Comparative disposition kinetics and plasma protein binding of gentamicin sulphate in three juvenile animal species

The pharmacokinetics of gentamicin was studied in lambs, calves and foals, respectively after single intravenous (i.v.) injections of 5 mg kg(-1) body weight. The plasma concentration-time curves of gentamicin sulphate were best fitted to follow a two-compartment open model in calves and foals and a three-compartment open model in lambs. Gentamicin showed high plasma level at 5 min post-injection. Then its concentration decreased gradually until its minimum detectable level at 10 and 12 h post-injection in foals and calves, respectively, was reached. In contrast, the plasma concentrations were much higher in lambs and persisted up to 48 h from the onset of injection. Values of pharmacokinetic parameters for gentamicin sulphate in different animals after i.v. injections were calculated. Pharmacokinetic data in lambs demonstrated a triphasic decline in plasma gentamicin concentration with slow terminal elimination phase (washout phase) with (t(1/2y)) of 7.7 h. Gentamicin showed a small volume of distribution Vd(ss) (80.3 ml kg(-1)) in lambs indicating that the drug is slightly distributed in extra-vascular tissues. The overall rate of total body clearance ClB in lambs was (0.46 ml kg(-1)) slower than in calves (1.5 ml kg(-1)) and foals (2.7 ml kg(-1)). In vitro protein binding per cent of gentamicin sulphate in plasma were 16.80, 11.03 and 7.98% in lambs, calves and foals. The results of this study emphasize the importance of determining the pharmacokinetics of gentamicin in each species of young animals separately.     

Pharmacokinetics of sodium amoxicillin in foals after intramuscular administration

Pharmacokinetic values of sodium amoxicillin (22 mg/kg of body weight) in foals were determined after a single IM injection in 6 Quarter Horse foals at 3, 10, and 30 days of age. Serum amoxicillin concentrations were measured serially over a 24-hour period. The absorption of amoxicillin was rapid and followed a 1st-order elimination. Mean peak serum concentrations occurred 30 minutes after the injection in foals at all ages and were 17.31 +/- 9.59 micrograms/ml when the foals were 3 days old, 23.28 +/- 9.86 micrograms/ml when the foals were 10 days old, and 21.35 +/- 6.39 micrograms/ml when the foals were 30 days old. Serum samples collected beyond 8 hours after administration contained amoxicillin concentrations less than 0.05 micrograms/ml. The elimination rate constant increased with increasing age (0.5265 +/- 0.0891 hour-1 when the foals were 3 days old, 0.6494 +/- 0.1114 hour-1 when the foals were 10 days old, and 0.7112 +/- 0.1016 hour-1 when the foals were 30 days old). Serum clearance increased with increasing age (498.4 +/- 82.6 ml/hr/kg at 3 days, 631.6 +/- 170.5 ml/hr/kg at 10 days, and 691.2 +/- 127.3 ml/hr/kg at 30 days). Serum half-life decreased with increasing age (1.34 +/-0.243 hour at 3 days, 1.10 +/- 0.239 hour at 10 days, and 0.991 +/- 0.139 hour at 30 days), whereas the extrapolated concentration at time zero and apparent volume of distribution did not change during the first 30 days of age.     

Clearance of penicillin G in the newborn calf

Sodium penicillin G was administered intravenously (4545 IU/kg) to calves on the day of birth (12-24 h old) and at 5, 10, and 15 days of age. Serum was collected at varying intervals for 120 min after injection and analysed for penicillin G. The mean total body clearance (ClB) of penicillin G on the day of birth was 2.98 ml/min/kg compared to 4.83 ml/min/kg at 5 days, 3.11 ml/min/kg at 10 days and 4.65 ml/min/kg at 15 days of age. Clearances at 5 and 15 days were significantly (P less than or equal to 0.05) higher than on the day of birth. The half-life (t1/2 beta), however, did not change significantly over the 15-day period of the study. These results indicate that the newborn calf has an appreciable ability to excrete penicillin G before it is 24 h old, and that total body clearance of the antibiotic increases rapidly in the immediate postnatal period.     

