Invited review: Treatment of cows with an extended postpartum anestrous interval

Recent advances in the synchronization of estrus and ovulation in dairy cows

Synchronization programs have become standard components in the current breeding management of cows in the dairy herds of most dairy industries. Many are based on protocols that allow timed inseminations (TAI) so as to circumvent the practical difficulties associated with estrus detection. These difficulties are exacerbated in modern herds of high producing cows either because of increasing herd size in which individual animal monitoring is difficult and often subjective, or because small intensively managed herds are milked in robotic systems that minimize animal: staff interactions. Additional reasons arise from high producing cows having less obvious symptoms of estrus, partly because of housing systems combined with intensive feeding and milking, partly because of higher metabolic clearance rates of reproductive hormones like estradiol and partly because of the increasing prevalence of prolonged post-partum anestrus and reproductive tract pathology. The most recently developed programs include protocols for resynchronization following first or subsequent inseminations. These re-synchronization protocols may involve selected forms of hormonal intervention during the diestrous and pro-estrous periods following TAI, or following pregnancy diagnosis by ultrasound from 28 days after TAI. The latter form of re-synchronization has become increasingly important with the recognition that late embryonic/early foetal death has become a major factor compromising the reproductive performance of high producing Holstein cows in many dairy industries. Although cows detected in estrus without any hormonal treatment before insemination have higher conception rates than those inseminated following synchronization and TAI, the low detection rates combined with embryonic death means that intervals from calving to conception (days open) are usually less when synchronization programs have been successfully implemented. One of the significant factors affecting a program's success is the compliance rate that may sometimes be less than 70%. Almost all programs involve strategically timed injections of prostaglandin F2alpha (PGF) and gonadotropin releasing hormone (GnRH). Injections of an estradiol ester and progesterone supplementation per vaginum may be included in some programs. The basic program is the "Ovsynch" regimen. Numerous variations have been tested and developed. Many involve increasingly complex protocols that increase the risk of non-compliance, none has consistently achieved conception rates that exceed 40% and few have reduced the incidence of embryonic death. These synchronization programs are the best that are currently available. They have not been able to overcome the consequences of lowered fertility associated with high levels of milk yield, forms of nutrition and environmental factors like heat stress that have profound effects on the physiology and metabolism of the high producing dairy cow.

Comparison of diagnostic approaches, and a cost-benefit analysis of different diagnostic approaches and treatments of anoestrous dairy cows

AIM

To compare diagnostic techniques, and to assess the economic effects of diagnosing and treating dairy cows not detected in oestrus before the planned start of mating (PSM).

METHODS

Cows from 12 herds were defined as anoestrus at Day -9 (where Day 0=PSM) based on presence of tail paint that had been applied at Day -35. The presence of a corpus luteum (CL) was diagnosed by palpation or ultrasonography on Day -9, or by determining the concentration of progesterone (P4) in milk at Days -16 and -9. Cows with concentrations of P4 in milk >1 ng/ml at one or both times were defined as CL+. Cows were randomly assigned to be treated with (a) nothing (Control; n=558); (b) gonadotrophin-releasing hormone (GnRH) on Day -9, prostaglandin F(2alpha) (PGF(2alpha)) on Day -2, and GnRH on Day 0, with set-time artificial insemination (AI) 16-20 h after the second GnRH treatment (Ovsynch; n=553); or (c) as for (b) but with placement of an intravaginal P4-releasing device on Day -9, and removal on Day -2 (Ovsynch+P4; n=551). Cows detected in oestrus between Day -2 and the second GnRH treatment did not receive the second GnRH treatment. Pregnancy diagnosis took place on three occasions, and the date of conception estimated, from which the PSM-to-conception interval was calculated. Agreement between the three diagnostic techniques for CL status was evaluated using Kappa analyses, and sensitivities and specificities were calculated using a Bayesian Monte Carlo approach that does not assume a gold standard. Partial budgets and decision trees were constructed to assess the cost effectiveness of diagnosis and treatment.

RESULTS

The level of agreement was higher between ultrasonography and concentration of P4 in milk (0.64) than for palpation and ultrasonography or concentration of P4 in milk (0.50 and 0.49, respectively). The Ovsynch+P4 treatment had a higher net benefit than Ovsynch relative to no treatment (NZ$80.40 and NZ$47.50/cow treated, respectively) in the absence of diagnosis of CL status. Following diagnosis, the Ovsynch+P4 treatment remained the most cost-effective option for both CL+ and CL- cows. It was concluded that the Ovsynch+P4 treatment without any diagnostic procedure was the most cost-effective option.

CLINICAL RELEVANCE

Treatment of anoestrous cows was more cost-effective than no treatment, with Ovsynch+P4 more cost-effective than Ovsynch in cows with or without a CL. Differentiation of anoestrous cows into CL+ and CL- groups for treatment was not cost-effective.

Immunohistochemical visualization of insulin receptors in formalin-fixed bovine ovaries post mortem and in granulosa cells collected in vivo

Insulin is crucial for granulosa cell (GC) function, follicle growth and ovulation in cows; low insulin levels increase the risk for anoestrus. Apart from insulin concentration, alterations in the insulin receptor (IR) density on GC may affect follicular growth and steroidogenesis. Data about the IR protein distribution in the bovine follicle are scarce. Therefore, we aimed to develop a quantifiable staining method for IR protein on histological sections of bovine follicles in different developmental stages, and to apply this technique on GC obtained in living cows. In a first experiment, bovine ovaries were collected post mortem, formalin fixed, routinely processed, and stained with monoclonal murine IR-antibodies, peroxidase-labeled goat anti-mouse antibodies, and substrate chromogen. Based on their diameter, follicles were morphologically classified as small antral (SAF; n = 141), dominant (DF; n=28) or subordinate (SF; n=8); DF and SF were further classified as healthy or atretic based on the ratio of estrogen and progesterone concentrations in their follicular fluid. Using specialized software, the proportion of pixels displaying a positive staining signal was computed as a measure for IR density in three selected follicular regions: GC, theca (T) and stroma (STR). Results were analyzed in an ANOVA model with follicle type, region and health status as fixed factors. In SAF, DF, and SF, IR density was notably higher in GC than T or STR; the latter two displayed very low or no IR presence. The IR density in SAF was stronger than in DF and tended to be stronger than in SF. Staining intensity was not altered in atretic compared to healthy follicles. In corpus luteum, cumulus-oocyte complexes and pre-antral follicles, no IR could be detected. In a second experiment, GC samples were collected from 20 live cows on 30 and 70 d post partum by transvaginal follicular fluid aspiration, projected on glass slides, and stained using the protocol described above. Most samples yielded sufficient GC and IR was clearly visualized. However, objective quantification of the staining signal was impeded by extensive variation in the arrangement and density of GC and the amount of cellular debris on the slides. Altogether, strong IR presence in GC, most notably in SAF, suggests acquisition of IR as a key event in early follicle growth. Furthermore, we have developed a quantifiable staining technique for bovine follicles that may be applicable for GC obtained in live cows, although this method requires further standardization.

Use of equine chorionic gonadotrophin in synchronised AI of seasonal-breeding, pasture-based, anoestrous dairy cattle

In seasonally calving dairy areas, a critical index of efficiency and profitability is the ability to maintain a short annual calving spread. In essence, this means that all cows need to conceive within 90 days of calving. Anovulatory anoestrus (AA) is a major barrier to reproductive performance under these conditions and the successful treatment of AA is an important aspect of reproductive intervention. The present paper reviews regimens used to treat AA in New Zealand and reports on a large-scale field trial investigating the effects of equine chorionic gonadotrophin (eCG) within a proven efficacious treatment protocol. The administration of eCG at the time of removal of a progesterone-releasing device in an 8-day, oestradiol benzoate (EB)-based treatment protocol increased the percentage of cows in calf after 7 and 28 days of breeding. The interaction between cow age and treatment with eCG was significant, with cows over 5 years of age having higher conception rates (P = 0.002) and 7 day in-calf rates (P = 0.002) than cows on a standard 8-day treatment protocol without eCG. The addition of eCG to a standard 8-day EB/progesterone protocol can improve reproductive success in seasonally calving AA dairy cows.

