Retained fetal membranes in cows: Manual removal versus nonremoval and its effect on reproductive performance

Sixteen primiparous Holstein cows with retained fetal membranes (RFM) were studied for postpartum prostaglandin release, uterine infection and resumption of estrous cyclicity after manual removal of RFM (eight cows) versus leaving the RFM untreated (eight cows). The RFM were results of induced parturition on Day 274 of gestation. Seventeen non-RFM primiparous cows were controls. The 15-keto-13, 14-dihydro-metabolite of prostaglandin F(2alpha) (PGFM) was measured in daily blood samples. Aerobic and anaerobic bacteria were cultured from weekly uterine swabs from Week 3 until results were negative. Resumption of estrous cyclicity was determined by milk progesterone three times weekly. Manual removal caused an immediate and large but short-lived increase in PGFM, probably due to the physical damage of uterine tissue. No sustained difference in postpartum PGFM release between cows with RFM manually removed and cows with RFM left untreated was detected. Non-RFM controls had lowest PGFM concentrations. Uterine infections were more frequent and more severe after manual removal of RFM. Untreated RFM-cows and controls were similarly affected. Most infections involved Actinomyces (formerly Corynebacterium ) pyogenes and/or Fusobacterium necrophorum . Actinomyces pyogenes was isolated in the third week postpartum in 5 8 cows with RFM manually removed versus 2 8 cows with RFM left intact and in 2 17 controls. Manual removal prolonged the interval from calving to first functional corpus luteum by 20 d. This study, using RFM resulting from induced parturition, shows that manual removal of RFM can delay the postpartum return to normal reproductive status without altering PGFM profiles.     

Follicular dynamics during postpartum anestrus and the first estrous cycle in suckled or non-suckled Brahman (Bos indicus) cows

Brahman (Bos indicus) cows, were selected at 28+/-10 days after calving and analyzed by real time rectal ultrasonography three times a week, in order to evaluate and compare follicular and corpus luteum development during postpartum (PP) anestrus and the first PP estrous cycle under sylvopastoril conditions. Suckling (S, n=11) or non-suckling (NS, n=5) cows were evaluated in a zone of tropical dry forest (450m of altitude, mean temperature=27 degrees C, annual rainfall=1000mm). Estrous detection was performed twice daily by direct observation. Progesterone was quantified using RIA. From 28+/-10 days postcalving to resumption of estrous cycles, there were no differences (P>0.05) between NS and S cows for diameter of the dominant or first subordinate follicle, follicular growth rate, or interdominance interval. Silent ovulation, corpus luteum formation and subsequent progesterone concentrations ranging from 0.3 to 9. 7ng/ml, were found in both groups. The first calving to ovulation and calving to standing estrus intervals were shorter (P<0.01) in NS (34.8+/-5.81 and 41.2+/-9.03 days) than in S (65+/-4.82 and 81+/-6. 21 days) cows. Follicular development and progesterone concentrations during the first PP estrous cycle did not differ (P>0. 05) between NS and S cows. These results suggest that Brahman cows could have an early PP resumption of follicular recruitment if fed under sylvopastoril system conditions. However, non-suckled cows did have an earlier standing estrus and ovulation than did suckled cows.     

Effects of short-term oilseed supplementation on plasma fatty acid composition,progesterone and prostaglandin F metabolite in lactating beef cows

Twenty-four 3-year-old Angus cows (512.2±21.6 kg) and six ruminally cannulated beef heifers (523.1±16.9 kg) were used to determine the impact of feeding oilseeds starting at the beginning of estrous synchronization until maternal recognition of pregnancy on plasma fatty acid composition. Starting ~60 days postpartum cows were synchronized with the Select Synch+controlled internal drug-release (CIDR) device and timed artificial insemination (AI) protocol. The day CIDR was inserted; cattle were randomly assigned to one of the three treatments being grazing only (CON) or a supplement containing whole soybeans (SOY); or whole flaxseed (FLX). Cattle continued to receive these diets for 28 days. Blood was collected every 3 days until 10 days after insemination and then every day until 18 days after insemination. All cattle grazed a common pasture and supplemented cattle were individually fed their respective supplements once daily. Ruminally cannulated heifers were used to evaluate the impact supplements had on forage intake, which was reduced (P=0.05) with oilseed supplementation. Feeding oilseeds increased total fatty acid intake (P<0.001) across treatments with SOY having greater (P<0.001) 18:2n-6 intake than either CON or FLX. Likewise, cattle fed FLX had greater (P<0.001) 18:3n-3 intake than either CON or SOY. There was a treatment×time interaction (P⩽0.05) for all fatty acids identified except for 20:5n-3 (P=0.99). Within 3 days after the start of supplementation, plasma concentrations of 18:2n-6 increased (P<0.001) for cattle fed SOY compared with CON or FLX, whereas flax-fed cattle did not exhibit an increase (P=0.02) until day 15 of supplementation over that of CON. Plasma concentrations for 18:3n-3 was greater (P<0.013) for FLX than both CON and SOY by day 12. Feeding flaxseed tended to (P=0.07) increase and increased (P=0.01) plasma concentrations of 20:4n-6 by day 18 over CON and SOY, respectively. Overall, treatment did not affect serum concentration of progesterone (P=0.18) or prostaglandin F metabolite (P=0.89). However, day after breeding had an effect on serum progesterone (P=0.01) with day 16 after timed AI being lower compared with other days. Feeding oilseeds during the time of estrous synchronization will not only increase the energy density of the diet but will provide key fatty acids around the time of maternal recognition of pregnancy.     

