Comparison of Breeding and Marketing Systems for Red Angus Cattle Using an Integrated Computer-Based Spreadsheet

An integrated computer-based spreadsheet was developed with data from 581 Red Angus-sired calves to compare synchronized AI and natural service breeding systems. This comparison was based on input costs, genetic merit of sires used for mating, and calf marketing system, using differences in net return. The spreadsheet integrated four elements into a decision summary: bull costs, AI costs, genetics merit, and marketing options. An economic sensitivity analysis was used to identify trends and key variables in the net return of each decision. Three prominent variables identified from economic analysis were bull purchase price, semen price, and percent genetic change. Bull purchase price was a primary factor in changes in net return; semen costs and genetic merit change explained rearrangements in ranking of net return. These two variables altered the ranking based on whether the estrous synchronization protocol used estrus detection or timed AI. The spreadsheet identified AI to be more cost effective than natural service when calves are marketed as finished cattle. Net revenue from AI calves was greater in all retained ownership scenarios; the weaned marketing scenario caused net return to vary by synchronization system for the combinations of costs and changes in genetic merit. However, there was a wide variance in identifying which breeding system provided the greatest benefit when calves were marketed as feeder cattle. Retaining ownership through finish and marketing either on the cash market or on a grid proved to be advantageous to AI in all of the estrous synchronization protocols provided. The economic advantage ranged from $142.98 to $214.16 per head compared with marketing at weaning. The spreadsheet developed provides a useful tool for evaluating the economic impacts of breeding system decisions.     

A review of current timed-AI (TAI) programs for beef and dairy cattle

This is a review of the physiology and endocrinology of the estrous cycle and how ovarian physiology can be manipulated and controlled for timed artificial insemination (TAI) in beef and dairy cattle. Estrus detection is required for artificial insemination (AI), but it is done poorly in dairy cattle and it is difficult in beef cattle. Protocols that synchronize follicle growth, corpus luteum regression and ovulation, allowing for TAI, result in improved reproductive performance, because all animals are inseminated whether they show estrus or not. As result, TAI programs have become an integral part of reproductive management in many dairy herds and offer beef producers the opportunity to incorporate AI into their herds. Gonadotropin-releasing hormone-based protocols are commonly used in North America for estrus synchronization as part of a TAI program. Protocols that increase pregnancy rates in lactating dairy cows and suckling beef cows have been developed. Protocols that improve pregnancy rates in heifers, acyclic beef cows, and resynchronized lactating dairy cows are also discussed.     

Factors affecting pregnancy rate to estrous synchronization and fixed-time artificial insemination in beef cattle

Application of AI in extensive beef cattle production would be facilitated by protocols that effectively synchronize ovarian follicular development and ovulation to enable fixed-time AI (TAI). The objectives were to determine whether use of a controlled internal drug release (CIDR) device to administer progesterone in a GnRH-based estrous synchronization protocol would optimize blood progesterone concentrations, improve synchronization of follicular development and estrus, and increase pregnancy rates to TAI in beef cows. Beef cows (n = 1,240) in 6 locations within the US Meat Animal Research Center received 1 of 2 treatments: 1)?an injection of GnRH [100 μg intramuscularly (i.m.)] followed by PGF(2α) (PGF; 25 mg i.m.) 7 d later (CO-Synch), or 2) CO-Synch plus a CIDR during the 7 d between GnRH and PGF injections (CO-Synch + CIDR). Cows received TAI and GnRH (100 μg i.m.) at 60 h after PGF. Progesterone was measured by RIA in blood samples collected 2 wk before and at initiation of treatment (d 0) and at PGF injection (d 7). Estrous behavior was monitored by Estrotect Heat Detectors. Pregnancy was diagnosed by ultrasonography 72 to 77 d after TAI. Plasma progesterone concentrations did not differ (P > 0.10) between synchronization protocols at first GnRH injection (d 0), but progesterone was greater (P < 0.01) at PGF injection (d 7) in cows receiving CO-Synch + CIDR vs. CO-Synch as a result of fewer CIDR-treated cows having progesterone ≤1 ng/mL at PGF (10.7 vs. 29.6%, respectively). A greater (P < 0.01) proportion of CO-Synch + CIDR vs. CO-Synch cows were detected in estrus within 60 h after PGF (66.7 vs. 57.8 ± 2.6%, respectively) and a greater (P < 0.01) proportion were pregnant to TAI (54.6 vs. 44.3 ± 2.6%, respectively). For both synchronization protocols, cows expressing estrus within 60 h before TAI had a greater pregnancy rate than cows without estrus. For cows with plasma progesterone ≤1 ng/mL at PGF injection, CO-Synch + CIDR increased pregnancy rate (65.2 ± 5.9 vs. 30.8 ± 3.4% with vs. without CIDR), whereas pregnancy rates did not differ (P > 0.10) between protocols (52.1 ± 2.1 vs. 50.0 ± 2.4%, respectively) when progesterone was >1 ng/mL (treatment × progesterone; P < 0.01). Inclusion of a CIDR in the synchronization protocol increased plasma progesterone concentration, proportion of cows detected in estrus, and pregnancy rate; however, the increase in pregnancy rate from inclusion of the CIDR was primarily in cows with decreasing or low endogenous progesterone secretion during treatment.     

