Endocrine milieu and developmental dynamics of ovarian cysts and persistent follicles in postpartum dairy cows

Ovarian follicular cysts and persistent follicles are follicular pathologies involved in reduced fertility of dairy cows. Two separate experiments were performed on high-yielding Holstein cows to characterize ovarian cyclicity and evaluate the developmental dynamics of follicle pathologies postpartum. In experiment 1, 58 cows were monitored by ultrasonography twice weekly from d 18±1 to 69±2 postpartum. First ovulation occurred 38±3, 27±2, 20±1, and 25±3 d postpartum in cows with 1 cycle (n=11), 2 cycles (n=21), 3 cycles (n=13), and 4 cycles (n=7), respectively. Follicular pathologies were developed in cows that were either acyclic (n=6) or had 1 or 2 cycles, but not in cows with more than 2 cycles. In experiment 2, 47 cows were monitored twice weekly from 10 d postpartum to second ovulation. Follicles ≥17 mm in diameter in 2 consecutive scans were aspirated, and concentrations of various hormones were measured. Cows were defined as cyclic (n=30; 64%) or with the potential to develop follicular pathology (n=17; 36%). Aspirated follicles (n=27) were classified into 3 main groups based on follicular growth rate, follicular diameter, and ovarian activity before and after follicular aspiration. Dominant follicles (n=4) were defined as large follicles (20 mm in diameter) with growth rate ≤1 mm/d and normal ovarian activity. Persistent follicles (n=6) had the same growth rate and diameter as the dominant follicles, but persisted at the same diameter for ≥10 d. Ovarian cysts (n=17) were defined as the largest follicular structures (19 to 32 mm in diameter), with abnormal growth rate (>1 mm/d) and abnormal ovarian activity. Single or turnover cysts did not differ in their growth parameters and were therefore combined and further classified according to follicular-fluid hormone concentrations. Estradiol-dominant cysts (n=7) were characterized by normal estradiol (284 to 659 ng/mL) and progesterone (20 to 113 ng/mL) concentrations, similar to those of the dominant follicle (554 to 993 ng/mL and 44 to 106 ng/mL, respectively). Progesterone-dominant cysts (n=5) were characterized by low estradiol (0.06 to 330 ng/mL) and high progesterone (586 to 3,288 ng/mL) concentrations. Low-steroidogenic active cysts (n=5) were characterized by low concentrations of both estradiol (23 to 61 ng/mL) and progesterone (17 to 205 ng/mL). Characterization of spontaneously forming cysts might enable definition of the formation of ovarian follicular pathologies in postpartum cows.     

Reproductive hormones associated with normal and abnormal changes in ovarian follicles in postpartum dairy cows.

Concentrations of reproductive hormones and ovarian changes were monitored every 4 days during the postpartum period in 35 dairy cows. The cows were classified as either control (22 cows) or cystic (13 cows) based on per rectum examination of the ovaries. Control cows were detected with a corpus luteum after the first postpartum ovulation while in cystic cows, ovarian follicles of at least 2.5 cm in diameter persisted in the absence of a corpus luteum for at least 14 days. The mean postpartum interval to the first follicle 1.5 to 2.0 cm in diameter was about 16 days for both groups. Ovulation was detected earlier postpartum for cows in the control group (18.4 +/- 1.7 days) than for cows in the cystic group (36.3 +/- 2.7 days). Luteinizing hormone in plasma increased during the early postpartum period (days 1 to 10) for both groups, but mean concentrations of luteinizing hormone, progesterone, and estradiol-17 beta in plasma were not different between groups then or on days -8, -4, or 0 (day of the first postpartum follicle 1.5 to 2.0 cm in diameter). During this period (days -8 to 0), estradiol-17 beta and luteinizing hormone in plasma were correlated positively, but regression coefficients differed between groups. These results suggest a partial hypothalamic and/or pituitary failure in releasing pituitary luteinizing hormone as a cause for postpartum ovarian cysts.     

Modeling of energy balance in early lactation and the effect of energy deficits in early lactation on first detected estrus postpartum in dairy cows.