Postpartum anestrus in dairy cattle

Fertility of the postpartum period is negatively influenced by the incidence of anestrus. The latter condition is characterized by the absence of estrous behavior, which may be an indication of suboptimal conditions (e.g., inadequate peripartum nutrition) or pathologic conditions (e.g., chronic debilitating diseases or uterine and ovarian diseases). Although initiation of ovarian follicular growth in the postpartum period is generally not affected, subsequent development (deviation) and the fate of the dominant follicle are the primary factors that affect reestablishment of ovarian cyclicity. Anestrus can be classified based on the three functional states of follicular development; that is, follicle emergence, deviation, and ovulation. Prevention of anestrus is preferable to treatment and can be achieved in part by maintaining a healthy periparturient period. To better understand the etiology of anestrus and its prevention, research is urgently needed in the following three areas: the role of peripartum disease conditions that influence reproduction, genes involved in ovulation, and the influence of proteins (e.g., leptin) that appear to be important links between metabolic signals and the neuroendocrine axis.

Resumption of ovarian cyclicity in post-partum beef and dairy cows

There is a variable anoestrous period following parturition in the cow. Follicular growth generally resumes within 7-10 days in the majority of cows associated with a transient follicle-stimulating hormone (FSH) rise that occurs within 3-5 days of parturition. Dairy cows that are not nutritionally stressed generally ovulate their first post-partum dominant follicle (approximately 15 days), whereas beef suckler cows in good body condition normally have a mean of 3.2 +/- 0.2 dominant follicles (approximately 30 days) to first ovulation; and beef cows in poor body condition have a mean of 10.6 +/- 1.2 dominant follicles (approximately 70-100 days) to first ovulation. The lack of ovulation of dominant follicles during the post-partum period is associated with infrequent luteinizing hormone (LH) pulses, with both suckling and low level of nutrition being implicated in the prolonged suppression of LH pulses in the absence of progesterone. In dairy cows, the normal pattern of early resumption of ovulation may be delayed in high-yielding Holstein-type cows generally because of the effects of severe negative energy balance, dystocia, retained placental membranes and uterine infections. First ovulation in both dairy and beef cows is generally silent (i.e., no behavioural oestrus) and is generally (>70%) followed by a short cycle. The key to optimizing resumption of ovulation in both beef and dairy cows is appropriate pre-calving nutrition and management so that cows calve down in optimal body condition (body condition score; BCS; 2.75-3.0) with post-partum body condition loss restricted to <0.5 BCS units.

Breed differences in calving interval in the humid Mexican tropic

The objective of this study was to evaluate the influence of breed, breed and sex of the calf, farm, calving number (CN), type of calving, and their interactions on CI using records from four different beef breeds performing in the humid tropical environment of Mexico. The influence of these factors on CN was also evaluated. CI and CN varied with farm, breed of the dam, and with breed of the dam by calf breed interaction (P<0.001), while CI also varied with CN. Significant differences between Bos indicus and Bos taurus breeds for CI (432 vs. 488 days) and for CN (2.13 vs. 1.92) were observed (P<0.001). The interaction effects observed between breed of the dam by breed of the calf on CI and on CN were due to a favorable F(1) calf effect on CI observed only in Angus cows, although with an apparent unexpected negative impact on CN.

Forms of reproductive disorders in cattle and buffaloes in Middle Egypt

The objective of this study was to investigate the common forms of reproductive disorders and trends of fertility in cattle and buffaloes in Middle Egypt, and investigate nutritional deficiencies or imbalances as a cause of infertility. During the period from 2003 to 2006 a total of 4276 animals (2755 cattle and 1521 buffaloes) were examined, during winter and summer at three districts of Middle Egypt. Based on the owner complains, animals were categorized as anestrum, repeat breeder and those for pregnancy diagnosis. Feedstuffs of these districts were assessed for nutrient and mineral contents. Animals were examined by rectal palpation and by transrectal ultrasonography. The results showed that, ovarian inactivity was the most common cause of anestrum, whereas endometritis was the main frequent finding of repeat breeding. District, season and year affected the incidences of infertility. The pregnancy rate remained constant (cattle) or increased (buffaloes) from 2003 to 2006. The incidence of ovarian inactivity in both species decreased over the same period. In winter, the commonly used feedstuffs would be adequate to supply the animals with needs, but in summer, rations seem to be deficient in many essential nutrients. In conclusion, ovarian inactivity is the main cause of infertility in cattle and buffaloes in Middle Egypt. There is a link between poor nutrition in summer and the high incidence of ovarian inactivity. Fertility trends during the past few years are encouraging.

Shortening the postpartum anoestrous interval in suckled crossbred dual purpose cows using progestagen intravaginal sponges plus eCG and PGF(2alpha)

One hundred and twenty-six suckled crossbred cows (Bos taurus x Bos indicus), with body condition score >or=3 (1-5 point scale), were employed in the present study to evaluate the effectiveness of intravaginal progestin-releasing sponges (IVS) for shortening anoestrous interval. Fifty-four cows were assigned to control group. Seventy-two cows were treated with IVS impregnated with 250 mg of medroxy-acetate-progesterone (MAP) as follows: day 0, IVS plus 5 mg of 17beta-E and 50 mg of MAP i.m.; day 6, 500 IU of equine chorionic gonadotropin and 25 mg prostaglandin F(2alpha) i.m.; day 8, IVS withdrawal and day 9, 1 mg 17beta-E i.m. Cows were also grouped according to postpartum days (dpp) at treatment: MAP <70 days (n = 25); control <70 days (n = 22); MAP >70 days (n = 47); control >70 days (n = 32). From IVS removal, cows were detected in oestrus and inseminated. Cows not detected in oestrus were timed artificial insemination 72 h after sponge removal. Treatment effect on oestrous rate (ER), conception rate (CR), pregnancy rate (PR) and treatment to conception intervals (TCI) and calving to conception intervals (CCI) were evaluated. The ER, CR and PR were analysed using PROC LOGISTIC, while TCI and CCI with PROC GLM of SAS. The groups MAP <70 days and MAP >70 days showed higher (p < 0.01) ER than control <70 days and control >70 days (84.0% and 76.6% vs 31.8% and 31.3% respectively). The PR was higher (p < 0.01) in MAP <70 days vs control <70 days (64.0% vs 22.7%) and also higher (p < 0.05) in MAP >70 days vs control <70 days (40.4% vs 18.8%). The TCI and CCI were shorter (p < 0.01) in MAP <70 days vs control <70 days (36.0 and 95.8 days; 95.3 and 158.6 days respectively). In conclusion, only cows treated with IVS before 70 dpp had a CCI shorter than 100 days, consequently this treatment shortened postpartum anoestrous interval in crossbred dual purpose cattle.

The role of endocrine insulin-like growth factor-I (IGF-I) in female bovine reproduction

Insulin-like growth factor-I (IGF-I) plays a pivotal role in cattle fertility, acting as a monitoring signal that allows reproductive events to occur when nutritional conditions for successful reproduction are reached. However, endocrine IGF-I is not a predictor of reproductive events, but rather an indirect estimator of the suitability of the animal to achieve the reproductive event in question. Although measuring circulating IGF-I concentrations might not have any clinical application in the cattle industry, endocrine IGF-I screening will continue to be important for the study of interactions between nutrition and reproduction. In addition, endocrine IGF-I screening could be used as an ancillary test for the selection of cattle for high reproductive potential, especially in herds of high genetic merit for milk production, in which a decline in fertility has been identified.

Different types of postpartum luteal activity affected by the exposure of heat stress and subsequent reproductive performance in Holstein lactating cows

The aim of the present study was to determine the effect of heat stress on postpartum (PP) luteal activity and subsequent reproductive performance in lactating cows. Thirty Holstein-Friesian (HF, >or=75%) cows (hot season, n = 15 and cool season, n = 15) were studied over 60 days after calving. The changes of temperature-humidity index (THI) were monitored within both seasons. Body condition scores (BCS), uterine involution and the ovarian structures were recorded. Plasma samples were obtained three times a week for the analysis of progesterone (P4) and prostaglandin F(2 alpha) metabolite (PG metabolite). Subsequent reproductive performance of the cows, calved within the same period was also evaluated. The means of THI for hot and cool seasons varied between 84-87 and 78-83 respectively. A drop of the mean BCS was recorded at 5 weeks PP in the cows during hot season (p < 0.01), however a delay of uterine involution during early PP period in hot season was not clearly seen. The cows with normal PP ovarian cyclicity during hot and cool seasons were 4/15 (26.7%) and 9/15 (60.0%) respectively. A higher percentage of abnormal luteal activity was found in the cows during hot season (p = 0.07) and delayed luteal cyclicity/anovulation was the most pronounced atypical P4 profile. The levels of PG metabolite were not different between groups and the relationship between the levels of PG metabolite and the time of uterine involution was not evident (p > 0.05). The heat detection rates and the pregnancy rates were higher in the cows during cool season (p < 0.05). Additionally, the higher first AI conception rates during cool season were recorded (p = 0.06). In conclusion, heat stress conditions had negative effects on BCS and altered a normal process of ovarian resumption PP, consequently resulted in lower reproductive performance in a tropical dairy herd.