肉牛定时输精程序的研究进展

定时输精(TAI)技术作为家畜繁殖技术的重大突破和革新,综合了同期发情和人工授精技术,不仅解决了在生产实践中发情鉴定难、配种受胎率较低的问题,同时也明显提高了生产效率。TAI技术的应用有助于促进肉牛良种产业化和提高经济效益。本文综述了国内外肉牛TAI技术的应用现状并对各程序进行比较,以期为肉牛繁殖新技术的研究和应用提供参考依据。     

Development of an estrus synchronization protocol for beef cattle with short-term feeding of melengestrol acetate: 7-11 synch

An estrus synchronization protocol (7-11 Synch) was developed to synchronize the first follicular wave and timing of ovulation in postpartum beef cows. In Exp. 1, follicular development and timing of ovulation in response to the following protocol were evaluated. Beef heifers (n = 12) and cows (n = 6), at random stages of the estrous cycle, were fed melengestrol acetate (MGA; .5 mg x animal(-1) x d(-1)) for 7 d and injected with PGF2alpha (PG; 25 mg) on the last day of MGA. A second injection of PG was administered 11 d after cessation of MGA. After the second injection of PG, estrus was synchronized in 6/12 heifers and 3/6 cows. The interval to estrus in heifers and cows was 54 and 64 h, respectively (P > .10). All animals exhibiting estrus ovulated first-wave follicles. Animals that failed to respond to the second injection of PG were in estrus later than 6 d after cessation of MGA and had corpora lutea that were unresponsive to the injection of PG. Based on the variation in interval to estrus following the first PG injection on the last day of MGA feeding in Exp. 1, an injection of GnRH (100 microg) was added to the protocol 4 d after the cessation of MGA to ensure ovulation or luteinization of dominant follicles and synchronization of first-wave follicular development. This revised protocol was termed "7-11 Synch." In Exp. 2, two estrus synchronization protocols were compared. Multiparous beef cows were stratified by breed and postpartum interval and randomly assigned to the 7-11 Synch (n = 44) or Select Synch protocols (GnRH injection followed by PG injection 7 d later; n = 45). Timing of estrus after the last PG injection (0 h) ranged from 42 to 102 h in the 7-11 Synch group and -30 to 114 h in the Select Synch group. Eight cows (18%) in the Select Synch group exhibited estrus 30 h before to 18 h after PG. Synchronized estrus peaked between 42 and 66 h after the last PG injection, and a maximum number of cows were in estrus at 54 h for both treatment groups. Synchrony of estrus from 42 to 66 h was greater (P < .05) in 7-11 Synch (91%: 41/44) than in Select Synch cows (69%: 31/45). Artificial insemination pregnancy rate from 42 to 66 h was greater (P < .05) in the 7-11 Synch group (66%: 29/44) than in the Select Synch group (40%: 18/45). In summary, the 7-11 Synch protocol improved synchrony of estrus without reducing fertility. This protocol has potential future application for fixed-time AI in beef cattle production systems.     