The general pattern of energy balance in early lactation was modeled. For this purpose, several lactation curves were investigated. The best fitting curve was fit in a random regression model that provided predicted energy balance curves for all lactations. By use of these curves, total energy deficit per lactation, postpartum interval of return to positive energy balance, and nadir of energy balance was determined. In predicted energy balances, nadir of energy balance was present, but variation in postpartum interval to nadir was small. First lactation cows had a smaller energy deficit in early lactation than did older cows. Differences among cows in nadir and total energy deficits in early lactation were large. Both were related to the postpartum interval to first detected estrus with a larger energy deficit and a smaller nadir corresponding to a larger postpartum interval to first detected estrus. From this study, it can be concluded that large energy deficits in early lactation delay first detected estrus.     

Relationship between ovarian activity and energy status during the early postpartum period of high producing dairy cows

The effect of energy status upon ovarian activity during early lactation was assessed in 54 multiparous Holstein cows. Dry matter intake and milk yield were measured daily from parturition through 9 wk of lactation. Milk composition and body weight were measured weekly during this time. Energy balance corrected for body weight loss was calculated weekly. Blood was collected via tail vein three times weekly and plasma analyzed for progesterone and nonesterified fatty acids. Fifteen cows were anestrus for the 9 wk based on their plasma progesterone (less than 1 ng/ml). These cows were compared with two cycling groups, one group of 25 cows showing corpus luteum activity within 40 d after parturition and a second group of 14 cows showing corpus luteum activity between 40 and 60 d postpartum. Anestrus cows ate less feed, produced less milk, and lost more body weight, resulting in a more negative energy status than cycling cows. Differences in energy balance among cow groups were greatest the first 3 wk postpartum. Anestrus cows and cows showing corpus luteum activity between d 40 and 60 obtained more energy from body reserves for milk production the first 2 wk of lactation, than cows cycling prior to d 40.     

Effect of negative energy balance on the insulin-like growth factor system in pre-recruitment ovarian follicles of post partum dairy cows

Post partum negative energy balance (NEB) in dairy cattle is associated with a delayed return to ovarian cyclicity and reduced fertility. This study compared the IGF system of pre-recruitment ovarian follicles between cows in mild (n = 6) or severe (n = 6) NEB during early lactation. Ovaries were collected in the second week post partum, when circulating concentrations of IGF-I and glucose were lower (P < 0.01) in severe NEB cows. mRNA expression for IGF-II, type 1 IGF receptor (IGF-1R) and IGF-binding proteins (IGFBP)-1 to IGFBP-6 was determined by in situ hybridisation in individual follicles using radiolabelled oligonucleotide probes. Follicles were classified as very small (1-2.5 mm) or small (2.5-5 mm) and healthy or atretic. Relative mRNA concentrations were measured as optical density (OD) units using image analysis. Thecal IGF-II mRNA expression was highest in very small, healthy follicles (P < 0.05). Granulosa cell IGFBP-2 was the only component to change with EB status, with higher mRNA expression in mild compared with severe NEB cows (P < 0.05). IGFBP-1 and IGFBP-3 mRNA expression were undetectable. IGF-1R, IGFBP-4 and IGFBP-5 mRNA expression were not significantly altered by follicle size or health, but IGFBP-5 tended to increase in atretic follicles. The pattern of IGFBP-6 mRNA expression in theca paralleled that of IGF-II mRNA, with higher (P < 0.05) levels in healthy, very small follicles. In conclusion, the reduced expression of IGFBP-2 mRNA in severe NEB cows may alter the bioavailability of circulating IGF-I and locally produced IGF-II to modulate the pre-recruitment stages of follicles required to maintain normal post partum ovarian cyclicity.     

