Epidemiology and Control of Gastrointestinal Nematodes of Cattle in Southern Climates.

Control of gastrointestinal nematodes (GIN) can have both economic and health benefits for cattle operations in the southern United States. In the past several decades, GIN control has relied almost exclusively on the use of anthelmintics. With the increase in anthelmintic resistance new strategies must be developed. Anthelmintic use should be minimized by integrating grazing management and a good herd health program into GIN control programs. This takes knowledge of GIN biology and epidemiology in the region (climate and weather) combined with specific information from the ranch.

Preparation and Response for Flooding Events in Beef Cattle.

Flooding appears to be occurring at an increased frequency and severity, resulting in significant losses to the beef cattle industry. Responding to the needs of beef cattle is a resource-intense occurrence and beyond that provided by most local jurisdictions. It is incumbent on livestock producers to develop continuity of operations or emergency plans designed to limit the financial losses and compromised animal welfare that occur when livestock are exposed to flood conditions. Livestock producers and the veterinary medical profession should also encourage and participate in the development of public emergency plans focused on limiting losses in this critical industry.

Coccidiosis in Large and Small Ruminants.

Coccidiosis is an important parasitic disease of young ruminant livestock caused by the protozoan parasite of the genus Eimeria. Infection with Eimeria can lead to subclinical production losses and clinical disease. The most common clinical sign is diarrhea. Control of coccidiosis in cattle, sheep, and goats is based on sound management, the use of preventive medications, and treatment of clinical cases as necessary.

Fluid therapy in small ruminants and camelids.

Body water, electrolytes, and acid-base balance are important considerations in the evaluation and treatment of small ruminants and camelids with any disease process, with restoration of these a priority as adjunctive therapy. The goals of fluid therapy should be to maintain cardiac output and tissue perfusion, and to correct acid-base and electrolyte abnormalities. Hypoglycemia, hyperkalemia, and acidosis are the most life-threatening abnormalities, and require most immediate correction.

Salivary gland thrombostasin isoforms differentially regulate blood uptake of horn flies fed on control- and thrombostasin-vaccinated cattle.

Thrombostasin (TS) is an anticlotting protein found in saliva of Haematobia irritans (horn flies). The polymorphic nature of the ts gene was first associated with success of horn flies blood feeding on a laboratory host, New Zealand White rabbits. In this study, we report results of similar studies testing blood uptake of horn flies feeding on a natural host, cattle. These studies confirmed the association of ts genotype with blood uptake of horn flies and showed that it was host species specific. In contrast to rabbits, blood uptake volumes of homozygous ts10 horn flies were lower than those of other ts genotypes when fed on control (ovalbumin-vaccinated) cattle. Cattle vaccinated with recombinant protein isoforms, rTS9 or rTB8, resisted horn fly feeding by yielding lower blood volumes compared with flies feeding on control cattle. The specific impact of vaccination, however, varied by ts genotype of flies. Cattle vaccinated with isoform rTS9 resisted flies of ts2, ts9, and tb8 genotype. Vaccination with isoform rTB8 produced resistance to ts8, ts9, and tb8 genotype flies. Horn flies of genotype ts10 were not affected by vaccination with either TS isoform and fed as well on rTS9- and rTB8-vaccinated as on control-vaccinated cattle. These experimental results confirm the efficacy of vaccines targeting horn fly salivary proteins and provide new insight into the dynamics of horn fly-cattle interactions in nature.

Salivary gland thrombostasin isoforms differentially regulate blood uptake of horn flies fed on New Zealand White rabbits.

Thrombostasin (TS) is a previously characterized anticlotting protein with multiple isoforms found in the saliva of horn flies. In this report, the effect of TS isoforms on blood feeding was assessed using individual flies that carried corresponding ts allelles. Laboratory studies of horn fly blood feeding were conducted using colony-reared flies fed on New Zealand White (NZW) rabbits. After timed 20-min feeding periods, each fly was characterized for gender, blood volume uptake, and ts genotype. The results showed that mean blood volumes obtained by individual flies were not related to fly gender but were correlated to the ts genotype(s) carried by each fly. A fly having one or both ts alleles coding for the TS9 isoform took less blood than those possessing one or both ts alleles coding for the TS10 isoform. These results confirm the significant role that TS plays in horn fly feeding and highlight the differential impact of TS protein isoforms that vary by as few as three amino acids.

Effect of dexamethasone administration on bulls with a localized testicular infection with bovine viral diarrhea virus.

The objective of this research was to evaluate reactivation of bovine viral diarrhea virus (BVDV) following dexamethasone treatment in 4 bulls that had previously been inoculated with BVDV, 3 of which had been demonstrated to have a localized testicular infection. Bulls were housed in an isolated pasture with in-contact steers. Beginning on day 0 of this study, all bulls received a daily dose of 0.1 mg/kg body weight (BW) of dexamethasone intravenously for 5 consecutive days. Blood was collected from the in-contact steers and semen, blood, and cerebrospinal fluid were collected from the bulls during and following dexamethasone treatment. Samples were assayed for BVDV using virus isolation and reverse transcription-nested polymerase chain reaction (RT-nPCR). Serum was assayed for antibody using standard virus isolation. Virus was not isolated from blood, cerebrospinal fluid, or semen from any of the 4 bulls during the study period. One of the bulls was positive for BVDV in semen by RT-nPCR throughout the study period. The BVDV was not recovered from any in-contact control steers during the 28-day study period, nor did any of the in-contact control steers seroconvert to BVDV. Raw semen from 1 bull that was RT-nPCR positive was intravenously inoculated into 7 seronegative steers based upon the Cornell Semen Test. The BVDV could not be recovered from the steers and none of them seroconverted to BVDV. The results indicated that reactivation of BVDV in bulls with a localized testicular infection is unlikely; however, further research is necessary to determine the full potential for BVDV transmission from bulls with a localized testicular infection.

