Acute systemic anaphylaxis in adult domestic fowl: evidence for the protective role of H2-histaminergic and beta 2-adrenergic receptors

Pentobarbital-anesthetized and spontaneously breathing, bovine albumin (BA)-sensitized adult domestic fowl showed acute systemic anaphylaxis to IV injection of antigen (BA), which was characterized by arterial hypotension, central venous hypertension, and bradycardia. Large doses of pyrilamine maleate (/1-receptor antagonist) partially inhibited acute systemic anaphylaxis. On the other hand, metiamide (a specific H2-antagonist) and propranolol (beta-adrenergic antagonist) markedly enhanced the anaphylactic response. Terbutaline (beta 2-agonist), dimaprit (a highly selective H2-agonist), and compound FPL 55712 (a slow-reacting substance of anaphylaxis receptor antagonist) either significantly inhibited or reversed the anaphylactic response. Cimetidine (a newer H2-antagonist) enhanced only central venous pressor response to BA. This investigation appears to suggest a minor role of histamine and a major role of slow-reacting substance of anaphylaxis as chemical mediatiors of anaphylaxis. A protective role of beta 2-adrenergic and H2-histaminergic receptors seem to operate in immediate hypersensitivity reactions in adult domestic fowl.     

Preliminary studies of pharmacological antigonism of anaphylaxis in the horse.

Systemic anaphylaxis was induced in seven groups of ponies. Systemic hypotension, pulmonary hypotension, and apnea were observed in the control group. Suppression of anaphylaxis was achieved most efficiently with sodium meclofenamate followed by acetylsalicylic acid and diethylcarboamazine. Tripelennamine and methysergide reduced anaphylaxis minimally and burimamide not at all. The findings suggest that histamine and serotonin are of relatively low significance in equine anaphylaxis whereas kinins, prostaglandins and slow reacting substance may be more important.     

Severity and nature of acidosis in diarrheic calves over and under one week of age

A prospective study of the severity of dehydration and acidosis was carried out in 42 calves under 35 days of age presented for treatment of neonatal diarrhea. Clinically the mean level of dehydration was 8 to 10%. The plasma volume was 65% of that in the hydrated calf but the calves only gained 6.5% in weight during therapy.

Calves under eight days of age often had a lactic acidosis. Blood pH was 7.118±0.026 (mean ± 1 standard error), bicarbonate concentration 18.8±1.3 mmol/L, base deficit 11.4±1.7 mmol/L and lactate of 3.6± 0.06 mmol/L. Calves over eight days usually had a nonlactic acidosis. Blood pH was 7.042±0.021, bicarbonate 10.8±1.0 mmol/L, base deficit 19.5±1.2 mmol/L and lactate 1.2±0.3 mmol/L. These values were all significantly different from those in younger calves.

Over all calves there was a poor correlation between the severity of acidosis and dehydration(r=0.05). The severity of lactic acidosis was related to the severity of dehydration. Mean bicarbonate requirements to correct acidosis were calculated to be 200 mmol(17 g of sodium bicarbonate)and 450 mmol(37 g of sodium bicarbonate)in calves under and over eight days of age respectively. Both groups of calves required a mean volume of 4L of fluid to correct dehydration.

     

An evaluation of antimicrobial therapy for undifferentiated bovine respiratory disease

A field trial of antimicrobial therapy for cases of undifferentiated bovine respiratory disease (UBRD) in beef calves was conducted at four Ontario feedlots. The primary purpose of the trial was to evaluate the efficacy of three different antimicrobials (oxytetracycline, penicillin, and trimethoprim-sulfadoxine) in the treatment of UBRD occurring within the first 28 days postarrival.

The response, relapse, and case fatality rates overall were 85.7%, 14.8%, and 1.4%, respectively, and were not significantly different among the three antimicrobials evaluated. Weight gains of calves treated with the different drugs were not statistically different over the feeding period. Calves that suffered a relapse posttreatment were first treated significantly earlier (p<0.001) in the postarrival period than those that did not relapse. Considered together, treated calves gained significantly less (p<0.05) over the first 28 days and throughout the entire feeding period than controls that were never sick. Cases of UBRD that responded to therapy and did not relapse had rates of gain that were not significantly different from the controls.

     

Nutritional and pathophysiologic effects of clinically apparent and subclinical infections of Ostertagia ostertagi in calves.

