2011: Effect of body condition at initiation of synchronization on estrus expression, pregnancy rates to AI and breeding season in beef cows Effect of body condition at initiation of synchronization on estrus expression, pregnancy rates to AI and breeding season in beef cows Ramanathan Kasimanickam,a William D Whittier,b John F. Currin,b John B. Hallc aDepartment of Veterinary Clinical Sciences, Washington State University, Pullman, WA; bDepartment of Large Animal Clinical Science, Virginia Polytechnic Institute and State University, Blacksburg, VA; cNancy M. Cummings Research Education and Extension Center, University of Idaho, Carmen, ID Abstract The objective was to examine the influence of body condition score (BCS) at synchronization initiation on estrus and pregnancy rates. Data were retrospectively collected from beef cattle breedings that occurred between fall 2003 and spring 2008 on 12 beef farms. The cows (N=5510) included in the analysis were synchronized with progesterone based CO-Synch or Ovsynch protocols. The BCS (1- emaciated; 9-obese) of all cows were recorded on Day 0 of synchronization at the time of insertion of a controlled internal drug release device (CIDR; Eazi-Breed™ CIDR®, Pfizer Animal Health, New York, NY). At the time of CIDR removal, pressure sensitive mount detectors (Kamar Heatmount® detector, Kamar Products, Inc., Zionsville, IN) were placed on all cows to aid in identification of cows displaying estrus until artificial insemination (AI). Cows were inseminated at observed estrus or at a fixed time and bulls (approximately 1:40 bull:cow ratio) were introduced 14 days after AI and maintained for a 45 to 50 d breeding period to impregnate cows that failed to conceive to AI. Cows were examined for pregnancy at 55 to 70 days and again at 120 days after AI. The BCS ranged from 3 to 8. The expression of estrus, AI and breeding season pregnancy rates were influenced by BCS (P<0.05). The estrus expression rates were 41.8%, 40.5%, 50.5%, 53.0%, 56.4% and 40.4% for BCS 3 to 8, respectively. The fixed-time AI pregnancy rates were 36.7%, 47.4%, 51.8%, 52.9%, 50.9% and 44.9% for BCS from 3 to 8, respectively. Breeding season pregnancy rates were 74.7%, 78.2%, 86.4%, 90.2%, 89.9%, and 87.9% for BCS from 3 to 8, respectively. In conclusion, a minimum BCS of 5 should be achieved prior to the breeding season to ensure acceptable reproductive performance in beef cows managed on forage. Keywords: Beef cows, body condition score, synchronization, estrus expression, pregnancy Introduction In a beef cattle operation, failure of cows to become pregnant during a breeding season of 85 days is the most important factor reducing net calf crop.1 Optimum reproduction in beef cows is often limited by prolonged postpartum anestrous intervals. Suckling and nutrition are major regulators of the duration of the postpartum anestrous interval. Reduced nutrient intake prepartum results in thin cows at calving, a prolonged postpartum anestrous interval, and fewer cows in estrus during the breeding season.2,3 Greater postpartum nutrient intake can enhance the secretion of luteinizing hormone (LH) and follicular growth. Metabolites and metabolic hormones could mediate the effects of nutrient intake on reproductive function.4,5 Effects of nutrition on reproduction may be more pronounced in thin and fat cows than in cows with moderate body condition. Sufficient body energy reserve is necessary for acceptable reproductive performance. Body condition score has been shown to be a good practical and applicable indicator of body energy reserves when compared to body weight.6,7 Body condition score at calving and nutrient supply during the early postpartum period affect the return to ovarian cyclic activity and subsequent pregnancy rates.8,9 The BCS of 5 at calving is critical to ensure acceptable postpartum reproduction in mature cows. However the change in BCS after calving may influence the reproductive outcome. The objective of this study was to determine the influence of body condition score at initiation of synchronization (30 to 90 d postpartum) on estrus expression rate and pregnancy rates for the AI and natural breeding seasons. 