Additional Lambs Research Articles

Prolonged pulmonary vasodilator action of inhaled nitric oxide by Zaprinast in awake lambs

Inhaled nitric oxide (NO) has been shown to selectively dilate the pulmonary vasculature. Zaprinast, an inhibitor of guanosine 3',5'-cyclic monophosphate-specific phosphodiesterase, augments smooth muscle relaxation induced by endothelium-dependent vasodilators. The present study was designed to determine whether intravenous administration of Zaprinast potentiates the vasodilating effects or prolongs the duration of action of intermittent NO inhalation. Eight awake lambs with U-46619-induced pulmonary hypertension breathed three concentrations of NO (5, 10, and 20 ppm) in a random order before and during an intravenous Zaprinast infusion (0.1 mg.kg-1.min-1). Inhaled NO decreased pulmonary arterial pressure (PAP) in a dose-dependent fashion, with mean PAP reduction at 5, 10, and 20 ppm NO inhalation of 6 +/- 1, 7 +/- 1, and 9 +/- 1 (SE) mmHg, respectively. Although the Zaprinast infusion did not change the magnitude of mean PAP reduction, it caused a statistically significant reduction of pulmonary vascular resistance and prolonged the duration of action of inhaled NO (half-times of vasodilator response to 5, 10, and 20 ppm NO inhalation: 1.9 +/- 0.1, 2.1 +/- 0.2, and 2.1 +/- 0.2 min, respectively; half-times of NO inhalation with Zaprinast: 9.7 +/- 1.7, 11.5 +/- 2.2, and 12.3 +/- 2.0, respectively). Plasma concentrations as well as the transpulmonary differences of guanosine 3',5'-cyclic monophosphate were increased by the Zaprinast infusion during NO inhalation. A stable level of pulmonary vasodilation was demonstrated in four additional lambs by combining intermittent NO breathing with an intravenous infusion of Zaprinast.

Stress-associated concentrations of plasma cortisol cannot account for reduced lymphocyte function and changes in serum enzymes in lambs exposed to restraint and isolation stress.

Lambs were used to evaluate the effect of stress-associated plasma concentrations of cortisol on measures of immune function. Lambs given restraint and isolation stress (RIS) were isolated from visual and tactile contact with other lambs for 6 h on three consecutive days. Additional lambs were infused with cortisol (CORT) to increase plasma concentrations similar to those in lambs subjected to RIS. Control lambs (CON) were undisturbed. On the 1st and 3rd d of the experiment, plasma was obtained hourly during treatment for quantification of cortisol and ACTH. Blood mononuclear cells were obtained 24 h before the 1st d of treatment and daily at the conclusion of treatment for responses to phytohemagglutinin (PHA), concanavalin A (Con A), and pokeweed mitogen (PWM); for production of interleukin 2 (IL2); and for identification of cells expressing major histocompatibility complex class II antigens (MHCII). Combined fitted profiles of cortisol in RIS and CORT lambs differed (P < .005) from those in CON on both days evaluated. Fitted profiles of cortisol were similar between RIS and CORT lambs on the 1st d of treatment but differed (P < .005) on the 3rd d. Combined fitted profiles of ACTH from CON and CORT lambs differed from those of RIS lambs on both days of treatment (P < .005). Lymphocyte responses to PHA (P < .01), Con A (P < .01), and PWM (P < .07) were less in RIS than in CON but did not differ between CON and CORT. Treatment did not affect IL2 or MHCII. Increased plasma cortisol measured during RIS cannot alone account for reduced lymphocyte proliferative responses.

Sarcocystosis with involvement of the central nervous system in lambs.

