Uterine contractions and fertility following clitoral massage of dairy cattle in estrus

Lactating and nonlactating Holstein cows received 30 s of gentle clitoral massage to determine its effect on uterine contractility and oxytocin concentrations in blood. Clitoral stimulation caused an immediate single uterine contraction, and this could be repeated at 2.5-min intervals. Oxytocin concentrations did not change during intensive blood sampling following clitoral massage. Thus, the uterine response is interpreted as neurally mediated. Eighteen full-time inseminators were allotted to two groups, balanced so that each day half were inseminating control and half treated animals (5 s of clitoral massage following insemination). The 56-day nonreturns for 2090 controls were 74.3% versus 74.0% for 2049 animals receiving clitoral massage. Heifers were more fertile than cows (81.9% versus 70.6% nonreturns), but there was no indication that clitoral massage altered the nonreturn rate in either age group. Also, the time of day animals were inseminated did not affect nonreturn rate.     

Effect of progesterone on the expression of estrus at the first postpartum ovulation in dairy cattle.

Fifty-two lactating Holstein cows were randomly assigned to receive either a progesterone-releasing (2 g of progesterone) or a control-releasing intravaginal device (0 g of progesterone). Intravaginal devices were inserted on d 10 and removed on d 15 postpartum. Daily blood samples were collected from d 10 to 90 postpartum for subsequent determination of progesterone concentrations. Observations for estrus were conducted three times daily in a dirt paddock containing a testosterone-treated cow. Serum concentrations of progesterone in the progesterone-releasing intravaginal device group were elevated on d 11, 12, 13, 14, and 15 compared with those of the control group. The days to first post-partum ovulation were similar between the treated and control groups, respectively (30.6 vs. 30.5 d). Also similar was the proportion of cows expressing estrus at first, second, and third postpartum ovulations (9/27 vs. 3/24, 14/23 vs. 15/21, and 14/21 vs. 9/15, respectively), length of the first postpartum estrous cycle (17.9 vs. 18.3 d), and peak serum concentrations of progesterone during the first estrous cycle (3.5 vs. 2.9 ng/ml). These data indicate that administration of progesterone early postpartum did not increase the proportion of cows expressing estrus at the first ovulation.     

Effects of progesterone intravaginal devices on synchronization of estrus in postpartum dairy cows

Effects of two intravaginal treatments of progesterone on the synchronization of behavioral estrus were compared in three groups of lactating dairy cows at 7 to 8 wk postpartum. Group 1 had progesterone-releasing intravaginal devices with attached estradiol benzoate capsules inserted for 12 d. Groups 2 and 3 had controlled internal drug release devices, containing progesterone alone, inserted for 9 or 12 d. Behavioral estrus was detected as early as 24, 32, and 36 h after removal of the devices in groups 1, 2, and 3, respectively. Estrus was better synchronized and the proportion of cows showing estrus after device removal was greater in group 1 than in groups 2 and 3. After removal of devices, mean milk progesterone of all cows that did not show estrus was higher than that of cows that showed estrus. In groups 1, 2, and 3, 1 of 7, 7 of 12, and 4 of 12 cows not showing estrus had high milk progesterone after removal of the devices, indicating the presence of functional corpora lutea. In cows not displaying estrus milk progesterone concentrations decreased, indicating these cows were cyclic, although behavioral estrus was absent.     

Intravaginal progesterone insert to synchronize return to estrus of previously inseminated dairy cows

