Saline-treated Cows Research Articles

Effects of bovine casein hydrolysate as a dry cow therapy on prevention and cure of bovine intramammary infection, milk production, and somatic cell count in the subsequent lactation

The primary objectives were to investigate the efficacy of bovine casein hydrolysate (bCNH) as a dry cow therapy at (1) preventing new intramammary infection (IMI) postpartum of all bacteria and coagulase-negative staphylococci (CNS), and (2) curing existing subclinical infections, mainly of CNS. The secondary objective was to measure the effects of bCNH on milk yield, composition, and somatic cell count (SCC) during the lactation postcalving. The trial was conducted as a randomized, blinded controlled experiment. Israeli Holstein dairy cows (n = 170) in first or higher lactations were recruited from 4 large commercial dairy herds. Cows were enrolled following clinical examination and bacteriological sampling of each quarter, which was the experimental unit. Random allocation was implemented at the cow level. All quarters of 100 cows were treated with 1 dose of bCNH (60 mg diluted in 20 mL of sterile solution) and those of 70 control cows were treated with saline solution. Clinical assessment of each cow's general appearance, teat-end leakage, and teat morphology was performed for 0, 1, 2, 3, 7, and 14 d after treatment, together with follow-up clinical observation and clinical examination of udder quarters. Quarter aseptic milk samples were obtained for bacteriological culture 48 h pretreatment, at time of treatment, and 3 and 5 d postcalving. Multivariable analyses were conducted to study the effects of bCNH on cure and prevention of IMI, adjusting for parity, farm, average of daily milk yield for 305 d, and average of monthly SCC values for 305 d of previous lactation. The odds of preventing IMI in cows treated with bCNH at dry-off were 2.15 times higher [95% confidence interval (CI): 1.15 to 4.00] than in cows treated with saline. Prevention was mostly of CNS. The odds of preventing CNS in cows treated with bCNH at dry-off were 2.20 times higher (95% CI: 1.58 to 3.07) than in control cows. The odds of curing IMI caused by CNS in cows treated with bCNH at dry-off were 4.80 times higher (95% CI: 0.75 to 30.75) than in saline-treated cows. Log SCC, adjusted to that of the previous lactation, was lower in the bCNH group compared with controls for 305 d in milk postcalving. The average milk yield per day for 305 d, adjusted to average daily milk yield of previous lactation, was higher by 2.1 kg in the bCNH group compared with controls (95% CI: 1.21 to 3.20). Clinical assessment of udders and cows posttreatment showed no negative effects of bCNH. Incidence of stillbirth, clinical mastitis, retained placenta, endometritis (5 to 12 d postcalving), ketosis, abortions, and reproduction did not differ between the 2 groups. Results suggest that a single intramammary administration of bCNH at dry-off effectively increases milk yield and lowers SCC, prevents new IMI during the dry period, and may be a beneficial alternative for curing existing IMI at dry-off, mainly by CNS.

Subclinical mastitis disrupts oocyte cytoplasmic maturation in association with reduced developmental competence and impaired gene expression in preimplantation bovine embryos.

Subclinical chronic mastitis was induced to examine the effects on oocyte developmental competence. Uninfected Holstein cows were intramammary administrated with serial (every 48h for 20 days) low doses of toxin of Staphylococcus aureus origin (Gram-positive; G+), endotoxin of Escherichia coli origin (Gram-negative; G-) or sterile saline (control). Follicular fluid of toxin- and saline-treated cows was aspirated from preovulatory follicles and used as maturation medium. Oocytes harvested from ovaries collected at the abattoir were matured and then fertilised and cultured for 8 days. The percentage of oocytes undergoing nuclear maturation, determined by meiotic nuclear stages, did not differ between groups. Cytoplasmic maturation, determined by cortical granule distribution, was affected by both toxins (PPPPTGS2) mRNA increased, whereas that of growth differentiation factor 9 (GDF9) decreased in matured oocytes. In addition, PTGS2 expression increased and POU class 5 homeobox 1 (POU5F1) expression decreased in 4-cell embryos developed from both G+ and G- oocytes. Thus, regardless of toxin type, subclinical mastitis disrupts oocyte cytoplasmic maturation and alters gene expression in association with reduced developmental competence.

