Infection rates in contaminated surgical procedures: a comparison of prophylactic treatment for one day or four days

Eighty-three calves with a complicated umbilical hernia were included in a randomised prospective study. The frequency of wound infection was compared in two groups. The first group received antibiotics for one day, the second group for four days. The infection rate in calves receiving antibiotics for one day was 25 per cent compared with 8 per cent in calves treated for four days (P less than 0.05). Male calves were more susceptible to infection than female calves.     

Osteomyelitis of the hyoid bones in two calves

Two calves were referred because of ptyalism and difficulty opening the mouth (Calf 1) and for elective umbilical hernia surgery under inhalation anaesthesia (Calf 2). Additional clinical signs were increased breath sounds and swelling in the region of the mandibular angle in Calf 1. Ultrasonography and endoscopy revealed oral inflammation and abscessation in the area of the base of the tongue in both calves. Infection of the hyoid apparatus was suspected based on ultrasonographic findings and confirmed by means of computed tomography. In Calf 1, there was no response to treatment with systemic antibiotics, nonsteroidal anti-inflammatory drugs and local lavage, and Calf 2 was not treated. Both calves were euthanized because of a poor prognosis and the diagnoses confirmed during postmortem examination. In Calf 1, the abscess was associated with complete destruction of the left epihyoid bone and partial destruction of the left stylohyoid and ceratohyoid bones. In Calf 2, the abscess was located at the distal end of the right stylohyoid bone near the epihyoid bone. Stomatitis or laryngeal and pharyngeal abscessation caused by sharp feed particles are common in cattle and infection of the hyoid apparatus should be included in the differential diagnosis.     

Occurrence and economic importance of congenital hernia in German Fleckvich calves

The frequency of congenital hernia was investigated in German Fleckvieh calves being driven up for sale on livestock markets for breeding and fattening calves in Miesbach and Traunstein. Data were collected on 77 livestock auctions in the years 1996 and 1997. Altogether 53,105 calves were examined and 1.8% of these calves showed a congenital umbilical hernia. The incidence of umbilical hernia was significantly influenced by the sex of the calf, the occurrence of multiple births, the market place/market date, the sire and the sire line. Red Holstein blood proportion, lactation number, duration of pregnancy and 305 day milk performance were not of significant importance. Herd milk level did not influence the incidence of congenital umbilical hernia, however, herdmate averages for calves differed significantly in their incidence. The average difference of the market price between male calves affected by congenital umbilical hernia and not affected male calves amounted to 75 DM, in female calves, however, only to 38 DM. The risk, that a congenital umbilical hernia is not closing within an age of 15 months, depends on the width of the hernial opening in the newborn calf. An opening of 4 cm and more has only a healing chance of 50% and less. However, negative effects on fattening and carcass traits could be not found. The genetic influence on congenital umbilical hernia was obvious. The analyses indicated that the incidence of congenital umbilical hernia observed could not be explained by one autosomal recessive gene locus, but it seemed much more likely that more than one gene locus is involved or a mixed multifactorial monogenic mode of inheritance may be the underlying genetic mechanism. Breeders should be aware of the implications of congenital hernias and thus, congenital hernia should get more attention in the selection process of young sires.     

Effects of Metaphylactic Antibiotics on Behavior of Feedlot Calves

Three 21-d trials were conducted at a commercial feedlot near Wellton, Arizona to determine the effects of metaphylactic injectable antibiotics on feeding and watering behavior and on animal health and growth performance of feedlot calves. Newly received male calves (n = 150, 150, and 148 for Trials 1, 2, and 3, respectively) were randomly assigned to one of four treatments: 1) no injectable antibiotic (control), 2) tilmicosin (TIL) subcutaneously (s.c.) 3) florfenicol i.m. (FIM), or 4) florfenicol s.c. (FSC). Throughout the 21-d trials, calves were observed and documented as morbid or healthy. Daily feeding and watering behaviors were collected for trials 2 and 3. A smaller (P=0.001) percentage of TIL, FIM, and FSC calves were identified as morbid (average, 27%) compared with control calves (47%), and ADG was greater (P=0.04) for TIL, FIM, and FSC calves (average, 0.42 kg/d) than for control calves (0.23 kg/d). Calves castrated before arrival had greater (P=0.001) ADG (0.53 vs 0.21 kg/d) and lower (P=0.05) mortality (0 vs 3.5%) during the first 21 d than did calves castrated upon arrival at the feedlot. Calves that remained healthy had greater (P=0.001) ADG than did calves that became morbid (0.78 vs−0.03 kg/d). Calves treated with TIL, FIM, or FSC had increased (P=0.02) feeding bouts per day in Trial 3 compared with control calves (average, 11 vs 9 bouts/d). Total feeding time was increased (P=0.005) for FIM calves compared with control, TIL, and FSC calves in Trial 3. No differences (P>0.10) were observed in watering behavior because of antibiotic treatment. Metaphylactic injectable antibiotics administered upon calves’ arrival at the feedlot did not reduce the total time newly received feedlot calves spent feeding, decreased the incidence of morbidity by 43%, and improved growth performance during the 21-d receiving period.     

