The aim of this study was to characterize the incidence and timing of pregnancy loss from service event (timed artificial insemination or timed embryo transfer) to parturition. Lactating Holstein-Friesian cows were randomly assigned to receive either AI (n = 243) or embryo transfer (ET, n = 863) with a fresh or frozen in vitro- produced blastocyst derived from oocytes collected from the ovaries of elite dairy donors (n = 14 Holstein-Friesian and n = 8 Jersey) and elite beef donors (n = 21 Angus) using transvaginal ovum pick-up. In addition, oocytes were collected from the ovaries of beef heifers of known pedigree following slaughter at a commercial abattoir (n = 119). Blood samples were collected on d 7 from all cows to determine progesterone concentration and from subsets of cows on d 18 (n = 524) and d 25 (n = 378) to determine mRNA abundance of interferon-stimulated gene-15 and pregnancy-specific protein B concentration, respectively, to provide an early pregnancy diagnosis. Transrectal ultrasonography was conducted to determine pregnancy status on d 32, d 62 and 125 after synchronized ovulation. Parturition date was recorded for all cows that reached a term delivery. The predicted probability of pregnancy (%) varied at each time point (d7, 18, 25, 32, 62, 125, parturition) depending on treatment (AI: 77.0, largest proportion of pregnancy loss occurred in the period from service event (AI on d 0 or ET on d 7) to d 18, with minimal loss occurring between d 62 and parturition (AI: 1.8%, fresh ET: 1.9%, frozen ET: 3.5%). Treatment differences in the predicted probability of pregnancy per service event were detected between fresh ET versus frozen ET on d 32 and both AI and fresh ET versus frozen ET on d 62, 125, and at parturition. There was greater probability of pregnancy loss between d 32 and 62 following ET (fresh: 11.3%, Frozen: 18.0%) than AI (4.0%). The percentage of cows that calved following transfer of a fresh embryo (45.5%) was similar to AI (44.0%), but less when a frozen embryo was transferred (30.2%). In conclusion, AI and fresh ET led to a greater probability of a cow becoming pregnant and maintaining the pregnancy to term than frozen ET. Cows that were still pregnant on d 62 had a very strong likelihood of maintaining the pregnancy to full-term parturition, irrespective of treatment. Further work is required to improve the likelihood of pregnancy establishment and reduce embryonic and fetal mortality following transfer of a cryopreserved in vitro-produced embryo.

Following a significant increase in herd and farm sizes after the removal of milk quotas in Europe, the past 10 years have seen a slight yet steady decline in the population of cattle. This includes a reduction of approximately 5% in dairy and beef cattle. This trend is driven by various factors, such as changing market demands, economic shifts, and sustainability challenges in the livestock sector. Despite this, technological advancements in reproductive management have continued to enhance efficiency and sustainability, particularly in dairy production. The main areas of rapid development, which will continue to grow for improving fertility and management, include: i) genetic selection (including improved phenotypes for use in breeding programs), ii) nutritional management (including transition cow management), iii) control of infectious disease, iv) rapid diagnostics of reproductive health, v) development of more efficient ovulation/estrous synchronization protocols, vi) assisted reproductive management (and automated systems to improve reproductive management), vii) increased implementation of sexed semen and embryo transfer, viii) more efficient handling of substantial volumes of data, ix) routine implementation of artificial intelligence technology for rapid decision-making at the farm level, x) climate change and sustainable cattle production awareness, xi) new (reproductive) strategies to improve cattle welfare, and xii) improved management and technology implementation for male fertility. This review addresses the current status and future outlook of key factors that influence cattle herd health and reproductive performance, with a special focus on dairy cattle. These insights are expected to contribute to improved performance, health, and fertility of ruminants in the next 20 years.

