Ovarian follicular activity and hormonal profile during estrous cycle in cows: the development of 2 versus 3 waves

Most estrous cycles in cows consist of 2 or 3 waves of follicular activity. Waves of ovarian follicular development comprise the growth of dominant follicles some of which become ovulatory and the others are anovulatory. Ovarian follicular activity in cows during estrous cycle was studied with a special reference to follicular waves and the circulating concentrations of estradiol and progesterone. Transrectal ultrasound examination was carried out during 14 interovulatory intervals in 7 cows. Ovarian follicular activity was recorded together with assessment of serum estradiol and progesterone concentrations. Three-wave versus two-wave interovulatory intervals was observed in 71.4% of cows. The 3-wave interovulatory intervals differed from 2-wave intervals in: 1) earlier emergence of the dominant follicles, 2) longer in length, and 3) shorter interval from emergence to ovulation. There was a progressive increase in follicular size and estradiol production during growth phase of each wave. A drop in estradiol concentration was observed during the static phase of dominant anovulatory follicles. The size of the ovulatory follicle was always greater and produced higher estradiol compared with the anovulatory follicle. In conclusion, there was a predominance of 3-wave follicular activity that was associated with an increase in length of interovulatory intervals. A dominant anovulatory follicle during its static phase may initiate the emergence of a subsequent wave. Follicular size and estradiol concentration may have an important role in controlling follicular development and in determining whether an estrous cycle will have 2 or 3-waves.     

Changes in Serum Copper and Zinc Levels in Peripartum Healthy and Subclinically Hypocalcemic Dairy Cows

The objective of this study was to determine the levels of serum copper and zinc in subclinically hypocalcemic peripartum dairy cows in comparison to healthy animals. Blood samples were taken from 219 multiparous Holstein cows near parturition (from 4 weeks prepartum to 4 weeks postpartum) and 51 cows with subclinical hypocalcemia. The results showed that the serum copper concentration increased gradually at 1 week prepartum and remained high for the first 4 weeks postpartum in the healthy periparturient dairy cows. The serum zinc concentration reached a nadir at 1 week postpartum and subsequently increased gradually to baseline. The serum zinc concentration was significantly decreased (P?<?0.01) in dairy cows with subclinical hypocalcemia compared with healthy cows. There was no significant difference in the serum copper concentration between cows with subclinical hypocalcemia and healthy cows. These data demonstrate that the concentrations of copper and zinc in serum change dramatically during the peripartum period in dairy cows, which is a tremendous challenge for the body and for the maintenance of dairy cow health. The present study further suggests that a decreased serum zinc concentration could be a cause of decreased productive performance and increased susceptibility to other diseases due to immunosuppression in dairy cows with subclinical hypocalcemia. Additionally, this decreased zinc concentration may be involved in the pathogenesis of subclinical hypocalcemia.     

Effect of Chromium Supplementation on Productive and Reproductive Performances and Some Metabolic Parameters in Late Gestation and Early Lactation of Dairy Cows

The objective of this study was to determine the effect of supplemental chromium as chromium-L-methionine (Cr-Met) on productive and reproductive performances and some metabolic parameters in late gestation and early lactation of dairy cows. Sixty multiparous Holstein dairy cows according to prior lactation, parity, body mass (682?±?33?kg), and expected calving date were divided equally (30 cows/treatment) and were randomly allocated to one of the two groups. One group received basal diet without Cr (control group) and another group received Cr-Met supplement added at manufacturer's recommended level (8?mg of "Cr"/head per day) from 21?days before expected calving date until 21?days of lactation. Supplemental Cr tended to increase milk yield (P?=?0.08) while percentage of lactose and lactose yield increased (P??0.05). Percentage of cyclic cows at 36?days postpartum and estrous behavior before AI was higher in the supplemented group.     

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.     

