Control and management of ovarian follicles in cattle to optimize fertility

Review: Manipulation of follicle development to improve fertility of cattle in timed-artificial insemination programs

The development of an ovulatory follicle is a fundamental premise for any reproductive management program that aims to optimize fertility in cattle. Controlling follicular development comprises the synchronized emergence of a new follicular wave, selection and growth of the dominant follicle, and synchronized ovulation of a high-quality oocyte. All these follicular events, primarily driven by gonadotropin secretion, occur under a very dynamic hormonal environment. In this sense, controlling follicular development demands essentially a precise manipulation of the hormonal environment to modulate gonadotropin secretion. Furthermore, the effectiveness of hormonal manipulation strategies in the management of follicular development depends on specific particularities of each situation, which can vary widely according to genetic groups (Bos taurus vs Bos indicus), nutritional, metabolic, and reproductive status. In this regard, the constant search for the refined synchrony between the hormonal treatments and reproductive events, considering these distinctions and particularities, have provided valuable information that contributed to the development of efficient reproductive programs. This manuscript discusses the physiological bases behind the development of fine-tuned timed-artificial insemination protocols for beef and dairy cattle that resulted in great improvements in reproductive efficiency of beef and dairy herds.

Morphological and Chemical Investigation of Ovarian Structures in a Bovine Model by Contrast-Enhanced X-ray Imaging and Microscopy

An improved understanding of an ovary's structures is highly desirable to support advances in folliculogenesis knowledge and reproductive medicine, with particular attention to fertility preservation options for prepubertal girls with malignant tumors. Although currently the golden standard for structural analysis is provided by combining histological sections, staining, and visible 2D microscopic inspection, synchrotron radiation phase-contrast microtomography is becoming a new challenge for three-dimensional studies at micrometric resolution. To this aim, the proper use of contrast agents can improve the visualization of internal structures in ovary tissues, which normally present a low radiopacity. In this study, we report a comparison of four staining protocols, based on iodine or tungsten containing agents, applied to bovine ovarian tissues fixed in Bouin's solution. The microtomography (microCT) analyses at two synchrotron facilities under different set-ups were performed at different energies in order to maximize the image contrast. While tungsten-based agents allow large structures to be well identified, Iodine ones better highlight smaller features, especially when acquired above the K-edge energy of the specific metal. Further scans performed at lower energy where the setup was optimized for overall quality and sensitivity from phase-contrast still provided highly resolved visualization of follicular and intrafollicular structures at different maturation stages, independent of the staining protocol. The analyses were complemented by X-ray Fluorescence mapping on 2D sections, showing that the tungsten-based agent has a higher penetration in this type of tissues.

An altered expression of components of the IGF system could contribute to follicular persistence in Holstein cows

In dairy cows, reproductive diseases such as cystic ovarian disease (COD) represent a major problem that impacts on dairy production. It has been postulated that the insulin-like growth factor (IGF) system may contribute to follicular persistence and development of COD. Thus, the aim of the present study was to analyze relevant members of the IGF system in a critical period immediately after the expected time of ovulation, to obtain information about their role in follicular persistence in dairy cows. Proteins of the IGF system were evaluated at 0 (expected day of ovulation), 5, 10 and 15 days of follicular persistence to determine whether the changes previously detected in cows with COD occur early in COD pathogenesis. The serum concentration of IGF1 was higher in cows with 10 and 15 days of follicular persistence than in control cows. IGF1 expression in granulosa cells was similar in the follicles analyzed. In contrast, in theca cells, persistent follicles of days 5 and 10 showed the lowest IGF1 expression. IGF binding protein (IGFBP) 2 and 3 expression was lower in persistent follicles than in dominant follicles of the control group. Although IGF receptor (IGFR) 1 expression was similar in the groups analyzed, p-IGFR1 expression was significantly higher in dominant follicles of the control group than in persistent follicles. These data suggest alterations in the IGF system at the early stages of follicular persistence. The evidences obtained allow supporting that the IGF system could plays a key role in dairy cattle reproduction.

Relationship between plasma concentrations of IGF-I and clinical endometritis, and response to progesterone synchrony in dairy cows during early lactation

The first aim of this study was to evaluate the relationship between the concentrations of plasma insulin-like growth factor-I (IGF-I) in the transition period and the incidence of clinical endometritis postpartum. The second aim was to evaluate the relationship between the concentration of plasma IGF-I in the transition period and the estrous synchrony response and pregnancy rate to a controlled internal drug release (CIDR) protocol. A total of 402 dairy cows, 250 multiparous and 152 primiparous, were enrolled. A blood sample was taken from all cows 2 and 1 wk precalving and wk 1, 3, 4, and 5 postcalving for subsequent analysis of IGF-I. Vaginal discharge score as a measurement of uterine health was recorded in wk 3, 4, and 5 postcalving. Estrous cycles of all cows were synchronized on ≥37 d in milk (mean = 59; range 37-93) using an 8-d CIDR protocol. All cows were scanned at 32 to 35 d after insemination to confirm pregnancy. Data were analyzed using Proc Mixed and Proc Logistic models in SAS (version 9.3; SAS Institute Inc., Cary, NC). Plasma IGF-I concentrations were significantly greater in the primiparous cows than in the multiparous cows, both before and after calving, and were therefore analyzed separately. In multiparous cows plasma IGF-I concentrations postcalving were significantly lower among cows with uterine infection than in those without infection, and multiparous cows with a plasma IGF-I concentration less than 40 ng/mL 1 wk after calving were 3 times more likely to suffer from a uterine infection 4 to 5 weeks postcalving (odds ratio 2.8; 95% confidence interval 1.0-7.6). Plasma IGF-I concentrations were significantly greater after calving in the 121 primiparous cows that exhibited estrus post-CIDR protocol (mean 125 ng/mL) than in the 25 primiparous cows that did not respond (mean 95 ng/mL). Multiparous cows with greater plasma IGF-I concentrations postcalving had a significantly greater chance of conceiving (mean plasma IGF-I concentration of conceiving cows = 86 ng/mL; nonconceiving = 70 ng/mL). These results show an association between greater concentrations of plasma IGF-I postcalving and response to CIDR protocol in primiparous animals (mean plasma IGF-I concentration of responders = 116 ng/mL; nonresponders = 95 ng/mL). In contrast no association was detected between concentrations of plasma IGF-I in relation to the response to the CIDR protocol in multiparous cows. In conclusion, changes in circulating concentrations of plasma IGF-I early postpartum may help predict reproductive status of dairy cows.

Effects of live yeast dietary supplementation on hormonal profile, ovarian follicular dynamics, and reproductive performance in dairy cows exposed to high ambient temperature

Two experiments were conducted to investigate the effects of dietary supplementation with live yeast culture on hormonal profile, ovarian follicular dynamics and reproductive performance of lactating dairy cows exposed to high ambient temperature. In Expt. 1, Holstein cows were fed a diet with (n = 6) or without (n = 6) 4 g yeast/h/d from 21 d before expected calving date until 8 weeks postpartum. Concentrations of glucose, insulin, insulin like growth factor-I (IGF-I), estradiol-17β (E-17β) and progesterone (P4) were determined in plasma, and transrectal ultrasonography was used to monitor ovarian follicular dynamics. In Expt. 2, 150 Holstein cows (75/dietary group) received same diets as Expt. 1 with the exception that diets were fed from d 1 to d 70 postpartum. The effect of dietary treatments on reproductive performance was examined. In Expt. 1, plasma IGF concentrations during dietary treatment were higher (P = 0.05) in cows fed diets supplemented with yeast. On d 60 postpartum, average plasma concentrations of glucose (48.3 vs. 41.0 mg/dL) and insulin (0.90 vs. 0.23 μU/mL), were also greater in cows fed diets supplemented with yeast compared to that in cow fed diets without supplementation. Similarly, plasma concentrations of E-17β at estrus (P = 0.016) and P4 on d 10 of the estrous cycle (P = 0.021) were greater in yeast-supplemented cows. Moreover, yeast supplementation resulted on average in an estrous cycle 2.6 d shorter (P = 0.05) and in the development of larger ovulatory follicles (18.4 vs. 17.2 mm in diameter; P < 0.01). In Expt. 2, days open were fewer and the proportion of pregnant cows at 120 and 150 d postpartum were greater (P < 0.01) in cows fed diets supplemented with yeast compared to those receiving diets without yeast. In summary, cows fed diets supplemented with yeast had greater plasma IGF-I, E-17β and P4 concentrations, larger ovulatory follicles, shorter estrous cycles, and improved reproductive performance. Therefore, live yeast dietary supplementation could enhance lactating dairy cow's fertility during heat stress through improvement in hormonal profile and development of larger ovulatory follicles.