文山州同期发情—定时输精技术在肉牛生产中的应用

[目的]为探讨同期发情—定时输精技术对云南省文山州母牛繁殖性能的影响,建立适宜于南方肉牛品种改良的轻简推广实用技术程序。[方法]通过肉牛同期发情—定时输精技术程序在文山州广南、砚山、富宁三县的应用效果作比较。[结果]结果表明,使用该技术程序后三县肉牛平均同期发情率为93.24%,平均受胎率达80.94%,应用效果良好;母牛体况对发情效果影响较大,有待提高母牛饲养管理水平。[结论]同期发情—定时输精技术对提高母牛受胎率的效果明显,值得在我国南方肉牛养殖业中大力推广。     

犊牛的饲养管理关键技术

肉牛是人类重要的畜产品来源之一,其肉质鲜美,营养丰富,深受消费者的喜爱。近年来,随着我国经济的飞速发展和人民生活水平的提高,牛肉作为一种高质量的蛋白质来源,可以为消费者提供非常理想的饮食体验,导致国内高品质牛肉需求量正在日益增长,肉牛养殖成为了农牧业的重要支柱产业之一。而犊牛的培育将直接影响到肉牛养殖业的健康发展,因而保证犊牛的健康,提高犊牛的成活率和生长效率对推进肉牛产业发展具有重大意义。本文针对犊牛的消化生理特点,总结了犊牛的饲养要点和管理方法,旨在为犊牛的高效养殖提供参考。     

不同肉牛育肥的牛肉产品生产对饲料粮消耗比较分析

在对繁殖母牛、哺乳犊牛和架子牛进行饲养试验及调查的基础上,结合所进行的架子牛育肥试验和犊牛直线育肥试验,参考肉牛饲养标准和已发表的肉牛育肥试验数据,并根据目前我国牛肉产品提供状况和肉用牛育肥的饲料资源情况,分别比较不同肉牛育肥牛肉产品生产所需要的粮食。结果表明,为获得等同重量的肉牛产品,直线育肥技术比后期集中育肥要消耗较少的粮食,而高档牛肉生产（高端肉产品生产）需要消耗更多的饲料粮。     

应用同期发情技术提高肉牛繁殖率的试验

[目的]我国发展肉牛养殖具有较大的潜力,为了更好地开展肉牛杂交改良工作,[方法]我们对一次前列腺素法、孕激素阴道栓法、补充少量促卵泡素诱导产双胎法进行了同期发情技术试验,[结果]表明处理牛同期发情率都在90%以上,取得了较好的效果.[结论] 说明周期发情技术在肉牛繁殖上应用具有明显提高繁殖率.     

Synchronization of estrus in suckled beef cows for detected estrus and artificial insemination and timed artificial insemination using gonadotropin-releasing hormone, prostaglandin F2alpha, and progesterone

We determined whether a fixed-time AI (TAI) protocol could yield pregnancy rates similar to a protocol requiring detection of estrus, or estrous detection plus TAI, and whether adding a controlled internal device release (CIDR) to GnRH-based protocols would enhance fertility. Estrus was synchronized in 2,598 suckled beef cows at 14 locations, and AI was preceded by 1 of 5 treatments: 1) a CIDR for 7 d with 25 mg of PG F(2alpha) (PGF) at CIDR removal, followed by detection of estrus and AI during the 84 h after PGF; cows not detected in estrus by 84 h received 100 mug of GnRH and TAI at 84 h (control; n = 506); 2) GnRH administration, followed in 7 d with PGF, followed in 60 h by a second injection of GnRH and TAI (CO-Synch; n = 548); 3) CO-Synch plus a CIDR during the 7 d between the first injection of GnRH and PGF (CO-Synch + CIDR; n = 539); 4) GnRH administration, followed in 7 d with PGF, followed by detection of estrus and AI during the 84 h after PGF; cows not detected in estrus by 84 h received GnRH and TAI at 84 h (Select Synch & TAI; n = 507); and 5) Select Synch & TAI plus a CIDR during the 7 d between the first injection of GnRH and PGF (Select Synch + CIDR & TAI; n = 498). Blood samples were collected (d -17 and -7, relative to PGF) to determine estrous cycle status. For the control, Select Synch & TAI, and Select Synch + CIDR & TAI treatments, a minimum of twice daily observations for estrus began on d 0 and continued for at least 72 h. Inseminations were performed using the AM/PM rule. Pregnancy was diagnosed by transrectal ultrasonography. Percentage of cows cycling at the initiation of treatments was 66%. Pregnancy rates (proportion of cows pregnant to AI of all cows synchronized during the synchronization period) among locations across treatments ranged from 37% to 67%. Pregnancy rates were greater (P < 0.05) for the Select Synch + CIDR & TAI (58%), CO-Synch + CIDR (54%), Select Synch & TAI (53%), or control (53%) treatments than the CO-Synch (44%) treatment. Among the 3 protocols in which estrus was detected, conception rates (proportion of cows that became pregnant to AI of those exhibiting estrus during the synchronization period) were greater (P < 0.05) for Select Synch & TAI (70%; 217 of 309) and Select Synch + CIDR & TAI (67%; 230 of 345) cows than for control cows (61%; 197 of 325). We conclude that the CO-Synch + CIDR protocol yielded similar pregnancy rates to estrous detection protocols and is a reliable TAI protocol that eliminates detection of estrus when inseminating beef cows.     

