Cloprostenol sodium and dinoprost tromethamine result in similar artificial insemination pregnancy rates in Bos taurus, Bos indicus, and Bos indicus × Bos taurus cattle synchronized with a Select Synch and CIDR plus timed–artificial insemination protocol

The Professional Animal Scientist 32 (2016):636–646; http://dx.doi.org/10.15232/pas.2015-01493 ©2016 American Registry of Professional Animal Scientists. All rights reserved.

C ldinoprost oprostenol sodium and tromethamine result

in similar artificial insemination pregnancy rates in Bos taurus, Bos indicus, and Bos indicus × Bos taurus cattle synchronized with a Select Synch and CIDR plus timed–artificial insemination protocol R. D. Esterman,* E. N. Alava,* B. R. Austin,* M. J. Hersom,* PAS, D. O. Rae,† M. Elzo,* PAS, and J. V. Yelich*1 *Department of Animal Sciences, and †College of Veterinary Medicine, University of Florida, Gainesville 32611

ABSTRACT Two experiments were conducted to evaluate breed [Angus (AN), Brahman (BR), and varying percentages of BR × AN breeding] and prostaglandin F2α (PGF) type [dinoprost tromethamine (dinoprost) vs. cloprostenol sodium (cloprostenol)] in suckled cows (Exp. 1; n = 504) and 2-yr-old virgin heifers (Exp. 2; n = 309) synchronized with a Select Synch + controlled intravaginal drugreleasing insert and timed-AI protocol (SSCT). On d −7, cows and heifers

Corresponding author: [email protected]

1

received gonadotropin-releasing hormone and controlled intravaginal drug-releasing inserts. At controlled intravaginal drug-releasing insert removal (d 0), cows were stratified by BCS, days postpartum, parity, and breed; heifers were stratified by BCS and breed. In both experiments cattle were randomly allotted to receive either dinoprost (25 mg) or cloprostenol (500 μg). Estrus was detected 3 times per day for 72 h after PGF, and AI was conducted by the am/pm rule. At 72 h after PGF, nonresponders were timed artificially inseminated and received gonadotropin-releasing hormone. The AI pregnancy rates were similar (P > 0.05) between PGF treatments in Exp.

1 (51%) and Exp. 2 (46%). In Exp. 1, AN (52%), 1/4 to 3/8 BR (42%), and 1/2 BR (59%) cows had similar AI pregnancy rates, whereas 1/2 BR (59%) had a greater (P < 0.05) AI pregnancy rates compared with cows with ≥3/4 BR (41%). In Exp. 2, heifer breed had no effect on AI pregnancy rates. In conclusion, dinoprost and cloprostenol in a SSCT protocol yielded similar AI pregnancy rates in cows and 2-yr-old virgin heifers across all breed types; however, AI pregnancy rates were influenced by breed type in cows but not 2-yr-old virgin heifers. Key words: artificial insemination,

Synchronization in Bos indicus × Bos taurus cows

Brahman, cattle, estrous synchronization

INTRODUCTION The gonadotropin-releasing hormone (GnRH) + prostaglandin F2α (PGF) protocol (Thatcher et al., 1989; Pursley et al., 1995) also known as the Select Synch protocol is an effective synchronization protocol in Bos taurus beef cattle (Geary et al., 2000; Dejarnette et al., 2001). However, AI pregnancy rates to this protocol are unacceptable in Bos indicus × Bos taurus cattle because of a limited estrous response after PGF (Lemaster et al., 2001). The AI pregnancy rates of the Select Synch protocol can be improved by adding a timed-AI + GnRH for cows not exhibiting estrus after PGF (Lemaster et al., 2001). Addition of a controlled intravaginal drug-releasing insert (CIDR; Lucy et al., 2001; Larson et al., 2006) to a GnRH + PGF protocol induces estrus in some anestrous cows, which can improve AI pregnancy rates. In Bos indicus × Bos taurus cows, there are studies evaluating modified Co-Synch

+ CIDR protocols (Saldarriaga et al., 2007; Zuluaga et al., 2010; Esterman et al., 2016) but limited studies evaluating the Select Synch and CIDR + timed-AI protocol (SSCT; Esterman et al., 2016). There are 2 types of PGF: one is chemically similar to the uterine-derived PGF called dinoprost tromethamine (dinoprost) and the other is the agonist cloprostenol sodium (cloprostenol). The half-life of cloprostenol in the blood stream is approximately 3 h compared with minutes for dinoprost (EMEA, 2004a,b). Cloprostenol and dinoprost appear to have equal effectiveness to synchronize Bos taurus cattle (Young and Anderson, 1986; Salverson et al., 2002), but there is limited research in Bos indicus and Bos indicus × Bos taurus cattle. Hiers et al. (2003) reported a 5% numerically greater fixed timed-AI pregnancy rate in Bos indicus × Bos taurus cows receiving cloprostenol compared with dinoprost in a Select Synch protocol concurrent with melengestrol acetate. There are no definitive reports in suckled cows and heifers of Bos indicus and Bos indicus × Bos taurus

Table 1. Physical description of cows in Exp. 1 by year and parity with means and ranges for days postpartum, age, BW, and BCS1

Year by parity Yr 1  Primiparous

n  

46

 Multiparous

111

Yr 2  Primiparous

  64

 Multiparous

114

Yr 3  Primiparous

  52

 Multiparous

117

1 2

Mean days postpartum at CIDR2 insertion (range)  

74 (39–95) 66 (37–97)   74 (31–103) 63 (32–84)   72 (29–99) 56 (29–77)

Mean age, yr (range)  

3.0 6.2 (4–14)   3.0 6.1 (4–15)   3.0 6.1 (4–16)

Mean BW, kg (range)  

500 (408–626) 561 (395–707)   519 (381–651) 567 (395–735)   519 (381–650) 562 (416–723)

BCS scale 1 to 9 (1 = emaciated and 9 = obese; Wagner et al., 1988). CIDR = controlled intravaginal drug-releasing insert.