Physiological and genetic differences between low and high index dairy cows

Selection of dairy cattle for increased milk production has decreased some indices of reproductive efficiency. For example, days open are increased by one day for every 100 kg of increased milk yield per lactation. Some of the change in days open can be explained by delayed onset of oestrous cyclicity and lower conception rate to artificial insemination in cows with greater milk production. Despite these negative associations between milk production and reproduction, reproduction in herds of high producing dairy cattle is not necessarily compromised relative to reproduction in herds of low producing dairy cattle. This is because there is a large environmental effect on dairy reproduction. High producing herds generally have better management and better oestrous detection. Therefore, high producing dairy herds may partially overcome the antagonistic relationship between milk production and reproduction. Physiological mechanisms that lead to poorer reproduction in high producing cows are partially defined. Negative energy balance that occurs in high producing dairy cows can be associated with a delay in the initiation of ovarian cycles and the interval to first breeding. Many of the effects of negative energy balance on postpartum reproduction can be explained by decreased serum luteinizing hormone (LH) that is associated with negative energy balance. Serum LH increases as cows move toward positive energy balance and greater LH stimulates growth and ovulation of ovarian follicles. We have initiated studies to address physiological differences in high and low index dairy cows. The reproductive endocrinology of cows from a control line (5,900 kg milk/lactation) and a select line (10,900 kg milk/lactation) of dairy cows at the University of Minnesota was studied over a two-year period. Cows in Year 1 were similar for serum concentrations of LH, follicle stimulating hormone (FSH), and oestradiol (preovulatory period). In both years, serum concentrations of progesterone during luteal phases, however, were decreased in select cows. The Year 2 cows also had a delay in the return to oestrous cyclicity that was associated with reduced LH. The possibility that decreased progesterone causes infertility in dairy cows will require further study. Collectively, these data suggest that changes in blood progesterone concentrations may explain, partially, lower fertility in high index dairy cows.

Hormonal profile and follicular dynamics concurrent with CIDR and insulin modified Ovsync TAI programs and their impacts on the fertility response in buffaloes

Fifty one cyclic Egyptian buffaloes were used to study the hormonal profile and follicular dynamics concurrent with CIDR and insulin modified Ovsync TAI programs and their impacts on the consequent fertility responses. The buffaloes were randomly assigned into 3 ovulation synchronization protocols: Ovsync-alone (n = 13, control) CIDR-sync (n = 20) and Insulin-sync (n = 18). Ovsync-alone protocol consisted of two im injections of 20 μg bueserlin (GnRHa) on Day 0 (GnRH 1) and on Day 9 (GnRH 2) with an im injection of 500 μg of cloprostenol sodium (PGF₂ α) on Day 7. The CIDR-sync protocol consisted of the same treatment protocol as in Ovsync in addition to intra-vaginal insertion of CIDR (contains 1.38 gm of progesterone) on Day 0 followed by removal on Day 7. The Insulin-sync protocol consisted of the same treatment protocol as in Ovsync plus 3 sc injections of insulin at a dose of 0.25 i.u/1 kg, on Days 7, 8, and 9. Buffaloes in all groups were inseminated 16 h after GnRH2 by the same inseminator using frozen semen in straws. Blood samples were collected on Days 0, 3, 5 for serum progesterone assay and on Day 9 to measure serum concentrations of estradiol, insulin and IGF-1. Transrectal ultrasonographic scanning of the ovaries was conducted on Days 7, 8 and 9 to record the diameter of the largest follicle. Pregnancy diagnosis was conducted on Day 30 post-TAI by trans-rectal ultrasonographic scanning of the uterus to calculate conception rate. The serum progesterone concentration showed an increase (p < 0.01) in pregnant compared with non-pregnant buffaloes in both Ovsync-alone and Insulin-sync groups, but not in CIDR-sync group (p > 0.05) on Days 3 and 5. The serum estradiol concentration on Day 9 showed an increase (p < 0.01) in pregnant compared with the non-pregnant buffaloes in all of the treated groups. In Insulin-sync and Ovsync-alone groups, the diameter of the largest follicle (LF) was larger (p < 0.01) in pregnant compared with non-pregnant buffaloes, but in CIDR-sync, the diameter of the (LF) was larger (p < 0.01) in non-pregnant compared with pregnant buffaloes. Also, the results showed that the greatest diameter of LF was observed in pregnant buffaloes in Insulin-sync compared with either pregnant or non-pregnant buffaloes in all groups. It is concluded that modified CIDR-sync and Insulin-sync could improve fertility response through modulating hormonal profile and follicular dynamics in buffaloes during low breeding season.

Factors affecting folliculogenesis in ruminants

This review addresses the reasons for the lack of progress in the control of superovulation and highlights the importance of understanding the mechanisms underlying follicular development. The present inability to provide large numbers of viable embryos from selected females still restricts genetic improvement, whilst variability in ovarian response to hormones limit the present capacity for increasing reproductive efficiency.

Females are born with a large store of eggs which rapidly declines as puberty approaches. If these oocytes are normal then there is scope for increasing the reproductive potential of selected females. Oocytes must reach a certain size before they can complete all stages of development and the final changes that occur late in follicular development. It is likely that oocytes that do not produce specific factors at precise stages of development will not be viable. Hence, it is important to characterize oocyte secreted factors since there are potential indicators of oocyte quality.

The mechanisms that determine ovulation rate have still not been fully elucidated. Indeed follicular atresia, the process whereby follicles regress, is still not known. A better understanding of these processes should prove pivotal for the synchronization of follicular growth, for more precise oestrous synchronization and improved superovulatory response.

Nutrition can influence a whole range of reproductive parameters however, the pathways through which nutrition acts have not been fully elucidated. Metabolic hormones, particularly insulin and IGFs, appear to interact with gonadotrophins at the level of the gonads. Certainly gonadotropins provide the primary drive for the growth of follicles in the later stages of development and both insulin and IGF-1, possibly IGF-2, synergize with gonadotrophins to stimulate cell proliferation and hormone production. More research is required to determine the effects of other growth factors and their interaction with gonadotropins.

There is evidence, particularly from studies with rodents, that steroids can also modulate follicular growth and development, although information is very limited for ruminants. There may be a rôle for oestrogens in synchronizing follicular waves, to aid in oestrous synchronization regimes and for removing the dominant follicle to achieve improved superovulatory responses. However more information is required to determine whether these are feasible approaches.

Heritability for litter size is higher in sheep than in cattle. Exogenous gonadotropins are a commercially ineffective means of inducing twinning in sheep and cattle. Although there are differences in circulating gonadotropin concentrations, the mechanism(s) responsible for the high ovulation appear to reside essentially within the ovaries. The locus of the Booroola gene, a major gene for ovulation rate, has been established but not specifically identified. However sheep possessing major genes do provide extremely valuable models for investigating the mechanisms controlling ovulation rate, including a direct contrast to mono-ovulatory species such as cattle.

In conclusion, the relationship between oocyte quality, in both healthy follicles and those follicles destined for atresia, must be resolved before the future potential for increasing embryo yield can be predicted. In addition, a greater understanding of the factors affecting folliculogenesis in ruminants should ensure that the full benefits ensuing from the precise control of ovarian function are achieved. The improved use of artificial insemination and embryo transfer that would ensue from a greater understanding of the processes of folliculo genesis, coupled with the new technologies of genome and linkage mapping, should ensure a more rapid rate of genetic gain.

Effects of lactation and pregnancy on metabolic and hormonal responses and expression of selected conceptus and endometrial genes of Holstein dairy cattle

Objectives were to characterize postpartum metabolic and hormonal differences between nonlactating and lactating dairy cows, evaluate lactation and pregnancy effects on endometrium and conceptus expression of selected genes, and characterize associations between conceptus and endometrial expression of genes in early pregnancy (d 17). Pregnant heifers were assigned randomly after calving to a lactating group (L, n=17) and a nonlactating group (NL, n=16). The L cows were fed a total mixed ration [1.65 Mcal of net energy for lactation (NE(L))/kg, 16.5% crude protein (CP)] ad libitum, and the NL cows were fed a maintenance ration (1.45 Mcal of NE(L)/kg, 12.2% CP) once per day. All cows were presynchronized and enrolled in a timed artificial insemination (TAI) protocol; 10 cows in the L and 12 in the NL received TAI. On d 17 after GnRH and TAI, cows were slaughtered and endometrial and conceptus tissues collected. The Affymetrix Bovine Genome DNA Microarray (Affymetrix Inc., Santa Clara, CA) was used to assess conceptus and endometrial gene expression. The L cows had higher body temperature than the NL cows (38.4 vs. 38.2°C), and the NL cows cycled earlier than the L cows (26.3 vs. 34.7 d in milk). Cows in the L group had greater plasma concentrations of β-hydroxybutyrate (4.90 vs. 2.97 mg/dL) and blood urea N (11.6 vs. 6.5mg/dL) and lower concentrations of glucose (74.0 vs. 79.9 mg/dL) compared with NL cows. Insulin-like growth factor-1 was lower for L compared with NL (140.5 vs. 198.2 ng/mL) and was greater for cows subsequently classified pregnant compared with cyclic (191.0 vs. 147.6 ng/mL). The concentration of progesterone from GnRH or TAI (d 0) until d 17 was lower for L cows than for NL cows. Gene expression analyses indicated that all conceptuses (n=13) expressed pregnancy-associated glycoprotein (PAG) genes PAG2, PAG8, PAG11, and PAG12. The same PAG family genes were observed in the endometrium of some pregnant cows. Simple and standard partial correlation analyses detected associations of conceptus PAG11 with prostaglandin regulatory genes. In conclusion, lactation altered metabolic status, delayed initiation of cyclicity, and decreased concentrations of progesterone in pregnant cows. Early expression of PAG genes in the conceptus may contribute to successful development of early pregnancy and possibly alter mechanisms related with embryo survival such as prostaglandin synthesis.