Effect of treatment with progesterone and oestradiol when starting treatment with an intravaginal progesterone releasing insert on ovarian follicular development and hormonal concentrations in Holstein cows

Ovarian follicular development and concentrations of gonadotrophin and steroid hormones were studied in non-lactating Holstein cows following administration of progesterone (P(4)) or oestradiol benzoate (ODB) at the start of treatment with an intravaginal progesterone releasing insert (IVP(4)) in a 2 by 2 factorial experiment. Cows were treated at random stages of the oestrous cycle with an IVP(4) device (Day 0) and either no other treatment (n=8), 200 mg of P(4) IM (n=9), 2.0 mg of ODB IM (n=8) or both P(4) and ODB (n=9). Seven days later devices were removed and PGF(2alpha) was administered. Twenty-four hours later 1.0mg of ODB was administered IM. Oestrus was detected in 97.1% and ovulation in 64.7% (effect of treatment, P=0.41) of cows within 96 h of removing inserts. In the cows that ovulated, day of emergence of the ovulatory follicle was delayed (P<0.01) and more precise (P<0.05) in cows treated with ODB compared to the cows treated with P(4). Interval from wave emergence to ovulation and the diameter of the ovulatory follicle was less (P<0.05) in cows treated with ODB compared to cows treated with P(4). Combined treatment with P(4) and ODB at the time of starting treatment with an IVP(4) device did not significantly change the pattern of ovarian follicular development compared to treatment with ODB alone. Concentrations of LH and FSH in plasma were less in cows treated with ODB between Days 0 and 4 (P<0.05) while treatment with P(4) increased concentrations of FSH in plasma between Days 0 and 4 (P<0.05). When anovulatory cows were compared to ovulatory cows, diameters of follicles (P<0.001) and growth rate of follicles (P<0.01) were less in anovulatory cows between Days 7 and 9, while concentrations of FSH in plasma were greater (P<0.01), concentrations of LH similar (P>0.90) and concentrations of oestradiol were less (P=0.01) in the anovulatory cows between Days 4 and 10. Our findings support a hypothesis that ovarian follicular development following administration of P(4) or ODB at the start of treatment with an IVP(4) device differs. Anovulatory oestrus may have been associated with reduced maturity and/or later emergence of ovarian follicles.     

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.     

Heat stress and seasonal effects on reproduction in the dairy cow--a review

In dairy cows inseminated during the hot months of the year, there is a decrease in fertility. Different factors contribute to this situation; the most important are a consequence of increased temperature and humidity that result in a decreased expression of overt estrus and a reduction in appetite and dry matter intake. Heat stress reduces the degree of dominance of the selected follicle and this can be seen as reduced steroidogenic capacity of its theca and granulosa cells and a fall in blood estradiol concentrations. Plasma progesterone levels can be increased or decreased depending on whether the heat stress is acute or chronic, and on the metabolic state of the animal. These endocrine changes reduce follicular activity and alter the ovulatory mechanism, leading to a decrease in oocyte and embryo quality. The uterine environment is also modified, reducing the likelihood of embryo implantation. Appetite and dry matter intake are both reduced by heat stress thus prolonging the postpartum period of negative energy balance and increasing the calving-conception interval, particularly in high producing dairy cows. The utilization of cooling systems may have a beneficial effect on fertility but dairy cows cooled in this way are still unable to match the fertility achieved in winter. Recent studies suggest that the use of gonadotropins to induce follicular development and ovulation can decrease the severity of seasonal postpartum infertility in dairy cows.     

Physiological classification of anovulatory conditions in cattle.