Progesterone Profiles in the Caudal Vena Cava and Jugular Vein in Response to Pulsatile Luteinizing Hormone Stimulation Induced by GnRH Treatment During the Mid-luteal Phase in Lactating Dairy Cows

The aim of this study was to examine whether increased frequency of luteinizing hormone (LH) pulses influences luteal progesterone (P4) secretion by measuring progesterone concentrations at the secreted (caudal vena cava) and circulating levels (jugular vein) in lactating dairy cows. Cows received six intravenous administrations of 2.5 μg of GnRH (gonadorelin acetate, n=4) or 2 ml saline (n=3) at 1-h intervals on 12.4 ± 0.4 (mean ± SE) days after ovulation. Blood samples were collected from the caudal vena cava and jugular vein every 12 min for 12 h (6 h before and after treatment). During the 6 h after treatment, frequency of LH pulses (5.3 ± 0.3 and 3.0 ± 0.0 pulses/6 h) and mean LH concentration (0.50 ± 0.06 and 0.38 ± 0.05 ng/ml) were greater (P<0.05) in GnRH-treated cows than in saline-treated cows. Mean P4 concentration and amplitude of P4 pulses in the caudal vena cava during the 6 h after treatment were greater (P<0.05) in GnRH-treated cows than in saline-treated cows, but the frequency of P4 pulses was not different between the groups. Mean P4 concentration in the jugular vein during the 6 h after treatment was also higher (P<0.05) in GnRH-treated cows than in saline-treated cows (7.0 ± 1.3 and 5.4 ± 0.9 ng/ml). These results indicate that the increased frequency of LH pulses stimulates progesterone secretion from the functional corpus luteum and brings about higher P4 concentrations in the circulating blood in lactating dairy cows.

Characteristics and retention of luteal structures, extended postinsemination cycle, progesterone, and pregnancy-specific protein B in serum after human chorionic gonadotropin treatment of dairy cows

Our objectives were to determine characteristics (size, number, and stayability) of luteal structures formed in response to human chorionic gonadotropin (hCG) administered on d 7 after timed artificial insemination (AI) and the influence of hCG on returns to estrus and pregnancy outcome. Holstein cows (n=328), milked 3 times daily, previously inseminated at first service were assigned randomly to a completely randomized design consisting of 2 treatments when at least 1 corpus luteum (CL) was detected on d 7 after AI. Treatment consisted of 1,000IU hCG or 1mL of saline (control) administered i.m. Blood was collected and luteal structures were mapped and sized by transrectal ultrasonography on d 7, 14, 21, 28, and 32 after AI. Blood also was collected on d 60 in all pregnant cows. Treatment with hCG induced new luteal structures in 70% of cows, regardless of pregnancy status or number of pretreatment CL. Cows producing greater than the median 46kg of energy-corrected milk per day were less likely to respond to hCG. The number of total luteal structures per cow, original CL volume, and total luteal volume (original CL + new luteal structures) were increased by hCG. Progesterone concentration was greater in pregnant than nonpregnant cows on d 14 unless cows responded to hCG by forming new luteal structures. Concentrations of progesterone were greatest in pregnant, hCG-treated cows. Pregnancy per AI at d 32 or 60 after first AI was less in hCG- than saline-treated cows because pregnancy outcome for hCG cows that had only 1 pretreatment CL and failed to respond to hCG was only 55 to 61% of that observed in controls. Proportions of cows returning to estrus from 18 to 25d after AI were less in hCG than control cows but greater for cows returning >25d. Regardless of treatment, 25% of cows in both treatments retained at least 1 original CL to d 28 after AI and were not pregnant on d 32. Progesterone concentrations in these nonpregnant cows with retained CL between d 14 and 28 after AI were intermediate between nonpregnant cows that returned to estrus by d 25 and all pregnant cows. Concentrations of pregnancy-specific protein B were elevated in some of these nonpregnant, CL-retained cows, indicating early pregnancy loss. Retention of original luteal tissue in nonpregnant cows to d 28 after AI indicated that pregnancy had been initiated but failed, as verified by concentrations of progesterone and pregnancy-specific protein B.