Pharmacokinetics and bioavailability of ticarcillin and clavulanate in foals after intravenous and intramuscular administration

The pharmacokinetics and bioavailability of ticarcillin and clavulanate were determined after intravenous (i.v.) or intramuscular (i.m.) administration of ticarcillin disodium (50 mg/kg) combined with clavulanate potassium (1.67 mg/kg) to groups of healthy foals at 3 days and 28 days of age. After i.v. administration of the combination to five foals, the disposition kinetics of ticarcillin and clavulanate were best described using a two-compartment open model. Mean plasma elimination-rate constant (beta) and clearance (ClB) for ticarcillin were significantly less (P less than 0.01), and volume of distribution at steady state (Vd(ss)) was significantly larger (P less than 0.05), in the foals at 3 days compared with 28 days of age. This indicated that renal excretion mechanisms were immature and ticarcillin was more widely distributed in 3-day-old foals. The mean elimination rate constant for clavulanate was significantly less (P less than 0.01) at 3 days than at 28 days of age. Values of the major kinetic terms describing the disposition of ticarcillin after i.m. administration to five 3-day-old foals were not significantly different from values of these parameters in the same foals at 28 days of age. After i.m. administration of the drug combination, plasma clavulanate concentrations peaked significantly later (P less than 0.01), and the elimination-rate constant (kd) for clavulanate was significantly less (P less than 0.01), in 3-day-old foals than in 28-day-old foals. The bioavailabilities of ticarcillin and clavulanate after i.m. administration in 3-day-old foals were 100% and 88.3%, respectively, and in 28-day-old foals were 100% and 27.4%, respectively. Mean plasma ticarcillin concentrations exceeded 16 micrograms/ml for a longer period after i.m. administration of the drug combination than after i.v. administration to foals of both age groups. By virtue of the frequency of administration required and the painful response elicited by i.m. injection, it is recommended that when the combination of ticarcillin disodium (50 mg/kg) and clavulanate potassium (1.67 mg/kg) is used in foals to treat infections caused by susceptible organisms (MIC less than or equal to 16 micrograms/ml), it should be administered i.v. four times daily.     

Milk and water intakes of foals sucking grazing mares.

Intakes of milk and milk nutrients were determined for 8 foals at 11-18 days of age and for 10 foals at 30-44 days and 60-74 days of age while sucking grazing mares. Water intakes (sources other than milk) of the foals were determined at 30-44 days and 60-74 days of age. Five of the 10 mares were fed a protein supplement (24% crude protein) in addition to grazing during the stud season. The protein supplement did not influence foal intakes of milk and milk nutrients, milk composition, weight gains of the mares or the growth rate of the foals. Foal milk intakes increased (P less than 0.05) from 16.9 kg/day at 11-18 days to 18.1 kg/day at 60-74 days of age. The water intakes of the foals increased (P less than 0.01) from 3.9 kg/day at 30-44 days to 5.5 kg/day at 60-74 days of age. Total fluid intakes per kg foal liveweight were 246, 202 and 172 g at 11-18, 30-44 and 60-74 days of age, respectively. For each kg of weight gain, foals consumed 12.8, 15.7 and 16.4 kg milk at 11-18, 30-44 and 60-74 days of age. Stage of lactation had a significant effect on the total solids, lactose and protein content of milk. The fat and gross energy content of milk remained constant.     

Changes in faecal bacteria and metabolic parameters in foals during the first six weeks of life

Many foals develop diarrhoea within the first two weeks of life which has been suggested to coincide with postpartum oestrus in their dams. To analyse the pathogenesis of this diarrhoea we have determined faecal bacteria in foals and their dams (n=30 each), and serum IGF-1 and γ-globulins for 6 weeks after birth. In addition, effects of β-carotene supplementation to mares (group 1: 1000 mg/day, n=15, group 2: control, n=15) on diarrhoea in foals were studied. Diarrhoea occurred in 92 and 79% of foals in groups 1 and 2, respectively, but was not correlated with oestrus in mares. Beta-carotene supplementation was without effect on foal diarrhoea. In mares, bacterial flora remained stable. The percentage of foals with cultures positive for E. coli was low at birth but increased within one day, the percentage positive for Enterococcus sp. was low for 10 days and for Streptococcus sp. and Staphylococcus sp. was low for 2-4 weeks. By 4 weeks of age, bacterial flora in foals resembled an adult pattern. Concentration of serum IGF-1 was low at birth (group 1: 149 ± 11, group 2: 166 ± 17ng/ml), increased after day 1 (day 7 group 1: 384 ± 30, group 2: 372 ± 36) but at no time differed between groups. Serum γ-globulin concentration in foals was low before colostrum intake and highest on day 1 (p<0.001 over time). In conclusion, neonatal diarrhoea in foals does not coincide with postpartum oestrus in their dams but with changes in intestinal bacteria and is not influenced by β-carotene supplementation given to mares.     