An outbreak of neurologic disease in a flock of 5-month- taining large rounded metrocytes and early bradyzoites, and old Rambouillet lambs on a sheep farm in west-central In- were associated with some degree of myositis with degendiana was investigated. Over a 4-week period during the eration of muscle fibers and lymphocytic perimysial infiltrasummer of 1990, 32 of 48 lambs in 1 pen were affected, and tion. 22 of these lambs died. Approximately 300 sheep were on Multifocal, nonsuppurative meningoencephalomyelitis was the farm. The affected lambs were confined to a single pen evident in the cerebrum, cerebellum, brain stem, and cerin a large open-sided pole barn and were the youngest group vital, thoracic, and lumbar spinal cord of all 3 lambs (Fig. of spring lambs on the farm. 1). Inflammation was characterized by glial nodules, multiClinical signs described by the owner and referring vet- focal necrosis with gliosis and mononuclear cell infiltration, erinarian included anorexia, weight loss, incoordination, stiff and lymphocytic infiltration around blood vessels and in the limbs, trembling, and generalized weakness. The condition meninges (Fig. 2). An immature schizont was found in the progressed rapidly in fatal cases, and death generally occurred pons of 1 of these lambs (Fig. 3). The density of neuroglia within 7 days of the onset of clinical signs. around this schizont was increased, but the schizont was not Three clinically affected lambs (2 live and 1 dead) were surrounded by microglia. Immunohistochemical examinasubmitted to the Animal Disease Diagnostic Laboratory, tion of paraffin-embedded sections of samples of brain from Purdue University, West Lafayette, Indiana, for diagnostic all 3 lambs using antisera to Toxoplasma gondii, Neospora evaluation. Both live lambs were thin, weak, and ataxic. All caninum, and Sarcocystis spp. was negative. 11 The FA test 3 lambs had bronchopneumonia of varying severity. One for pseudorabies was negative, and no viral agent was isolamb had moderate subcutaneous edema of the neck and lated. inguinal region and mild serous effusions in the pleural, peri- The small intestine of 1 lamb was infected by coccidia and cardial, and peritoneal cavities. Tissue samples from all 3 cryptosporidia. After the diagnosis of intestinal coccidiosis lambs were routinely processed for histopathologic exami- was conveyed, the referring veterinarian directed the owner nation. Samples of pneumonic lung were inoculated on blood to add amprolium to the lambs’ feed. Following treatment, and MacConkey’s agar in an attempt to culture for aerobic affected lambs improved clinically, no more died, and no bacteria. Selected areas of the pneumonic lungs were ex- additional lambs developed clinical signs. amined for bovine respiratory syncytial virus (BRSV), in- Approximately 6 weeks later, a team of diagnostic perfectious bovine rhinotracheitis virus (IBR), and sonnel visited the farm for an on-site evaluation, to collect Parainfluenza-3 virus (P13) by direct immunofluorescence convalescent sera from affected and nonaffected lambs, to (FA) and were inoculated onto bovine turbinate cells for virus collect fecal samples from dogs, and to choose a convalescent isolation. A portion of the brain from 1 of the live lambs lamb for further diagnostic evaluation. was examined for pseudorabies virus by FA and was also Hay was found stacked in 1 comer of the pole barn, and inoculated onto cell cultures. grain was stored in uncovered wooden bins at the opposite

Optimum use of subcutaneous melatonin implants to enhance the reproductive performance of seasonal and non-seasonal sheep joined in spring and early summer

This paper reviews data from five research trials and 108 clinical trials conducted in three countries to validate the optimum use of melatonin to advance seasonal breeding patterns of a variety of breeds of sheep. In order to define the optimum time for treatment in breeding flocks, ewes of three different breeds were treated with controlled-release 18-mg melatonin implants (Regulin®), with treatments commencing at various times ranging from 9 to 3 weeks prior to joining with fertile rams. Mating and conception patterns were recorded by regular observation for raddle marks and fecundity was assessed by mid-pregnancy ultrasonography. These research trials were conducted at a latitude of 38°S in Merino ewes of slight seasonality, in Merino-based cross-breeds of intermediate seasonality and in highly seasonal British breed Romney Marsh ewes. A single implant treatment, commencing at 30–40 days prior to spring or early summer joining, resulted in coincidence in timing of the peak of the inductive phase of the ovarian response to melatonin with the peak of oestrus and mating which arose from the pheromonal influence of the rams. Thus, this treatment strategy maximises the potential advantages to be obtained from both the melatonin treatment and the rams. Subsequent clinical trial programmes in Australia, the UK and New Zealand confirmed this treatment strategy and tested the available periods of the year during which effective responses could be obtained under farm conditions. It was shown that, whereas Merino and Merino cross-breeds were responsive to melatonin treatment over a wide part of spring and early summer, the British breed ewes responded only during a relatively short period of the season around the time of the summer solstice. Treatments which commenced too early in British breeds were ineffective or gave negative results, possibly because of a failure of such breeds to be able to fully interpret the pharmacological short-day signal before they have experienced an adequate period of long-day priming. For all breeds, treatments given late in summer at a time of decreasing natural daylight were also ineffective since, by this time, ewes were already experiencing a naturally occurring inductive photoperiodic signal. Overall, the studies reviewed in this paper showed that melatonin pretreatment of spring and early summer joined ewe flocks resulted in both a modest decrease in the number of barren ewes and an increase in the number of multiple births. The effects were seen in flocks of high or low basal performance and in both maiden and mature ewes, but in no case were the responses associated with the induction of supraphysiological litter size. Mean increases in litter size, for different breeds of ewe, ranged from 14.3 to 28.6 additional lambs born per 100 ewes treated, with variation between trials largely accounted for by expected sampling errors associated with the precise measurement of the discontinuous variable of litter size in relatively small sample sizes of 50–200 animals per group. Treatment of mothers with melatonin prior to joining had no effect on the sex ratio, birth weight or appearance of offspring. Melatonin pretreatment of breeding ewes was also associated with an earlier mean conception (lambing) date and a compaction of the conception (lambing) patterns but the magnitude of these measured effects was dependent upon the extent to which untreated control flocks were responsive to the pheromonal influence of rams. Overall the data extends, to a practical field level, the proper use of melatonin to at least partially overcome the seasonal constraint to breeding in sheep, and provides a sound basis for future research and clinical experimentation in this area.