Treatment of premature calves with clinically diagnosed respiratory distress syndrome

BACKGROUND: Respiratory distress syndrome (RDS) has been reported previously in premature calves. However, there have been no published data on the effect of surfactant replacement therapy in the treatment of premature calves with RDS. HYPOTHESIS: Surfactant replacement therapy added to the standard treatment for premature calves clinically diagnosed with RDS would increase the viability of the calves. ANIMALS: Twenty-seven premature calves with clinically diagnosed RDS. METHODS: Twenty calves were instilled intratracheally with bovine lung surfactant extract and provided with standard treatment for RDS (surfactant group). Seven calves were given only standard care for RDS without surfactant therapy and placed in the control group. Standard treatment for newborn calves with RDS includes warming, administration of intranasal oxygen, fluid replacement, administration of antibiotics, and immunoglobulin solution. Arterial blood samples were collected from the calves at 3 observation points, the first just before treatment (hour 0) and at 2 hours (hour 2) and 24 hours (hour 24) after treatment was started to determine if ventilation was adequate, improving, or deteriorating. Blood gases, pH, bicarbonate, and lactate concentrations were measured. RESULTS: In the surfactant group, mean partial pressure of oxygen significantly increased at hours 2 and 24. Mean partial pressure of carbon dioxide decreased and mean arterial blood pH increased at hour 24 in the surfactant group compared with the control group (P < .05). Of the 20 calves in the surfactant group, 12 survived and 8 died. All 7 calves in the control group died. CONCLUSIONS AND CLINICAL IMPORTANCE: The results of this study suggest that surfactant replacement therapy may reduce neonatal deaths in premature calves with clinically diagnosed RDS.     

Topically applied furazolidone or parenterally administered oxytetracycline for the treatment of infectious bovine keratoconjunctivitis

The effectiveness of topically applied furazolidone (FZ) or parenterally administered oxytetracycline (OTC) for treatment of infectious bovine keratoconjunctivitis was determined in a field study. Between June 13 and Aug 6, 1985, a study was conducted on a ranch in northern California. Eyes of Hereford calves (n = 103) were examined 3 times each week for 7 weeks. After daily examinations on June 13 and 14, calves were allotted randomly to 3 groups. On June 17, calves (that had corneal ulcers) of groups 1 (n = 35) and 2 (n = 35) were treated with OTC and FZ, respectively. Treatments were administered again only if new ulcers were observed, if an existing ulcer worsened, or if a healed ulcer recurred. Calves of group 3 remained untreated (controls). Corneal ulcers developed in 35 of the FZ-treated calves, in 33 of the OTC-treated calves, and in 33 of the untreated calves. Corneal perforations were observed in 3 untreated and 2 FZ-treated calves but were not observed in any OTC-treated calves. Panophthalmitis developed in one eye of an untreated calf. Corneal ulcers in the OTC-treated calves were smaller and healed more rapidly than did corneal ulcers in calves of the other groups. By the 22nd day of the study (July 3), the number of OTC-treated calves with corneal ulcers was less than that of the other 2 groups. Calves of the OTC treatment group had the fewest multiple corneal ulcer recurrences, but calves of all 3 groups had a similar number of single corneal ulcer recurrences.(ABSTRACT TRUNCATED AT 250 WORDS)     

Chloramphenicol, lincomycin and oxytetracycline disposition in calves with experimental pneumonic pasteurellosis