Evaluation of a recombinant salivary gland protein (thrombostasin) as a vaccine candidate to disrupt blood-feeding by horn flies.

The potential for controlling blood-feeding by the cattle pest, Haematobia irritans irritans (horn fly), was tested by vaccination against thrombostasin (TS), an inhibitor of mammalian thrombin that is released into skin during horn fly blood-feeding. The increase in blood meal size that occurred for flies feeding on sensitized non-vaccinated hosts was blocked and egg development in female flies was delayed when horn flies fed on rabbits and cattle immunized with recombinant TS. This demonstration of the impact of disrupting TS action by vaccination provides a novel approach toward control of this veterinary pest and offers a paradigm for limiting blood-feeding in other medically-important insect species.

Pluronic F127 gel formulations of deslorelin and GnRH reduce drug degradation and sustain drug release and effect in cattle.

The objective of this study was to compare the effectiveness of intramuscular sustained release Pluronic F127 (PF127) gel formulations of deslorelin, a potent GnRH agonist, and GnRH to their solution formulations in inducing the release of luteinizing hormone and formation of luteal tissue in cattle. Injectable gel formulations of deslorelin and GnRH were prepared using Pluronic F127 (25%, w/w), a block copolymer. PF127 gels sustained the in vitro release of deslorelin as well as GnRH at similar rates and reduced drug degradation in muscle tissue when compared to the solution formulations. Deslorelin, as well as GnRH, elicited desirable elevations in plasma LH and progesterone concentrations in vivo. When compared to the solution formulations, the gel formulations of both drugs induced a broader peak of LH. Also, the peak LH levels were lower and the peak times were delayed with the gel formulations compared to the solution formulations. While the solution dosage form of deslorelin and GnRH elicited similar responses, the PF127 gel formulation of deslorelin induced peak LH levels at an earlier time (3 h for deslorelin versus 5.25 h for GnRH). The results indicate that, deslorelin exerts a pharmacological effect in cattle. The LH response to deslorelin as well as GnRH can be altered by controlling the input or the release rate of the drug. PF127 gel formulations can sustain peptide release and reduce peptide degradation.

Development and in-vitro evaluation of sustained release poloxamer 407 (P407) gel formulations of ceftiofur.

The objective of this study was to develop sustained release Poloxamer 407 (P407) gel formulations of ceftiofur for treating foot infections in cattle. The formulations contained 25-35% (w/v) P407 alone or with polyvinyl pyrrolidone (PVP), carboxy methylcellulose (CMC), or hydroxylpropyl methylcellulose (HPMC) as an additive. The in-vitro release profiles of ceftiofur from the P407 formulations and the gel dissolution profiles were obtained simultaneously. Ceftiofur release followed zero order kinetics and correlated well with the weight percentage of P407 dissolved, indicating that the overall rate of release of ceftiofur is controlled by dissolution of the P407. An increase in P407 content from 25 to 35% resulted in a decrease in the rate of ceftiofur release. However, it appears that other factors may have also affected the drug release rate. Inclusion of PVP, CMC, and HPMC in the gel decreased the rate of release of ceftiofur to some extent. A decrease in the temperatures of the release medium decreased the release rate of ceftiofur, but not the rate of gel dissolution. The pH of the release medium showed a very slight effect on the release of ceftiofur and did not affect gel dissolution due to the non-ionic nature of P407.

Lactate metabolism in resting and contracting canine skeletal muscle with elevated lactate concentration.

This study was undertaken to quantitatively account for the metabolic disposal of lactate in skeletal muscle exposed to an elevated lactate concentration during rest and mild-intensity contractions. The gastrocnemius plantaris muscle group (GP) was isolated in situ in seven anesthetized dogs. In two experiments, the muscles were perfused with an artificial perfusate with a blood lactate concentration of ~9 mM while normal blood gas/pH status was maintained with [U-(14)C]lactate included to follow lactate metabolism. Lactate uptake and metabolic disposal were measured during two consecutive 40-min periods, during which the muscles rested or contracted at 1.25 Hz. Oxygen consumption averaged 10.1 +/- 2.0 micromol. 100 g(-1). min(-1) (2.26 +/- 0.45 ml. kg(-1). min(-1)) at rest and 143.3 +/- 16.2 micromol. 100 g(-1). min(-1) (32.1 +/- 3.63 ml. kg(-1). min(-1)) during contractions. Lactate uptake was positive during both conditions, increasing from 10.5 micromol. 100 g(-1). min(-1) at rest to 25.0 micromol. 100 g(-1). min(-1) during contractions. Oxidation and glycogen synthesis represented minor pathways for lactate disposal during rest at only 6 and 15%, respectively, of the [(14)C]lactate removed by the muscle. The majority of the [(14)C]lactate removed by the muscle at rest was recovered in the muscle extracts, suggesting that quiescent muscle serves as a site of passive storage for lactate carbon during high-lactate conditions. During contractions, oxidation was the dominant means for lactate disposal at >80% of the [(14)C]lactate removed by the muscle. These results suggest that oxidation is a limited means for lactate disposal in resting canine GP exposed to elevated lactate concentrations due to the muscle's low resting metabolic rate.