Endocrine profiles of dairy cows following experimentally induced clinical mastitis during early lactation

Concentrations of LH, cortisol, estradiol-17beta (E(2)), prolactin and 13,14-dihydro-15-keto-prostaglandin F(2alpha) (PGFM) were determined in cows with experimentally induced clinical mastitis during early lactation. Cows free of intramammary infection (IMI) and in the luteal phase of the estrous cycle were balanced by lactation number and days in milk and assigned to either control (n=5) or treatment (n=5) groups. Treated cows were infected experimentally (day 0), in two mammary quarters, with Streptococcus uberis and developed clinical mastitis within 60 h after inoculation as evidenced by increased mastitis scores, elevated rectal temperatures, mammary swelling and isolation of S. uberis pathogen. Four days following bacterial challenge, blood samples were collected every 20 min for 8 h for determination of PGFM and LH following administration of oxytocin and GnRH, respectively. Blood samples were also collected on days 0, 4 and 7 of the experiment to determine concentrations of E(2), prolactin and cortisol. Four days after bacterial challenge, concentrations of cortisol were higher (P=0.04) in experimentally infected cows than controls. Experimentally challenged cows had increased (P=0.02) concentrations of cortisol on days 4 and 7 compared with day 0. Control cows had no significant increase in blood cortisol during the experimental period. Baseline concentrations of PGFM did not differ between groups; however, peak concentrations of PGFM following oxytocin challenge were elevated (P=0.006) in cows with clinical mastitis compared with control animals. Prolactin, E(2) and LH did not differ between cows with clinical mastitis or controls. Experimentally induced mastitis during early lactation elevated concentrations of cortisol during the luteal phase of the estrous cycle. Furthermore, mastitic cows demonstrated an increased PGFM response following oxytocin administration. Altered reproductive efficiency in cows with clinical mastitis caused by Gram-positive pathogens may be the result of increased uterine sensitivity to prostaglandin F(2alpha) (PGF(2alpha)).     

Characteristics of corpus luteum formed from the first wave dominant follicle following hCG in cattle

Two experiments were conducted to characterize the development and function of corpus luteum (CL) induced by hCG. In Experiment 1, cows (n = 18) were randomly assigned either to serve as controls (CONT, n = 6) or to receive hCG on Day 7 with (hCG-LUT, n = 6), or without (hCG-CONT, n = 6) surgical removal of the spontaneous CL on Day 12. The diameters of the hCG-induced and spontaneous CL of similar age did not differ (P > 0.05) between Days 1 and 4. At Day 5, the CONT (spontaneous) CL diameter (29.3 +/- 1.4 mm) was larger (P < 0.05) than that of the hCG-LUT (24.5 +/- 1.5 mm) or the hCG-CONT (24.6 +/- 1.7 mm) induced CL. Similarly, induced CL diameter for hCG-LUT and hCG-CONT groups was smaller (P < 0.01) than the CONT (spontaneous) CL between Days 10 to 14. Plasma progesterone (P(4)) levels were not different (P > 0.05) among treatment groups until Day 12. On Day 14, the P(4) concentration of hCG-LUT cows decreased (P < 0.01) to 1.1 +/- 0.9 ng/ml, then increased to 3.1 +/- 0.9 ng/ml by Day 18. Comparative values for hCG-CONT and CONT cows were 5.8 +/- 0.8 and 4.2 +/- 0.8; 4.5 +/- 0.8 and 5.5 +/- 0.8 ng/ml, respectively. The onset of regression of CL as well as estrous cycle length were similar (P > 0.05) for all treatment groups. In Experiment 2, the effects of intrauterine infusion of indomethacin on the diameter, function and life span of hCG-induced CL were examined. A slight, albeit not significant, suppression of PGFM levels was observed in indomethacin-infused cows (n = 4) compared with the controls (n = 4) in blood samples obtained once a day during the infusion period. However, in 2 cows from which blood samples were collected every 6 h, the control cow showed several pulses of PGFM while the indomethacin-treated cow exhibited none. Induced CL diameter and lifespan were not affected by indomethacin infusion. However, mean P(4) levels were higher (P < 0.05) between Days 16 and 20 in the indomethacin-infused group. In conclusion, the results suggest that 1) hCG-induced CL are functional but appear to be smaller and secrete less P(4) than spontaneous CL of similar age, and 2) the small size and reduced secretary function observed is not necessarily due to PGF(2alpha) secreted by the uterine endometrium but, probably, to inherent characteristics.     

