Circannual changes in progesterone secretion in intact ewes, luteinizing hormone secretion in ovariectomized estradiol-implanted ewes, and prolactin secretion in three sheep breeds anticipated to differ in seasonality of reproduction.

Changes in progesterone secretion in intact ewes (7 or 9 per breed) and luteinizing hormone secretion in ovariectomized, estradiol-implanted ewes (9 or 10 per breed) were monitored for 12 mo in Suffolk, tropically adapted St. Croix, and OOS ewes. The OOS line is a composite population of 50% Dorset, 25% Rambouillet, and 25% Finnish Landrace breeding that was selected for 10 yr for ability to lamb in October and early November. Ewes were isolated from rams, and blood samples were collected twice weekly. Circulating prolactin concentrations were also determined from blood samples collected near the summer and winter solstice and vernal and autumnal equinox. Intact OOS ewes entered anestrus later, began the subsequent breeding season sooner, and had a shorter seasonal anestrus than Suffolk and St. Croix ewes (P ≤ 0.005). St. Croix ewes did not differ from Suffolk ewes in date of onset or cessation of breeding or duration of anestrus (P ≥ 0.06). Breed differences in duration of luteinizing hormone inhibition in ovariectomized ewes were essentially identical to those observed for duration of anestrous. Prolactin concentrations varied during the year: annual changes were larger in relatively seasonal Suffolk ewes than in tropically-derived St. Croix ewes (P<0.01), and OOS ewes were intermediate to, and tended to differ from (P<0.10), the other two breeds. We conclude that OOS ewes developed by selection for fertility in spring matings had an abbreviated seasonal anestrus that is one of the shortest ever reported for temperate breeds, and that tropical St. Croix sheep did not have a shorter seasonal anestrus than Suffolk sheep under temperate conditions and ram isolation.

Tocopherol induced angiogenesis in placental vascular network in late pregnant ewes.

BACKGROUND: Tocopherols have biphasic, proangiogenic and antiangiogenic therapeutic effects. The objective of this clinical trial was to clarify tocopherol's placental angiogenic potential in late pregnant ewes following oral supplementation. METHODS: Eighteen pregnant ewes during late gestation were selected for this study. Ewes were given oral supplementation of 500 mg of alpha-tocopherol (aT; N=6) or 1000 mg of gamma-tocopherol (gT; N=7) or placebo (CON; N=5) once daily from 107 to 137 days post breeding. Serum was obtained at weekly intervals and tissue samples were obtained at the end of supplementation to: 1) evaluate tocopherol concentrations in serum, uterus and placentome; 2) evaluate relative mRNA expressions of Vascular Endothelial Growth Factor (VEGF), Placental Growth Factor (PlGF), endothelial Nitric Oxide Synthase (eNOS) and Hypoxia Inducible Factors (HIF) in uterus, caruncle and cotyledon; 3) analyze the morphometry of the placental vascular network. RESULTS: Supplementation of aT or gT resulted in increased concentrations in serum, placentome and uterus compared to control (P<0.05). In aT group, mRNA expressions of PlGF, eNOS and HIF-1alpha in cotyledon were greater than the CON group. In gT group, mRNA expressions of VEGF, eNOS, HIF-1 alpha and HIF-2 alpha in caruncle and uterus, and HIF-1alpha in cotyledon, were greater than the CON group. Morphometry analysis revealed increased angiogenesis in the supplemented groups. CONCLUSION: Daily oral supplementation of aT or gT increased angiogenesis in the placental vascular network in pregnant ewes during late gestation. Increase in placental angiogenesis may provide nutrients required for the development and growth of fetus during late pregnancy.

A field study of the effects of a monovalent Leptospira borgpetersenii serovar Hardjo strain hardjobovis vaccine administered with oxytetracycline on reproductive performance in beef cattle.