The objective of this study was to determine the effect of the timing of presumptive conceptus attachment (pCA) and its relationship with subsequent pregnancy loss (PL) in lactating dairy cows following timed artificial insemination with conventional (TAI-C) or X-sorted (TAI-S) semen or timed embryo transfer (TET) with frozen-thawed in vitro-produced (IVP) embryos. Lactating cows (n = 417, predominantly Holstein-Friesian) located in 3 herds were blocked based on parity, calving date, and economic breeding index and randomly assigned to receive TAI-C (n = 136), TAI-S (n = 136) or TET with a single, grade-1 frozen-thawed IVP blastocyst (n = 145). Cows were synchronized with a 10-d Progesterone-Ovsynch protocol, and were either inseminated (TAI-C, TAI-S) 16 h after the second GnRH or received TET on d 7 after presumptive estrus. Serum progesterone was measured in all cows on d 7 after expected ovulation. For all cows that had not returned to estrus, serum pregnancy-specific protein B (PSPB) was measured on d 7, 17, and daily from d 19 through 28 after expected ovulation to characterize the timing of pCA. The day of pCA was defined as the first day of an increase in PSPB of ≥12.5% from baseline (d 17) followed by 2 more consecutive days of ≥12.5% increase from the previous day. Pregnancy was diagnosed in cows that had not returned to estrus via ultrasound examination on d 32, 62, and 120 postovulation, and calving data were recorded. Day of pCA (mean; 95% CI) was earlier for TAI-C (20.0; 19.7, 20.3) compared with TET (20.6; 20.3, 20.9), and TAI-S (20.3; 19.9, 20.6) was not different from the other 2 treatments. Calving/service event (C/SE) was greater (83.2% vs. 54.4%) and PL during the interval from pCA to expected calving date was less (16.8% vs. 45.6%) for cows with early pCA (≤d 20; 23/137) compared with cows that had late pCA (≥d 21; 36/79). The incidence of PL was greater for cows assigned to TAI-S (30.7%) and TET (33.8%) than TAI-C (16.4%). Consistent with previous studies, measuring time to pCA provides new insights into understanding early pregnancy establishment and PL in lactating dairy cows. The timing of pCA was later for TET compared with TAI-C and may be associated with increased risk of PL. Further research into the regulatory mechanisms underlying conceptus attachment is warranted.

Assisted reproductive technologies, particularly sex-sorted semen and in vitro embryo production (IVP) can contribute to accelerating genetic gain in both dairy breeds and beef breeds suitable for mating with dairy cows by increasing the number of offspring produced from genetically elite dams. Use of sexed semen has rapidly increased in recent years, accelerating herd genetic gain through selection of the best genetic merit dams to breed replacements, allowing non-replacement dams to be bred to beef sires or to act as recipients of beef embryos to improve calf marketability. IVP offers significant advantages over traditional multiple ovulation embryo transfer (MOET) including increased flexibility in sire usage allowing multiple pregnancies from elite dam-sire combinations to be generated, the ability to produce more embryos per unit time per genetically elite female, the ability to use oocytes from prepubertal females and the more efficient use of rare or high-cost semen straws. Despite these benefits, significant challenges relating to pregnancy loss after embryo transfer, particularly after cryopreservation of IVP embryos, and issues relating to peri- and postnatal health and development of IVP offspring remain to be resolved and hamper the more widespread application of the technology. Improving our understanding of the underlying physiological and molecular mechanisms that regulate early embryo development, embryo-endometrial interactions and lead to successful pregnancy establishment is necessary to understand and elucidate the causes of pregnancy loss and provide a basis for new strategies to improve pregnancy outcomes and reproductive efficiency.