Oxygen Extraction in Lamb Skeletal Muscle

Past studies have found that total-body O2 extraction during hypoxia was less in 1-wk-old lambs than in older animals. It was proposed that reduced O2 extraction was secondary to suppression of growth-related oxygen consumption (VO2) in tissues such as skeletal muscle, bone, kidney, and skin, rather than a defect in peripheral O2 use. To determine the capacity of immature skeletal muscle to extract O2, we isolated the hind limb circulation of eight ketamine-anesthetized, 7- to 18-d-old lambs exposed to stagnant hypoxia by inflation of a right atrial balloon catheter. Femoral arterial and venous PO2, PCO2, pH, Hb concentration, O2 saturation, and femoral arterial blood flow (Q) were measured and hind limb O2 delivery (DO2), extraction ratio, and VO2 calculated. Individual critical levels of DO2 below which VO2 was dependent on O2 supply were determined by dual-line best-fit regression analysis. In six of eight animals, VO2 was clearly independent of supply until DO2 reached critically low levels. However, O2 extraction during extreme hypoxia appeared submaximal (baseline O2 extraction ratio, 0.22 +/- 0.06; at critical levels of DO2, 0.51 +/- 0.11; at the lowest level of Q, 0.64 +/- 0.15). When 2,4-dinitrophenol, an uncoupler of oxidative phosphorylation, was administered to four additional lambs exposed to stagnant hypoxia, O2 extraction below critical levels of DO2 increased from 0.48 +/- 0.15 to 0.79 +/- 0.10 (p less than 0.001, unpaired t test). These data suggest that initial limitations in O2 extraction were a result of the suspension of O2-consuming processes, not an irreversible defect in peripheral O2 use.

Retrovirus-associated ovine pulmonary carcinoma (sheep pulmonary adenomatosis) and lymphoid interstitial pneumonia. I. Lesion development and age susceptibility.

To determine the lesion development of retrovirus-induced ovine pulmonary carcinoma (OPC), ten neonatal lambs were inoculated intratracheally with either 1) lung fluid preparations derived from a sheep with Type D retrovirus-associated OPC and concurrent ovine lentivirus (OvLV)-associated lymphoid interstitial pneumonia (LIP) (n = 8); or 2) lung fluid from a sheep with only OvLV-LIP (n = 2). Seven of eight neonates that received Type D retrovirus-associated OPC/OvLV-LIP lung fluid developed both OPC and LIP lesions between 9 and 32 weeks after inoculation. Mild OPC lesions consisted of foci of type II alveolar epithelial cells lining alveoli surrounded by minimal alveolar macrophage infiltrates. More severe OPC lesions consisted of multifocal aggregates of cuboidal to columnar neoplastic cells forming acini or masses associated with abundant alveolar macrophage infiltrates. Lesions of LIP consisted of peribronchiolar and perivascular lymphoid hyperplasia and heterogeneous interstitial leukocytic infiltrates. The two neonates that received OvLV-LIP lung fluid developed rapid and severe LIP, but not OPC lesions. Two lambs (inoculated as neonates with virus-free lung fluid) and three lambs (uninoculated contacts) served as controls and did not develop OPC. To investigate age susceptibility for development of OPC, 20 additional lambs within defined age groups (neonates, 2 weeks old, 5 weeks old, and 10 weeks old) received ultracentrifuged tumor homogenate. Neonatal to 5-week-old lambs inoculated with Type D retrovirus-associated OPC/OvLV-LIP tumor homogenate were equally likely to develop OPC, but lambs inoculated at 10 weeks of age were more refractory to tumor development.(ABSTRACT TRUNCATED AT 250 WORDS)