Acute dietary restriction in heifers alters expression of genes regulating exposure and response to gonadotrophins and IGF in dominant follicles

Dietary restriction in growing cattle and severe negative energy balance in lactating cows have been associated with altered gonadotropin secretion, reduced follicle diameter, reduced circulating oestradiol concentrations and anovulation. Therefore, we hypothesised that acute dietary restriction would influence the fate and function of the dominant follicle by altering the expression for genes regulating gonadotrophin and IGF response in ovarian follicles. Newly selected dominant follicles were collected 7-8 days after prostaglandin F(2α) (PGF) administration from heifers (n=25) that were individually fed a diet supplying 1.2 maintenance (M; control, n=8) or 0.4 M (restricted, n=17) for a total duration of 18-19 days. Heifers within 0.4 M were ovulatory (n=11) or anovulatory (n=6) depending on whether the dominant follicle present at PGF ovulated or became atretic following luteolysis. Control animals were all ovulatory. Acute dietary restriction decreased IGF-I (P<0.001) and insulin (P<0.05) in circulation; oestradiol (P<0.01) and IGF-I (P<0.01) in follicular fluid; and mRNA for FSHR (P<0.01) in granulosa cells but increased mRNA for IGFBP2 (P<0.05) in theca cells of the newly selected dominant follicle. However, this only led to anovulation when dietary restriction also decreased mRNA for CYP19A1 (P<0.05), IGF2 (P<0.01) and IGF1R (P<0.05) in granulosa cells and LHCGR (P<0.05) in theca cells of follicles collected from heifers fed 0.4 M. These results suggest that the catabolic environment induced by dietary restriction may ultimately cause anovulation by reducing oestradiol synthesis, FSH-responsiveness and IGF signaling in granulosa, and LH-responsiveness in theca cells of dominant follicles.

Follicular turnover and hormonal association in postpartum goats during early and late lactation

To clarify the effect of lactation period on ovarian follicular activity and associated hormonal levels in goats, six goats were monitored daily by ultrasonographic examination with blood sampling during early (Days 5 to 25; Day 0 was the day of kidding) and late (Days 40 to 60) lactation. While the presence of a corpus luteum of pregnancy retarded follicular growth in the ipsilateral ovary until Days 11-13 postpartum, the total follicular number (TFN) and area (TFA) increased during late lactation due to the significant increase in the number of medium- and large-sized follicles and decrease in the number of small follicles. Four goats showed a similar pattern of follicular development during the period studied characterized by the emergence of five and six waves during the early and late lactation, respectively. The largest follicle diameter of the first three waves monitored during early lactation was significantly smaller as compared with the diameter of those existing during late lactation. TFN showed a positive correlation with FSH but showed a negative correlation with immunoreactive (ir-) inhibin and estradiol during the postpartum period. TFA was positively correlated with ir-inhibin, estradiol and PRL and negatively correlated with FSH during the monitored periods. The plasma levels of ir-inhibin and progesterone were significantly higher during late lactation compared with the levels recorded during early lactation. Ir-inhibin levels showed a significant positive correlation with LH and estradiol during early and late lactation but showed a negative correlation with FSH during the whole lactation period. LH was positively correlated with estradiol and PRL during early and late lactation, respectively. These results suggest that the lactation period has a detrimental effect on ovarian activity during the early postpartum period in goats.

Initial body condition score affects hormone and metabolite response to nutritional restriction and repletion in yearling postpubertal beef heifers

Twenty Simmental x Angus, half-sibling, postpubertal heifers (initial BW of 443 +/- 9 kg) were allotted randomly into 2 treatment groups to evaluate if initial BCS affects response of the hypothalamic-pituitary-ovarian axis to metabolic signals elicited by energy restriction and repletion. During a preliminary feeding period, diets were formulated so that each heifer in the designated treatment would reach a BCS of 5 (moderate condition; MOD) or a BCS of 7 (heavy condition; FAT). Once each heifer had reached desired BCS, diets were formulated to supply 30% of NE(m) requirements until each heifer became anestrous (serum concentrations of progesterone < 1 ng/mL; restriction period). Blood collections took place on d 1 of each period, on d 43 of energy restriction and d 44 of energy repletion, and when heifers were confirmed to recommence estrous cycles. When heifers were cycling, their estrous cycles were synchronized to ensure hormone sampling occurred during late diestrus or early proestrus. Energy restriction resulted in decreased concentrations of LH (FAT, P = 0.02; MOD, P < 0.001), IGF-1 (FAT, P < 0.001; MOD, P = 0.003), and insulin (P < 0.001); in contrast, concentrations of GH (P < 0.001) and plasma urea nitrogen (P < 0.001) increased. During repletion, LH concentration increased (P = 0.03) in MOD condition heifers but was still less (P = 0.002) than d 1 of restriction, whereas LH concentration tended to increase in FAT heifers (P = 0.06) until it was similar (P = 0.40) to d 1 of restriction. Repletion also increased concentrations of IGF-1 (P < 0.001), insulin (P < 0.001), and glucose (P < 0.001), whereas concentrations of GH (P < 0.001), NEFA (P < 0.001), and plasma urea nitrogen (P < 0.001) decreased. For both treatments, concentrations of GH after repletion were similar (FAT, P = 0.88; MOD, P = 0.10) to those on d 1 of restriction. After repletion, FAT condition heifers had decreased concentrations of IGF-1 (P < 0.001), insulin (P < 0.05), and glucose (P < 0.001), but greater concentrations of acetate (P < 0.01) and butyrate (P < 0.05), than MOD heifers. Anestrus or resumption of estrous cycles seems to be activated gradually in response to dietary manipulation, unrelated to certain metabolite changes.

Insulin-like growth factor I in sera, ovarian follicles and follicular fluid of cows with spontaneous or induced cystic ovarian disease

The objective of this research was to determine changes in IGF-I levels in serum and follicular fluid, and immunoreactivity of the follicle wall of cows with spontaneous (slaughter specimens) or ACTH-induced follicular cysts, and to compare results to normal cycling (control) cows after selection of the ovulatory follicle. Concentrations of IGF-I in serum did not differ between control and cystic animals (p=0.76). Fluid from the ovulatory follicle in control cows had 41% higher concentrations of IGF-I than that from cystic follicles collected at slaughter (spontaneous cysts; p<0.05) and 70% higher than that in induced follicular cysts (p<0.05). An intense positive immunostaining with anti-IGF-I was observed in granulosa cells (p<0.05) and in the theca interna (p<0.05) of secondary and tertiary follicles in all three groups of animals, but staining was less intense in cystic (p<0.05) and atretic follicles (p<0.05). This study provides evidence to suggest that cystic ovarian disease in cattle is associated with decreased concentrations of IGF-I in follicular fluid, but not in serum, and decreased production of IGF-I in the follicular wall. These data support the notion that IGF-I plays a role in the regulation of folliculogenesis, and may participate in the pathogenesis of cystic ovarian disease in cattle.

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.

Estrogen to progesterone ratio affects hormonal and lipid follicular fluid profiles in dairy cows

Aim:  The present study described hormonal and lipids concentrations of follicles that develop under high progesterone plasmatic levels, mimicking the second follicular wave. Methods:  All follicles were removed by aspiration in order to generate a new follicular wave. Follicular fluid was then obtained from either 3 day old follicles (F3) or 6 day old follicles (F6). This experimental protocol was carried out at 20 days and 90 days post-partum on Frisian dairy cows that had already returned to cyclicity. Results:  Estrogen active follicles (ratio of estrogen to progesterone in follicular fluid higher than 1) have higher levels of VEGF, IGF-I and linoleic acid, and have lower levels of NEFA, oleic and arachidonic acid. Non-estrogen active follicular fluid concentrations of IGF-I and NEFA were similar to plasma concentrations. In contrast, estrogen active follicles showed higher IGF-I and lower NEFA levels than plasmatic ones that could be used to sustain follicular growth. Conclusions:  The results show that estrogen active follicles might have their own metabolism. (Reprod Med Biol 2007; 6: 45-51).