Evaluation of follicular growth patterns by ultrasound combined with measurement of circulating reproductive hormones has allowed designation of three functionally critical follicular sizes during the final stages of follicular growth: emergence (-4 mm), deviation (-9 mm), and ovulation (variable from 10 to 20 mm). Classification of anovulatory conditions on the basis of these three critical points is logical and provides for rational diagnosis and treatment of the underlying physiological condition. In extreme undernutrition, there is growth of follicles to emergence but not to deviation; however, the underlying pathophysiology is not defined because of relatively few scientific investigations of this condition. Anovulatory conditions with growth of follicles to deviation but not to ovulatory size have been extensively studied. Undernutrition and/or suckling can cause this anovulatory condition. It is characterized by a greater negative feedback effect of estradiol on GnRH/LH pulses than found in normally cycling cows. Another anovulatory condition that is common in high producing lactaing dairy cows is characterized by growth of follicles to larger than ovulatory size, such as is observed in cows with follicular cysts. This condition is characterized by an insensitivity of the hypothalamus to the positive feedback effects of estradiol. Thus, these last two common anovulatory conditions appear to be primarily due to changes in the responsiveness of the hypothalamus to estradiol. Treatments that increase circulating progesterone concentrations can help in the treatment of these two conditions by potentially altering GnRH/LH pulses and allowing the final stages of follicular growth or resetting the hypothalamic responsiveness to the positive feedback effects of estradiol.     

First ovulation and ketone body status in the early postpartum period of dairy cows

The effect of ketone body status on occurrence of first ovulation during early lactation was assessed in 84 multiparous dairy cows under field conditions. Animals were equally distributed across 8 farms and were controlled by the same herd fertility monitoring program. Cows were visited twice antepartum and 6 times postpartum at weekly intervals between 5:30 and 8:30 AM. On these occasions, body condition scores and milk yields were measured, blood and milk samples were taken, cows were gynecologically examined, and parameters of reproduction were determined. The onset of first ovulation was specified by milk progesterone determination and rectal palpation. Cows starting postpartum ovarian cyclicity within or after 30 d were classified as early and late responders (ER and LR, respectively). Resumption of the estrous cycle within 30 d postpartum is considered optimal under practical conditions, and classification based on this threshold value resulted in groups of equal size and equal distribution of ER + LR cows within farms. Ketone bodies measured were beta-hydroxybutyrate in serum and acetoacetate and acetone in serum and milk. Blood serum and milk ketone body concentrations during the first 6 wk of lactation were higher in LR than in ER, whereas plasma glucose and nonesterified fatty acid and milk fat, protein and urea concentrations did not differ between groups. Maximal concentrations of ketone bodies from parturition to first ovulation were better predictors of the onset of the estrous cycle than mean or minimal concentrations over the same period. Milk acetone and serum beta-hydroxybutyrate concentrations provided the most reliable information with regard to resumption of ovarian activity of all ketone bodies.     

Reproductive responses of early postpartum dairy cattle to continuous treatment with a GnRH agonist (deslorelin) for 28 days to delay the resumption of ovulation

An experiment was conducted to investigate the potential of chronic delivery of a potent GnRH agonist (deslorelin) via subcutaneous implants to delay the resumption of ovulatory cycles in postpartum dairy cattle. Cows received either a single deslorelin implant (n=40; DES) within 7 days of calving or were untreated (n=24; CON). Blood samples were collected thrice weekly during the period the implants were in place. Plasma concentrations of progesterone (P4) and 17beta-oestradiol (E2) were measured along with selected serum metabolites. Implants were removed after 28 days and cattle monitored daily for behavioral oestrus. Serial weekly blood samples were collected to detect the occurrence of ovulation. Cows were artificially inseminated as they were detected in oestrus from 30 days after implant removal. Pregnancy status was subsequently determined by manual palpation of uterine contents at strategic intervals.Insertion of implants induced ovulation in 3/40 cows as determined by a rise in progesterone 7 days later. Deslorelin implants delayed the onset of ovulatory cycles compared with untreated herdmates (mean 43.4+/-4.2 versus 57.3+/-1.6 days postpartum; P<0.001). A noticeable delay of at least 12 days was observed between implant removal and the first animals ovulating. Mean plasma E2 concentrations during the period the implants were in place were similar for DES and CON cows that experienced a prolonged spontaneous postpartum anoestrus (low P4 >60 days), although both groups had concentrations only 20% of CON cows that had ovulated prior to 30 days postpartum.The patterns of recovery following implant removal were highly variable. A number of DES cows showed a low and transient rise in plasma progesterone around 21 days after implant removal. Some cows displayed oestrus but did not appear to form a fully functional corpus luteum with this phenomenon being more prevalent among DES cows (7 of 37 versus 1 of 21; P<0.05). Overall, significantly more DES cows were detected in oestrus without ovulating compared to CON cows. Final pregnancy rates did not differ between DES and CON groups. The mean time to conception for DES cows was longer (21.2+/-5.6 versus 41.1+/-7.4 days, CON versus DES; P<0.01). This difference was not present if the time from first ovulation to conception was compared (50.5+/-5.3 versus 43.5+/-9.3 days, CON versus DES; P>0.05). Deslorelin implants provided a reliable method of inducing anoestrus when treatment was initiated prior to 3 days postpartum. A variable pattern of recovery was observed which delayed conception but did not ultimately reduce the final proportion pregnant at the completion of mating. The study demonstrates the potential of GnRH agonists to control postpartum reproductive function to manipulate the fertility of dairy cows.     