Administration of human chorionic gonadotropin 7 days after fixed-time artificial insemination of suckled beef cows1

We determined the effects of administering hCG 7 d after a fixed-time AI (TAI) on ovarian response, concentrations of progesterone, and pregnancy rates in postpartum suckled beef cows. Cows at 6 locations received 100 microg of GnRH (Fertagyl, Intervet Animal Health, Millsboro, DE) and a controlled internal drug release (CIDR) device (CIDR EAZI-Breed, Pfizer Animal Health, New York, NY), followed in 7 d by 25 mg of PGF(2alpha) (Lutalyse, Pfizer Animal Health) and CIDR removal. At 64 h after CIDR removal, cows received an injection of GnRH and AI (d 0), and then were stratified by days postpartum and parity and assigned randomly to 2 treatments administered 7 d after TAI: 1) 1 mL of saline (saline; n = 252); or 2) 1,000 IU of hCG (Chorulon, Intervet Animal Health; n = 254). Blood samples were collected on d -21, -10, and 33 relative to TAI (d 0) at all locations, on d 7 and 68 at 5 locations, and on d 14 at 1 location to determine concentrations of progesterone. Transrectal ultrasonography was used to determine pregnancy status on d 33 and 68 at all locations, to monitor response of follicles and corpora lutea (CL) in response to treatment at 1 location (n = 106) on d 7 and 14, and to determine the number of CL present in pregnant cows on d 33 in 3 locations (n = 130). Pregnant cows had greater (P < 0.05) concentrations of progesterone at the time of treatment (d 7) compared with nonpregnant cows (3.7 +/- 0.1 vs. 2.6 +/- 0.2 ng/mL, respectively). On d 14, hCG-treated cows had a greater (P < 0.05) volume of luteal tissue (12.1 +/- 0.5 vs. 7.3 +/- 0.5 cm(3), respectively) and greater concentrations of progesterone (6.8 +/- 0.4 vs. 5.4 +/- 0.5 ng/mL, respectively) compared with saline-treated cows. A greater (P < 0.01) percentage of hCG-treated cows (90.6%) had multiple CL on d 14 compared with saline-treated cows (0%), and a greater percentage of pregnant cows treated with hCG (74.6%) had multiple CL on d 33 compared with saline-treated cows (3.0%). Pregnancy rates of hCG-treated cows (56.3%) tended (P = 0.07) to differ from those of saline-treated cows (50.0%). Concentrations of progesterone in pregnant hCG-treated cows were greater (P < 0.05; 7.7 +/- 0.3 vs. 5.8 +/- 0.3 ng/mL, respectively) on d 33 than for pregnant saline-treated cows, but were similar between treatments on d 68 (7.2 +/- 0.3 vs. 6.7 +/- 0.4 ng/mL, respectively). We conclude that treatment with hCG increased the volume of luteal tissue on d 14 and concentrations of progesterone on d 14 and 33 after TAI. Treatment with hCG tended to increase pregnancy rates at 5 of 6 locations from 1.1 to 27 percentage points (average = 10.2) compared with saline, but cumulative pregnancy rates determined on d 68 after TAI were similar between treatments.

Postinsemination treatment of primiparous and multiparous cows with cloprostenol failed to affect ovulation and pregnancy rate in dairy cattle

Previous studies have demonstrated the facilitating effect of a single cloprostenol treatment postinsemination on ovulation and pregnancy rate in dairy cattle and Italian buffalos. This study was conducted to test the effects of 500 μg cloprostenol given intramuscularly immediately postinsemination to 55 primiparous and 60 multiparous Holstein cows ( Bos taurus; TR) of a typical dairy operation in East Germany and to compare them with 57 primiparous and 48 multiparous saline-treated cows (CON). Animals of the TR and CON groups did not differ or only differed marginally for age at treatment, interval calving–treatment, lactation number, milk production on the day of treatment, body condition score, and their peri- and postparturient case histories. All animals were clinically and reproductively healthy on the day of treatment. They were inseminated once 12 h after the onset of estrus, scanned 24 h after insemination to confirm ovulation, and tested for pregnancy by transrectal palpation between Days 42 and 48 postinsemination. Treatment did not affect the number of cows ovulating. The overall combined pregnancy rate (PR) was 47.3%. Pregnancy rate did not differ statistically between TR and CON (46.1% vs. 48.6%; P > 0.05). In conclusion, this study failed to demonstrate beneficial effects of a postinsemination treatment of primiparous and multiparous cows with cloprostenol on ovulation and PR in a typical dairy cattle operation in East Germany.