Nutritional and physiologic effects of clinically apparent and subclinical Ostertagia ostertagi infections were studied in 3 groups of 5 calves each. Group-1 calves were inoculated with 100,000 Ostertagia ostertagi third-stage larvae (L3)/calf/wk for 14 weeks. Group-2 calves were inoculated with 10,000 L3/calf/wk for 14 weeks, and group-3 calves were no inoculated. Calves in group 1 had decreased dry matter intake and feed utilization from 4 weeks after initial inoculation. Group-2 calves had no changes in dry matter intake, but had decreased feed utilization at 12 and 14 weeks. Calves with clinically apparent infections (group 1) lost a mean weight of 11.8 kg, whereas calves with suclinical infections (group 2) lost a mean of 46.6 kg, and control calves lost a mean of 60.7 kg. Calves with O ostertagi infections (group 1 and 2) also had decreased carcass quality at slaughtering, which was reflected in decreased dressing weights and increased water-holding capacity of the rib-eye muscle. Calves in groups 1 and 2 also had lower carcass yield and rib-eye muscle weight, and group-1 calves had decreased protein content. Results of hematologic, pathologic, parasitologic, and clinical examinations mirrored nutritional changes.     

The physiological and physical status of single calves at birth in a dairy herd in New Zealand

AIM: To determine the physiological status of calves at birth and the perinatal factors that might predispose newborn calves to debility and death, using criteria previously established for newborn lambs.

METHODS: Friesian mixed-aged cows and heifers on a dairy farm in New Zealand that were close to calving were separated from the main herd and observed 24 h a day until they calved. Cows in which labour did not progress for over 1 h or which were in distress were assisted. About 12–13 min after birth, rectal temperature was measured and a blood sample was taken from each calf. The packed cell volume (PCV) and plasma lactate, glucose and fructose concentrations were determined. The time to stand for each calf and the air temperature and weather conditions at birth were recorded.

RESULTS: The parameters measured were within normal ranges for newborns for the majority of calves. Calves sired by an Angus bull and born to heifers (AngusX) had significantly higher plasma lactate and fructose concentrations than Friesian calves born to cows, but there were no significant differences between the two breeds in any of the other parameters measured. Calves of both breeds born with assistance had significantly higher plasma lactate concentrations than those born without. Friesian calves that were assisted at birth had significantly lower PCvs and took significantly longer to stand than calves born without assistance. Assisted AngusX calves were significantly heavier than their unassisted counterparts. Calves born during windy and wet weather and when air temperatures were below 10°C had lower rectal temperatures, took longer to stand and had higher plasma glucose concentrations than those born in dry weather and when air temperatures were above 10°C.

CONCLUSIONS: Calves with physiological parameters outside the normal range had experienced difficult labour and/or intrapartum hypoxaemia. Placental insufficiency and maternal undernutrition during late pregnancy did not apparently contribute to neonatal problems in the present study.     

Comparative serological response in calves to eight commercial vaccines against infectious bovine rhinotracheitis, parainfluenza-3, bovine respiratory syncytial, and bovine viral diarrhea viruses

A field trial was conducted to compare the serological responses in calves to eight commercial vaccines against infectious bovine rhinotracheitis virus (IBRV), parainfluenza-3 virus (PI3V), bovine respiratory syncytial virus (BRSV), and/or bovine viral diarrhea virus (BVDV). Calves given IBRV, P13V, BRSV, and BVDV vaccines had significantly higher antibodies to these viruses than unvaccinated controls; however, serological responses to killed BVDV vaccines were low. Calves with preexisting antibodies to IBRV, PI3V, BRSV, and the Singer strain of BVDV had lower seroconversion rates following vaccination than calves that were seronegative initially.

Serological responses in calves to IBRV, PI3V, BRSV, and BVDV differed among various commercial vaccines. Antibody titers to IBRV were higher in calves vaccinated with modified-live IBRV vaccines than in those vaccinated with killed IBRV vaccines. Following double vaccination with modified-live IBRV and PI3V vaccines, seroconversion rates and antibody titers to IBRV and PI3V were higher in calves vaccinated intramuscularly than in those vaccinated intranasally. Calves given Cattlemaster 4 had significantly higher titers to BRSV and PI3V, and lower titers to BVDV, than calves given Cattlemaster 3, suggesting that the addition of BRSV to Cattlemaster 4 caused some interaction among antigens.