Preovulatory, postovulatory, and postmaternal recognition effects of concentrations of progesterone on embryonic survival in the cow

Although fertilization rate usually is very high when male fertility is normal, pregnancy rates are below expectations when defined by the birth of live offspring in response to first service. Factors that affect establishment and retention of pregnancy include 1) preovulatory influences on the follicle and oocyte, 2) early postovulatory uterine and luteal function, 3) concentrations of hormones associated with trophoblastic and endometrial function during maternal recognition of pregnancy, and 4) less-well understood factors during the peri-attachment period. For example, decreased progesterone during preovulatory follicular development leads to a persistent follicle, premature resumption of meiosis, and a high incidence of embryonic death between the 2- and 16-cell stages. Elevated PGF(2alpha) during d 4 to 9 of the estrous cycle not only caused luteolysis but also had a direct embryotoxic effect during the morula-to-blastocyst transition. Ideal conditions during placentation and attachment are not clearly defined. Late embryonic mortality might be increased after ovulation of persistent or immature follicles. Nominal increases in secretion of PGF(2alpha) between d 30 and 35 might be important for attachment and placentation. Lower survival of embryos from wk 5 to wk 7 to 9 of gestation in the cow was associated with lower circulating concentrations of progesterone on wk 5. To maximize embryonic survival in the cow, management must provide high progesterone before estrus, quality detection of estrus, and timely insemination. Luteolytic influences of estradiol-17beta or PGF(2alpha) must be minimized early after mating and during maternal recognition of pregnancy, and high progesterone is needed during the late embryonic/early fetal period.

Histological Characteristics and Steroid Concentration of Ovarian Follicles at Different Stages of Development in Pregnant and Non-pregnant Dairy Cows

The aim of the study was to investigate the histological characteristics and steroid concentrations in follicular fluid of different populations of follicles at different stages of development, during pregnancy and the oestrous cycle in cows. Follicles from ovaries collected at a slaughterhouse were allocated into three size categories (small, 2-5.9 mm; medium, 6-13.9 mm; and large, 14-20 mm) in pregnant and non-pregnant cows. Slices were stained with HE and PAS for histological analysis. Follicular fluid was pooled according to size and pregnancy status and estradiol, testosterone and progesterone concentrations in follicular fluid were determined by RIA. Characteristics of healthy follicles did not differ, regardless of follicle size or pregnancy status. Total histological atresia was significantly higher in pregnant cows than in non-pregnant cows (p < 0.05). Estradiol increased and testosterone decreased significantly, while follicles increased in size, in both non-pregnant and pregnant cows (p < 0.05). Nonpregnant cows had the highest estradiol values in follicles of all sizes. Medium and large follicles from pregnant cows showed the lowest testosterone concentration (p < 0.05). Progesterone levels increased with follicle size only in non-pregnant animals. In large follicles, progesterone concentration was significantly higher in non-pregnant cows than in pregnant cows (p < 0.05). Considering steroid concentration and histological findings, most large follicles might be atretic during pregnancy in cattle.

Strategies for improving fertility in the modern dairy cow

The high producing dairy cow of the 21st century is subfertile during lactation. Our objectives are to characterize physiological periods limiting reproductive performance and to describe integrated management strategies to improve pregnancy rates. Ovarian recrudescence with normal re-occurring estrous cycles and restoration of fertility to first service are associated with a reduced occurrence of periparturient metabolic and reproductive disorders. Marked negative changes in energy balance and reduced immunocompetence influence gonadotropic and metabolic hormones. Induced ovarian inactivity was associated with enhanced uterine involution. Post-partum health and reproductive performance were improved when by-pass lipids enriched in polyunsaturated fatty acids were fed in the pre- and post-partum periods. Pharmaceutical control of follicle, CL, and uterine function with PGF, GnRH and intravaginal progesterone releasing inserts, has permitted development of more optimal timed-insemination programs for first service. Likewise, resynchronization of nonpregnant cows coupled with the use of ultrasound for early pregnancy diagnosis provides the opportunity for a second timed-insemination within 3 days of a nonpregnant diagnosis. Bovine somatotropin (bST) increases embryo development and embryo survival when coupled with a timed-insemination program or cows detected in estrus. Presence of a conceptus alters endometrial expression of genes and proteins in response to bST and nutraceuticals (i.e., unsaturated fatty acids such as eicosapentaenoic and docosahexaenoic acid in by-pass lipids) to improve pregnancy rates. Postovulatory increases in progesterone may enhance pregnancy rates in targeted populations of lactating dairy cows, but timing and magnitude of the progesterone increases are pharmaceutically dependent.

JSAR Innovative Technology Award. Development of ovulation synchronization and fixed time artificial insemination in dairy cows

Recently, reproductive management has become more difficult as a result of increased herd size. Problems with missing estrous signs and decrease in conception rate by artificial insemination (AI) performed at wrong timing have caused low AI conception rates. In 1995, ovulation synchronization and fixed-time AI (Ovsynch/TAI) was developed in the USA as a new reproductive technology, which was accepted as an useful reproductive management tool in many countries. However, no information on the use of Ovsynch/TAI was available in Japan. It was, therefore, warranted to show the ovulation rate and conception rate after Ovsynch/TAI using gonadotropin releasing hormone analogue (GnRH-A, fertirelin acetate) and prostaglandin F2alpha (PGF2alpha)-THAM, both were commercially available in this country. The conception rate after Ovsynch/TAI has been known to vary among different herds and individuals. Investigation and analysis of factors affecting the conception rate was also warranted to improve the conception rate. A series of experiments were carried out to establish Ovsynch/TAI using domestically produced GnRH-A and PGF2alpha and to study factors affecting conception rate after Ovsynch protocol. Ovsynch using 100 microg GnRH-A and 25 mg PGF2alpha were observed using ultrasonography. As a result, a high synchronization rate of ovulation at 16 to 20 h after the second GnRH injection was confirmed. The conception rate after Ovsynch/TAI was compared in 87 cows with the conception rate after AI at estrus induced by PGF2alpha (139 cows). Conception rate after Ovsynch/TAI was higher than the figure after AI at induced estrus (59.1% vs 20.9%, P<0.05). The dose of GnRH-A was also studied and a practical dose of GnRH-A was found to be 50 microg per cow. To clarify some factors affecting the conception rate after Ovsynch/TAI, 1,558 cows were investigated for the state of their ovaries, days after calving, parity, season, ovarian cyclicity postpartum and nutritional state at the day of Ovsynch. The overall conception rate after Ovsynch/TAI was 51.5%. Fifty-six cows (3.6%) showed estrus at 6 to 7 d after the first injection of GnRH-A. The conception rate after Ovsynch/TAI was low in cows that were 40 to 60 d postpartum, those in their 5th lactation or more, those bred in July to August, and those recovering ovarian cyclicity later than 56 d postpartum. The conception rate after Ovsynch/TAI was high in cows in which body condition score (BCS) was 3.75 at dry period and 3.0 at the day of Ovsynch. In conclusion, Ovsynch/TAI is an effective tool for the reproductive management of dairy cows. A steady and sufficient conception rate after Ovsynch/TAI could be expected by taking the factors affecting the conception rate into the consideration.

Pregnancy rates and metabolic profiles in cattle treated with propylene glycol prior to embryo transfer

The objective of this study was to determine the effect of a sustained propylene glycol administration to recipients of frozen/thawed in vivo derived bovine embryos. Heifers were treated with oral propylene glycol for the last 20 days before embryo transfer (n = 142), and untreated as controls (n = 133). Progesterone, insulin, insulin-like growth factor-I, glucose, urea and triglyceride were analysed in blood on Day 0 and Day 7 of the estrous cycle corresponding to embryo transfer. The heifers were selected as recipients when showing progesterone levels <2.0 ng/ml (Day 0) and >2.5 ng/ml (Day 7), according to corpus luteum quality on Day 7 by technicians unaware of animals treated. Within treated animals, significantly more recipients were selected, and increased progesterone, corpus luteum quality, pregnancy and calving rates were recorded. Day 7 progesterone concentrations were higher in heifers treated and transferred. Propylene glycol increased insulin and insulin-like-growth factor-I, but glucose, urea and triglyceride did not vary. Furthermore, insulin-like-growth factor-I, glucose and triglyceride increased at estrous time, but urea decreased and insulin remained unaltered. Together with the sustained gain in pregnancy rates throughout the experiment (2 years), other evidences suggested that the observed effects did not rely on nutritional deficiency. Thus, propylene glycol improved pregnancy rates after embryo-transfer, and progesterone, insulin and insulin-like-growth factor-I are probably involved in this effect.