Energy balance, metabolic status, and the first postpartum ovarian follicle wave in cows administered propylene glycol

Mature Holstein cows were drenched daily with either 500 mL of water (control; n = 28) or propylene glycol (PPG; n = 28) from d 10 before parturition until d 25 postpartum. Follicular development was monitored thrice weekly by transrectal ultrasound. Blood samples were collected every 30 min from a subset of 10 cows per treatment on d −10, 2, and 25 to assess glucose and insulin response to treatments, and on d 10 postpartum, blood was collected every 10 min for 12 h to determine LH pulse profiles. Both insulin and glucose were elevated on d 2 and 25 following PPG administration, but only insulin was elevated on d −10. On d 10 postpartum, the number of LH pulses, mean LH, and pulse amplitude were not different between control and PPG cows. The proportion of first postpartum dominant follicles that became ovulatory, atretic, or cystic was not different between control and PPG cows. Despite evidence of improved metabolic status, PPG failed to increase LH pulse frequency, and failed to increase the proportion of first postpartum follicle waves resulting in ovulation. The dominant follicle of each cow was retrospectively categorized as being ovulatory (n = 17), nonovulatory high estradiol (n = 6), nonovulatory low estradiol (n = 24), or cystic (n = 8). Differences in dry matter intake and energy balance among cows in the different follicle categories were apparent as early as 3 wk before parturition. The nonovulatory low estradiol cows had lower pre- and postpartum dry matter intake and energy balance compared with ovulatory cows. The nonovulatory low estradiol cows also had postpartum metabolic hormone and metabolite profiles indicative of more severe negative energy balance.     

Inducing ovulation early postpartum influences uterine health and fertility in dairy cows

The objective of the current study was to evaluate the effect of GnRH early postpartum on induction of ovulation, uterine health, and fertility in dairy cows. Holstein cows without a corpus luteum (CL) at 17 ± 3 DIM were assigned randomly to receive i.m. GnRH (n = 245) at 17 ± 3 and 20 ± 3 DIM or remain as controls (n = 245). Ovaries were scanned by ultrasonography twice weekly totaling 4 examinations. Ovulation was characterized by the appearance of a CL ≥20 mm at any ultrasound or CL <20 mm in 2 consecutive examinations. Clinical and cytological endometritis were diagnosed at 35 DIM. Compared with control, GnRH increased ovulation up to 3.5 d after the last treatment (78.7 vs. 45.0%) and did not affect the prevalence of clinical endometritis (23.9 vs. 18.6%) or cytological endometritis (30.9 vs. 32.8%). Prevalence of clinical endometritis increased in cows that had calving problems (32.6 vs. 15.9%) and metritis (40.6 vs. 15.8%). Metritis increased prevalence of cytological endometritis (50.7 vs. 23.5%). Treatment with GnRH did not affect pregnancy per artificial insemination at 32 (37.6 vs. 38.6%) or 74 d after artificial insemination (35.0 vs. 31.5%), but reduced pregnancy loss (6.8 vs. 18.1%). No overall effect of GnRH treatment on hazard of pregnancy was observed; however, an interaction between GnRH treatment and ovulation showed that GnRH-treated cows that ovulated had increased hazard of pregnancy by 300 DIM compared with GnRH-treated and control cows that did not ovulate (hazard ratio = 2.0 and 1.3, respectively), but similar to control cows that ovulated (hazard ratio = 1.1). Gonadotropin-releasing hormone early postpartum induced ovulation without affecting uterine health, but failed to improve pregnancy per artificial insemination or time to pregnancy, although it reduced pregnancy loss.     

Association between early postpartum rumination time and peak milk yield in dairy cows