Mean BCS (range)  

5.1 (4.0–6.0) 5.1 (4.0–6.0)   5.2 (4.0–6.5) 5.1 (3.5–6.5)   5.0 (4.0–6.5) 5.3 (3.5–6.5)

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evaluating cloprostenol and dinoprost in a SSCT protocol. Therefore, 2 experiments were conducted to evaluate the effectiveness of cloprostenol compared with dinoprost in a SSCT protocol in suckled cows (Exp. 1) and 2-yr-old virgin heifers (Exp. 2) of Angus, Brahman, and varying percentages of Brahman × Angus breeding.

MATERIALS AND METHODS All experimental procedures were conducted in accordance with acceptable practices as outlined by the Guide for the Care and Use of Agricultural Animals in Agricultural Research and Teaching (FASS, 2010), and animals were handled in accordance with The University of Florida Institutional Animal Care and Use Committee protocol number E821.

Animals, Methods, and Statistical Analysis, Exp. 1 Experiment 1 was conducted over a 3-yr period during the months of February to March at the University of Florida Beef Unit in north central Florida. Three-year-old suckled primiparous (n = 162) and multiparous (n = 342) postpartum cows of varying percentages of Brahman (Bos indicus) and Angus (Bos taurus) breeding were used, and a physical description of the cows is presented in Table 1. The 6 breed types (Table 2) represented included Angus, Brahman, and different percentages of Brahman × Angus breeding with approximately 3/4 Angus 1/4 Brahman, 5/8 Angus 3/8 Brahman (Brangus), 1/2 Angus 1/2 Brahman, and 3/4 Brahman 1/4 Angus. On d −7, all cows were administered a CIDR (1.38 g of progesterone CIDR, Zoetis, Florham Park, NJ) and GnRH (100 μg i.m.; Fertagyl, Merck Animal Health, Summit, NJ), and BCS (1 = emaciated, 9 = obese; Wagner et al., 1988) were recorded. On d 0, CIDR were removed and cows were stratified by BCS, days postpartum (DPP), and parity and randomly allotted to receive either cloprostenol

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Table 2. Physical description (mean ± SD) of cows in Exp. 1 by breed and parity across 3 yr for days postpartum (DPP), cow age, BW, and BCS1

Breed by parity Angus (AN)  Primiparous  Multiparous 3/4 AN 1/4 BR  Primiparous  Multiparous 3/8 AN 5/8 BR  Primiparous  Multiparous 1/2 AN 1/2 BR  Primiparous  Multiparous 3/4 BR 1/4 AN  Primiparous  Multiparous Brahman (BR)  Primiparous  Multiparous 1 2

DPP at CIDR2 insertion

n  

26 80   34 72   18 39   45 90   15 35   24 26

 

83 ± 13 66 ± 13   73 ± 19 60 ± 14   69 ± 21 60 ± 15   76 ± 17 64 ± 13   67 ± 17 57 ± 14   66 ± 18 55 ± 11

Age, yr  

3 6.8 ± 2.8   3 5.7 ± 2.0   3 6.1 ± 1.8   3 6.3 ± 2.6   3 5.8 ± 2.6   3 5.0 ± 1.1

BW, kg  

500 ± 50 561 ± 59   524 ± 55 559 ± 62   530 ± 59 572 ± 65   522 ± 52 568 ± 55   500 ± 58 570 ± 62   514 ± 40 556 ± 80

BCS  

4.7 ± 0.1 4.9 ± 0.1   5.0 ± 0.1 5.0 ± 0.1   5.1 ± 0.1 5.1 ± 0.1   5.3 ± 0.1 5.2 ± 0.1   5.3 ± 0.1 5.4 ± 0.1   5.1 ± 0.1 5.3 ± 0.1

BCS scale 1 to 9 (1 = emaciated and 9 = obese; Wagner et al., 1988). CIDR = controlled intravaginal drug-releasing insert.

(n = 250; 500 μg i.m. Estrumate, Merck Animal Health) or dinoprost (n = 254; 25 mg i.m. Lutalyse Sterile Solution, Zoetis). To aid in estrous detection, each cow received an Estrotect patch (Estrotect, Rockway Inc., Spring Valley, WI) at CIDR removal. Estrus was visually detected for 1 h 3 times daily at 0700, 1200, and 1700 h for 72 h following PGF. Estrus was defined as a cow standing to be mounted by another cow or having a half to full red Estrotect patch. Cows in estrus were inseminated by the am/pm rule. All cows not displaying estrus by 72 h after PGF were timedartificially inseminated and administered GnRH (100 μg i.m.; Fertagyl) between 76 to 80 h after PGF. Cows were inseminated using frozen–thawed semen from multiple sires (yr 1 = 13 sires; yr 2 = 16 sires; yr 3 sires = 19) that were preassigned to cows per mating program of the research unit. The same 3 AI technicians inseminated cows during all 3 yr. Pregnancy was diagnosed 29 d after the

timed-AI using a real-time B-mode ultrasound (Aloka 500V, Corometrics Medical Systems, Wallingford, CT) with a 5.0-MHz transducer during all 3 yr. After the timed-AI, estrous detection and AI continued for an additional 30 d, at which time fertile cleanup bulls were placed with cows for an additional 53 d for a breeding season length of 83 d each year. Breeding season pregnancy rates were determined by rectal palpation approximately 40 d after the end of the breeding season. Estrous response was defined as the number of cows detected in estrus and inseminated within 72 h after PGF divided by the total number of cows treated. Conception rate was defined as the number of cows that displayed estrus, were inseminated, and became pregnant, divided by the number of cows that displayed estrus and were inseminated. Timed-AI pregnancy rate was defined as the number of cows that failed to exhibit estrus and received timed-AI and became preg-