Circulating PgF2alpha and nutritional parameters at parturition in dairy cows with and without retained placenta: Relation to prepartum diet

Reproductive and biochemical parameters were studied at parturition in multiparous single-carrying Holstein cows. These were compared in animals with (n=14) and without (n=40) a retained placenta and then according to 2 prepartum diets (corn silage/concentrate, n=44; grass silage/concentrate, n=10) in cows with and without retained placentas. Cows with retained placentas had a 4-day shorter gestation period and gave birth to 5 kg-lighter calves than cows without retained placentas. Furthermore, their plasma PGFM -PgF2alpha main metabolite- (3325 vs 5675 pg/ml; P<0.01) and glucose (79.2 vs 95.2 mg/100ml; P<0.05) levels were lower and their protein concentration was higher (85.7 vs 76.5 g/l; P<0.05) than those of cows without retained placentas. Retained placenta incidence in cows fed grass-silage was higher than in cows fed corn-silage (60% vs 18.2%; P<0.05). Cows with retained placentas and fed corn silage had shorter gestation lengths, gave birth to lighter calves, and had less circulating glucose at calving (77.6 vs 96.5 mg/100ml; P<0.05) than cows without retained placentas and fed the same forage. Cows with retained placentas and fed grass silage had less PGFM (2172 vs 4530 pg/ml; P<0.05) than cows without retained placentas and fed the same forage. Calving number, sex ratio and preceeding milk yield were not different between the two groups of cows whatever their prepartum diet. In the dairy cow, retained placenta could be due to a PgF2alpha or an energy deficiency at calving. Roles of the dietary polyunsaturated fatty acids toward the Pg synthesis and of the energy supply before calving in relation to retained placenta are discussed here.     

Progesterone concentration, follicular development and induction of cyclicity in dairy cows receiving intravaginal progesterone inserts

Objectives were to evaluate progesterone concentrations after cows had initiated estrous cycles following calving and induction of estrous cycles in postpartum anovular high-producing Holstein dairy cows treated with controlled internal drug releasing (CIDR). In experiment 1 (EXP1), 62 cows that had initiated estrous cycles received a new CIDR (NCIDR) containing 1.38 g of progesterone or a 7-d used autoclaved CIDR (UCIDR) 48h after luteolysis for 7 d. Ovaries were examined by ultrasonography, and plasma analyzed for concentrations of progesterone. In experiment 2 (EXP2), 515 cows diagnosed as anestrus were randomly assigned to untreated control, NCIDR or UCIDR for 6d. Plasma was analyzed for concentration of progesterone 12 d after CIDR removal to determine ovulation. In EXP1, milk yield and body condition did not influence progesterone concentrations. Concentration of progesterone tended to increase faster (P=0.10) in cows receiving UCIDR than NCIDR, but both treatments reached a plateau at 90min. Cows receiving the NCIDR had greater (P=0.04) concentrations of progesterone during the 7-d treatment, but they were mostly subluteal (<1.0 ng/mL) after d 2. After removal, concentrations of progesterone were greater for NCIDR than UCIDR for the first 45 min, and were similar thereafter. Multiparous cows had lesser (P=0.004) concentrations than primiparous cows throughout the study. The pattern of ovarian follicular development was not affected by treatment. In EXP2, induction of onset of estrous cycles increased (P<0.01) with progesterone treatments, but was similar between NCIDR and UCIDR. Proportion of cows experiencing shorter than typical length estrous cycles after first AI tended to be greater (P=0.09) for control cows than those receiving the CIDR, and for cows remaining anestrous than those in which onset of estrous cycles was induced. Pregnancy per AI and pregnancy loss were similar among treatments. Cows that resumed estrous cyclicity prior to first AI had greater (P=0.01) pregnancy per AI. Treatment of high-producing Holstein cows that had previously initiated onset of estrous cycles with CIDR resulted in subluteal concentrations of progesterone, but in anestrous high-producing cows increased induction of estrous cycles with no effect on fertility at first insemination.     