Limited information is available on the relationship between rumination time (RT) in the early postpartum period and milk production later in lactation. Therefore, the objectives of this study were to (1) investigate the association of change in RT and average RT during the immediate postpartum period with peak milk yield (PMY) in dairy cows, and (2) determine the best model based on days in milk (DIM) to evaluate this association. Cows from 33 free-flow automatic milking system farms were included in this study, where retrospective milk production and RT data were collected for 12 mo. Cows were categorized by parity number into parity 1 (P1, n = 1,538), parity 2 (P2, n = 1,354), or parity ≥3 (P3+, n = 1,770). For each cow, PMY was identified as the highest daily milk yield up to 180 DIM for P1 and 120 DIM for P2 and P3+ cows. Five change in RT variables and 5 average RT variables were created corresponding to the first 2 to 6 DIM. Change in RT variables were the slope coefficients for change in RT/d related to DIM = 1 extracted from simple linear regressions, and average RT variables were the arithmetic mean RT. Five models analyzing PMY and corresponding variables calculated over the first 2 to 6 DIM had fixed effects of average RT, change in RT, parity, average RT × parity interaction, change in RT × parity interaction, and a random intercept for farm. Peak milk yield occurred at (median) 75, 44, and 46 DIM for P1, P2, and P3+, respectively. Overall PMY was (mean ± standard deviation) 54 ± 11 kg and it increased as parity increased. A positive association was found between change in RT and PMY, and average RT and PMY for P2 and P3+ cows in all 5 models corresponding to the first 2 to 6 DIM, indicating that greater average RT and quicker increase in RT after calving are associated with greater PMY for multiparous cows. Although the model including all 6 DIM had the greatest accuracy, results indicated that rumination data collected over the first 2 DIM may also provide adequate information for the association of average RT and change in RT with PMY in P2 and P3+ cows. For each 100 min/d increase in change in RT over the first 6 DIM, PMY increased by 4.3 (95% confidence interval: 2.2–6.3) and 4.8 (95% confidence interval: 3.2–6.5) kg for P2 and P3+ cows, respectively. Peak milk yield increased by 2.3 (95% CI: 1.7–2.8) and 2.2 (95% confidence interval: 1.7–2.6) kg for each 100 min increase in average RT over the first 6 DIM for P2 and P3+ cows, respectively. No association was observed between rumination behaviors and PMY for P1 cows. Results from this study indicate that the length of time for multiparous cows to achieve a stable RT in the early postpartum period combined with average RT during the same period may be useful in predicting their overall lactation milk production.     

Natural antibodies related to energy balance in early lactation dairy cows

The objectives of this study were to determine the presence of natural antibodies (NAb) in plasma and milk of individual dairy cows and to study the relation between NAb concentrations and energy balance (EB) and dietary energy source. Cows (n = 76) were fed a mainly glucogenic, lipogenic, or a mixture of both diets (50:50 dry matter basis) from wk 3 before the expected calving date until wk 9 postpartum. Diets were isocaloric (net energy basis) and equal in intestinal digestible protein. Blood and milk were sampled weekly. Liver biopsies were taken in wk −2, 2, 4, and 6 relative to calving. Data are expressed as LSM ± SEM. The NAb titers are expressed as the ²log values of the highest dilution giving a positive reaction. The NAb concentration in plasma binding either keyhole limpet hemocyanin (KLH) or Escherichia coli lipopolysaccharide (LPS) increased with parity. The NAb concentration binding KLH was greater for cows fed the glucogenic diet (9.63 ± 0.08) compared with the lipogenic diet (9.26 ± 0.08). In milk, cows fed the glucogenic diet had smaller NAb concentrations binding KLH (3.98 ± 0.18) and LPS (2.88 ± 0.17) compared with cows fed the mixed diet (KLH: 4.93 ± 0.18; LPS: 3.70 ± 0.17). The NAb concentration in plasma had a positive relation with energy balance variables: EB, dry matter intake, milk yield, and plasma cholesterol, whereas NAb concentration in milk had a negative relation with energy balance variables: EB, dry matter intake, and plasma cholesterol. Additionally, NAb concentrations in milk had a positive relation with plasma nonesterified fatty acid concentration and milk fat and protein percentage. There was a tendency for a positive relation of NAb concentration binding LPS in plasma and somatic cell count in milk. No significant relations were detected between NAb concentrations in milk or plasma and plasma β-hydroxybutyrate concentration and liver triacyl glyceride content. In conclusion, NAb are present in both milk and plasma of dairy cows peripartum and NAb concentrations increase with parity. Furthermore, our data indicate that a negative energy balance in dairy cows in early lactation can be associated with compromised innate immune function as indicated by decreased NAb concentration in plasma.     

Improving energy supply to late gestation and early postpartum dairy cows.