nant, divided by the total number of cows that received timed-AI. Overall AI pregnancy rate was defined as the total number of cows that were inseminated and became pregnant, divided by the total number of cows treated. Breeding season pregnancy rate was defined as the total number of cows that became pregnant during the breeding season, divided by the total number of cows treated. The GLIMIX procedure of SAS (SAS Institute Inc., Cary, NC) was used for the statistical analysis of all categorical data. For statistical analysis of treatment response variables, year was included as a random effect and DPP and BCS were included as covariates. The initial statistical model included PGF treatment, cow breed, AI technician, parity, and all appropriate interactions. This will be referred to as the individual breed model. Cow parity was divided into 2 categories (primiparous vs. multiparous). Terms with a significance value of P ≥ 0.10 were removed from the complete model in a stepwise manner to derive the final reduced model for each variable. If a main effect was determined to be significant (P ≤ 0.05), mean separation was conducted using the LS means function of SAS. Differences were deemed to be significant when P ≤ 0.05 and a tendency when 0.05 < P ≤ 0.10. When covariates were significant (P ≤ 0.05), they were treated as independent variables. The effect of interval from PGF to estrus onset (36, 48, 60, and 72 h after PGF) on conception rate was not significant, so conception data were pooled for the main analysis. There were no effects (P ≤ 0.05) of PGF treatment, breed, or PGF treatment × breed on any of the response variables evaluated. Therefore, an ancillary analysis was conducted where the 6 breed types were pooled into 4 breed groups including (1) Angus, (2) 1/2 Angus 1/2 Brahman, (3) 3/4 Brahman 1/4 Angus and Brahman, and (4) 3/4 Angus 1/4 Brahman and 5/8 Angus 3/8 Brahman (Brangus). This will be referred to as the pooled breed model. The 4 breed groups are representative of breed composi-

Synchronization in Bos indicus × Bos taurus cows

tions commonly used by commercial producers in subtropical regions. Additionally, there are reported differences in ovarian physiology (Alvarez et al., 2000), endocrine physiology (Randel, 1984; Portillo et al., 2008), behavioral estrus (Rae et al., 1999), and synchronized AI pregnancy rates (Rae et al., 1999) across the different breed compositions represented in the study. The statistical model for the pooled breed model was similar to the individual breed model. The model included PGF treatment, cow breed, AI technician, parity, and all appropriate interactions, with year included as a random effect.

all 4 yr. Response variables included estrous response, conception rate, timed-AI pregnancy rate, overall AI pregnancy rate, and breeding season pregnancy rate as described for Exp. 1. After the timed-AI, estrous detection and AI continued for an additional 35 d, at which time fertile cleanup bulls were placed with heifers for an additional 70 to 85 d for a breeding season length of 105 to 120 d. Breeding season pregnancy rates were determined by rectal palpation approximately 40 d after the end of the breeding season. The GLIMIX procedure of SAS was used for the statistical analysis of all categorical data. For statistical analysis of treatment response variables, year was included as a random effect and BCS was included as a covariate. The initial statistical model included PGF treatment, AI technician, breed, and appropriate interactions. As with Exp. 1, this will be referred to as the individual breed model. Terms with a significance value of P ≥ 0.10 were removed from the complete model in a stepwise manner to derive the final reduced model for each variable. If a main effect was determined to be significant (P ≤ 0.05), mean separation was conducted using the LS means function of SAS. Differences were deemed to be significant when P ≤ 0.05 and a tendency when 0.05 < P ≤ 0.10. When a covariate was significant

Animals, Methods, and Statistical Analysis, Exp. 2 In Exp. 2, 2-yr-old virgin heifers of similar breed composition as Exp. 1 were used over a 4-yr period. Physical descriptions of the cattle are presented in Table 3. Heifers were treated with the same synchronization, estrus detection, AI program, and pregnancy detection methods described in Exp. 1. Heifers were inseminated using frozen–thawed semen from multiple sires (yr 1 = 18 sires; yr 2 = 15 sires; yr 3 = 16 sires; yr 4 = 19 sires) that were preassigned to heifers as per the mating program of the research unit. The same 2 technicians inseminated heifers during

Table 3. Physical description (mean ± SD) of 2-yr-old heifers by year and breed in Exp. 2 including BW and BCS1 Item Exp. year  1  2  3  4 Breed   Angus (AN)   3/4 AN 1/4 BR   3/8 AN 5/8 BR   1/2 AN 1/2 BR   3/4 BR 1/4 AN   Brahman (BR) 1

n  

89 74 71 74   51 56 45 70 40 47

BW, kg  

433 ± 38 465 ± 43 470 ± 36 490 ± 37   473 ± 54 473 ± 42 471 ± 38 513 ± 46 458 ± 42 458 ± 42

BCS  

5.5 ± 0.6 5.2 ± 0.5 5.4 ± 0.4 5.4 ± 0.6   5.3 ± 0.5 5.3 ± 0.5 5.2 ± 0.6 5.4 ± 0.5 5.5 ± 0.5 5.2 ± 0.6

BCS scale 1 to 9 (1 = emaciated and 9 = obese; Wagner et al., 1988).

639

(P ≤ 0.05), it was treated as an independent variable. The effect of interval from PGF to estrus onset (36, 48, 60, and 72 h after PGF) on conception rate was not significant, so data were pooled for the main analysis. As with Exp. 1 there were no effects (P > 0.05) of PGF treatment, breed, or PGF treatment × breed on any of the response variables evaluated, so an ancillary analysis was conducted with the 4 breed groups as described in Exp. 1 and will be referred to as the pooled breed model. The statistical analysis for the pooled breed model was similar to the individual breed model. The model included PGF treatment, AI technician, breed, and all appropriate interactions, with year included as a random effect.