Luteal competency during the resumption of ovarian cyclicity in postpartum Brahman cows

Twenty pluriparous, spring-calving Brahman cows were used to determine luteal competency, as measured by serum progesterone concentrations, during the first and the second postpartum estrous cycles. Prior to and after calving, all cows were maintained in good body condition on Coastal bermudagrass pasture (IFN 1-00-703). The calves were allowed to suckle ad libitum, and sterile marker bulls were maintained with the cow herd as an aid in estrus detection throughout the trial. Cow weight and body condition score were recorded within 24 hours after calving and again at the first behavioral estrus observed. From day 1 through day 14 (day 0 = estrus) of both the first and the second postpartum estrous cycles, blood samples were collected from each cow, processed to yield serum and analyzed by radioimmunoassay for progesterone concentrations. There was a higher incidence of abnormal estrous cycles following the first postpartum estrus (35%) than following the second (5%) postpartum estrus (P<0.05). The abnormal first estrous cycles were characterized by either a short luteal phase (four cows) or by standing estrus behavior without luteal tissue formation (three cows). When serum progesterone concentrations were compared for all cows during the first estrous cycle with those during the second estrous cycle, there was less progesterone released during the cycle (P<0.05) and lower peak progesterone concentrations (P<0.10) during the first estrous cycle. However, if the abnormal cows were excluded from the analyses, there was no difference (P>0.10) in either progesterone concentrations through the 14 days measured or in peak progesterone concentrations between the first and the second postpartum estrous cycles. It can be concluded from this study that the higher incidence of abnormal luteal function following the first postpartum estrus may contribute to the decreased conception rates observed when cows are bred at their first postpartum estrus.     

Effect of exogenous progesterone on prostaglandin F2 alpha release and the interestrous interval in the bovine

The present study was developed to determine if administration of progesterone, early in the estrous cycle of the cow, stimulated an advanced pulsatile release of PGF2 alpha from the uterine endometrium resulting in a decreased interestrous interval. Twenty-three cyclic beef cows were randomly assigned to receive either sesame oil or progesterone (100 mg) on Day 1, 2, 3 and 4 of the estrous cycle. Peripheral plasma concentrations of progesterone and the metabolite of prostaglandin F2 alpha, 15-keto-13,14-dihydro-prostaglandin F2 alpha (PGFM) were measured by radioimmunoassay. Administration of exogenous progesterone increased peripheral plasma concentration of progesterone in treated (3.67 ng/ml) compared to control (1.28 ng/ml) cows from Day 2 through 5 of the estrous cycle. Progesterone administration shortened the interestrous interval (16.7 d) compared to controls (21.6 d). The shortened interestrous intervals in treated cows resulted from an earlier decline in peripheral plasma progesterone. Decline of peripheral plasma progesterone concentrations is coincident with an increased pulsatile release of PGFM in both progesterone treated and control cows. Results indicate that administration of exogenous progesterone stimulates an earlier maturation of endometrial development, causing an advanced release of PGF2 alpha which shortens the interestrous interval of the cow.     

Dietary supplementation with safflower seeds differing in fatty acid composition differentially influences serum concentrations of prostaglandin F metabolite in postpartum beef cows

Synthesis and secretion of prostaglandin F2alpha (PGF2alpha) is elevated following parturition and exerts divergent effects on the re-establishment of fertile estrous cycles in cows. The objective of these experiments was to determine if oil seed supplements differing in fatty acid composition differentially influence serum concentrations of the specific PGF2alpha metabolite, PGFM. Safflower seed supplements were formulated to provide 5% of dry-matter intake as fat. In Trial 1, 24 multiparous beef cows were individually fed control (beet pulp-soybean meal) or cracked high-linoleate safflower seed (78% 18:2n-6) supplements for 80 d postpartum. Linoleate supplemented cows had greater (P < 0.001) serum concentrations of PGFM than control cows. In Trial 2, primiparous beef cows (n = 36) were individually fed control (cracked corn-soybean meal), cracked high-linoleate (76% 18:2n-6) or -oleate (72% 18:1n-9) safflower seed supplements for 92 d postpartum. As in Trial 1, serum concentrations of PGFM were greater (P < or = 0.04) in linoleate than control or oleate supplemented cows. Serum concentrations of PGFM, however, did not differ (P = 0.40) among oleate and control supplemented cows. Although potential impacts on reproductive performance remain to be proven, dietary oil supplements high in linoleate, but not oleate, increased serum concentrations of PGFM compared to control supplements.     