Recent Developments in Oestrous Synchronization of Postpartum Dairy Cows with and without Ovarian Disorders

This report reviews the most recent developments in prostaglandin-based oestrous synchronization programmes for postpartum dairy cows and addresses the efficiency of controlled breeding protocols based on such developments for cows with abnormal ovarian conditions. A double prostaglandin protocol applied 11-14 days apart seems to be capable of bringing most cows to oestrus. Because of varying oestrus onset times, improved conception rates are obtained following artificial insemination (AI) at detected oestrus rather than fixed-time AI in prostaglandin-treated cows. The administration of oestradiol or human chorionic gonadotrophin, or both these hormones, after prostaglandin treatment, improves the synchrony of oestrus yet does not enhance the conception rate. Progesterone-based treatments for oestrous synchronization are considered the most appropriate for non-cyclic or anoestrous postpartum dairy cows; prostaglandin alone being ineffective because of the absence of a mature corpus luteum in these cows. Improved oestrus synchrony and fertility rate have been reported using short-term progesterone treatment regimes (7-9 days) with or without oestradiol benzoate combined with the use of a luteolytic agent given 1 day before, or at the time of, progesterone withdrawal. The ovulation synchronization (Ovsynch) protocol, based on the use of gonadotrophin releasing hormone and prostaglandin, was developed to coordinate follicular recruitment, CL regression and the time of ovulation. This protocol allows fixed time insemination and has proved effective in improving reproductive management in postpartum dairy cows. However, timed AI following Ovsynch seems to have no beneficial effects in heifers, because of an inconsistent follicle wave pattern, and in anoestrous cows, given their lack of prostaglandin responsive CL. To date, there are several prostaglandin based, fixed-time insemination oestrous synchronization protocols for use in early postpartum dairy cows with ovarian disorders such as ovarian cysts and acyclicity.

Treatment of suckling beef cattle with a progestagen sponge and oestradiol benzoate or equine chorionic gonadotrophin

The ovarian responses of anoestrus beef cows to a combined treatment with medroxy-progesterone acetate (MAP) sponges and oestradiol benzoate or equine chorionic gonadotrophin (eCG) were evaluated. Forty-five suckling Hereford cows were allocated to three equal groups. Group 1 received a MAP sponge for seven days plus an injection of 2 mg oestradiol benzoate when the sponge was inserted (day 0) and 1 mg when the sponge was withdrawn; group 2 received identical treatment until day 7, when a dose of 400 iu of eCG was administered, and group 3 were left untreated as control animals. From day 0 to day 11 the cows' ovaries were examined daily by transrectal ultrasonography, and their oestrous behaviour was observed from 24 hours to 96 hours after the sponge was removed. Data from cows that had a corpus luteum present before the sponge was withdrawn were not used in subsequent analyses; there were four in group 1, five in group 2 and four in group 3. In 19 of the 21 cows in groups 1 and 2 a new follicular wave was observed to emerge at a mean (sd) interval of 3.9 (0.3) days after the insertion of the sponge, whereas in group 3 it occurred in all 11 cows after 3.4 (0.6) days. Only the six cows that had a follicle of 9 mm or larger in diameter ovulated (P < or = 0.001). Nine of the 11 cows in group 1 came into oestrus, compared with two of the 10 in group 2 and none of the control cows (P < or = 0.001). Ovulation was observed in four, two and none of the cows in groups 1, 2 and 3, respectively.

Effect of oestradiol benzoate given after prostaglandin at two stages of follicle wave development on oestrus synchronisation, the LH surge and ovulation in heifers

Oestrus synchronization following prostaglandin-induced luteolysis is variable and dependent on follicle wave status in cattle. Oestradiol benzoate (ODB) has been used following prostaglandin to reduce the interval to oestrus and ovulation, but the effect of follicle wave status at the time of ODB administration is not clear. The aim of this study was to characterize the endocrine and follicular responses following ODB after luteolysis at different stages of the follicle wave. Prostaglandin was administered at either emergence or dominance of the second follicle wave. Twenty-four hours later animals received either 0.5mg ODB in oil or a control oil injection. Follicular development was monitored daily by ultrasonography, oestrous behavior was determined and blood samples were collected. In animals treated with ODB at emergence, there was a reduction (P<0.05) in the maximum diameter of the ovulatory follicle (11.7+/-1.2 mm versus 13.1+/-0.1 mm) and in the interval from prostaglandin to oestrus (52.0+/-2.3 h versus 88.0+/-9.6h), to the LH surge (53.3+/-3.5 h versus 89.1+/-6.5 h) and to ovulation (96+/-0.0 h versus 129.6+/-9.6h), compared with controls. In animals treated with ODB at dominance, there was a reduction (P<0.05) in the interval from prostaglandin to the LH surge (54.0+/-3.1 h versus 70.9+/-4.8 h), but not in the interval from prostaglandin to oestrus (53.3+/-2.7 h versus 65.7+/-4.5 h; P=0.11), to ovulation (96.0+/-0.0 h versus 110.4+/-4.8 h; P=0.12) or the maximum diameter of the ovulatory follicle (12.7+/-0.3 mm versus 13.6+/-0.4 mm; P=0.12), compared with controls. Treatment did not affect (P>0.05) the length of the subsequent oestrous cycle or corpus luteum size. In conclusion, the use of ODB advanced, but did not alter the temporal relationships among oestrus, the LH surge and ovulation, regardless of stage of follicle development at treatment.

Reproductive responses following royal jelly treatment administered orally or intramuscularly into progesterone-treated Awassi ewes

An experiment was conducted to determine whether natural royal jelly (RJ) paste administered orally or intramuscularly (i.m.) in conjunction with exogenous progesterone is associated with improved reproductive responses in ewes. Thirty 3-6-year-old Awassi ewes were randomly allocated into three (RJ-capsule, RJC; RJ-injection, RJI and control, CON) groups of 10 ewes each. All ewes were treated with intravaginal progesterone sponges for 12 days. Ewes in the RJC and RJI were administered orally or i.m. with a total of 3g of RJ given in 12 equal doses of 250 mg per ewe per day starting at the time of sponge insertion. At the time of sponge withdrawal (day 0, 0 h), ewes were exposed to three rams and checked for breeding marks at 6-h intervals for 3 days. Blood samples were collected from all ewes for analysis of progesterone concentrations. Pretreatment progesterone levels were <0.5 ng x ml(-1) in 16/30 and >1.3 ng x ml(-1) in the remaining ewes indicating luteal function and cyclicity. Similar reproductive responses and progesterone levels occurred in ewes of the RJC and RJI; therefore, data of the two groups were pooled. Following sponge insertion, progesterone levels increased rapidly and reached maximum values of 5.8+/-0.2 ng x ml(-1) within 2 days among ewes of the three groups, and then declined gradually to day 0 values of 1.6+/-0.1 and 1.9+/-0.1 ng x ml(-1) for the RJ-treated and CON ewes, respectively. The rate of progesterone decline was greater (P<0.001) in RJ-treated than in CON. Mean progesterone levels during the 12-day period were lower (P<0.001) in RJ-treated than in CON (2.8+/-0.2 ng x ml(-1) versus 3.3+/-0.2 ng x ml(-1)). Treatment with RJ resulted in greater (P<0.05) incidence of oestrus and shorter (P<0.05) intervals to onset of oestrus than CON. Based upon progesterone levels, ovulation occurred following day 0 in all ewes. Progesterone increased on day 3 in RJ-treated and on day 4 in CON ewes. Progesterone remained elevated through day 18 in 8/20 RJ-treated and 1/10 CON ewes (P=0.09). All pregnant ewes exhibited oestrus 14 h earlier (P<0.02), ovulated approximately 1 day earlier and had higher (P<0.001) luteal phase progesterone levels than non-pregnant ewes. Non-pregnant had higher (P<0.04) body weights than pregnant ewes. In conclusion, results demonstrate that both RJ treatments in conjunction with exogenous progesterone were equally capable of improving oestrus response and pregnancy rate.