29 Materials and methods Cattle and synchronization protocols Data used in this study were retrospectively collected from fall 2003 to spring 2008 beef cattle breedings that occurred on 12 Virginia Correctional Center beef farms. Angus crossbred beef cows (N=5510) from 12 locations (six spring and six fall breeding locations) were synchronized with Ovsynch- CIDR or CO-Synch-CIDR protocols (Figure 1). Cows (N=2176) synchronized with the Ovsynch-CIDR protocols received 100 g of gonadotropin-releasing hormone (GnRH; Cystorelin, Merial, Athens, GA) and a CIDR on Day 0, 25 mg prostaglandin F2 (PGF, Lutalyse, Pfizer Animal Health, New York, NY) and CIDR removal on Day 7, 100 g GnRH 48 h after PGF on Day 9, and fixed-time AI 16 h after GnRH on Day 10. Cows (N=3334) synchronized with the CO-Synch-CIDR protocol received 100 g GnRH and a CIDR device on Day 0, 25 mg PGF and CIDR removal on Day 5 (5-d CO-Synch-CIDR; N=830) or 7 (7-d CO-Synch-CIDR; N=2504), and 100 g GnRH on Day 10 at the time of AI, 72 h (5-d CO-Synch- CIDR) or 66 h (7-d CO-Synch-CIDR) after CIDR removal. Cow BCS were recorded on Day 0 of synchronization. Estrus detection At the time of CIDR removal, all cows received a pressure sensitive mount detector to aid in identification of cows displaying estrus. Cows were observed for at least 30 minutes in the morning, at noon and late afternoon on Day 8, 9 and 10. A cow was determined to be in estrus if it was observed to stand for mounting or had an activated (color change from white to red), lost (with mount marks) or partially activated pressure sensitive mount detector. Bulls (approximately 1:40 bull:cow ratio) were introduced 14 days after AI and maintained for a 45 to 50 d breeding period. Pregnancy determination The pregnancy status of each cow was determined 55 to 70 d after fixed time AI either by per- rectal palpation or by trans-rectal ultrasonography (Sonosite® 180 Plus™, Sonosite Inc., Bothell, WA) Reproductive parameters Estrus expression rate was calculated by dividing the number of cows that expressed estrus by number of cows that received a pressure sensitive mount detector; AI pregnancy rate (PR) was calculated by dividing the number of cows that become pregnant to AI by number of cows inseminated; breeding season PR was calculated by dividing the number of cows pregnant following AI and natural service exposure by total number of cows exposed to breeding. Data management Cows were excluded from the analysis if they failed to calve during the season or if they received the synchronization treatment within 30 days of calving or 90 days after calving. Cows inseminated at observed estrus in 2004-05 were included in the analysis to account for AI pregnancy. Five-d CO-Synch CIDR and 7-d Co-Synch CIDR were pooled as CO-Synch-CIDR [5-d CO-Synch-CIDR AI-PR = 53.1% (291/548) vs. 7-d Co-Synch-CIDR AI-PR=50.5% (1406/2786); P=0.26. Note that data for two doses of PGF were excluded from 5-d CO-Synch-CIDR data from 2006 fall breeding10]. Cows were inseminated by experienced (with previous experience of a minimum of 1000 inseminations) technicians and clinicians. Inseminators randomly inseminated cows at each location. Since most inseminations occurred on the same day across several locations, different groups of inseminators inseminated cows at different locations, AI technicians were not included in the model. Sires were selected to avoid inbreeding and assigned randomly within locations. During a single breeding season, all AI sires were not utilized in all farms. Also, the number of cows inseminated was low for some sires; hence, AI sires was offered as a random effect. 30 Statistical analyses The data were analyzed using a statistical software program (SAS Version 9.1 for Windows, SAS Institute, Cary, NC). The mixed procedure was used to evaluate differences in estrus expression rates, AI and breeding season pregnancy rates among the body condition scores. The data were managed to provide appropriate contemporaries for comparisons. The independent variables included in the estrus expression rate model were location (12), breeding season-year nested within location, BCS (3 to 8), days post-calving at protocol initiation (31 to 40; 41 to 50; 51 to 60; 61 to 70; 71 to 80; 81 to 90), dam age groups (2, 3 to 6 and ≥7 years) synchronization protocol × BCS, breeding season × BCS and breeding season × dam age groups. The independent variables included in the AI pregnancy rate model were location, breeding season-year nested within location, BCS, days post-calving at protocol initiation, dam age groups, synchronization protocol (Ovsynch-CIDR and CO-Synch-CIDR), synchronization protocol × BCS, synchronization protocol × age groups, breeding season × BCS and breeding season × dam age groups. The independent variables included in the breeding season pregnancy rate model were location, breeding season-year nested within location, BCS, dam age groups, breeding season × BCS and breeding season × dam age groups. Results Mean  SE values of BCS and age of cows from different locations are shown in Table 1. Body condition scores ranged from 3 to 8. The estrus expression rate for all cows was 51.8% (2854/5510). The AI pregnancy for all cows was 51.5% (2835/5510) and the breeding season pregnancy for all cows was 87.9% (4843/5510). Estrus expression Accounting for location, breeding season-year location, age groups and days post-calving, estrus expression was influenced by BCS (Table 2; P<0.05). Estrus expression