RESULTS AND DISCUSSION In Exp. 1, AI pregnancy rates were not different (P > 0.05; Table 4) between cloprostenol and dinoprost treatments when used in the SSCT in suckled Angus, Brahman, and Brahman × Angus cows. When data were analyzed in the individual breed model, there were no (P > 0.05) breed (Table 5) and PGF treatment × breed effects (data not shown) on AI pregnancy rates, indicating that the cloprostenol and dinoprost treatments were equally effective across all breeds in the individual breed model. In nonlactating Bos indicus × Bos taurus cows synchronized with a modified Co-Synch protocol, Hiers et al. (2003) reported no difference in fixed-timed AI pregnancy rates between cloprostenol and dinoprost treatments. Additionally, Salverson et al. (2002) reported similar AI pregnancy rates in Bos taurus heifers synchronized with 14-d melengestrol acetate (MGA) treatment followed 19 d later with either cloprostenol or dinoprost. In a study by Stevenson and Phatak (2010), they observed no differences in fixed-timed-AI pregnancy rates between cloprostenol and dinoprost in dairy cows synchronized with an OvSynch protocol. Therefore, results from the present study add to the literature that there are no signifi-

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Esterman et al.

Table 4. Experiment 1 treatment and parity effects on estrous and conception and pregnancy rates of suckled Angus, Brahman, and Brahman × Angus cows synchronized with a controlled intravaginal progesteronereleasing device (CIDR) and 2 types of prostaglandin F2α (PGF) including cloprostenol sodium (cloprostenol) or dinoprost tromethamine (dinoprost) at CIDR removal1 AI pregnancy rate, No./No. (%)5

Breeding season pregnancy rate, No./No. (%)6

Variable

Estrous response, No./No. (%)2

Conception rate, No./No. (%)3

Timed-AI pregnancy rate, No./No. (%)4

Cloprostenol Dinoprost

142/250 (57) 129/254 (51)

88/142 (62) 80/129 (62)

47/108 (44)a 41/125 (33)b

135/250 (54) 121/254 (48)

232/250 (93) 239/254 (94)

Primiparous Multiparous

72/162 (44)c 199/342 (58)d

50/72 (69)e 118/199 (59)f

31/90 (34) 57/143 (40)

81/162 (50) 175/342 (51)

145/162 (90)c 328/342 (96)d

Means lacking a common superscript within a column tended to differ (P = 0.08). Means lacking a common superscript within a column differ (P < 0.05). e,f Means lacking a common superscript within a column tended to differ (P = 0.10). 1 All cows received gonadotropin-releasing hormone (GnRH; 100 μg) at the initiation of a 7-d CIDR treatment. Cows received either cloprostenol (500 μg) or dinoprost (25 mg) at CIDR removal. Estrus was detected for 72 h, and cows that exhibited estrus received AI based on the am/pm rule. Cows not exhibiting estrus by 72 h received timed-AI and GnRH at 76 to 80 h after PGF. 2 Percentage of cows displaying estrus 72 h after PGF of total treated. 3 Percentage of cows pregnant to AI of the total that exhibited estrus and received AI. 4 Percentage of cows pregnant to timed-AI of the total that received timed-AI. 5 Percentage of cows pregnant during the synchronized breeding of the total treated. 6 Percentage of cows pregnant during the breeding season of the total treated.

a,b c,d

cant differences in AI pregnancy rates between cloprostenol and dinoprost treatments when used across different synchronization protocols and breeds of cattle including Bos taurus, Bos indicus, and cattle with varying percentages of Bos indicus × Bos taurus breeding. As with the AI pregnancy rates, estrous response (54%) did not differ (P > 0.05) between PGF treatments (Table 4). Additionally, there were no (P > 0.05) breed (Table 5), and PGF treatment × breed effects (data not shown) on estrous response in the individual breed model. Esterman et al. (2016) recently reported a similar 72 h estrous response (51%) in Bos indicus × Bos taurus cows, as did Larson et al. (2006; 57%) in Bos taurus cows; cows in both experiments were synchronized with the Select Synch and CIDR + timed-AI protocol with dinoprost as PGF source. Conception rates (62%) did not differ (P > 0.05) between PGF treatments (Table 4). Additionally, there

were no (P > 0.05) breed (Table 5) or PGF treatment × breed effects (data not shown) on conception rates in the individual breed model. Furthermore, conception rates were similar (P > 0.05) in the individual breed model for cows that exhibited estrus at 36 (13/20 = 65%), 48 (70/107 = 65%), 60 (66/113 = 58%), and 72 h (19/28 = 68%) after PGF. There was also no effect (P > 0.05) of AI technician on conception rate. These results indicate that fertility of the PGF-induced estrus, regardless of whether it was induced by cloprostenol or dinoprost, resulted in similar conception rates among suckled cows of Angus, Brahman, and Brahman × Angus breeding. Esterman et al. (2016) in Bos indicus × Bos taurus (66%) and Larson et al. (2006) in suckled Bos taurus cows (67%) reported similar conception rates in suckled cows synchronized with the Select Synch and CIDR + timed-AI protocol with dinoprost as PGF source. Studies in lactating dairy cows (Seguin et al.,

1985; Martineau, 2003), dairy heifers (Martineau, 2003), and Bos taurus beef heifers (Salverson et al., 2002) have all observed similar estrous responses and conception rates between cloprostenol and dinoprost treatments across several different synchronization protocols. Timed-AI pregnancy rate tended (P = 0.08) to be greater in cloprostenol compared with dinoprost treated cows (Table 4), but there were no (P > 0.05) breed (Table 5) or PGF treatment × breed (data not shown) effects in the individual breed model. Whether this indicates that cloprostenol is more effective compared with dinoprost in initiating luteolysis and thereby resulting in more cows ovulating a fertile follicle to GnRH at the timed-AI is unclear. The rate of luteolysis was not be determined because no blood samples were collected before and after PGF treatment in the present study. Although, in estrous cycling Bos indicus × Bos taurus cows synchronized with

641

Synchronization in Bos indicus × Bos taurus cows

Table 5. Experiment 1 individual and pooled breed model effects on estrous and conception and pregnancy rates for suckled Angus (AN), Brahman (BR), and BR × AN cows synchronized with a controlled intravaginal progesterone-releasing device (CIDR) and 2 types of prostaglandin F2α (PGF) including cloprostenol sodium or dinoprost tromethamine at CIDR removal1