Sixty-five multiparous Holstein cows were used to test the effects of feeding diets of varied ruminal carbohydrate availability during the transition period on dry matter intake, blood metabolites, and lactational performance. Cows received total mixed rations containing either cracked corn or steam-flaked corn beginning 28 d prior to expected calving date. At parturition, cows were assigned to a postpartum total mixed ration that contained either cracked corn or steam-flacked corn. Diets were fed until 63 d in milk. No treatment effects on prepartum or postpartum dry matter intake, body weight, and body condition score were observed. Cows fed steam-flaked corn had lower blood urea N concentrations during the prepartum period and lower plasma nonesterified fatty acid concentrations during the prepartum and postpartum periods. Cows fed steam-flaked corn postpartum produced 2.3 kg/d more milk than cows fed cracked corn during the first 63 d in milk. Fat corrected milk showed no treatment effect. Seven cows were used to evaluate treatment effects on ruminal fermentation and digesta kinetics. Prepartum and postpartum treatments had minimal effects on ruminal fermentation. Feeding steam-flaked corn prepartum decreased apparent fiber digestibility and ruminal NH3 N. Feeding steam-flaked corn postpartum decreased the acetate to propionate ratio. Prepartum and postpartum treatments did not affect digesta kinetics. An increase in ruminal carbohydrate availability during the postpartum period enhanced milk production, but had variable results on ruminal fermentation.     

Effects of whole cottonseed diet and recombinant bovine somatotropin on ovarian follicles in lactating dairy cows

The effects of whole cottonseed (WCS) in the diet and the administration of bovine somatotropin (bST) on ovarian follicular dynamics and plasma progesterone (P4) concentrations were examined in cows during a period of synchronized follicular growth. Lactating Holstein cows (n = 28) were randomly assigned to treatments in a 2 x 2 factorial arrangement. Diets consisted of WCS (15% of dry matter) or no WCS, and bST at a dose of 0 or 208 mg/14 d. Dietary treatments began within 24 h of calving and bST treatments began within 7 d postpartum. Cows received GnRH at 65 +/- 3 d postpartum (d 0), PGF2alpha, (d 7), a second dose of GnRH (d 9), and were inseminated 16 h later (d 10). Ovarian changes were monitored daily by ultrasonography from d 0 to 9. On d 9,93% of cows had a preovulatory follicle and 86% ovulated. For Class 2 (6 to 9 mm) follicles, a diet x bST interaction was detected, with bST stimulating Class 2 follicles in cows fed WCS, but not in cows on the control diet. Neither diet nor bST affected numbers of Class 1 (2 to 5 mm) or Class 3 (> or = 10 mm) follicles or sizes of the subordinate and dominant follicles. During the luteal phase of the cycle, lactating cows fed WCS tended to have elevated concentrations of plasma P4, whereas bST was without effect. Plasma concentrations of high-density lipoprotein cholesterol were increased in cows fed WCS. Number and diameter of corpora lutea did not differ among treatments.     

Adrenal responsiveness in pre- and postpartum dairy cows.

Adrenal responsiveness was evaluated by injecting 10 multiparous dairy cows with 200 IU adrenocorticotropin between -13 and -2 days prepartum (I) and postpartum between 24 and 40 h (II) and 21 and 24 days (III). Concentrations of glucocorticoids following injection were influenced by day of injection, temperature, and minimum percent relative humidity but not by breed, breed X injection day interaction, or age of cow. Likewise differences in regressions for adrenal response and mean response (ng/ml) for the three injections were nil. Mean concentrations at peak (45, 60, and 120 min postinjection samples) adjusted for preinjection concentrations also did not differ for the three periods of injection. Mean concentrations of glucocorticoids in plasma for daily samples between -13 and -2 days prepartum were 5.3 +/- .4 (n = 61), reached a peak of 14.8 +/- .3 ng/ml the day of calving, and remained high for 2 days postpartum. Estradiol increased through prepartum sampling from 23.3 to 339.6 +/- 94.1 pg/ml the day of calving, then declined abruptly. Progestins began to decline about -5 days prepartum from mean concentration of 4.09 +/- .62 (n = 25) and attained low concentrations (.30 +/- .06 ng/ml) 2 days postpartum. Although there was a surge of glucocorticoids at parturition, this was not associated with a modification in adrenal responsiveness or with prepartum concentrations of other steroid hormones of plasma. Adrenal potential in prepartum and postpartum dairy cows appears well maintained.     