Effects of bull exposure on postpartum ovarian activity of dairy cows

The effects of bull exposure on postpartum reproduction have been previously studied in beef, but not in dairy cattle. The objective of this experiment was to investigate effects of bull exposure on postpartum reproductive characteristics during early lactation in high-producing Holstein dairy cattle. Forty-five multiparous dairy cows (9764 +/- 140 kg milk/lactation) were randomly grouped at the time of calving. Treatment 1 (NBE) was never exposed to the bull, treatment 2 (2 x BE) experienced fenceline contact with a mature Holstein bull twice daily during routine detection of oestrus, and treatment 3 (CBE) was in continuous proximity to the bull. All cows were observed for oestrous behaviour twice daily for 1/2 h following milking. Blood samples were collected every other day for progesterone (P4) assay. Postpartum ovarian reactivation, indicated by the occurrence of the first sustained rise in P4, was later (P = 0.02) during the postpartum period in both bull-exposed (2 x BE, CBE) treatments compared to the NBE treatment. Time postpartum until completion of the first ovarian cycle tended (P = 0.08) to be shorter in NBE cows compared to bull-exposed cows. Peak P4 concentrations were higher (P = 0.05) in NBE cows compared to bull-exposed cows prior to the second postpartum ovulation. Results indicate an extended period to ovarian reactivation in dairy cattle exposed to a bull, but bull exposure had no effect on long-term reproductive performance of exposed cows.     

Effect of peripartum dietary energy supplementation of dairy cows on metabolites, liver function and reproductive variables

Multiparous Holstein cows (n=58) were used to study the effects of peripartum dietary supplementation on metabolic status, liver function and reproduction variables. Diets for cows were as follows: (a) no supplementation (CTL), (b) prilled fatty acids as 1.9% of DM (PrFA), (c) calcium salts of long chain n-6 fatty acids as 2.24% of DM (CaLFA) or (d) daily topdressing with 769 g of 65% propylene glycol (PGLY). Supplements were fed during the last 21 days before expected calving except for PGLY that continued until 21 days after parturition. Ovarian activity was monitored by transrectal ultrasonography and days to first ovulation were recorded. Liver biopsies were obtained on day 8 and 21 postpartum and analyzed for triglyceride content and mRNA expression of pyruvate carboxylase, cytosolic phosphoenolpyruvate carboxykinase, carnitine palmytoyltransferase 1A, and peroxisome proliferator-activated receptor-alpha. At 71 days following parturition, stage of ovarian cycles was synchronized and at day15 of the cycle oxytocin was injected i.v., blood samples were obtained at frequent intervals, and analyzed for 13,14 dihydro, 15-keto PGF(2alpha) (PGFM). Milk production and milk components were not different among treatment groups. Cows in PGLY gained body condition score (BCS) prepartum and net energy balance prepartum tended to be greater, but was not different postpartum from other groups. PGLY supplementation increased plasma insulin concentration prepartum, but not during the postpartum period. No significant differences were observed in plasma concentrations of glucose, NEFA, and insulin-like growth factor or hepatic triglyceride content, but all supplements tended to decrease beta hydroxybutyrate postpartum compared to CTL cows. Abundance of mRNA of gluconeogenic and lipid oxidation genes was not different among treatment groups. Days to first ovulation and uterine PGF(2alpha) production in response to an oxytocin treatment were not significantly different among treatment groups. Peripartum supplementation did not result in the substantial improvement of metabolic profile in early lactation nor significantly affect days to first ovulation and PGFM response to an oxytocin treatment.     