Statistical model and breed

Estrous response, No./No. (%)2

Individual    Angus   3/4 AN 1/4 BR   5/8 AN 3/8 BR   1/2 AN 1/2 BR   1/4 AN 3/4 BR  Brahman   P-value Pooled  Angus   3/4 AN 1/4 BR, 5/8 AN 3/8 BR   1/2 AN 1/2 BR   1/4 AN 3/4 BR, Brahman   P-value

62/106 (58) 55/106 (52) 36/57 (63) 70/135 (52) 22/50 (44) 26/50 (52) 0.45   62/106 (58) 91/163 (56) 70/135 (52) 48/100 (48) 0.43

Timed-AI pregnancy rate, No./No. (%)4

Conception rate, No./No. (%)3  

40/62 (65) 30/55 (55) 20/36 (56) 51/70 (73) 12/22 (55) 13/26 (49) 0.52   40/62 (65)ab 50/91 (55)b 51/70 (73)a 27/48 (56)ab 0.10

 

15/44 (34) 22/51 (43) 8/21 (38) 29/65 (45) 8/28 (29) 6/24 (25) 0.45   15/44 (34) 30/72 (42) 29/65 (45) 14/52 (27) 0.20

Breeding season pregnancy rate, No./No. (%)6

AI pregnancy rate, No./No. (%)5  

55/106 (52) 52/106 (49) 28/57 (49) 80/135 (59) 20/50 (40) 21/50 (42) 0.20   55/106 (52)ab,e 80/163 (49)ab,c 80/135 (59)a,d 41/100 (41)b,f 0.04

 

101/106 (95) 99/106 (93) 52/57 (91) 128/135 (95) 47/50 (93) 46/50 (92) 0.91   101/106 (95) 151/163 (93) 128/135 (95) 93/100 (93) 0.77

Means lacking a common superscript within a column differ (P < 0.05). Means lacking a common superscript within a column tended to differ (P = 0.07). e,f Means lacking a common superscript within a column tended to differ (P = 0.10). 1 All cows received gonadotropin-releasing hormone (GnRH; 100 μg) at the initiation of a 7-d CIDR treatment. Cows received either cloprostenol sodium (500 μg) or dinoprost tromethamine (25 mg) at CIDR removal. Estrus was detected for 72 h, and cows that exhibited estrus received AI based on the am/pm rule. Cows not exhibiting estrus by 72 h received timed-AI and GnRH at 76 to 80 h after PGF. 2 Percentage of cows displaying estrus 72 h after PGF of total treated. 3 Percentage of cows pregnant to AI of the total that exhibited estrus and received AI. 4 Percentage of cows pregnant to timed-AI of the total that received timed-AI. 5 Percentage of cows pregnant during the synchronized breeding of the total treated. 6 Percentage of heifers pregnant during the breeding season of the total treated. a,b c,d

a Select Synch protocol with either dinoprost or cloprostenol, Hiers et al. (2001) reported no significant differences in luteolysis as determined by progesterone concentrations before and after PGF treatment. Moreover, the tendency for a treatment effect on timed-AI pregnancy rates could be a result of limited animal numbers that received timed-AI. Therefore, additional research is needed to clarify this finding. Last, there were no effects (P > 0.05) of PGF treatment (Table 4), breed (Table 5), or PGF treatment × breed (data not shown) on breeding season pregnancy rates in the individual breed model.

The main effect of parity influenced some of the reproductive response to the synchronization treatment (Table 4). Parity affected estrous response (P < 0.5), and there was a 14-percentage point increase in multiparous cows that exhibited estrus during the 72 h after CIDR removal compared with primiparous cows. Moreover, conception rate tended (Table 4; P = 0.10) to be greater by 10 percentage points in primiparous compared with multiparous cows. In contrast, timed-AI pregnancy rate and AI pregnancy rate (Table 4) did not differ between primiparous and multiparous cows. However, more (P < 0.05) multipa-

rous cows became pregnant during the breeding season compared with primiparous cows. In suckled Bos taurus (Larson et al., 2006) and Bos indicus × Bos taurus (Esterman et al., 2016) cows synchronized with the same Select Synch and CIDR + timed-AI protocol, parity had no effect on estrous response, conception rate, timed-AI pregnancy rate, and AI pregnancy rates. However, in those studies most primiparous cows were 2 yr old at the initiation of the synchronization protocol. In the present study, all of the primiparous cows had their first calf at 3 yr of age. What effect age at first calving has on response to the

642 synchronization protocol is unclear because there are no contemporary primiparous 2-yr-old cows in the present study. Additionally, estrous cycling status was not determined in the current study, so it is unknown whether a greater number of primiparous cows were cycling at CIDR insertion compared with multiparous cows. Estrous cycling status at the start of a synchronization treatment can effect subsequent pregnancy rates in both Bos taurus (Stevenson et al., 2003; Larson et al., 2006) and Bos indicus × Bos taurus (Lemaster et al., 2001). Breeding season pregnancy rates were 6 percentage points greater (P < 0.05) for multiparous cows compared with the primiparous cows. As indicated previously, there were no effects (P > 0.05) of PGF treatment, breed, or PGF treatment × breed on any of the response variables evaluated in the individual breed model. Consequently, an ancillary analysis was conducted, which will be referred to as the pooled breed model. The breeds were pooled into 4 groups that reflected breed combinations used in commercial cow-calf operations in subtropical regions. Similar to the individual breed model, there were no PGF treatment or PGF treatment × breed effects (P > 0.05) on any of the response variables evaluated in the pooled breed model (data not shown). It is interesting to note that there was no effect of breed on estrous response (Table 5) in either the individual or pooled breed models. It has been well established that estrus can be difficult to detect in Brahman, and Brahman × Angus cattle (Randel, 1984; Galina et al., 1996). However, because cows were managed in mixed breed groups, social interactions and increased number of cows in estrus during the synchronized breeding may have superseded any effect breed had on estrus expression (Landaeta-Hernandez et al., 2002). There tended to be a breed effect (Table 5) on conception rate (P = 0.10) in the pooled breed model. The Angus (65%) and 1/2 Angus 1/2 Brahman (73%) cows had the great-

