = 434) received a 5-mL i.m. injection of Lutalyse (5 mg of dinoprost tromethamine/mL; Zoetis Animal Health), whereas those assigned to the HiCON treatment (n = 435) received a 2-mL s.c. injection of Lutalyse HighCon. All heifers received a 100-μg injection of GnRH and were inseminated 54 ± 2 h after CIDR removal. To ensure there were sufficient experimental units to test the hypothesis, a power analyses (using various preliminary observations and published reports) indicated that 393 heifers per treatment would be sufficient to detect 3% difference in pregnancy rates (α = 0.05; β = 0.80).
Figure 1.
Schematic of treatments. All heifers were exposed to the 7-d CO-Synch + CIDR protocol. On day 7, heifers received a 2-mL i.m. injection of GnRH (100-μg gonadorelin hydrochloride; Zoetis Animal Health, Parsippany, NJ) and a controlled internal drug releasing (EAZI-BREED CIDR; 1.38-g progesterone; Zoetis Animal Health) insert. On day 0, at CIDR removal, estrous detection patches (Estrotect; Rockway Inc., Spring Valley, WI) were applied and heifers were randomly assigned to receive 1 of 2 PGF2α treatments. Heifers assigned to the CONTROL treatment (n = 417) received a 5-mL i.m. injection of Lutalyse (5 mg of dinoprost tromethamine/mL; Zoetis Animal Health), whereas those assigned to the HiCON treatment (n = 424) received a 2-mL s.c. injection of Lutalyse HighCon (12.5 mg of dinoprost tromethamine/mL; Zoetis Animal Health). All heifers received a 100-μg injection of GnRH and were exposed to TAI 54 ± 2 h after CIDR removal. Pregnancy diagnosis was performed via transrectal ultrasonography between days 35 and 55 after TAI. Final pregnancy diagnosis was performed at least 35 d after the end of the breeding season (Exp. 1).
Estrous detection patches were utilized for estrus detection between CIDR removal and fixed-time AI (TAI). Heifers were considered to be in estrus when at least 50% of the rub-off coating was removed from the patch, or when the patch was absent at TAI. No less than 10 d after TAI, heifers were exposed to bulls for the remainder of the breeding season at 6 locations (SD-1, SD-2, SD-3, SD-4, SD-7, and ND).
Transrectal ultrasonography (Aloka 500V, Vancouver, BC, Canada or Ibex Pro, E.I. Medical Imaging, Loveland, CO) was performed by 2 experienced veterinarians between days 35 and 55 after TAI to determine the presence of a conceptus heartbeat, thereby assessing pregnancy rates to AI (PR/AI). Final pregnancy rates were determined by transrectal ultrasonography at least 35 d after the end of the breeding season.
Experiment 2
Yearling, Angus-based crossbred heifers (n = 190) were managed at 2 locations. Heifers at location 1 (n = 100; 340 ± 3 kg BW; L1) were managed at the West Central Research and Extension Center near North Platte, NE. Each heifer was offered a ration consisting of 6.4-kg grass hay, 3.6-kg wet corn gluten feed, and 0.45 kg of 1 of 2 mineral supplements.
Heifers were synchronized using a melengestrol acetate (MGA)—PGF2α protocol (Figure 2). Heifers were offered 0.5 mg of MGA (Zoetis Animal Health, Parsippany, NJ) pellets in their diet per day from days 1 to 14. On day 33, heifers were blocked by previous developmental treatments (Springman et al., 2017) and assigned to either CONTROL (n = 50) or HiCON (n = 50) treatment. An estrous detection patch was applied concurrently with the PGF2α injection.
Figure 2.
MGA-PGF2α protocol. MGA (Zoetis Animal Health, Parsippany, NJ) was offered to heifers at a rate of 0.5 mg/d for 14 d. On day 33, heifers were administered either 5 mL of Lutalyse (CONTROL; n = 95; Zoetis Animal Health) i.m. or 2 mL of Lutalyse HighCon (HiCON; n = 95; Zoetis Animal Health) s.c. Estrus detection (ED) was conducted for 6 d following PGF2α treatment at location 1. Heifers not detected in estrus were given a second PGF2α injection and were placed with bulls. Heifers at location 2 that did not express estrus by 96 h after PGF2α treatment were administered 2 mL of GnRH (Factrel; Zoetis Animal Health), and exposed to TAI. Pregnancy was diagnosed via transrectal ultrasonography between 51 and 57 d after initial PGF2α injection. Final pregnancy diagnosis was conducted via transrectal ultrasonography 129 and 107 d after PGF2α treatment, for locations 1 and 2, respectively (Exp. 2).