Pulmonary O2 toxicity in lambs: physiological and biochemical effects of endotoxin infusion

Hyperoxic adult rats have prolonged survival and reduced morphological evidence of lung injury when treated with a single dose of bacterial endotoxin; this effect is mediated by an augmentation of antioxidant enzyme activity in lung homogenate. To determine whether endotoxin would prolong survival and influence antioxidant enzyme levels in lambs whose physiological response to O2 breathing can be serially measured, we administered a single intravenous dose of endotoxin (0.75 microgram/kg body wt) to 13 lambs before exposing them to greater than 95% O2 (n = 11) or air (n = 2). Seven additional lambs were placed in O2 after receiving only saline vehicle. All lambs had been instrumented to measure pulmonary vascular pressures and cardiac output, and 10 lambs had lung lymph fistulas. O2-exposed control lambs developed noncardiogenic pulmonary edema and respiratory failure within 85 +/- 10 h (range 76-110 h); antioxidant enzymes were not increased, but reduced glutathione (GSH) levels fell and oxidized glutathione (GSSG) increased, reflecting the oxidant stress of O2 exposure. By contrast, endotoxin-treated O2-exposed lambs had a delayed increase in microvascular permeability to protein, a reduced rate of lung edema formation, normal gas exchange after 72 h in O2, and prolonged survival (136 +/- 15 h; range 90-160 h; all variables P less than 0.05). Despite prolonged survival, postmortem lung water content was no greater in the lambs that received endotoxin. Treatment with endotoxin did not increase antioxidant enzyme levels in lung homogenate, but levels of GSH relative to GSSG were significantly elevated.(ABSTRACT TRUNCATED AT 250 WORDS)

Fostering lambs by odor transfer: the add-on experiment.

Lamb-specific odor is used by ewes to discriminate between their own and alien offspring. Recent studies have demonstrated that fostering can be facilitated by transferring own-lamb odor to alien lambs via cloth stockinettes. The objective of the present study was to investigate the effectiveness of the odor-transfer technique in enticing ewes with a single lamb to adopt an additional lamb ("add-on" procedure). Shortly after birth, nylon stockinettes were placed on the single offspring of 49 ewes and 49 additional alien lambs designated for fostering. Approximately 20 h following parturition, stockinettes were removed from 41 natural lambs and placed on alien lambs (experimental treatment). In the control treatment (eight ewes) own and alien lambs retained their own stockinettes. Four acceptance tests were conducted, 24 h apart, starting at the onset of fostering. Successful adoptions were attained for 21 of 31 experimental ewes (68%) exposed to add-on lambs similar in facial coloration to their own lambs. Only 2 of 10 experimental ewes (20%) with whiteface natural lambs adopted blackface add-on lambs. One of eight control ewes (12.5%) adopted an add-on lamb. Of the 24 ewes that adopted alien lambs 10 (41.7%) demonstrated immediate acceptance and 20 (83.3%) had adopted lambs by the second test day. A higher proportion of primiparous than multiparous ewes adopted alien lambs. The presence of own-lamb odor on stockinettes worn by add-on lambs appears to facilitate fostering. However, the presence of own-lamb odor may not be a significant-enough cue to override obvious differences in facial coloration between own and add-on lambs.(ABSTRACT TRUNCATED AT 250 WORDS)

Active immunisation against androstenedione in a synchronised early lambing flock

Active immunisation against androstenedione (Fecundin, Coopers Animal Health) increases ovulation and lambing rates. A study undertaken during the 1984-85 breeding season in randomly cycling ewes mated during October and November showed an increase in lambing rate of 24 lambs/100 ewes mated amongst ewes treated with Fecundin (Vipond, Keeling and Hunter, 1986). Fecundin increased the Incidence of triplet and quad births, suggesting that the greater benefit from the product would be derived in a situation where management could ensure the survival of additional lambs. The early lambing flock is such a case. Ovulation rates tend to be lower than later on in the breeding season, so fewer triplets might be expected amongst treated ewes. Management tends to be of a high standard, and the value of the early finished lamb is high.

Effects of number of lambs suckled and supplemental protein source on lactating ewe performance.

