Effect of lasalocid, monensin and thiopeptin on rumen protozoa

The effects of lasalocid, monensin and thiopeptin on the total number and the generic composition of rumen protozoa were determined in vivo and in vitro. Feeding lasalocid or monensin to cattle on either high grain or high roughage diets reduced total protozoal counts. Addition of lasalocid or monensin (6 to 48 micrograms ml-1) to the in vitro rumen fermentation resulted in marked reduction in protozoal numbers. The inhibition was dose dependent. Thiopeptin had no effect on rumen protozoa either in vivo or in vitro. Among the protozoal types, holotrichs (Dasytricha, Isotricha and Charonina) were unaffected by either lasalocid or monensin. Among the entodiniomorphs, Entodinium, Diplodinium and Ophryoscolex were more sensitive than the other types. Ophryoscolex purkynei was more sensitive to monensin than to lasalocid. Protozoal inhibition by lasalocid and monensin was transient because prolonged antibiotic feeding resulted in the selection of a resistant population in the rumen of cattle.     

Lasalocid toxicity in cattle: acute clinicopathological changes

Thirty-six steers (148 to 500 kg) divided into six equal groups were used in a toxic syndrome study of lasalocid and monensin given as a single oral dose. One group was given a placebo, a second group received monensin (25 mg/kg body weight) and the other four groups received lasalocid at 1, 10, 50 or 100 mg/kg body weight (bw). No toxic signs developed in cattle given placebo or lasalocid at 1 or 10 mg/kg bw dose. The earliest toxic signs were muscle tremors, tachycardia and rumen atony. After 24 h, the cattle were dehydrated, anorectic and had diarrhea. Deaths occurred between d 1 and 22.5 in the groups receiving lasalocid at 50 and 100 mg/kg bw and monensin. Altered values in blood leucocytes, erythrocytes, hemoglobin, hematocrit, total protein, albumin, creatinine, urea nitrogen, total bilirubin, creatine kinase, lactic dehydrogenase, calcium, chloride and inorganic phosphate occurred 1 d after dosing: urine pH and specific gravity also changed 1 d after dosing. Maximum changes occurred at d 3. Most of the changes were indicative of dehydration rather than specific organ damage.     

In vitro muscle cell proliferation and protein turnover as affected by serum from pigs fed antimicrobials

The effect of antimicrobial supplementation of pigs on the capacity of their sera to influence proliferation and protein turnover in cultured muscle cells was evaluated. Mitogenic activity of sera increased when pigs were fed ASP250 (P less than .005) or carbadox (P less than .001), whereas the mitogenic activity of serum from pigs receiving the basal diet remained unchanged (P = .5). Additionally, sera from ASP250-fed pigs significantly decreased (P less than .001) total cellular protein degradation compared with sera obtained from the same pigs prior to supplementation. Neither ASP250 nor carbadox stimulated proliferation of myogenic cells when added to the culture media. Inclusion of ASP250 in swine diets altered the composition of their sera in a way that stimulated muscle cell proliferation and reduced the rate of protein degradation in cultured myogenic cells. Likewise, the inclusion of carbadox in swine diets increased the ability of their sera to stimulate cultured muscle cell proliferation.     

A comparison of two intramuscular doses of xylazine–ketamine combination and tolazoline reversal in llamas

The anesthetic and cardiorespiratory effects of a low dose (LD, 0.4 mg kg^?1 xylazine and 4 mg kg^?1 ketamine) and a high dose (HD, 0.8 mg kg^?1 xylazine and 8 mg kg^?1 ketamine) of IM xylazine–ketamine combination were compared in a randomized cross‐over study using six castrated male llamas. Three llamas in each dosage group (LDT, HDT) were assigned to receive IM tolazoline (2 mg kg^?1) after 30 minutes of recumbency. All IM injections were given in the semitendinosus or semimembranosus muscles. Pulse, respiratory rate, and indirect arterial blood pressure were recorded every 10 minutes, and hemoglobin oxygen saturation was recorded every 5 minutes during lateral recumbency. Samples for arterial blood gas analysis were collected 5 minutes following recumbency and every 30 minutes thereafter. Base‐to‐apex ECG was monitored continuously. Analgesia was evaluated every 5 minutes by both a 30 minutes skin pinch and a needle prick of the toe. Most llamas breathed room air throughout anesthesia. Two llamas that developed severe hypoxemia (SpO₂ < 75%) received 5 minutes of nasal oxygen insufflation, but were maintained on room air for the rest of the anesthetic period. anova for repeated measures and Tukey's test were used to analyze cardiorespiratory data. Fischer's exact test was used to compare the ability of each to provide >30 minutes of lateral recumbency and analgesia. A p‐value < 0.05 was considered significant. Both dosages provided reasonably rapid induction following injection (LD: 10.8 ± 6.3 minutes; HD: 5.0 ± 1.1 minutes; p = 0.07). Duration of lateral recumbency and analgesia were 34.7 ± 6.7 and 27.3 ± 4.6 minutes, respectively, in the LDT llamas. None of the three remaining LD llamas remained in lateral recumbency for longer than 12 minutes. Duration of lateral recumbency and analgesia were 87.3 ± 18.5 and 67.7 ± 16.0 minutes, respectively, for the HD llamas that did not receive tolazoline. The HDT llamas were recumbent for a significantly shorter time (43.3 ± 0.6 minutes; p = 0.05). The ability to provide >30 minutes of recumbency and analgesia was better in the HD group (6/6) than in the LD group (2/6) (p = 0.03). No differences between dosages were seen in pulse rate, respiratory rate, or arterial pressures. No ECG abnormalities were seen. Transient hypoxemia was seen in the first 10 minutes of lateral recumbency in the HD group by both hemoglobin oxygen saturation (84 ± 9.5%) and by blood gas PaO₂ (44.5 ± 5.8 mm Hg). It was concluded that the HD provided more consistent results than the LD, but induced transient hypoxemia. Tolazoline shortened the recovery time in llamas receiving the HD.     