Induction of cyclicity in postpartum anestrous beef cows using progesterone, GnRH and estradiol cypionate (ECP)

The objective of the present study was to determine whether treatment of postpartum multiparous and primiparous anestrous beef cows with an intravaginal progesterone-releasing insert (CIDR) and PGF(2alpha), with and without the addition of GnRH or estradiol cypionate (ECP) at the time of CIDR insertion, is effective in stimulating onset of estrous cycles. Postpartum lactating Angus primiparous (n=47, 2 years of age, 495+/-6 kg) and multiparous (n=76, >or=3 years of age, 553+/-9 kg) cows were assigned by calving date to four blocks spaced 21-day apart. Cows were assigned sequentially by calving date to four treatment groups: (1) PGF(2alpha) (n=30), (2) CIDR-PGF(2alpha) (n=30), (3) GnRH-CIDR-PGF(2alpha) (n=33), and (4) ECP-CIDR-PGF(2alpha) (n=27). Intravaginal CIDR inserts were in place from days -7 to 0. A single 100 microg injection of GnRH or 2 mg ECP were administered on day -7, and 25mg PGF(2alpha) was administered on day 0. Day 0 averaged 38+/-1 day postpartum. Blood samples were collected on days -19, -9, 0, 5, 9, 12, 16, 19, 23, 26, and 30 for determination of plasma progesterone concentrations. Pre-treatment luteal activity (progesterone>or=1 ng/ml) was detected in 19% of primiparous and 8% of multiparous cows. Progesterone concentrations on day 0 were greater (P<0.001) in primiparous (3.2+/-0.3 ng/ml) than multiparous (2.0+/-0.2 ng/ml) cows. Following CIDR withdrawal, progesterone concentrations from days 5 to 30 were used to categorize response profiles as either: (1) treatment-induced onset of estrous cycles, (2) continued anestrus, or (3) spontaneous ovulation and subsequent formation of a CL. Incidence of treatment-induced onset of estrous cycles, which was defined as progesterone concentrations >or=1 ng/ml in three or more consecutive samples from days 9 to 19, was influenced by treatment and parity. Percentages of cows initiating estrous cycles were greater (P<0.001) in the three CIDR-treated groups than in the PGF(2alpha) group (55 and 8%, respectively). Percentages of cows initiating estrous cycles in the CIDR-PGF(2alpha), GnRH-CIDR-PGF(2alpha), and ECP-CIDR-PGF(2alpha) groups were 55, 58, and 52%, respectively. Incidence of treatment-induced estrous cycles in the three CIDR-treated groups of cows was greater (P=0.008) in primiparous (76%) than multiparous (43%) cows. Treatment of postpartum anestrous primiparous and multiparous beef cows with CIDR-PGF(2alpha) approximately 40-day postpartum provides an approach to increase the percentage of cows that have reinitiated estrous cycles by the start of the breeding season.     

Change in morphology of corpora lutea, central luteal cavities and steroid secretion patterns of postpartum suckled beef cows after melengestrol acetate with or without prostaglandin F2alpha

Change in morphology of the corpus luteum (CL) and patterns of progesterone and estradiol secretion after treatment with melengestrol acetate (MGA) were monitored in postpartum beef cows. Twenty Angus cows were randomly assigned to MGA or MGA + prostaglandin F(2alpha) (PGF) treatments. All cows were fed 0.5 mg of MGA per cow per day for 14 d. The MGA-treated cows (n = 10) were allowed to return to estrus spontaneously at the second estrus after withdrawal of MGA from the feed. The MGA + PGF-treated cows (n = 10) received an injection containing 25 mg of PGF(2alpha) 17 d after the last feeding of MGA. Cycle 1 was defined as the first luteal phase after MGA feeding and Cycle 2 represented the subsequent cycle or luteal phase after PGF. Blood sampling and transrectal ultrasonography of the ovaries was done daily through the completion of 2 estrous cycles upon removal of MGA from the feed. Blood samples were analyzed for plasma progesterone and estradiol concentrations. Area of CL and fluid-filled cavities within each CL were determined by ultrasonography. Concentrations of progesterone and area of CL were similar between cycles and treatments. Estradiol concentrations were higher (P < 0.05) in Cycle 2 than in Cycle 1. Fluid-filled cavities were larger (P < 0.001) in Cycle 1 than in Cycle 2 for both mid-luteal (Days 5 to 9) and late-luteal (Days 10 to 14) phases. Multiple CL (2 or more during 1 cycle) were observed in 5 cows. Progesterone concentrations and total area of luteal tissue did not change with respect to treatment or cycle, but CL morphology was altered in the first cycle after MGA treatment. Of the 19 cows that ovulated after withdrawal of MGA, 3 experienced a short luteal phase. These data characterize changes that occur among cows that are fed melengestrol acetate during the postpartum period and enhance observations from prior studies regarding MGA use.     