Effect of prepartum diet on postpartum ovarian activity in Holstein cows in a pasture-based dairy system

The hypothesis was that supplementation during the late prepartum period will differentially affect reproductive and productive variables according to parity. Primiparous (n=22) and multiparous (n=22) pregnant autumn calving Holstein cows were stratified in two groups according to parity (primiparous or multiparous) and within each group were randomly assigned to two treatments: (a) low supplemented (LS) or (b) high supplemented (HS) prepartum diet. The LS group was offered 5.2 kg/cow/day (DM basis) of wheat silage, and the HS group 4.7 kg cow/day (DM basis)/of corn silage and 3.6 kg (DM basis) of wheat bran+12 g of urea. Both groups grazed on natural pastures. After calving, all cows received the same diet. The experimental period was from 3 weeks before calving to 7 weeks postpartum (PP); body condition score (BCS) and blood samples for hormonal analyses were obtained weekly and ovarian ultrasonography was conducted three times per week. The loss in BCS around calving was less pronounced in HS cows, but only multiparous supplemented cows maintained BCS throughout the study. Non-esterified fatty acids (NEFA) increased during the prepartum period in the LS but not in the HS cows, with peak values occurring on day 14 PP in all groups. During the remainder of the experiment NEFA was greater in LS than in HS cows. Prepartum treatment did not affect the proportion of cows that had ovulations from the first dominant follicle postpartum, but decreased the interval to first ovulation in multiparous cows (22.9 compared with 38.2 days; P<0.05). This was associated with greater plasma IGF-I concentrations at the time the dominant follicle of the first follicular wave reached its maximum diameter (8.0 compared with 3.6 nmol/L; P<0.05). However, prepartum treatment had no effect on onset of ovarian activity in primiparous cows. Supplementation had no effect on milk production or milk protein percentage but increased milk fat percentage. We conclude that feeding a high-supplemented prepartum diet to multiparous cows allowed them to maintain BCS around calving, and this was associated with greater concentrations of IGF-I and an earlier onset of estrous cycles after calving.     

Effect of Organic Selenium Supplementation on Selenium Status,Oxidative Stress,and Antioxidant Status in Selenium-Adequate Dairy Cows During the Periparturient Period

The periparturient period represents a stressful time for dairy cows as they transition from late gestation to early lactation. Oxidation stress occurs during this period owing to the increased metabolic activity. Antioxidants supplementation slightly above the suggested requirements may be beneficial in relieving this kind of stress. The objective of this study was to determine whether supplementing selenium (Se) yeast to diets with adequate Se concentrations affects Se status, oxidative stress, and antioxidant status in dairy cows during the periparturient period. Twenty multiparous Holstein cows were randomly divided into two groups with ten replicates in each group. During the last 4 weeks before calving, cows were fed Se-yeast at 0 (control) or 0.3 mg Se/kg dry matter (Se-yeast supplementation), in addition to Na selenite at 0.3 mg Se/kg dry matter in their rations. The concentrations of Se, reactive oxygen species (ROS), hydrogen peroxide (H₂O₂), hydroxyl radical, malonaldehyde (MDA), α-tocopherol and glutathione (GSH), the activities of glutathione peroxidase (GSH-Px), superoxide dismutase (SOD) and catalase (CAT), and the total antioxidant capacity (T-AOC) in plasma or erythrocyte of dairy cows were measured at 21 and 7 days prepartum, and at 7 and 21 days postpartum. Cows fed Se-yeast supplement during the last 4 weeks of gestation had higher plasma Se and lower MDA concentrations at 7 days prepartum, and at 7 and 21 days postpartum, and had higher whole blood Se and lower plasma ROS and H₂O₂ concentrations at 7 and 21 days postpartum compared with control cows. Se-yeast supplementation increased plasma and erythrocyte GSH-Px activities and erythrocyte GSH concentration at 7 days postpartum as compared to Se-adequate control cows. Compared with control cows, the enhanced SOD and CAT activities, increased α-tocopherol and GSH concentrations, and improved T-AOC in plasma at 7 and 21 days postpartum in Se-yeast-supplemented cows were also observed in this study. The results indicate that feeding Se-adequate cows a Se-yeast supplement during late gestation increases plasma Se status, improves antioxidant function, and relieves effectively oxidative stress occurred in early lactation.     