rates were 41.8%, 40.5%, 50.5%, 53.0%, 56.4% and 40.4% for BCS 3 to 8, respectively (Figure 2). Estrus expression rates were ranged from 37.2% to 54.8% for days post-calving (Figure 3) and were significantly different among age groups (Table 5). Decreased number of two-year-old cows expressed estrus compared to older groups. No interactions of breeding season × body condition score and breeding season × dam age groups were observed (P>0.1). AI pregnancy rate The AI pregnancy rate ranged from 48.3 to 56.4%. Accounting for location, breeding season- year location, synchronization protocol and days post-calving, pregnancy to AI was influenced by BCS (Table 3; P<0.05). Pregnancy rates to AI were 36.7%, 47.4%, 51.8%, 52.9%, 50.9% and 44.9% for BCS 3 to 8, respectively (Figure 2). Pregnancy rates to AI ranged from 42.1% to 54.5% for days post-calving (Figure 3) but did not differ among age groups (Table 5; P>0.1). The AI pregnancy rates were not different between the Ovsynch-CIDR (52.3%) and CO-Synch-CIDR (50.9%) protocols (Table 6; P<0.05). However, AI and breeding season pregnancy rates between the fall breeding season (52.9%) and the spring breeding season (50.1) were significantly different (Table 6; P<0.05). In addition, AI pregnancy rates varied among locations (Figure 4; P<0.05). No interactions of synchronization protocol × body condition score, breeding season × body condition score and breeding season × dam age groups (P>0.1) were observed. Breeding season pregnancy Breeding season pregnancy rates ranged from 78.7% to 95.4% and were influenced by BCS (P<0.05; Table 5). The breeding season pregnancy rates were 74.7%, 78.2%, 86.4%, 90.2%, 89.9%, and 87.9% for BCS from 3 to 8, respectively. No differences between breeding season pregnancy rates were detected among age groups (Table 5). However, breeding season pregnancy rates between the fall breeding season (92.9%) and the spring breeding season (86.8%) were significantly different (Table 6; 31 P<0.05). The breeding season pregnancy varied among locations (Figure 4; P<0.05). No interactions of breeding season × body condition score were observed (P>0.1). Discussion The results of this study indicate that the BCS at breeding influenced estrus expression, and AI and breeding season pregnancy rates. Reduced nutrient intake during the prepartum period increases the interval from parturition to first estrus in beef cows.8,11,12 Restricted energy suppresses the hypothalamic secretion of luteinizing hormone releasing hormone (LHRH). However the mechanisms through which restricted energy intake suppresses LHRH may be through alterations in the growth hormone (GH), insulin like growth factor (IGF)-1, and IGF binding protein (IGFBP) axis in response to nutritional stress.13 The IGF-1 was greater between two and ten weeks post-calving in cows that resumed ovarian cyclicity than in cows that remained anestrus. Days post-calving and age of dam significantly affected estrus expression. Estrus expression rates increased as the days post-calving increased. Decreased number of two-year-old cows expressed estrus compared to older cows. Primiparous cows utilize energy for growth after parturition which results in a low LH pulse frequency and longer postpartum anestrous interval, one to four weeks longer than in multiparous cows.14 In the current study, cows with BCS 5, 6 and 7 achieved greater than 50% AI pregnancy rates (Figure 2). Lake, et al., showed that first service conception rates were 36.1% for cows with BCS 4 and 50.0% for cows with BCS 6.15 The authors of that study suggested that the cows should be managed to achieve a BCS of >4 before parturition to improve reproductive success. They also showed that cows with BCS 4 at parturition are capable of maintaining this body condition score during lactation. Dietary energy restriction has a negative impact on reproduction. Among cows that lost body condition during the mid-trimester of gestation, those that increased their nutrient intake one to three months before calving had substantially improved pregnancy rates compared to cows that continued to lose body condition until parturition.6 However, cows that maintained body condition from mid-gestation until calving had a greater pregnancy rate than cows that lost and regained body condition. Reproductive performance is decreased in primiparous compared to mature cows. The stress of calving, lower intakes of high forage diets and the requirements for growth and lactation impose nutritional demands that are often not met. Inadequate nutrient intake before or after calving has a greater detrimental effect on reproduction in heifers than in cows. Heifers bred to calve at two years of age resume ovarian cyclicity 20 to 40 days later than mature cows. Doornbos, et al., reported that multiparous cows have greater pregnancy rates than