OBJECTIVE: To determine whether vaccination with a monovalent Leptospira borgpetersenii serovar Hardjo strain hardjobovis vaccine coupled with parenteral long-acting oxytetracycline treatment would improve the reproductive performance of beef cows. DESIGN: Randomized controlled field trial. ANIMALS: 1,446 Angus-cross beef cows in 8 locations. PROCEDURES: Cows were given 2 doses, 4 weeks apart, of vaccine (treatment; n=741) or placebo (control; 705). Cows in the treatment group were also given a single dose of a long-acting oxytetracycline formulation (20 mg/kg [9.1 mg/lb], SC) at the time of booster vaccination. Estrus synchronization was performed, followed by fixed-time artificial insemination; bulls were introduced 14 days after insemination. Serum and urine samples were obtained on a random subset of cows (n=194) for detection of serologic titers and leptospiruria, and locations were categorized as positive or negative for leptospirosis on the basis of detection of leptospiruric cows. RESULTS: No differences in pregnancy and calving rates between treatment and control groups were detected. Pregnancy rate following artificial insemination was lower among cows in locations positive for leptospirosis than among cows in locations negative for leptospirosis; however, overall pregnancy rate, calving rate following artificial insemination, and overall calving rate did not differ between groups when cows were grouped on the basis of location leptospirosis status. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that under the conditions of the present study, administration of a monovalent Leptospira vaccine in conjunction with systemic administration of oxytetracycline did not significantly improve reproductive performance of beef cows.

Effect of breed and sperm concentration on the changes in structural, functional and motility parameters of ram-lamb spermatozoa during storage at 4 degrees C.

The objectives of this study were (1) to determine the changes in structural, functional and motility parameters of ram-lamb semen stored at two different concentrations at 4 degrees C for 8 days in egg-yolk based extender and (2) to determine the effect of breed of ram-lambs on the changes in structural, functional and motility parameters of ram-lamb semen from different breeds stored at two different concentrations at 4 degrees C for 8 days in egg-yolk based extender. Two different concentrations suitable for laparoscopic and cervical insemination were employed in this experiment. A total of 14 ram-lambs (Polled Dorset-5, Suffolk-5, Katahdin-4) with satisfactory breeding potential were selected. Semen samples were collected by electro-ejaculation. Semen samples were extended to 50 and 200 million sperm per ml with a commercial egg yolk based extender (Triladyl, Minitube of America, Verona, WI, USA) at room temperature and were stored at 4 degrees C. The sperm DNA fragmentation index (DFI), percentages of high mitochondrial membrane potential (hMMP) and plasma membrane integrity (PMI) were assessed using flow cytometry as part of structural and functional parameters on Days 0, 1, 4, 6, and 8. A computer assisted sperm analyser (HTM-IVOS, Version 10.8, Hamilton Thorne Research, Beverly, MA, USA) was used to assess the sperm motility parameters on Days 0, 1, 4, 6, and 8. PROC MIXED procedure was used to determine the effect of days of storage, concentration and breed. The concentration and days of storage significantly affected the sperm structural, functional and motility parameters (P<0.0001). Significant concentration x days of storage interaction was found for all structural and functional parameters. There was a significant concentration x days of storage interaction for average path velocity, curvilinear velocity, straightness and linearity. Overall changes in the sperm structural, functional and sperm motility parameters over the storage period were less dramatic in the 200 x 10(6) ml(-1) concentration when compared to 50 x 10(6) ml(-1) concentration. The hMMP and total progressive motility were influenced by breed. In conclusion, the quality of structural, functional and motility parameters declined as days of storage were increased and the magnitude of changes in the parameters was less dramatic at the higher concentration.

Association of classical semen parameters, sperm DNA fragmentation index, lipid peroxidation and antioxidant enzymatic activity of semen in ram-lambs.

