Effect of administration of vitamin E and selenium during the dry period on mammary health and milk cell counts in dairy ewes.

The effect of parenteral administration of two subcutaneous injections of vitamin E and Se (5 mg and 0.1 mg/kg of body weight, respectively) during the dry period on the mammary health and milk somatic cell counts of 25 dairy ewes was investigated. Supplementation reduced somatic cell counts (5.4 vs. 6.0 log10) during the subsequent lactation but had no effect on the incidence of clinical mastitis (4% vs. 6%) and intramammary infections (9.0% vs. 11.3%). Furthermore, the administration of vitamin E and Se was associated with differences in differential cell counts of milk samples (macrophages, 48.8% vs. 38.4%; polymorphonuclear neutrophils, 40.1% vs. 50.7%; and eosinophils, 0.7% vs. 1.4% for control ewes and ewes receiving supplements, respectively). The administration of these supplements also increased erythrocyte glutathione peroxidase activity (139.5 vs. 86.3 U/ml of packed cell volume) and the percentage of blood neutrophils that reduced nitroblue tetrazolium after bacterial extract stimulation (48.6% vs. 38.7%). Parenteral administration of vitamin E and Se to ewes during the dry period appeared to have influenced mammary gland status during the subsequent lactation and particularly total and differential milk cell counts.

Total and differential cell count by direct microscopic method on ewe milk.

On 700 milk samples from single half udders of Comisana ewes, somatic cell count (SCC) and differential cell count (DCC) were determined, using a Fossomatic 90 cell counter (Foss Electric, Denmark) (SCCF) and milk smears stained with May Grünwald-Giemsa (DCCS). SCC and DCC were also determined with modified KOVAH SYSTEM (Hicor Biomedical Inc. Irvine, CA, USA) (SCCK and DCCK, respectively). Out of 665 milk samples from half udders without clinical signs of mastitis, 640 (Class I) were sterile, while 25 (Class II) were bacteriologically positive. Out of 35 milk samples (Class III) from half udders with clinical signs of mastitis, 25 were bacteriologically positive. Mean results (after logarithmic transformation of cells/ml/10(3)) of SCCF and SCCK for all the 700 milk samples were 1.89 +/- 0.58 and 1.86 +/- 0.60 with linear correlation coefficient (r) of 0.960, while least squares means for Class I, II and III were 1.78, 2.23 and 3.73 respectively and 1.75, 2.19 and 3.74 with r of 0.894, 0.979 and 0.987. Mean results of DCCS and DCCK were 38.1 +/- 23.3, 34.9, 52.1, and 82.2 PMNL% and 41.8 +/- 21.7, 38.6, 60.2, and 87.3 PMNL% with r of 0.855, 0.812, 0.697 and 0.805. The results showed high correlation coefficients and a good reliability between SCCK and SCCF and high correlation coefficients for DCC methods. In conclusion, it could be suggested that the possibility of routine use of the KOVAH SYSTEM method is particularly useful in detecting if an abnormal SCC is due to a polymorphonuclear neutrophil leukocytes increase.

Experimental infection of calves with strains of Bovid herpesvirus-4.

Fourteen calves were inoculated intranasally (i.n.) with the viral isolates as follows: 5 with 85/BH 16TV, 1 with 85/BH 17TV, 1 with 85/BH 18TV, 2 with 85/BH 231TN and 5 with 85/BH 232TN. Strain 85/BH 16TV was the only one which caused overt respiratory-like disease in all inoculated calves. Onset of the disease was observed after 7-8 days of incubation and was characterized by fever, depression, nasal discharge and coughing. Virus was isolated from the nasal swabbings of calves obtained from post-infection day (PID) 2-10. The other viral strains did not cause any sign of disease although virus was isolated regularly from the nasal swabbings of the inoculated calves. Virus was recovered from central nervous system tissues of calves that were infected with 85/BH 16TV or 85/BH 232TN strains and were killed on PID 4 or 8. Virus was also isolated from other tissues, such as lymph node, nasal mucosa (PID 8), or lung (PID 4). It was speculated that the nervous system could be one of the target areas of the virus of the naturally occurring infection by BHV-4. This might indicate a possible role of the nervous system (site of latency?) in the pathogenesis of BHV-4 as is the case in certain herpesviral infections of man and the lower animals.

Comparative studies of strains of infectious bovine rhinotracheitis virus isolated from latently infected calves.

Three strains (479 C, 778 TL, 982 LE) of infectious bovine rhinotracheitis (IBR) virus isolated from latently infected calves were compared with the prototype strain of IBR virus (LA strain) in studies which included restriction endonuclease analysis, experimental infection, and reciprocal cross protection tests in cattle. From the restriction endonuclease analysis it appeared that the 3 "latent" viruses were derived from the same isolate, and that it differed slightly from the LA strain. However, latency does not seem to have affected the pathogenicity or the immunogenicity of the virus. This is demonstrated by the identical clinical and virologic response of calves subjected to experimental infection with the various strains under study, and by the finding that when the LA strain and a "latent" strain (982 LE) were tested in cross protection tests in cattle, they proved to be mutually protective.