All heifers were managed together and continuously observed for estrus from days 33 to 39. Heifers were considered to be expressing estrus when at least 50% of the rub-off coating was removed from the patch or when the patch was absent. Heifers were AI 12 h after estrus was detected. Heifers not detected in estrus between days 33 and 39 (n = 16) were given an injection of Lutalyse HighCon and placed with 2 bulls for natural service exposure. Heifers exposed to AI were placed in a separate pasture for 10 d before being placed with those not detected in estrus. Heifers remained with bulls for a 60-d breeding season at a ratio of 1:50. Pregnancy rates to AI and final pregnancy rates were diagnosed via transrectal ultrasonography (Aloka, Hitachi Aloka Medical America Inc., Wallingford, CT) 51 and 127 d after the initial PGF2α injection, respectively.
A second group of yearling, Angus-based crossbred heifers was managed at the Kelly Ranch near Sutherland, NE (n = 90; 326 ± 4 kg BW; location 2, L2) and was offered a ration containing 0.6-kg wet distiller grains, 2.4-kg grass hay, 3.2-kg corn silage, and 0.2-kg balancer pellets. Heifers were synchronized with the MGA-PGF2α protocol as previously described for L1 and assigned randomly to receive CONTROL (n = 45) or HiCON (n = 45) treatment.
Heifers were observed for estrus continuously from days 33 to 36. Heifers detected in estrus were AI approximately 12 h later. Heifers not expressing estrus by 96 h (n = 14) were administered 2 mL of GnRH and TAI. Ten days following AI, 2 bulls were placed with heifers at a ratio of 1:45 during a 40-d breeding season. Pregnancy rates to AI were diagnosed via transrectal ultrasonography 57 d after the initial PGF2α injection, and BW was concurrently recorded. A final pregnancy diagnosis was performed 50 d after the initial pregnancy diagnosis on heifers not diagnosed pregnant to AI, and BW was simultaneously recorded.
Statistical Analysis
The GLIMMIX procedure of SAS (SAS Institute, Inc., Cary, NC) was used for all statistical analyses. For Exp. 1, the model included the fixed effects of treatment, location, and the treatment × location interaction. The response variables analyzed were estrus expression, PR/AI, and final pregnancy rates. For Exp. 2, the model included the fixed effects of treatment, location, and the treatment × location interaction. The response variables analyzed were estrus detection time points, ADG, PR/AI, and final pregnancy rates. Artificial insemination sire and AI technician were distributed evenly among treatments; therefore, these variables were not included in the model. Individual heifer was considered the experimental unit. Means were declared significant for both experiments at P ≤ 0.05, with 0.05 < P < 0.10 considered a tendency.
RESULTS AND DISCUSSION
Experiment 1
Initial BW differed (P < 0.01) among locations, but did not differ (P = 0.49) between treatments (406 ± 2 kg). Body weight among locations ranged from 380.6 ± 4.0 kg at location SD-4 to 432.4 ± 2.2 kg at location SD-7. Estrus response rates for all heifers at all locations are summarized in Table 1. Estrus expression between day 0 and TAI did not differ between CONTROL and HiCON treatments (P = 0.68); however, estrus expression differed among locations (P < 0.01), with the greatest estrus response at location SD-6 (65 ± 5%) and poorest at location SD-5 (36 ± 4%). No treatment × location interaction was detected (P = 0.37). Lactating dairy cows receiving dinoprost tromethamine either i.m. or s.c. had a similar decline in concentrations of progesterone, and the proportion of cows that underwent luteal regression by 12, 24, 36, and 48 h after PGF2α treatment was similar between treatments (Chebel et al., 2007). In addition, beef heifers receiving an i.m. or s.c. injection of dinoprost tromethamine had no difference in estrus response (Colazo et al., 2002). In the current study, the lack of difference between estrus response of CONTROL and HiCON treatment groups indicates that both treatments were equally effective at inducing regression of the corpus luteum when administered in the 7-d CO-Synch + CIDR protocol.