Effects of number of lambs suckled and supplemental protein source on ewe performance were determined. Lactation performance of ewes nursing twin or triplet lambs was compared in Exp. 1 and 2. In Exp. 1, ewes giving birth to and nursing triplets produced 21% (P less than .05) more milk/unit metabolic body weight, were 10% more efficient in the conversion of feed to milk and produced 26% (P less than .05) more kg of lamb/ewe on d 42 of lactation than did ewes giving birth to and nursing twins. In Exp. 2, lactation performance of ewes giving birth to triplets and rearing only two lambs was compared with performance of ewes giving birth to triplets and rearing three lambs. Ewes rearing three lambs produced 28% (P less than .08) more milk and were 26% (P less than .05) more efficient in converting feed to milk than were those rearing two lambs. This suggests that direct nursing stimulation of the mammary gland is responsible for the improvement in milk production observed when ewes nurse additional lambs. The efficacy of slowly degradable protein sources for improved lactation was studied in Exp. 3 and 4. When blood meal was fed to twin-rearing ewes at 3.30% of the diet (25% of total dietary protein), milk production was greater (3,176 vs. 2,506 g/d, P less than .05) and efficiency of milk production was greater (1.05 vs .79 g milk/g feed, P less than .05) than when ewes were fed supplemental soybean meal. Ewes in this experiment fed supplemental meat and bone meal also tended to produce more milk than those fed soybean meal.(ABSTRACT TRUNCATED AT 250 WORDS)

The performance of weaned lambs offered diets containing different proportions of fresh perennial ryegrass and white clover

ABSTRACTSix weaned lambs were allocated to each of eight restricted feeding treatments with 1·00, 0·85, 0·71, 0·57, 0·43, 0·29, 0·15 or 0 of the diet as perennial ryegrass and the remainder as white clover, and to one ad libitum treatment with perennial ryegrass offered alone. A further six lambs were offered white clover ad libitum starting on day 15. Lambs on the restricted treatments received the same daily allowance of dry matter relative to live weight, adjusted at weekly intervals to allow the greatest possible intake without any rejection of herbage. Fresh cut herbage was offered daily and measurements were made over 69 days. Twelve additional lambs were slaughtered at the beginning of the experiment, and all lambs on restricted treatments were slaughtered at the end.Increasing the proportion of clover in the diet increased the intake of nitrogen, empty-body-weight gain, carcass weight gain and nitrogen retention. When herbage was offered ad libitum, lambs ate significantly more clover than ryegrass and gained weight faster.The weight of gut contents decreased as the proportion of clover in the diet increased. The digestibility of the organic matter, energy and nitrogen of the mixed diets simply reflected the digestibilities of the two herbages and their proportions in the mixture.

Effects of insulin on ventricular function in diabetic lambs with acidosis.

Diabetes mellitus (DM) was induced in 10 lambs by giving alloxan (150 mg/kg). Two to 4 days later, mean values for glucose were 748 mg/dl, and for arterial pH 7.25 (acute group). Two additional lambs were studied after 3 mo of DM (chronic group). Data were compared with 7 controls (glucose 128 mg/dl, pH 7.36). Left ventricular (LV) performance was assessed from function curves and measurements of LV dP/dtmax. Stroke volume ejected at LV end-diastolic pressure of 5 cmH2O (SV5) was calculated from regression analysis of each curve. SV5 averaged 2.83 +/- 0.34 ml in controls and 2.90 +/- 0.23 ml in the acute diabetics (not significant). Mean values for LV dP/dtmax also did not differ. A significant correlation was found between SV5 and LV weight (P less than 0.001). SV5 was normalized as ml/100 g LV, and average values for the three groups were identical. Insulin (10 U/kg) caused a progressive fall in SV5 in diabetics with severe acidosis (pH 7.00), but not in those with less acidosis (pH 7.28). In nondiabetics given lactic acid (pH 7.01), SV5 fell to 60% of initial values 1 h after insulin. Acidemic animals not given insulin showed no reduction in LV performance in the same time interval. Adrenergic support is necessary to prevent cardiac failure associated with acidosis. The present findings are ascribed to inhibition by insulin of catecholamine inotropic action on myocardium.

Effect of stocking rate, time of lambing and inclusion of lucerne on prime lamb production in north-east Victoria