     

The influence of the rumen on the absorption of drugs: studies using meclofenamic acid administered by various routes to sheep and cattle

As part of a general study of the pharmacokinetics of drugs in the ruminant animal, the absorption and distribution kinetics of meclofenamic acid between the gastro-intestinal tract and plasma of sheep and cattle were investigated. Meclofenamic acid is a non-steroidal anti-inflammatory drug which has been shown to possess anti-anaphylactic activity in cattle (Aitken & Sanford, 1969; 1972; Wells, Eyre & Lumsden, 1973) and sheep (Alexander, Eyre, Head & Sanford, 1970) and although marketed only for the horse in the United Kingdom (Arquel, Warner-Lambert) is known to be used in ruminant animals as an anti-inflammatory drug, for its inhibitory effects on prostaglandin synthesis (Smith G. G. A. 1977, personal communication) and for its anti-pyretic action (Van Miert, Van der Wal-Komproe & Van Duin, 1977). The aims of the study were first to evaluate the contribution of reticular (oesophageal) groove closure in directing orally administered drug directly to the abomasum and to assess the rate of absorption through the ruminal epithelium. Second, since Aitken & Sanford (1975) have described the plasma levels of meclofenamate after administration of sodium meclofenamate to cattle by the oral, intravenous and intra-ruminal routes, it was decided to complement their study and to measure the plasma levels after intra-muscular injection of sodium meclofenamate. This route is more convenient in cattle than the oral and intravenous routes examined by them. Lastly, the biphasic pattern of plasma levels of meclofenamate observed by Aitken & Sanford (1975) following oral administration of sodium meclofenamate to cattle was further examined using weaned and unweaned calves in an attempt to confirm their view that some of the drug is delivered to the abomasum directly, by-passing the rumen, by closure of the reticular groove.     

Comparison of pathophysiologic changes in the lungs of calves challenge exposed with Escherichia coli-derived endotoxin and Pasteurella haemolytica, alone or in combination

Pulmonary responses to intratracheal challenge exposure with Pasteurella haemolytica, with or without Escherichia coli-derived endotoxin, E coli endotoxin alone, or saline solution were compared in anesthetized, mechanically ventilated neonatal calves. Baseline values for dynamic compliance, total pulmonary resistance, functional residual capacity, arterial blood gas tensions, hemogram, leukogram, and systemic and pulmonary arterial pressures were recorded for each calf. After baseline data were obtained, calves were challenge exposed with logarithmic-growth phase P haemolytica organisms with or without E coli endotoxin, E coli endotoxin alone, or saline solution (0.9% NaCl). Physiologic data were obtained immediately after challenge exposure and at various intervals over the next 6 hours. Calves challenge exposed with P haemolytica alone developed sever hypoxemia, had increased alveolar-arterial oxygen difference and threefold increases in total pulmonary resistance, became hypercarbic, had decreased functional residual capacity, and developed systemic hypotension without change in pulmonary arterial pressure. At necropsy, these calves had extensive multifocal areas of necrohemorrhagic and purulent pneumonia. Ratio of extravascular lung water to lung dry weight was not significantly increased in lung specimens obtained from calves challenge exposed with P haemolytica, but ratio of lung wet weight to dry weight was increased, indicating that increased lung wet weight was attributable largely to increased solids and not to fluid alone. (Extravascular lung water measurement excludes fluid from the vascular compartment.) Intratracheal challenge exposure with endotoxin failed to alter lung function and caused minor changes in lung structure consisting of focal areas of hemorrhage and edema.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of closure of the reticular groove on the bioavailability and disposition kinetics of meclofenamate in sheep

Sodium meclofenamate is a non-steroidal anti-inflammatory drug with anaphylactic protective activity in cattle. The objectives of this study were to describe the pharmacokinetic behaviour of sodium meclofenamate after intravenous and oral administration to sheep and to determine the influence of closure of the reticular groove on the bioavailability of the drug. Sodium meclofenamate was administered by the intravenous (2.2 mg/kg) and oral (20 mg/kg) routes to sheep (n = 6). During the oral study the reticular groove was closed by intravenous administration of lysine vasopressin (0.3 IU/kg) or left open (saline solution). The closure of the reticular groove was assessed by determination of the blood glucose curves after oral administration of a glucose solution. After intravenous administration of meclofenamate, the distribution and elimination half-lives of the drug were 7.2 min and 542 min respectively, V_ss was 1.68 L/kg and Cl_B was 2.47 mL/min kg. Two different patterns of the plasma concentration curves were observed after oral administration of sodium meclofenamate. When the reticular groove was closed, two peaks were observed ( t _max-2 12-15 min, C _max-1 3.30-24.01 μg/mL; and t _max-2', 52.50-75 min, C _max-2' 6.45-11.08 μg/mL).     