Pharmacokinetics of gentamicin in mares in late pregnancy and early lactation

The disposition of drugs may differ between pregnant and nonpregnant animals, necessitating a change in dosage. We hypothesized that volume of distribution or clearance may be different for aminoglycoside antibiotics in pregnant mares vs. nonpregnant lactating mares. To examine this hypothesis, we administered gentamicin sulfate to seven Thoroughbred and Quarterhorse mares on two occasions, followed by plasma drug gentamicin assay and pharmacokinetic analysis. The first dose was administered 1-4 weeks before parturition (mean weight 578 kg) and the second dose was administered in the period 1-4 weeks after parturition (mean weight 518 kg). The dose administered at each time was approximately 6.6 mg/kg, intravenously (i.v.). Plasma gentamicin concentrations were determined using fluorescence polarization immunoassay and pharmacokinetic analysis was performed using a two-compartment open model. The plasma concentration vs. time profiles and total area-under-the-curve were almost identical for mares at late gestation vs. early lactation. Mean volume of distribution at steady-state was 0.15 (+/-0.02) and 0.16 (+/-0.03) L/kg, systemic clearance was 1.06 (+/-0.17) and 1.11 (+/-0.17) mL/kg/min, and mean (harmonic) elimination half-life was 2.2 and 2.1 h, for pregnant and nonpregnant mares, respectively. We concluded that there were no differences in drug distribution and clearance between pregnant and nonpregnant lactating mares. Gentamicin was also assayed in plasma of newborn foals after an injection of 6.6 mg/kg to three of the mares within 60 min of parturition. Gentamicin was undetectable in plasma samples from these foals and, therefore, apparently does not cross the placenta of mares at term.     

Feeding and drinking behavior of mares and foals with free access to pasture and water

The feeding and drinking behavior of 11 mares and 15 foals living on pasture with free access to water was recorded during 2,340 15-min focal samples taken over 2 yr. Lactating mares on pasture spent about 70% of the day feeding. Foals began feeding on their first day of life. As they grew older, they spent progressively more time feeding, but still spent only 47 +/- 6% of the time feeding by 21 wk of age. Foals fed primarily during the early morning and evening. While grass formed the major proportion of the diet of both foals and mares, they also ate clay, humus, feces, bark, leaves and twigs. Almost all feeding by foals was done while their mothers were feeding. Movement to water sources was frequently, but not invariably, carried out by an entire herd. Frequency (P = .005) but not duration (P greater than .05) of drinking bouts by mares increased as the temperature increased. Frequency was greatest at 30 to 35 C, at which temperature mares drank once every 1.8 h. Frequency of drinking varied with the time of day (P less than .01), being rarest during the early morning (0500 to 0900 h eastern daylight time) and most frequent during the afternoon (1300 to 1700 h). Drinking by foals was very rare. The youngest age at which a foal was observed to drink was 3 wk, and 8 of 15 foals were never observed to drink before weaning.     

Gentamicin pharmacokinetics in horses given small doses of Escherichia coli endotoxin

The pharmacokinetics of gentamicin (3 mg/kg of body weight) were evaluated in 6 healthy horses and in 6 horses after they were given Escherichia coli endotoxin (0.113 microgram/kg). In the horses given endotoxin, there were a maximum temperature increase of 1.97 +/- 0.44 degrees (C) and a fever index (between the 2 groups) of 8.754 units. Other mild signs of endotoxemia also occurred. Statistically significant changes were not observed in the rate constants for distribution (alpha) or elimination (beta) or in body clearance (ClB) of gentamicin in the 2 groups of horses. In the horses given endotoxin, significant (P less than 0.05) increases were found in the serum concentration data (A, B, and CoS), and significant decreases were found in the apparent volume of distribution [Vd(area)] and in the volume of the central compartment (Vc). The alterations in gentamicin kinetics in the horses given endotoxin are believed to result from the decrease in Vc. This indicates that the extracellular fluid volume available for gentamicin distribution may be reduced by endotoxin.     