Relationship among insulin-like growth factor-I, blood metabolites and postpartum ovarian function in dairy cows

The relationship among nutritional status, systemic insulin-like growth factor-I (IGF-I) and ovarian function early postpartum were investigated. A total of 27 Holstein-Friesian cows, 10 that cycled normally within 20 days postpartum, 5 diagnosed with follicular cysts, 8 with persistent corpus luteum (CL) after the first ovulation postpartum and 4 with inactive ovaries were used for the study. Blood samples were collected 1-3 times per week, for 60 days pre- and postpartum, for IGF-I, progesterone, estradiol, free fatty acids (FFA), blood urea nitrogen (BUN), and aspartate aminotransferase (AST) determination. Inactive ovary and cystic cows had a higher body condition score before calving and lost more condition than normal or persistent CL cows. Immediately postpartum, IGF-I levels were higher and rose sharply in cows that cycled normally than in cystic, inactive ovary or persistent CL cows. At calving and early postpartum, FFA was higher in inactive ovary and cystic than in normal and persistent CL cows. There was a significant strong positive relationship between IGF-I and BUN, and strong negative relationships between IGF-I and FFA and AST in all groups. There was a positive relationship between serum IGF-I and estradiol in normal cystic and inactive ovary cows. This study found that overconditioned cows during the dry period or at calving, lost more body condition postpartum. These cows also had a deeper and longer period of negative energy balance (NEB), poor liver function and low circulating IGF-I concentrations early postpartum. Such cows were likely to have poor reproductive function as seen in development of cystic ovaries, persistent CL and inactive ovary. Changes in serum IGF-I early postpartum may help predict both nutritional and reproductive status in dairy cattle.

Insulin-like growth factor-I as a possible hormonal mediator of nutritional regulation of reproduction in cattle

The current review aims to establish insulin-like growth factor-1 (IGF-I) as the factor that signals nutritional status to the reproductive axis, and show that assessment of IGF-I in blood early postpartum during the negative energy balance (NEB) period could be used to predict both nutritional and reproductive status in dairy cattle. The review also explores the effect of nutritional status on circulating IGF-I concentrations and the endocrine role of IGF-I on the reproductive axis. IGF-I plays an important role in gonadotropin-induced folliculogenesis, ovarian steroidogenesis and corpus luteum (CL) function. It also modulates pituitary and hypothalamus function. IGF-I clearly has an endocrine role on the reproductive axis. Severe under nutrition significantly reduces plasma IGF-I concentrations. During the critical period of NEB in high yielding dairy cattle early postpartum, IGF-I concentrations are low in blood and its levels are positively correlated to energy status and reproductive function during this period. Changes in circulating IGF-I immediately postpartum may help predict both nutritional and reproductive status in dairy cattle. IGF-I is therefore one of the long sought factors that signal nutritional status to the reproductive axis.

Synchronization of estrus in beef heifers using either melengesterol acetate (MGA)/prostaglandin or MGA/Select Synch

The objective of this study was to evaluate synchronization, conception, and pregnancy rates of yearling beef heifers synchronized with either the Select Synch protocol preceded by 7 days of MGA feeding (MGA/Select Synch) or the traditional MGA/PGF protocol. Heifers in the MGA/Select Synch group (n = 402) were fed MGA (0.5 mg/day/head) for 7 days, received an injection of GnRH (100 microg) the day following the last MGA feeding and an injection of PGF (25 mg) 7 days after GnRH. Heifers in the MGA/PGF group (n = 394) received MGA (0.5 mg/day/head) for 14 days, followed by an injection of PGF (25 mg) 17 days later. Synchronization rates tended (P = 0.08) to be higher for the MGA/Select Synch (82%) compared to the MGA/PGF (77%)-treated heifers. Conception and pregnancy rates to AI were similar (P > 0.10), 57 and 46% for the MGA/Select Synch heifers and 61 and 47% for the MGA/PGF heifers, respectively. Mean estrous response (h) was earlier (P < 0.05) for the MGA/Select Synch versus MGA/PGF treatment, 56 versus 61 h post-PGF treatment, respectively. In summary, short-term (7 days) MGA feeding preceding the Select Synch protocol produced similar synchronization, conception, and pregnancy rates as the traditional MGA/PGF protocol.

Milk yield, energy balance, hormone, follicular and oocyte measures in early and mid-lactation Holstein cows

The purpose of the study was to determine the influence of energy status on metabolic and endocrine measures, follicular development, and the quality of oocytes obtained from cows during early and mid-lactation (ML). We selected Holstein cows at calving to be assigned to the early lactation (EL) group (n = 8), while we assigned cows at about day 90 postpartum to the ML group (n = 7). We obtained blood samples twice weekly from 4 weeks before aspiration to the aspiration periods for metabolite and hormone determinations. We performed ultrasound-guided transvaginal follicular aspiration (TVFA) twice weekly on all cows for a 10-week period. We obtained follicular fluid from the largest follicle > 10 mm in diameter for hormone determinations. We analyzed data by ANOVA, using the general linear model (GLM) procedures. Energy balance was positive (2.43 +/- 0.32 Mcal/kg) for ML cows and negative (-1.55 +/- 0.33 Mcal/kg) for EL cows. Serum progesterone (P4) for ML cows decreased rapidly from the first aspiration session (2.7 +/- 0.1 ng/ml) and reached a nadir at Week 8 (0.33 +/- 0.1 ng/ml), while follicular fluid P4 increased from 0.9 +/- 0.5 to 5.6 +/- 0.05 ng/ml. Serum and follicular fluid P4 remained relatively constant over the entire aspiration period for EL cows. Follicular fluid insulin-like growth factor I (TGF-I) concentrations increased linearly for EL and ML cows, but the increase was more rapid (159 +/- 36 to 200 +/- 36 ng/ml) for ML cows than for EL cows (145 +/- 36 to 164 +/- 36 ng/ml). Serum IGF-I followed the same pattern for ML cows but declined for EL cows. Early lactation cows experienced a rapid decrease in serum nonesterified fatty acids (NEFA; 0.32 +/- 0.2 to 0.22 +/- 0.2 meq/l), while serum NEFA concentrations were relatively stable (0.19 +/- 0.2 to 0.22 +/- 0.2 meq/l) for ML cows over the aspiration period. The number of follicles obtained from the twice weekly aspiration sessions increased linearly for both EL and ML cows (P < 0.05) over the 10-week period. However, the number of follicles increased from 14.2 +/- 0.5 (Day 119) to 18.1 +/- 0.5 (Day 190) in the ML cows, compared to the changes from 14.9 +/- 0.3 (Day 32) to 15.7 +/- 0.5 (Day 90) for the EL cows. These results indicate that cows are physiologically under more production stress during EL, but increasing follicular fluid and serum IGF-I throughout ML may reflect potential differences in follicle and oocyte measures, compared to cows in EL.

Effects of propylene glycol drenching on energy balance, plasma glucose, plasma insulin, ovarian function and conception in dairy cows

We postulated that daily drenching of propylene glycol to cows in early lactation would increase plasma glucose and insulin concentrations and improve fertility in postpartum cows. Thirty-six Holstein cows were assigned to treatment or control groups. Each treatment cow was given 500 ml of propylene glycol by drenching daily from 7 to 42 days of lactation. Blood samples for glucose, insulin, nonesterified fatty acids (NEFA), and plasma urea N were collected at 0, 30, and 90 min postdrenching once weekly during 1-6 weeks. Blood samples were collected for progesterone analysis and cows were palpated three times per week until 11 weeks to assess ovarian status. Propylene glycol did not affect dry matter intake (DMI), milk yield or energy balance in treatment cows. After drenching, propylene glycol increased (P<0.01) plasma glucose and insulin and decreased (P<0.01) NEFA; plasma urea N of the treatment group tended (P=0.07) to be higher than that of the control group through 90 min. Days to first service, days open, and services per conception were not different between groups. Conception rates to first insemination were 33% in the control group and 57% in treated cows, but these were not significantly different. First ovulation of treatment cows occurred earlier than that of control cows (32.3 versus 44.5 days, P=0.06) and the length of the first luteal phase was longer in treated cows (13.1 versus 7.3 days, P<0.05). These data are consistent with the hypothesis that insulin is important for normal ovarian function. During negative energy balance, treatment with propylene glycol, which induced small increases in plasma concentrations of insulin, prevented the short luteal phase characteristic of the first estrous cycle in control cows.

