Experimental Lambs Research Articles

Reduced postnatal cerebral glucose metabolism measured by PET after asphyxia in near term fetal lambs.

The effects of fetal asphyxia on cerebral function and development, involve the transition from fetal to neonatal life. Changes in cerebral glucose metabolism may be an early postnatal indicator of fetal asphyxia. The objective is to develop an experimental lamb model involving the transition from fetal to neonatal life and to examine the effect of fetal asphyxia with cerebral hypoxic ischemia on early postnatal cerebral glucose metabolism. Fetal asphyxia was induced by total umbilical cord occlusion in eight near-term fetal lambs (134-138 days) with the ewe under isoflurane-opiate anesthesia. The mean occlusion time until cardiac arrest was 14.5 (4.2) min (SD). Lambs were immediately delivered and standardized resuscitation was instituted after 2 min asystole. At 4 hr postnatal age, [18-F]Fluoro-2-deoxy-glucose (18-FDG) was injected intravenously in eight asphyxiated lambs and in eight controls. Cerebral glucose metabolism was examined by positron emission tomography (PET). As a result the mean arterial blood pressure, acid-base values, blood glucose and serum lactate at 4 hr postnatal age did not differ significantly between lambs subjected to umbilical cord occlusion and controls. EEG was abnormal in all lambs subjected to cord occlusion and normal in the controls at 4 hr postnatal age. Global cerebral metabolic rate (CMRgl) as determined by PET was significantly lower in lambs subjected to cord occlusion mean/median (SD) 22.2/19.6 (8.4) micromol/min/100 g) than in controls mean/median (SD) 37.8/35.9 (6.1); P < 0.01). Global CMRgl is significantly reduced in newborn lambs 4 hr after fetal asphyxia induced by umbilical cord occlusion. A reduction in CMRgl is an early indicator of global hypoxic cerebral ischemia.

Surfactant levels after reversible tracheal occlusion and prenatal steroids in experimental diaphragmatic hernia

In normal lungs, fetal tracheal occlusion (TO) induces lung growth but decreases the number of type II cells; this is remedied if TO is released (TR) before delivery. In the current study, the effects of TO with or without TR on pulmonary structure and surfactant were assessed in the ovine model in which lung hypoplasia was induced by creation of a diaphragmatic hernia (CDH). A left-sided CDH was created in fetal lambs at 80 days gestation; TO was done at 108 days; and TR at 129 days. All ewes were given 1 dose of glucocorticoids at 135 days. At 136 days, the fetus was delivered. Lung weight to body weight ratio, mean terminal bronchiole density, type II cell density, bronchoalveolar lavage fluid (BAL) phosphatidylcholine (PC), BAL surfactant protein A (SP-A) and B (SP-B), and lung tissue SP-A and SP-B were assessed in CDH, CDH with TO, CDH with TO and TR, and controls. CDH lungs were hypoplastic and structurally immature, but had increased type II cell density. TO with or without TR caused lung growth with normalization of lung parenchymal architecture and type II cell density. Although the BAL SP-A and BAL SP-B were similar in all 4 groups, the BAL PC was low in CDH with or without TO or TR. Also, lung tissue SP-B levels were low in CDH with or without TO or TR. However, lung tissue SP-A levels were normal in CDH, but low in CDH with TO with or without TR. Despite the finding that lung morphology was improved in CDH with TO with or without TR animals, surfactant content and composition remained abnormal. Although surfactant secreted early by the fetus into alveolar spaces contained normal levels of BAL SP-A and BAL SP-B, the low levels of BAL PC and low lung tissue stores of SP-B indicate that these experimental lambs may experience respiratory insufficiency soon after birth. This implies that prophylactic surfactant at birth might be beneficial for CDH.

Reproductive characteristics of Ethiopian highland sheep: I. Genetic parameters of testicular measurements in ram lambs and relationship with age at puberty in ewe lambs