heifers.16 Kress, et al., evaluated calving rates among young multiparous cows and found that cows  5 years old had a greater calving rate than young cows.17 Renquist, et al., demonstrated a quadratic relationship between age and pregnancy rate and concluded that reproductive performance of ten-year-old cows decreased.18 However, they suggested that age was not a significant determinant when BCS was included in the model and concluded that the effect of age is associated with the decreasing BCS of older cows at breeding. In the current study, the AI pregnancy rates were not different among age groups (P>0.1). This may be attributed to a good heifer management and nutritional program in these locations. It is interesting to note that the estrus expression rate was lower for the two-year-old cows compared to older cows. Breeding season pregnancy rates were influenced by BCS (P<0.05; Figure 4). The breeding season pregnancy rates were 76.4%, 84.7%, 88.0%, 90.2%, 89.2%, and 87.0% for BCS 3 to 8, respectively; and AI and breeding season pregnancy rate between fall and spring were significantly different. More cows were pregnant during the fall compared to the spring season. In Virginia the primary grasses during spring are fescue (Festuca arundinacea), bluegrass (Poa pratensis) and clover (Trifolium pratense). Fescue toxicity and heat stress may play a role in reduced pregnancy during the spring season compared to fall. In females, the fescue endophyte may affect ovarian gamete maturation, ovulation, gamete transport and fertilization, conceptus transport, and/or embryo attachment and the effects on the postpartum anestrous interval are possibly caused by neurohormonal imbalances that lead to improper ovarian function.19-21 The possible effects endophyte-infected fescue in the male include sperm 32 production, sperm motility, libido, and testicular development.22 These effects may be reflected in this study by reduced AI and breeding season pregnancy rates in spring compared to fall. Days post-calving at protocol initiation significantly influenced the AI pregnancy rate. It is interesting to note that the days post-calving also affected estrus expression rates indicating that the late calving cows are still under the influence of postpartum anestrus. However if the cows were in moderate body condition they become pregnant. Lents, et al., showed that BCS at calving influenced the size of the dominant follicle at the first postpartum estrus in mature suckled cows and suggested that cows be managed to calve in moderate BCS.23 There were no differences in the AI and breeding season pregnancy between Ovsynch-CIDR and CO-Synch-CIDR synchronization protocols. No interactions between synchronization protocols by BCS and between synchronization protocols by days post-calving were observed. A progesterone-supplemented protocol is recommended for improving fertility by inducing cyclicity in anestrous postpartum beef cows. If anestrus is the problem, then all cows should benefit from progesterone-supplemented synchronization protocols. The results indicated that cows with BCS 5 to 7 achieved > 50% AI pregnancy. Ciccioli, et al., concluded neither BCS at calving nor postpartum nutrition influenced estrous behavior at the first postpartum estrus.24 They suggested that the lack of effect of BCS at calving on reproductive performance in that study could be related to the minimal differences in BCS of the thin and moderate condition cows at calving, or that all cows had less than optimal BCS at calving for adequate performance. Spitzer, et al., demonstrated that BCS 4 to 6 at calving influences the duration from parturition to estrus.25 They also found greater pregnancy rates for cows with a BCS of 6 at parturition compared with cows with a BCS of 4 or 5. Greater nutrient intake postpartum can have a positive effect26-28 or no effect29-32 on duration of the postpartum anovulatory interval. Results of other experiments indicate that postpartum energy intake may influence pregnancy rate at the first postpartum estrus,11,33 however, the effect of energy intake on pregnancy rate was not significant. Reduced nutrient intake during estrous cycles did not affect fertilization rate3 but did reduce conception rate.34 Lack of consistency among studies may involve the amount of energy intake, duration of the feeding period, BCS at calving, BCS change during postpartum period, and age of cows. Fuel sensors, such as glucose, insulin or leptin, are known to be directly involved in the regulation of fertility at each level of the hypothalamus- pituitary-gonadal axis. Ciccioli, et al., suggested that the concentrations of IGF-1, leptin, insulin, glucose, nonesterified fatty acid, or thyroxin in blood may not individually signal the onset of postpartum ovarian function, but they may act in concert