J.E. Larson

Control of the estrous cycle to improve fertility for fixed-time artificial insemination in beef cattle: a review.

Early estrus-synchronization protocols focused on regressing the corpus luteum (CL) with an injection of PGF(2alpha) followed by detection of estrus or involved the use of exogenous progestins that prevent estrus from occurring. Later, protocols combining the use of PGF(2alpha) and exogenous progestins were developed. Gonadotropin-releasing hormone was utilized to control follicular waves, synchronize ovulation, or to luteinize large dominant follicles. Our research aimed to develop reliable protocols that 1) relied solely on fixed-timed AI (TAI); 2) required a maximum of 3 animal handlings, and 3) were successful in estrous-cycling and noncycling females. In cows, insertion of an intravaginal progesterone insert during the 7-d interval between the initial GnRH and PGF(2alpha) injections enhanced pregnancy rates by 9 to 10%. In a multi-location study, a TAI protocol yielded pregnancy rates similar to a protocol involving detection of estrus plus a fixed-time clean-up AI for females not detected in estrus (54 vs. 58%, respectively, for cows and 53 vs. 57%, respectively, for heifers). Initiation of estrous cycles in noncycling cows is likely the primary manner in which beef producers may improve fertility in response to estrus synchronization and TAI protocols. Treatment of noncycling females with progesterone and GnRH increases the percentage of cycling females and improves fertility to a TAI, but inducing cyclicity with hCG failed to enhance fertility in TAI protocols. Supplementing progesterone after TAI failed to increase pregnancy rates in beef cattle. In contrast, administration of hCG 7 d after TAI induced an accessory CL, increased progesterone, and tended to enhance pregnancy rates. Development of TAI protocols that reduce the hassle factors associated with ovulation synchronization and AI provide cattle producers efficient and effective tools for capturing selective genetic traits of economic consequences. Location variables, however, which may include differences in pasture and diet, breed composition, body condition, postpartum interval, climate, and geographic location, affect the success of TAI protocols.

Effects of supplemental progesterone on the development, metabolism and blastocyst cell number of bovine embryos produced in vitro

The objectives of the present experiment were to determine whether supplementation with progesterone (LO, 1 ng mL(-1) or HI, 100 ng mL(-1)) during either the first (Culture-1, Day 1 to 3) or second (Culture-2, Day 4 to 7) phase of culture of in vitro-produced embryos alters embryo development, embryo metabolism or blastocyst cell number. The percentage of oocytes that cleaved, the percentage of cleaved embryos that developed to the morula stage or greater, the blastocyst stage or greater or the hatched blastocyst stage were similar among treatments. Quantities of glucose metabolised per blastocyst per hour were similar, but when metabolic data was normalised for numbers of cells in each blastocyst, the LO treatment during Culture-2 metabolised more glucose (P=0.03) compared with all other treatments. Embryos receiving LO progesterone tended to have greater (P=0.085) metabolism of glucose compared with embryos receiving HI progesterone. Quantities of pyruvate oxidised per blastocyst per hour, and per cell, were similar among treatments. The number of cells per blastocyst in the control group was increased (P=0.039) compared with cells in progesterone-treated groups. In conclusion, supplementation with progesterone during the culture of in vitro-produced embryos does not appear to improve embryo characteristics.

Accuracy of pregnancy specific protein-B test for early pregnancy diagnosis in dairy cattle.

The objective was to evaluate the accuracy of an ELISA for pregnancy specific protein B (PSP-B) for early pregnancy diagnosis in dairy cattle. Blood from lactating (>100 d postpartum) dairy cows (n = 738), was collected on Days 28, 30, and 35 (Day 0 = estrus), analyzed with an ELISA for PSP-B, and the cows designated as pregnant, probable, unlikely, or non-pregnant. Immediately after blood collection, transrectal ultrasonography (TRUS) was done for pregnancy diagnosis, and the results used as a criterion standard test for comparison with PSP-B. At Day 28, 46.3% were diagnosed by TRUS as pregnant. The PSP-B sensitivity was 93.9% on Day 28 and similar on Days 30 and 35. The PSP-B specificity, positive predictive value, negative predictive value, and accuracy were all >94% on Day 28 and similar on Days 30 and 35. However, the accuracy was significantly less compared to TRUS (P < 0.01). The percentage of all samples from cows that were probably pregnant or unlikely to be pregnant was 5.6%. At Days 28, 30, and 35, percentages of uncertain samples were 8.5, 4.8, and 3.3%, respectively (P < 0.01), and Kappa values were 0.92, 0.92, and 0.95. False negative and false positive results were attributed to low concentrations of PSP-B in pregnant animals and to persistence of pregnant concentrations of PSP-B in females with pregnancy loss, respectively. In conclusion, PSP-B ELISA was a sensitive, specific, and accurate test for pregnancy diagnosis (relative to TRUS) at Days 28, 30, and 35 after breeding.