A study was conducted to estimate heritabilities of, and genetic correlations among, body weight (WT) and testicular measurements — scrotal circumference (SC), testicular diameter (TD), testicular length (TL) and epididymal diameter (ED) — in ram lambs between 6, 9 and 12 months old, and relationship of the testicular traits with age at puberty in ewe lambs (AP). Two fat-tailed sheep breeds, the Horro and Menz, indigenous to the Ethiopian highlands were studied. Experimental lambs were produced by mating 250 oestrus-synchronized ewes of each breed to 10 sires in a single-sire mating system over three mating periods which produced, for this study, a total of 361 ram lambs and 148 ewe lambs, with substantial pedigree information, in two dry seasons (October/November 1992 and 1993) and one wet season (June/July 1993). Mean AP was 322.7 days. Breed was not significant ( P > 0.05) for all testicular measurements, except ED at 9 months for which the Horro had a higher ( P < 0.01) value (20.6, s.e. 0.38 versus 19.3 s.e. 0.30). Horro ewe lambs had their first oestrus 28 days earlier ( P < 0.05) than the Menz. Heritability estimates were obtained from a sire model (M1) and from an individual animal model with additive direct and maternal effects (M2). The maternal effect was not fitted in M2 for AP. Repeatability and heritability estimates were also obtained by analysing records at the three ages in a repeated measures model (M3). M1 and M2 heritability estimates were generally low to moderate but were associated with large standard errors. Heritability estimates for testicular measurements were generally similar to those for WT. Among the testicular measurements, SC had the highest heritability estimates at 6 (0.45, s.e. 0.24 for M1) and at 12 months (0.41, s.e. 0.21 and 0.41, s.e. 0.20 for M1 and M2, respectively). Model 3 heritability estimates were 0.29 (s.e. 0.14), 0.24 (s.e. 0.12), 0.09 (s.e. 0.07), 0.11 (s.e. 0.08) and 0.12 (s.e. 0.08) for WT, SC, TD, TL and ED, respectively. Only repeatability estimates for WT (0.34, s.e. 0.02) and SC (0.25, s.e. 0.03) were significant. Heritability of AP was estimated at 0.16 (s.e. 0.21) by M1 and 0.14 (s.e. 0.19) by M2. Genetic correlations of AP with testicular measurements, especially with SC (−0.57, s.e. 0.38 and −0.78, s.e. 0.33, at 9 and 12 months, respectively) and TD (−0.72, s.e. 0.33 and −0.83, s.e. 0.48), were desirable and generally high. Adjustment of testicular measurements for liveweight consistently resulted in a reduction in estimates of heritability and genetic correlations. SC was suggested as the most appropriate selection candidate for the genetic improvement of both male and female reproductive performance in these breeds.

Means and heritabilities of concentrations of antibody to Trichostrongylus colubriformis and other nematode parasites in lambs from three to seventeen months of age

Serum levels of antibody (Ab) to the larval (L3) stage of the internal parasite Trichostrongylus colubriformis were measured in 1577 lambs, the progeny of 64 rams. The lambs were part of an experiment to evaluate sires from a genetic selection project, breeding for Low or High faecal egg counts (FEC). Blood samples for Ab were taken from December, weaning, at 3 months of age until 17 months of age. Serial blood samples were also taken from 66 lambs in the selection lines themselves, to monitor Ab to T. colubriformis and three other nematode species. Lambs in both experiments were exposed to a natural parasite challenge on pasture, following anthelmintic treatment at weaning. Subsequent cycles of natural challenge and anthelmintic treatment followed. From the progeny test data, using an animal-model restricted maximum likelihood program, heritability estimates for log e (Ab) at weaning, 4–5, 6–7 and 8–17 months of age were 0.18±0.08, 0.10±0.05, 0.25±0.05 and 0.23±0.08 respectively, and corresponding repeatability estimates (apart from weaning) were 0.24±0.04, 0.32±0.03 and 0.23±0.07. From the selection line data, least squares means for the Low FEC line were 49% higher than in the High FEC line for anti- T. colubriformis, monthly range, 24% to 73%, and the same trends were found for antibodies to T. axei, T. vitrinus and H. contortus. These results show that heritable and repeatable measurements of Ab concentration are found in parasitised lambs from about three months of age onwards, and that genetic selection for Low FEC is positively associated with antibody levels in lambs postweaning.

Chronic lung injury in preterm lambs. Disordered respiratory tract development.