An intravaginal progesterone insert (CIDR insert; 1.38 g of progesterone) was evaluated for synchronization of returns to estrus (SR), conception rate (CR), and pregnancy rate (PR) in dairy cows previously artificially inseminated (AI). Healthy, nonpregnant, lactating Holstein cows, > or = 40 and < or = 150 d postpartum at eight commercial farms were used. Cows detected in estrus and receiving AI 2, 3, or 4 d after one injection of PGF2alpha (25 mg) were assigned as either controls (n = 945), or to receive a CIDR insert (n = 948) for 7 d (14 to 21 +/- 1 d after AI). Cows were observed for returns to estrus from 18 to 26 +/- 1 d after initial AI (resynchrony period) and were reinseminated if in estrus. Vaginal mucus on CIDR inserts (97.3% retention) at removal was scored: 1 = no mucus; 2 = clear; 3 = cloudy; 4 = yellow; and 5 = red or brown. Percentage of cows in estrus (SR) during the 3 d after CIDR insert removal was contrasted to the highest 3-d cumulative percentage in estrus for controls. Cows conceiving to initial AI were omitted in calculations of SR, CR, and PR during resynchrony. Mucous scores of 3 or 4 (mild irritation) were observed in 65% of cows and a score of 5 (more severe irritation) was observed in 2%; otherwise, health was unaffected. The PR to initial AI was lower for cows subsequently receiving CIDR inserts than for controls (32.7 vs. 36.7%). The CIDR insert increased SR (34.1 vs. 19.3% in 3 d) and overall estrus detection (43% in 4 d vs. 36% in 9 d) compared with controls. For the 9-d resynchrony period, CR and PR for CIDR-treated (26.7, 12.2%) and control (30.9, 11.1%) cows did not differ significantly. The CIDR inserts improved synchrony of returns to estrus, slightly reduced PR to initial AI, but did not affect CR or PR to AI during the resynchrony period.     

Effectiveness of rump-mounted devices and androgenized females for detection of estrus in dairy cattle

Detection of estrus was evaluated in 1124 estrous cycles for the effectiveness of rump-mounted devices and androgenized females equipped with chin-ball markers. Estrous number, location, type of detection method (compared with visual observation of estrus), and milk progesterone influenced standing behavior. Rates of disagreement with visual observation of estrus were 13.2, 17.0, and 18.5% for Kamar, Hot Flash, and the two devices used simultaneously. Frequency of observed standing behavior was greater with fourth and subsequent estrous periods. Percentage of high milk progesterone during suspected estrus for cows inseminated was 3.8% for controls, 11.0% for Kamar cattle, 18.5% for Hot Flash cattle, and 12.6% when both devices were used. Androgenized cattle equipped with chin-ball markers marked 47% of the cattle observed in estrus but no cows with high milk progesterone. Combination of rump-mounted devices and androgenized females increased the percentage of estrous detection by 1.3 to 6.2% compared with device or androgenized female used alone. Loss rates of rump-mounted devices exceeded 40%. High milk progesterone at estrus was associated with lower fertility.     

Dexamethasone influences endocrine and ovarian function in dairy cattle

Multiparous nonlactating Holstein cows were used to determine the effect of dexamethasone on ovarian follicular development and plasma hormone concentrations. Animals were randomly divided into two groups, control (C; n = 5) and treatment (T; n = 6), but managed as one group. Both groups were synchronized with two injections of PGF2alpha (25 mg i.m.) 11 d apart. One day after ovulation (d 0) the T group received a daily injection of dexamethasone (44 microg/kg of body weight; i.m.) until the first dominant follicle stopped growing or up to d 12 postovulation. The C group received vehicle injections. Blood samples were collected daily from all cows. Concentrations of LH and FSH did not differ between the C and T cows, whereas progesterone concentrations were lower in T than in C cows from d 4 onward. Treatment x day interaction influenced plasma insulin concentrations such that T cows had insulin concentrations 2.9- to 6.0-fold those of C cows between d 2 and 9. Dexamethasone decreased IGF-I and -II concentrations from d 5 onward. Concentrations of plasma leptin and the various IGF binding proteins were not affected by dexamethasone. Total number of follicles (> or = 5 mm) and plasma estradiol concentrations were less in T than in C cows on d 0, 1, and 4. The growth rate of the dominant follicles and maximum diameter of the dominant and subordinate follicles were not affected by dexamethasone. The diameter of the CL was 21 to 39% larger in T than in C cows between d 6 and 10. Treatment x day interaction influenced plasma cholesterol concentrations such that cholesterol levels decreased 46.8% in T cows and 19.5% in C cows between d 0 and 10. Plasma glucose concentrations were greater in T than in C cows between d 1 and 10. In summary, dexamethasone had significant effects on metabolism without a major impact on growth of the first-wave dominant follicle. Dexamethasone-induced suppression of luteal function was associated with decreased plasma IGF-I and -II concentrations.     