Reactivation of Bovid herpesvirus 1 and 2 and parainfluenza-3 virus in calves latently infected.

Two experiments were carried out to determine whether Bovid herpesvirus (BHV) 2 is able to induce a recurrent infection in experimentally infected calves. In the first experiment the stress induced by dexamethasone (DMS) treatment failed to reactivate the clinical condition or to induce shedding of BHV2. However, treatment with DMS reactivated a latent BHV1 infection in all calves previously inoculated with BHV2 and also in two noninoculated controls. Probably, because of the interference by BHV1 the study failed to resolve the question as to whether BHV2 could induce a recurrent infection. Consequently, a second experiment was performed using calves devoid of antibody to BHV1 and, therefore, probably, free of virus. By this study it was demonstrated that BHV2 can remain as a latent infection in cattle, which, when immunosuppressed as with DMS, can be reactivated. A finding of considerable interest in this experiment was that in 1 calf a concurrent piroplasma infection was also, unexpectedly, discovered. Recrudescence of latent BHV1 infection was induced by DMS treatment of calves possessing antibody to the virus. The infection once reactivated, was readily transmitted by contact to three other calves devoid of antibody to BHV1. In the same experiment Parainfluenza-3 (PI-3) virus was unexpectedly isolated from all calves. It was speculated that all calves were latently infected with PI-3 virus with concurrent infection by HBV1 acting as a stress inducing PI-3 reactivation. These studies seem to indicate that mixed infections could have an important role in the mechanism involved in the establishment of latent infections and viral reactivation.

Reactivation in calves of Bovid herpesvirus 2 latent infection.

Seven calves which had recovered from an experimentally induced infection with Bovid herpesvirus 2 (BHV 2) were subjected to a course of dexamethasone (DMS) treatment six months later. BHV 2 was recovered from nasal swabs obtained from each calf 11 days after the start of DMS treatment. The virus was also isolated from the skin, nervous system tissue and lymph nodes of a calf killed 11 days after the start of DMS treatment in which a concurrent piroplasma infection was also, unexpectedly, discovered. It is suggested that the skin and nervous system are possible anatomical sites for the latency of BHV 2 in the host.

Attempts to reactivate bovid herpesvirus-2 in experimentally infected calves.

A study was carried out to determine whether bovid herpesvirus-2 (BHV-2) is able to induce a recurrent infection in experimentally infected calves. Twelve calves infected with the virus were treated with dexamethasone (DMS) beginning 69 days after the infection, ie, several weeks after the animals had recovered from the disease and were negative for BHV-2. The stress induced by DMS treatment failed to reactivate the clinical condition or to induce shedding of BHV-2. However, treatment with DMS reactivated a latent infectious bovine rhinotracheitis (IBR) virus infection in all calves previously inoculated with BHV-2, and also in 2 noninoculated controls. The reactivation of IBR virus occurred without any clinical evidence of the disease, but the virus was isolated from nasal and pharyngeal swabbings and from the organs. A proliferative ganglionitis of the trigeminal ganglion was also observed. Because of the interference by IBR virus, this study did not resolve the question as to whether BHV-2 can induce a recurrent infection.

Distribution of Bovid herpesvirus 2 in calves inoculated intravenously.

The behavior of Bovid herpesvirus 2 in the skin, lymph nodes, and nervous system of calves injected intravenously with the virus was studied. After a latent phase that lasted up to 40 hours after inoculation, the virus produced a systemic infection which was characterized by primary localization of virus in the skin, lymph nodes, and nervous system. Between postinoculation days 7 and 12, the infection tended to persist in the skin only. The finding of intranuclear inclusions in the pyramidal cells of the cerebral cortex and in the neurons of the superior cervical and stellate ganglia supports the hypothesis that the virus might utilize the structures of the nervous system for its replicative cycle in the calf.

Preliminary studies on the diffusion of bovid herpesvirus 2 in experimentally infected calves.

This preliminary study on the diffusion of the Bovid herpesvirus 2 (BHV2) in calves inoculated intravenously, allowed to identify the target organs of the virus. In particular, in the first phase of the infection, i.e. post infection day (PID) 2, the virus resulted extensively widespread in the body of the calf, whereas in a subsequent phase, PID6, the virus was recovered only from the skin, the lymph nodes and the nervous system. Finally virus was not recovered in any of the tissues obtained from the calf killed at PID 12. Based on the results it might be speculated that, under the experimental conditions of these tests, the infection of cattle by BHV2 develops through two stages. The first stage would be characterized by a systemic condition in that the virus is present in the whole organism; the second stage which follows, consists in a localized infection, the virus being present only in some districts of the organism (skin, lymph nodes, nervous system) which could be considered as the definitive target sites for virus replication.