The objectives of this study were to (1) compare in vitro embryo production using conventional (CONV) or sex-sorted (SS) semen for in vitro fertilization (IVF) of oocytes collected from elite genetic merit dairy and beef donors, and (2) compare pregnancy per embryo transfer (P/ET) in lactating dairy cows following transfer of fresh dairy or beef embryos derived from CONV or SS semen. Oocytes were collected once weekly for a period of 4 successive weeks using ultrasound-guided transvaginal ovum pick-up from the ovaries of elite beef (Angus, n = 37) and dairy (Holstein-Friesian, n = 51) heifers and cows. Following in vitro maturation, oocytes were fertilized with frozen-thawed CONV or SS semen from a panel of beef (n = 6) or dairy (n = 9) sires of proven fertility and cultured in vitro to the blastocyst stage. A total of 507 grade 1 blastocysts (n = 468 fresh, n = 39 frozen-thawed) were transferred to lactating Holstein-Friesian recipients that had been synchronized using a 10-d progesterone-Ovsynch protocol. Recipients were blocked based on parity, DIM, and Economic Breeding Index, and randomly assigned to receive a single beef-CONV, beef-SS, dairy-CONV, or dairy-SS embryo. Pregnancy diagnosis was carried out using transrectal ultrasound on d 32 after synchronized estrus and confirmed on d 63. Pregnancy loss was characterized as loss between d 32 and 63. The number of oocytes recovered per ovum pick-up session (14.9 vs. 8.1), blastocyst yield (28.7% vs. 16.1%) and the number of blastocysts produced per IVF session (2.8 vs. 1.0) were greater for beef donors than dairy donors. Overall, blastocyst yield and the number of blastocysts produced per IVF were similar for CONV (20.0% and 1.7) and SS (24.7% and 2.1) semen. Pregnancy per ET on d 32 and 63 was not different between beef and dairy embryos (d 32: 55.3% and 61.3%; d 63: 46.4% and 56.0%, respectively) or between embryos derived from CONV and SS semen (d 32: 58.8% and 57.9%; d 63: 50.1% and 52.3%, respectively). Pregnancy loss was not different between dairy and beef embryos or between embryos derived from CONV and SS semen. There was no association between serum progesterone concentration on d 7 and pregnancy rate on d 32 or d 63. In conclusion, oocyte recovery and blastocyst development were greater for beef donors compared with dairy donors. Blastocyst development was similar when CONV and SS were used for IVF, and P/ET was similar for dairy and beef embryos and for embryos derived from CONV and SS semen.

The objective was to compare pregnancy per service event (P/S) in lactating dairy cows following timed artificial insemination (AI) or timed embryo transfer (ET) using either fresh or frozen in vitro produced (IVP) embryos. Oocytes were collected once per week for up to 9 weeks using transvaginal ovum pick-up from elite dairy donors (ET-DAIRY; n = 40; Holstein-Friesian and Jersey) and elite beef donors (ET-ELITE-BEEF; n = 21; Angus). Both ET-DAIRY and ET-ELITE-BEEF donors were comprised of heifers and cows. In addition, oocytes were collected from the ovaries of beef heifers of known pedigree following slaughter at a commercial abattoir (ET-COMM-BEEF; n = 119). Following in vitro maturation and fertilization, presumptive zygotes were cultured in vitro to the blastocyst stage. Grade 1 blastocysts were either transferred fresh or frozen for on-farm thawing and direct transfer. 1106 recipient cows (all lactating, predominantly Holstein-Friesian) located on 16 herdlets were blocked based on parity, calving date and economic breeding index, and randomly assigned to receive AI (n = 243) or ET (n = 863) after estrous synchronization with a 10-d Progesterone-synch protocol. Cows assigned to ET were further randomized to receive fresh (n = 187) or frozen (n = 178) ET-ELITE-BEEF embryos, fresh (n = 169) or frozen (n = 162) ET-DAIRY embryos, or fresh (n = 80) or frozen (n = 87) ET-COMM-BEEF embryos. Pregnancy was diagnosed using trans-rectal ultrasound on d 32 to 35 after synchronized ovulation and confirmed on d 62 to 65, at which time fetal sex was determined. Pregnancy per service event at d 32 was not different between AI (48.8%) and ET (48.9%) and did not differ between dairy and beef embryos (50.3% vs 48.1%, respectively). However, P/S was less on d 32 following transfer of frozen embryos (41.6%) compared with fresh embryos (56.1%). Pregnancy loss between d 32 and 62 was greater for ET (15.1%) compared with AI (4.7%), with greater losses observed for frozen beef (18.5%), fresh beef (17.3%) and frozen dairy (19.2%) compared with fresh dairy (6.0%) embryos. Serum P4 concentration on d 7 was associated with P/S at d 32 and d 62. Cows in the quartile with the least serum P4 concentrations (Q1) had less probability of being pregnant on d 32 (33.4%) compared with cows in the 3 upper quartiles for serum P4 (45.7%, 55.6% and 61.2 for Q2, Q3 and Q4, respectively). Sex ratio (M:F) at d 62 was skewed toward more male fetuses following ET (61.1:38.9) compared with AI (43.2:56.8) and was consistent with the sex ratio among in vitro blastocysts (61.2:38.8). In conclusion, P/S was similar for AI and ET, although pregnancy loss between d 32 and d 62 was greater for ET than for AI.