Pathologic changes associated with induced small intestinal strangulation obstruction and nonstrangulating infarction in horses

Arteriovenous (ischemic strangulation obstruction, ISO) or venous (hemorrhagic strangulation obstruction, HSO) occlusions were created in the jejunum of 5 anesthetized horses and were left in situ for 1-, 2-, or 3-hour intervals. Segments were evaluated grossly for color, thickness, and motility. The horses were euthanatized, and the degree of mucosal slough, edema, congestion, and hemorrhage was determined histologically. Segments subjected to ISO became dark, but did not contain edema or hemorrhage. Segments subjected to HSO were characterized by progressive congestion, edema, and hemorrhage especially in the mucosal layer. Histologically, the mucosal epithelium was affected approximately equally by ISO or HSO, although more gross changes were evident in segments subjected to HSO.     

Characterization of protection from systemic infection and disease by use of a modified-live noncytopathic bovine viral diarrhea virus type 1 vaccine in experimentally infected calves

OBJECTIVE: To evaluate protection against systemic infection and clinical disease provided by use of a modified-live noncytopathic bovine viral diarrhea virus (BVDV) type 1 vaccine in calves challenged with NY-1 BVDV. ANIMALS: 10 calves, 5 to 7 months of age. PROCEDURES: Calves were allocated (n = 5/group) to be nonvaccinated or vaccinated SC on day 0 with BVDV type 1 (WRL strain). Calves in both groups were challenged intranasally with NY-1 BVDV on day 21. Calves' rectal temperatures and clinical signs of disease were recorded daily, total and differential WBC and platelet counts were performed, and serum neutralizing antibody titers against NY-1 BVDV were determined. Histologic examinations and immunohistochemical analyses to detect gross lesions and distribution of viral antigens, respectively, were performed. RESULTS: After challenge exposure to NY-1 BVDV, nonvaccinated calves developed high rectal temperatures, increased respiratory rates, viremia, leukopenia, lymphopenia, and infection of the thymus. Vaccinated calves did not develop high rectal temperatures or clinical signs of respiratory tract disease. Vaccinated calves appeared to be protected against systemic replication of virus in that they did not develop leukopenia, lymphopenia, viremia, or infection of target organs, and infectious virus was not detected in peripheral blood mononuclear cells or the thymus. CONCLUSIONS AND CLINICAL RELEVANCE: The modified-live BVDV vaccine protected calves against systemic infection and disease after experimental challenge exposure with NY-1 BVDV. The vaccine protected calves against infection and viremia and prevented infection of target lymphoid cells.     

Distal aortic aneurysm presumed to be secondary to an infected umbilical artery in a foal

ABSTRACT

Case History: Two calves delivered following elective caesarean section showed behaviour typical of neonatal maladjustment syndrome described in foals, i.e., indifference to environmental stimuli, lack of affinity for the dam, failure to find the udder, refusal to suck, aimless wandering or motionless standing. Calves were subjected to a clinical examination immediate after delivery and there were no signs of defects, illness, pain, dehydration, hypoxia, acidaemia or other causes for the unresponsive behaviour.

Clinical Findings and Treatment: Both calves were subjected to the thoracic squeeze technique, one at 6 hours and the other at 20 hours after delivery. A soft rope was looped around the thorax and gentle pressure was applied to the free end of the rope, squeezing the calf’s chest for 20 minutes. Both calves exhibited a sleep-like state manifested by closed eyes, no body movements, slow breathing and a decrease in heart rate, for the entire squeezing period. When the rope was removed the calves woke up immediately, rose and walked towards the dam. When led to the dam’s udder, the weaker calf began to suck. Both were reported, by the stockperson, to follow the dam and suck normally the following day.