The cause of chronic lung disease of early infancy, often called bronchopulmonary dysplasia (BPD), remains unclear, partly because large-animal models that reliably reproduce BPD have not been available. We developed a model of BPD in lambs that are delivered prematurely and ventilated for 3 to 4 wk after birth to determine whether the histopathology of chronic lung injury in premature lambs mimics that which occurs in preterm infants who die with BPD, and to compare two ventilation strategies to test the hypothesis that differences in tidal volume (VT) influence histopathologic outcome. The two ventilation strategies were slow, deep ventilation (20 breaths/min, 15 +/- 2 ml/kg body weight VT; n = 5) or rapid, shallow ventilation (60 breaths/min, 6 +/- 1 ml/kg body weight VT; n = 5). Lambs were delivered at 125 +/- 4 d gestation (term = 147 d), treated with surfactant, and mechanically ventilated with sufficient supplemental oxygen to maintain normal arterial oxygenation (60 to 90 mm Hg). Quantitative histologic analysis revealed lung structural abnormalities for both groups of experimental lambs compared with lungs of control term lambs that were < 1 d old (matched for developmental age; n = 5) or 3 to 4 wk old (matched for postnatal age; n = 5). Compared with control lambs, chronically ventilated preterm lambs had pulmonary histopathology characterized by nonuniform inflation patterns, impaired alveolar formation, abnormal abundance of elastin, increased muscularization of terminal bronchioles, and inflammation and edema. Slow, deep ventilation was associated with less atelectasis, less alveolar formation, and more elastin when compared with rapid, shallow ventilation. We conclude that prolonged mechanical ventilation of preterm lambs disrupts lung development and produces pulmonary histopathologic changes that are very similar to those that are seen in the lungs of preterm infants who die with BPD. This chronic lung disease is not prevented by surfactant replacement at birth, does not appear to require arterial hyperoxia, and is influenced by VT.

Effect of naloxone on intake and growth hormone concentration in lactating and non-lactating ewes

Thirty-two ewes (16 Suffolk and 16 Targhee) were used in two experiments to investigate effects of energy requirements, naloxone, breed, and number of lambs/ewe on feed intake and growth hormone (GH) concentrations. These experiments tested the hypothesis that the setpoint for intake, mediated through endogenous opioid tone, would be greater in lactating ewes than non-lactating ewes. Experiment 1 was conducted during lactation (43 d postpartum) with ewes confined individually with their lambs. Experiment 2 was conducted when ewes were non-pregnant and non-lactating. Naloxone treatments were 0, 0.5, 1.5, or 3 mg of naloxone/kg of ewe BW. After 3.5 h of fasting, ewe DMI was measured every 20 min for 5.5 h and expressed as g/kg of BW. Blood samples were taken at 15 min intervals for 5 h after naloxone was administered. Although level of naloxone and experiment influenced the repeated measures analysis of DMI ( P=0.01), no experiment × level of naloxone interaction was detected ( P=0.86). Increasing level of naloxone had a negative quadratic ( P<0.05) effect on DMI during the first 30 min in Experiments 1 and 2. Total DMI for the 5.5 h collection period was not influenced ( P>0.23) by naloxone level. An experiment by breed interaction was detected for DMI ( P=0.04). In Experiment 1, DMI was greater ( P=0.02) for Targhee than Suffolk ewes but breeds did not differ ( P=0.68) in DMI during Experiment 2. Number and frequency of GH pulses responded quadratically ( P=0.02) to increasing level of naloxone. Number, frequency, and height of GH pulses and mean GH concentration were greater in Experiment 1 than Experiment 2, and greater for Targhee than for Suffolk ewes ( P<0.05). Mean GH concentration ( P<0.05) and GH pulse height ( P<0.10) were greater for ewes with twin lambs than single lambs. An experiment × number of lambs born/ewe interaction was detected ( P=0.05) for mean GH concentration. Mean GH concentration was greater ( P=0.01) in Experiment 1 for ewes rearing twin lambs than single lambs. Mean GH concentration did not differ ( P=0.78) between ewes rearing single and twin lambs in Experiment 2. Although level of naloxone influenced number and frequency of GH peaks, the does of naloxone that would inhibit feeding did not differ between forage-fed ewes at high and low energy requirements.

Utilization of concentrate diets containing acorns ( Quercus aegilops and Quercus coccifera) and urea by growing Awassi lambs

Thirty individually penned Awassi lambs (mean BW 25.3±0.45 kg and 4–5 months of age) were used in a growth experiment. This was followed by a digestion and nitrogen balance experiment using 12 lambs (mean BW 35.5±0.43 kg and 6 months of age). Lambs in both experiments were divided into three equal groups and fed one of the three concentrate mixes, two of which contained ground acorns ( Quercus aegilops and Quercus coccifera) at 25% and 50% levels of DM (% dry weight). The aim of the work was to evaluate the usefulness of acorns as an alternative energy source for growing lambs. Concentrates were given according to BW (restricted to 3.5% of BW). Daily weight gain (DWG) of lambs fed the control diet or 25% acorn diet was similar (186 and 189 g) but higher ( P<0.01) than lambs on the 50% acorn diet (142 g). Feed conversion ratio (kg DM/kg LW gain) was lower ( P<0.01) for the 50% acorn diet. Digestibility coefficients of dietary constituents (DM, OM, ash, NDF, ADF, and N) were reduced ( P<0.001 and P<0.01) as a result of acorn substitution for barley. Nitrogen retention (g/day) was also lower ( P<0.05) for acorn diets, but similar ( P>0.05) across treatments when expressed as percentage (%) of apparently digested N. The low cost of acorns compared with barley suggest that substitution of acorns for barley at a maximum level of 25% would be economically advantageous.