Phenotypic relationships between the interval from calving to first luteal activity and fertility in a seasonal dairy production system

In seasonal dairy production systems a high level of reproductive performance is required to maintain a 365-day calving interval. Compared with many countries New Zealand dairy cattle are fertile, with an average calving interval of 368 days and first service conception rates of around 55%. However, fertility has been demonstrated to have declined over the past 15-years. An extended interval from calving to first luteal activity (CLA) has previously been identified as a major cause of infertility in New Zealand dairy cows. This paper investigates the phenotypic relationship between CLA and reproductive performance in a population of second cross FriesianxJersey dairy cattle. The data consists of 1780 lactations, from 801 individuals that were managed in a seasonal, pasture-based dairy production system. Overall, reproductive performance in the herd was high, with first service conception rates of over 60% and more than 80% of the herd pregnant within 42-days of the start of the breeding period. Animals were divided into six groups of at least 270 animals per group based on CLA (</=16, 17-20, 21-26, 27-34, 35-50, >50 days). First service conception rates and the interval from the start of mating to conception were not statistically different between the CLA groups (p>0.05), despite the number of oestrous cycles prior to first mating being inversely proportional to CLA. However, only 47% of animals with a CLA of >70 days (n=88) were pregnant within 21-day of the start of mating, compared with 65% of animals with CLA of <70 days. Animals that had not ovulated by 1-week prior to the start of mating also had reduced reproductive performance (45% versus 67% pregnant within 21-days of the start of mating, p<0.001). The poor reproductive performance of animals with CLA>70 days is likely to be due to a lower proportion of animals having ovulated by the start of mating (0.28 versus 0.95, p<0.001). Contrary to previous findings in non-seasonal production systems the length of CLA was not related to fertility, except when CLA was greater than 70 days.

The acute effect of bull presence on plasma profiles of luteinizing hormone in postpartum, anoestrous dairy cows

The objective of this study was to investigate whether bull exposure affects LH profiles in postpartum, anoestrous dairy cows. Eight cows between 10 and 17 days after parturition were used. On Day 1, blood samples were taken at 10 min intervals for 8 h. On Day 2, blood sampling continued at 10 min intervals and after 2 h a bull was introduced behind a fence, and blood sampling continued for another 8 h. Time of resumption of luteal activity was between 25 and more than 80 days after parturition for these animals and was not related (P>0.1) with frequency of LH pulses, amplitude of pulses and basal LH concentration on either Day 1 or Day 2. In 6 of the 8 cows, average and basal LH concentration were greater (P<0.001) during the 8 h of bull presence (0.56 +/- 0.33 and 0.39 +/- 0.26 ng/ml, respectively) compared to the 8 h without a bull (0.50 +/- 0.30 and 0.35 +/- 0.24 ng/ml, respectively). Pulse amplitude did not differ (P=0.85) between Day 2 (0.45 +/- 0.24 ng/ml) or Day 1 (0.45 +/- 0.14 ng/ml). LH pulse frequency was greater (P<0.1) on Day 2 (5.3 pulses/8h) compared to the Day 1 (4.6 pulses/8h). In conclusion, fenceline bull exposure early postpartum seems to have an acute effect on LH-release in anoestrous dairy cows. Whether sustained bull exposure can hasten first ovulation after calving through an effect on LH release in dairy cows is an interesting area of research.

Effects of Pasture Feeding During the Periparturient Period on Postpartum Anovulation in Grazed Dairy Cows

Extended postpartum anovulatory intervals (PPAI) are a major contributor to infertility in seasonal dairy systems constrained to 365-d calving intervals. This study was conducted to evaluate the effects of pasture-based dietary energy intakes during the transitional calving period on PPAI. Sixty-eight multiparous Holstein-Friesian cows were assigned to high [11.9 kg of dry matter (DM)/d] or low (4.8 kg of DM/d) pasture intakes for 29 +/- 7.7 d prepartum. After calving, cows within each prepartum diet were assigned to either a high (13.5 kg of DM/d) or low (8.6 kg of DM/d) pasture intake for 35 d in a 2 x 2 factorial arrangement. Progesterone concentrations were measured in milk samples collected twice weekly to determine PPAI, which was defined as the day on which progesterone level was elevated to > or = 3 ng/mL with subsequent concentrations being consistent with an ovulatory cycle. Blood samples were collected before initiation of treatments, and at d -21, -14, -7, 0 (day of calving), 1, 2, 3, 4, 7, 14, 21, 28, and 35 in all cows. The PPAI was associated with body condition score, concentrations of plasma insulin and insulin-like growth factor-I, and growth hormone. Postpartum intake did not affect these metabolic hormones or PPAI, but yield of FCM during the first 35 d was reduced by 23% among cows on a restricted intake. No relationships were found between PPAI and milk production characteristics. These data demonstrate that when pasture is the sole dietary source during the calving transition period, PPAI may be influenced by prepartum intake levels, whereas postpartum intake influences milk yield, but not PPAI. The underlying mechanism(s) that associates the prepartum period to PPAI may involve the sensitivity of the growth hormone-insulin-like growth factor axis to dietary intake levels. Nonetheless, PPAI in grazing multiparous dairy cows appears largely unresponsive to intake levels during the calving transition period.

Influence of parity on follicular dynamics and resumption of ovarian cycle in postpartum dairy cows

The present study examined ovarian changes preceding the resumption of the ovarian cycle in postpartum dairy cows with different parities under similar body nutritional conditions. In postpartum primi- (n=6), bi- (n=4), and multiparous (n=6) Holstein dairy cows, ovarian ultrasonographic observations starting at 7 days after calving were performed every other day and then daily after the confirmation of clinical signs of oestrus for the detection of postpartum first ovulation. Blood samples were collected at the same time as ultrasonography and analyzed for oestradiol and progesterone to monitor ovarian activity. To evaluate the nutritional condition of the cows, body weight and body condition score (BCS, 1=emaciated to 5=obese) were measured weekly and blood samples for the analysis of glucose, insulin, and non-esterified fatty acid (NEFA) were collected at the same time until postpartum second ovulation. Dominant follicles (>8mm in diameter) of the first follicular wave were detected at 7 days after calving in all cows. The first wave follicle ovulated in five of six multiparous cows, whereas no first wave follicle ovulated in any of the primiparous cows. The days to first ovulation after calving in primiparous cows (31.8+/-8.3 days) were significantly greater (p<0.05) than those in multiparous cows (17.3+/-6.3 days), but were not significantly different from biparous cows (28.8+/-8.6 days). There was a significant relationship between parity and days to first ovulation after calving (p<0.05). BCS was maintained at a level of more than 2.5 during the postpartum period in all cows and there was no influence of parity on postpartum changes in BCS, glucose, insulin, or NEFA throughout the experiment. The present study demonstrated a negative relationship between parity and number of days from calving to first ovulation in dairy cows under similar body nutritional conditions. It is possible that the influence of parity on the resumption of ovarian cycle is modulated by the factors different from the nutrition-related changes during the postpartum period in dairy cows.

The Effect of Progesterone and Oestradiol Benzoate on Fertility of Artificially Inseminated Repeat-breeder Dairy Cows during Summer