Effects of parity on uterine involution and resumption of ovarian activities in postpartum Chinese Holstein dairy cows

Favorable uterine involution and ovarian activity are very important for the next reproductive cycle of postpartum cows. The objective of this study was to evaluate the effect of parity on uterine involution and resumption of ovarian activity in Chinese Holstein dairy cows after calving under similar postpartum nutritional conditions. Traits of the status of uterus and ovaries detected by ultrasonography, dry matter intake (DMI), milk yield, body condition score (BCS), and estradiol concentration in milk samples were analyzed for 46 Chinese Holstein dairy cows in various parities (primiparous = 18; biparous = 13; multiparous = 15). The results showed that there was no significant difference for DMI, BCS, and milk yield among different parities; all cows were considered to be under similar nutritional conditions. Days of the previous gravid uterine horn involution were significantly greater in primiparous dairy cows than in biparous and multiparous dairy cows. Days from calving to ovulation (first and second) and the number of follicular waves to first ovulation were significantly greater in primiparous cows than in multiparous cows. In summary, there was a significant negative relationship between parity and postpartum uterine involution and resumption of ovarian activity in Chinese Holstein cows under similar body conditions.     

Prepartum heat stress in dairy cows increases postpartum inflammatory responses in blood of lactating dairy cows

Uterine diseases and heat stress (HS) are major challenges for the dairy cow. Heat stress alters host immune resilience, making cows more susceptible to the development of uterine disease. Although HS increases the incidence of uterine disease, the mechanisms by which this occurs are unclear. We hypothesize that evaporative cooling (CL) to alleviate HS in prepartum cows has carry-over effects on postpartum innate immunity. Nulliparous pregnant Holstein heifers were assigned to receive either forced CL that resulted in cool conditions (shade with water soakers and fans; n = 14) or to remain under HS conditions (barn shade only; n = 16) for 60 d prepartum. Postpartum, all cows were housed in a freestall barn equipped with shade, water soakers, and fans. Respiratory rate and rectal temperature during the prepartum period were greater in HS heifers compared with CL heifers, indicative of HS. Although milk production was decreased in HS cows compared with CL cows, the incidence of uterine disease and content of total or pathogenic bacteria in vaginal mucus on d 7 or d 21 postpartum was not affected by treatment. Whole blood was collected on d 21 and subjected to in vitro stimulation with lipopolysaccharide. Lipopolysaccharide-induced accumulation of IL-1β, IL-10, and MIP-1α was greater in blood collected from HS cows compared with CL cows. Our results imply that prepartum HS during late pregnancy has carry-over effects on postpartum innate immunity, which may contribute to the increased incidence of uterine disease observed in cows exposed to prepartum HS.     

Dynamics of gonadotropin release following ovariectomy and injection of gonadotropin-releasing hormone in early postpartum dairy cows

The influence of the ovary and of injection of low doses of gonadotropin-releasing hormone on secretion and gonadotropin-releasing hormone-induced release of gonadotropins in early postpartum cows was examined in a 2 x 2 factorial design (6 cows/group). Twelve cows were ovariectomized 2 d postpartum (calving = d 0; groups 1 and 2) and 12 cows were left intact (groups 3 and 4). Groups 1 and 3 received gonadotropin-releasing hormone (5 micrograms) every 120 min for 70 h from d 6 to d 9; groups 2 and 4 received saline by the same regimen. All animals received 50 micrograms gonadotropin-releasing hormone on d 9. Mean concentrations of FSH were higher following ovariectomy compared with those of intact cows 6 to 8 d postpartum, whereas no differences in FSH were observed between cows receiving gonadotropin-releasing hormone or saline during this period. Concentrations of LH were similar in intact and ovariectomized cows on d 6 to 8 but were increased in cows receiving gonadotropin-releasing hormone compared with cows receiving saline. Ovariectomy did not alter the gonadotropin-releasing hormone-induced release of gonadotropins on d 9. Injection of gonadotropin-releasing hormone on d 6 to 8 resulted in a decreased gonadotropin-releasing hormone-induced release of gonadotropins on d 9. It was concluded that removal of ovarian influence resulted in increased secretion of FSH but did not affect gonadotropin-releasing hormone-induced release of LH and FSH during the early postpartum period.     