The effects of pneumonia on the pharmacokinetics of chloramphenicol, lincomycin, and oxytetracycline were evaluated in two-month-old calves. Pneumonia was induced by injection of Pasteurella haemolytica cultures directly through the thoracic wall into each lung. Six days prior to induction of pneumonia, the antibiotics were administered in a single i.v. dose. The antibiotics were administered again 48 (i.v.), 60 and 72 h (i.m.) following injection of P. haemolytica. The pharmacokinetics of chloramphenicol (25 mg/kg) and lincomycin (10 mg/kg) were not significantly different in calves with pneumonia. The hybrid rate constant beta for oxytetracycline was increased in calves with pneumonia from 0.0034 +/- 0.0003/min to 0.0048 +/- 0.0007/min between 2 h and 8 h. Thus the elimination half-life in serum was shortened from 212.4 +/- 20.3 min to 149.3 +/- 19.5 min. In addition, there was an apparent but not statistically significant decrease in K12 with pneumonia. These findings accentuate the need for observance of 12-h dose intervals with oxytetracycline.     

Risk Factors for Congenital Umbilical Hernia in German Fleckvieh

Risk factors for congenital umbilical hernias were investigated in German Fleckvieh calves up for sale at livestock markets. Data from 53,105 calves were collected from 77 livestock auctions in 1996 and 1997. The overall incidence of congenital umbilical hernia was 1.8%. A significant influence on incidence was exerted by the sex of the calf, the occurrence of multiple births, the market place/market date, the sire and the sire line. The proportion of Red Holstein blood in the calf, the dam's lactation number, gestation length, 305 day milk performance and the herd milk level were not significant factors. Herdmate averages for calves differed significantly in their incidence. Heritability estimates on the liability scale for congenital umbilical hernia were about 0.4 and progeny groups of sires at risk for congenital umbilical hernia were in the range 0.1% to 14.2%. The segregation pattern could not be explained either by an autosomal recessive or by an autosomal dominant monogenic model. It seems likely that more than one gene locus is involved in the underlying genetic mechanism. Breeders should be aware of the genetic implications of congenital umbilical hernias.     

Effect of antibiotics in milk replacer on fecal shedding of Escherichia coli O157:H7 in calves

The objective of this study was to compare the concentration and duration of fecal shedding of Escherichia coli O157:H7 between calves fed milk replacer with or without antibiotic (oxytetracycline and neomycin) supplementation. Eighteen 1-wk-old Holstein calves were orally inoculated with a strain of E. coli O157:H7 (3.6 x 10(8) cfu/calf) made resistant to nalidixic acid (NA). Rectal samples were obtained three times weekly for 8 wk following oral inoculation. Fecal shedding of NA-resistant E. coli O157:H7 was quantified by direct plating or detected by selective enrichment procedure. Eight weeks after inoculation, calves were killed, necropsied, and tissues (tonsils, retropharyngeal and mesenteric lymph nodes, and Peyer's patches) and gut contents (rumen, omasum, abomasum, ileum, cecum, colon, and rectum) were sampled to quantify or detect NA-resistant E. coli O157:H7. The percentage of calves shedding NA-resistant E. coli O157:H7 in the feces in the antibiotic-fed group was higher (P < 0.001) early in the study period (d 6 and 10) compared with the control group fed no antibiotics. There was no difference between treatment and control groups in the concentration of E. coli O157 in feces that were positive at quantifiable concentrations. A comparison of the duration of fecal shedding between treated and untreated calves showed no significant difference between groups. At necropsy, E. coli O157:H7 was recovered from the rumen and omasum of one calf in the control group and from retropharyngeal lymph node and Peyer's patch of two calves in the antibiotic group. Supplementation of milk replacer with antibiotics may increase the probability of E. coli O157:H7 shedding in dairy calves, but the effect seems to be of low magnitude and short duration.     

Experimental trichophytosis in calves caused by cultures of Trichophyton verrucosum and Trichophyton equinum

Tests were performed on 130 one-month-old calves. In 16 animals, treatment with a suspension of Trichophyton verrucosum culture at the dosage of 5 mil. conidia for an area of 10 x 10 of the clipped skin caused clinical trichophytic changes. The length of the incubation time was shorter in the calves scarified before inoculation of the infecting culture (10 to 13 days), as compared with the group of calves without scarification of the skin (11 to 19 days). Only 3 in 6 calves, infected by the same dose into non clipped skin, did contract trichophytosis, manifesting themselves as separate mycotic deposits, which appeared 26 to 35 days after inoculation. Trichophytic changes lasted longest in the group with scarification of the infected area. The ID50 in T. verrucosum and T. equinum cultures was about 1500 conidia per one calf in the case of the method of infecting into clipped scarified skin (area 100 sq cm). A 10 times lower dose (150 conidia per one calf) of the T. verrucosum suspension did not induce visible mycotic changes, but the T. equinum inoculation produced infection in one of 10 calves.     