An experiment was conducted to examine the effect of progesterone (P(4)) and oestradiol benzoate (ODB) on fertility of repeat-breeder lactating dairy cows during summer. One hundred repeat-breeder lactating dairy cows were randomly allocated to four groups (Tr1, Tr2, Tr3 and C) in a study conducted at a private dairy farm. All cows were injected with 2 mg ODB (day 0), which were at random stages of their oestrous cycles. Cows in Tr1, Tr2 and Tr3 were administered with intravaginal progesterone-releasing devices (controlled internal drug-releasing, CIDR) at the time of ODB injection for 7 days and those in group C were untreated and served as controls. Following CIDR removal, all cows were given an intramuscular injection of 25 mg Prostaglandin (PGF(2 alpha)). Twenty-four hours after the PGF(2 alpha) injection, cows in Tr1, Tr2 and C groups were injected with 1 mg ODB. Cows in Tr3 group were injected with 10 microg gonadotropin-releasing hormone (GnRH) agonist 48 h after CIDR removal. Artificial insemination was performed between 24 and 30 h following the second ODB injection for cows in Tr1 group and at the time of GnRH injection for cows in Tr3 group. Cows in Tr2 and C groups were inseminated at detected oestrus. Plasma P(4) and oestradiol 17beta (E(2)) concentrations were determined for all cows daily from day 0 to day 9. Plasma concentrations of P(4) and E(2) among cows of groups Tr1, Tr2 and Tr3 were increased and reached maximum values within 48 h following administration and were greater (p < 0.001) than those of group C cows. The proportion of cows detected in oestrus based on P4 concentration on day 9 was 88%, 72%, 88% and 60% in groups Tr1, Tr2, Tr3 and C, respectively. Oestrous detection rate differed (p < 0.01) significantly between time-inseminated groups (Tr1 and Tr3) and those inseminated at observed oestrous (Tr2 and C) groups. Pregnancy rates based on ultrasonography performed on day 28 were 52%, 56%, 60% and 40%, and those based on rectal palpation on day 45 were 32%, 44%, 36% and 28% for Tr1, Tr2, Tr3 and C cows (p > 0.1), respectively. Whereas pregnancy rates for cows with four or more previous services in all groups (54.55%) were higher (p < 0.03) than those for cows with three previous services (29.49%). In pregnant cows, mean days from calving to the day of insemination were higher (p < 0.01) among cows with four or more previous services (204 +/- 8.0 days) than those with three previous services (157 +/- 6.0 days). Results indicate that treatment with a combination of ODB and CIDR in repeat-breeder dairy cows causes elevation in plasma concentrations of E(2) and P(4). Oestrous detection rate was better in cows that were primed with P(4) than those without P(4) priming. Cows with four or more previous services had significantly higher pregnancy rates than those with three previous services.

The detection of estrus in cattle raised under tropical conditions: what we know and what we need to know

Lack of accuracy in estrus detection in cattle is a major constraint affecting the implementation of techniques such as artificial insemination (AI) and embryo transfer (ET). For this reason clinicians have opted to pharmacologically manipulate the estrus cycle. The advantages and shortcomings of using this approach to improve the implementation of AI and ET are discussed in this review. Moreover, in order to highlight the reasons why estrus detection is difficult in cows kept at grazing in the tropics, this review underlines social and behavioral traits hindering the capacity of the casual observer to accurately identify cows in estrus.

Effect of pretreatment with insulin on the response of buffaloes with inactive ovaries to gonadotrophin-releasing hormone agonist treatment in summer

The aim of the present study was to evaluate the effect of a pretreatment with insulin on the response of buffalo cows with inactive ovaries to gonadotrophin-releasing hormone agonist (GnRHa) treatment during hot summer months (July and August). Thirty-six Egyptian buffalo cows with inactive ovaries were randomly allocated into three groups: (1) group treated with GnRHa (G1, n = 16) in which each buffalo received an intramuscular injection of 250 mg of GnRHa (Day 0; gonadorelin, Fertagyl); (2) group treated with insulin before the GnRHa injection (G2, n = 8) in which each buffalo received a subcutaneous injection of biphasic insulin at a dose of 0.25 IU kg(-1) bodyweight once daily starting at Day -3 for 3 consecutive days, followed by an intramuscular injection of 250 mg of GnRHa on Day 0; and (3) the control group (G3, n = 12) in which each buffalo cow received an intramuscular injection of 2.5 mL of sterile saline on Day 0. The ovaries of all animals were examined by trans-rectal ultrasonography (5 MHz) on Days -7, -3 and 0 and continued thereafter at 4-day intervals until oestrus or the end of the experiment. On the same days that ultrasound examinations were performed blood samples were collected to measure the progesterone concentrations. Administration of insulin for 3 days before GnRHa injection (G2) significantly (P < 0.05) increased the diameter of the largest follicle from 6.85 +/- 0.64 to 12.4 +/- 0.88 mm. There was a significant (P < 0.01) increase in the oestrous induction rate in G2 compared with both G1 and G3 during the first 12 days after the treatment interval. It is concluded that pretreatment with insulin for 3 days before GnRHa injection increases the diameter of the dominant follicle and therefore the oestrous induction rate of acyclic buffaloes.

Timed artificial insemination of two consecutive services in dairy cows using prostaglandin F2alpha and gonadotropin-releasing hormone

Timed artificial insemination (TAI) protocols use PGF(2alpha) and GnRH injections to synchronize ovulation. The objective was to evaluate the PGPG protocol (d 0, PGF(2alpha); d 3, GnRH; d 11, PGF(2alpha); d 13, GnRH and TAI) for first TAI and also examine methods for second TAI in nonpregnant cows. A factorial test of the first PGF(2alpha) and first GnRH injections within the PGPG protocol was performed (the last PGF(2alpha) and GnRH injections were deemed essential to the TAI). Lactating dairy cows (n = 804) in a commercial herd were assigned to 1 of 5 first-TAI treatments, which were PGPG, GPG (d 0, no treatment; d 3, GnRH; d 11, PGF(2alpha); d 13, GnRH and TAI), PPG (d 0, PGF(2alpha); d 3, no treatment; d 11, PGF(2alpha); d 13, GnRH and TAI), and PG (d 0, no treatment; d 3, no treatment; d 11, PGF(2alpha); d 13, GnRH and TAI); the Ovsynch protocol (GnRH, 7 d, PGF(2alpha), 2 d, GnRH and TAI) was the positive control. For resynchronization, cows received either GnRH or the control (no injection) on d 22 after TAI. Nonpregnant cows on d 28 were then treated with PGF(2alpha) on d 29, GnRH on d 31, and TAI [i.e., resynchronization treatments of ReGPG (received GnRH on d 22) and RePG (did not receive GnRH on d 22)]. Pregnancy rates for PGPG, GPG, PPG, PG, and Ovsynch were similar at d 28 after first TAI. Analyses of multiple explanatory factors by logistic regression detected an effect of uterine or ovarian abnormality on the d-28 pregnancy rate (normal more likely to be pregnant). Day-42 pregnancy rates were affected by uterine or ovarian abnormality (normal more likely to be pregnant), postpartum disease occurrence (healthy cows more likely to be pregnant), milk production, and days in milk. Treatment was not significant for the d-42 pregnancy rate. Effects of postpartum disease, milk production, and days in milk on the d-42 pregnancy rate were apparently manifested through their effects on embryonic loss between d 28 and 42 of pregnancy. High-producing cows that received TAI early postpartum were most likely to experience embryonic loss. Day-42 pregnancy rates after the resynchronization treatment were affected by an interaction of the first synchronization treatment with the resynchronization treatment. We concluded that although PGPG can be used for TAI, a simpler TAI protocol that includes the last 2 injections (PGF(2alpha), 2 d; GnRH and TAI) would be equally effective.

The bovine dominant ovarian follicle

Central roles in reproductive biology (i.e., growth and development of the oocyte, steroidogenesis, and ovulation) are played by the ovarian dominant follicle (DF). The DF is different from other follicles because it can escape atresia (the fate of all other follicles), and if exposed to the LH surge, its cells will differentiate into the corpus luteum. The DF was originally studied by looking at the surface of ovary through a surgical approach. Current studies employ a less-invasive ultrasound technique to track the growth and development of the DF. Recruitment and selection, the processes that give rise to the DF, and dominance, the physiological state of the mature DF, are important areas of basic research. Results of these basic studies are easily translated into real-world problems in farm animal reproduction. Superovulation, for example, overrides the selection mechanism and increases the number of ovulations. Understanding the factors that affect the size of the recruited pool should increase success rates (i.e., number of collected embryos) for superovulation. In most animals, the DF is short-lived, existing for long enough to allow for the final maturation of the oocyte. Some DF become atretic because they mature during the luteal phase and are never exposed to the LH surge. For other DF, the LH surge redirects the DF toward its ultimate demise (i.e., luteinization, ovulation, and differentiation into the corpus luteum). The DF is managed pharmacologically within protocols for timed AI. When timed AI fails, there may be abnormal corpus luteum development and early embryonic loss; outcomes that are secondary to inadequate follicular cell maturation and incomplete oocyte capacitation in the DF. Future work on the DF will clarify its underlying biological functions so that a variety of needs in farm animal reproduction can be efficiently managed.

