Effects of chemically or virus-induced immunodepression on response of chickens to avian leukosis virus

The effects of chemically or virus-induced immunodepression on the infection profile (development of viremia and antibody) and shedding of avian leukosis virus (ALV) were studied in progeny chickens of experimental or commercial breeder flocks. Chickens were infected with ALV subgroup A by contact at hatching and by oral inoculation at 4-5 weeks of age. In the first experiment, chickens were inoculated with a virulent strain of infectious bursal disease virus (IBDV) at 1 day or 6 weeks of age. In the second experiment, chickens were neonatally treated with cyclophosphamide (CY), or were inoculated with strain T of reticuloendotheliosis virus (REV) at hatching, or were inoculated with strain JM of Marek's disease virus (MDV) at 2 weeks of age. The infection profile and cloacal shedding of ALV in chickens exposed to ALV and inoculated with immunodepressive viruses or CY were compared with those in hatchmates exposed only to ALV. In two of four chicken lines tested in the first experiment, shedding of ALV, as determined by virological assays of cloacal swabs at 22 weeks of age, was significantly higher in chickens infected with IBDV at 1 day of age than in uninfected hatchmates. The rate of shedding of ALV in one of these two lines was also significantly higher in chickens infected with IBDV at 6 weeks of age than in uninfected chickens. Further, the frequency of ALV-antibody detection at 22 weeks of age was significantly lower in chickens of these two lines infected with IBDV at 1 day of age than in uninfected chickens. In the second experiment, neonatal treatment with CY significantly increased the frequency of viremic chickens of both experimental and commercial flocks. The frequency of ALV-viremic chickens at 22 weeks of age was considerably higher in the REV- and MDV-inoculated groups (54% and 44%, respectively) than in control hatchmates (29%), but only in chickens of the commercial line. These findings suggest that chemically or virus-induced immunodepression may lead to an increase in rates of viremia and shedding of ALV in chickens infected with virus after hatching, especially in certain genetic lines.     

New serotype 2 and attenuated serotype 1 Marek's disease vaccine viruses: selected biological and molecular characteristics

Two new Marek's disease vaccine viruses, Md11/75C/R2 (serotype 1) and 301B/1 (serotype 2), were evaluated in chickens with maternal antibodies (ab+) or without maternal antibodies (ab-). Strain Md11/75C/R2 was mildly pathogenic in ab--chickens, but this pathogenicity was markedly reduced in ab+ chickens. Md11/75C/R2 spread less by contact and replicated better, both in vivo and in vitro, than CVI988/C, another serotype 1 vaccine virus. Strain 301B/1 was similar to SB-1, another serotype 2 vaccine virus: both were nonpathogenic for ab--chickens, spread readily by contact, and replicated well in vivo. In vitro, 301B/1 grew more rapidly and produced larger plaques than SB-1. Notable characteristics of strain CVI988/C included absence of pathogenicity, poor replicative ability, and the absence of one epitope detected by a common serotype-1-specific monoclonal antibody. All four viruses could be distinguished from each other by restriction enzyme analysis of viral DNA. We conclude that Md11/75C/R2, although exceptionally protective, may require further attenuation. On the other hand, 301B/1, which in other studies induced higher levels of protection than SB-1, is nonpathogenic and may be considered for use as a commercial vaccine.     

Differential expression of insulin‐like growth factor family members in immature cumulus–oocyte complexes from dairy cows with different genotypes

It has been evident the improvement of in vitro embryo production (IVEP) in dairy cows. Nevertheless, it is known that differences in the number and quality of oocytes between taurine and zebu females impact the efficiency and economic viability of IVEP. As the insulin‐like growth factor (IGF) system is related to follicular and oocyte development, we aimed to quantify mRNA abundance of IGF system members and pregnancy‐associated plasma protein‐A (PAPPA) in the cumulus–oocyte complexes (COCs) of Gir, 1/2 Holstein × 1/2 Gir and Holstein cows. Four pools of 30 immature COCs from Gir, 1/2 Holstein × 1/2 Gir and Holstein cows were obtained by ovum pickup (OPU), and the oocytes and cumulus cells (CC) were mechanically separated and stored at ?80°C. Total RNA was extracted from pools of 30 oocytes and their respective CC. Expression of target genes was assessed by real‐time RT‐PCR. In oocytes, the abundance of IGFR1 mRNA was higher (p < .05) in Gir cows compared with the other breeds. In contrast, in CC, mRNA encoding IGF2 (p < .05), IGFR2 (p < .05) and IGFBP4 (p < .01) was higher in Holstein donors compared with Gir and 1/2 Holstein × 1/2 Gir cows. Additionally, the abundance of PAPPA mRNA was higher in oocytes (p < .001) and CC (p < .01) in Gir and 1/2 Holstein × 1/2 Gir cows compared with the Holstein donors. In conclusion, the higher abundance of PAPPA mRNA in the oocytes and CC from Gir and cross‐breed donors combined with the low expression of IGFBP4 in the CC suggests an enhancement of the bioavailability of IGF‐free when compared with Holstein COCs.     

Detection of antibodies against reticuloendotheliosis viruses by an enzyme-linked immunosorbent assay

A microplate indirect enzyme-linked immunosorbent assay (ELISA) for antibodies against reticuloendotheliosis virus (REV) was consistently more sensitive than indirect immunofluorescent-antibody tests. Limits of antibody detection were comparable to those obtained in virus neutralizations. Detection of REV-infected chickens long after infection and after immunofluorescent antibody has waned makes ELISA especially suitable for screening chicken flocks.     

Trends in the use of pesticides and pestiside residues on Queensland wool

Objective To determine the amounts of organophosphorous and synthetic pyrethroid residues on Queensland wool sampled between 1995 and 1997, and to study if pesticide use changed during the period.
Design Estimated amounts of residues were obtained from a survey of Queensland wool clips, and information on pesticide use was obtained from a trace-back postal survey of flock managers.
Procedure Trends in amounts of residues over time were assessed using analysis of variance and simple linear regression models, and changes in pesticide use was assessed using x² tests.
Results Significant linear reductions in organophosphorous (P = 0.0012), synthetic pyrethroid (P = 0.0044) and total (P = 0.0002) residues were detected. The proportion of woolgrowers treating for louse infestation (P = 0.0046) treating twice or more (P = 0.0006) and treating more than 4 months after shearing (P = 0.0001) decreased between 1994 and 1997. However, the proportion of growers who treated for blowfly strike (P = 0.0124) and used insect growth regulator pesticides increased (P < 0.0001). The use of handjetting to apply pesticides for blowfly strike control increased and the use of dips decreased (P < 0.0001).
Conclusion Residues of organophosphorous compounds and synthetic pyrethroids reduced in Queensland wool between 1994 and 1997. Although woolgrowers treated for louse infestation less, pesticide use to control blowfly strike increased. The increasing use of insect growth regulators in the industry needs to be monitored.