Effects of Body Positioning on Swallowing and Esophageal Transit in Healthy Dogs

Background: Contrast videofluoroscopy is the imaging technique of choice for evaluating dysphagic dogs. In people, body position alters the outcome of videofluoroscopic assessment of swallowing.
Hypothesis/Objective: That esophageal transit in dogs, as measured by a barium esophagram, is not affected by body position.
Animals: Healthy dogs ( n = 15).
Methods: Interventional, experimental study. A restraint device was built to facilitate imaging of dogs in sternal recumbancy. Each dog underwent videofluoroscopy during swallowing of liquid barium and barium-soaked kibble in sternal and lateral recumbancy. Timing of swallowing, pharyngeal constriction ratio, esophageal transit time, and number of esophageal peristaltic waves were compared among body positions.
Results: Transit time in the cervical esophagus (cm/s) was significantly delayed when dogs were in lateral recumbency for both liquid (2.58 ± 1.98 versus 7.23 ± 3.11; P = .001) and kibble (4.44 ± 2.02 versus 8.92 ± 4.80; P = .002). In lateral recumbency, 52 ± 22% of liquid and 73 ± 23% of kibble swallows stimulated primary esophageal peristalsis. In sternal recumbency, 77 ± 24% of liquid ( P = .01 versus lateral) and 89 ± 16% of kibble ( P = .01 versus lateral) swallows stimulated primary esophageal peristalsis. Other variables were not significantly different.
Conclusions and Clinical Importance: Lateral body positioning significantly increases cervical esophageal transit time and affects the type of peristaltic wave generated by a swallow.     

Immunohistochemical Localization of Oestrogen Receptors α and β, Progesterone Receptor and Aromatase in the Equine Placenta

The functions of placental oestrogens during equine pregnancy are still unclear. Yet, they may act predominantly as local regulators of growth and differentiation in the microplacentomes. Thus, expression patterns of oestrogen receptors (ERs) α and β were investigated in the microcotyledonary placenta from pregnant mares at 110, 121, 179, 199 and 309 days of gestation by immunohistochemistry. In microplacentomes, both the ER isoforms were detected in trophoblast (T) cells, chorionic villous stroma (FS), microcaruncular epithelium (ME) and microcaruncular stroma (MS). Proportions of positive cells were 38–91% (T), 11–41% (FS), 55–89% (ME), 17–51% (MS) for ERα and 66–76% (T), 21–37% (FS), 41–68% (ME) and 24–55% (MS) for ERβ. Between days 110 and 199, proportions of cells positive for progesterone receptor (PR) varied between 19% and 62% (T), 3% and 50% (CS), 15% and 46% (ME), and 4% and 33% (MS). At day 309, PR was virtually absent in T, CS and ME (percentages < 0.1), whereas in MS 14.3% of cells were still positive. The expression of ERs and PR in equine microplacentomes gives evidence for a role of placental steroids as regulators of placental growth, differentiation and function. The detection of ERα, ERβ and PR in foetal and maternal vascular tissue suggests that placental steroids are also involved in the control of placental angiogenesis and /or vascular functions. The co-localization of ERs with aromatase in T suggests auto- or intracrine functions of oestrogens in this cell type.     