Reproductive performance of lactating dairy cows and heifers resynchronized for a second insemination with an intravaginal progesterone-releasing device for 7 or 8d with estradiol benzoate injected at the time of device insertion and 24h after removal

One aim of this study was to compare the reproductive performance of cows and heifers when resynchronizing returns to estrus for a second insemination by treating with an intravaginal progesterone-releasing device (IVD) for 7 or 8d when estradiol benzoate (EB) was administered at the start of treatment and again 24h after device removal. An additional aim was to document the pattern of onset and characteristics of estrus with each resynchrony treatment. Lactating cows in three herds were synchronized for a first estrus and AI by treatment with an IVD for 8d, starting on Day 0, cloprostenol (0.5 mg im) at device removal and EB at device insertion (2.0 mg im) and 24h after removal (1.0 mg im). Cows were resynchronized for a second estrus starting on Day 23 by reinsertion of IVDs for 7 (IVD-7-EB; n=449) or 8d (IVD-8-EB; n=445) with EB (1.0 mg im) administered at device insertion and 24h after removal. Cows were resynchronized for a third estrus by administration of EB (1.0 mg im) on Day 46, but subsequent treatments (no further treatment, reinsertion of CIDR or administration of EB on Day 55) varied among herds as part of separate studies. Maiden heifers (7-Day, n=68; 8-Day, n=69) were similarly treated as cows in a separate herd, but doses of EB were always 1.0 mg im at device insertion and 0.75 mg im 24h after removal. Heifers were not resynchronized for a third estrus. Cattle were inseminated on detection of estrus at each synchronized estrus. Cumulative pregnancy rates 4 week (66.0%, 276/418 versus 59.1%, 247/418) and 7 week (72.7%, 304/418 versus 67.7%, 283/418) after the start of AI were greater (P<0.05) in the IVD-7-EB cows compared to the IVD-8-EB cows, respectively; this was associated with a 9% increase in conception rates at the second estrus (P=0.051) in the IVD-7-EB cows. Treatment did not significantly affect reproductive performance in heifers. Characteristics of estrus measured with radiotelemetry did not differ significantly between the two treatment groups, but more cows were detected in estrus 36 h after removal of IVDs in the IVD-8-EB cows compared to the IVD-7-EB cows (P<0.05). We concluded that reproductive performance in resynchronized dairy cows but not heifers was greater following resynchronization of estrous cycles after AI with an IVD for 7 compared to 8d when EB was injected at the start of treatment and 24h after device removal.

Evaluation of Progesterone Supplementation in a Prostaglandin F2α-Based Presynchronization Protocol Before Timed Insemination

The objective of the study was to determine the effects of treatment with a controlled internal drug-release (CIDR) insert containing progesterone in a PGF2alpha-based presynchronization protocol on pregnancy rates at first service in lactating Holstein cows. A total of 1,318 (656 treatment and 662 control) cows from 5 farms were used in the analysis. Cows received a CIDR insert as part of the presynchronization protocol of 2 PGF2alpha injections given 14 d apart. The CIDR insert was applied during 7 d before the second PGF2alpha injection, whereas control cows received no CIDR insert. Serum progesterone concentrations were measured in samples collected at 37 +/- 3 d in milk (DIM; 7 d after the first PGF2alpha injection) and at 58 +/- 3 DIM, just before initiation of the Ovsynch protocol. According to serum concentrations of progesterone, cows were classified as having either high (> or = 1 ng/mL) or low (< 1 ng/mL) progesterone. The proportion of cows with low progesterone at 37 +/- 3 DIM was similar for cows treated later with the CIDR insert (60.7%; n = 654) and for control cows (59.2%; n = 657). In contrast, use of the CIDR insert resulted in fewer low-progesterone cows (17.4%; n = 402) compared with control cows (30.6%; n = 399) at 58 +/- 3 DIM. No significant effect of the CIDR insert was detected on overall pregnancy rates. Pregnancy rates, as measured by the percentage of cows pregnant at 37 +/- 3 d post timed artificial insemination, for control cows having high or low progesterone at 58 +/- 3 DIM were 46.6 and 22.1%, respectively. For the CIDR group, pregnancy rates were 40.4 and 11.4%, respectively, for high- and low-progesterone cows at 58 +/- 3 DIM. Overall pregnancy rates were 36.4 and 34.5% for control cows and cows receiving the CIDR insert, respectively. A significant decreasing trend was observed in the proportion of cows having low progesterone as the body condition score increased, at 37 +/- 3 and 58 +/- 3 DIM. A significant increasing trend in the pregnancy rate was observed as body condition score increased. In conclusion, incorporation of CIDR inserts into a presynchronization protocol reduced the proportion of cows having low progesterone; however, the pregnancy rate did not differ between control cows and those receiving the CIDR insert. Earlier expression of estrus after the second PGF2alpha injection, and consequently improper timing of initiation of the Ovsynch protocol, could have negatively affected fertility in the CIDR-treated cows.

Conception rates to artificial insemination in primiparous, suckled cows exposed to the biostimulatory effect of bulls before and during a gonadotropin-releasing hormone-based estrus synchronization protocol1,2

The objective of these studies was to evaluate whether exposing primiparous, suckled beef cows to the biostimulatory effect of bulls alters breeding performance associated with an estrus synchronization protocol that included GnRH followed 7 d later by PGF(2alpha) and fixed-time AI (TAI). This was a composite analysis of 3 experiments that evaluated (1) the effects of bull exposure at different days after calving (yr 1); (2) the biostimulatory effects of bull excretory products (yr 2); and (3) the biostimulatory effects of familiar and unfamiliar bulls (yr 3) on the resumption of ovarian cycling activity. In all studies, cows were exposed (biostimulated; n = 94) or not exposed (nonbiostimulated; n = 67) to bulls or excretory products of bulls for at least 60 d before the beginning of the estrus synchronization protocol. Average calving day did not differ among years and was 52 +/- 5 d. Year did not affect the proportions of biostimulated and nonbiostimulated cows that were cycling at the beginning of the estrus synchronization protocol; however, a greater (P < 0.001) proportion of biostimulated than nonbiostimulated cows were cycling at this time. In each year, cows were given GnRH followed by PGF(2alpha) 7 d later. Cows were observed for estrus twice daily (am and pm) after PGF(2alpha). Cows that exhibited estrus before 54, 60, and 64 h after PGF(2alpha) were inseminated by AI 12 h later in yr 1, 2, and 3, respectively. Cows that failed to show estrus were given GnRH and TAI at 62, 72, and 72 h after PGF(2alpha) in yr 1, 2, and 3, respectively. Conception rates were determined by transrectal ultrasonography 35 d after TAI in each year. The percentages of cows that exhibited estrus after PGF(2alpha) and before TAI, the interval from PGF(2alpha) to estrus, and the percentages of cows inseminated 12 h after estrus or at TAI did not differ between biostimulated and nonbiostimulated cows and were 51%, 54.7 +/- 7.3 h, 35%, and 65%, respectively. Conception rates for cows bred by AI 12 h after estrus did not differ between biostimulated and nonbiostimulated cows; however, the TAI conception rate was greater (P < 0.05) for biostimulated cows (57.6%) than for nonbiostimulated cows (35.6%). We conclude that TAI conception rates in an estrus synchronization protocol that includes GnRH followed 7 d later by PGF(2alpha) may be improved by the biostimulatory effect of bulls in postpartum, primiparous cows.

Comparison of Two Estrus-Synchronization Protocols and Timed Artificial Insemination in Dairy Cattle

The objective of this study was to evaluate the effect of the Ovsynch protocol with and without exogenous progesterone on pregnancy rate (PR) in cows in which estrous cycles were previously synchronized with 2 doses of PGF(2alpha) and that were not detected in estrus during the presynchronization period. The study was conducted in Chihuahua, Mexico (8,650 Holstein milking cows; 305-d mature equivalent milk yield = 13,790 kg). On d 47 postpartum, estrous cycles in cows were synchronized by using 2 doses of PGF(2alpha) 14 d apart. Any cow detected in estrus during this presynchronization period was inseminated. Cows not detected in estrus were selected at random and assigned to receive progesterone supplementation or to serve as controls. Controls (n = 594) were subjected to the Ovsynch protocol and cows in the progesterone supplemented treatment (n = 594) were subjected to the Ovsynch protocol plus an intravaginal insert containing 1.9 g of progesterone inserted at the time of the first GnRH injection and removed 7 d later. Progesterone-supplemented cows had a greater PR (31.2%) compared with controls (22.7%). Plasma progesterone concentrations at artificial insemination (AI) were <1 ng/mL and did not differ between treatments. At 14 d post-AI, however, more cows that received progesterone supplementation had concentrations of progesterone >1 ng/mL compared with controls. It was concluded that after a presynchronization period, cows subjected to the Ovsynch program and supplemented with exogenous progesterone had a greater PR and greater concentrations of progesterone after AI than those subjected to the Ovsynch protocol and not supplemented with progesterone.