Ovarian follicular and luteal dynamics in wapiti during seasonal transitions

Transitions from the anovulatory to the ovulatory season (n=20) and ovulatory to anovulatory season (n=11), were monitored daily by transrectal ultrasonography in wapiti. In 17 of 20 observations, the first interovulatory interval (IOI) was short (9.1+/-0.3 days; mean+/-S.E.M.) compared with later in the ovulatory season (21.3+/-0.1) and the last IOI (21.2+/-0.6 days). With one exception, the short IOI were composed of only one wave of follicular development. Subsequent IOI were composed of two or three waves. Maximum diameters of the first two ovulatory follicles were similar (11.3+/-0.4 mm versus 11.3+/-0.2 mm), but both were larger (P<0.05) than the last two ovulatory follicles of the ovulatory season (10.3+/-0.3 and 10.1+/-0.4 mm). Multiple ovulations occurred in three hinds at the first ovulation of the season and in one hind at the second ovulation, but were not at any other time. Day-to-day profiles of CL diameter and plasma progesterone concentration were smaller (P<0.05) for short versus long IOI. Maximum diameter (12.8+/-0.6 mm versus 12.5+/-0.6 mm) and the diameter profile of the last CL of the season were not different from that of the previous CL. In summary, transition to regular ovulation occurred over a 3-week interval and was preceded by one short IOI (9 days). Multiple ovulations were detected only at the onset of the ovulatory season. The characteristics of the last IOI of the ovulatory season were similar to those reported during the rut. The wave pattern of follicle development was maintained throughout both fall and winter transition periods and follicular wave emergence was preceded by a surge in serum FSH concentrations. Transition to anovulation occurred over a 3-month interval and was marked by a failure of the dominant follicle to ovulate after a typical luteal phase.     

Folliculogenesis during the transitional period and early ovulatory season in mares

Individual follicles were monitored by ultrasonography in 15 mares during the transitional period preceding the first ovulation of the year and in 9 mares during the first interovulatory interval. During the transitional period, 7 mares developed 1-3 anovulatory follicular waves characterized by a dominant follicle (maximum diameter greater than or equal to 38 mm) that had growing, static, and regressing phases. The emergence of a subsequent wave (anovulatory or ovulatory) did not occur until the dominant follicle of the previous wave was in the static phase. After the emergence of the subsequent wave, the previous dominant follicle regressed. The mean (+/- s.d.) length of the interval between successive waves was 10.8 +/- 2.2 days. Before the emergence of waves (identified by a dominant follicle), follicular activity seemed erratic and follicles did not reach greater than 35 mm. During the interovulatory interval, 6 mares developed 2 waves (an anovulatory wave and a subsequent ovulatory wave) and 3 mares developed only 1 detected wave (the ovulatory wave). The ovulatory follicle at the end of the transitional period reached 20 mm earlier (Day - 15), grew slower (2.6 +/- 0.1 mm/day; mean +/- s.e.m.) but reached a larger diameter on Day - 1 (50.5 +/- 1.1 mm) than for the ovulatory follicle at the end of the interovulatory interval (Day - 10, 3.6 +/- 0.2 mm/day, 44.4 +/- 1.0 mm, respectively; P less than 0.05 for each end point). The interval from cessation of growth of the largest subordinate follicle to the occurrence of ovulation was longer (P less than 0.05) for end of the transitional period (9.5 +/- 0.7 days) than for the end of the interovulatory interval (6.8 +/- 0.6 days). Results demonstrated the occurrence of rhythmic follicular waves during some transitional periods and the occurrence of 2 waves during some of the first oestrous cycles of the year.     