Evaluation of tetracycline in milk following extra-label administration of topical tetracycline for digital dermatitis in dairy cattle

Digital dermatitis (DD) is a painful infectious foot lesion commonly treated topically with extra-label tetracycline. Our objectives were to determine the concentrations of tetracycline in milk and plasma and to calculate a withdrawal interval following topical application at various doses. Another objective was to evaluate agreement between tests for measuring tetracycline in milk. A randomized block trial was conducted on 2 farms, where 50 cows with active DD lesions on 2 feet were allocated to 1 of 5 treatment groups (n = 10 cows per group). Treatment groups consisted of topical applications of tetracycline hydrochloride, in a paste or as a powdered form under a bandage, at 3 different dosing levels (2, 5, and 25 g) on each of the 2 affected feet. Following enrollment and treatment, samples were collected from milk, teat skin, and blood every 8 to 24 h for up to 7 d postdosing. Concentrations of tetracycline were measured by liquid chromatography-mass spectrometry and milk samples were further tested using the Charm ROSA TET test (Charm Sciences Inc., Lawrence, MA). Tetracycline was present in milk, plasma, and teat skin from all treatment groups. Tetracycline concentrations varied depending on time of sampling, method of application, and dosing level. At 8 h post-treatment, 11% of cows had tetracycline present in milk higher than 100 ng/mL (ppb) but none higher than 300 ng/mL. The 25-g treatment group had the longest estimated withdrawal interval, the highest observed concentrations (210–244 ng/mL) of tetracycline present in milk, and the longest observed consecutive period of tetracycline presence (from 8 to 72 h) among all treatment groups. Compared with liquid chromatography-mass spectrometry, the Charm test had a sensitivity of 77 and 100% for measuring tetracycline in milk at ≥30 and ≥100 ng/mL, respectively. Post-treatment samples of the teat skin were taken from 15 cows on 6 occasions, and every cow had tetracycline present in at least 1 of those 6 samples. This confirms an association between topical DD treatment with tetracycline and contamination of the teat. A total of 22% of blood samples had detectable tetracycline, and the majority (63%) occurred at 8 h post-treatment. At 100 ng/mL, the estimated cow-level milk withdrawal interval ranged from 0 to 70 h. At 300 ng/mL, the estimated cow-level withdrawal interval ranged from 0 to 34 h, and was 0 h at the bulk tank level. We recommend that conservative measures be adopted after extra-label use of topical tetracycline for DD treatment, including using a low dose and strategic post-treatment testing for tetracycline-class drugs in milk.     

Postpartum ovarian follicular dynamics and estrous activity in lactating dairy cows

The objectives of this study were to characterize early postpartum follicular dynamics in dairy cows in relation to their estrual activity and subsequent reproductive performance using 50 (26 primiparous and 24 multiparous) lactating Holstein cows. Ovaries and uterine horns of postpartum lactating cows were examined by ultrasonography 3 times weekly and continued until first services occurred after a 45-d voluntary waiting period. No differences were detected in fertility between primiparous and multiparous cows. In 40 of 50 cows, first postpartum ovulation was observed within 4 follicular waves, and the follicular wave patterns and ovarian cycles in most cows returned to normal as in cattle having normal estrous cycles after the second postpartum ovulation. Cows with the longest intervals from calving to first ovulation produced the most milk and also had prolonged intervals to first estrous activity. Differences in follicular dynamics before first ovulation altered intervals to first estrus, first service, and uterine involution, but these differences did not affect pregnancy rate, number of services, and days open. First postpartum insemination after 3 follicular waves tended to have greater pregnancy rates than those after 2 follicular waves. First inseminations at first estrus could produce greater pregnancy rates than those at subsequent periods of estrus.     