Table 1.
Estrus response at the time of fixed-time AI in heifers after receiving conventional or high concentrate PGF2α (Exp. 1)
| Treatmenta | |||||
|---|---|---|---|---|---|
| Item | CONTROL | HiCON | Overall | SEM | P-value |
| n/n (%) | |||||
| Location | |||||
| SD-1 | 11/25 (44.0) | 16/25 (64.0) | 27/50 (54.0)wxy | 13.9 | 0.15 |
| SD-2 | 15/29 (51.7) | 17/27 (63.0) | 32/56 (57.1)wx | 13.1 | 0.39 |
| SD-3 | 33/70 (47.1) | 30/70 (42.9) | 63/140 (45.0)xyz | 8.3 | 0.61 |
| SD-4 | 13/31 (41.9) | 10/29 (34.5) | 23/60 (38.3)yz | 12.7 | 0.56 |
| SD-5 | 27/63 (42.9) | 18/64 (28.1) | 45/127 (35.4)z | 8.7 | 0.09 |
| SD-6 | 25/40 (62.5) | 29/43 (67.4) | 54/83 (65.1)w | 10.8 | 0.65 |
| SD-7 | 43/110 (39.1) | 38/110 (34.6) | 81/220 (36.8)z | 6.6 | 0.49 |
| ND | 35/65 (53.9) | 41/67 (61.2) | 76/132 (57.6)w | 8.5 | 0.39 |
| Overall | 202/433 (46.7) | 199/435 (45.7) | 3.8 | 0.68 | |
aAll heifers were estrus synchronized using the 7-d CO-Synch + CIDR protocol. On day 7, heifers received a 100-μg injection of GnRH (Factrel; Zoetis Animal Health, Parsippany, NJ) and a CIDR (EAZI-BREED CIDR; Zoetis Animal Health) insert. On day 0, at CIDR removal, estrous detection patches (Estrotect; Rockway Inc., Spring Valley, WI) were applied and heifers were randomly assigned to receive 1 of 2 PGF2α treatments. Heifers assigned to the CONTROL treatment (n = 417) received a 5-mL i.m. injection of Lutalyse (5 mg of dinoprost tromethamine/mL; Zoetis Animal Health), whereas those assigned to the HiCON treatment (n = 424) received a 2-mL s.c. injection of Lutalyse HighCon (12.5 mg of dinoprost tromethamine/mL; Zoetis Animal Health). All heifers received a 100-μg injection of GnRH and were exposed to TAI 54 ± 2 h after CIDR removal. Estrous detection patches were concurrently observed for activation. Heifers were considered to be in estrus when at least 50% of the rub-off coating was removed from the patch, or when the patch was absent.
w,x,y,zPercentages within column for location differ (P ≤ 0.05).
Pregnancy rates to TAI for all heifers at all locations are summarized in Table 2. Pregnancy rate to TAI did not differ between CONTROL and HiCON treatments (P = 0.65); however, there was an effect of location (P < 0.01) on PR/AI, which was greatest at location SD-4 (61 ± 6%), and poorest at location SD-5 (38 ± 4%). No treatment × location interaction was detected (P = 0.18). At the conclusion of the breeding season, final pregnancy rates did not differ between CONTROL and HiCON treatments (P = 0.95). Final pregnancy rates differed (P < 0.01) among location and ranged from 78% to 98% (Table 3).
Table 2.