Influence of age on the disposition kinetics of chloramphenicol in equine neonates

The effect of age on the pharmacokinetics of chloramphenicol was determined after IV administration of chloramphenicol sodium succinate (25 mg/kg of body weight) to 6 foals at 1 day and 3, 7, 14, and 42 days of age. The disposition of chloramphenicol was best described, using a two-compartment open model in all foals at all ages evaluated. Significant age-related changes were observed in values for the major kinetic terms describing the disposition of chloramphenicol in foals; the greatest changes were observed between 1 day and 3 days of age. The mean +/- SD value for elimination rate constant (beta) for chloramphenicol in 1-day-old foals (0.131 +/- 0.06 h-1) was significantly (P less than 0.005) lower than the value in 3-day-old foals (0.514 +/- 0.156 h-1), and both values were significantly (P less than 0.05) lower than values for beta in 7-, 14-, and 42-day-old foals. With increasing age, the increase in the mean value for beta resulted in decrease in the harmonic mean elimination half-time (t1/2 beta) for chloramphenicol, from 5.29 hours in 1-day-old foals to: 1.35 hours in 3-day-old foals; 0.61 hour in 7-day-old foals; 0.51 hour in 14-day-old foals; and 0.34 hour in 42-day-old foals. At 1, 3, and 7 days of age, values for t1/2 beta of chloramphenicol in a premature foal born after parturition was induced with oxytocin, were considerably longer than comparable t1/2 beta values for term foals born naturally.(ABSTRACT TRUNCATED AT 250 WORDS)     

Safety of altrenogest in pregnant mares and on health and development of offspring

Fifty-one light-horse mares were utilized to evaluate the safety of an oral progestin, altrenogest, administered throughout gestation on: gestation length, embryonic and fetal loss, periparturient events, health and development of offspring, and future reproductive capabilities of the mares. Pregnancies were established by inseminating mares with 250 × 10⁶ progressively motile spermatozoa from the same stallion every other day throughout estrus or by non-surgical transfer of embryos. Mares were randomly assigned to 1 of 2 treatments upon confirmation of pregnancy on day 20: 1) controls, 2 ml of neobee oil orally per 44.5 kg of body weight; and 2) treated, 2 ml of altrenogest dissolved in neobee oil at a concentration of 2.2 mg/ml orally per 44.5 kg of body weight. Treatments were administered daily from day 20 to 320 of gestation.There were no significant differences between treatment groups for duration of gestation, placental weight, time to placental expulsion and incidence of retained placental membranes. Number of female foals born from altrenogest treated mares (14 of 23) was greater (P<.05) than the number from untreated control mares (4 of 16). Female foals born from altrenogest treated mares had larger clitori (P<.05) than those from control mares. Times to sternal recumbency, standing and nursing were similar for the 2 groups (P>.05). Body weight and height at withers, heart girth circumference and length and width of cannon were measured at time of birth and at 2, 4, 6, 8, 12 and 16 weeks of age. Measurements did not differ (P>05) between treated and control foals for any development parameters.Beginning on day 20 postpartum, mares were teased daily. During estrus, mares were inseminated every other day with 250 × 10⁶ motile spermatozoa. Teasing and/or insemination was continued for 2 cycles or until mares were 35 days pregnant. The number of mares pregnant after 1 cycle and after 2 cycles of insemination was similar (P>.05) for treated and control mares. Nineteen of 21 treated mares and 15 of 16 control mares were pregnant after 2 cycles of insemination. Number of cycles per pregnancy was similar (P>.05) for treated and control mares (1.37 vs 1.13) as was number of days mares exhibited estrus (6.30 vs 6.13). Number of inseminations per cycle did not differ (P>.05) between treated and control mares (2.92 vs 3.00). In summary, there was no effect of treatment with altrenogest from day 20 to 320 of gestation on periparturient events, viability and growth of offspring and subsequent reproductive performance of mares.     

West Nile Virus Antibody Titers and Total Immunoglobulin G Concentrations in Foals from Mares Vaccinated in Late Gestation