Changes in ovarian function in mature beef cows grazing endophyte infected tall fescue

The objective was to examine follicular and luteal development and function in mature, lactating beef cows grazing endophyte free (E-) or endophyte infected (E+) tall fescue during the early postpartum period. Angus, Hereford, and Angus x Hereford cows were exposed to pasture for 37-39 days before synchronized estrus. Serum concentrations of prolactin were evaluated during the luteal phase before the synchronized estrus. Every Monday, Wednesday, and Friday for one estrous cycle ovaries were monitored by transrectal ultrasonography and blood was collected for determination of serum concentrations of progesterone and estradiol in cows that responded to synchronization. Signs of fescue toxicosis in E+ cows included decreased serum concentrations of prolactin (84.9+/-13.6 pg/ml versus 32.3+/-12.0 pg/ml; P < 0.009) measured during the luteal phase (day 37 of grazing) and decreased body condition of cows and weight of cows and calves (P < 0.001). Neither serum concentrations of progesterone or estradiol, nor diameter of the CL differed between treatments. Diameter of the largest follicle tended to be smaller for cows grazing E+ fescue, especially between days 8 and 12 of the estrous cycle (P < 0.08). Numbers of class 1 (3-5 mm) and class 3 (>10 mm) follicles were similar (P > 0.05) between treatments, but number of class 2 (6-9 mm) follicles was reduced in E+ cows for most of the cycle (days 10 through 20; P < 0.03). Length of synchronized estrous cycle, days open, calving interval, and pregnancy rate at 30, 45, 60, and 90 days post-breeding was similar (P > 0.05) among treatment groups. Even though follicular dynamics (diameter of the largest follicle and number of class 2 follicles) were altered in cows grazing E+ tall fescue, follicular function was apparently not affected by ergot alkaloids.     

Reproductive responses following postpartum suppression of ovarian follicular development with a deslorelin implant during summer heat stress in lactating dairy cows

The objective was to evaluate pregnancy rate to a timed artificial insemination (TAI) protocol in the autumn for cows treated with a non-degradable GnRH agonist implant (Deslorelin [DESL], 5mg) during the summer heat stress period compared with non-treated controls (CON). Cows were randomly assigned to receive or not a DESL implant within 1-4 days postpartum (dpp) twice weekly, from 25 June through 8 August 2001. All cows in DESL implant and CON treatments were injected with PGF(2alpha) 7 days after enrollment. Ultrasonography (US) monitored numbers of ovarian follicles and corpus luteum (CL) at approximately 10, 30, 35/36, 45/44, 56/55 and 66/63dpp, while DESL implants were in situ and concurrently CON, respectively. DESL implants were removed at two specific days, 28 August and 4 September. Cows had DESL implant in situ for a range of 28-67 days, depending on date of enrollment and implant removal. Within 61-100dpp, 31 days after implant removal, DESL implant and CON cows were initiated in a Presynch-Ovsynch and TAI protocol. Pregnancy was evaluated by US and palpation per rectum at 28 and 46 days after TAI, respectively. Plasma concentrations of progesterone were analyzed for sets of blood samples collected during the Presynch-Ovsynch and at TAI day followed 8 days later. Cows in the DESL-implant treatment had more (P<0.01) Class 1 (3-5mm) follicles, less (P<0.01) Class 2 (6-9mm), Class 3 (> or =10mm) follicles and CL compared with CON cows. Proportion of cows having initiated estrous cycles after calving was less (P<0.01) in the DESL-implant treatment (52.2%, 58/111) compared with CON (93.7%, 104/111) at the beginning of Ovsynch. Pregnancy rate to TAI was less (P<0.01) in the DESL implant (27.5%, 33/120) compared with CON (53.9%, 69/128). Pregnancy rate to TAI was less (P<0.01) in DESL-implanted cows that had initiated estrous cycles after calving (30.6%, 19/62) compared with CON (53.7%, 65/121) cows having initiated estrous cycles after calving. Furthermore, pregnancy rate was less (P<0.01) for cows having ovulations that had initiated estrous cycles after TAI in the DESL implant (39.1%, 18/46) compared with CON (62.1%, 54/87) treatments. Pregnancy losses from day 28 to day 46 of pregnancy did not differ between DESL implant (15.1%, 5/33) and CON (13.0%, 9/69) treatments. The DESL implant induced a delay in initiation of a new wave of follicular development during the postpartum-heat stressed period. The lesser pregnancy rate in the DESL-implant treatment group may be due to a pool of heat stress damaged follicles that were depleted in the control group with re-occurring follicle waves.     

Ability of induced corpora lutea to maintain pregnancy from the third month of gestation to term in cattle

The local relationship between the pregnant uterine horn and the CL during maternal recognition of pregnancy is well-documented. It continues beyond that time; pregnancies were maintained in lutectomized cows when CL were induced on the ovary ipsilateral, but not contralateral, to the uterine horn of pregnancy during Days 28-53. This study evaluated factors affecting maintenance of pregnancy by CL induced after Day 53, in lutectomized cows that had received exogenous progesterone from Day 29 to 15 days after induction of a CL. Twenty-four suckled beef cows were lutectomized on Day 29 of gestation; pregnancy was maintained with progesterone from two controlled internal drug releasing (CIDR) inserts, exchanged every 5 days. Beginning on Day 53, ovaries and viability of pregnancy were evaluated by ultrasonography every 5 days. When a follicle >or=10 mm in diameter was present ipsilateral to the fetus, each cow received 1,000 IU of hCG. Following induction of a CL (20 of 24), progesterone was reduced to a single CIDR for 5 days, then removed. Retention of pregnancy was confirmed by rectal palpation and calving. Cows with induced CL maintained pregnancy to term, including four with the CL contralateral to the fetus. Three cows failed to form normal CL by Day 98 and lost pregnancy after removal of exogenous progesterone. One cow that did not respond to hCG lost pregnancy during exogenous progesterone. In conclusion, CL induced after Day 53 maintained pregnancy to term, even when induced contralateral to the pregnant uterine horn.     

