Restoring forest herb communities through landscape-level deer herd reductions: Is recovery limited by legacy effects?

White-tailed deer (Odocoileus virginianus) overbrowsing has altered plant species diversity throughout deciduous forest understories in eastern North America. Here we report on a landscape-level (306 km²) project in Pennsylvania, USA that tracked the herbaceous community response to deer herd reductions. From 2001 to 2007, we estimated deer densities, browse impact on woody seedlings, and censused the herbaceous flora in permanent plots throughout the area. We assessed herb layer species richness, abundance, and dominance and measured three known phytoindicators of deer impact: Trillium spp., Maianthemum canadense, and Medeola virginiana. We predicted that browse-sensitive taxa would increase in abundance, size, and flowering as would overall species diversity following deer culls and browse impact that declined by an order of magnitude by 2007. Following intensified deer harvests, we observed a limited recovery of the herbaceous community. Trillium spp. abundance, height, and flowering; M. canadense cover; and M. virginiana height all increased following herd reductions. Similarly, forb and shrub cover increased by 130% and 300%, respectively. Nevertheless, species diversity (i.e., richness and dominance) did not vary. Our work demonstrates that reducing deer densities can provide rapid morphological and population-level benefits to palatable species without a concomitant recovery in diversity. We suggest that decreasing deer populations alone may not promote plant diversity in overbrowsed, depauperate forests without additional restoration strategies to mitigate a browse-legacy layer dominated by browse-resistant species.     

Effect of intensity of fecal pat sampling on estimates of Escherichia coli O157 prevalence

OBJECTIVE: To evaluate site-to-site variation within fecal pats from cattle with regard to detection of Escherichia coli O157 and determine the effect on the accuracy of prevalence estimates of assay of multiple samples collected from the same fecal pat. SAMPLE POPULATION: 120 freshly voided fecal pats collected from 2 beef feedlots. Procedures-5 samples were systematically collected from each fecal pat and analyzed for E coli O157 via selective preenrichment techniques, immunomagnetic separation, and biochemical tests. Presumptive isolates were definitively identified via agglutination assays and polymerase chain reaction techniques. Best estimators of prevalence were calculated from the distribution of E coli O157-positive samples per pat. RESULTS: Of the 120 fecal pats, 96, 13, 4, 2, 3, and 2 fecal pats had 0, 1, 2, 3, 4, and 5 E coli O157-positive samples, respectively. The greatest estimate of E coli O157 prevalence (20%) was achieved when all 5 samples were assessed; this estimate represented a 2.4- fold increase in prevalence, compared with that provided via analysis of 1 sample/pat (8.2%). Compared with assessment of 5 sites/pat, the relative sensitivity of detecting an E coli O157-positive fecal pat via analysis of 1 site/pat was 40.1%. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that estimates of E coli O157 prevalence derived from sampling of 1 location/pat are likely underestimates of the true prevalence of this pathogen in fecal pats (and by extension, cattle). Additional research is warranted to confirm these results in situations of high and low prevalence and across different feedlots.     

Influence of the Th2 immune response established by Nippostrongylus brasiliensis infection on the protection offered by different vaccines against Chlamydophila abortus infection

Chlamydophila abortus is the aetiological agent of enzootic abortion in small ruminants in which it infects the placenta to cause abortion during the last trimester of gestation. In a mouse model, a Th1 immune response involving IFN-γ production and CD8⁺ T cells is necessary for the infection to be resolved. The authors previously demonstrated that infection with Nippostrongylus brasiliensis, a rodent gastrointestinal nematode extensively used in experimental models to induce Th2 responses, alters the specific immune response against C. abortus infection, increasing bacterial multiplication in liver and reducing specific IFN-γ production. The aim of the present work was to clarify whether a Th2 immune response has any influence on the success of vaccination using both inactivated and attenuated vaccines. The results showed that the Th2 response established prior to vaccination did not influence the induction of protection offered by the vaccines. However, the effectiveness of this protective response can be altered, depending on the adjuvant employed in the inactivated vaccines, when the Th2 response is established after vaccination, just before challenge with C. abortus.     

Effects of alpha2-adrenergic receptor agonists on urine production in horses deprived of food and water

OBJECTIVE: To quantitate the dose- and time-related effects of IV administration of xylazine and detomidine on urine characteristics in horses deprived of feed and water. ANIMALS: 6 horses. PROCEDURE: Feed and water were withheld for 24 hours followed by i.v. administration of saline (0.9% NaCI) solution, xylazine (0.5 or 1.0 mg/kg), or detomidine (0.03 mg/kg). Horses were treated 4 times, each time with a different protocol. Following treatment, urine and blood samples were obtained at 15, 30, 60, 120, and 180 minutes. Blood samples were analyzed for PCV and serum concentrations of total plasma solids, sodium, and potassium. Urine samples were analyzed for pH and concentrations of glucose, proteins, sodium, and potassium. RESULTS: Baseline (before treatment) urine flow was 0.30 +/- 0.03 mL/kg/h and did not significantly change after treatment with saline solution and low-dose xylazine but transiently increased by 1 hour after treatment with high-dose xylazine or detomidine. Total urine output at 2 hours following treatment was 312 +/- 101 mL versus 4,845 +/- 272 mL for saline solution and detomidine, respectively. Absolute values of urine concentrations of sodium and potassium also variably increased following xylazine and detomidine administration. CONCLUSIONS AND CLINICAL RELEVANCE: Xylazine and detomidine administration in horses deprived of feed and water causes transient increases in urine volume and loss of sodium and potassium. Increase in urine flow is directly related to dose and type of alpha2-adrenergic receptor agonist. Dehydration in horses may be exacerbated by concurrent administration of alpha2-adrenergic receptor agonists.     