The effect of subclinical ketosis in early lactation on reproductive performance of postpartum dairy cows

Data generated from 796 Holstein cows enrolled in a clinical trial to investigate the health effect of a monensin controlled release capsule were analyzed to investigate the association between circulating serum β-hydroxybutyrate (BHBA) concentration in the peri-parturient period and subsequent reproductive performance. Overall, accounting for both repeated measures within cow and clustering at the herd level, non-pregnant cows after first insemination tended to have increased circulating BHBA concentrations from 3 wk before calving to 9 wk after calving relative to pregnant cows. Including the interaction between the week of sample collection and pregnancy outcome, non-pregnant cows had higher circulating BHBA concentrations in the second week after calving than cows diagnosed pregnant after first artificial insemination. Within individual weeks, cows with circulating BHBA concentrations ≥1,000 μmol/L in the first week postpartum were less likely to be diagnosed pregnant after first insemination. In the second week postpartum, the cows with circulating BHBA concentrations ≥1,400 μmol/L were significantly less likely to be pregnant after first artificial insemination. A dose response relationship was found when a comparison of the probability of pregnancy after first insemination and duration of elevated circulating ketone bodies was investigated. The probability of pregnancy was reduced by 20% in cows diagnosed subclinically ketotic in either the first or second week postpartum. Nevertheless, cows above the subclinical ketosis threshold in both the first and second week postpartum were 50% less likely to be pregnant after first insemination. Similarly, the median time to pregnancy increased in cows experiencing elevated BHBA concentrations in either (124 d) or both (130 d) the first and second week postpartum relative to cows never experiencing elevated BHBA concentrations (108 d). To further investigate this, the effect of elevated circulating BHBA was permitted to vary with time. The effect decreased with time, such that the daily probability of pregnancy increased similar to nonsubclinically ketotic cows by approximately 160 d in milk. From this analysis, both the relative circulating concentration of BHBA and the duration of elevated circulating BHBA were negatively associated with the probability of pregnancy at first service.     

Risk factors and effects of postpartum anovulation in dairy cows

The objectives were to identify risk factors for and to quantify the effect of postpartum anovulation on reproductive performance in dairy cows. Data from 2,178 Holstein cows in 6 commercial herds enrolled in a randomized clinical trial were used. Data on periparturient disease incidence, calving history, and body condition score were collected. Cows were examined at wk 5 postpartum for reproductive tract disease; cytological endometritis was defined as ≥6% polymorphonuclear cells in endometrial cytology, and purulent vaginal discharge was defined as the presence of mucopurulent or purulent vaginal discharge. Cows were followed until 300 d in milk (DIM) for reproductive performance. Serum nonesterified fatty acids (NEFA) concentration was measured once during the week before expected calving. Serum β-hydroxybutyrate, NEFA, and haptoglobin were measured at wk 1, 2, and 3 postpartum. Serum progesterone (P4) was measured at wk 3, 5, 7, and 9 postpartum. The end of the postpartum anovulation period was defined as the first sampling time at which P4 was >1 ng/mL. Statistical analyses were performed using logistic regression models and Cox proportional hazard models. The prevalence of anovulation was 72, 44, 26, and 17% at wk 3, 5, 7, and 9, respectively. Cows were classified according to their ovulatory status as having luteal function at 21 DIM (Cyc21), as having low P4 at 21 DIM but having luteal function at least once at 35 or 49 or 63 DIM (Cyc63), or being anovulatory at 63 DIM (Anov63; no samples with P4 >1 ng/mL). Factors associated with early ovulation (Cyc21) included season, parity, decreased haptoglobinemia, and decreased serum NEFA concentration before and after parturition. Risk factors for prolonged anovulation (Anov63) included cytological endometritis, increased haptoglobinemia, and greater serum NEFA concentrations before and after parturition. Cows classified as Anov63 had an increased median time to first breeding compared with Cyc63 (74.1 vs. 73.2 d). The effect of prolonged postpartum anovulation on median time to pregnancy was conditional on parity group; a detrimental effect was present in cows of parity ≥3 (129 d for Cyc21, 151 d for Cyc63, and 180 d for Anov63), but no effect was observed in cows of parity ≤2. Overall, these findings suggest that postpartum anovulation was associated with indicators of energy balance and uterine inflammation, and with detrimental effects on reproductive performance.     