肉牛品改冷配技术体系中的计算机管理系统

在我国南方很多省份,肉牛主要以散养为主,导致母牛发情后常不能及时冷配,而冷配员却又闲着的现状,从而使母牛配种率低、存栏母牛有下降趋势。针对此情况,研发了肉牛冷配软件(软著登字2009SR11157,软件产品登记测试(2009-12-S2701)),对发情(乏情)预报、发情控制以及冷配员日常工作等方面进行计算机管理。冷配员通过规范地记录日常工作数据,逐步输入计算机,利用软件制定的日常工作计划实施冷配。结果表明:(1)对发情正常但漏配的母牛,通过软件准确预报有效黄体期,实施1次PG同期发情技术,同期发情率高于直肠检查组;(2)对乏情母牛,既实现了不通过直肠检查尽早发现、及时治疗缩短产犊间隔的目的,又获得了较高的受胎率;(3)规范了母牛的繁殖记录、提高了数据利用效率,并促进了牛繁殖数据记录的持续开展。     

安格斯肉牛冻精与隔年产犊牦牛杂交改良效果分析

通过对上年未产犊牦牛采用补饲与同期发情处理技术,并采用安格斯肉牛细管冻精开展牦牛杂交,出生的犏牛犊采用犊牛培育技术,对不同培育条件对犏牛犊牛生长发育的影响,研究结果表明,采用上年未产犊母牦牛补饲技术,与对照组相比,试验组隔年产犊母牦牛的发情率、受胎率、产犊率及犊牛成活率分别为86.67%、82.23%、78.34%和96.46%,分别提高22.84%、27.59%、33.03%和7.62%,差异显著(P<0.05)。采用犏牛犊牛培育技术,与传统对照组相比,犊牛培育组和培育对照组公、母犏牛初生的体高、体斜长、胸围、管围体重明显增加,差异显著(P<0.05)。上年未产犊母牦牛补饲与同期发情处理技术结合犏牛犊牛培育技术,显著提高其杂交一代犏牛的生长发育速度,提高犊牛的繁殖成活率。     

Castration of calves: a survey among Swiss suckler beef farmers

In fall 2004, a survey of a representative sample of 1185 Swiss suckler beef farmers was carried out by questionnaire (return rate 51.9%). 32.7% of the respondents castrated their calves without the help of a veterinarian, 37.8% mandated a veterinarian to carry out the castrations and 29.4% did not castrate their bull calves at all. On average, 8 calves were castrated per farm and year at an average age of 7 days when the castration was carried out by a farmer or 34 days when the castration was carried out by a veterinarian. Almost all farmers castrated their calves with the rubber ring, and a majority considered no other method as feasible. 73.9% of the veterinarians used the Burdizzo technique, 14.9% applied rubber rings, and 11.2% performed a surgical procedure. 22.6% of the farmers and 85.4% of the veterinarians used sedation; local anaesthesia was performed in 32.1% of the castrations carried out by farmers and in 84.5% of the castrations carried out by veterinarians. 65.7% of the farmers were concerned by the change of the Swiss Animal Protection Ordinance (2001), when pain relief became mandatory. 47.6% of these farmers changed their castration routine: 53.1% now mandated a veterinarian, 33.0% used sedation or local anaesthesia and 8.9% abandoned castration of their calves. 59.8% of the farmers intended to participate in a future course for laymen, to study and train the technique of local anaesthesia for castration. Castration of their calves is for many suckler beef farmers an inevitable husbandry procedure. The political goal, that all calves shall be castrated with local anaesthesia can only be reached when livestock owners are informed about the distress caused by the castration and convinced of the benefit of the local anaesthesia.Veterinarians are important information carriers in this process. The implementation also produces work, be it the more complex castration procedure or the education of the farmers who want to carry out the local anaesthesia themselves.     