Esterman et al.

est conception rates of the 4 breed groups. In contrast, cows between 3/4 and 5/8 Angus breeding (55%) had conception rates that were similar to cows that were ≥3/4 Brahman (56%) breeding. With that said, animal numbers are limited in the conception rate data. Further evaluation is necessary to determine what effect breed has on fertility of a detected estrus in Select Synch and CIDR + timedAI protocol. Additionally, follicle growth rates and ovulatory follicle size between the breed combinations need further evaluation. Bos taurus cattle have larger ovulatory follicles compared with Bos indicus cattle (Carvalho et al., 2008; Bastos et al., 2010). In contrast, Alvarez et al. (2000) reported that Brahman (15.6 mm) cows in a subtropical environment had larger follicles from which ovulation occurred compared with Angus cows (12.8 mm). In a group of suckled 1/2 Herford 1/2 Brahman cows synchronized with a Select Synch + CIDR protocol, Saldarriaga et al. (2007) reported that cows exhibiting estrus after CIDR removal had ovulatory follicles averaging 13 mm (range: 9.4 to 15.1 mm) in diameter and 93% of the follicles ovulated. They hypothesized that follicles of larger size should ovulate oocytes that have a greater chance of resulting in a viable pregnancy (Perry et al., 2005). Additionally, the effect that heterosis in the 1/2 Angus 1/2 Brahman genotype has on reproductive success to a synchronized breeding should not be discounted and requires further investigation. There was no affect (P > 0.05) of breed on timed-AI pregnancy rate (Table 5) in the pooled breed model, and timed-AI pregnancy rates ranges from 27 to 45%. In contrast, AI pregnancy rate was affected (P = 0.04) by breed in the pooled breed model (Table 5). The 1/2 Angus 1/2 Brangus cows had a greater (P < 0.05) AI pregnancy rate compared with cows that were ≥3/4 Brahman and tended (P = 0.07) to have a greater pregnancy rate compared with cows that were between 1/4 and 3/8 Brahman. Furthermore, Angus cows tended (P

= 0.10) to have a greater AI pregnancy rate compared with cows that were ≥3/4 Brahman. The literature is clear that there are differences in estrous cycle patterns, ovarian follicular development, and ovulatory capacity of follicles between Bos taurus and Bos indicus cattle (Alvarez et al., 2000; see Sartori et al., 2010). Additionally, Carvalho et al. (2008) indicated that Bos indicus cattle are more sensitive to high concentrations of progesterone, which suppresses luteinizing hormone secretion and reduces follicle growth during a progesterone based synchronization protocol. However, it is unclear how much the suppressive effect of progesterone on luteinizing hormone secretion changes as the percentage of Bos indicus breeding decreases. Portillo et al. (2008) showed that the amount of luteinizing hormone released to a GnRH challenge on d 7 of the estrous cycle decreased as the percentage of Bos indicus breeding increased. Therefore, additional research with CIDR based synchronization protocols that use GnRH and PGF is needed to determine whether protocol effectiveness is influenced by the percentage of Bos indicus breeding. In summary, results suggest that beef cattle producers synchronizing suckled Brahman cows or cows with varying percentages of Brahman × Angus breeding with the Select Synch and CIDR + timed-AI synchronization protocol in subtropical environments should expect variations in AI-pregnancy rates. When included as a covariate in both the individual and pooled breed models, DPP and BCS had no effect (P > 0.05) on any of the response variables evaluated. This is similar to a report by Esterman et al. (2016) in Bos indicus × Bos taurus cows synchronized with the Select Synch and CIDR + timed-AI protocol. As with that study, cows in the present study had an adequate BCS (5.1) with a mean DPP of 68 d at the start of the synchronization treatment. Along with the ability of the CIDR to induce estrous cycles in anestrous Bos taurus (Lucy et al., 2001; Larson et al., 2006) and Bos indicus × Bos

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taurus cows (Esterman et al., 2016), it is not surprising that neither BCS nor DPP affected overall AI pregnancy rates in the current study. In Exp. 2, the 2-yr-old heifers were synchronized with the same Select Synch and CIDR + timed-AI synchronization protocol and had the same breed combinations as Exp. 1. Estrous response, conception rate, timed-AI pregnancy rate, AI pregnancy rate, and breeding season pregnancy rate did not differ (P > 0.05) between cloprostenol and dinoprost treatments (Table 6) when analyzed with either the individual or pooled breed models. Moreover, there were no (P > 0.05) breed (Table 7) or PGF treatment × breed effects (data not shown) for either the individual or pooled breed model for the aforementioned response variables with the exception of estrous response. As observed in Exp. 1, cloprostenol and dinoprost resulted in similar AI pregnancy rates across the different breed types in the 2-yr-old heifers in both the individual and pooled breed models. Salverson et al. (2002) reported similar AI pregnancy rates for cloprostenol and dinoprost treatments administered 19 d after a 14-d

MGA treatment in yearling Bos taurus heifers. Larson et al. (2006) observed an 11.6 percentage point greater AI pregnancy rate in yearling Bos taurus heifers synchronized with the Select Synch and CIDR + timedAI compared with the overall mean of all breeds in the current study. In addition, the AI pregnancy rates for the Angus and Brahman heifers were similar to yearling Bos taurus heifers synchronized with a 14-d MGA treatment followed by PGF 17 or 19 d later (Salverson et al., 2002). There are no comparisons in the literature that have investigated response to the Select Synch and CIDR + timedAI protocol between contemporary groups of Angus, Brahman, and 2-yrold heifers of differing percentages of Brahman × Angus breeding within a single geographic location. There was a breed effect (P < 0.05) on estrous response in both the individual and pooled breed models (Table 7). For the individual breed model, Angus, Brangus, and 1/2 Angus 1/2 Brahman had similar estrous responses, which were greater (P < 0.05) compared with the 3/4 Angus 1/4 Brahman, 3/4 Brahman 1/4 Angus, and Brahman heifers. In