Retrievable patent ductus arteriosus plug for interventional, transvenous occlusion of the patent ductus arteriosus. Evaluation in lambs and preliminary clinical results.

The clinically most widely used devices (Porstmann-plug, Rashkind-umbrella, Botallooccluder) have inherent specific limitations (eg, transarterial approach, residual shunts, limited retrieval). The authors assess practicability, efficacy, and tissue reaction of the new retrievable transvenous plug device for the occlusion of the persistent patent ductus arteriosus (PDA). A foam plug (polyvinyl alcohol) is mounted on a titanium core pin where, at both ends, small legs (titanium nickel alloy) with titanium heads are anchored, to ensure safe fixation in the ductus. The device is introduced transvenously through a long sheath (Mullins sheath) and held by a modified biopsy forceps allowing complete retrieval until final release. A common lamb model of large PDAs (n = 11) was used to test for practicability and the histomorphologic outcome. Clinical results were obtained from a consecutive series of 16 patients (aged 13 to 71 years). In all lambs, placement of the plug within the PDA was possible. Histopathology (follow-up 10 to 215 days; mean 112 days) revealed an adequate ingrowing of the device and no pathologic foreign body reaction. The diameter of the human PDAs ranged from 3 to 7 mm (mean 5 mm). The size of the sheath used for introducing the plug (diameter 8 to 16 mm) ranged from 8 to 16 French. Fourteen of 16 PDAs were closed immediately after or on day 1 after implantation, 1 was closed after the 12-month follow-up, and 1 needed an additional plug after 30 months for definitive closure. The device demonstrated practicability and biocompatibility in our experimental lamb model and effectively closed the PDA in a consecutive series of 16 patients. A greater number of patients and a longer follow-up period are necessary for the definitive clinical assessment of the new device.

Responses of Romney sheep to selection for resistance or susceptibility to nematode infection

AbstractDivergent breeding lines of Romney sheep, selected as lambs for consistently low or high faecal worm egg count (FEC) following natural multispecific challenge by nematode parasites, have been maintained at Wallaceville Animal Research Centre since 1979. From the start of the trial until 1992, 821 and 736 experimental lambs in lines selected for increased resistance (R) and increased susceptibility (S), respectively, were generated, with the use of 44 different sires. In order to assess genetic responses to selection, FEC and productivity data were analysed using restricted maximum likelihood procedures. By 1988 the two lines had diverged in average loge (FEC+100) by 0·67 log units, and by 1992 divergence had increased to 1·48 log units, representing 2·90 genetic standard deviations of divergence. No significant correlated responses were observed in live weights. However, by 1992 the mean score for breech soiling (dags) in the R line was proportionally 0·41 greater than in the S line (F &lt; 0·001). Yearling fleece weight was proportionally 0·15 greater in S-line than in R-line animals when grazed together under identical levels of challenge (P &lt; 0·001) but the lines did not differ significantly in fleece weight when they were grazed apart. The R line had significantly higher reproductive success than the S line (P &lt; 0·05), as measured by lambs weaned per ewe mated (1·01 v. 0·92, respectively). It is concluded that selective breeding can change the degree of resistance or susceptibility to nematode infection in Romney sheep, and selection for productivity needs to be continued at the same time in any practical breeding programme.