杂交方式对肉牛产肉性能的影响

从1985起，系统性的选择了国外8个优良肉牛品种西门塔尔、利木赞、夏洛莱、皮埃蒙特牛等的冻精，采用级进和多元杂交的方式，产生了14个不同的肉牛杂交组合，用统一的方案进行了肥育、屠宰试验，研究了不同杂交方式对产肉性能的影响，为现阶段加速发展肉牛产业提供科学依据。     

Canadian veterinarians' use of analgesics in cattle, pigs, and horses in 2004 and 2005

Anecdotal evidence suggests that many veterinarians may not use analgesics in livestock for routine surgical procedures or painful disease states. To investigate this, we conducted a national mail survey of a random sample of 1431 Canadian veterinarians (response rate, 50.1%). Questions primarily concerned veterinarians' analgesic usage for common surgeries and medical conditions in beef and dairy cattle, pigs, and horses, and attitudes toward pain management. More than 90% of veterinarians used analgesic drugs for equine surgeries, for cesarean section in sows and cows, and for bovine claw amputation and omentopexy. However, in these and other categories, the analgesics used were often inadequate, and many veterinarians did not give analgesics to young animals. When castrated, < 0.001% of piglets received analgesia, compared with 6.9% of beef calves and 18.7% of dairy calves < or = 6 mo of age, 19.9% of beef calves and 33.2% of dairy calves > 6 mo of age, and 95.8% of horses. Respondents largely agreed that there are no long-acting, cost-effective analgesics available for use in livestock (median rating 8/10; interquartile range 4-9), and that the long or unknown withdrawal periods of some drugs outweighed the benefits of using them (median rating 7/10; interquartile range 4-9). The results indicate an urgent need for veterinarians to manage pain in livestock better. Continuing education would help, as would an increase in the number of approved, cost-effective analgesic drugs with known withdrawal periods.     

牦牛高效繁殖技术生产安犏牛试验研究

当年产犊牦牛采用“补饲+隔离断乳+生殖技术诱导”的高效繁殖技术,隔年产犊牦牛采用“补饲+生殖技术诱导”的高效繁殖技术,并采用安格斯肉牛细管冻精实施犏牛生产杂交试验,研究结果表明,采用牦牛高效繁育技术,与对照组相比,高效繁育组当年产犊母牦牛的发情率、受胎率、产犊率及犊牛成活率分别为67.50%、61.67%、56.67%和95.59%,分别提高38.33、35.83、35.83和11.59个百分点,差异极显著(P<0.01);采用牦牛高效繁育技术,与对照组相比,高效繁育组隔年产犊母牦牛的发情率、受胎率、产犊率及犊牛成活率分别为88.00%、83.00%、78.00%和96.16%,分别提高23.95%、25.76%、34.49%和7.25%,差异显著(P<0.05)。采用牦牛高效繁殖技术,显著提高当年产犊牦牛和隔年产犊牦牛的发情受胎效果,杂交后代犏犊牛的成活率也显著提高。     

肉牛犊牛饲养管理及疾病防治

肉牛具有生长周期短、产肉效率高、经济效益高、市场需求大的特征。近年,随消费者的物质生活水平显著提升,对牛肉制品的需求量不断增加,直接促进肉牛养殖产业的发展。肉牛养殖场养殖效益的好坏,受到新生犊牛饲养管理、早期断奶管理、疾病防治等各方面因素影响,做好犊牛养殖管理,能有效减少疫病的发生,避免由于传染性疾病危害造成严重经济损失,保证养殖户的经济效益,为广大消费者提供优质安全的牛肉制品。     

Greater participation by veterinarians in the reproductive management of dairy cattle