Use of plasma concentrations of 13,14-dihydro,15-keto-PGF2 alpha (PGFM) in the diagnosis of sub-clinical endometritis and its relationship to fertility in the postpartum dairy cow

The objective of this study was to determine the value of using plasma concentrations of PGFM to diagnose subclinical endometritis in the dairy cow, and its relationship to subsequent fertility. A total of 274 cows between 24 to 29 d post partum was divided into 4 groups on the basis of clinical features of the uterus and ovary. Cows in Group 1 (n = 74) had a normal, involuting uterus and a CL on the ovary; cows in Group 2 (n = 51) had a normal, involuting uterus but no CL on the ovary; cows in Group 3 (n = 83) did not have a normal, involuting uterus but had a CL on the ovary; and cows in Group 4 (n = 66) did not have a normal, involuting uterus or a CL on the ovary. A blood sample was obtained from each cow on the day they were placed on the study, and plasma concentrations of PGFM and P4 were determined using RIA. Cows were artificially inseminated (AI) at the first observed estrus after Day 60 post partum, and pregnancy was determined by palpation of the uterus per rectum between 45 and 50 d postAI. Reproductive responses evaluated were conception rate to first service, days open, and percentage of cows pregnant by 90, 120, 150 and 180 d post partum. Data were analyzed using GLM procedures of SAS and a 2 x 2 factorial with contrast procedures. Polynomial regression analysis was used to determine the shape of the PGFM, P4 and fertility curves. There was no difference among mean PGFM concentrations of cows in each group. The rate of decline of plasma PGFM concentrations was lower in cows with an abnormal uterus and a CL on the ovary compared with those without a CL. A lower percentage of cows with abnormal uteri was pregnant by 90 d post partum compared with cows with normal uteri. From the results of this study, it was concluded that plasma PGFM concentrations between Days 24 to 29 post partum were not effective in identifying cows with subclinical endometritis.     

The effect of aspirin administration and parity on plasma salicylate concentrations and postpartum reproductive parameters in Brahman cows

Forty pluriparous (M) and 20 primiparous (P) suckled Brahman cows were used to evaluate the effect of aspirin and parity on plasma 13,14-dihydro-15-keto-prostaglandin F2alpha (PGFM) and progesterone (P4) concentrations and some reproductive parameters. On Day 7 after calving (PP), the cows were allocated within parity into 2 groups: the aspirin group received concentrate containing aspirin at a rate of 100 mg/kg of body weight every 12 h until Day 13 PP; and the control received concentrate every 12 h for the same interval. Blood samples were collected after first and last aspirin feeding and daily from Day 1 PP to Day 6 PP and from Day 14 PP to Day 21 PP, twice daily from Day 7 PP to Day 13 PP, and weekly until first non-return to estrus. Plasma salicylate concentrations in the aspirin group cows were affected by parity (P < 0.01) and time after feeding (P < 0.0001). P cows showed higher plasma salicylate concentrations with a later peak and slower decrease than M cows. Aspirin-treated P cows had longer PP intervals than either control P, control M, or aspirin-treated M cows. Cows receiving aspirin had a lower pregnancy rate, an increased incidence of abnormal estrous cycles, and a decline in the presence of corpora lutea after estrus. Cows that formed a corpora lutea and had received aspirin had higher P4 release between Day 6 and 14 after estrus. Aspirin-treated cows that did not form corpora lutea had lower P4 release between Days 9 and 14 after estrus. A treatment by parity interaction affected mean PGFM proportions (P < 0.01) during the treatment period. Aspirin-fed P cows increased PGFM release as measured by mean proportion of Day 6 PP values. Aspirin-fed M cows showed a decrease in mean PGFM proportions. Aspirin feeding during the early PP showed different effects on some reproductive parameters in P and M Brahman cows, indicating differences in PP physiology between parities.     