An economic evaluation of estrous synchronization and timed artificial insemination in suckled beef cows

Partial budget analysis was used to determine the economic outcome of estrus synchronization (ES) and timed artificial insemination (TAI) in commercial cow-calf production. Suckled beef cows (n = 1,197) from 8 locations were assigned randomly within each location to 1 of 2 treatment groups: 1) cows were inseminated artificially after synchronization of ovulation using the CO-Synch + CIDR protocol, which includes a 100-μg injection of GnRH (OvaCyst; TevaAnimal Health, St. Joseph, MO) when a controlled internal drug-releasing device (CIDR; Pfizer Animal Health, New York, NY) containing 1.38 g of progesterone was inserted. The CIDR was removed 7 d later, and cows received a 25-mg injection of PGF(2α) (PGF; Lutalyse; Pfizer Animal Health), followed in 66 h with TAI and a second 100-μg injection of GnRH (TAI; n = 582), and 2) cows were exposed to natural service (NS) without estrous synchronization (Control; n = 615). Within each herd, cows from both treatments were maintained together in similar pastures and were exposed to bulls 12 h after the last cow in the TAI treatment was inseminated. Overall, the percentage of cows exposed to treatments that subsequently weaned a calf was greater (P < 0.05) for TAI (84%) than Control (78%) cows. In addition, survival analysis demonstrated that cumulative calving distribution differed (P < 0.05) between the TAI and Control treatments. Weaning weights per cow exposed to treatments were greater (P < 0.01) for cows in the TAI treatment (193.4 ± 4.3 kg) than those cows in the Control treatment (175.9 ± 4.3 kg). Overall, increased returns plus decreased costs (

Embryo production in superovulated Angus cows inseminated four times with sexed-sorted or conventional, frozen-thawed semen

82.32) minus decreased returns plus increased costs (

Progesterone status, parity, body condition, and days postpartum before estrus or ovulation synchronization in suckled beef cattle influence artificial insemination pregnancy outcomes

33.18) resulted in a

Impacts of Reproductive Technologies on Beef Production in the United States

49.14 advantage per exposed cow in the TAI treatment compared with the Control treatment. Location greatly influenced weaned calf weights, which may have been a result of differing management, nutrition, genetic selection, production goals, and environments. We concluded that ES and TAI had a positive economic impact on subsequent weaning weights of exposed cows.

Human chorionic gonadotropin influences ovarian function and concentrations of progesterone in prepubertal Angus heifers1

This study tested the hypothesis that four inseminations of commercially frozen sexed semen (>or=2.1x10(6) sperm per 0.25-mL straw) in superstimulated embryo donors would yield a percentage and quantity of transferable embryos similar to that achieved with conventional frozen semen. Bos taurus, angus cows (n=32), stratified by age and body condition, were randomly allocated to receive four inseminations of frozen-thawed semen, either conventional semen (>or=15x10(6) sperm/straw; Conventional) or sexed semen (>or=2.1x10(6) sperm/straw; Sexed) from one of two AI sires. From 10 to 13 d after estrus, follicle-stimulating hormone (FSH) was given twice-daily, with prostaglandin F(2alpha) given twice on the last day. Cows were inseminated once (1x) at first detected estrus and twice (2x) and once (1x) at 12 and 24h later, respectively, with nonsurgical embryo recovery 7 d after first detected estrus. The study was repeated 30 d later (switch-back experimental design). The total number of ova per flush was similar between Conventional and Sexed treatments (10.9+/-1.8 vs. 10.5+/-1.6), but the number of Grade 1 embryos was greater (P<0.01) for Conventional (4.3+/-0.8 vs. 2.3+/-0.7). Conversely, the mean number of unfertilized ova was greater (P<0.05) for Sexed (5.6+/-1.0 vs. 3.0+/-1.2). There was no significant difference between treatments for numbers of degenerate, Grades 2 or 3, and transferable embryos and no significant differences between bulls in percentage of transferable embryos (44.4% and 46.7%). However, fertilization rates and percentage of transferable embryos were affected (P<0.05) by period and donor. In conclusion, superstimulated donor cows inseminated four times had fewer Grade 1 embryos and more unfertilized ova with sexed versus conventional semen.