Number of oocytes obtained from cows by OPU in early, but not late lactation increased with plasma insulin and estradiol concentrations and expression of mRNA of the FSH receptor in granulosa cells

The effects of lactation stage and hormonal profile on the quality and quantity of oocytes and the gonadotrophic sensitivity of granulosa cells (GC) from small antral follicles obtained by sequential aspirations from ovaries of high producing dairy cows were examined. Cows in late lactation (263(+/- 60) days postpartum) and 98(+/- 16) days pregnant in positive energy balance (EB) showed no significant changes in plasma concentrations of estradiol, progesterone, insulin, IGF1 or expression of mRNA of the FSH receptor in GC from small antral follicles during the 49 days experimental period. There were no changes in the number and quality of oocytes obtained from each aspiration. In cows in early lactation (72.8 +/- 6 days postpartum), plasma insulin concentrations increased and were positively correlated with plasma estradiol concentration. Due to the sequential aspirations progesterone blood concentrations were low in early lactation cows. Expression of mRNA of the FSH receptor increased in GC from small antral follicles of early lactation cows together with the number of oocytes obtained with aspiration sessions. No differences were found in morphological quality or function between oocytes obtained from small antral follicles from cows in early or late lactation. In early, but not late lactation, the number of oocytes was correlated with both insulin and E2 plasma concentrations. Improved EB and sensitivity of GC to FSH may be involved in oocyte recruitment in early lactation.     

Associations between the manipulation of patterns of follicular development and fertility in cattle

The wave-like patterns of ovarian follicular development in cattle can be manipulated by shortening the luteal phase with prostaglandin F2alpha (PGF), lengthening the period of follicle dominance with progesterone or curtailing follicle development with GnRH or oestradiol as 17beta, benzoate or cypionate. These hormones can also be used to synchronise ovulation allowing timed inseminations without detected oestrus. Progesterone, PGF, GnRH and oestradiol benzoate have each been used to increase conception rates in some situations, but their use has reduced them in others. For example, inseminations made within 96 h of a single injection of PGF administered during the luteal phase were associated with increased conception rates in dairy cows whereas double injection protocols reduced conception rates. The three forms of oestradiol and GnRH have greater effects on follicular development following divergence and dominance than following wave emergence. This can mean that follicles of differing maturity will be present about 7 days later and can result in varied intervals to the onset of oestrus following a PGF injection. The consequent variation in ovulation time can be reduced by injecting GnRH or an oestradiol during pro-oestrus. This means that some less mature follicles will ovulate, forming corpus luteum (CL) associated with a slower rise in plasma progesterone and lower mid-luteal concentrations. The lower conception rates recorded with single timed inseminations with synchronised ovulations have been associated with increased prevalences of short cycles in lactating dairy cows (with GnRH), with long luteal phases in cows and heifers (with oestradiol benzoate) and with embryo loss following positive pregnancy diagnosis (as with Ovsynch in lactating Holstein cows). Extensive Canadian studies have demonstrated that these same hormones can be successfully used without these limitations and reliably obtaining conception rates over 50% and up to 70% in beef cattle that have been supplemented with a progestin during the period of ovarian follicle synchronisation. The inherently lower fertility of Holstein cows during early lactation may be contributing to the reduced effectiveness of hormonal treatments for synchronised follicle development and ovulation. The role of reduced dose rates of GnRH in compromising this effectiveness needs to be determined if the potential of these treatments realised with beef cattle is to be achieved with lactating Holstein cows.     