Pregnancy rates to fixed-time AI in heifers after receiving conventional or high concentrate PGF2α (Exp. 1)
| Treatmenta | |||||
|---|---|---|---|---|---|
| Item | CONTROL | HiCON | Overall | SEM | P-value |
| n/n (%) | |||||
| Location | |||||
| SD-1 | 12/25 (48.0) | 9/25 (36.0) | 21/50 (42.0)yz | 13.9 | 0.39 |
| SD-2 | 9/29 (31.0) | 16/27 (59.3) | 25/56 (44.6)xyz | 13.2 | 0.03 |
| SD-3 | 34/70 (48.6) | 29/70 (41.4) | 63/140 (45.0)yz | 8.3 | 0.39 |
| SD-4 | 22/31 (71.0) | 15/29 (51.7) | 37/60 (61.7)x | 12.7 | 0.13 |
| SD-5 | 27/63 (42.9) | 21/64 (32.8) | 48/127 (37.8)z | 8.7 | 0.25 |
| SD-6 | 19/40 (47.5) | 25/43 (58.1) | 44/83 (53.0)xy | 10.8 | 0.33 |
| SD-7 | 44/110 (40.0) | 40/110 (36.4) | 84/220 (38.2)z | 6.6 | 0.58 |
| ND | 28/66 (42.4) | 28/67 (41.8) | 56/133 (42.1)yz | 8.7 | 0.94 |
| Overall | 195/434 (44.9) | 183/435 (42.1) | 3.8 | 0.65 | |
aAll heifers were estrus synchronized using the 7-d CO-Synch + CIDR protocol. On day 7, heifers received a 100-μg injection of GnRH (Factrel; Zoetis Animal Health, Parsippany, NJ) and a CIDR (EAZI-BREED CIDR; Zoetis Animal Health) insert. On day 0, at CIDR removal, estrous detection patches (Estrotect; Rockway Inc., Spring Valley, WI) were applied and heifers were randomly assigned to receive 1 of 2 PGF2α treatments. Heifers assigned to the CONTROL treatment (n = 417) received a 5-mL i.m. injection of Lutalyse (5 mg of dinoprost tromethamine/mL; Zoetis Animal Health), whereas those assigned to the HiCON treatment (n = 424) received a 2-mL s.c. injection of Lutalyse HighCon (12.5 mg of dinoprost tromethamine/mL; Zoetis Animal Health). All heifers received a 100-μg injection of GnRH and were exposed to TAI 54 ± 2 h after CIDR removal. Pregnancy rate to TAI was recorded between days 35 and 55 after TAI.
x,y,zPercentages within column for location differ (P ≤ 0.05).
Table 3.
Final pregnancy rates in heifers after receiving conventional or high concentrate PGF2α (Exp. 1)
| Treatmenta | |||||
|---|---|---|---|---|---|
| Item | CONTROL | HiCON | Overall | SEM | P-value |
| n/n (%) | |||||
| Location | |||||
| SD-1 | 14/16 (87.5) | 13/17 (76.5) | 27/33 (81.8)yz | 8.8 | 0.21 |
| SD-2 | 28/29 (96.6) | 26/27 (96.3) | 54/56 (96.4)x | 6.8 | 0.97 |
| SD-3 | 69/70 (98.6) | 68/70 (97.1) | 137/140 (97.9)x | 4.3 | 0.74 |
| SD-4 | 26/31 (83.9) | 21/29 (72.4) | 47/60 (78.3)z | 6.5 | 0.08 |
| SD-5b | – | – | – | – | – |
| SD-6b | – | – | – | – | – |
| SD-7 | 105/110 (95.5) | 103/110 (93.6) | 208/220 (94.6)x | 3.4 | 0.59 |
| ND | 18/21 (85.7) | 34/36 (94.4) | 52/57 (91.2)xy | 6.9 | 0.21 |
| Overall | 260/277 (93.9) | 265/289 (91.7) | 2.6 | 0.95 | |
aAll heifers were estrus synchronized using the 7-d CO-Synch + CIDR protocol. On day 7, heifers received a 100-μg injection of GnRH (Factrel; Zoetis Animal Health, Parsippany, NJ) and a CIDR (EAZI-BREED CIDR; Zoetis Animal Health) insert. On day 0, at CIDR removal, estrous detection patches (Estrotect; Rockway Inc., Spring Valley, WI) were applied and heifers were randomly assigned to receive 1 of 2 PGF2α treatments. Heifers assigned to the CONTROL treatment (n = 417) received a 5-mL i.m. injection of Lutalyse (5 mg of dinoprost tromethamine/mL; Zoetis Animal Health), whereas those assigned to the HiCON treatment (n = 424) received a 2-mL s.c. injection of Lutalyse HighCon (12.5 mg of dinoprost tromethamine/mL; Zoetis Animal Health). All heifers received a 100-μg injection of GnRH and were exposed to TAI 54 ± 2 h after CIDR removal. Final pregnancy diagnosis was performed at least day 35 after the end of the breeding season.