Clinical Relevance: Provided all other disease processes are excluded, very young calves that exhibit indifference to environmental stimuli and lack of affinity for the dam may be good candidates for application of the thoracic squeeze technique that has been demonstrated to have clinical efficacy in foals with neonatal maladjustment syndrome.     

Analgesic and cardiopulmonary effects of premedication with tramadol in calves anesthetized with the infusion of guaifenesin and thiamylal

This study examined the analgesic and cardiopulmonary effects of intravenous (IV) tramadol during general intravenous anesthesia in calves. Calves were premedicated with diazepam (0.2 mg/kg, IV) with tramadol (2 mg/kg, IV) (group T) or saline (group S). Anesthesia was induced by thiamylal sodium (4 mg/kg, IV) and maintained with an infusion (2 ml/kg/hr) of 5% guaifenesin containing thiamylal sodium (2 mg/ml). Additional thiamylal sodium (1–2 mg/kg, IV) was administered when interference from the calves was observed during surgery. The total counts of additional thiamylal sodium administration, analgesia score using a visual analog scale, recovery time, and cardiopulmonary function in the different groups were assessed and compared. Group T showed significantly fewer counts of additional drug administration and a significantly higher analgesia score. Tramadol may provide adequate analgesia with minimal cardiopulmonary changes in calves during general anesthesia.     

Characterization of protection against systemic infection and disease from experimental bovine viral diarrhea virus type 2 infection by use of a modified-live noncytopathic type 1 vaccine in calves

OBJECTIVE: To evaluate protection resulting from use of a modified-live noncytopathic bovine viral diarrhea virus (BVDV) type 1 vaccine against systemic infection and clinical disease in calves challenged with type 2 BVDV. ANIMALS: 10 calves, 5 to 7 months of age. PROCEDURES: Calves were allocated (n = 5/group) to be nonvaccinated or vaccinated SC on day 0 with BVDV 1 (WRL strain). Calves in both groups were challenged intranasally with BVDV type 2 isolate 890 on day 21. Rectal temperatures and clinical signs of disease were recorded daily, and total and differential WBC and platelet counts were performed. Histologic examinations and immunohistochemical analyses to detect lesions and distribution of viral antigens, respectively, were performed. RESULTS: After challenge exposure to BVDV type 2, nonvaccinated calves developed high rectal temperatures, increased respiratory rates, viremia, leukopenia, lymphopenia, and infection of the thymus. Vaccinated calves did not develop high rectal temperatures or clinical signs of respiratory tract disease. Vaccinated calves appeared to be protected against systemic replication of virus in that they did not develop leukopenia, lymphopenia, viremia, or infection of target organs, and infectious virus was not detected in peripheral blood mononuclear cells or the thymus. CONCLUSIONS AND CLINICAL RELEVANCE: The modified-live BVDV type 1 vaccine protected against systemic infection and disease after experimental challenge exposure with BVDV type 2. The vaccine protected calves against infection and viremia and prevented infection of target lymphoid cells.     

Elimination of the gametocytes of Theileria annulata of cattle by primaquin phosphate

Calves were experimentally infected with Theileria annulata and five drugs were administered in an attempt to exterminate the gametocytes of the parasite. The results of the experiment proved that primaquin phosphate is an effective parasiticide. The gametocytes from 30 calves treated with primaquin phosphate were exterminated completely. A further eight calves were treated with sulfamethoxypyrazine, trimethoprim, naganin and acaprin, but these drugs were not found to be effective in eliminating the gametocytes. The phase, size and colour of the gametocytes in these calves were the same as those of the four untreated control calves.     

The effect of dexamethasone-induced immunosuppression on the development of faecal antibody and recovery from and resistance to rotavirus infection.