Characterization of the elastic properties of amorphous silicon carbide thin films by acoustic microscopy

A 590 MHz high frequency acoustic microscope has been used as a non-destructive local probe to measure the elastic properties of amorphous silicon carbide thin films supported as coatings on silicon substrates and as free-standing membranes. The films were amorphous hydrogenated and hydrogen free silicon carbide a-Si 0.5C 0.5(H) thin layers deposited by using two deposition techniques, namely plasma enhanced chemical vapor deposition (PECVD) and laser ablation deposition (LAD). Surface acoustic images showed a good homogeneity of the elastic properties of the films. Experimental Lamb mode velocities were deduced from the fast Fourier transform (FFT) treatment of the local acoustic response, V( z), and compared with values obtained from calculated models taking into account the different propagation modes of acoustic waves. The values of the longitudinal, V L, and shear, V T, velocities were determined to be, respectively, 9462 and 5853 m/s for a-Si 0.5C 0.5:H PECVD films and 10340 and 6397 m/s for a-Si 0.5C 0.5 LAD films. Elastic parameters such as Young modulus, E, and Poisson ratio ν were deduced from these velocity values. In good agreement with the results obtained with other techniques (bulge and indentation measurements), the Young modulus was shown to increase with the Si–C bond density of the a-SiC films with values of 196 GPa and 273 GPa for PECVD and LAD films, respectively. The Poisson ratio was found to be independent of the microstructure of the SiC films with a constant value of 0.19.

Dynamics of Preference by Sheep Offered Foods Varying in Flavors, Nutrients, and A Toxin

We conducted two experiments to determine how toxicosis affected preference of sheep for foods varying in flavors, nutrients, and a toxin. The first experiment determined how toxicosis affected the preference of lambs (fed a basal ration of alfalfa pellets) for foods that varied in energy and a toxin. Thirty lambs (10/treatment) were given LiCl by gavage (0, 50, or 100 mg/kg body wt/day), and 1 hr later were offered for 15 min/day foods containing different amounts (low, medium, high) of energy (barley) and a toxin (LiCl) added to alfalfa. The proportions of barley and LiCl changed every three to six days during the 30-day study. The results showed: (1) lambs' food preferences were high > medium > low for barley in the absence of LiCl; (2) lambs quickly regulated intake of foods in response to changes in barley and LiCl concentrations, even with short exposures (15 min/day); (3) lambs maintained intake of LiCl at about 57 mg/kg body wt by adjusting intake of food containing LiCl in accord with the amount of LiCl they received by gavage; and (4) as barley levels increased, intake of foods containing LiCl increased. The second experiment determined the relative influence of flavors, nutrients, and toxins on food preferences of lambs. We did this by treatments in which different flavors (onion and oregano at 1%) were paired with different levels of energy (depending on the addition of wheat to rabbit pellets) or a toxin (LiCl). At six-day intervals, we varied the types of food offered, either changing the nutrient or toxin content and the flavors. The resulting analyses of preference showed lambs markedly preferred foods high in nutrients and low in toxins, regardless of flavor, when changes in food flavor were not correlated with changes in nutrient and toxin concentrations. Thus, in both experiments lambs quickly regulated intake of foods varying in nutrients and a toxin according to the lambs' toxicological and nutritional state. Even with brief eating bouts lambs discriminated accurately and exhibited little permanent preference or aversion in postconditioning preference tests. The lambs remained in an unbiased testing mode, sampling anew the food. This is adaptive because the toxin and nutrient contents of plants vary with season and location. Most taste aversion studies emphasize the permanence of aversions and miss the dynamic sampling power of animals.

Twin/Non-Twin Discrimination By Lambs: an Investigation of Salient Stimulus Characteristics

Abstract A series of experiments was conducted to elucidate the stimuli that mediate twin/non-twin discrimination among 2-3 week old lambs. After being separated from their mother, lambs emitted more distress bleats when tested in isolation than when penned with their familiar twin, but separated from that lamb by a barrier of evenly spaced wood bars. A similar, albeit weaker effect was found for paired vs isolated non-twins. Twins separated by the barrier bleated less than did the non-twins in this condition. In contrast, bleat rates did not differ when subject lambs were tested in the presence of their twin vs a non-twin on the opposite side of a solid opaque barrier. Intact lambs in a final experiment bleated less when tested with their tranquillized twin vs a tranquillized non-twin agemate. The tranquillized stimulus lambs displayed atypical behavior patterns, including suppression of bleats and reduced activity levels. These data indicate that full bodily contact, vocalizations or normal behavioral patterns are not necessary for lambs to be recognized by their twin. Rather, twin/non-twin discrimination (and the effect of a twin on the rate of distress bleating) appears to depend upon visual, and possibly olfactory cues.