Concentrations of steroids and expression of messenger RNA for steroidogenic enzymes and gonadotropin receptors in bovine ovarian follicles of first and second waves and changes in second wave follicles after pulsatile LH infusion

The objectives were to compare expression of mRNA for cytochrome P450 cholesterol side-chain cleavage (P450scc), cytochrome P450 17alpha-hydroxylase (P450c17), cytochrome P450 aromatase (P450arom), 3beta-hydroxysteroid dehydrogenase Delta(4), Delta(5) isomerase (3beta-HSD), FSH receptor (FSHr) and LH receptor (LHr) in bovine ovarian follicles of the first and second waves of the bovine oestrous cycle and to determine if LH infusion changes growth, steroidogenesis and gene expression in second wave follicles. Transrectal ultrasonography was used to examine follicular size changes during the oestrous cycle in non-lactating Holstein cows (n=31). Saline or purified bovine LH was infused intravenously into cows at emergence of follicular waves for 2 or 4 days using a computer-controlled syringe pump (n=5-6 per treatment). Treatments were: wave 1, saline (W1S); wave 2, saline (W2S) or LH (25 microg/h; W2LH). During infusion, blood samples were collected at 12min intervals for 8h via i.v. catheters for measurement of serum LH concentrations. Ovaries were removed from cows on days 2 or 4 after emergence of follicular waves. Follicles were frozen and stored at -80 degrees C. Follicular fluid (FF, 50 microl) was collected for determination of progesterone (P4), oestradiol-17beta (E2) and androstenedione (A4) concentrations. Frozen sections (14 microm) were used for in situ hybridization to measure expression of mRNA (% pixel intensity) for P450scc, P450c17, P450arom, 3beta-HSD, FSHr, and LHr. LH infusion resulted in a serum LH pattern (high frequency) similar to the early luteal phase. There were no significant differences in size of follicles among the three treatment groups. Follicular fluid concentrations of E2 and A4 in W2S were lower than those of W1S on day 2 of a follicular wave. LH infusion into cows during the midluteal phase increased follicular fluid E2 and A4 concentrations in second wave follicles on day 2 of a follicular wave (W2LH) compared to those of W2S. The increase in follicular fluid E2 on day 2 in wave 2 follicles after LH infusion occurred possibly through an increase in mRNA expression of P450c17 and 3beta-HSD. In conclusion, follicular fluid concentrations of E2 and A4 were lower in W2S than in W1S and E2 and A4 concentrations were restored by infusion of LH in W2LH with an increase in mRNA expression of P450c17 and 3beta-HSD.

Mechanisms that prevent and produce double ovulations in dairy cattle

This review integrates information on follicular and hormonal physiology and epidemiology into a novel physiological model for regulation of the ovulation rate in lactating dairy cows. First, the basic mechanisms that produce a single ovulation are examined. Follicular deviation is a critical new concept in our understanding of selection of a single dominant follicle. Follicular deviation is characterized by an abrupt deviation in the growth rates between the two largest follicles when the future dominant follicle reaches a diameter of 8.5+/-1.2 mm (mean and SD). The mechanisms involved in this selection process are not completely defined but appear to involve acquisition of LH receptors on granulosa cells of the dominant follicle, increased estradiol production by the dominant follicle, and inhibition of circulating FSH concentrations. Second, lactation number and milk production were found to be critical epidemiological factors associated with increased ovulation rate and twinning in dairy cattle. Finally, high steroid metabolism is proposed as the critical link between high milk production and double ovulation. It is proposed that high milk production increases steroid metabolism due to increased blood flow to the digestive tract and subsequently to the liver. The liver represents the primary site of steroid metabolism, and blood entering the liver is cleared of steroids. At the time of selection of the dominant follicle, the normal increase in circulating estradiol concentrations and subsequent depression in circulating FSH is blunted due to estradiol metabolism. Thus, FSH remains elevated for a time sufficient to allow follicles to undergo the physiological changes necessary to proceed to ovulation.

Short synchronization system for estrus cycles in dairy heifers: a preliminary report

In previous studies we demonstrated that the administration of a luteolytic dose of cloprostenol to dairy cows in luteal phase, followed by hCG plus estradiol benzoate (EB) 12 h later, led to successful timed AI 48 h after the initiation of treatment. This article reports two consecutive studies. In Study 1 we determined the pregnancy rate of dairy heifers in luteal phase (established by palpation per rectum) treated with cloprostenol followed by 250 IU of hCG plus 1 mg of EB 12 h later, and inseminated 48 h after cloprostenol injection. Study 2 was designed to evaluate the efficiency this synchronization protocol, irrespective of the estrus stage of the animals. In Study 1, 1272 Friesian heifers aged 14 to 16 months with a palpable corpus luteum received 500 mcg cloprostenol. Heifers were then synchronized either according to the hCG plus EB protocol (hCG-EB, n=637), or by a second dose of cloprostenol 11 d later (PG, n=636). Animals in this last group served as controls and were inseminated 72 and 96 h after the second cloprostenol injection. The pregnancy rate was significantly higher (P<0.0001) in the hCG-EB group (59.5%, 379/637) than in PG (44.8%, 285/636). In Study 2, 135 contemporary heifers (with no corresponding information on estrus stage) were subjected to the same protocol as those in the hCG-EB group of Study 1. These animals were classified in retrospect according to estrus stage established by plasma progesterone concentration. Pregnancy rates were 66.7% (24/36), 51% (25/49) and 58% (29/50) for animals in the follicular, early/late luteal, and mid-luteal phase, respectively. The total pregnancy rate was 57.8% (78/135). These findings indicate an improved pregnancy rate for heifers subjected to single insemination after cloprostenol/hCG/EB synchronization, compared to double insemination after synchronization by 2 cloprostenol injections 11 d apart. The cloprostenol/hCG/EB protocol did result in acceptable pregnancy rates after timed AI of dairy heifers regardless of their estrus cycle phase.

Regulation of ovarian follicular growth by somatotropin and insulin-like growth factors in cattle

Somatotropin (ST), insulin-like growth factor (IGF)-I, and IGF-II affect animal growth and lactation as well as animal reproduction. Understanding the effects of ST and the IGF on reproduction is important because ST and IGF-I undergo dynamic changes prior to the postpartum breeding period. In addition, administration of recombinant bovine somatotropin (rbST) to lactating cows is a common practice that increases blood concentrations of ST and IGF-I during the breeding period. In vivo, administration of rbST caused greater ovarian follicular development. The effects of rbST may represent direct actions of ST because ST receptors are found within granulosa cells as well as oocytes. Alternatively, the actions of ST may be indirectly mediated by increased IGF-I and (or) nutrient partitioning that occurs after rbST. Both IGF-I and IGF-II are synthesized within the ovary. Ovarian IGF are, therefore, a composite of IGF from both endocrine (liver) and autocrine and paracrine (ovary) sources. The IGF stimulate ovarian function by acting synergistically with gonadotropins to promote growth and steroidogenesis of ovarian cells. Actions of IGF-I and -II are restrained by a series of IGF binding proteins (IGFBP) that either originate from the blood or are synthesized locally within the follicle. Degradation and differential synthesis of IGFBP are important mechanisms regulating IGFBP amounts. The relative amounts of IGFBP may ultimately determine ovarian IGF action. Future studies of ST and IGFs should focus on the hormones, receptors, and binding proteins as well as the metabolic requirements for normal ovarian function in dairy cattle.

Impact of follicular aspiration on folliculogenesis as influenced by dietary energy and stage of lactation

Prolonged dietary energy restriction has been shown to influence the secretion of ovarian hormones and follicular development. Energy balance affects the ability of the cow to support a functional reproductive system during early lactation. Follicular aspiration is a tool that can be used to assess the impact of dietary energy and stage of lactation on follicle development in dairy cattle. Follicular aspiration was conducted twice weekly from d 30 to 100 postpartum in cows fed either 104 or 80% of NRC energy requirements. Oocyte numbers recovered increased linearly from d 30 to 100 postpartum. Cows on high energy diets produced more high quality oocytes, but also produced more poor quality oocytes than cows fed the lower energy diet. Follicles < 5 mm predominated throughout. Cows in early (d 28) and mid (d 117) lactation were used to assess stage of lactation effects on serum and follicular fluid hormones, and quality of oocytes recovered by follicular aspiration procedures for 10 wk. Serum IGF-1 decreased in early lactation cows, but increased in midlactation cows. Follicular fluid progesterone in early lactation cows decreased from 275 to 235 ng/ml, whereas in midlactation cows it increased from 65 to 550 ng/ml at aspiration wk 10. The percentage of high quality ova was higher in early lactation cows (11%) than midlactation cows (6%), but fell to 1% by aspiration wk 7 and increased to 10% by wk 10, whereas percentage of high quality ova in midlactation cows steadily declined to 2% by wk 10. Milk yield and energy balance affect patterns of folliculogenesis in lactating dairy cows.