Histological and Immunohistochemical Characterization of Equine Anovulatory Haemorrhagic Follicles (AHFs)

Anovulatory haemorrhagic follicles (AHFs) are often the reason for ovulation failure in the mare. As the underlying factors that lead to AHF development are not well understood, it was of interest to investigate the vascularization of AHFs compared with normal follicles and corpora lutea (controls). In the present study, the ovarian cell populations investigated immunohistochemically included granulosa and luteal cells as well as various vascular structures. None of these cell types showed differences in the expression of vascular endothelial growth factor A (VEGF-A) between control ovaries containing normal follicles and corpora lutea and ovaries with AHFs. In contrast, a considerable reduction in the proportion of Flk-1-expressing cells, together with a decreased intensity of staining, was apparent in the AHFs. This greatly reduced expression of Flk-1 in the luteinized cells and the vascular structures of AHFs may lead to a distinct decrease in the potential pro-angiogenic activity of VEGF-A in these structures compared with the situation in normal follicles and corpora lutea. Furthermore, the authors suspect that the distinct expression of angiopoietin2 and VEGF-A seen in the cells within the inner fibrous layers of the AHFs was caused by hypoxia resulting from deficient vascularization, as suggested by the irregularity of the capillaries present in the luteinized wall of the AHF. In addition, whereas LH-receptor (LH-R) expression occurred uniformly in all stages of development of the corpora lutea in normal control ovaries, there was highly variable labelling for LH-R in all the AHFs examined, thereby indicating a possible numerical deficiency of LH-receptors in AHFs. The authors concluded that, despite the apparent expression of sufficient VEGF-A in the AHFs allows ovulation and corpus luteum formation, a relative lack of receptor, Flk-1, effects the pro-angiogenic activity of VEGF-A which could be a reason for ovulation failure associated with AHF formation.     

Growth factor messenger RNA levels in muscle and liver of steroid-implanted and nonimplanted steers

Ribonuclease protection assays were used to measure steady-state semimembranosus muscle and/or hepatic levels of IGF-I, IGFBP-3, IGFBP-5, hepatocyte growth factor (HGF), and myostatin messenger RNA (mRNA) in steers implanted from 32 to 38 d with Revalor-S, a combined trenbolone acetate and estradiol implant. Insulin-like growth factor-ImRNA levels were 69% higher (P < 0.01, n = 7) in the livers of implanted steers than in the livers of nonimplanted steers. Similarly, IGF-I mRNA levels were 50% higher (P < 0.05, n = 7) in the semimembranosus muscles of implanted steers than in the same muscles from nonimplanted steers. Hepatic IGFBP-3 mRNA levels were 24% higher (P < 0.07, n = 7) in implanted steers than in nonimplanted steers. Hepatic HGF and IGFBP-5 mRNA levels did not differ between implanted and nonimplanted steers. Similarly, muscle IGFBP-3, IGFBP-5, HGF, and myostatin mRNA levels were not affected by treatment. Previous data from these same steers have shown that circulating IGF-I and IGFBP-3 concentrations were 30 to 40% higher (P < 0.01, n = 7) in implanted steers than in nonimplanted, control steers. Additionally, the number of actively proliferating satellite cells that could be isolated from the semimembranosus muscle was 45% higher (P < 0.01, n = 7) for implanted steers than for nonimplanted steers. Viewed together, these data suggest that increased muscle IGF-I levels stimulate increased satellite cell proliferation, resulting in the increased muscle growth observed in Revalor-S implanted steers.     

The Development and Application of the Modern Reproductive Technologies to Horse Breeding

Although the horse was probably the first animal to experience and benefit from artificial insemination, it trailed the field somewhat with regard to the application of embryo transfer and other oocyte and embryo-related modern breeding technologies. But with a late run it is now back in mid-field and gaining fast on the other large domestic species in the application of the many technological advances of the past 20 years to sound breeding practice. Improvements in extenders and cryoprotectants have resulted in a veritable upsurge in the transport and insemination of cooled and frozen stallion semen, and parallel improvements in ovulation induction and synchrony, exogenous gonadotrophic stimulation of multiple fertile ovulations and simplified, more efficient methods for non-surgical transfer of embryos to recipient mares, coupled with relaxation of breed society registration restrictions, have together contributed to a similar upsurge in the application of embryo transfer to all breeds and athletic types of horses worldwide, with the continuing and notable exception of the Thoroughbred. Although conventional in vitro fertilization remains something of an unjumped fence in equids, other modern breeding technologies like hysteroscopic low-dose insemination, fluorescence-activated sex sorting of stallion spermatozoa, between-species embryo transfer, embryo freezing and bisection, transvaginal ultrasound-guided oocyte collection, intracytoplasmic sperm injection for fertilization (ICSI), gamete intrafallopian transfer (GIFT) and now nuclear transfer (cloning), have all been applied to equids with encouraging success. Cloning, especially, holds enormous promise for the Sporthorse industry to re-create champion geldings in stallion form for breeding purposes.