Detection of pseudorabies virus infection in subunit-vaccinated and nonvaccinated pigs using a nucleocapsid-based enzyme-linked immunosorbent assay.

The potential of a pseudorabies virus (PRV) nucleocapsid protein (NC)-based enzyme-linked immunosorbent assay (ELISA) as a screening assay for PRV infection in subunit-vaccinated and nonvaccinated pigs was studied. The NC-ELISA compared favorably to a commercial ELISA for detecting PRV infection in nonvaccinated pigs. Virus-specific antibody was first detected by the NC-ELISA between days 14 and 21 in 5 pigs challenged intranasally with 10(4) PFU of virus. Antibody continued to be detected in these pigs through day 42, when the experiment was terminated. The NC-ELISA also detected antibody in 23 of 24 pigs from PRV-infected herds. In contrast, the commercial ELISA detected antibody 1 week earlier than the NC-ELISA in experimentally infected pigs but failed to detect antibody in 3 naturally exposed pigs that were identified by the NC-ELISA. Infection in these animals was confirmed by radioimmunoprecipitation analysis. The potential usefulness of the NC-ELISA for detecting infection in vaccinated pigs was also evaluated. The nucleocapsid-specific antibody responses of 10 PRV envelope glycoprotein subunit-vaccinated pigs were monitored prior to and following nasal exposure to a low dose (10(2.3) PFU) of PRV. Sera were collected periodically for 113 days after infection. Nucleocapsid-specific antibody responses measured by the NC-ELISA remained below the positive threshold before challenge but increased dramatically following virus exposure. Maximum ELISA responses were obtained on day 32 postchallenge (p.c.). Mean ELISA responses decreased thereafter but remained well above the positive threshold on day 113 p.c. PRV nucleocapsid protein can be used effectively as antigen in the ELISA for detecting PRV infection in both nonvaccinated and subunit-vaccinated pigs.

Genomic selection using beef commercial carcass phenotypes.

In this study, an industry terminal breeding goal was used in a deterministic simulation, using selection index methodology, to predict genetic gain in a beef population modelled on the UK pedigree Limousin, when using genomic selection (GS) and incorporating phenotype information from novel commercial carcass traits. The effect of genotype-environment interaction was investigated by including the model variations of the genetic correlation between purebred and commercial cross-bred performance (ρX). Three genomic scenarios were considered: (1) genomic breeding values (GBV)+estimated breeding values (EBV) for existing selection traits; (2) GBV for three novel commercial carcass traits+EBV in existing traits; and (3) GBV for novel and existing traits plus EBV for existing traits. Each of the three scenarios was simulated for a range of training population (TP) sizes and with three values of ρX. Scenarios 2 and 3 predicted substantially higher percentage increases over current selection than Scenario 1. A TP of 2000 sires, each with 20 commercial progeny with carcass phenotypes, and assuming a ρX of 0.7, is predicted to increase gain by 40% over current selection in Scenario 3. The percentage increase in gain over current selection increased with decreasing ρX; however, the effect of varying ρX was reduced at high TP sizes for Scenarios 2 and 3. A further non-genomic scenario (4) was considered simulating a conventional population-wide progeny test using EBV only. With 20 commercial cross-bred progenies per sire, similar gain was predicted to Scenario 3 with TP=5000 and ρX=1.0. The range of increases in genetic gain predicted for terminal traits when using GS are of similar magnitude to those observed after the implementation of BLUP technology in the United Kingdom. It is concluded that implementation of GS in a terminal sire breeding goal, using purebred phenotypes alone, will be sub-optimal compared with the inclusion of novel commercial carcass phenotypes in genomic evaluations.

Gene flow in a national cross-breeding beef population.

Future progress in genetic improvement and the monitoring of genetic resources in beef cattle requires a detailed understanding of the population under selection. This study examines the gene flow in the UK beef population with an uncommon breeding structure involving interaction between the beef and dairy populations. British Cattle Movement Service records were used as the primary source of information, and these data were triangulated with UK government statistics, other industry information sources and existing literature to build up a profile of the UK beef industry. Estimates were made of the breed composition of suckler cows, breeding bulls and the prime slaughter population. Cross-bred animals made up 85% and 94%, respectively, of the commercial beef breeding cow and prime slaughter populations. Holstein/Friesian (through cross-breeding) made up the largest proportion of genes in both these populations with 33% and 28%, respectively. The next five most popular breeds were specialist beef breeds: Limousin (22% and 18%), Charolais (11% and 6%), Simmental (9% and 11%), Angus (7% and 8%) and Belgian Blue (6% and 6%). Combined, the top seven beef breeds accounted for 94% of beef genetics in the prime slaughter population, and 80% of this came from non-native breeds. The influence of dairy breeds in the commercial beef breeding population was highlighted by the fact that 44% of replacement commercial beef breeding females were sourced from beef-sired crosses in the dairy herd, and in total 74% of all maternal grand dams of prime slaughter animals were Holstein/Friesian. The use of selection index technology was also investigated by analysing breeding bull sale results, with the correlation between the terminal sire index and sale price of young breeding bulls being generally moderate but significant, ranging from 0.21 to 0.38 across the major beef breeds. The most influential source of genetics in the commercial suckler beef herd was natural service breeding bulls. These were mostly sourced from pedigree breeders, and accounted for 47.8% of the genetics in the prime beef population. Artificial insemination sires were responsible for 16.6% of prime beef genetics, with the remaining 35.6% coming from dairy breeds, 95% of which was Holstein/Friesian.