bHeifers at SD-5 and SD-6 were not exposed to clean-up bulls after TAI; therefore, they were not included in overall pregnancy diagnosis analyses.
x,y,zPercentages within column for location differ (P ≤ 0.05).
Each location was unique in its management practices, and thus, location affected the estrus synchrony and fertility in this study. Each location was producer-owned and differed in nutrition, facilities, animal handling practices, and individual production goals. Varying management practices among locations may have contributed to the reported differences in estrus response, PR/AI, and final pregnancy rates observed.
Experiment 2
Initial BW was similar (P = 0.36) between treatments (333 ± 4 kg); however, BW differed (P = 0.01) between locations (340 vs. 326 ± 3 kg, L1 vs. L2). Additionally, BW at first pregnancy diagnosis was similar (P = 0.26) between treatments (392 ± 4 kg) but also differed (P = 0.04) by location (386 vs. 397 ± 4 kg, L1 vs. L2). Heifers at L2 had a greater ADG (P < 0.01) between day 33 and AI pregnancy diagnosis compared with heifers at L1 (0.90 vs. 1.3 ± 0.03 kg/d). At final pregnancy diagnosis, heifer BW was similar (P = 0.71) between locations (424 ± 14 kg), and treatment groups (P = 0.85; 425 ± 11 kg). The discrepancy in BW and ADG between locations could be a result of different nutritional management strategies. Heifers at L2 initiated the study at a lower BW, yet due to a higher energy ration fed through the treatment period, may have compensated to reach a similar final BW.
The percentage of heifers detected in estrus is summarized in Table 4 and was similar between CONTROL and HiCON treatments at ≤60 h (P = 0.15), ≤72 h (P = 0.51), and at 72 h (P = 0.27). These data indicate that the percentage of heifers that expressed estrus in the CONTROL and HiCON treatment groups was similar at each interval. There was a tendency (P < 0.08) for a location effect at ≤60 and ≤72 h. The tendency for a location effect on estrus response times was likely a result of differing management practices. The total percentage of heifers observed in estrus throughout the detection period was also similar between treatment groups (P = 0.40) and is comparable to results of a 5-mL i.m. injection of dinoprost tromethamine previously reported (Salverson et al., 2002). Beef heifers administered with dinoprost tromethamine s.c. had similar mean intervals to estrus and rates of ovulation to heifers administered i.m. (Colazo et al., 2002). Heifers in the current study received the same total quantity of dinoprost tromethamine (25 mg/dose), regardless of treatment, therefore, similar estrus response and timing were expected.
Table 4.
Time of estrus for yearling beef heifers given 2 alternate PGF2α injections (Exp. 2)
| Treatmenta | P- valueb | |||||
|---|---|---|---|---|---|---|
| CONTROL | HiCON | SEM | TRT | Location | T × L | |
| Estrus response, % | ||||||
| ≤60 h | 48 | 59 | 5.2 | 0.15 | 0.07 | 0.81 |
| 72 h | 22 | 16 | 4.3 | 0.27 | 0.69 | 0.72 |
| ≤72 h | 71 | 75 | 4.7 | 0.51 | 0.08 | 0.96 |
| Total response | 82 | 87 | 3.9 | 0.40 | 0.85 | 0.40 |
aHeifers were administered 1 of 2 alternate PGF2α products on day 33 as part of a MGA-PGF2α protocol. CONTROL: 5 mL of Lutalyse (Zoetis Animal Health, Parsippany, NJ; n = 95) i.m. or HiCON: 2 mL of Lutalyse HiCon (Zoetis Animal Health; n = 95) s.c.
bTRT: PGF2α injection treatment main effect; Location: location main effect; T × L: PGF2α injection treatment × location interaction.
