Amino acid comparison of infectious bursal disease viruses placed in the same or different molecular groups by RT/PCR-RFLP.

Infectious bursal disease virus (IBDV) strains have been identified and placed into molecular groups by a reverse transcriptase (RT)/polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP) assay. The predicted amino acid sequences corresponding to the region of the genome examined by RFLP were determined and compared for 14 IBDV strains from different molecular groups and 11 IBDV strains that were identified in molecular group 6. Among the viruses within molecular group 6, 13 amino acid positions had mutations, and among the viruses in different molecular groups, 27 amino acid positions had mutations. In addition to having more mutations, viruses compared from different molecular groups also had mutations at key positions that were previously reported to be important for the formation of neutralizing epitopes. Three of these IBDV strains with unique RFLP patterns were used to challenge 1-wk-old broiler chickens with maternal immunity to IBDV. One of these viruses, T1, broke through this maternal immunity as evidenced by detection of the virus by RT/PCR-RFLP and production of an active virus neutralizing antibody response to classic and variant IBDV strains. Unique amino acid mutations in the T1 virus that may have contributed to its ability to break through this maternal immunity were observed at amino acids 318 and 322. The results indicate that RFLP profiles and nucleotide sequences can be used to predict the relative similarities and differences among IBDV strains, but determining the actual antigenic differences among viruses requires testing in vivo.

Antibody titers to infectious bursal disease virus in broiler chicks after vaccination at one day of age with infectious bursal disease virus and Marek's disease virus.

The effect of day-of-age vaccination with infectious bursal disease virus (IBDV) alone or in combination with Marek's disease virus (MDV) in broiler chicks was investigated. One-day-old commercial broiler progeny obtained from IBDV-immunized breeder flocks were vaccinated subcutaneously according to the manufacturer's directions with live-attenuated commercially available vaccines as follows: IBDV alone, MDV alone, IBDV + MDV, and unvaccinated control. IBDV was not detected after vaccination by reverse transcriptase/polymerase chain reaction in any of the bursal, thymic, and splenic tissues tested. Serum IBDV antibody levels, as monitored by enzyme-linked immunosorbent assay (ELISA), showed similar rates of decline among the four groups, and, by day 28 postinoculation, serum antibody levels in all groups were below detectable limits. IBDV-specific neutralizing maternal antibody (MA) titers in the IBDV + MDV and control groups, as monitored by the virus neutralization assay (VN), remained higher and declined more slowly throughout the experiment as compared with VN titers in the IBDV- and the MDV-vaccinated groups. In a second experiment, groups of one-day-old broiler chicks were vaccinated as in Experiment 1. Serum IBDV antibody detected by ELISA and VN assay declined parallel to those observed in Experiment 1. Histopathologic lesions characteristic of IBDV were not observed in any of the groups. Vaccination with MDV alone was associated with increased rates of IBDV neutralizing MA decline similar to those caused by vaccination with IBDV alone, whereas concurrent vaccination with IBDV + MDV was not associated with increased rates of IBDV neutralizing MA decline over that of nonvaccinated controls. Results of these studies indicate that IBDV vaccination at 1 day of age does not cause accelerated IBDV-specific MA decline as detected by ELISA but does appear to cause an accelerated decline in neutralizing IBDV-specific MA. Furthermore, vaccination with IBDV at 1 day of age appeared to slow the accelerated rate of IBDV neutralizing antibody decline caused by MDV vaccination.

Effects of programmed gain strategies on performance and carcass characteristics of steers.

In Trial 1, 161 Angus x Simmental crossbred steers (initial BW 305 +/- 1.0 kg) were used in a completely randomized design experiment to determine the effects of intake restriction and programmed gain on cattle performance and carcass composition and characteristics. Five feeding systems were tested using step-wise increases in programmed intake level. Initially steers were fed to gain 1.13 kg/d. Intake was then increased to achieve a gain of 1.36 kg/d. At the end of the feeding period, steers had ad libitum access to feed. Duration of intake restriction and the period of unrestricted intake was varied. Feeding steers at restricted intakes and then increasing daily gain by increasing feed intake using four different schedules all reduced (P < .05) daily feed intake and total feed intake compared with providing ad libitum access to feed throughout the trial. Furthermore, daily feed efficiency was increased (P < .05) by two of the feeding systems compared with offering ad libitum access to feed throughout the trial. The feeding system used did not affect (P > .10) quality grade of the carcasses. In Trial 2, 77 individually penned Angus x Simmental crossbred steers (initial BW 273 +/- 1.2 kg) were used to determine the effects of various feed intake restriction systems. For systems 1 through 4, multiple periods of restriction and realimentation were investigated; the duration and magnitude of restriction were varied. Feed intake was not restricted for steers in system 5. The feed restriction systems used in this experiment did not result in decreased total feed intake or changes in carcass composition as compared with offering ad libitum access to feed. Reducing total energy intake seems to be a prerequisite to altering feed efficiency of steers in limit-feeding systems.