Reproduction in Dairy Cows Following Progesterone Insert Presynchronization and Resynchronization Protocols

The objectives of this study were to evaluate the effects of an intravaginal insert containing progesterone (CIDR, controlled internal drug releasing) administered in presynchronization and resynchronization protocols on cyclicity, detection of estrus, pregnancy rate, and pregnancy loss to first AI; reinsemination patterns; and pregnancy rates to second postpartum AI before and after the time of first-service pregnancy diagnosis in dairy cows. Holstein cows (n = 1,052) were blocked by parity and BCS at 3 +/- 3 d in milk (study d 0 = day of calving) and assigned randomly to 1 of 3 presynchronization treatments. During the presynchronization programs, all cows received 2 injections of PGF2alpha, on study d 35 and 49. Cows enrolled in the control presynchronization treatment received AI after detected estrus from study d 49 to 62. Cows enrolled in the CIDR estrus-detection (CED) presynchronization treatment received a CIDR insert from study d 42 to 49 and AI on detection of estrus from d 49 to 62. Cows enrolled in the CIDR timed AI (CTAI) presynchronization treatment received the same treatment as CED, but were subjected to timed AI on study d 72 after the Ovsynch (GnRH, 7 d PGF2alpha, 2 d GnRH, 24 h timed AI) protocol. The control and CED cows not inseminated by study d 62 were enrolled in the Ovsynch protocol on the same day and received timed AI on study d 72. After first AI, cows were assigned to no resynchronization (RCON) or resynchronization with a CIDR insert (RCIDR) between 14 and 21 d after AI. Blood samples collected on study d 35, 49, and 62 were analyzed for concentrations of progesterone and cows were classified as anestrous when progesterone was < 1.0 ng/mL in the first 2 samples. On study d 62, anestrous cows with progesterone > or = 1.0 ng/mL were classified as having resumed cyclicity. Pregnancy was diagnosed at 31 and 60 d after first AI and at 42 d after second AI. A greater proportion of anestrous cows in CED and CTAI became cyclic by d 62 postpartum than control cows. Resynchronization with the CIDR insert increased the pregnancy rate at 31 d after first AI in CED and CTAI, and at 60 d after AI in all cows because of reduced pregnancy loss. These results indicate that presynchronization with the CIDR insert increased induction of cyclicity in anestrous cows and that resynchronization with the CIDR insert did not affect the reinsemination rate but did reduce pregnancy loss and increased the pregnancy rate at 60 d after first AI.

The effect of nutritional management of the dairy cow on reproductive efficiency

The cause of low fertility in dairy cows is multifactorial. Poor nutrition during the dry and early postpartum periods results in reduced glucose, insulin, insulin-like growth factor (IGF-I) and low LH pulse frequency with concomitant increases in beta-hydroxy butyrate, non-esterified fatty acids (NEFA) and triacylglycerol. Cows must mobilize large lipid, but also some protein reserves, with a consequent increased incidence of such metabolic disorders as hypocalcaemia, acidosis, ketosis, fatty liver and displaced abomasums. The occurrence of milk fever and ketosis affects uterine contractions, delays calving and increases the risk of retained foetal membranes (RFM) and endometritis. The nutritional risk factors that cause RFM are hypocalcaemia, high body condition score (BCS) at calving and deficiencies in Vitamin E and selenium. The risk factors for endometritis are hypocalcaemia, RFM, high triacylglycerol and NEFA. Thus, metabolic disorders predispose cows to gynaecological disorders, thereby reducing reproductive efficiency. Cows that are overconditioned at calving or those that lose excess body weight are more likely to have a prolonged interval to first oestrus, thereby prolonging days open. Nutritionally induced postpartum anoestrus is characterized by turnover of dominant follicles incapable of producing sufficient oestradiol to induce ovulation due to reduced LH pulse frequency. High nutrition can also increase metabolic clearance rate of steroid hormones such as progesterone or oestradiol. Lower concentrations of oestradiol on the day of oestrus are highly correlated with the occurrence of suboestrus, thereby making the detection of oestrus in high yielding cows even more difficult. Nutrition also affects conception rate (CR) to AI. Cows that develop hypocalcaemia, ketosis, acidosis or displaced abomasums have lower CRs and take longer to become pregnant. Excessive loss of BCS and excess protein content of the ration can reduce CR while supplemental fats that attenuate the production of F2alpha can improve CR. The increased metabolic clearance rate of progesterone (P4), which decreases blood concentrations during early embryo cleavage up to the blastocyst stage is associated with decreased CRs. In conclusion, poor nutritional management of the dairy cow, particularly before and after calving, is a key driver of infertility.

Estrous behavior and initiation of estrous cycles in postpartum Brahman-influenced cows after treatment with progesterone and prostaglandin F2α1,2

Spring-calving, crossbred (1/4 to 3/8 Brahman) primiparous (n = 56) and multiparous (n = 102) beef cows were used to evaluate the effects of progesterone, delivered via a controlled internal drug-releasing (CIDR) device, and prostaglandin F(2alpha) (PGF(2alpha)) on estrous behavior, synchronization rate, initiation of estrous cycles, and pregnancy rate during a 2-yr period. To determine luteal activity, weekly blood samples were collected 3 wk before initiation of a 75-d breeding season. Treated cows received a CIDR for 7 d beginning on d -7 of the breeding season. On d 0, CIDR were removed, and cows receiving CIDR were administered PGF(2alpha); control cows received no treatment. Cows were exposed to bulls, and estrous activity was monitored using a radiotelemetry system for the first 30 d of the breeding season. Treatment with CIDR-PGF(2alpha) increased (P < 0.05) the number of mounts received (22.5 +/- 3.0 vs. 13.7 +/- 3.9 for CIDR-PGF(2alpha) vs. untreated control cows, respectively) but did not influence duration of estrus or quiescence between mounts. Number of mounts received and duration of estrus were greater (P < 0.05) in multiparous compared with primiparous cows. Synchronization of estrus was greater (P < 0.05) in cows treated with CIDR-PGF(2alpha) (56%) compared with control cows (13%) during the first 3 d of the breeding season. More (P < 0.05) anestrous cows treated with CIDR-PGF(2alpha) than anestrous control cows were in estrus during the first 3 d (59 vs. 12%) and 30 d (82 vs. 63%) of the breeding season. Treatment with CIDR-PGF(2alpha) decreased (P < 0.05) the interval to first estrus after treatment during the first 30 d of the breeding season compared with control cows (5.5 +/- 1.1 vs. 9.0 +/- 1.4 d). First service conception rate was greater (P < 0.05) in CIDR-PGF(2alpha)-treated cows compared with control cows. Cyclic cows at initiation of the breeding season had an increased (P < 0.05) 75-d pregnancy rate compared with anestrous cows, and the pregnancy rate tended (P = 0.10) to be greater in multiparous compared with primiparous cows. We conclude that treatment of Brahman-influenced cows with progesterone via a CIDR for 7 d, along with administration of PGF(2alpha) at CIDR removal, increases the number of mounts received, improves synchronization and first service conception rates, decreases the interval to first estrus after treatment, and may be effective at inducing estrous cycles in anestrous cows.

Reproduction performance and management of dairy cattle

Internationally, reproductive performance of dairy cattle is declining. Under the low production, pasture-based and seasonal calving system used in New Zealand, reproductive performance is also declining, but remains higher than for many other industries. The seasonal calving system requires a high level of reproductive performance to ensure a 365 day inter-calving interval. About 80% of cows are detected in oestrus and inseminated in the first 3 weeks of the seasonal breeding programme and have a conception rate of 55% to 65% to this first insemination. This results in approximately 75% and approximately 90% of cows being pregnant by 6 weeks and by the end of the breeding programme, respectively. However, reproductive performance is declining due to multiple factors including increasing herd size, reduced oestrus detection sensitivity and specificity, declining body condition score at calving and increased rate of body condition score loss postpartum. Continuing selection for increased milk production is also having negative effects on reproduction. The mechanisms by which high production and negative energy balance are reducing reproductive performance are becoming better understood. However, practical solutions for the problem are challenging for veterinarians and consultants, especially given the consumer preference for less interventions.

Reproductive performance in the subsequent lactation of dairy cows previously treated for failure to be detected in oestrus

AIM

To describe the effect of treatment of cows not detected in oestrus (NDO) with progesterone (P4) and oestradiol benzoate (ODB) in one lactation, on the reproductive and productive performance in the subsequent lactation.

METHODS

Cows (n=770 from nine herds) which were NDO 10 days before the planned start of the seasonal breeding programme (PSM) were blocked by herd, age (2 or >2 years old) and ovarian status (i.e. with or without a palpable corpus luteum; CL), and treated either with an intravaginal progesterone-releasing device and ODB and resynchrony, or were left as untreated controls. In the following lactation, data were collected on the occurrence of endometritis, NDO, breeding dates, pregnancy test results and milk production. The effect of treatment and ovarian status in the previous lactation on the incidence of disease, and the proportions submitted for service, conceived and pregnant in the subsequent lactation were analysed. Calving dates and intervals from start of breeding to first insemination and conception were analysed using Kaplan Meier survival analysis. Additional multivariate analyses were undertaken to include known confounders such as age, breed, herd, calving date and milk production, as well as the cyclic status (i.e. previously cycling, NDO, or "late-calving") in the previous lactation, to examine the potential "carryover" effects of previous status on the reproductive performance in the subsequent lactation.