Heifer pregnancy rates are summarized in Table 5. A treatment × location interaction (P = 0.03) was detected for PR/AI between L1 (44 vs. 64 ± 7%, CONTROL vs. HiCON) and L2 (73 vs. 62 ± 7%, CONTROL vs. HiCON). The PR/AI achieved were similar to those reported in previous studies (Springman et al., 2017; Tibbitts et al., 2017). Final pregnancy rates were similar between treatments (P = 0.11) and did not differ (P = 0.96) by location.
Table 5.
Pregnancy rates of yearling beef heifers given 1 of 2 alternate PGF2α injections (Exp. 2)
| Treatmenta | P- valueb | |||||
|---|---|---|---|---|---|---|
| CONTROL | HiCON | SEM | TRT | Location | T × L | |
| AI pregnancyc, % | 63 | 60 | 5.3 | 0.62 | 0.06 | 0.03 |
| Overall pregnancyd, % | 98 | 93 | 2.7 | 0.11 | 0.96 | 0.85 |
aHeifers were administered 1 of 2 alternate PGF2α products on day 33 as part of a MGA-PGF2α protocol. CONTROL: 5 mL of Lutalyse (Zoetis Animal Health, Parsippany, NJ; n = 95) i.m. or HiCON: 2 mL of Lutalyse HighCon (Zoetis Animal Health; n = 95) s.c.
bTRT: P-value represents the main effects of treatment; Location: P-value represents main effects of location; T × L: P-value represents the treatment × location interaction.
cPregnancy was diagnosed via transrectal ultrasonography a minimum of 51 d after PGF2α treatment.
dFinal pregnancy diagnosis was conducted via transrectal ultrasonography a minimum of 107 d after PGF2α treatment.
The following year, in 2017, additional yearling Angus-based heifers located at WCREC (n = 98) were exposed to an MGA-PGF2α protocol. Heifers were managed the same as L1, with the exception that all heifers received a 2-mL s.c. injection of Lutalyse HighCon on day 33. Heifers were observed for estrous activity for 4 d after PGF2α injection and were AI 12 h after estrus detection. Heifers that were not detected in estrus (n = 13) received a second injection of Lutalyse HighCon and were placed with fertile bulls for a 45-d breeding season. Heifers that were exposed to AI were placed in a separate pasture for 10 d and then placed with the heifers that did not express estrus. The percentage of heifers exhibiting estrus was 52 ± 5% at ≤60 h, 77 ± 4% at ≤72 h, and 24 ± 4% at 72 h, with a total estrus response of 87 ± 3%. The percentage of heifers confirmed pregnant to AI was 70 ± 5%, and final pregnancy rate was 93 ± 3%. This additional data further support the results from Exp. 1 and 2 that Lutalyse HighCon is effective at synchronizing estrus in beef heifers. However, we realize the limitations of the Exp. 2 based on the power of the experiment to determine differences among treatments, but the collective data and nonsignificance of the statistical analyses support our conclusions.
In both experiments, heifers in the HiCON treatment had similar rates of estrus expression when compared with the CONTROL heifers. Furthermore, AI and final pregnancy rates were similar between treatments.
IMPLICATIONS
The beef industry regularly incurs economic losses due to carcass lesions resulting from improper injection technique (Pratt, 2004). Intramuscular injections cause muscle trauma which results in an increase in connective tissue around the site during wound healing; therefore, this tissue damage negatively affects beef tenderness (Boleman et al., 1998) and consumer acceptability of beef (Fajt et al., 2011). Additionally, needle movement which can occur during administration of an i.m. injection may result in a portion of the exogenous product being administered subcutaneously (Powell, 2013). The Beef Quality Assurance program advises producers to use an s.c. route of administration when possible to improve tenderness. Subcutaneous injections may result in a reduced amount of carcass damage and less trimming at slaughter and are thus more favored in the beef industry. Lutalyse HighCon is a high concentrate PGF2α product that may be administered either i.m. or s.c. Lutalyse HighCon is a novel, high concentrate PGF2α product on the pharmaceutical market that is a suitable alternative to conventionally concentrated PGF2α products, such as Lutalyse, in estrus synchronization protocols for beef heifers.
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