This study was conducted to determine whether prepartum vaccination of mares would enhance passive transfer of West Nile virus (WNV)-specific antibodies and to characterize the pattern of decline for maternally derived WNV antibodies in foals. Seventeen light horse mares were allocated to WNV or control treatments. At 30 days before expected foaling, mares were vaccinated for encephalomyelitis, tetanus, herpesvirus, and influenza. At this time, WNV mares were vaccinated with a killed WNV vaccine. Blood samples were taken from mares 30 days before expected foaling, from mares and foals within 24 hours of foaling (0 days), and from foals at 7, 30, 60, 90, 120, 150, and 180 days of age as well as 30 days after an initial (PV1) and subsequent (PV2) WNV vaccination. Serum was analyzed for titer to WNV and total immunoglobulin G (IgG). Although WNV titer did not change over time in control mares, an increase (P < .05) was observed in WNV titer for WNV mares vaccinated 30 days before expected foaling. Foals of WNV dams had greater (P < .05) WNV titers than foals of control dams. Mean WNV titers of all foals increased from 0 to 7 days and declined through 180 days of age. Total IgG of foals increased from days 0 to 7, declined from days 30 to 120, and increased from days 150 through PV2. These results suggest that vaccination of mares for WNV in late gestation has a beneficial effect on foal WNV titer.     

A survey of reproductive performance in Thoroughbred mares and morbidity, mortality and athletic potential of their foals

A survey was performed to evaluate the reproductive performance of Thoroughbred mares, estimate risks of dystocia and of morbidity and mortality in foals during the first year post partum and their physical acceptability at age one year. The study population consisted of registered Thoroughbred mares and their foals owned by residents of 4 Western Canadian provinces. Owners were identified using information obtained from the North American Jockey Club, and questionnaires were mailed regarding mares bred in 1988 and their foals born in 1989. Eighty-three per cent of mares were reported to be pregnant at some stage following breeding, and 80% of pregnant mares subsequently gave birth to live foals. Estimates of morbidity and mortality were greater than previously reported, 25% of foals had health problems and 5% died during the first 2 weeks postpartum. Twenty-seven per cent of foals surviving 2 weeks were reportedly affected by some health problem between age 15 days and one year, and 6% died during this period. The case fatality rates of horses with upper respiratory tract infections and diarrhoea were much lower than case fatality rates for infectious diseases occurring less frequently. The rate of death or euthanasia among horses with musculoskeletal problems was relatively high after age 2 weeks. Foals with health problems up to age 2 weeks, or between age 15 days and one year were 5 to 7 times more likely to be classified as physically unacceptable for athletic use. Angular limb deformity was the health problem most commonly reported in foals receiving unacceptable physical assessments, and assessments of longterm athletic potential were apparently not affected by the occurrence of infectious diseases.     

Pharmacokinetics and tissue residues of gentamicin in lactating cows after multiple intramuscular doses are administered

Gentamicin was administered IM to 6 healthy, mature, lactating cows at a dosage of 3.5 or 5 mg/kg of body weight every 8 hours for 10 consecutive days (total, 30 doses). Endometrial biopsies were done at 72, 136 or 144, and 216 hours after the first dose was administered. On the 10th day, just before the last dose of gentamicin was administered, blood samples (designated 10th-day base-line samples) were obtained, and serial blood samples were obtained for 144 hours after the last injection was given. The cows were catheterized on the 10th day, and urine was obtained for 10 to 18 consecutive hours. Milk samples were also obtained. The cows were slaughtered at different times after the last dose was given, and samples were taken from 22 tissues and organs. Serum, milk, urine, and tissue gentamicin concentrations were determined by radioimmunoassay. Serum gentamicin concentrations were best fitted to a 2-compartment open model. The mean half-lives for absorption, distribution, and elimination were 0.16 +/- 0.14, 2.59 +/- 0.53, and 44.91 +/- 9.38 hours, respectively. Total body clearance and renal clearance were 1.65 +/- 0.69 and 1.32 +/- 0.25 ml/min/kg, respectively. The percentage of the dose excreted unchanged in the urine at 8 hours after the last dose was given was 98 +/- 15. As expected, of the tissues examined, the gentamicin concentrations in the kidney cortex and medulla were 1,500 times greater than those in serum. Renal function remained within the baseline range during the 10 days of gentamicin treatment.(ABSTRACT TRUNCATED AT 250 WORDS)     