Combined use of Ovsynch and progesterone supplementation after artificial insemination in dairy cattle

The objective of this study was to evaluate the effects of different Ovsynch protocols combined with progesterone (P4) supplementation after artificial insemination (AI) of Holstein-Friesian cows. Cows were randomly synchronized at 52 to 63 d after parturition with either the classical Ovsynch protocol (GnRH on d 0, PGF(2α) on d 7, GnRH 48 h after PGF(2α)) or with a modified Ovsynch protocol (second GnRH 60 h after PGF(2α)). On d 4 after timed AI (TAI), the cows were blocked by parity and randomly divided into 2 groups. Half of the cows were supplemented with P4 (P4+) by applying a P4-releasing intravaginal device intravaginally for 14 d, whereas the other half remained untreated (P4-). In 50% of randomly chosen cows, plasma P4 was measured on d 4, 5, and 18 after TAI. Sonographic pregnancy diagnosis was performed on d 33 after TAI in a total of 398 cows. Health status and body condition score (BCS) of all cows were examined at several stages of the study. Cows in the modified Ovsynch protocol tended to have higher P4 values on d 4 after TAI than cows in the classical Ovsynch protocol (2.1 ± 0.2 vs. 1.6 ± 0.2 ng/mL), but no difference in pregnancy per AI (P/AI) was observed between the 2 Ovsynch protocols (38.4% vs. 44.1%). Independent of the Ovsynch protocols, P4+ cows tended to have higher P/AI compared with P4- cows (44.4% vs. 38.1%). The retention of fetal membranes and BCS at the time of insemination affected P/AI. Moreover, an interaction between BCS at the time of insemination and P4 supplementation was apparent; that is, the difference in P/AI between P4+ and P4- cows was significant in cows with BCS ≥3.25. Progesterone-supplemented cows showed higher P4 values on d 5 (4.9 ± 0.2 vs. 2.6 ± 0.2) and d 18 (7.8 ± 0.2 vs. 6.3 ± 0.2) after TAI, respectively. In conclusion, the elongation of the time interval between the injections of PGF(2α) and the second GnRH from 48 to 60 h had no effect on P/AI. Progesterone supplementation after insemination improved the P/AI of the Ovsynch protocols, but this effect was more apparent in cows with BCS ≥3.25.     

Detection of estrus in dairy cows by electrical measurements of vaginal mucus and by milk progesterone.

Electrical resistance (ohms) of mucus were analyzed in 20 postpartum Holstein cows by use of a probe inserted into the anterior vagina every other day for 30 days. Composite milk samples were taken on the same day, and progesterone was determined by radioimmunoassay. Cows were observed twice daily for standing estrus and reproductive organs palpated weekly per rectum (rectal palpation). Fifteen cows which were cycling showed increasing progesterone 6 to 7 days after the onset of estrus with values of 8.1 to 10.0 ng progesterone/ml milk on days 10 to 17. Concentrations had declined rapidly 2 days before onset of the next estrus. Progesterone in milk was affected by cow and by day of the cycle. Electrical resistance followed a similar cyclical pattern, but variability was large and only cows differed. The correlation between milk progesterone and mucus resistance was .22. Progesterone concentrations for four cows with follicular cysts fluctuated randomly with a mean of 2.6 ng/ml. Mean resistance of vaginal mucus was 44 omega for both cycling and cystic cows, indicating that a single measurement of electrical resistance every 2nd day was unreliable in distinguishing physiological states. One cow had high progesterone in milk on days 19 to 25 and was diagnosed pregnant by rectal palpation 3 wk later. Cows were not seen in estrus 28% of the time when milk progesterone and rectal palpation indicated they were in the follicular phase of the estrous cycle and were cycling.     