with other factors to indicate the adequacy of nutrients.24 So it is plausible that differences in endocrine function or metabolic signals during the postpartum period could influence ovarian activity and fertility. In summary, the BCS of beef cows at the time of initiation of synchronization protocol influenced estrus expression, AI and breeding season pregnancy rates. A minimum BCS of 5 should be achieved prior to the breeding season to ensure acceptable reproductive performance. Further research is needed to elucidate the mechanism(s) that control postpartum ovarian activity and estrous behavior to maximize reproductive efficiency in beef cattle. Lipid biomarkers play a key role in reproduction. It would be of interest to investigate the impact of different types of lipid biomarkers, perhaps integrated into feed, on ovulation capacity and embryonic development. Acknowledgements The authors thank Select Sires Inc, Plain City, OH for providing partial financial support. The authors also extend their gratitude to the staff of Virginia Department of Corrections for their support with data collection. References 1. Wiltbank JN, Warwick EJ, Vernon EH, et al: Factors affecting net calf crop in beef cattle. J Anim Sci 1961;20:409- 415. 2. Bossis I, Wettemann RP, Welty SD, et al: Nutritionally induced anovulation in beef heifers: Ovarian and endocrine function preceding cessation of ovulation. J Anim Sci 1999;77:1536-1546. 33 3. Perry RC, Corah LR, Cochran RC, et al: Influence of dietary energy on follicular development, serum gonadotropins, and first postpartum ovulation in suckled beef cows. J Anim Sci 1991;69:3762-3773. 4. Wettemann RP, Bossis I: Energy intake regulates ovarian function in beef cattle. Proc Am Soc Anim Sci 2000. Available from: http://www.asas.org/JAS/symposia/proceedings/0934.pdf 5. Armstrong JD, Cohick WS, Harvey RW, et al: Effect of feed restriction on serum somatotropin, insulin-like growth factor-I-(IGF-I) and IGF binding proteins in cyclic heifers actively immunized against growth hormone releasing factor. Domest Anim Endocrinol 1993;10:315-324. 6. Wagner JJ, Lusby KS, Oltjen JW, et al: Carcass composition in mature Hereford cows: Estimation and effect on daily metabolizable energy requirement during winter. J Anim Sci 1988;66:603-612. 7. Houghton PL, Lemenger RP, Horstman LA, et al: Prediction of postpartum beef cows body composition using weight to height ratio and visual body condition score. J Anim Sci 1990;68:1428-1437. 8. Richards MW, Spitzer JC, Warner MB: Effect of varying levels of postpartum nutrition and body condition at calving on subsequent reproductive performance in beef cattle. J Anim Sci 1986;62:300-306. 9. Selk GE, Wettemann RP, Lusby KS, et al: Relationships among weight change, body condition and reproductive performance or range beef cows. J Anim Sci 1988;66:3153-3159. 10. Kasimanickam R, Day ML, Rudolph JS, et al: Two doses of prostaglandin improve pregnancy rates to timed-AI in a 5- day progesterone-based synchronization protocol in beef cows. Theriogenology 2009;15:762-767. 11. Richards MW, Wettemann RP, Schoenemann HM: Nutritional anestrus in beef cows: body weight change, body condition, luteinizing hormone in serum and ovarian activity. J Anim Sci 1989;67:1520-1526. 12. Bishop DK, Wettemann RP, Spicer LJ: Body energy reserves influence the onset of luteal activity after early weaning of beef cows. J Anim Sci 1994;72:2703-2708. 13. Roberts AJ. Nugent III RA, Klint J, et al: Circulating insulin-like growth factors I, insulin-like growth factor binding protein, growth hormone, and resumption of estrus in postpartum cows subjected to dietary energy restriction. J Anim Sci 1997;75:1909-1917. 14. Yavas Y, Walton JS: Postpartum acyclicity in suckled beef cows: a review. Theriogenology 2000;54:5-25. 15. Lake SL, Schooljegerdes EJ, Atkinson RL, et al: Body condition score at parturition and postpartum supplemental fat effects on cow and calf performance. J Anim Sci 2005;83:2908-2917. 16. Doornbos DE, Bellows RA, Burfening PJ, et al: Effects of dam age, prepartum nutrition, and duration of labor on productivity and postpartum reproduction in beef females. J Anim Sci 1984; 59:1-10. 17. Kress DD, Doornbos DE, Anderson DC: Performance of crosses among Hereford, Angus, and Simmental cattle with different levels of Simmental breeding: V. Calf production, milk production and reproduction of three- to eight-year- old dams. J Anim Sci 1990;68:1910-1921. 18. Renquist BJ. Oltjen JW, Sainz RD, et al: Effects of age on body condition and production parameters of mulitparous beef cows. J Anim Sci 2006;84:1890-1895. 19. Paterson J, Forcherio C, Larson B, et al: The effects of fescue toxicosis on beef cattle productivity. J Anim Sci 1995;73:889-898. 