Pharmacokinetics of gentamicin in the calf: developmental changes

The purpose of this study was to determine the pharmacokinetic values for gentamicin in neonatal calves and to compare these values with those in adult cattle (cows). Gentamicin (4 mg/kg of body weight) was administered IV to 7 Holstein bull calves on days 1 (between 12 and 24 hours of age), 5, 10, and 15 after birth, and was administered once IV to 7 Holstein cows. Serum was collected from each animal before administration and at 22 different time intervals from 2 to 400 minutes after injection. Sera were analyzed for gentamicin concentrations. Decay of serum gentamicin concentrations was best described by a 2-compartment pharmacokinetic model. Elimination half-life (t1/2 (beta)) of gentamicin decreased from day 1 (149 minutes) to day 5 (119 minutes), but did not change between days 5 and 15 (111 minutes). Compared with the t1/2(beta) in 1- and 15-day-old calves, the t 1/2 (beta) in cows was shorter (76 minutes). In the calves, apparent volume of distribution (based on total area under the disposition curve) did not change between 1 (393 ml/kg) and 5 (413 ml/kg) days of age, decreased on day 10 (341 ml/kg) and cows day 15 (334 ml/kg), and was markedly smaller than that in cows (140 ml/kg). Total body clearance of gentamicin in cows (1.29 ml/min X kg) was lower than that seen in calves on day 1 (1.92 ml/min X kg) and on day 15 (2.10 ml/min X kg). The decrease in apparent volume of distribution of gentamicin was mirrored by a large decrease in the extracellular fluid volume, as measured by inulin space.(ABSTRACT TRUNCATED AT 250 WORDS)     

断奶前马驹与母马粪便菌群多样性分析

试验旨在探究断奶前马驹和母马粪便菌群多样性,为丰富此阶段马驹肠道菌群多样性提供依据。选取5匹5岁（2胎）、平均体重（453.34±54.23）kg、健康的纯血马母马,以及母马所生的5匹马驹,出生日期相近（±5 d）,平均体重（185.65±9.54）kg,3公2母。母马和马驹在相同环境下饲养,母马日粮组成及营养水平相同,马驹除哺乳外采食的粗饲料和精料补充料相同。马驹6月龄断奶,在断奶前1周用灭菌收粪袋采集母马和马驹的粪便样品。结果显示,母马粪便中菌群α多样性Chao1和ACE指数显著高于马驹（P < 0.05）,分别比马驹高18.94%和15.62%;母马与马驹共有的菌种数为1 399个,母马与马驹特有的菌种数分别为150和68个;在门水平,母马与马驹粪便中排在前十的菌分别是厚壁菌门、变形菌门、拟杆菌门、放线菌门、广古菌门、疣微菌门、螺旋体菌门、Unidentified_Bacteria、纤维杆菌门和无壁菌门,母马粪便中厚壁菌门丰度显著高于马驹（P < 0.05）;拟杆菌门母马比马驹高33.93%,差异不显著（P > 0.05）。由此可见,母马粪便菌群多样性显著高于断奶前马驹;母马与断奶前马驹粪便主要菌是厚壁菌门、拟杆菌门和变形菌门,母马粪便中厚壁菌门和拟杆菌门丰度均高于断奶前马驹。     

代乳粉对不同日龄驴驹生长性能的影响

旨在评价代乳粉对不同日龄驴驹生长性能的影响。分别选取2、3、4、5月龄出生日期、体重、胎次相近且健康状况良好的驴驹各10头,将相同月龄的驴驹随机分为试验组和对照组,每组5头,对照组驴驹随母驴哺乳,试验组驴驹饲喂代乳粉,试验期为30d。试验期间观察不同月龄驴驹的健康状况,测定并比较各月龄对照组及试验组驴驹在试验第0、10、20、30天的体重及体尺指标（体高、胸围、体斜长）,计算同月龄试验组和对照组驴驹的体重及各项体尺指标在试验期内不同时间段的日均变化值。结果表明,2月龄试验组驴驹的试验第10、20、30天体重均极显著（P〈0．01）高于对照组,5月龄试验组驴驹的试验第20天和第30天体重分别显著（P〈0．05）和极显著（P〈0．01）高于对照组（P〈0．05）,2、3、4、5月龄试验组驴驹在试验第0～10天、第10～20天、第20～30天,以及试验期间（第0～30天）的日增重均高于相应月龄驴驹的对照组;5月龄试验组驴驹的试验第10、20、30天体高均显著（P〈0．05）高于对照组,2、5月龄试验组驴驹在试验第0～10天、第10～20天、第20～30天以及试验期间（第0～30天）的体高日增长均高于相应月龄驴驹的对照组;2月龄试验组驴驹的试验第20天和第30天胸围均极显著（P〈O．01）高于对照组;3月龄试验组驴驹的试验第10、20、30天胸围均极显著（P〈O．01）高于对照组;5月龄试验组驴驹的试验第20天和第30天胸围均显著（P〈0．05）高于对照组;2、3、4、5月龄试验组驴驹在试验期间（第0～30天）的胸围日增长均高于相应月龄驴驹的对照组;2、5月龄试验组驴驹的试验第30天体斜长显著（P〈0．05）高于相应月龄驴驹的对照组,3月龄试验组驴驹的试验第10、20、30天体斜长均显著（P〈0．05）高于对照组,4月龄试验组驴驹的试验第20天和第30天体斜长均显著（P〈O．05）高于对照组,2、3A、5月龄试验组驴驹在试验第10～20天、第20～30天,以及试验期间（第0～30天）的体斜长日增长均高于相应月龄驴驹的对照组。综上提示,饲喂代乳粉能够促进驴驹的生长发育,在生产实践中利用代乳粉替代驴乳饲喂驴驹具有可行性。     