Results of a grazing study involving Border Leicester x Merino ewes and their progeny are reported for a 4-year period 1969 to 1972. The study was conducted at Rutherglen in north-east Victoria. The 1260 ewes observed throughout the study were allotted to 42 treatment plots with 30 ewes per plot. Thirty of the plots were located on annual pasture (subterranean clover, barley grass) involving three replicates of ewes stocked at 7.4,9.9 and 12.4 ewes ha-l for ewes joined over 7-week periods to commence lambing about May 5, June 23 or August 8. Additionally, an extra three plots with spring lambing were grazed at 14.8 ewes ha-1. A further 12 plots contained lucerne on one third of the plot area. The ewes on these plots also lambed for a 7-week period commencing August 8, and provided three replicates of 7.4 9.9, 12.4 and 14.8 ewes ha-1. First services were concentrated early in the joining period in the spring-lambing ewes, there were few returns to services and few ewes failed to mate. On the other hand, among ewes joined to lamb in autumn, first services were distributed over the entire joining period, and many ewes returned to service or failed to mate. The mating pattern of ewes joined to lamb in winter were intermediate between the autumn and spring lambing groups. Although the liveweight of spring-lambing ewes was lighter at mating, the number of lambs born per 100 ewes joined was greater than for winter lambing, and these in turn were greater than for autumn lambing ewes. The response to an additional 1 kg liveweight at mating was 1.7, 2.0 and 2.8 additional lambs born per 100 ewes joined for autumn, winter and spring lambing, respectively. Wool production per hectare increased linearly with increase in stocking rate; it was marginally affected by time of lambing and was greatest where lucerne was provided. The number of lambs reared per ha increased linearly with increase in stocking rate, albeit there was some decline in carcase weight and a small decline in numbers of lambs reared per ewe. Lambs born in autumn and winter were generally slaughtered in prime condition at 31 kg liveweight, except in the drought year of 1972, but more lambs were produced from a winter lambing than from autumn lambing. When lambing was in August-September there was a slight increase in the numbers of lambs reared above that of winter lambing, but the proportion of lambs marketed at less than 31 kg was greatly increased. Where lucerne was provided to spring-lambing ewes the greatest weight of meat per hectare was produced, and few lambs were less than 31 kg. In descending order of magnitude, the major factors affecting carrying capacity were season, year, stocking rate and time of lambing. Seasonal shortcomings in nutrition were alleviated by the provision of supplementary feed. At the lighter stocking rates of 7.4 and 9.9 ewes ha-1 the amounts of supplements fed were very low, even in the drought year of 1972. These two lowest stocking rates could be maintained indefinitely without excessive use of supplementary feed. Discernible changes in botanical composition with partial loss of productive grass and clover species, reduction in pasture growth rate, increased use of supplementary feed and lowered wool production of ewes, occurred with spring lambing without lucerne, particularly at 12.4 and 14.8 ewes ha-1. Pasture composition and growth details were very similar with either autumn or winter lambing.

The effect of milk intake on the intake of cut and grazed herbage by lambs

ABSTRACTFifty-three lambs were artificially reared from 1 day old. From 14 days of age they were either housed and offered cut herbage or grazed at pasture.Five milk feeding treatments were allocated to both the housed and the grazing lambs; these were a total of 50, 70, 90 and 110 kg of ewes' milk given over 12 weeks and milk substitute for 4 weeks. Three additional lambs were housed and offered milk ad libitum.Digestibilities of the dietary components, herbage and milk intakes and lamb growth rates were measured.Similar digestibility coefficients were obtained for milk and for herbage when consumed together compared with individually.Milk intake was negatively correlated with herbage intake and positively correlated with growth rate.Under conditions permitting ad libitum intake, lambs at pasture had higher intakes of herbage than lambs offered cut herbage indoors. Equations are given which enable herbage intake at a particular age to be predicted from total milk intake.

Immunity to experimental enteritis in lambs vaccinated prenatally

The role of prenatal immunisation in the prevention of enteric disease in young lambs was studied. In the first series of experiments, fetal lanibs were immunised orally with vaccine containing killed Escherichia coli. At birth, before ingestion of colostrum, lambs were killed, blood and intestinal contents were collected and single cell suspensions prepared from spleen, mesenteric lymph nodes and jejunum. Specific antibody was detected in intestinal contents and blood serum, and numerous specific antibody forming cells were found among cells from the spleen, mesenteric lymph nodes and lamina propria of the jejunum of immunised lambs. Only trace amounts of antibody and low numbers of antibody forming cells were detected in tissues from non-immunised lambs. A second series of experiments examined the efficacy of prenatal immunisation of lanibs with killed Salmonella typhimurium vaccine as a means of protecting against experimental enteritis. Whereas non-immunised lambs were severely affected by challenge at birth with live S typhimurium, immunised lambs were protected and prenatal intramuscular immunisation conferred a greater degree of protection than prenatal oral immunisation. Additional lambs were challenged with S typhimurium when weaned at five weeks old. Non-immunised lambs were severely affected by challenge, while Iambs immunised intramuscularly as fetuses and again orally after birth were protected. Lambs immunised orally before and after birth were not protected from postweaning challenge.

