Effects of protozoa on bacterial nitrogen recycling in the rumen

The effects of protozoa on ruminal NH3-N kinetics and bacterial N recycling were measured in five sheep (57.6+/-7.1 kg BW, x +/- SD) with ruminal and duodenal cannulas in naturally faunated, defaunated, and refaunated periods. The sheep were fed a diet of 239 g of alfalfa haylage and 814 g of barley concentrate per day (DM basis) divided into 12 equal portions and allocated at 2-h intervals. A pulse dose of 300 mg of 15N as [15N]NH4Cl was administered into the rumen (on d 1 and 15) and 300 mg of 15N as [15N]urea was administered intravenously to the blood (d 8). Enrichment of 15N was measured in ruminal NH3-N, bacterial N, and plasma urea N over a period of 35 h. Total collection of urine was made for 5 d and analyzed for purine derivatives to calculate the flow of microbial N. Ruminal parameters and nutrient digestibilities were also measured. Sheep were defaunated using a rumen washing procedure 50 d prior to measurements in the defaunated period. Sheep were refaunated with ruminal contents from a faunated sheep receiving the same diet. Measurements began 26 d following refaunation, at which time protozoal numbers had returned to those in the originally faunated sheep. Data reported in parentheses are for faunated, defaunated, and refaunated sheep, respectively. Total culturable and cellulolytic bacterial numbers were unaffected by defaunation, but there was an increase in flow of microbial N from the rumen (10.8, 17.3, and 11.1 g N/d; P < .05) in the defaunated period. Flux, irreversible loss, and intraruminal recycling of NH3-N and recycling of NH3-N from plasma urea N were not affected by defaunation. Defaunation had no effect on reducing the absolute amount (13.8, 10.0, and 11.3 g N/d; P > .20) of bacterial N recycling and the percentage of N flux through the bacterial N pool. Total-tract digestion was reduced in defaunated compared with faunated sheep by 8, 17, 15, and 32% for OM, N, NDF, and ADF, respectively. In conclusion, defaunation improved ruminal N metabolism through the enhancement of bacterial protein synthesis, and improvement in the flow of microbial protein to the host animal.     

Porcine circovirus-2 DNA concentration distinguishes wasting from nonwasting pigs and is correlated with lesion distribution, severity, and nucleocapsid staining intensity.

The emergence of severe porcine circoviral disease in North America is associated with Porcine circovirus-2 genotype b (PCV-2b), which has led to speculation that PCV-2b is more virulent than PCV-2a. The objectives of this study were to 1) correlate the PCV-2 DNA concentration and lesions in wasting (WST) and age-matched healthy (HLTH) pigs from 2 clinically affected farms, and unaffected (UNFCT) pigs from a farm with no prior clinical or diagnostic history of PCVD; and 2) to determine the initial estimates of sensitivity and specificity of PCV-2 quantitative polymerase chain reaction (qPCR). PCV-2b was confirmed in all 3 farms. Compared with HLTH pigs, WST pigs demonstrated significantly more prevalent thymic atrophy, failure of normal pulmonary collapse, and ascites (P < 0.017 for all). The HLTH and UNFCT pigs had significantly more pronounced lymphoid germinal centers and proliferative paracortical T-dependent zones, compared with WST pigs (P < 0.017). Across all tissues, PCV-2 DNA concentrations were significantly higher in WST compared with HLTH and UNFCT pigs (P < 0.017 for all). The PCV-2 DNA concentrations were strongly correlated with PCV-2 nucleocapsid staining intensity in lymph node, spleen, Peyer's patches, lung, liver, and kidney (0.60 < or = r < or = 0.84). In the current study, the PCV-2 DNA log10 cutoff concentrations best able to distinguish WST from HLTH and UNFCT pigs were between 7.0 and 8.0 per gram for tissues, and between 4.0 and 5.0 per milliliter for sera. The presence of PCV-2b in UNFCT pigs is evidence that PCV-2b by itself is not sufficient to induce severe disease.     

THE KANGAROO ISLAND STRAIN OF PIG IN BIOMEDICAL RESEARCH

The feral pig from Kangaroo Island, South Australia, has descended from British breeds released onto the Island by early explorers approximately 180 years ago. It has developed into a smaller pig than the modern commercial equivalent, with distinctive and reproducible physical characteristics and a physiology which appears to bestow on it some advantages in terms of fitness and vigour. It has adapted easily to laboratory and intensive piggery conditions where it has reproduced satisfactorily. It has a higher erythrocyte count and PCV than the equivalent Large White and a lower white blood cell count. Plasma Na, K and glucose were significantly higher and HCO₃ urea and creatinine lower in the Kangaroo Island strain. It represents a useful strain of pig for biomedical research, approaching in size the miniature pigs used overseas. A useful approach to routine bleeding of pigs is described.     

Breeding wheat for resistance to biotic stresses

Although common wheat and durum may be attacked by a large number of diseases and pests, less than 20 diseases and about five insect or mite pests are of major significance. Some of these have a global distribution and occur in most wheat-growing areas, whereas others are restricted to certain geographic regions or climatic zones. A small group of diseases and pests, such as Karnal bunt and Russian wheat aphid, are a major threat to countries and regions in which they are absent. Although there is genetic variation in response to most diseases and pests, resources available to national programs limit the number that can be included as breeding objectives. Ideal sources of resistance are those present in closely related, commercial genotypes, but care must be exercised to avoid genetic uniformity. Any effort to transfer resistance from related species and genera should be considered long term. The chance of successful exploitation of resistance based on alien genetic material declines with reducing genetic relatedness between recipient and donor species. Breeders must maintain an awareness of potential problems associated with very high levels of resistance controlled by single genes. Lower levels of resistance with established durability or resistance based on a number of genes may be preferred. In many situations, resistance with moderate to low effectiveness will contribute significantly to crop protection. Unusually susceptible genotypes should be avoided irrespective of perceived risk based on local surveys. Molecular and other markers for genes of interest are having an increasing role in the selection process. Although genetic engineering in wheat is in its infancy, significant contributions to disease resistance, starting with virus resistances, can be expected. This revised version was published online in August 2006 with corrections to the Cover Date.     

Habitat fragmentation,livelihood behaviors,and contact between people and nonhuman primates in Africa

Landscape Ecology - Deforestation and landscape fragmentation have been identified as processes enabling direct transmission of zoonotic infections. Certain human behaviors provide opportunities...     

Inheritance of the stem rust resistance phenotype Pg-a in oats

Forty stem rust resistant oat cultivars and lines were selected from Australian oat breeding programs, Quaker Oat Nurseries and a Brazilian oat collection. Most, including the Pg-a reference stock Omega, were crossed with a susceptible line in order to study the inheritance of resistance. Omega was crossed with 15 resistant selections and a further 15 intercrosses were made among resistant selections. All selected lines possessed Pg-a which was inherited as a pair of recessive complementary genes. All crosses among resistant lines failed to segregate. In the majority of resistant/susceptible crosses, the F2 ratio was 1 resistant: 2 intermediate: 13 susceptible, whereas in others it was 1 resistant: 15 susceptible. Progenies of plants with intermediate reactions always segregated. Although Kyto with Pg-12 was a parent of Omega, Pg-12 was not present in any resistant line and was not involved in the Pg-a response. The respective complementary genes were isolated in stem rust susceptible lines, which when intercrossed, segregated in F2 to produce resistant plants in the expected frequencies and with the typical Pg-a phenotype. The lack of effective genetic variability for stem rust resistance among important sources of germplasm used by Australian oat breeders is a major cause for concern.