20. Rhodes MT, Paterson JA, Kerley MS, et al: Reduced blood flow to peripheral and core body tissues in sheep and cattle induced by endophyte-infected tall fescue. J Anim Sci 1991;89:2033-2043. 21. Porter JK, Thompson FN Jr: Effects of fescue toxicosis on reproduction in livestock. J Anim Sci 1992;70:1594-1603. 22. Alamer MA, Erickson BH. Effect of fungus-infested fescue on testicular development and hormonal secretions in the beef bull (abstract). J Anim Sci 1990;68(Suppl 1):40. 23. Lents CA, White FJ, Ciccioli NH, et al: Effects of body condition score at parturition and postpartum protein supplementation on estrous behavior and size of the dominant follicle in beef cows. J Anim Sci 2008;86:2549-2556. 24. Ciccioli NH, Wettemann RP, Spicer LJ, et al: Influence of body condition at calving and postpartum nutrition on endocrine function and reproductive performance of primiparous beef cows. J Anim Sci 2003;81:3107-3120. 25. Spitzer JC, Morrison DG, Wettemann RP, et al: Reproductive responses and calf birth and weaning weights as affected by body condition at parturition and postpartum weight gain in primiparous beef cows. J Anim Sci 1995;73:1251-1257. 26. Wright IA, Rhind SM, Whyte TK, et al: Effect of body condition at calving and feeding level after calving on LH profiles and duration of the post-partum anoestrous period in beef cows. Anim Prod 1992;55:41-46. 27. Stagg K, Diskin MG, Sreenan JM, et al: Follicular development in long-term anoestrous suckler beef cows fed two levels of energy postpartum. Anim Reprod Sci 1995;38:49-61. 28. Vizcarra JA, Wettemann RP, Spitzer JC, et al: Body condition at parturition and postpartum weight gain influence luteal activity and concentrations of glucose, insulin, and nonesterified fatty acids in plasma of primiparous beef cows. J Anim Sci 1998;76:927-936. 29. Wright IA, Rhind SM, Russel AJF, et al: Effects of body condition, food intake and temporary calf separation on the duration of the post-partum anoestrous period and associated LH, FSH, and prolactin concentrations in beef cows. Anim Prod 1998;45:395-402. 30. Whittier JC, Clanton DC, Deutscher GH: Effect of post-partum levels of nutrition on productivity of 2-year-old heifers. Anim Prod 1988;47:59-64. 31. Stagg K, Spicer LJ, Sreenan JM, et al: Effect of calf isolation on follicular wave dynamics, gonadotropin and metabolic hormone changes, and interval to first ovulation in beef cows fed either of two energy levels postpartum. Biol Reprod 1998;59:777-783. 34 32. Wiltbank J N, Rowden WW, Ingalls JE, et al: Influence of post-partum energy level on reproductive performance of Hereford cows restricted in energy intake prior to calving. J Anim Sci 1964;23:1049-1053. 33. Spitzer JC, Niswender GD, Seidel GE Jr, et al: Fertilization and blood levels of progesterone and LH in beef heifers on restricted energy diet. J Anim Sci 1978;46:1071-1077. 34. Hill JR, Lamond DR Jr, Henricks DM, et al: The effects of undernutrition on ovarian function and fertility in beef heifers. Biol Reprod 1970;2:78-84. Table 1. Mean  SE values of body condition score and age of beef cows in different locations. Season Location Body Condition Score Age (y) Fall 1 5.27  0.05 4.79  0.11 2 6.31  0.09 5.47  0.38 3 5.53  0.04 5.62  0.13 4 5.43  0.05 4.23  0.06 5 5.64  0.03 4.02  0.08 6 5.55  0.06 4.18  0.16 Spring 7 5.54  0.12 5.38  0.25 8 5.28  0.05 5.23  0.25 9 5.79  0.40 4.24  0.62 10 5.21  0.04 4.44  0.34 11 5.65  0.08 4.36  0.29 12 5.17  0.10 5.19  0.22 Table 2. The General Linear Model for the effects on estrus expression rate of Angus-cross beef cows (N=5510). Source d.f. Sum of Squares F ratio Prob > F Location 11 82.4517 4.1268 <0.0001 Breeding Season-year within location 44 63.4232 6.6214 <0.0001 Body Condition Score* 5 2.2319 4.1246 <0.0338 Days post-calving at protocol initiation† 5 5.8309 18.3948 <0.0015 Age group‡ 2 2.9817 5.9985 <0.03238 d.f – degrees of freedom; *1-emaciated and 9-obese; †Days post-calving groups: 31-40; 41-50; 51-60; 61-70; 71-80 and 81-90; ‡Age groups: 2; 3-6 and >6 35 Table 3. The General Linear Model for the effects on AI pregnancy rate of Angus-cross beef cows (N=5510). Source d.f. Sum of Squares F ratio Prob > F Location 11 16.6242 4.1253 <0.0001 Breeding Season-year within location 44 58.5227 23.2381 <0.0001 Body Condition Score§ 5 2.0121 3.6128 <0.0313 Days post-calving at protocol initiation¶ 5 11.1174 3.9213 <0.0001 Age group** 2 1.2158 1.5781 <0.3316 Synchronization protocol†† 1 5.2459 24.5168 <0.0123 Synchronization protocol by body condition score 5 0.0216 0.6921 <0.4571 Breeding season by body condition score 11 0.04328 0.7081 <0.6570 Synchronization protocol by days post- calving at protocol initiation 5 0.0721 0.7218 <0.8212 d.f – degrees of freedom; §1-emaciated and 9-obese; ¶Days post-calving groups: 31-40; 41-50; 51-60; 61-70; 71-80 and 81-90; **Age groups: 2; 3-6 and >6; ††Refer to Figure 1 for treatment; Table 4. The General Linear Model for