Decreased pulmonary transvascular fluid filtration in awake newborn lambs after intravenous furosemide.

We studied the effect of furosemide on pulmonary transvascular filtration of fluid and microvascular permeability to plasma proteins by measuring steady-state lung lymph flow and protein flow, pulmonary arterial and left atrial pressures in nine 1-wk-old unanesthetized lambs before and after rapid intravenous infusion of furosemide, 1 mg/kg in 10 experiments and 8 mg/kg in 5 experiments. With rapid diuresis induced by furosemide (an eightfold increase in urine flow), lung vascular pressures decreased, protein concentrations of lymph and plasma increased, and there was a consistent decrease in lymph flow and lymph protein flow, more pronounced after the larger dose. Five additional lambs received 8 mg/kg of furosemide intravenously in the presence of saline-induced pulmonary edema; in these experiments, the decrease in vascular pressures, increase in transvascular protein gradient, and decrease in lymph flow were greater than in lambs without pulmonary edema. These findings suggest that furosemide decreases transvascular filtration of fluid in the lung by diminishing the transvascular hydraulic pressure gradient and increasing the transvascular gradient for protein osmotic pressure. In five acute experiments on anesthetized lambs with kidneys removed, 8 mg/kg of intravenous furosemide decreased lymph flow one-half as much as it did in the presence of kidneys, with no change in lung vascular pressures or protein concentrations. The results of experiments in lambs without kidneys are consistent with a reduction in the vascular surface area for exchange of fluid and protein in the lung.

PAH clearance, sodium excretion, and PAH extraction ratio in acidotic near-term lambs treated with hypertonic sodium bicarbonate.

The electrolyte changes and renal hemodynamic adjustment to hypertonic sodium bicarbonate (NaHCO3) correction of a metabolic acidosis were studied in 4 neonatal lambs and in 2 controls. PAH clearance increased from 0.92 to 1.65 ml/min/kg (p less than 0.05), urine flow from 0.37 to 0.61 ml/min/kg (p less than 0.05), and Na excretion from 8.4 to 23.7 muEq/min/kg (p less than 0.05) during the NaHCO3 infusion. These increases were transient and returned to pre-infusion levels following NaHCO3 infusion. Calculation of Na intake and output revealed a net retention of 5.1 mEq/kg in the study lambs which was reflected in a rise of serum Na and osmolarity (Osm) during the post-NaHCO3 -infusion period. The extraction ratio of sodium p-aminohippurate (EPAH) and its relationship to arterial pH were studied in 4 additional lambs. The EPAH did not change with metabolic acidosis but for unknown reasons, the infusion of NaHCO3 resulted in a temporary depression of EPAH (p less than 0.001).

Experimental Development of a Cambendazole-Resistant Strain of Haemonchus contortus in Sheep