the pooled breed model, the Angus and 1/2 Angus 1/2 Brahman heifers had a similar (P > 0.05) estrous response, but the Angus had greater estrous response compared with the 3/4 to 5/8 Angus and heifers that were ≥3/4 Brahman heifers. In both estrous cycling and prepubertal Bos taurus heifers synchronized with the Select Synch and CIDR + timed-AI protocol, Lamb et al. (2006) reported a 72-h estrous response of 74%, which compares to a 67% estrous response in Angus heifers in the current study. Moreover, the mean 72-h estrous response was 49% for all breed groups in the present study. Estrous cycling status was not determined in the present study, although all heifers were approximately 2 yr old, had moderate BCS (5.4), and should have attained puberty before the synchronization protocol was implemented regardless of breed. Moreover, most Brahman and crossbred Brahman heifers typically attain puberty by 24 mo of age (Reynolds et al., 1963; Plasse et al., 1968). Therefore, it is unlikely that pubertal status had an effect on estrous response in the current study. Estrus can be difficult to detect in Brahman, and Brahman × Angus

Table 6. Experiment 2 treatment effects on estrous and conception and pregnancy rates of Angus, Brahman, and Brahman × Angus 2-yr-old heifers synchronized with a controlled intravaginal progesterone-releasing device (CIDR) and 2 types of prostaglandin F2α (PGF) including cloprostenol sodium (cloprostenol) or dinoprost tromethamine (dinoprost) at CIDR removal1

Variable

Estrous response, No./No. (%)2

Conception rate, No./No. (%)3

Timed-AI pregnancy rate, No./No. (%)4

Cloprostenol Dinoprost

80/153 (52) 72/156 (46)

50/80 (63) 45/72 (63)

18/73 (25)a 32/84 (38)b

AI pregnancy rate, No./No. (%)5

Breeding season pregnancy rate, No./No. (%)6

67/153 (44) 76/156 (49)

136/153 (89) 142/156 (91)

Means lacking a common superscript within a column tended to differ (P = 0.07). All heifers received gonadotropin-releasing hormone (GnRH; 100 μg) at the initiation of a 7-d CIDR treatment. Heifers received either cloprostenol (500 μg) or dinoprost (25 mg) at CIDR removal. Estrus was detected for 72 h, and heifers that exhibited estrus received AI based on the am/pm rule. Heifers not exhibiting estrus by 72 h received timed-AI and GnRH at 76 to 80 h after PGF. 2 Percentage of heifers displaying estrus 72 h after PGF of total treated. 3 Percentage of heifers pregnant to AI of the total that exhibited estrus and received AI. 4 Percentage of heifers pregnant to timed-AI of the total that received timed-AI. 5 Percentage of heifers pregnant during the synchronized breeding of the total treated. 6 Percentage of heifers pregnant during the breeding season of the total treated. a,b 1

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Table 7. Experiment 2 individual and pooled breed model effects on estrous and conception and pregnancy rates for Angus (AN), Brahman (BR), and BR × AN 2-yr-old heifers synchronized with a controlled intravaginal progesterone-releasing device (CIDR) and 2 types of prostaglandin F2α (PGF) including cloprostenol sodium or dinoprost tromethamine at CIDR removal1

Statistical model and breed

Estrous response, No./No. (%)2

Individual    Angus   3/4 AN 1/4 BR   5/8 AN 3/8 BR   1/2 AN 1/2 BR   1/4 AN 3/4 BR  Brahman   P-value Pooled model  Angus   3/4 AN 1/4 BR, 5/8 AN 3/8 BR   1/2 AN 1/2 BR   1/4 AN 3/4 BR, Brahman   P-value

34/51 (67)a 20/56 (36)b,c 25/45 (56)a 37/70 (53)a 14/40 (35)b 22/47 (47)b,d 0.01   34/51 (67)a 45/101 (45)b 37/70 (53)ab 36/87 (41)b 0.02

Timed-AI pregnancy rate, No./No. (%)4

Conception rate, No./No. (%)3  

21/34 (62) 12/20 (60) 16/25 (64) 22/37 (60) 7/14 (50) 17/22 (77) 0.68   21/34 (62) 28/45 (62) 22/37 (60) 34/36 (67) 0.93

 

7/17 (41) 9/36 (25) 4/20 (20) 13/33 (39) 8/26 (31) 9/25 (36) 0.40   7/17 (41) 13/56 (23) 13/33 (39) 17/51 (33) 0.38

Breeding season pregnancy rate, No./No. (%)6

AI pregnancy rate, No./No. (%)5  

28/51 (55) 21/56 (38) 20/45 (44) 35/70 (50) 15/40 (38) 26/47 (55) 0.27   28/51 (55) 41/101 (41) 35/70 (50) 41/87 (47) 0.37

 

47/51 (82) 51/56 (91) 41/45 (91) 66/70 (94) 35/40 (87) 44/47 (94) 0.27   42/51 (82) 92/101 (91) 66/70 (94) 79/87 (91) 0.30

Means lacking a common superscript within a column differ (P < 0.05). Means lacking a common superscript within a column tended to differ (P = 0.07). 1 All cows received gonadotropin-releasing hormone (GnRH; 100 μg) at the initiation of a 7-d CIDR treatment. Cows received either cloprostenol sodium (500 μg) or dinoprost tromethamine (25 mg) at CIDR removal. Estrus was detected for 72 h, and cows that exhibited estrus received AI based on the am/pm rule. Cows not exhibiting estrus by 72 h received timed-AI and GnRH at 76 to 80 h after PGF. 2 Percentage of heifers displaying estrus 72 h after PGF of total treated. 3 Percentage of heifers pregnant to AI of the total that exhibited estrus and received AI. 4 Percentage of heifers pregnant to timed-AI of the total that received timed-AI. 5 Percentage of heifers pregnant during the synchronized breeding of the total treated. 6 Percentage of heifers pregnant during the breeding season of the total treated. a,b c,d