RESULTS

Treatment of NDO cows resulted in an earlier calving date (Julian calving date 214, 95% CI=207-221, vs 224, 95% CI=220-228; p=0.005), more female calves reared (31.4% vs 23.3%; p=0.01), and reduced risk of being NDO (33.9% vs 46.1%; p=0.002) in the subsequent lactation compared with controls. There were no differences in the incidence of peripartum disease, or the proportion of cows submitted, conceived or pregnant between the Treatment and Control groups in the subsequent lactation (p>0.2). Previously CL-positive (+ve) NDO cows were less likely to produce a female calf that was reared (19.0% vs 29.9%; p=0.005), more likely to be treated as NDO (26.4% vs 18.6%; p=0.02), less likely to conceive by the end of the subsequent lactation's breeding programme (82.2% vs 87.8%; p=0.09), and took longer to conceive (41 vs 33 days from the PSM to conception) than cows that were NDO-CL-negative (-ve) in the previous lactation. There was no interaction between ovarian status and treatment for any of the outcome variables (p>0.05). Cows that were NDO or late-calving in the previous lactation were more likely to be NDO (p<0.005), treated as NDO (p<0.005), and have longer PSM to conception intervals (p<0.005) in the subsequent lactation than cycling herdmates, despite inclusion of factors known to confound reproductive performance in analyses.

CONCLUSIONS

Treatment of NDO cows resulted in more female calves reared, earlier calving and a reduced risk of being NDO in the subsequent lactation. Status (i.e. NDO-CL+ve or NDO-CL-ve) affected some reproductive measures in the subsequent lactation, and the effect of treatment in the subsequent lactation differed between the two groups for some measures. Reproductive performance in the subsequent lactation was not improved despite the earlier calving date and longer calving to PSM intervals. Additionally, the previous season's status was still important in the subsequent season's reproductive performance, despite adjusting for known confounders of fertility.

CLINICAL RELEVANCE

The economic benefits from treatment of NDO cows are likely limited to effects of an earlier calving date and potential for longer lactation and increased milk yield, increased number of calves derived from artificial insemination and from a reduced number of NDO cows in the subsequent lactation. Effects of improved reproductive performance in the subsequent lactation were not demonstrated and hence should not be included in any economic analysis of therapy of NDO cows.

Comparison between cloprostenol-induced and spontaneous oestrus fertility in dairy cows

A short calving to conception interval is of main importance to achieve high economic efficiency in dairy cow industry. In order to reduce this interval, several hormonal treatments have been put on the market, in which cloprostenol, a synthetic analogue of prostaglandin F2alpha (PGF2alpha). The aim of this study was to compare fertility of cloprostenol-induced oestrus to that of spontaneous oestrus in dairy cows. In a group of 525 cows, 280 (treated group) were administered 0.5 mg cloprostenol i.m. after transrectal corpus luteum (CL) detection, and inseminated at detected oestrus during the following week. The other 245 cows (control group) were inseminated during spontaneous oestrus. Whey progesterone concentrations were checked at treatment and at insemination in order to remove from the study cows whose P4 levels indicate a non-functional CL, or a lack of luteolysis respectively. Moreover, cows that were not inseminated due to genital problems were also excluded from this study. Conception (59% vs 54.5%) and calving rates (93.7% vs 93%) were not significantly different between the two groups.

Manipulation and control of the estrous cycle in pasture-based dairy cows

Treatments designed to synchronize luteolysis, preovulatory follicular development, and ovulation, and resynchronize estrus after a first AI have improved responses to synchronization treatments. Protocols based only on the use of PGF result in variable onset of estrus. Concentrations of progesterone prior to administering PGF have affected submission rates and fertility while administration of estradiol benzoate (EB) after inducing luteolysis has improved the synchrony of estrus and ovulation in some studies. In pasture-based dairy cows, GnRH-based protocols have generally resulted in one-third of both anestrous and cycling cows conceiving following synchronization of ovulation and timed AI. Protocols which use intravaginal progesterone releasing inserts (IVP4) are effective in inducing estrus in over 90% of treated dairy cows. Resynchronization of estrus after reinsertion of an IVP4 also improves the synchrony of returns to estrus, but pregnancy rates to the first AI have been reduced in some studies, and submission rates at a resynchronized estrus are less than at the first synchronized estrus. Administration of EB can be used to synchronize follicle wave emergence in resynchronized cows with intervals to new wave emergence comparable to that in cows synchronized for a first AI, but plasma concentrations of progesterone following treatment may be reduced. Synchronization of estrus and ovulation can be enhanced by administration of EB or GnRH during proestrus, but dose, timing and stage of follicular development at the time of treatment can affect outcomes.

Relationship between the First Ovulation within Three Weeks Postpartum and Subsequent Ovarian Cycles and Fertility in High Producing Dairy Cows

The aim of this study was to investigate the relationship between the first ovulation within 3 weeks postpartum and subsequent ovarian cycles and fertility in high producing dairy cattle in Hokkaido, Japan. In Experiment 1, 110 cows (44 primiparous and 66 multiparous) were used to determine the effects of the first ovulation within 3 weeks postpartum on subsequent ovarian cycles. Milk samples were collected twice weekly from 7 to 100 days postpartum. The first ovulation was identified by an increase in milk progesterone (P4) to more than 1 ng/ml within 3 weeks postpartum. The numbers of cows showing ovulation and anovulation within 3 weeks postpartum were 31 (70.5%) and 13 (29.5%) in the primiparous cows and 35 (53.0%) and 31 (47.0%) in the multiparous cows, respectively. The patterns of ovarian resumption after calving were classified into two types (normal ovarian cycles and abnormal ovarian cycles) on the basis of milk P4 concentrations. Initiation of normal ovarian function in cows ovulated within 3 weeks postpartum occurred earlier than in anovulated cows regardless of the number of calvings (primiparous, 27.8 days vs. 44.4 days; multiparous, 30.6 days vs. 55.7 days; P<0.01). Out of the multiparous cows that ovulated within 3 weeks postpartum, initiation of normal ovarian function followed by a normal luteal phase was earlier than when it was followed by an abnormal luteal phase (25.5 days vs. 40.4 days; P<0.05). Milk P4 concentrations after the first ovulation were lower than those after the second ovulation in both the primiparous and multiparous cows (P<0.05). In Experiment 2, 22 multiparous cows were used to determine the effects of the first ovulation within 3 weeks postpartum on subsequent fertility. Blood samples were collected once a week from 0 to 3 weeks postpartum. The interval from parturition to first service in ovulated cows was shorter than in anovulated cows (68.4 days vs. 94.8 days; P<0.05). The conception rate by 100 days after calving tended to be higher in ovulated cows than in anovulated cows (50.0% vs. 16.7%, P=0.09). In conclusion, our data strongly suggests that ovulation within 3 weeks postpartum is a crucial phenomenon for subsequent resumption of ovarian function and conception, and thus it can be used as an index of subsequent reproductive performance.

Factors affecting conception and expression of oestrus in anoestrous cows treated with progesterone and oestradiol benzoate

Nutrient balance affects the resumption of ovarian cyclic activity following calving in dairy cattle. However, few data are available about the relationships between nutrient balance and expression of oestrus or conception. It was hypothesised that previously anoestrous cows that conceived to first insemination and cows that expressed oestrus at the subsequent expected return to oestrus would be less likely to be in negative energy balance (i.e. would have higher body condition score, higher glucose, insulin-like growth factor (IGF), leptin or insulin concentrations, and lower non-esterified fatty acids (NEFA), blood urea nitrogen (BUN), beta hydroxy butyrate (BOH) concentrations 12-15 days after insemination) than herd mates not conceiving or expressing oestrus. Anoestrous cows were treated with progesterone and oestradiol benzoate (Day 0 = end of treatment period) and retrospectively categorised as conceiving (n = 108) or not conceiving (n = 108) to insemination. A subset of cows not conceiving to insemination were categorised as expressing (n = 44) or not expressing (n = 44) oestrus between Days 14 and 28 after initial insemination. Cows conceiving had a lower NEFA concentration (P = 0.014) than non-conceiving cows. Cows subsequently detected in oestrus had higher body condition scores (P = 0.016), IGF concentrations (P = 0.008) and milk protein percentages (P = 0.038), and lower BOH concentrations (P = 0.018) than cows not expressing oestrus. No difference in concentrations of leptin, insulin, glucose, blood urea nitrogen or milk yield were found between cows conceiving or not conceiving and those detected in oestrus or not detected in oestrus (P > 0.1). It is concluded that some measures of metabolic status at the time of pregnancy recognition affects the probability of pregnancy and of subsequent expression of oestrus in those treated, anoestrous cows not conceiving.