Effects of dietary supplementation of pioglitazone on metabolism,milk yield,and reproductive performance in transition dairy cows

The objective of this study was to investigate the effect of dietary supplementation of pioglitazone (PGT), a specific ligand for PPARγ, on metabolic dynamics, milk production, and reproductive performance of transition dairy cows. Eighty multiparous Holstein cows in their second or more lactations were blocked by the calving date and parity and assigned randomly to four dietary groups (n = 20 cow/treatment) including control (no PGT−/−), supplemented with PGT (6-mg PGT/kg body weight) from Day −14 to +21 relative to parturition (PGT+/+) or only during prepartum (PGT+/−) or postpartum periods (PGT−/+). Postpartum body condition score and body weight loss decreased (P < 0.05) in all PGT-supplemented groups. Milk yield was not affected by PGT supplementation (P > 0.05). Percentage of milk fat decreased (P < 0.05) in all PGT-treated groups; however, milk fat yield was lower (P < 0.05) in PGT (+/+) and PGT (+/−) groups compared with PGT (−/−). Peripartum (Day −7 to +7) concentrations of plasma nonesterified fatty acids and β-Hydroxybutyrate decreased in PGT (+/+) but not in the PGT (−/−) group (P < 0.05). During the postpartum period, PGT reduced (P > 0.05) plasma concentrations of nonesterified fatty acids in all PGT-treated groups but did not affect β-Hydroxybutyrate level. Plasma concentrations of triglycerides decreased in all PGT-supplemented groups. Supplementation of PGT increased the peripartum concentrations of plasma glucose in PGT (+/+) and PGT (+/−) groups compared with control. Plasma concentrations of insulin-like growth factor 1 were higher in PGT (+/+) compared with the control group during both the peripartum and postpartum periods. Plasma concentrations of growth hormone and insulin were not affected by PGT treatment (P > 0.05). Mean days to ovulation were lower in PGT (+/+) and PGT (-/+), and the proportion of cows ovulating by Day 14 postpartum was higher in PGT (+/+) compared with control. Days open were shorter in PGT (+/+), PGT (+/−), and PGT (−/+) groups compared with control. However, the proportion of pregnant cows at 120 days in milk were higher in all PGT-supplemented groups. The results showed positive effects of dietary supplementation of PGT, especially supplementation during both the prepartum and postpartum periods, on metabolic dynamics, ovarian function, and reproductive performance in transition dairy cows.     

Postpartum acyclicity in suckled beef cows: a review

Prolonged postpartum acyclicity in suckled beef cows is a source of economic loss to beef cattle producers. Duration of postpartum acyclicity is influenced by suckling status, nutritional status, calving season, age, and several other factors. Although uterine involution begins and ovarian follicular waves resume soon after parturition, dominant follicles of these waves fail to ovulate, due to a failure to undergo terminal maturation. As a result, postpartum anovulatory dominant follicles are smaller than the ovulatory follicles in cyclic cows. Failure of postpartum dominant follicles to undergo terminal maturation is due to absence of appropriate LH pulses, a prerequisite for follicular terminal maturation prior to ovulation. Absence of LH pulses early post partum is primarily due to depletion of anterior pituitary LH stores, although GnRH pulses are also absent during this period due to suckling. Following replenishment of LH stores between Days 15 and 30 post partum, absence of LH pulses is due to continued sensitivity of the hypothalamic GnRH pulse-generator to the negative feedback effect of ovarian estradiol-17beta, which results in absence of GnRH pulses. This negative feedback effect of estradiol-17beta is modulated by suckling which stimulates release of endogenous opioid peptides from the hypothalamus. As the postpartum interval increases, sensitivity of the GnRH pulse-generator to the negative feedback effect of ovarian estradiol-17beta decreases. This is followed by an increasing frequency of GnRH discharges and LH pulses, terminal follicular maturation, ovulation, and continued cyclicity. The first ovulation post partum is usually followed by a short cycle due to premature luteolysis because of premature release of PGF2alpha from the uterine endometrium, which is possibly intensified by the suckling-induced oxytocin release from the posterior pituitary. A model for the postpartum ovulatory acyclicity and for the resumption of cyclicity is presented.