Rotavirus-naive and rotavirus-immune gnotobiotic calves were treated with high doses of dexamethasone (DX) to suppress the immune system. Calves were then infected with a virulent rotavirus inoculum, J-160, to investigate the role of immune responses both in recovery from primary rotavirus infection and in resistance to secondary rotavirus infection. Treatment of calves with DX markedly suppressed in vitro responsiveness of peripheral blood lymphocytes to mitogens within 48 h of the start of DX treatment. Suppression was similar in rotavirus-naive and rotavirus-immune calves. In contrast, the effect of DX treatment on specific antibody responses differed depending on when DX treatment started in relation to rotavirus infection. When DX treatment commenced prior to primary rotavirus infection both systemic and local specific antibody responses were inhibited. These calves, in which mitogen and antibody responses were suppressed, exhibited greater clinical signs than did control calves after infection with virulent rotavirus, but virus excretion was affected in only one of the two calves. When DX treatment was started after primary rotavirus infection but before secondary infection, systemic and local antibody responses to the primary infection and to the challenge infection were not affected. These calves resisted challenge with virulent virus as did DX-untreated rotavirus-immune calves, even though mitogen responses were suppressed. We conclude that in a primary rotavirus infection, virus excretion ceased when both antibody and mitogen responses were suppressed. Resistance to secondary rotavirus infection occurred when mitogen responsiveness was suppressed, but when antibody levels were normal. Thus, no evidence was obtained that fully functional cell-mediated immune mechanisms are essential for resistance to rotavirus infection. Evidence was provided for the ability of parenteral treatment with DX to suppress mucosal as well as systemic antibody responses.     

A field trial of preshipment vaccination of calves

A field trial to investigate the efficacy of vitamins ADE, a Haemophilus somnus bacterin, a pasteurella bacterin, and two intranasal infectious bovine rhinotracheitis-parainfluenza type 3 vaccines administered to beef calves at least three weeks prior to weaning and shipment was conducted.

Over 1000 calves were vaccinated, but of the 692 calves shipped from the ranch of origin, only 276 calves were located in Ontario, or Quebec, feedlots. The average treatment rate was 30%. Neither vitamins ADE, H. somnus bacterin, pasteurella bacterin or the porcine tissue culture infectious bovine rhinotracheitis-parainfluenza type 3 vaccine had a significant effect on treatment rates for respiratory disease. Calves vaccinated with the temperature sensitive infectious bovine rhinotracheitis-parainfluenza type 3 vaccine had a significantly (p < 0.05) lower treatment rate than the nonvaccinated, and the porcine tissue culture infectious bovine rhinotracheitis-parainfluenza type 3 vaccinated, calves. Calves vaccinated with the temperature sensitive infectious bovine rhinotracheitis-parainfluenza type 3 vaccine did not have a significantly reduced treatment rate in comparison to nonvaccinated calves from the same source.

     

Colostral transfer of gamma glutamyl transpeptidase in calves

Serum gamma glutamyl transpeptidase (GGT) levels in blood samples taken from normal calves which bad suckled colostrum were much higher than those found in healthy adult cattle. Levels of over 60 times the normal adult level were observed. These high levels of GGT took approximately 5 weeks to decline to adult values. Calves which appeared to have not received or absorbed colostrum had GGT levels which would be considered normal in adult cattle. A calf with serum gamma globulin levels which indicated an intermediate amount of colostrum absorption had a level of GGT which was intermediate between that expected for normal adult cattle and that found in calves which had more fully absorbed colostrum. The mean GGT level observed in colostrum from 6 newly-calved cows was over 800 times the mean serum GGT level of the same 6 cows. It therefore appears most likely that GGT is concurrently absorbed with colostrum by calves and this gives rise to the very high levels seen in normal calves.

Calves with very high levels of serum GGT also had raised levels of alkaline phosphatase (AP) which slowly declined but never reached normal adult levels within the 53-day period of observation.

It therefore appears that high levels of both GGT and AP are achieved by calves at the time of colostrum absorption and it is concluded that clinical interpretation of serum GGT and AP levels in young calves is closely dependent upon parallel knowledge of their serum gamma globulin levels.     

犊牛感光过敏的诊断与病因分析

近年来,规模化奶牛场常中有犊牛发生感光过敏,且犊牛发病率占有较高的比例。经过调查分析,发病犊牛大多在1月龄内,还属于未断奶阶段,病灶发生在无色素沉着皮肤或无毛皮肤区域,表现为脱毛、脱屑、充血、水肿、渗出、结痂等病理变化。犊牛发生感光过敏前曾有过腹泻、高烧、气喘等病症,使用过注射用头孢噻呋、恩诺沙星注射液、磺胺类药物、土霉素注射液、庆大霉素注射液等药品,且有适当波长的紫外线照射,最终确诊为药源性感光过敏,分析具体原因是使用了致光过敏的药物,且用药量过大,用药时间过长。因此,要科学去除致犊牛感光过敏的因素,提高犊牛期的科学用药水平,增强基层兽医对本病的认识。