Plasma pharmacokinetics and milk residues of flunixin and 5-hydroxy flunixin following different routes of administration in dairy cattle

The objective of this study was to determine if the plasma pharmacokinetics and milk elimination of flunixin (FLU) and 5-hydroxy flunixin (5OH) differ following intramuscular and subcutaneous injection of FLU compared with intravenous injection. Twelve lactating Holstein cows were used in a randomized crossover design study. Cows were organized into 2 groups based on milk production (<20 or >30 kg of milk/d). All cattle were administered 2 doses of 1.1 mg of FLU/kg at 12-h intervals by intravenous, intramuscular, and subcutaneous injections. The washout period between routes of administration was 7 d. Blood samples were collected from the jugular vein before FLU administration and at various time points up to 36 h after the first dose of FLU. Composite milk samples were collected before FLU administration and twice daily for 5 d after the first dose of FLU. Samples were analyzed by ultra-HPLC with mass spectrometric detection. For FLU plasma samples, a difference in terminal half-life was observed among routes of administration. Harmonic mean terminal half-lives for FLU were 3.42, 4.48, and 5.39 h for intravenous, intramuscular, and subcutaneous injection, respectively. The mean bioavailability following intramuscular and subcutaneous dosing was 84.5 and 104.2%, respectively. The decrease in 5OH milk concentration versus time after last dose was analyzed with the nonlinear mixed effects modeling approach and indicated that both the route of administration and rate of milk production were significant covariates. The number of milk samples greater than the tolerance limit for each route of administration was also compared at each time point for statistical significance. Forty-eight hours after the first dose, 5OH milk concentrations were undetectable in all intravenously injected cows; however, one intramuscularly injected and one subcutaneously injected cow had measurable concentrations. These cows had 5OH concentrations above the tolerance limit at the 36-h withdrawal time. The high number of FLU residues identified in cull dairy cows by the United States Department of Agriculture Food Safety Inspection Service is likely related to administration of the drug by an unapproved route. Cattle that received FLU by the approved (intravenous) route consistently eliminated the drug before the approved withdrawal times; however, residues can persist beyond these approved times following intramuscular or subcutaneous administration. Cows producing less than 20 kg of milk/d had altered FLU milk clearance, which may also contribute to violative FLU residues.     

Ovarian follicular responses to high doses of pulsatile luteinizing hormone in lactating dairy cattle

Two experiments in lactating dairy cows examined ovarian follicular responses to high, frequent doses of exogenous LH pulses at levels associated with follicular cysts. In Experiment 1, estrus was synchronized in 12 cyclic lactating cows >40 d postpartum. Emergence of the second follicular wave (d 0) was determined by ultrasonography. Starting on d 1, cows received LH (40 microg/h; n = 7) or saline (2 mL/h; n = 5) in hourly pulses for up to 5 (n = 5) or 7 (n = 7) d. On d 2, all cows received two injections of PGF2alpha, 12 h apart. In experiment 2, 14 lactating cows (7 to 12 d postpartum) received LH (40 microg/h; n = 7) or saline (1 mL/h; n = 7) in hourly pulses for 7 d, beginning 24 h after start of the first follicular wave. Daily samples were used to determine serum concentrations of progesterone (P4), estradiol-17beta (E2), LH, and FSH. Profiles of LH were determined from blood samples collected at 12-min intervals for 8 h on d 3. During infusion of LH, serum P4 and FSH were similar across treatments in both experiments. Serum E2 concentrations were similar in experiment 1, but serum E2 was greater on d 2, 3, and 5 in LH-treated cows in experiment 2. Infusion increased LH pulse frequency and amplitude in both experiments. Formation of cysts did not differ between LH- and saline-treated cows in either experiment (1 of 7 vs. 0 of 5 and 1 of 6 vs. 0 of 7, respectively). Cows that ovulated had similar intervals to ovulation in experiment 1 [6.0 +/- 0.1 d (LH) vs. 6.4 +/- 0.2 d (saline)], but in experiment 2, ovulation was 14 d earlier in LH-treated cows (5.6 +/- 1.8 d vs 19.9 +/- 1.5 d). In conclusion, high concentrations of LH are not solely responsible for formation of cysts in lactating dairy cows. Pulsatile infusion of LH stimulated follicular growth and steroidogenesis and decreased time to first ovulation in anestrous postpartum cows.     

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.     