A unique aspect of seasonal-calving pasture-based systems of dairy production is the intense focus placed on achieving a concentrated herd-calving period in late winter and early spring. Hence, excellent reproductive performance is required during a short breeding period. A concentrated calving period also produces a problem in the form of a large number of male dairy calves being born at the same time; as these calves have little economic value due to poor beef merit, they present a potential welfare concern. A solution exists in the form of sex-sorted semen, but this is typically associated with poorer pregnancy per artificial insemination, and hence, the use of sex-sorted semen must be carefully considered. The logical strategy to use sex-sorted semen is to target the best genetic merit dams in the herd to generate replacement heifers, thereby accelerating herd genetic gain. On the other hand, if all dairy farmers adopt such a strategy, there will be a corresponding reduction in elite genetic merit male dairy calves being born, potentially reducing availability of the next generation of future bulls to be used for artificial insemination. Use of in vitro embryo production on elite dairy donors could avoid this problem by acting as a multiplier, potentially in tandem with Y-sorted semen to skew the offspring sex ratio towards more male calves. Use of sexsorted semen on the best genetic merit dams can also facilitate a marked increase in the usage of beef semen on any dams that are deemed unsuitable for sex-sorted semen. The use of "beef on dairy" requires selection of beef bulls that generate offspring with traits that meet the key requirements of both the dairy farmer (e.g., gestation length and calving ease) and the beef farmer that must be motivated to purchase the calves (e.g., growth rate, age at slaughter, carcass value). Beef breed dams that have elite genetic merit for these traits could also be considered for in vitro embryo production, potentially in tandem with Y-sorted semen, to facilitate genetic gain for the growing "beef-on-dairy" market. It is possible to transfer a beef embryo (75-100% beef breed genetics) into dairy dams that are not required to generate replacements, but this is likely to remain a niche practice as there are many barriers to widespread adoption. Such combinations of assisted reproduction have the potential to improve the efficiency and sustainability metrics of seasonalcalving pasture-based dairy herds.& COPY; 2023 The Author(s). Published by Elsevier B.V. on behalf of The Animal Consortium. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

A unique aspect of seasonal-calving pasture-based systems of dairy production is the intense focus placed on achieving a concentrated herd-calving period in late winter and early spring. Hence, excellent reproductive performance is required during a short breeding period. A concentrated calving period also produces a problem in the form of a large number of male dairy calves being born at the same time; as these calves have little economic value due to poor beef merit, they present a potential welfare concern. A solution exists in the form of sex-sorted semen, but this is typically associated with poorer pregnancy per artificial insemination, and hence, the use of sex-sorted semen must be carefully considered. The logical strategy to use sex-sorted semen is to target the best genetic merit dams in the herd to generate replacement heifers, thereby accelerating herd genetic gain. On the other hand, if all dairy farmers adopt such a strategy, there will be a corresponding reduction in elite genetic merit male dairy calves being born, potentially reducing availability of the next generation of future bulls to be used for artificial insemination. Use of in vitro embryo production on elite dairy donors could avoid this problem by acting as a multiplier, potentially in tandem with Y-sorted semen to skew the offspring sex ratio towards more male calves. Use of sex-sorted semen on the best genetic merit dams can also facilitate a marked increase in the usage of beef semen on any dams that are deemed unsuitable for sex-sorted semen. The use of "beef on dairy" requires selection of beef bulls that generate offspring with traits that meet the key requirements of both the dairy farmer (e.g., gestation length and calving ease) and the beef farmer that must be motivated to purchase the calves (e.g., growth rate, age at slaughter, carcass value). Beef breed dams that have elite genetic merit for these traits could also be considered for in vitro embryo production, potentially in tandem with Y-sorted semen, to facilitate genetic gain for the growing "beef-on-dairy" market. It is possible to transfer a beef embryo (75-100% beef breed genetics) into dairy dams that are not required to generate replacements, but this is likely to remain a niche practice as there are many barriers to widespread adoption. Such combinations of assisted reproduction have the potential to improve the efficiency and sustainability metrics of seasonal-calving pasture-based dairy herds.