The association between metabolic parameters and oocyte quality early and late postpartum in Holstein dairy cows

The objective of this was to study the association between metabolic parameters and oocyte quality in postpartum lactating dairy cows as assessed by oocyte morphology and development after fertilization and culture in vitro. Holstein-Friesian spring-calving cows were used (n = 16, parity 3.0 ± 0.36, weight at calving 611 ± 16.2 kg, previous 305-d milk yield 6,454.0 ± 276.4 kg). Bodyweight (BW) and body condition score were recorded at approximately 2 wk before expected calving date, at calving, and then weekly until the end of the experiment (approximately 80 d postpartum). Blood plasma samples were collected weekly, starting 2 wk before the expected calving date and continuing until the end of the experiment and were analyzed for nonesterified fatty acids (NEFA), β-hydroxybutyrate (BHBA), insulin, insulin-like growth factor-I, and glucose. Transvaginal oocyte recovery was carried out twice weekly on each cow for a period of approximately 12 wk starting 14 d after calving until approximately 80 d postpartum. A linear decrease in BW was observed from calving (d 0) to d 28, after which it remained stable. Body condition score decreased from 14 d precalving, reaching a nadir at approximately d 35 to 42, after which it increased to the end of the period. Nonesterified fatty acid concentrations were significantly elevated from the week before calving until d 42 postcalving, whereas BHBA concentration was significantly elevated from calving to d 49 postcalving. Insulin-like growth factor-I concentration dramatically decreased from d -14 to a nadir on d 7. A significant increase in glucose concentration occurred from d -7 to d 0, followed by a precipitous decrease to d 7. Based on the metabolic profiles (particularly NEFA and BHBA concentrations), data from d 0 to 42 postpartum (period 1) were compared with corresponding data from d 42 to 80 (period 2). Apart from body condition score, all of the physiological parameters measured (milk yield, BW, and blood metabolites) differed significantly between the 2 periods. In particular, insulin-like growth factor-I, insulin, and glucose concentrations were higher post-d 42, whereas BHBA and NEFA were lower compared with pre-d 42 postpartum. The number of oocytes recovered per session and oocyte quality grade did not differ between periods. Positive associations of follicles aspirated and insulin, BHBA, and NEFA were detected. The number of oocytes recovered was positively associated with milk yield, BW, and glucose and NEFA concentrations. The number of cleaved oocytes was positively associated with BW and NEFA concentration. In conclusion, the data do not provide evidence of an effect of lactation-induced metabolic stress on oocyte developmental competence in the postpartum dairy cow assessed in terms of morphological quality and ability to develop following in vitro fertilization.     

Effects of milk production capacity and metabolic status on HPA function in early postpartum dairy cows

Increasing milk yields in modern dairy cows cause concern that high yield may impair the cows' health and welfare, for example, via negative effects on metabolic status and hypothalamo-pituitary-adrenocortical (HPA) function. This study aims to investigate whether a high level of milk production, and the associated metabolic status, affects HPA function in dairy cows and changes their adaptive capacity. Additionally, it aims to establish whether possible effects of milk production level only show under challenging conditions. Holstein-Friesian cows, which produced on average 11,443 and 7727 kg of fat and protein-corrected milk (FPCM)/305 d in their previous lactation, were compared. During the dry period, the cows were fed to requirements or overfed. High milk yield and the concomitant large energy deficit were associated with 1) increased pituitary (re)activity, i.e., increased ACTH baseline concentrations and higher ACTH concentrations after corticotropin-releasing hormone (CRH) administration, and 2) decreased adrenocortical reactivity, i.e., lower cortisol responses after ACTH administration. Although significant, the effects of milk production level on HPA function were relatively small. Animals showed seemingly normal hormonal responses to CRH and ACTH administration. Also, cortisol baseline concentrations were unaffected. It seems, therefore, unlikely that the adaptive capacity of the high-producing cows was significantly impaired compared with their low-producing herdmates.