Effect of artificial insemination on submission rates of lactating dairy cows synchronised and resynchronised with intravaginal progesterone releasing devices and oestradiol benzoate

This study investigated the hypothesis that a reduction in submission rates at a resynchronised oestrus is not due to the resynchrony treatment involving intravaginal progesterone releasing devices (IVDs) and oestradiol benzoate (ODB) but is associated with artificial insemination (AI) at the first synchronised oestrus. In Experiment 1, cows were synchronised for first oestrus with IVDs, with ODB administered at the time of device insertion (Day 0, 2 mg IM) and 24 h after removal (Day 9, 1 mg IM) and PGF(2alpha) injected at the time of device removal. Cows were then either inseminated (I) for 4 days or not inseminated (NI) following detection of oestrus (first round of AI). Every animal was resynchronised for a second round of AI by reinsertion of IVDs on Day 23 with administration of ODB (1 mg IM) at the time of insertion as well as 24 h after removal (Day 32). Cows detected in oestrus and inseminated for 4 days at the second round of AI were resynchronised for a third round by repeating the resynchrony treatment starting on Day 46 and inseminating cows on detection of oestrus for 4 days. In Experiment 2 the same oestrous synchronisation and resynchronisation treatments were used, but the timing of treatments differed. The cows had their cycles either presynchronised (treatment start Day -23) without AI and then resynchronised, starting on Day 0, for the first round of AI for AI at detected oestrus for 4 days, or they were synchronised (treatment start Day 0) for the first round of AI. In Experiment 1, 91.4% (64/70) and 92.6% (63/68) (P = 0.79) of cows in the I and NI treatments, respectively, were detected in oestrus after the initial synchronisation. At the second round of AI, submission rates for insemination were lower in the I group compared to the NI cows (74.5%, 35/47 versus 92.6%, 63/68, respectively; P = 0.007). Pregnancy rates (proportion treated that were classified as becoming pregnant) in I and NI cows 4 weeks (61.4%, 43/70 versus 63.2%, 43/68) and 7 weeks (77.1%, 54/70 versus 69.1%, 47/68) after the AI start date (AISD) did not differ significantly between treatments. In Experiment 2, presynchronisation and then resynchronisation of oestrous cycles before the first round of AI did not affect oestrous detection rates at the first round of AI (100%, 44/44 versus 98.0%, 50/51; P = 0.54), or pregnancy rates 1 week (63.6%, 28/44 versus 60.8%, 31/51; P = 0.70), 4 weeks (72.7%, 32/44 versus 76.5%, 39/51; P = 0.76) and 7 weeks (81.8%, 36/44 versus 88.2%, 45/51; P = 0.40) after AISD compared to cows that had their cycles synchronised for the first round of AI. These findings support our hypothesis that a reduction in submission rates at a resynchronised oestrus is associated with AI at the first synchronised oestrus and not due to a resynchrony treatment involving IVDs and ODB. This study supports the concept that early embryonic loss following AI at a synchronised oestrus could cause a reduction in submission rates following resynchronisation of oestrus, although investigation of the effect of passing an AI catheter or semen components were not studied per se.

Pregnancy loss in dairy cattle in the Waikato region of New Zealand

AIM

To define the incidence rate of pregnancy loss and risk factors for those losses in pasture-fed dairy cattle in the Waikato region of New Zealand.

METHODS

Cows (n=2,004) from 10 pasture-fed, spring-calving dairy herds in the Waikato were enrolled following confirmation of pregnancy 29-45 days after insemination, for inseminations that occurred within the first 16 days of the seasonal breeding period. Transrectal ultrasonographic examinations for pregnancy were conducted at approximately 6, 8, 10, 14 and 22 weeks gestation, and subsequent calving data were recovered. Pregnancy loss was defined as having occurred when a confirmed pregnancy was not re-diagnosed, when gross abortion was detected, or when a cow calved <265 days after the confirmed conception date. Data were analysed using reverse stepwise logistic regression and Cox's proportional hazards analysis.

RESULTS

A total of 128 (6.4%) pregnancy losses were detected. The incidence rate was higher in early compared to late gestation (10.9 vs 2.8 losses/10,000 cow-days between Weeks 6-10 vs Weeks 10-14, respectively; p<0.001). Higher rates of loss were associated with the occurrence of clinical mastitis (Hazards ratio (HR)=1.57; p=0.071), being treated for anoestrus (HR=1.69; p=0.007), and in cows that had calving-to-conception intervals < or =63 days compared with those that had calving-to-conception intervals >92 days (HR=2.49; p=0.06). In addition, the rate of pregnancy loss differed between herds (p=0.05).

CONCLUSIONS

The highest rate of pregnancy loss occurred in early gestation. Clinical mastitis, anoestrus and calving late in the calving season were risk factors for pregnancy loss.

CLINICAL RELEVANCE

Pregnancy diagnosis using ultrasonography can be undertaken from 28 days post-insemination. However, due to the high rate of pregnancy loss at this stage of gestation, herdowners need to be warned of possible losses, and cows should be re-examined to confirm pregnancy before certification of pregnancy status is given.

Gross abnormalities, bacteriology and histological lesions of uteri of dairy cows failing to conceive or maintain pregnancy

AIM

To describe the gross pathology, bacteriology and histopathology of the reproductive tracts of dairy cows that failed to conceive or maintain pregnancy.

METHODS

The reproductive tracts of 105 cows that were not pregnant at the end of the seasonal breeding programme were retrieved following slaughter. The tracts were examined grossly, both horns of the uterine lumen were swabbed for bacteriology, and tissue was collected from each horn and the body of the uterus for histopathology. Grossly enlarged uteri and tracts containing purulent vaginal content were excluded. Histopathology was performed on three sections of uterine tissue from each of three cows in which no gross pathological changes were detected and from which no bacteria were isolated, from three cows in which no gross pathology was detected but from which bacteria were isolated, and from three cows in which gross pathological changes were detected but from which no bacteria were isolated.

RESULTS

Thirty-six (34%) cows had one or more gross lesions which involved the ovary, uterine tube, uterus or vagina. Bacteria were isolated from the uteri of 22 (21%) cows. Isolates included Arcanobacterium pyogenes (n = 1), Escherichia coli (n = 1), Fusobacterium spp (n = 1), Haemophilus somnus (n = 5), Streptococcus acidominimus (n = 12), S. bovis (n = 2), S. uberis (n = 1) and S. salivarious (n = 1). In only five cows were both gross pathology and bacteria detected. There was no relationship between the isolation of bacteria and the diagnosis of gross pathology of the uterus. There were no differences in the degree of histopathological changes in the uteri from the three groups of cows examined, and lesions present were minor.

CONCLUSIONS

Gross pathological changes and intra-uterine bacteria were found in 34% and 20% of cows, respectively, but the correlation between the two was poor. Histopathological changes were unremarkable, suggesting the bacteriological findings were coincidental, that causative agents of infertility were not present at the time of examination, or that unrelated causes such as nutritional anoestrus may have been responsible for the failure of some cows to conceive.

Technical and economic effects of an inline progesterone indicator in a dairy herd estimated by stochastic simulation

For several years progesterone in milk or blood has been recognized as an indicator of different cow states related to reproduction. For this study, an existing simulation model was modified in order to analyze the technical and economic effects of including information on progesterone status in an automatic inline monitoring system. Implementation of an inline progesterone indicator was assumed to directly affect the estrus detection rate, the period until treatment for post-partum anestrus and the number of mistimed AIs. Different implementations of an inline progesterone indicator were simulated in a typical Danish dairy herd with 120 cows and in other herd situations represented by: a herd with poor reproduction efficiency, a herd with a high estrus detection rate and a herd using a 9 week postponed AI period for primiparous cows. It was concluded that implementation of an inline progesterone indicator in a dairy herd previously using visual estrus detection has a break-even price of 3-81 euros per cow-year depending on differences in implementation type and herd reproduction management. The highest break-even price was found using the assumptions that simulated a herd with initially poor reproductive efficiency. With the assumptions that simulated a typical Danish herd the break-even price was 46 euros per cow-year. Attributable effects of using the indicator, including effects of labor time, are discussed.