Increasing estrus expression in the lactating dairy cow

Using an activity monitoring system (AMS) equipped with an accelerometer, 2 experiments were conducted to test the hypotheses that (1) enhancing progesterone before inducing luteolysis or (2) exposing cows to estradiol cypionate (ECP) or testosterone propionate (TP) after luteolysis would increase occurrence and intensity of estrus. Our goal was to determine if more cows could be detected in estrus by an AMS compared with other estrus-detection aids. In experiment 1, cows (n = 154) were fitted with both an AMS collar and a pressure-sensitive, rump-mounted device (HeatWatch; HW) and assigned to 3 treatments: (1) no CL + progesterone insert (CIDR) for 5 d, (2) CL only, or (3) CL + 2 CIDR inserts for 5 d to achieve a range in concentrations of progesterone. Prostaglandin F_2α was administered to all cows upon CIDR insert removal or its equivalent. Progesterone concentration up to 72 h posttreatment was greatest in CL + 2 CIDR, followed by CL only, and no CL + CIDR cows. Estrus occurred 14 to 28 h earlier in no CL + CIDR compared with CL-bearing cows. Estrus intensity was greater for CL + 2 CIDR than for CL-only cows. The AMS and HW detected 70 and 59% of cows defined to be in estrus, respectively. In experiment 2, cows (n = 203) were equipped with both an AMS and a friction-activated, rump-mounted patch (Estrotect patch) and assigned to receive 1 mg of ECP, 2 mg of TP, or control 24 h after PGF_2α. Concentrations of estradiol 24 and 48 h after treatment were greater in ECP cows compared with controls. Estrus expression detected by AMS or patches in cows defined to be in estrus tended to be greater or was greater for ECP compared with controls, respectively. Compared with controls and in response to TP or ECP, estrus occurred 8 to 18 h earlier and was of greater intensity for ECP cows, respectively. The AMS and patches determined 73 and 76% of cows defined to be in estrus, respectively. Of cows exposed to the AMS, HW, or patches, 70, 61, and 75%, respectively, were detected in estrus and more than 93% of these subsequently ovulated. In contrast, of the residual cows not detected in estrus, 62 to 77% ovulated in the absence of detected estrus. Only ECP was successful in inducing more expression and intensity of estrus, and proportions of cows detected in estrus exceeded 80%. Given the large proportion of cows equipped with AMS collars ovulating in the absence of estrus, further research is warranted to determine if more pregnancies can be achieved by inseminating those cows not detected in estrus at an appropriate time when PGF_2α is administered to induce luteolysis.     

Reproduction in dairy cows following progesterone insert presynchronization and resynchronization protocols

The objectives of this study were to evaluate the effects of an intravaginal insert containing progesterone (CIDR, controlled internal drug releasing) administered in presynchronization and resynchronization protocols on cyclicity, detection of estrus, pregnancy rate, and pregnancy loss to first AI; reinsemination patterns; and pregnancy rates to second postpartum AI before and after the time of first-service pregnancy diagnosis in dairy cows. Holstein cows (n = 1,052) were blocked by parity and BCS at 3 ± 3 d in milk (study d 0 = day of calving) and assigned randomly to 1 of 3 presynchronization treatments. During the presynchronization programs, all cows received 2 injections of PGF_2α, on study d 35 and 49. Cows enrolled in the control presynchronization treatment received AI after detected estrus from study d 49 to 62. Cows enrolled in the CIDR estrus-detection (CED) presynchronization treatment received a CIDR insert from study d 42 to 49 and AI on detection of estrus from d 49 to 62. Cows enrolled in the CIDR timed AI (CTAI) presynchronization treatment received the same treatment as CED, but were subjected to timed AI on study d 72 after the Ovsynch (GnRH, 7 d PGF_2α, 2 d GnRH, 24 h timed AI) protocol. The control and CED cows not inseminated by study d 62 were enrolled in the Ovsynch protocol on the same day and received timed AI on study d 72. After first AI, cows were assigned to no resynchronization (RCON) or resynchronization with a CIDR insert (RCIDR) between 14 and 21 d after AI. Blood samples collected on study d 35, 49, and 62 were analyzed for concentrations of progesterone and cows were classified as anestrous when progesterone was <1.0 ng/mL in the first 2 samples. On study d 62, anestrous cows with progesterone ≥ 1.0 ng/mL were classified as having resumed cyclicity. Pregnancy was diagnosed at 31 and 60 d after first AI and at 42 d after second AI. A greater proportion of anestrous cows in CED and CTAI became cyclic by d 62 postpartum than control cows. Resynchronization with the CIDR insert increased the pregnancy rate at 31 d after first AI in CED and CTAI, and at 60 d after AI in all cows because of reduced pregnancy loss. These results indicate that presynchronization with the CIDR insert increased induction of cyclicity in anestrous cows and that resynchronization with the CIDR insert did not affect the reinsemination rate but did reduce pregnancy loss and increased the pregnancy rate at 60 d after first AI.     