The objective was to determine relationships among classical semen characteristics, sperm chromatin structure assay (SCSA), lipid peroxidation and antioxidant enzymatic activity in ram-lamb semen. Fifty-seven ram-lambs were electroejaculated, and routine semen evaluation was conducted (as part of a breeding soundness evaluation). The percentage of sperm DNA fragmentation index (%DFI) and the percentage of sperm with abnormally high DNA stainability (HDS; immature spermatozoa) were determined by SCSA using the metachromatic properties of acridine orange. Semen was centrifuged at 800 x g for 15 min to separate spermatozoa and seminal plasma and the aliquots were stored at -70 degrees C until analyzed. Lipid peroxidation, superoxide dismutase (SOD), and glutathione peroxidase (GPx) levels in seminal plasma and spermatozoa were measured by spectrophotometric assays. The classical semen parameters were negatively related to lipid peroxidation and GPx activity in spermatozoa; motility and morphology were negatively related to %DFI (P < 0.05). Based on Kruskal-Wallis pair-wise comparison of median values among breeding soundness outcome groups, %DFI was lower in the satisfactory group compared to other groups (P < 0.05) and the lipid peroxidation and GPx activity in seminal plasma and spermatozoa were lower in satisfactory and questionable groups (P < 0.05). However, the SOD was lower in the unsatisfactory group (P < 0.05). In summary, classical semen parameters were negatively related to % DFI, lipid peroxidation and GPx activity in ram-lamb spermatozoa and seminal plasma. There were indications that SOD and GPx have crucial protective roles against the toxic effect of reactive oxygen species (ROS) in ram-lamb semen.

Economic implications of bovine leukemia virus infection in mid-Atlantic dairy herds.

OBJECTIVE: To determine the baseline costs of bovine leukemia virus (BLV) infection, including costs of clinical disease and subclinical infection, in a dairy herd representative of the mid-Atlantic region and compare these costs with the cost of a test-and-manage BLV control program. DESIGN: Stochastic spreadsheet model. SAMPLE POPULATION: A commercial Holstein dairy herd with 100 milking cows. PROCEDURES: A spreadsheet model was developed. The overall cost of infection included the cost of clinical disease (ie, lymphosarcoma [LS]) and the effects of subclinical infection on milk production and premature culling. Model input values and distributions were designed to reflect economic conditions in the mid-Atlantic region. Relative costs of infection and control were calculated for infection prevalences of 20, 50, and 80%. RESULTS: Estimated mean cost to the producer per case of LS was 412 dollars; for a herd with a 50% prevalence of BLV infection, annual incidence of LS was 0.66. Mean annual cost of subclinical infection at a 50% prevalence of infection was 6,406 dollars. Mean annual cost of a test-and-manage control program was 1,765 dollars. The cost of clinical disease and subclinical infection varied substantially with the prevalence of infection, whereas the cost of control varied with herd size. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that a basic BLV control program may be economically beneficial in herds in which the prevalence of BLV infection is > or = 12.5%. Farm-specific considerations may factor prominently when weighing the costs and benefits of an individual BLV control program.

Comparison of culling rates among dairy cows grouped on the basis of serologic status for bovine leukemia virus.

OBJECTIVE: To determine the association between serologic status for bovine leukemia virus (BLV) and culling rates by use of survival times in a commercial Holstein dairy herd. DESIGN: Longitudinal study. ANIMALS: 593 milking cows. PROCEDURE: Cattle were tested for antibodies against BLV by use of agar gel immunodiffusion or ELISA 4 times each year from 1989 to 1993 and then annually through 1999. Dates of birth, first calving, and culling or death were obtained from Dairy Herd Improvement Association records. Most cows were enrolled in the study on the date of first calving. Survival times were compared among seropositive, seronegative, and seroconverted cows with the Kaplan-Meier method and a Cox regression model stratified on the basis of year of birth. RESULTS: Complete records were available for 593 of 685 (87%) cattle in the dairy herd during the study period. Median survival time for all cows was 31.7 months. Survival times, which correspond to cull rates, did not differ significantly between seropositive and seronegative cattle, whereas cattle that seroconverted during the study had a significantly longer survival time. Year of birth was positively and significantly associated with survival time. CONCLUSIONS AND CLINICAL RELEVANCE: BLV serologic status was not associated with cull rate as measured by survival time in this dairy herd. This finding is in contrast to results of studies that used survival analysis techniques; our results may influence management decisions concerning BLV.