First Service Pregnancy Rates Following Post-AI Use of hCG in Ovsynch and Heatsynch Programmes in Lactating Dairy Cows

Lactating dairy cows (n = 667) at random stages of the oestrous cycle were assigned to either ovsynch (O, n = 228), heatsynch (H, n = 252) or control (C, n = 187) groups. Cows in O and H groups received 100 microg of GnRH agonist, i.m. (day 0) starting at 44 +/- 3 days in milk (DIM), and 500 microg of cloprostenol, i.m. (day 7). In O group, cows received 100 microg of GnRH (day 9) and were artificially inseminated without oestrus detection 16-20 h later. In H group, cows received 1 mg oestradiol benzoate (EB) i.m., 24 h after the cloprostenol injection and were artificially inseminated without oestrus detection 48-52 h after the EB injection. Cows in C group were inseminated at natural oestrus. On the day of artificial insemination (AI), cows in all groups were assigned to subgroups as follows: human Chorionic Gonadotrophin (O-hCG) (n = 112), O-saline (n = 116), H-hCG (n = 123), H-saline (n = 129), C-hCG (n = 94) and C-saline (n = 93) subgroups. Cows in hCG and saline subgroups received 3000 IU hCG i.m. and or 10 ml saline at day 5 post-AI (day 15), respectively. Pregnancy status was assessed by palpation per rectum at days 40 to 45 after AI. The logistic regression model using just main effects of season (summer and winter), parity (primiparous and pluriparous), method(1) (O, H and C) and method(2) (hCG and saline) showed that all factors, except method(1), were significant. Significant effects of season (p < 0.01), hCG and parity (p < 0.01), and a trend of parity and season (p < 0.1) were detected. A clear negative effect of warm period on first service pregnancy rate was noted (p < 0.01). The pregnancy rate was the lowest in the H protocol during warm period (p < 0.05). Treatment with hCG 5 days after AI significantly improved pregnancy rates in those cows that were treated with the H protocol compared with saline treatments (41.5% vs 24.8%; p < 0.01). O and H were more effective in primiparous than in pluriparous cows (46.1% vs 29.9%; p < 0.1 and 43.6% vs 24.6%; p < 0.01). First service pregnancy rates were higher in primiparous hCG-treated than in pluriparous hCG-treated cows (57.9% vs 32.3%; p < 0.01). The pregnancy rate was higher for the hCG-treated cows compared with saline-treated cows during warm period (37.9% vs 23.6%; p < 0.001).

CASE STUDY: Naloxone Increases Serum Calcium Concentrations after Parturition in Multiparous Holstein Cows

This experiment was conducted to investigate the effect of naloxone, an opioid receptor antagonist, within the first 6 h postpartum in Holstein cows on serum Ca concentrations. Six hours after parturition and first milking, cows were assigned randomly to receive (i.v.) either saline (n = 6) or 0.01 mg/kg of BW of naloxone (n = 6). Blood samples were collected at 10 min intervals from 10 min before until 50 min after treatments. Mean serum Ca was not different (P > 0.05) between groups before treatments. Naloxone caused a transient increase (P < 0.05) in serum Ca concentrations within 20 min after bolus administration. Mean serum Ca was not altered (P = 0.30) in saline-treated cows. The results provide evidence that endogenous opioid peptides play a role in Ca homeostasis, and that their action is mediated through opioid receptors.

Dopamine Antagonist Alters Serum Cortisol and Prolactin Secretion in Lactating Holstein Cows

The role of dopamine in regulating glucocorticoid and prolactin secretion was investigated in lactating Holstein cows by characterizing serum cortisol and prolactin responses to fluphenazine, a dopamine receptor antagonist. Twelve anovulatory cows received an intravenous bolus injection of either saline (n=6) or 0.3mg of fluphenazine/kg of body weight (n=6) in wk 2 postpartum. Blood samples were collected every 30min for 4h before and 4h after saline or fluphenazine injection. Serum progesterone concentration was 0.13±0.1ng/mL and did not differ between groups. No difference in serum cortisol concentrations was detected between groups before treatments. Fluphenazine increased serum cortisol concentrations within 30min after fluphenazine administration (>30ng/mL) and concentrations remained elevated throughout the sampling period. Cortisol remained unchanged in saline-treated cows (<10ng/mL). Prolactin concentrations also increased after fluphenazine administration (103.1±3.1ng/mL), but were unaffected by saline (18±3.1ng/mL). Prolactin concentrations remained elevated throughout the sampling period in fluphenazine-treated cows. Our results indicated that a dopamine antagonist increased cortisol, suggesting that endogenous dopamine, at least in part, regulates cortisol and prolactin secretion. These effects are regulated through dopamine receptors in anovulatory lactating dairy cows during the early postpartum period.