Persistence of residues in milk following antibiotic treatment of dairy cattle

A study was conducted to determine the persistence of antibiotic residues in milk beyond the recommended withdrawal period. Composite milk samples (n = 122) were collected from 58 lactating dairy cows in the university herd receiving antibiotic treatments for any reason but only when administered as a single drug. Samples were obtained 72 h posttreatment and sampling continued every 24 h until result for antibiotic residue was negative by the Bacillus stearothermophilus disc assay. The antibiotic (n = 7) administered accounted for significant variation in drug persistence; however, route of administration, case number (for cows treated for more than one episode), number of days treated, animal's body weight, lactation number, and daily milk production did not affect drug persistence. Chi-square analysis indicated that 21% of milk samples were positive for residues beyond the recommended withholding period. Milk samples from cows treated with cephapirin and penicillin were the only samples that exceeded recommended withdrawal times. Often doses administered exceeded label directions.     

Chronic mastitis is associated with altered ovarian follicle development in dairy cattle

Connection between mastitis and fertility is multifaceted; therefore, several aspects need more elucidation. In particular, the aim was to investigate if naturally occurring chronic mastitis has an effect on ovarian function. At the time of slaughter, a milk sample and both ovaries were collected from 68 cows. The presence and intensity of chronic mastitis was diagnosed by the combined evaluation of bacteriological examination and somatic cell count of the milk of each individual quarter according to the measures of the National Mastitis Council. Animals were divided into 4 groups characterized by a low (n=15), mild (n=14), intense (n=19), or severe (n=16) degree of infection. A count of visible follicles on each ovary was followed by a quantitative analysis of microscopic traits on a selected group of animals (n=16). The latter included the classification and count of the entire preantral follicle population, and the morphometric analysis of the vascular bed extension and connective stroma in the cortical region. Finally, the expression of growth and differentiation factor-9 (GDF-9) was studied. The number of follicles with diameters ranging from 1 to 3 mm and 4 to 7 mm was not affected by the degree of infection. A significant effect of the degree of udder infection was observed on the number of follicles with a diameter larger than 8 mm. Furthermore, the intensity of mastitis had no effect on the number of primordial and primary follicles, but severely affected cows showed a lower number of secondary follicles (0.5±0.1 vs. 0.2±0.03). Quantitative analysis demonstrated a decrease in the density of blood vessels (6.30±1.08 vs. 4.68±0.28) expressed as ratio of vascular bed/total area) and a higher incidence of fibrous stroma (1.60±0.99 vs. 6.04±3.08 expressed as ratio of connective tissue/total area) in the cortical area of the most affected animals. Finally, the level of GDF-9 protein within the oocytes of different follicle size was lower in the animals with the severe form of chronic mastitis (1.34±0.05 vs. 0.78±0.21 expressed as arbitrary units). In conclusion, decreased fertility of cows with chronic mastitis takes place through an effect on the ovary altering the dynamics of folliculogenesis. Within the ovary, this implies a reduction of the vascular bed and an increase in the fibrotic tissue together with a direct effect on oocyte-specific factors as GDF-9, all of which are essential regulatory elements of folliculogenesis.