Effect of injecting lambs with soyflour extract on serum soy protein antibody concentration and rate of gain

Two experiments, involving 84 paired suckled lambs, were completed to evaluate the effect of stimulating high levels of antibodies to soyflour (SF) on rate of gain. In both experiments, the lambs were creep fed from birth and weaned at 6 weeks of age to a pelleted complete diet containing 16% soybean meal (SBM). One lamb of each pair was injected s.c. in the neck with SF extract and the other sham injected. A second injection was given to each lamb 21 days after the first. In Experiment 1, 27 pairs of purebred Polypay or Targhee lambs were injected at 1 week or less of age and their rate of gain determined at 3-week intervals for 12 weeks. In Experiment 2, 15 pairs of 6-week-old crossbred lambs were injected and their rate of gain determined for two 28-day intervals. At the end of each experiment, blood serum samples were taken and the antibody concentration to glycinin (S7) and β-conglycinin (S11) determined. Injection with SF increased the antibody concentrations to S7 and S11 in both experiments ( P < 0.05). The sham injected lambs had antibody concentrations (mean ± SEM) to S7 and S11 of 257 ± 17.8 and 128.2 ± 10.7 in Experiment 1 and 114 ± 25.5 and 142 ± 30.5 ng ml −1 for Experiment 2. The SF injected lambs in Experiments 1 and 2 had serum antibody concentrations to S7 and S11 of 2575 ± 233 ng ml −1 and 1433 ± 299 ng ml −1 and 2286 ± 250 ng ml −1 and 2450 ± 396 ng ml −1, respectively. Injection of extracts of SF did not reduce the rate of gain of lambs ( P > 0.10). While a variety of materials such as environmental microbial challenge, vaccines, inflammatory agents and synthetic chemicals have been identified as immunomodulators, little research has focused on the role of dietary protein in this process. The results of this research indicate that immunomodulation by at least one of the major dietary protein sources, SBM, does not have a negative effect on overall animal performance as measured by growth rate.

Effect of mating season and body condition on ovulation, fertilization and pregnancy rates in crossbred ewes

In three experiments, ewes kept under the ambient photoperiod at 57 °N were given daily at 15:00 h from March onwards an oral dose of 3 mg of melatonin in a 4:1 mixture of water and ethanol or, in the case of controls, the vehicle alone. All ewes were challenged daily with a vasectomized ram for the detection of behavioural oestrus. In Experiment 1, the mean interval (± standard error of the mean (s.e.m.)) from the start of melatonin treatment on 5 March to first behavioural oestrus for Border Leicester × Scottish Blackface ewes that had remained barren over the winter period was 87 ± 5.8 days (n = 8) compared with 222 ± 10.3 (n = 7) for controls. Corresponding intervals from the start of melatonin treatment on 24 March for the same breed of ewe in Experiment 2 were 80 ± 3.7 (n = 6) and 211 ± 9.4 (n = 6) days. In Experiment 3, 22 Scottish Blackface ewes that lambed between 11 January and 22 February were paired by lambing date for weaning at either 6 or 14 weeks. All ewes received melatonin from 22 March until 5 August. Apart from one ewe from the 14 week group that failed to show oestrus, all other ewes responded to melatonin and exhibited first behavioural oestrus at mean intervals from initial dosing of 77 ± 4.6 days and 75 ± 3.2 days for the 6 week and 14 week groups, respectively. Melatonin suppressed prolactin in both dry (Experiments 1 and 2) and lactating ewes (Experiments 1, 2 and 3), but in the only experiment in which it was tested (Experiment 1), its continuous administration throughout pregnancy failed to prevent the late-pregnancy rise in prolactin. It had no effect on gestation length or the subsequent growth rate of lambs; its effect on lamb birth weight was equivocal, causing a significant decrease in twin lambs in Experiment 2 and no effect in Experiment 1. Detailed sequential measures of the nature of the episodic release of luteinizing hormone (LH) (Experiment 2) provided no evidence that melatonin induced a progressive increase in the activity of the gonadotrophin releasing hormone (GnRH) pulse generator.The ovarian response to the daily oral administration of melatonin from March onwards contrasts with literature reports on the failure of continuous-release implants of melatonin to stimulate behavioural oestrus when inserted as early as April or May.

Scarcity of gamma delta T cells in intestinal epithelia containing coccidia despite general increase of epithelial lymphocytes.