Eradication of bovine brucellosis in the 10th Region de Los Lagos,Chile

The process of Bovine Brucellosis Eradication that began in 1996 in the 10th Region de Los Lagos of Chile will be reviewed. The region comprises the most important dairy area of the country and it has the largest concentration of brucellosis infected herds. Based on the information gathered by an epidemiological surveillance system, the results of the eradication process for the years 1996 till 2001 are presented as rates of Milk Ring Test (MRT) positive dairies, rates of brucellosis reactors (bovines) in livestock markets and slaughterhouses, and the annual incidence and prevalence of brucellosis infected herds.

During the period the rates of positive dairies, bovine reactors in livestock markets and slaughterhouses, and the annual incidence and prevalence of infected herds have experienced a decrease, while the rate of bovine reactors in slaughterhouses has remained stable. Data on the preventive measures taken, such as vaccination of female bovines and Certification of Brucellosis Free Herds, are also shown. The surveillance system has allowed the detection of infected herds, while the measures of prevention and cleaning of infected herds have allowed a reduction in the incidence and prevalence of the infection by Brucella abortus.     

Risk factors for Aujeszky's disease in pig herds and detection of field virus antibodies in fattening pigs in the state of Yucatan, Mexico

Two epidemiological studies were conducted from August 1997 to May 1998: a case-control study to identify herd level risk factors for antibodies to Aujeszky's disease virus (ADV) in sows in the state of Yucatan, Mexico and a cross-sectional study to determine the prevalence of antibodies against ADV in fattening pigs. In the case-control study, data on herd management and biosecurity were obtained from all the 27 ADV known field-virus-seropositive farms (cases) and 62 randomly selected seronegative farms (controls) by questionnaire. Breeding animals of these seropositive farms had received a gE-deletion vaccine. In the cross-sectional study, 26 farrow-to-finish farms of the 27 seropositive farms were used and blood samples taken from 60 fattening pigs per herd (15 pigs for each stage of production). Serum samples were analyzed by the screening-ELISA and gE-ELISA tests. In the case-control study, three of the 15 risk factors were significant. Odds ratios for distance to the nearest farm (< or = 2.5km), not sampling for the detection of ADV and herds with origin of breeding animals within the state were 9.5, 18.1 and 8.7. In the cross-sectional study, 11 (42.3%) of the 26 sampled farms were seropositive to vaccine antibodies. None of the piglets were positive to antibodies against field virus risk--suggesting that the strategy of vaccinating only the breeding animals reduced the ADV infection of the piglets.     

SPIKE and D-PIKE: innovative experiences that engage students early and position them to succeed in food-supply veterinary medicine

Recent trends in urbanization of the population, increased need for bio-security on large farms, and more food-animal or mixed-animal practitioners approaching retirement age are forcing a renewed focus on recruiting and training veterinary students with an interest in production-animal medicine. The increasing number of veterinary students coming from urban backgrounds has led to a need to expose these students to standard animal-production practices and to interest them in a career involving food animals. This article describes one such program developed at Iowa State University, in which 14 students obtained hands-on experience in all aspects of swine and dairy production across a wide sampling of herd size, housing style, bio-security levels, and production phases. The participating students, ranging from senior undergraduates to third-year veterinary students, gained valuable insight not only into daily farming practices but also the knowledge and skills necessary to provide quality veterinary care to these clients. The first year of this program has yielded positive feedback from all participants, including the veterinary practices, private producers, corporate sponsors, and students. Current applicants cite positive comments from past participants as motivating their interest in the program. This program has the potential to expand as an opportunity to educate selected students in the field of food-supply veterinary medicine and to help fill the anticipated void in this area.     

Bilateral Leydig cell tumor in a six-year-old intersex goat affected by Polled Intersex Syndrome

A 6-year-old, sterile, Blanca Celtibérica breed adult doe was referred to our faculty. The doe had external female genitalia, a short anogenital distance, and normally shaped udders. Masculinization signs in the head shape and male behavior were also noted at the time of referral. Genetic analysis demonstrated normal 2n = 60 XX karyotype and an absence of the sex-determining region Y (SRY). The animal was homozygous for a DNA deletion responsible for the Polled Intersex Syndrome (PIS). A uterus and 2 uterine horns were present at the postmortem examination. Gartner's ducts and degenerated Wolffian derivatives persisted. There were 2 intra-abdominal testicle-like structures, one of which consisted of epididymal and deferent ducts. An advanced Leydig cell tumor, resulting in almost total destruction of the intratesticular structures, was also observed. Leydig cell tumors usually produce testosterone. Thus, these histologic findings are compatible with the evident virilization.