A cambendazole-sensitive strain of Haemonchus contortus became partially resistant to drug after 4 successive exposures in experimentally infected lambs. The drug exposures of this strain through 4 successive generations of parasite were 5, 5, 10, and 20 mg/kg of body weight, respectively. After first infected lambs were dosed at a 5-mg/kg level, subsequent infections of this cambendazole-exposed strain were experimentally induced in additional lambs using larvae cultured from feces from dosed lambs. The response of 2nd to 4th successive generations of H. contortus exposed to drug indicated that strain had become partially cambendazole-resistant. After 4th drug exposure, a definitive controlled test was conducted with 48 lambs to compare activity of cambendazole at dose levels of 20 and 40 mg/kg against drug-exposed strain and original unexposed strain. Efficacies at 20and 40-mg/kg dose levels in lambs infected with drug-exposed strain were 71.5 and 92.7%, respectively; efficacies at similar dose rates in lambs infected with unexposed strain were 97.7 and 99.9%, respectively. The differences in drug efficacy between 2 strains were highly significant regardless of dose levels within each strain. Recently, Drudge (1970) briefly summarized available information on existence and development of anthelmintic-resistant populations or strains of nematode parasites of livestock. Supportive evidence indicated that the degree of resistance is relative, a function of dose level, as opposed to complete refractivity. Currently, this evidence may be summarized as follows: (1) thiabendazole-parbendazolecambendazole(benzimidazole compounds) resistant Haemonchus contortus in sheep and cattle (Drudge et al., 1964; Smeal et al., 1968; Theodorides, Scott, and Ladermann, 1970; Colglazier, Kates, and Enzie, 1970, 1972; Herlich, 1973); (2) thiabendazole-parbendazole-resistant Trichostrongylus colubriformis in sheep (Hotson, Campbell, and Smeal, 1970); (3) phenothiazine-resistant H. contortus in sheep (Drudge, Leland, and Wyant, 1957a, b; Drudge et al., 1959; Leland et al., 1957; Colglazier, Enzie, and Lehmann, 1967); (4) thiabendazole-resistant equine strongyles (Drudge and Lyons, 1965); (5) phenothiazine-resistant equine strongyles (Drudge, 1965); (6) organophosphorus(Famophos, Famphor) resistant Ostertagia circumcincta in sheep (Douglas and Baker, 1968, and pers. comm.). Observations of drug resistance among helminths, however, have not been limited to strongyloid nematodes. Komiya et al. (1955), and Komiya, Ishizaki, and Kutsumi (1957) reported limited Received for publication 12 September 1972. evidence that strains of Ascaris spp. may be resistant to santonin. Also, Rogers and Bueding (1971) reported that female Schistosoma mansoni in mice and hamsters, after surviving exposure to relatively high doses of hycanthone, produced eggs that gave rise to a generation of schistosomes resistant to hycanthone and two related drugs. Drudge (1970) noted that laboratory attempts to induce resistance or to increase tolerance (to anthelmintics) of resistant forms have not been successful. Reports of such studies, however, have been limited. Sinclair (1953) was unsuccessful in producing a phenothiazine-resistant strain of T. colubriformis by repeated drug exposures. Hasche and Todd (1963) and Silangwa and Todd (1966) also failed to induce resistance to phenothiazine experimentally with populations of H. contortus in sheep and Haemonchus, Cooperia, and Trichostrongylus in calves. The purpose of our work was to determine whether a drug-resistant population of H. contortus could be produced experimentally from a strain known to be highly sensitive to one of newer anthelmintics. Cambendazole was selected for these trials because (1) it is a benzimidazole compound chemically related to thiabendazole and parbendazole, drugs with which resistant strains of nematodes have been associated, and (2) it is a new anthelmintic which has been shown to have broad-spectrum activity in domestic animals (Baker and

Fatty acid composition of carcass, heart, liver, and blood lipids in young lambs fed diets containing vegetable or animal fats.

Thirty-two crossbred twin lambs were weaned at 3 days of age and artificially reared, for a period of 8 weeks, on milk substitutes containing either tallow or corn oil, at the rate of 26.6% on a dry matter basis. Six additional lambs, twins of six of the artificially reared animals, were left with their dams and used as controls. Lambs fed tallow had legs of lamb which contained more fat (P &lt; 0.01) than those fed corn oil; however, lambs fed corn oil had fatter livers (P &lt; 0.01). On the contrary, the fat content of heart tissues was not influenced by the type of fat consumed. Fatty acid composition of lipids extracted from the leg of lamb, heart, and liver, in general, reflected the fatty acid composition of the dietary fat. Constituent fatty acids of plasma lipids were found in proportions which were also influenced by the type of fat consumed.

Effects of hypoxia and acidity on the initiation of respiration

The effects of hypoxia and acidity on the initiation of respiration of term lambs were studied by two methods that discern chemoreceptor activation. (1) Perfusion of the right common carotid artery with blood with lower pO2, but similar pGO2 and pH to that in the fetal carotid artery invoked slow and erratic respirations after 15 sec. in 2 of 4 lambs and none in 2 other lambs. In contrast, perfusion of blood with lowered pH as well as low pO2 invoked more rapid and persistent respirations in all 5 additional lambs studied. (2) In another group of experiments, fetal carotid sinus nerve potentials were amplified for simultaneous oscillographic visualization, for broadcast by loud speaker, and for FM tape recording. The magnitude of chemoreceptor activity was determined, during ventrlcular diastole to preclude baroreceptor activity, by integrating and summating the recorded wave forms. The degree of chemoreceptor activity, as determined during basal fetal conditions, during administration of hypoxic and hypoxic-hypercarblc gas mixtures to the ewes, and after clamping of the umbilical cord was found to be proportional to the magnitude of the stimulus, such that after cord occlusion a marked increase in chemoreceptor activity was noted. The experiments show that increased H + ion concentration in carotid arterial blood potentiates the hypoxic stimulation of chemoreceptors and that a marked chemoreceptor discharge follows clamping of the umbilical cord. The results are compatible with a hypothesis that respirations are initiated in the newborn by a summation of neural stimuli, including an important traffic of chemoreceptor impulses, to the medullary respiratory centers.