Pharmacokinetics of erythromycin in foals and in adult horses

The pharmacokinetic parameters of erythromycin in foals were determined following intravenous administration of 5.0 mg/kg to animals aged 1, 3, 5 and 7 weeks. The distribution of the drug was described by a two-compartment open model, and no significant differences were observed between coefficients on which the parameters were based. Pharmacokinetic values were also determined for four mares given 5.0 mg/kg intravenously and for six 10–12 week-old foals given 20.0 mg/kg intravenously. The half-life of erythromycin for all groups of animals (foals less than 7 weeks, mares, foals 10–12 weeks) was 1.0–1.1 h; the apparent volume of distribution was between 2.3 and 7.2 l/kg, and the clearance of the drug from the body was between 1.9 and 5.0 mg/kg/h. No drug could be detected in the serum following oral administration of 5.0 mg/kg erythromycin estolate; detectable levels were found for 5 h in mares given 12.5 mg/kg, and for 8 h in foals given 20.0 mg/kg orally. Peak levels in foals given the drug orally were 0.42 μg/ml at 120 min after administration. Foals given 10.0 mg/kg of erythromycin base intramuscularly had serum concentrations detectable 12 h later, the peak level achieved was 1.44 μg/ml serum 90 min after administration and concentrations exceeded 0.25 μg/ml for 6 h. In the mares the milk concentrations were approximately twice those in serum. Recommendations were made for drug dosage to be used in the treatment of Corynebacterium equi pneumonia of foals.     

Effects of experimentally induced Streptococcus suis infection on the pharmacokinetics of penicillin G in pigs

The pharmacokinetics of potassium penicillin G were studied in both healthy (n = 8) and experimentally Streptococcus-suis-infected (n = 6) pigs following intramuscular administration (15,000 iu/kg). Streptococcus-suis infection was induced artificially in young cross-bred pigs by subcutaneous inoculation with 9 x 10(8) to 10(9) colony-forming units of S. suis. The rectal temperature of infected pigs was significantly increased (P less than 0.01) before penicillin G injection and this was maintained for 8 h after the drug was given. Other clinical symptoms were also present. The serum concentration-time data for penicillin were found to fit a one-compartment open model with first-order absorption in the two groups of pigs. Significant changes were not observed between healthy and diseased pigs in following parameters: A, Ka, Ke and Tmax. However, in diseased pigs, significant increases (P less than 0.01) were found in Vd and ClB, and significant decreases (P less than 0.01) in Cmax and AUC occurred. The increased body clearance (ClB) and greater apparent volume of distribution (Vd) of penicillin G could partly explain why the serum values of the drug were much lower in diseased pigs than in healthy pigs.     

Induction of parturition in mares: effect on passive transfer of immunity to foals

Parturition was induced in 11 mares, using a synthetic prostaglandin. Eight mares, not treated, were used as controls. There was no significant difference between the serum immunoglobulin G (IgG) concentrations of the treated and control mares. The concentration of IgG in the colostrum of treated mares compared favorably with that reported for naturally foaling mares. Four foals from treated mares died or were euthanatized because of weakness during the 1st 24 hours after birth. The mean IgG concentration in the surviving foals from treated mares at 24 to 36 hours of age was 1,561 mg/100 ml, which was significantly (P less than 0.01) lower than the mean concentration of 2,731 mg/100 ml in foals from control mares. The mean serum IgG concentration in foals from control mares was significantly (P less than 0.01) greater than that of their dams, whereas the mean serum IgG concentration of the foals from treated mares was significantly (P less than 0.01) lower than that of their dams.