Failure to spread bovine virus diarrhoea virus infection from primarily infected calves despite concurrent infection with bovine coronavirus

Previous reports on the spread of bovine virus diarrhoea virus (BVDV) from animals primarily infected with the agent are contradictory. In this study, the possibility of transmission of BVDV from calves simultaneously subjected to acute BVDV and bovine coronavirus (BCV) infection was investigated. Ten calves were inoculated intranasally with BVDV Type 1. Each of the 10 calves was then randomly allocated to one of two groups. In each group there were four additional calves, resulting in five infected and four susceptible calves per group. Virulent BCV was actively introduced in one of the groups by means of a transmitter calf. Two calves, susceptible to both BVDV and BCV, were kept in a separate group, as controls. All ten calves actively inoculated with BVDV became infected as shown by seroconversions, and six of them also shed the virus in nasal secretions. However, none of the other eight calves in the two groups (four in each) seroconverted to this agent. In contrast, it proved impossible to prevent the spread of BCV infection between the experimental groups and consequently all 20 study calves became infected with the virus. Following infection, BCV was detected in nasal secretions and in faeces of the calves and, after three weeks in the study, all had seroconverted to this virus. All calves, including the controls, showed at least one of the following clinical signs during days 3-15 after the trial started: fever (> or =40 degrees C), depressed general condition, diarrhoea, and cough. The study showed that BVDV primarily infected cattle, even when co-infected with an enteric and respiratory pathogen, are inefficient transmitters of BVDV. This finding supports the principle of the Scandinavian BVDV control programmes that elimination of BVDV infection from cattle populations can be achieved by identifying and removing persistently infected (PI) animals, i.e. that long-term circulation of the virus without the presence of PI animals is highly unlikely.     

Pathological studies on systemic mycoses in calves.

Systemic mycoses were found in 19 (4.7%) of 406 calves less than 6 months old which were autopsied during the past 10 years. Alimentary mycosis occurred in 12 (63.2%) of 19 cases. In alimentary mycosis, mucormycosis showed the highest rate of occurrence (91.7%, 11/12 calves) followed by aspergillosis 41.7% and candidiasis was 9.3%. Mucormycosis and aspergillosis were characterized by focal hemorrhagic necroses with hyphal proliferation and thrombi in the mucosa and muscular layers of the forestomach, abomasum, and small intestine. Candidiasis was characterized by hyperkeratosis with pseudohyphae and microconidia in the mucosa of the omasum. Four of 12 calves (33.3%) had mixed infections of the alimentary tract consisting of Mucorales and Aspergillus species. Pulmonary aspergillosis was found in 10 (52.6%) of 19 calves. There were micro-abscesses with hyphal proliferation or asteroid bodies in the lungs. Infections involving both the alimentary tract and respiratory organs were noted in 3 (10.5%) of 19 calves. Disseminated mycosis was found only in one calf. In alimentary mycosis, administration of antibiotics for the treatment of diarrhea and early weaning were thought to be an important predisposing factor.     

Antibiotic disposition in experimental pneumonic pasteurellosis: gentamicin and tylosin.

The effects of severe respiratory disease on the disposition of antibiotics were evaluated using two drugs chosen because of their widely differing solubility characteristics. The experiments were carried out in series, using five calves for each drug. The drugs were given to seven week old calves before and after induction of pneumonia by bilateral intrapulmonary administration of 3 mL of 5 X 10(7) colony forming units of Pasteurella haemolytica. Following inoculation, the calves developed clinical signs of pneumonia and were given gentamicin (5 mg/kg) or tylosin (10 mg/kg) 48, 60 and 72 hours after Pasteurella administration. There was a statistically significant decrease in distribution rate but not elimination rate of gentamicin. For tylosin, there was a significant increase in elimination rate. These results indicate the kinetics of tylosin but not gentamicin are sufficiently altered as to support a need for increased frequency of administration with severe respiratory disease in calves.     