Hormonal and Lactational Responses to Growth Hormone-Releasing Hormone Treatment in Lactating Japanese Black Cows

Ten multiparous lactating Japanese Black cows (beef breed) were used to evaluate the effects of bovine growth hormone-releasing hormone (GHRH) analog on milk yield and profiles of plasma hormones and metabolites. The cows received 2 consecutive 21-d treatments (a daily s.c. injection of 3-mg GHRH analog or saline) in a 2 (group)×2 (period) Latin square crossover design. The 5 cows in group A received GHRH analog during period 1 (from d 22 to 42 postpartum) and saline during period 2 (from d 57 to 77 postpartum), and those in group B received saline and GHRH analog during periods 1 and 2, respectively. Mean milk yield decreased in saline treated compared with that during the 1-wk period before treatment 7.4 and 19.1% during periods 1 (group B) and 2 (group A), respectively. Treatment with GHRH analog increased milk yield 17.4% (period 1, group A) and 6.3% (period 2, group B). Treatment with GHRH analog induced higher basal plasma concentrations of growth hormone (GH), insulin-like growth factor-1 (IGF-1), insulin, and glucose compared with saline-treated cows. In glucose challenge, the GHRH analog-treated beef cows had greater insulin secretion than the saline-treated beef cows. In insulin challenge, however, there were no significant differences in the areas surrounded by hypothetical lines of basal glucose concentrations and glucose response curves between GHRH analog- and saline-treated cows. These results demonstrate that GHRH analog treatment facilitates endogenous GH secretion in lactating Japanese Black cows, leading to increases in milk yield and plasma concentrations of IGF-1, insulin, and glucose.

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 (40μg/h; n=7) or saline (2mL/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 PGF2α, 12h apart. In experiment 2, 14 lactating cows (7 to 12 d postpartum) received LH (40μg/h; n=7) or saline (1mL/h; n=7) in hourly pulses for 7 d, beginning 24h after start of the first follicular wave. Daily samples were used to determine serum concentrations of progesterone (P4), estradiol-17β(E2), LH, and FSH. Profiles of LH were determined from blood samples collected at 12-min intervals for 8h 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.

Oxytocin induces PGE 2 release from bovine cervical mucosa in vivo

Oxytocin receptor (OTR) concentrations in bovine cervical mucosa rise steeply a few days before estrus to high concentrations and fall rapidly after estrus. To study the physiological role of these OTR, the effect of OT on the release of PGE 2 from the cervical mucosa of periestrous cows in vivo was determined by inserting bags made of dialysis tubing containing isooncotic saline solution in the endocervix for two 2-h periods, a fresh bag for each period. During the first period no treatment was given, during the second period OT (100 IU) or saline was injected i.m. PGE 2 content in the second bag was significantly greater in OT-treated cows than in saline-treated cows. In a second experiment cervical resistance to stretch, achieved by distention of a balloon inside the cervical canal, was measured in periestrous cows before and 10 h after i.m. injection of OT, or endocervical application of 2.5 mg PGE 1 in a jelly, or the inactive jelly. A significant reduction in the resistance was achieved with both OT and PGE 1; in the doses given the effect of PGE 1 was longer lasting than that of OT.

Effect of an acute ergotamine challenge on reproductive hormones in follicular phase heifers and progestin-treated cows

The objective of this research was to determine if ergotamine, an ergopeptine alkaloid isolated from Neotyphodium-infected grasses and associated with toxicoses in livestock, altered plasma concentrations of reproductive hormones in follicular phase heifers and in cows given a progestin implant. In Experiment 1, blood was sampled for 8 h from four cycling heifers 2 days after synchronized luteolysis. Heifers were treated with ergotamine tartrate (19 μg/kg) i.v. or saline vehicle in a simple cross-over design after 1 h of pre-treatment blood sampling. Heifers received oxytocin (100 USP units) i.v. 4 h after ergotamine or saline treatment. Ergotamine reduced ( P<0.01) prolactin concentrations from 1 to 4 h post-treatment and increased ( P<0.01) 13,14-dihydro-15-keto prostaglandin F 2α (PGFM) concentrations from 2 to 5 h post-treatment. A PGFM response to oxytocin was not detected. In Experiment 2, blood was sampled for 8 h from six cycling cows 10 days after receiving a s.c. norgestomet implant. Cows were treated i.v. with ergotamine (20 μg/kg) or saline in a simple cross-over design after 1 h of pre-treatment blood sampling. Cows received gonadorelin (GnRH, 100 μg) i.v. 1 h after ergotamine or saline. Cows received oxytocin (100 USP units) i.v. 4 h after ergotamine or saline treatment. Ergotamine reduced ( P<0.01) serum prolactin concentrations by 120 min after treatment, with prolactin returning to pre-treatment concentrations by 200 min after treatment. Saline-treated cows had lower ( P<0.01) prolactin by 280 min after treatment. Ergotamine-treated cows had higher ( P<0.01) PGFM concentrations compared to saline-treated cows 120–240 min after treatments, but the groups exhibited similar increases in PGFM after oxytocin. Plasma LH and FSH concentrations increased to peaks 100–120 min after GnRH for both groups. However, the LH response to GnRH was greater ( P<0.01) for ergotamine-treated cows. In summary, ergotamine lowered prolactin and elevated PGFM concentrations in follicular phase heifers and cows on norgestomet therapy. Ergotamine increased the LH response to exogenous GnRH in cows with norgestomet implants. These data highlight the potential of ergopeptine alkaloids to affect reproduction through altered endocrine function.