cattle (Randel, 1984; Galina et al., 1996). Granted, heifers were managed in a single group each year, and estrus was evaluated 3 times a day with the aid Estrotect patches, which should have enhanced the ability to detect estrus across all breed groups. Estrus is easier to detect when multiple animals are in estrus at the same time and there is an increase in the mounting activity of heifers (LandaetaHernandez et al., 2002), so this should have also assisted in detecting estrus across all breeds. However, LandaetaHernandez et al. (2002) reported that social dominance affected estrus response in synchronized Angus and Brahman cows managed as a contemporary group, which resulted in domi-

nant animals either within or across breeds not allowing subordinates to mount them during a synchronized estrus. As observed in Exp. 1, conception rate was not affected (P > 0.05) by PGF treatment (Table 6) nor were there breed (Table 7) or PGF treatment × breed (data not shown) effects for the individual or pooled breed models in Exp. 2. Additionally, conception rates were similar (P > 0.05) for the 2-yr-old heifers that exhibited estrus at 36 (5/8 = 63%), 48 (23/40 = 58%), 60 (35/59 = 59%), and 72 h (32/45 = 71%) after PGF. Salverson et al. (2002) observed similar conception rates between cloprostenol and dinoprost treat-

ments administered 19 d after a 14-d MGA treatment in Bos taurus heifers. Lamb et al. (2006) observed a similar conception rate in Bos taurus heifers synchronized with the Select Synch + timed-AI with a CIDR compared with the Angus heifers as well as the other breed combinations used in this study. Rae et al. (1999) also observed similar first service conception rates in Angus, Brahman, and Brahman × Angus heifers synchronized with an estradiol–progestin treatment followed by a 9-d norgestomet implant. Results from the present study suggest that as long as the 2-yr-old heifer exhibits estrus, conception rates will likely be similar among Angus, Brahman, and heifers of varying percentages

Synchronization in Bos indicus × Bos taurus cows

of Brahman × Angus when synchronized with a Select Synch and CIDR + timed-AI protocol. The acceptable conception rates observed in heifers (63%) is similar to observations in Exp. 1 with suckled cows (62%). Together, the results from the heifers and cows suggest that improving estrus expression after CIDR removal in a Select Synch and CIDR + timedAI protocol in Brahman and cattle of varying percentages of Brahman × Angus requires further investigation. Timed-AI pregnancy rate tended (P = 0.07) to be greater for dinoprost compared with cloprostenol treated heifers (Table 7), which is opposite of timed-AI pregnancy rates observed in Exp. 1 with suckled cows. Although, there was no (P > 0.05) heifer breed (Table 7) or PGF treatment × breed (data not shown) effect for either the individual or pooled breed models. Salverson et al. (2002) observed a similar timed-AI pregnancy rate between cloprostenol and dinoprost administered 19 d after a 14-d MGA treatment in a small group of Bos taurus cows. It is unclear why timedAI pregnancy rate was decreased for cloprostenol compared with dinoprost treated heifers in the current study, because all previous reports indicate similar AI pregnancy rates for cloprostenol compared with dinoprost. This tendency may just be a result of limited animal numbers in the current experiment, and it will require further investigation. Larson et al. (2006) observed similar timed-AI pregnancy rates to the current study in Bos taurus heifers synchronized with the Select Synch and CIDR + timed-AI protocol. Breeding season pregnancy rates were similar (P > 0.05) for both the individual and pooled breed models (Table 6). However, there was no (P > 0.05) heifer breed (Table 7) or PGF treatment × breed (data not shown) effect in the individual or pooled breed models for breeding season pregnancy rate.

IMPLICATIONS Producers can use either cloprostenol or dinoprost with equal effec-

tiveness in suckled cows and 2-yr-old Angus, Brahman, and cattle with varying percentages of Brahman × Angus breeding synchronized with the Select Synch and CIDR + timedAI protocol. However, AI pregnancy rates of the Select Synch and CIDR + timed-AI protocol can be influenced by percentage of Brahman breeding in suckled cows but not 2-yr-old heifers, and producers should recognize this when implementing this protocol in their cowherds.

ACKNOWLEDGMENTS This research was supported by USDA-T-STAR 2006-04674.

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Stevenson, J. S., G. C. Lamb, S. K. Johnson, M. A. Medina-Britos, D. M. Grieger, K. R. Harmoney, J. A. Cartmill, S. A. Z. El-Zarkouny, C. R. Dahlen, and T. J. Maple. 2003. Supplemental norgestomet, progesterone, or melengestrol acetate increases pregnancy rates in suckled beef cows after timed inseminations. J. Anim. Sci. 81:571–586. Stevenson, J. S., and A. P. Phatak. 2010. Rates of luteolysis and pregnancy in dairy cows after treatment with cloprostenol or dinoprost. Theriogenology 73:1127–1138. Thatcher, W. W., K. L. Macmillan, P. J. Hansen, and M. Drost. 1989. Concepts for regulation of corpus luteum function by the conceptus and ovarian follicles to improve fertility. Theriogenology 31:149–164. Wagner, J. J., K. S. Lusby, J. W. Oltjen, J. Rakestraw, R. P. Wettemann, and L. E. Walters. 1988. Carcass composition in mature Hereford cows: Estimation and effect on daily metabolizable energy requirement during winter. J. Anim. Sci. 66:603–612. Young, I. M., and D. B. Anderson. 1986. First service conception rate in dairy cows treated with dinoprost tromethamine early post partum. Vet. Rec. 118:212–213. Zuluaga, J. F., J. P. Saldarriaga, D. A. Cooper, J. A. Cartmill, and G. L. Williams. 2010. 2010 Presynchronization with gonadotropin-releasing hormone increases the proportion of Bos indicus-influenced females ovulating at initiation of synchronization but fails to improve synchronized new follicular wave emergence or fixed-time artificial insemination conception rates using intravaginal progesterone, gonadotropin-releasing hormone, and prostaglandin F2α. J. Anim. Sci. 88:1663–1671.