Comparative pharmacokinetics of gentamicin, neomycin and oxytetracycline in newborn calves

The pharmacokinetics of three antibiotics--gentamicin, neomycin and oxytetracycline were determined in newborn calves. The kinetic determinations, using two-compartment open models, were made at increasing ages from 1 day to 42 days and compared with those made from older calves (250+ days). Although all three antibiotics are eliminated unchanged primarily by glomerular filtration, there were marked differences in the development of elimination processes for individual drugs. The pharmacokinetics of neomycin were not influenced by age. Although the elimination half-life of gentamicin appeared to decrease with age, the changes were not significant and were due to an increased elimination rate in only one calf. There was no change with age in the remaining three calves. Oxytetracycline elimination was significantly reduced in newborn calves. This was exemplified by a decrease in the half-life of elimination t1/2 (beta) from 672.5 +/- 99.4 in the newborn to 385.6 +/- 76.8 at 6 weeks of age, and 377.3 +/- 40.8 min in the 250-day-old calf. These changes were consistent in all four calves. The rate of elimination remained low for the first 4 weeks of life. The volume of distribution Vd, area was not changed after the first week of life. Based on pharmacokinetic changes, an adjustment of dosage is indicated for oxytetracycline in the newborn calf as compared to the older calf or adult.     

Animal and farm influences on the dynamics of antibiotic resistance in faecal Escherichia coli in young dairy calves

It is believed that the intensive use of antibiotics in the management of disease in pre-weaned calves contributes to high levels of antibiotic resistance in commensal and pathogenic bacteria. We described the temporal dynamics of antibiotic-susceptibility patterns seen in bovine enteric Escherichia coli in pre-weaned calves on dairy farms and dedicated calf-rearing facilities. Cohorts of 30 calves at each of six farms were sampled at 2-week intervals during the pre-weaning period. Faecal E. coli isolates were analyzed for antibiotic susceptibility to 12 antibiotics with the disk-diffusion method and grouped using cluster analysis of inhibition-zone patterns. The influences of calf age, farm-type, and individual-calf antibiotic therapy on the clusterings were assessed using stratified analyses and cumulative multinomial logistic regression using generalized estimating equation with antibiotic-resistance cluster as an ordinal-dependent variable. The model controlled for farm and cohort by a nested design and included a repeated measure on calf at each sampling occasion. E. coli from calves 2 weeks of age were more likely to be increasingly multiply resistant than E. coli from day-old calves (OR = 53.6), as were 4- and 6-week-old calves (OR = 29.8 and 16.4, respectively). E. coli from calves on dedicated calf-rearing facilities were more likely to be increasingly multiply resistant than E. coli from dairy-reared calves (OR = 2.4). E. coli from calves treated with antibiotics within 5 days prior to sampling were also more likely to be increasingly multiply resistant than E. coli from calves not exposed to individual antibiotic therapy (OR = 2.0).     

Birth weight and measurements of various body parts of stillborn calves of a large dairy cattle herd]

Stillborn calves (80 animals) originating from one dairy herd were used for studies on allometric measures in newborn calves. In the first approach some factors were neglected and only the effect of the calves' sex was considered. Differences in mean birthweight between male and female calves were reflected in organ and other body constituent weights too, but with different relations between them. Enlarged thyroid glands could be observed in both sexes but more often in female calves meaning that there is no correlation between thyroid size and body weight. Strong correlations of bones, muscles and outer body measures and looser ones of internal organs (thymus, liver, lung, kidneys, spleen) and endocrine glands (adrenal glands) with body weight were found especially in male calves. In some calves the sometimes enlarged liver looked like a fatty liver with its pale yellowish appearance and crumbly consistency.     

Acute phase proteins assessment for an early selection of treatments in growing calves suffering from bronchopneumonia under field conditions

Blood samples were taken from calves with respiratory disease the first day of examination for determination of the serum concentration of haptoglobin, fibrinogen, alpha-2- and gamma-globulins, and albumin. A clinical examination was performed daily for the duration of the disease. The animals were retrospectively classified in two categories: those animals requiring no treatment or antibiotics alone (group A), and antibiotics associated to anti-inflammatory drugs (group B). The serum proteins were tested in order to check whether they were able to distinguish, on the first day of clinical examination, between calves requiring anti-inflammatory treatment (group B) or not (group A). About 80% of calves were properly classified in both groups by the combined use of the two serum proteins haptoglobin and fibrinogen: these two proteins, and especially haptoglobin, were useful for the identification of calves requiring an anti-inflammatory treatment.     