Effect of Naloxone on Serum Luteinizing Hormone Concentration in Anovulatory Holstein Cows During the Early Postpartum Period

This experiment was conducted to investigate the effect of naloxone (NAL), an opioid receptor antagonist, on pituitary LH secretion in anovulatory Holstein cows during the early postpartum period when cows were expected to be in negative net energy balance. Twenty-three cows (11 primiparous) received either saline ( n = 12) or 1 mg/kg BW NAL i.v. ( n = 11) on Day 14 or 15 postpartum. Jugular blood samples were collected at 15-min intervals for 2 hr before and 2.5 hr after NAL or saline. All cows received 3 ug gonadotropin releasing hormone (GnRH) at 2.5 hr post-NAL or -saline and blood collection was continued for 1 hr. Mean serum progesterone concentration was 0.33 ± 0.2 ng/ml. Mean net energy balance for all cows was -5.5 ± 0.6 Mcal/day. Naloxone caused a transient increase (P < 0.05) in serum LH concentrations in both primi- and multiparous cows within 45 min after administration. In contrast, serum LH concentrations remained unchanged in saline-treated cows. GnRH increased (P < 0.05) LH and there was no effect of treatment. These results suggest that modulation of LH secretion, at least in part, may be mediated via endogenous opioids in dairy cows before first postpartum ovulation.

The synchrony of prostaglandin-induced estrus in cows was reduced by pretreatment with hCG

The induction of optimal synchrony of estrus in cows requires synchronization of luteolysis and of the waves of follicular growth (follicular waves). The aim of this study was to determine whether hormonal treatments aimed at synchronizing follicular waves improved the synchrony of prostaglandin (PG)-induced estrus. In Experiment 1, cows were treated on Day 5 of the estrous cycle with saline in Group 1 (n=25; 16 ml, iv, 12 h apart), with hCG in Group 2 (n=27; 3000 IU, iv), or with hCG and bovine follicular fluid (bFF) in Group 3 (n=21; 16 ml, iv, 12 h apart). On Day 12, all cows were treated with prostaglandin (PG; 500 μg cloprostenol, im). In Experiment 2, cows were treated on Day 5 of the estrous cycle with saline (3 ml, im) in Group 1 (n=22) or with hCG (3000 IU, iv) in Group 2 (n=20) and Group 3 (n=22). On Day 12, the cows were treated with PG (500 μg in Groups 1 and 2; 1000 μg in Group 3). Blood samples for progesterone (P4) determination were collected on Day 12 (Experiment 1) or on Days 12 and 14 (Experiment 2). Cows were fitted with heat mount detectors and observed twice a day for signs of estrus. Four cows in Experiment 1 (1 cow each from Groups 1 and 2; 2 cows from Group 3) had plasma P4 concentrations below 1 ng/ml on Day 12 and were excluded from the analyses. In Experiment 1, cows treated with hCG or hCG+bFF had a more variable (P=0.0007, P=0.0005) day of occurrence of and a longer interval to estrus (5.9±0.7 d, P=0.003 and 6.2±0.8 d, P=0.005) than saline-treated cows (3.4±0.4 d). The plasma P4 concentrations on Day 12 were higher (P<0.0001) in hCG- and in hCG+bFF-treated cows than in saline-treated cows (9.4±0.75 and 8.5±0.75 vs 4.1±0.27 ng/ml), but there was no correlation (P>0.05) between plasma P4 concentrations and the interval to estrus. In Experiment 2, cows treated with hCG/500PG and hCG/1000PG had a more variable (P=0.0007, P=0.002) day of occurrence of and a longer interval to estrus (4.2±0.4 d, P=0.04; 4.1±0.4 d, P=0.03) than saline/500PG-treated cows (3.2±0.1 d). The concentrations of plasma P4 on Days 12 and 14 of both hCG/500PG- and hCG/1000PG-treated cows were higher (P<0.05) than in saline/500PG-treated cows (7.3±0.64, 0.7±0.08 and 7.7±0.49, 0.7±0.06 vs 5.3±0.37, 0.5±0.03 ng/ml). The concentrations of plasma P4 on Days 12 or 14 and the interval to estrus were not correlated (P>0.05) in any treatment group. The concentrations of plasma P4 on Days 12 and 14 of hCG/500PG- or hCG/1000PG-treated cows were correlated (r=0.65, P<0.05; r=0.50, P<0.05). This study indicated that treatment of cows with hCG on Day 5 of the estrous cycle reduced the synchrony of PG-induced estrus and that this reduction was not due to the failure of luteal regression.