Relative accuracy of the identification of ovarian structures in the cow by ultrasonography and palpation per rectum

Manual palpation or ultrasonographic examination of the cow's genital tract are currently used by veterinarians involved in reproductive management, but knowledge of the potential and the limitations of both methods is important to obtain an optimal accuracy in the diagnosis of physiological and pathological ovarian structures. This review presents the main features of manual and ultrasonographic characteristics of follicles, corpora lutea (with or without a cavity), follicular and lutenized cysts and the reliability of the two methods is compared. Manual diagnosis of follicles <10 mm is rather inaccurate, but ultrasound offers the possibility to diagnose follicles <5 mm and to measure their inner diameter. The predictive values of the presence or absence of a corpus luteum as determined by palpation are similar (78 vs. 75%). Manual or ultrasonographic diagnosis of the growing or regressing corpus luteum is rather difficult. The positive predictive value of a mature corpus luteum diagnosed by ultrasonography is lower (87%) than the negative predictive value (92%). Compared to manual palpation, ultrasonography permits a better estimation of the number and to determine more precisely the size of the mature corpus luteum. The positive values for follicular cysts diagnosed by palpation or by ultrasonography are 66 and 74% respectively, and for luteal cysts, the values are 66 and 85%, respectively.Manual palpation or ultrasonography are useful tools to diagnose ovarian structures in the cow. The accuracy of such methods can be enhanced by securing information on the reproductive history of the animal, palpation of uterine horns, vaginal examination or progesterone determinations.

Synchronising ovulation in dairy cows with either two treatments of gonadotropin-releasing hormone and one of prostaglandin, or two treatments of prostaglandin

OBJECTIVE

To compare oestrus synchronisation using two treatments of gonadotropin-releasing hormone (GnRH) and one of prostaglandin F2 alpha (PG) with a double prostaglandin synchronisation protocol under southern Australian conditions.

DESIGN

A clinical trial.

PROCEDURE

Eight hundred and forty, seasonally calving, lactating dairy cows within nine herds in the Tallangatta district of northeast Victoria were randomly allocated to treatment and control groups. The treatment (GnRH) group received gonadotropin-releasing hormone followed by prostaglandin F2 alpha and then a second treatment with gonadotropin-releasing hormone. These cows were inseminated at a fixed time after the second gonadotropin-releasing hormone treatment. Cows in the control (PG) group received two injections of prostaglandin F2 alpha, 14 days apart, and were inseminated according to detected oestrus.

RESULTS

The effect of GnRH treatment on first service conception rate (CRS1) and 30 day pregnancy rate (PR30) varied between herd (P < 0.001 and P < 0.02, respectively). A significant difference in CRS1 between treatment (GnRH) and control (PG) groups existed in pooled data from eight of the nine herds (38.1% vs 65.9%, P < 0.001). A significant difference also existed in PR30 between treatment (GnRH) and control (PG) groups in pooled data from eight of the nine herds (64.1% vs 72.4%, P = 0.03). Pregnancy rates after 56 days of mating for both groups were not significantly different (79.8% vs 84.1%, P = 0.13 for treatment (GnRH) and control (PG) groups, respectively). Submission rates (proportion of cows submitted for insemination) for the treatment (GnRH) groups were 100%. There was significant variation in submission rates in the control (PG) groups.

CONCLUSION

The GnRH protocol may be of benefit in herds where a poor response to the double prostaglandin program is anticipated. However, in the majority of herds in this trial, the double prostaglandin program achieved better results with fewer inseminations.

Development during single IVP of bovine oocytes from dissected follicles: interactive effects of estrous cycle stage, follicle size and atresia

Previous work suggests that a number of factors such as follicle size, day of estrous cycle, and level of atresia influence the developmental potential of bovine oocytes in vitro. To understand better the interactions of these factors, 1299 follicles > or =3 mm in diameter were dissected from ovaries of synchronized dairy cows on four days (d2, d7, d10, or d15) during the estrous cycle. The oocyte from each follicle was collected and matured, fertilized, and cultured singly to d8 (d0 of culture = IVF). Control follicles (302) were similarly dissected and processed from an ovary pair randomly collected from the abattoir on each slaughter day. Results showed that development to blastocyst was greater in oocytes collected during phases of follicular growth (d2 and d10) than those collected during phases of follicular dominance (d7 and d15; 44.8% vs. 36.0%, respectively: P < 0.001) over all follicle size categories (3-5 mm, 6-8 mm, 9-12 mm and > or =13 mm). Oocyte competence tended to increase with increasing follicle size (P < 0.1). Follicular cells from follicles containing an oocyte that developed to morula or greater by d8 (484 samples) were analyzed by flow cytometry to measure the level of apoptosis. Results showed an increase in mean percent apoptotic cells in subordinate follicles (18.65 +/- 0.86 over all size categories), particularly those of medium size (25.55 +/- 2.2 for 6-8 mm size follicles; P < 0.001), during the dominance phase compared to growth phase (9.25 +/- 0.95 over all sizes; P < 0.05). These results show a significant affect of the stage of estrous cycle on both oocyte competence and levels of follicular atresia.

Persistent dominant follicle alters pattern of oviductal secretory proteins from cows at estrus

The experimental objective was to compare synthesis of oviductal secretory proteins of dairy cows bearing a persistent dominant follicle (PDF) versus a fresh dominant follicle (FDF) at estrus. On Day 7 after synchronized estrus (Day 0), cows received an intravaginal progesterone device and injection of prostaglandin F2alpha (PGF2alpha). On Day 9, cows received an injection of a GnRH agonist (FDF group; n = 3) or received no injection (PDF group, n = 3). On Day 16, all cows received PGF2alpha, and progesterone devices were removed. At slaughter on Day 18 or Day 19, oviducts ipsilateral and contralateral to the dominant follicle were divided into infundibulum, ampulla, and isthmus regions. Explants from oviductal regions were cultured in minimal essential medium supplemented with [3H]leucine for 24 h. Two-dimensional fluorographs of proteins in conditioned media were analyzed by densitometry. Rate of incorporation of [3H]leucine into macromolecules was greater in the infundibulum, ampulla, and isthmus of FDF cows (p < 0.01). Overall, intensities of radiolabeled secretory protein (P) 2 and P13 were greater for FDF than for PDF. In the ampulla, P14 was more intense for FDF while P7 was more intense for PDF. Abundance of P1 in the isthmus was greater for PDF cows. Across regions, P5, P6, P8, P9, and P11 were more intense for PDF than for FDF in the ipsilateral side. In the contralateral side, P19 was more intense for PDF than for FDF, whereas P6, P8, P9, and P11 were more intense for FDF. Differences in biosynthetic activity and in secreted oviductal proteins from cows bearing a PDF may contribute to the decrease in fertility associated with a PDF.

Ovarian follicular wave synchronization and induction of ovulation in postpartum beef cows

An experiment was designed to evaluate a) the effect of a progesterone-estradiol combined treatment on ovarian follicular dynamics in postpartum beef cows, and b) ovulation and the subsequent luteal activity after short-term calf removal and GnRH agonist treatment. Multiparous Angus cows (25 to 40 d after calving) were assigned to the following treatments: untreated (Control, n = 9); short term calf removal (CR, n = 8); progesterone (CIDR, n = 9) and progesterone plus estradiol-17 beta (CIDR + E-17 beta, n = 9). Progesterone treatment (CIDR) lasted 8 d and the day of device insertion was considered as Day 0. Cows in the CIDR + E-17 beta group also received an i.m. injection of 5 mg of E-17 beta on Day 1. On Day 8, calves were removed for 48 h (CR, CIDR and CIDR + E-17 beta groups) and 6 h before the end of calf removal these cows also received an i.m. injection of 8 micrograms of Busereline (GnRH). Anestrus was confirmed in all cows by the absence of luteal tissue and progesterone concentrations below 1 ng ml-1 at the beginning of the experiment. Although mean (+/- SEM) interval from the beginning of the experiment (Day 0) to wave emergence did not differ (P > 0.05) among treatment groups (Control, 1.9 +/- 1.0, range -2 to 7 d; CR, 3.9 +/- 0.7, range 0 to 6 d; CIDR, 2.8 +/- 0.5, range 0 to 4 d and CIDR + E-17 beta, 4.1 +/- 0.2, range 3 to 5), the variability was less (P < 0.05) in the CIDR + E-17 beta group. The proportion of cows ovulating 24 to 48 h after GnRH administration tended (P = 0.08) to be higher in cows from CIDR + E-17 beta group (8/9) than in those of CR (5/8) or CIDR (6/9) groups, respectively and was associated with a higher proportion (P < 0.05) of CIDR + E-17 beta treated cows (9/9) that had a dominant follicle in the growing/early static phase at the time of GnRH treatment compared to the other GnRH treated groups (5/8, and 4/9 for CR and CIDR groups, respectively). Two CR cows ovulated 0-24 h after GnRH and only one Control cow ovulated the day before the time of GnRH administration. Cows pretreated with progesterone had longer (P < 0.05) luteal lifespan (CIDR, 14.5 +/- 0.7, CIDR + E-17 beta, 13.9 +/- 0.6 d) than those not treated with CIDR (Control, 5, CR, 4.0 +/- 0.4). We conclude that progesterone plus estradiol treatment results in tightly synchronized wave emergence and high GnRH-induced ovulation rate with normal luteal activity in postpartum beef cattle.