the effects on breeding season pregnancy rate of Angus-cross beef cows (N=5510). Source d.f. Sum of Squares F ratio Prob > F Location 11 14.4218 22.1246 <0.0001 Breeding Season-year within location 44 87.2445 7.8351 <0.0001 Body Condition Score‡‡ 5 2.4513 4.7862 <0.0211 Age group§§ 2 3.2193 0.5781 <0.2714 Breeding season by body condition score 11 1.6739 0.8463 <0.5438 d.f – degrees of freedom; ‡‡1-emaciated and 9-obese; §§Age groups: 2; 3-6 and >6; Table 5. Effect of age of the dam (in years) on the AI and breeding season pregnancy* in Angus cross beef cows (N=5510) Age groups N Estrus Expression Rate (95% CI) AI-PR (95% CI) Breeding season PR (95% CI) 2 1317 47.9 (43.1, 50.9)a 53.5 (48.2-57.6)a 86.8 (81.1, 90.8)a 3 to 6 2920 54.0 (49.7, 57.8)b 52.7 (48.2-56.7)a 87.7 (80.9, 94.1)a > 6 1273 50.8 (47.1, 53.1)b 50.3 (41.4-53.3)a 88.7 (84.3, 91.4)a ab different superscripts within column are statistically significant, P<0.05; CI – Confidence Interval PR – Pregnancy rate 36 Table 6. Effect of synchronization protocol, breeding season on the AI and breeding season pregnancy* in Angus cross beef cows (N=5510). Source Level N AI-PR (95% CI) Breeding season PR (95% CI) Synchronization¶¶ Ovsynch-CIDR 2176 52.3 (48.9, 57.4)a 87.4 (83.4, 91.7)a CO-Synch-CIDR 3334 50.9 (48.2, 53.7)a 88.2 (81.8, 93.6)a Breeding season Spring 2816 50.1 (48.9, 52.4)a 86.8 (83.8, 89.6)a Fall 2694 52.9 (49.6, 55.4)b 89.0 (85.6, 93.3)b ab Different superscripts within source and between level are different (P<0.01) ¶¶Refer to Figure 1 for treatment CI – Confidence Interval PR – Pregnancy rate CIDR – Controlled internal drug release device 37 Ovsynch-CIDR Day 0 Day 7 AM Day 9 PM Day 10 AM GnRH PGF2 48 h GnRH 16 h TAI 7-d CO-Synch-CIDR Day 0 Day 7 AM Day 10 AM GnRH PGF2 66 h GnRH+TAI 5-d CO-Synch-CIDR Day 0 Day 5 AM Day 8 AM GnRH PGF2 72 h GnRH+TAI Figure 1. Treatment protocols for estrous synchronization. Angus crossbred beef cows (N = 5510) from 12 locations (six spring and six fall breeding locations) were synchronized with Ovsynch-CIDR, or CO- Synch-CIDR protocols. Cows synchronized with Ovsynch-CIDR protocols received 100 g gonadotropin-releasing hormone (GnRH; Cystorelin, Merial, Athens, GA) + controlled internal drug release device (CIDR; Eazi-Breed CIDR, Pfizer Animal Health, New York, NY) on Day 0, 25 mg prostaglandin F2 (PGF; Lutalyse, Pfizer Animal Health) and CIDR removal on Day 7, 100 g GnRH 48 h after PGF on Day 9, and fixed-time AI 16 h after GnRH on Day 10. Cows synchronized with CO- Synch-CIDR protocols received 100 g GnRH + CIDR device on Day 0, 25 mg PGF and CIDR device removal on Day 5 (5-d CO-Synch-CIDR; N=830) or 7 (7-d CO-Synch-CIDR; N=2504), and 100 g GnRH on Day 10 at the time of AI, 72 h (5-d CO-Synch-CIDR) or 66 h (7-d CO-Synch-CIDR) after CIDR removal. Cow BCS (1-emaciated; 9-obese) were recorded on Day 0 of synchronization. Five-d CO- Synch CIDR and 7-d Co-Synch CIDR were pooled as CO-Synch-CIDR for the analysis. CIDR CIDR CIDR 38 rabc Different superscripts within estrus expression are statistically significant (P<0.05) ab Different superscripts within AI pregnancy are statistically significant (P<0.05) ab Different superscripts within breeding season pregnancy are statistically significant (P<0.05) Figure 2. Influence of body condition score on on estrus expression, and AI and breeding season pregnancy (Mean percentage ± SEM) in cows (N=5510) following porgesterone supplemented synchronization protocol. Numbers in paenthesis are number of cows for the corresponding body condition scores. Numbers in black are percentage of cows expressed estrus. Numbers in white are percentage of cows pregnant to AI. Numbers in the box are percentage of cows pregnant for the breeding season pregnancy. 41.8 40.5 50.5 53.0 56.4 40.4 36.7 47.4 51.8 52.9 50.9 43.9 74.7 78.2 86.4 90.2 89.9 87.7 0.0 20.0 40.0 60.0 80.0 100.0 3 4 5 6 7 8 P er ce nt ag e Body Condition Score Estrus Expression AI Pregnancy Breeding Season Pregnancy a bc c c a (79) (348) (1834) (2089) (1103) (57) a b b bbb bb a a abab 39 abc Different superscripts within AI pregnancy are statistically significant (P<0.05) abc Different superscripts within AI pregnancy are statistically significant (P<0.05) Figure 3. Effect of days post-calving at protocol initiation on estrus expression and AI pregnancy (Mean percentage ± SEM) in cows (N=5510) following porgesterone supplemented synchronization protocol. Numbers in parenthesis are number of cows for the corresponding days post-calving. Numbers in black are percentage of cows expressed estrus. Numbers in white are percentage of cows pregnant to AI. Numbers in the box are percentage of cows pregnant for the breeding season pregnancy. 