Enhanced Antigen-Specific Responses in Bovine Mammary Glands Following Administration of Interleukin-2

This study examined the feasibility of using interleukin-2 as a vaccine adjuvant to enhance specific immunity in the bovine mammary gland. In trial 1, cows were immunized by intramammary infusion of keyhole limpet hemocyanin with either saline (n=3) or interleukin-2 (n=3) as adjuvants. In trial 2, cows were immunized by intramuscular injection near the supramammary lymph node with keyhole limpet hemocyanin in conjunction with saline (n=4). Freund's incomplete adjuvant (n=4). or interleukin-2 (n=4). Local immunization with interleukin-2 as an adjuvant significantly increased antibody titers in milk over preimmunization levels and levels in saline-treated cows. The use of Freund's incomplete adjuvant and interleukin-2 as adjuvants in cows that were immunized systemically enhanced both sera and lacteal antibodies to keyhole limpet hemocyanin. However, cows that were administered interleukin-2 responded more quickly than those given Freund's incomplete adjuvant. Only those cows that received interleukin-2 as an adjuvant demonstrated significant increases in blood lymphocyte proliferation to keyhole limpet hemocyanin, pokeweed mitogen, and interleukin-2. The results of these two trials suggest that immunization with interleukin-2 as an adjuvant may be more effective than Freund's incomplete adjuvant in enhancing specific immunity in the bovine mammary gland and may possibly be an effective adjuvant in mastitis immunization protocols.

Effect of gonadotropin-releasing hormone on estrus, ovulation, and ovum cleavage rates of dairy cows.

In a 2 x 2 factorial experiment, 110 Holstein cows (55 first-breeding and 55 repeat-breeding), free of genital abnormalities, were injected i.m. at the time of insemination with either saline solution or 100 micrograms of GnRH. Blood samples were drawn from the tail vein or artery of 22 cows (10 first- and 12 repeat-breeding) immediately before GnRH injection and again 1 and 2 h later to determine whether the GnRH induced the release of LH. The GnRH caused LH release in 18 of 22 cows, with a greater (P < .05) mean concentration of LH than that in saline-treated cows at 1 h (2.3 vs 7.0 ng/mL) and 2 h (2.5 vs 6.0 ng/mL) after injection. Length of estrus and time of ovulation were calculated from estrus checks and ovarian palpations per rectum at 8-h intervals. The GnRH injections produced no change in duration of estrus (19.2 h) or time of ovulation postestrus (9.5 h). The cows were slaughtered 41 to 90 (mean = 60) h after ovulation to determine the ovum cleavage rate and the number of accessory sperm in the zona pellucida. The GnRH treatment increased the incidence of twin ovulations but did not increase the number of accessory sperm or improve the proportion of ova that cleaved in either first-service or repeat-breeding cows.

Pulsatile infusion of gonadotropin-releasing hormone initiates luteal activity in nutritionally anestrous beef cows.