Seroprevalence of Dictyocaulus viviparus in first grazing season calves in Sweden

A serological survey was carried out to determine the prevalence and geographical distribution of Dictyocaulus viviparus in calves after their first grazing season in Sweden. A total of 754 animals from 76 randomly selected herds in seven geographical regions were examined between September 24 and December 19, 2001. To get an indication about the geographical distribution of the infection 41 herds with beef-suckler calves were investigated. On each farm, blood was collected from 8 to 10 animals after an average of 26 +/- 24 days post-housing to determine specific IgG1 levels against a possible lungworm sperm antigen that is highly specific against patent infections of D. viviparus. We also investigated the seroprevalence of lungworm infection in relation to cattle management. In one region additional samples were analysed from 35 herds either with: (a) beef-suckling calves that were dewormed at housing, (b) untreated organically raised dairy calves, and finally from conventionally raised dairy calves either, (c) with or, (d) without a prophylactic anthelmintic treatment programme against gastrointestinal parasites on pasture. A questionnaire was used to obtain information about herd size and management, including measures to control nematode parasites on the farm. A total of 86 (11.8%) out of 754 animals had antibodies against D. viviparus, and at least one infected individual was detected in 30 (39.5%) of the 76 herds examined. Lungworm infected animals were found throughout the country and there was no significant differences between regions, although in southern and southwestern Sweden 70.0% of the herds were infected. Furthermore, there were no major differences in the seroprevalence in relation to management. Between 40.0 and 44.4% of the herds were infected irrespective of management, with the exception of calves from organic herds where no seropositive samples were found (0%). This result is in contrast to previous findings of lungworms in Sweden, and indicates that the parasite status on organic farms is diverse.     

Evaluation of the stable fly (Stomoxys calcitrans) as a vector of enzootic bovine leukosis

Experiments reported here were directed at 2 questions: (1) Can the stable fly (Stomoxys calcitrans) transmit enzootic bovine leukosis? (2) Could early viremia augment the probability of transmission by this insect? In one vector experiment, calves and bovine leukemia virus (BLV)-infected cows were housed with and without stable flies. The calves were monitored serologically during a 3-month postexposure period, using the agar gel immunodiffusion test. All fly-infested and fly-free calves remained BLV-seronegative. For a second vector experiment, donor calves, newly injected with blood from BLV-infected cows with high virus expression, were tethered alternately between uninoculated, weaned BLV-seronegative calves. These groups were housed with or without flies in 2 replicate trials. The inoculated calves from the first replicate seroconverted at 16 and 23 days after inoculation; the inoculated calves from the second replicate seroconverted at 11, 16, 16, and 37 days after inoculation. All uninoculated calves remained BLV-seronegative. In a manual transmission experiment, 50 unfed stable flies were allowed to complete a meal on each of 3 BLV-seronegative calves after feeding on a BLV-seropositive cow with high (42%) virus expression. One control calf was injected with blood from the cow. Seroconversion occurred in the control calf and 1 calf on which flies were given access. A scanning electron microscopic study was made of the everted and closed mouth parts of the stable fly. Given the lymphocyte count in blood from the cow used in the manual vector transmission experiment, it was calculated that 3,950 mouth part volumes would be necessary to transmit BLV.(ABSTRACT TRUNCATED AT 250 WORDS)     

母带犊牛与离母犊牛的血清代谢组学差异

本试验旨在比较母带犊牛和离母犊牛的血清代谢组学差异,为开发犊牛代乳粉提供方向。挑选8头健康且体重[（13.88±0.54） kg]接近的新生犊牛（牦牛■×犏牛♀）为母带犊牛组,犊牛随母哺乳;另外挑选8头体重[（13.75±0.82） kg]接近的新生犊牛（牦牛■×犏牛♀）为离母犊牛组,犊牛饲喂代乳粉。2组犊牛10 d后自由采食相同饲粮。试验期90 d。试验结束当天晨饲前对2组犊牛进行采血,采用超高效液相色谱-四极杆飞行时间质谱（UPLC-QTOF/MS）对血清样品进行代谢组学分析。以差异倍数（FC）、变量重要性投影（VIP）和t检验P值作为筛选依据,筛选标准为FC<0.5或FC>1.5、VIP>1和P<0.01。结果表明,共筛选出DL-3苯乳酸、D-山梨糖醇和橙皮素等共30个差异代谢物（FC<0.5或FC>1.5、VIP>1和P<0.01）。差异代谢物通路分析表明,与血清代谢物的改变最为相关的是D-谷氨酰胺和D-谷氨酸代谢、牛磺酸和亚牛磺酸代谢、精氨酸和脯氨酸的代谢、乙醛酸和二羧酸代谢以及谷胱甘肽代谢5条代谢通路。离母犊牛血清中具有抑菌作...