Highly sensitive second antibody format enzymeimmunoassay for determination of 13,14-dihydro-15-keto-PGF2alpha in blood plasma of mithun (Bos frontalis)

As an alternative to radioimmunoassays, a simple, highly sensitive and quick enzymeimmunoassay (EIA) for determination of 13,14-dihydro-15-keto-PGF(2alpha) (PGFM) in blood plasma of mithun (Bos frontalis; bovine) on microtitreplates using second antibody coating technique and PGFM-horseradish peroxidase as a label has been developed. The wells of the microtitreplate were coated with affinity-purified goat IgG (antirabbit IgG) that binds the hormone specific antibody. The EIA was carried out directly in 20microl plasma. The PGFM standard curve, with doses ranging from 0.1 to 50pg/well was linear. The sensitivity of the assay was 5pg/ml. PGFM standard curve in buffer showed parallelism with serially diluted mithun plasma containing high endogenous PGFM. Plasma PGFM concentrations estimated by using the developed EIA and commercially available PGFM EIA kit in the same samples were significantly correlated (r=0.98) and showed linearity. Intra- and inter-assay coefficients of variation were below 7%. Recovery of known concentrations of added PGFM in charcoal stripped plasma was linear (r=0.99). The developed EIA was further validated biologically by estimating PGFM in cyclic cows for the entire estrous cycle and in peri-parturient cows beginning day 7 prior to calving till day 30 post-calving; the concentrations were along with the expected lines as reported in bovine. In conclusion, the EIA developed in this study is simple, highly sensitive, valid and sufficiently reliable method for estimation of PGFM directly in bovine plasma.     

Temporal changes in serum prostaglandin F2alpha and oxytocin in dairy cows with short luteal phases after the first postpartum ovulation

Luteolysis in the cow depends upon an interaction between prostaglandin F(2alpha) (PGF(2alpha)) and oxytocin. The objectives of our study were 1) to determine oxytocin concentrations in postpartum dairy cows and 2) to identify the temporal relationship between oxytocin and PGF(2alpha) release patterns during luteolysis in normal and abbreviated estrous cycles in the postpartum period. Serum oxytocin and PGF(2alpha) metabolite (PGFM) concentrations from nine cows which had short estrous cycles (< 17 d) were compared with those of six cows which had normal estrous cycles. Serum basal oxytocin concentrations in short estrous cycle cows (23.7 to 31.1 pg/ml) were higher (P<0.05) than those of normal estrous cycle cows (14.6 to 19.8 pg/ml). Oxytocin concentrations increased to peak values in both short and normal cycle cows, during luteolysis. Basal PGFM concentrations (112.2 to 137.4 pg/ml) were higher in cows with short cycle (P<0.05) than in cows with normal cycles (62.9 to 87.5 pg/ml). The increase in PGFM concentrations during luteolysis was significant in both normal cycle and short cycle cows (P<0.05). Increases in serum PGFM concentrations were always associated with increases in serum oxytocin concentrations in normal cycle and short cycle cows and the levels decreased simultaneously before the subsequent estrus. Results support the idea of a positive relationship between PGF(2alpha) and oxytocin concentration during the estrous cycle as well as a possible synergistic action of these hormones in the induction of luteolysis in dairy cattle.     

Use of medroxyprogesterone acetate (MAP) in lactating Holstein cows within an Ovsynch protocol: follicular growth and hormonal patterns

To evaluate the effects of incorporating medroxyprogesterone acetate (MAP) in an Ovsynch protocol, cyclic lactating dairy cows were assigned randomly to two groups (control and MAP, n=8 each). Ovsynch treatment (Day 0: GnRH, Day 7: PG, Day 9: GnRH) was initiated at random stages of the estrous cycle (control) and an intravaginal polyurethane sponge impregnated with 300mg of MAP was inserted intravaginally in the MAP group at Day 0 and removed at Day 7 of the Ovsynch protocol (MAP treatment). Ovaries were scanned daily from Day 0 until the second GnRH treatment on Day 9 and from then every 6h for 36 h. Milk samples were collected three times weekly starting 17 days before the initiation of treatment to determine the stage of the cycle at the beginning of the Ovsynch protocol. Blood samples were collected to monitor estradiol (E2), progesterone (P4), LH, and 15-ketodihydro-PGF(2alpha) (PGFM) by RIA. Response to the first GnRH treatment varied with the stage of the cycle at the time of initiation of treatment, as cows in metestrous and late diestrous did not ovulate. In cows ovulating, growth rate of the new follicle was not affected by the addition of MAP. No treatment differences were found in E2 concentrations which reached a maximum at Day 9, consistent with the maximum follicular size. At Day 7, cows with luteal concentrations of P4 had increased concentrations of PGFM, but cows with basal P4 did not show an active release of prostaglandins. There were no treatment differences in the ovulatory response to the second GnRH-induced ovulation, with 11 of the 16 cows ovulating between 16 and 32 h. The addition of MAP to the Ovsynch protocol could not mimic the normal high progesterone levels needed to prevent premature ovulations in those cows with premature CL regression.