The objective of this study was to evaluate the timing of artificial insemination (AI) with frozen-thawed sex-sorted semen on pregnancy per AI (P/AI) in dairy heifers. A 6-d progesterone Co-Synch protocol was used for ovulation synchronization of dairy heifers, with timed AI (TAI) coincident with (TAI-0) or 8 h (TAI-8) after the second injection of GnRH, corresponding to either 48 h or 56 h after removal of the progesterone-releasing intravaginal device. Pregnancy diagnosis was conducted by transrectal ultrasound scanning of the uterus 34 d after TAI (n = 816 records available for analysis). Generalized linear mixed models were used to examine the effects of treatment on P/AI. Treatment (n = 2), herd (n = 11), and treatment × herd were included as categorical fixed effects. Heifer body weight and Economic Breeding Index values for milk production, fertility, calving performance, beef carcass, cow maintenance, cow management, and health were included as continuous fixed effects. Heifer ID was included as a random effect. Pregnancy per AI was greater for TAI-8 heifers (59%) compared with TAI-0 heifers (50%). Pregnancy per AI ranged from 38% to 75% between herds but there was no treatment × herd interaction. The fertility subindex (positive) and the cow management subindex (negative) were the only continuous animal variables associated with P/AI. Delaying the timing of AI with frozen-thawed sex-sorted semen by 8 h in dairy heifers enrolled on a 6-d progesterone Co-Synch protocol improved P/AI.

Reproduction, Fertility and Development is an international journal publishing original research , review and comment in the fields of reproduction and developmental biology in humans, domestic animals and wildlife

Reproduction, Fertility and Development is an international journal publishing original research , review and comment in the fields of reproduction and developmental biology in humans, domestic animals and wildlife

Reproduction, Fertility and Development is an international journal publishing original research , review and comment in the fields of reproduction and developmental biology in humans, domestic animals and wildlife

Reproduction, Fertility and Development is an international journal publishing original research , review and comment in the fields of reproduction and developmental biology in humans, domestic animals and wildlife

The contribution of the calf enterprise to the profit of the dairy farm is generally considered small, with beef bull selection on dairy farms often not considered a high priority. However, this is likely to change in the future as the rapid rate of expansion of the dairy herd in some countries is set to plateau and improvements in dairy herd fertility combine to reduce the proportion of dairy breed calves required on dairy farms. This presents the opportunity to increase the proportion of beef breed calves born, increasing both the value of calf sales and the marketability of the calves. Beef embryos could become a new breeding tool for dairies as producers need to reassess their breeding policy as a consequence of welfare concerns and poor calf prices. Assisted reproductive technologies can contribute to accelerated genetic gain by allowing an increased number of offspring to be produced from genetically elite dams. There are the following 3 general classes of donor females of interest to an integrated dairy-beef system: (1) elite dairy dams, from which oocytes are recovered from live females using ovum pick-up and fertilized in vitro with semen from elite dairy bulls; (2) elite beef dams, where the oocytes are recovered from live females using ovum pick-up and fertilized with semen from elite beef bulls; and (3) commercial beef dams (≥50% beef genetics), where ovaries are collected from the abattoir postslaughter, and oocytes are fertilized with semen from elite beef bulls that are suitable for use on dairy cows (resulting embryo with ≥75% beef genetics). The expected benefits of these collective developments include accelerated genetic gain for milk and beef production in addition to transformation of the dairy herd calf crop to a combination of good genetic merit dairy female calves and premium-quality beef calves. The aim of this review is to describe how these technologies can be harnessed to intensively select for genetic improvement in both dairy breed and beef breed bulls suitable for use in the dairy herd.

Reproduction, Fertility and Development is an international journal publishing original research , review and comment in the fields of reproduction and developmental biology in humans, domestic animals and wildlife