Lymphocytes of intestinal epithelia were examined in lambs experimentally infected with coccidia. Fourteen conventional, coccidia-free 3-week-old lambs of the Dala breed were given either 250,000 (eight lambs in experiment 1) or 100,000 (six lambs in experiment 2) sporulated oocysts of Eimeria ovinoidalis (> 99.9% pure) via a stomach tube. Nine lambs (five in experiment 1 and four in experiment 2) of the same age served as uninoculated controls. The infected lambs developed diarrhea and dehydration between days 10 and 13 after infection. Intestinal specimens were collected 10-20 days after inoculation. A heavy multifocal infection of the epithelium comprising schizonts, gamonts, and oocysts resulted, with changes being most pronounced in the large intestine and the terminal part of ileum. Lesions included villous atrophy, villous fusions, and crypt hyperplasia. Computer-assisted morphometric analysis was applied to immunoperoxidase-stained sections for quantification of intraepithelial T cell subsets and included the distal jejunum of lambs of experiment 1. A significant increase in the epithelial area of the distal jejunum occupied by CD8+ lymphocytes was found in the infected lambs as compared with uninfected controls (18.3% versus 3.7%). The increased presence of CD8+ cells may be of significance in the intestinal immune response to ovine coccidiosis. A moderate, overall increase was also found for the gamma delta lymphocytes in the jejunal epithelium. Examination of the ileum of infected lambs of both experiments showed a scarcity of gamma delta cells (0.4% of epithelial area) in stretches of epithelium infected by coccida as compared with adjacent noninfected epithelium (4.0% of epithelial area).(ABSTRACT TRUNCATED AT 250 WORDS)

Controlled Release Chromic Oxide and Alkaline Peroxide Lignin Marker Methods

Two digestion trials, using 20 ram lambs (Experiment 1) and 8 cows (Experiment 2) provided ad libitum access to mature prairie grass hay, were conducted to evaluate controlled release intraruminal chromic oxide boluses and alkaline hydrogen peroxide lignin as markers for estimating forage intake by the fecal output/indigestibility ratio. A soybean meal and 3 urea based supplements were fed to lambs in Experiment 1. For both experiments, daily fecal output was weighed and sampled for 6 days (Experiment 1) and 5 days (Experiment 2) beginning 7 days after oral administration of controlled release boluses. Rectal fecal grab samples were also collected at 1000 daily and at 4-hour intervals on day 4 of collections for Experiment 2. For both experiments Cr2O3 excretion rates based on total collections were used to evaluate Cr2O3 controlled release boluses and alkaline hydrogen peroxide lignin predictive value in place of manufacturer's stated release rate. In experiment 1, fecal Cr2O3 output was 224 mg/day +/- 3.9 compared to the manufacturer's stated release rate of 201 mg Cr2O3/day. Fecal alkaline hydrogen peroxide lignin recovery was 97.8% +/- 1.9. Samples composited over the 6-day collection period predicted fecal output, apparent dry matter digestibility, and dry matter intake similar (P = .44, .15 and .55; respectively) to actual values. Supplemental treatment and dry matter intake had no effect (P > .38) on daily fecal Cr2O3 output or alkaline hydrogen peroxide lignin recovery. In Experiment 2, fecal Cr2O3 was 1,662 mg/day +/- 63 compared to the manufacturer's stated release rate of 1,505 mg Cr2O3/day. Fecal alkaline hydrogen peroxide lignin recovery was 95.9% +/- 7. Using 5-day composited samples, predicted fecal output, dry matter digestibility, and dry matter intake were similar (P = .49, .21 and .49; respectively) to actual values. Increasing the number of daily grab samples increased R2 values between actual and predicted fecal output and dry matter digestibility. Fecal grab samples and total fecal collection samples provided a similar relationship (R2=.71) between actual and predicted dry matter intake when each were composited over 5 days. Time of day did not affect fecal Cr2O3 or alkaline hydrogen peroxide lignin concentrations. These results suggest that grab samples collected once daily on 5 consecutive days can be used to predict fecal output when Cr2O3 controlled release boluses are used. Although recoveries of fecal alkaline hydrogen peroxide lignin were near 100% in these experiments, digestibility estimates using this internal marker were variable and adversely influenced predictions of dry matter intake.