Evaluation of the 5-day versus a modified 7-day CIDR breeding program in dairy heifers

Our objective was to assess the effects of progesterone before initiating an estrus- or ovulation-synchronization program in addition to the influence of parity, BCS, and days postpartum on resulting pregnancy rates per AI. Experimental data were combined from 73 herd-year studies consisting of more than 8,500 suckled beef cows exposed to variants of the CO-Synch program. Blood was harvested from samples collected at 10 and 0 d before the onset of CO-Synch, and progesterone concentrations of the samples were determined. The progesterone environment preceding synchronization was assessed in 3 ways on the basis of progesterone concentrations measured in the 2 defined blood samples. All binomial logistic regression models used procedure GLIMMIX in SAS and included the fixed effects of program duration, inclusion of progesterone via an intravaginal insert, parity, days postpartum at AI, BCS, and appropriate interactions. In addition, model 1 included 3 categories of progesterone concentrations (low [<1 ng/mL], medium [1.00 to 3.99 ng/mL], and high [≥4.00 ng/mL] concentrations) at 10 and 0 d before synchronization and their interaction. Model 2 included 4 categories defining the stage of the estrous cycle (late diestrus, early diestrus, and proestrus-estrus-metestrus) or anestrus, at which cows started the synchronization program. Model 3 defined cows as cycling or noncycling at the onset of the program. Significant effects of progesterone supplementation, which hormone was used to initiate the timed AI program, parity, BCS, days postpartum, and progesterone status assessed in 3 ways were consistent in nearly all models. Progesterone status at the onset of synchronization was not important to pregnancy outcomes in multiparous cows, whereas pregnancy rate per AI was suppressed in primiparous cows that began in a low-progesterone environment (proestrus, estrus, metestrus, or anestrus). A significant 3-way interaction of parity, BCS, and days postpartum in 2 models reinforced the importance of these factors to AI pregnancy outcomes. Ancillary analyses identified the significant effects of cycling status and BCS as well as days postpartum on luteolytic response to PGF(2α). Pregnancy loss of 2.7% to 4.2% was detected to occur between a positive pregnancy diagnosis at 35 d post-AI and later stages of pregnancy. We concluded that progesterone status at the onset of the synchronization program is critical to pregnancy outcomes in primiparous but not multiparous cows.

Fixed-time artificial insemination in replacement beef heifers after estrus synchronization with human chorionic gonadotropin or gonadotropin-releasing hormone

Estimations of world population growth indicate that by the year 2050 we will reach nine billion habitants on earth. These estimates impose a tremendous challenge in the current agricultural systems as food supply will need to increase by 100 % in the next 40 years (Food and Agriculture Organization of the United Nations 2009). Beef will be a primary protein source that will assist in meeting the requirements for a portion of the protein in diets of this expanding global populace. Beef is a high-quality protein that contains all essential amino acids for the human body and also contains additional essential nutrients such as iron, zinc, B vitamins, riboflavin, selenium, choline, and conjugated linoleic acid (CLA). Adopting reproductive technologies at greater rates than currently used is a viable method to dramatically enhance production efficiency of beef cattle enterprises.Artificial insemination (AI), estrous synchronization and fixed-time AI (TAI), semen and embryo cryopreservation, multiple ovulation and embryo transfer (MOET), in vitro fertilization, sex determination of sperm or embryos, and nuclear transfer are technologies that are used to enhance the production efficiency of beef operations. In many cases, the development of these technologies is responsible for significant changes to traditional livestock production practices. However, adoption of these technologies appears to has not grown at the same rate in the United States as other formidable beef producing nations. For example, sales of beef semen for AI increased from 3.3 to 11.9 million units between 1993 and 2011 in Brazil, whereas that in the United States has increased from 2.9 to 3.8 million units during the same period. The significant increases in adoption of reproductive technologies in developing countries is likely as a result of the development of practical estrous synchronization and TAI systems that have allowed beef producers the opportunity to eliminate detection of estrus in their AI programs with a high degree of success. In the United States, slow adoption rates of these technologies may result in a future loss of international market share of beef products as other nations take advantage not only of the additional kilogram of beef that can be produced but also the improved quality of beef that can be realized through incorporation of reproductive technologies and resultant genetic improvement. However, current difficulties the US producers have with the incorporation of applied reproductive technologies, such as TAI, MOET, and sex semen, must not be the reason to overlook and incorporate more traditional reproductive technologies such as castration, breeding season management, or weaning. In many cases, beef producers in the United States fail to incorporate these more traditional technologies, which results in a reduction in production efficiency of the US beef industry. This chapter will focus on both traditional and more developed reproductive technologies that will play a role in enhancing future production efficiencies of the US beef cattle production system.