37.2 47.9 50.9 54.5 52.8 54.8 42.1 48.8 51.6 54.5 52.3 50.9 0.0 20.0 40.0 60.0 80.0 100.0 31 to 40 41 to 50 51 to 60 61 to 70 71 to 80 81 to 90 P er ce nt ag e Days postcalving at protocol initiation Estrus Expression AI pregnancy (309) (543) (796) (1007) (1959) (896) a b bc bc bcc a b bc ccc 40 ab D if fe re nt s up er sc ri pt s ar e st at is ti ca ll y si gn if ic an t ( P < 0. 05 ) F ig ur e 4. E ff ec t o f lo ca ti on s (N = 12 ) on A I pr eg na nc y (M ea n pe rc en ta ge ± S E M ) in b ee f co w s (N = 55 10 ) sy nc hr on iz ed w it h pr og es te ro ne s up pl em en te d pr ot oc ol s. N um be rs in p ar en th es is a re n um be r of c ow s in se m in at ed f ro m th e co rr es po nd in g lo ca ti on . 48 .3 53 .4 55 .1 48 .3 55 .2 48 .7 56 .4 52 .5 49 .5 50 .6 50 .7 52 .5 81 .2 91 .5 91 .2 79 .8 93 .2 78 .7 95 .4 94 .6 88 .3 87 .6 90 .1 91 .6 0. 0 20 .0 40 .0 60 .0 80 .0 10 0. 0 1 2 3 4 5 6 7 8 9 10 11 12 Percentage L oc at io ns A I pr eg na nc y B re ed in g S ea so n P re gn an cy (4 10 ) (2 79 ) (3 34 ) (7 61 ) (8 27 ) (4 21 ) ab c a ab ab ab c bc a ab c ab c ab c c (8 12 ) (3 48 ) (4 35 ) (1 81 ) (3 26 ) (3 26 ) ab c a a a b c bc bc bc bc bc (4 10 ) (2 79 ) (3 34 ) (7 61 ) (8 27 ) (4 21 ) ab c a ab ab ab c bc a ab c ab c ab c c (8 12 ) (3 48 ) (4 35 ) (1 81 ) (3 26 ) (3 26 ) ab c a a a b cd bc bc bc bc bc cd d 41 42 OMNIBLANK: << /ASCII85EncodePages false /AllowTransparency false /AutoPositionEPSFiles true /AutoRotatePages /None /Binding /Left /CalGrayProfile (Dot Gain 20%) /CalRGBProfile (sRGB IEC61966-2.1) /CalCMYKProfile (U.S. Web Coated \050SWOP\051 v2) /sRGBProfile (sRGB IEC61966-2.1) /CannotEmbedFontPolicy /Warning /CompatibilityLevel 1.6 /CompressObjects /Tags /CompressPages true /ConvertImagesToIndexed true /PassThroughJPEGImages true /CreateJobTicket false /DefaultRenderingIntent /Default /DetectBlends true /DetectCurves 0.0000 /ColorConversionStrategy /UseDeviceIndependentColor /DoThumbnails false /EmbedAllFonts true /EmbedOpenType true /ParseICCProfilesInComments true /EmbedJobOptions true /DSCReportingLevel 0 /EmitDSCWarnings false /EndPage -1 /ImageMemory 1048576 /LockDistillerParams false /MaxSubsetPct 100 /Optimize true /OPM 1 /ParseDSCComments true /ParseDSCCommentsForDocInfo true /PreserveCopyPage true /PreserveDICMYKValues true /PreserveEPSInfo true /PreserveFlatness false /PreserveHalftoneInfo false /PreserveOPIComments true /PreserveOverprintSettings true /StartPage 1 /SubsetFonts true /TransferFunctionInfo /Apply /UCRandBGInfo /Preserve /UsePrologue false /ColorSettingsFile () /AlwaysEmbed [ true ] /NeverEmbed [ true ] /AntiAliasColorImages false /CropColorImages false /ColorImageMinResolution 300 /ColorImageMinResolutionPolicy /OK /DownsampleColorImages true /ColorImageDownsampleType /Bicubic /ColorImageResolution 300 /ColorImageDepth -1 /ColorImageMinDownsampleDepth 1 /ColorImageDownsampleThreshold 1.50000 /EncodeColorImages true /ColorImageFilter /DCTEncode /AutoFilterColorImages true /ColorImageAutoFilterStrategy /JPEG /ColorACSImageDict << /QFactor 0.15 /HSamples [1 1 1 1] /VSamples [1 1 1 1] >> /ColorImageDict << /QFactor 0.15 /HSamples [1 1 1 1] /VSamples [1 1 1 1] >> /JPEG2000ColorACSImageDict << /TileWidth 256 /TileHeight 256 /Quality 30 >> /JPEG2000ColorImageDict << /TileWidth 256 /TileHeight 256 /Quality 30 >> /AntiAliasGrayImages false /CropGrayImages false /GrayImageMinResolution 300 /GrayImageMinResolutionPolicy /OK /DownsampleGrayImages true /GrayImageDownsampleType /Bicubic /GrayImageResolution 300 /GrayImageDepth -1 /GrayImageMinDownsampleDepth 2 /GrayImageDownsampleThreshold 1.50000 /EncodeGrayImages true /GrayImageFilter /DCTEncode /AutoFilterGrayImages true /GrayImageAutoFilterStrategy /JPEG /GrayACSImageDict << /QFactor 0.15 /HSamples [1 1 1 1] /VSamples [1 1 1 1] >> /GrayImageDict << /QFactor 0.15 /HSamples [1 1 1 1] /VSamples [1 1 1 1] >> /JPEG2000GrayACSImageDict << /TileWidth 256 /TileHeight 256 /Quality 30 >> /JPEG2000GrayImageDict << /TileWidth 256 /TileHeight 256 /Quality 30 >> /AntiAliasMonoImages false /CropMonoImages false /MonoImageMinResolution 1200 /MonoImageMinResolutionPolicy /OK /DownsampleMonoImages true /MonoImageDownsampleType /Bicubic /MonoImageResolution 1200 /MonoImageDepth -1 /MonoImageDownsampleThreshold 1.50000 /EncodeMonoImages true /MonoImageFilter /CCITTFaxEncode /MonoImageDict << /K -1 >> /AllowPSXObjects false /CheckCompliance [ /None ] /PDFX1aCheck false /PDFX3Check false /PDFXCompliantPDFOnly false /PDFXNoTrimBoxError true /PDFXTrimBoxToMediaBoxOffset [ 0.00000 0.00000 0.00000 0.00000 ] /PDFXSetBleedBoxToMediaBox true /PDFXBleedBoxToTrimBoxOffset [ 0.00000 0.00000 0.00000 0.00000 ] /PDFXOutputIntentProfile () /PDFXOutputConditionIdentifier () /PDFXOutputCondition () /PDFXRegistryName () /PDFXTrapped /False /CreateJDFFile false /Description << /ENU ([Based on '[Press Quality]'] Use these settings to create Adobe PDF documents best suited for high-quality prepress printing. 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