Effect of lamb growth rate and growth pattern on carcass fat levels

AbstractA total of 252 lambs was subjected to two contrasting growth rates (high and low) for 7 weeks commencing at 6 weeks of age, factorially arranged with two contrasting growth rates (high and low) from 13 weeks to slaughter. Growth rate was controlled either by weaning lambs at 6 weeks and feeding indoors throughout on differing levels of a concentrate diet (84 lambs in experiment 1) or by grazing at differing sward heights up to weaning at 13 weeks after which weaned lambs were grazed at differing sward heights and where necessary housed from early October and offered differing levels of concentrate and silage (168 lambs in experiment 2). Lamb slaughter weights on each growth rate treatment covered the range 40 to 48 kg live weight.Increasing the growth rate between 6 and 13 weeks from 213 to 320 glday in experiment 1 and from 191 to 291 g/day in experiment 2 did not significantly affect the fat depth measured at various locations throughout the carcass, the weight of perinephric and retroperitoneal fat, fat grade or the total lipid content of soft tissue dissected from the shoulder joint when lambs were taken to slaughter weights. Increasing the growth rate between 13 weeks and slaughter from 136 to 338 g/day in experiment 1 and from 99 to 146 g/day in experiment 2 significantly increased the depth of carcass fat and fat grade but, though lipid content of the tissue in the shoulder also increased, this difference was not significant.Carcass fat depth, perinephric and retroperitoneal fat, fat grade and lipid content of the shoulder tissue increased as slaughter weight increased. The effect of carcass weight on carcass fat was greater on the high plane of feeding from 13 weeks than on the low plane. For example, mean fat depth increased by 0·52 mm/kg increase in carcass weight on the high plane compared with 0·13 mm/kg on the low plane.Comparing the effect of plane of feeding and carcass weight on carcass fat depth the high finishing plane of feeding had an effect equivalent to an increase of 3·8 kg carcass weight. The equivalent figure for the depth of tissue over the 12th rib was 2·8 kg while in relation to fat grade the effect was smaller at 1·0 kg carcass weight.

Learning to suckle from an artificial teat within groups of lambs: Influence of a knowledgeable partner

This work was aimed at finding evidence of observational learning in sheep. The task to be learned was that of suckling milk from a bucket provided with teats. Lambs were reared in groups of either four neonates and an older lamb accustomed to artificial suckling (14 experimental lambs) or five neonates (16 controls). One-hour observations were made five times a day. The lambs that learned were grouped and observed for three hours once a week. All experimental lambs learned within three days as compared to nine for the 16 controls. Experimental lambs moved and sniffed or sucked the bucket more often than the controls (2.0 ± 1.5 vs. 1.5 ± 1.0% time spent moving, 7.1 ± 6.2 vs. 1.6 ± 1.8 sniffing/hour, 3.7 ± 3.6 vs. 1.7 ± 1.7% time spent sucking, P < 0.05). The time to first suckling was not related to these measurements, neither was it related to other behavioural traits. Learning to suckle from the teat-bucket may be a socially transmitted phenomenon, and not only by enhancement of investigation.

Effects of acute acid loading on parathyroid hormone secretion and on urinary calcium and cAMP excretion in the growing lamb

Growing lambs fed a diet containing NaHCO3 were made acidotic by intravenously infusing HCl at the rate of 1 mmol/min over a 4 h period. Acid infusion led to a fall in blood and urine pH and a prompt increase in urinary Ca excretion. This in turn led to a fall in plasma Ca concentration and a rise in parathyroid hormone (PTH) levels. Urinary cAMP excretion was unaffected by acid infusion. In separate experiments lambs made acidotic by feeding a diet containing NH4Cl were given infusions of PTH at the rate of 1 microgram/h. Infusion of the hormone was accompanied by a rise in plasma Ca and an increase rather than a decrease in urinary Ca excretion and no change in urinary cAMP excretion. These results point to the kidney as the primary site of response to acid loading in the lamb, a failure to reabsorb Ca in these conditions necessitating the release of PTH and an increase in bone resorption in order to maintain normal plasma Ca levels.

Experimental cerebrospinal elaphostrongylosis (Elaphostrongylus rangiferi) in sheep.

Seven lambs were inoculated with 150-3,000 infective larvae of Elaphostrongylus rangiferi and subsequently killed for autopsy. From one week post inoculation (p.i.), a marked eosinophilia was found, and one of the lambs showed signs of coughing, increased respiratory frequency and elevated body temperature. Pruritus was observed in three lambs during the period 5-10 weeks p.i. Gross and microscopic lesions were found in the liver, lungs, myocardium, kidneys, spinal nerve roots and in the central nervous system (CNS). The lesions resembled those previously reported in experimentally infected goat kids. The migratory route of the infective larvae seemed to be haematogenous. Developing nematodes were sectioned in the CNS of a lamb killed at day 30 p.i. The nematodes found in the brain of this lamb were significantly thicker than those observed in the spinal cord. Intact nematodes were not detected in the remaining lambs which were all killed 149-151 days p.i. None of the experimental lambs shed E. rangiferi first-stage larvae in the faeces. These findings indicate that E. rangiferi gradually dies out in sheep and will not complete its life cycle in this animal species.