A program involving greater veterinary participation in detection of estrus and artificial insemination of cattle was evaluated in a 700-cow dairy herd from January 1987 through August 1988. Previous reproductive performance was below normal. First-service pregnancy rate from artificial insemination was 42%, and mean number of nonpregnant days for the cows was 120. Between postpartum days 55 and 62, all cows with functional corpus luteum assessed by rectal palpation were administered prostaglandin each Monday morning. Return visits were made to the herd each Thursday and Friday to observe cows and to inseminate those in estrus. On the other 5 days of the week, the owner or his employees inseminated all cows in estrus. The first-service pregnancy rate for 842 cows observed in estrus and inseminated by the veterinarian was 59%. The pregnancy rate for cows inseminated by the owner and his employees increased from 42% to 50%. The mean number of nonpregnant days for all 700 cows decreased from 120 to 98 days, resulting in approximately $46,000 of increased income for the dairyman or approximately a 4 to 1 return on investment in veterinary service. Results indicate that veterinarians could improve herd reproductive performance and solve chronic herd breeding problems by more actively participating with their clients in estrus detection and artificial insemination programs in cattle. The program allows practicing veterinarians an opportunity to observe cows for estrous behavior, establish their own pregnancy rate data, demonstrate to owners the importance of observing primary signs of estrus, and teach expert artificial insemination techniques.     

Estrus synchronization of beef cattle with a combination of melengestrol acetate and an injection of progesterone and 17beta-estradiol

Our hypothesis was that estrus synchronization in beef cattle using melengestrol acetate (MGA) and an injection of progesterone (P4) and 17beta-estradiol (E2) to regress dominant ovarian follicles would improve pregnancy rate (number conceived/number in group) to AI compared with feeding only MGA or injecting PGF2alpha. During 2 yr, peripubertal heifers (n = 52) and cows (n = 327) received either 1) MGA for 18 d (d 0 = 1st d of MGA) plus an injection of P4 and E2 in sesame oil (vehicle) on d 11 to regress persistent ovarian follicles (MGA+P4), 2) MGA for 18 d plus vehicle on d 11 (MGA), or 3) two injections of PGF2alpha 10 d apart (d 7 and 17, PG). Concentration of P4 was assessed in blood samples obtained on d 0, 7, and 17 to indicate estrual status (anestrual or estrual) during treatment to induce estrus synchrony. Observations for detection of estrus occurred every 6 h for 180 h following treatment cessation. Females showing estrus were inseminated 6 to 12 h after estrus detection. Conception to AI was determined by ultrasonography 35 to 40 d later. Conception rate was greater (P < .05) in females in the PG than in those in the MGA group but did not differ from conception rate of females in the MGA+P4 group. Among anestrual females, estrus synchrony rates were greatest (P < .10) among females treated with MGA+P4. Among females that were estrual before treatment cessation, estrus synchrony rates were greater (P < .10) among females treated with MGA+P4 or PG than among those given MGA. Pregnancy rates were greater (P < .05) among females that were anestrual before treatment cessation and treated with MGA or MGA+P4 than among those treated with PG. Estrus synchronization using MGA+P4 and E2 differentially improves estrus synchronization and pregnancy rates among anestrual and estrual beef cattle while maintaining conception rates similar to those of PGF2alpha-treated females.     

ASAS centennial paper: Contributions in the Journal of Animal Science to the development of protocols for breeding management of cattle through synchronization of estrus and ovulation

American Society of Animal Science members, publishing in Journal of Animal Science (JAS), completed research that resulted in understanding the estrous cycle of cattle, which led to the ability to inseminate cattle on a given day with pregnancy rates similar to those achieved by 21-d breeding by a fertile and sound bull. Research published in JAS led to understanding estrus, ovulation, the estrous cycle, and postpartum interval for cattle (1930s through 1960s) and hormonal factors affecting corpus luteum lifespan of cattle (1950s through 1980s). Research during the 1940s to 1960s, using gonadotropins and progesterone to manage the estrous cycle of cattle, established the concepts for estrous synchronization and stimulated commercial research directed at developing cost-effective progestogen estrous synchronization products, leading to commercially available products from 1967 through today (Repromix, melengestrol acetate, Syncro-Mate-B, controlled internal drug release). Prostaglandin F(2alpha) products were approved for estrous synchronization (1970s, 1980s), and GnRH products were approved for use in cattle to treat ovarian follicular cysts (1970s, 1980s). Research published in JAS was essential for understanding the biology of and potential value of both PGF(2alpha) and GnRH and contributed both to new knowledge and scientific bases for future Food and Drug Administration Center for Veterinary Medicine approval of those products. Research during the1980s through 2000s led to understanding ovarian follicular waves and described the timing of follicular recruitment, selection, dominance, and atresia; this research was essential for the ability to effectively manage follicles to achieve success with timed AI. The knowledge gained through research published in JAS resulted in development of the numerous estrous synchronization and breeding management protocols that are cost-effective and meet the breeding management needs of most beef and dairy enterprises.