Thirty-five nonlactating Hereford and Hereford x Angus cows weighing 469 +/- 8 kg, with a body condition score (BCS) of 5.5 +/- .6 and exhibiting normal estrous cycles, were fed to lose 1% of BW per week (n = 27) or to maintain BW (n = 8). Blood samples were collected every 7 d to monitor luteal activity and BW and BCS were recorded every 2 wk. When concentrations of progesterone in plasma were < 1 ng/mL for three consecutive weeks, anestrous cows (BCS, 3.1 +/- .7; BW loss, 24 +/- 5%) were assigned to pulses (i.v.) of saline (2 mL every hour), GnRH-4 (2 micrograms of GnRH every 4 h), or GnRH-1 (2 micrograms of GnRH every hour). Cows were confined to stalls for 4 d and two jugular cannulas were inserted 2 d before infusion of GnRH. Infusions began on d 0 and continued through d 14. Progesterone was quantified in daily blood samples and LH was quantified in samples collected every 10 min for 4 h on d-1, 0, 2, 4, 6, 8, 10, 12, 14, and 15. On d 16, cows were returned to pasture and blood samples were collected every 2nd d through d 30. Pulsatile infusion of GnRH increased (P < .05) the amplitude of LH pulses but did not affect pulse frequency. During infusion of GnRH every hour or every 4th h, concentrations of LH in serum were increased compared with those in saline-treated cows (P < .001), and cows receiving GnRH hourly had greater (P < .005) LH than cows given GnRH every 4 h.(ABSTRACT TRUNCATED AT 250 WORDS)

Ovarian Follicular Waves in Dairy Cows After Administration of Gonadotropin-Releasing Hormone at Estrus

A crossover design experiment was conducted to examine the effects of GnRH on hormonal concentrations and changes in ovarian structures of lactating dairy cows during the estrous cycle. Cows were assigned randomly to receive either 100μg of GnRH or saline 12h after estrus (d 0) was first observed. Ultrasonographic examinations of the ovaries performed daily throughout the estrous cycle detected either three (n = 7) or four (n = 6) follicular waves. Transient increases in FSH generally preceding the follicular wave containing the dominant (preovulatory) follicle, and the emergence of the dominant follicle before the subsequent estrus occurred later in GnRH-treated than in saline-treated cows with either three or four follicular waves. Day of emergence of dominant follicles within follicular waves was preceded 83% of the time by a transient increase in FSH and was followed consistently by increased serum estradiol-17β which generally reached peak concentrations concomitant with the peak diameter of the dominant follicle. Although clearly defined pulses were detected in 19 out of 26 sampling periods on d 7 and 14, number of FSH pulses and percentage of cows with pulses of FSH were similar in GnRH-treated and saline-treated cows with three or four follicular waves. In conclusion, treatment of cows with GnRH 12h after the onset of estrus delayed the appearance of the next ovulatory follicle in cows with either three or four follicular waves. Regardless of treatment, emergence of dominant follicles was preceded in most cases by a transient increase in FSH and followed consistently by increased estradiol-17β.

Ibuprofen treatment of endotoxin-induced mastitis in cows

Summary Ibuprofen treatment was compared with saline solution treatment in an endotoxin-induced experimental model of bovine mastitis. Acute mastitis was induced in healthy lactating Holstein cows (n = 12) by intrammamary inoculation of 1 mg of Escherichia coli 026:B6 lipopolysaccharide in a single quarter per cow. Cows were assigned at random to ibuprofen (25 mg/kg of body weight, iv, n = 6) or 0.9% sodium chloride solution control (1.25 ml/kg, iv, n = 6) treatment groups. Ibuprofen or saline solution was administered once, 2 hours after endotoxin administration. The clinical course of endotoxin-induced mastitis and hematologic, clinical biochemical, and plasma mineral changes were monitored and compared between ibuprofen-treated and control cows. Clinical monitoring and blood sample collection were performed at 0, 2, 4, 6, 8, 12, 24, 48, 96, and 192 hours after endotoxin challenge. Rectal temperature and heart and respiratory rates were significantly (P ≤ 0.05) increased in saline treated cows, compared with cows treated with ibuprofen. Blood eosinophil count and serum phosphorus, sodium, and total carbon dioxide concentrations were significantly (P ≤ 0.05) decreased in saline-treated cows, compared with cows treated with ibuprofen. Ibuprofen treatment did not significantly change ruminations per minute, electrical conductivity of milk, quarter size, or quarter inflammation. The remaining hematologic, serum biochemical, plasma mineral, and coagulation values also were not changed significantly in response to ibuprofen treatment. Untoward effects attributed to ibuprofen administration were not observed. These results indicate that ibuprofen may provide empiric relief of clinical signs of coliform-induced mastitis.