Differences in swimbladder volume between Baltic and Norwegian spring-spawning herring: Consequences for mean target strength

Fish swimbladders, where present, contribute most to the scattering of sound by fish, as measured by the target strength (TS). The volumes of the swimbladders of two different European stocks of Atlantic herring were compared to consider the effect on estimates of TS. Swimbladder volumes of Baltic and Norwegian spring-spawning herring (Clupea harengus) were measured, together with individual herring fat content. Swimbladder volumes were found to differ significantly between the two herring stocks. Baltic herring have a larger swimbladder volume, which is suggested to be associated with the fish's low fat content, which in turn may be linked to its specific energy budget and the low salinity of the Baltic Sea. A buoyancy model that considered the different salinity conditions and fat proportions was used to evaluate the observed differences in swimbladder volume. The swimbladder volume data were subsequently used to model the mean target strength as a function of depth and growth pattern. Backscattering of the swimbladder was modelled using the modal-series-based deformed-cylinder model (MSB-DCM), describing the swimbladder as a gas-filled, elongated prolate spheroid. The fish body component was modelled as a fluid-filled ellipsoid using the distorted wave Born approximation (DWBA). Modelling results support a different TS-to-size relationship for Baltic herring, with a stronger echo, due to the larger swimbladder. Depth- and length-dependent TS relationships based on the model results are suggested.     

Multiple-locus variant-repeat assay (MLVA) is a useful tool for molecular epidemiologic analysis of Streptococcus agalactiae strains causing bovine mastitis

Group B streptococci (GBS) were considered a major cause of mastitis in cattle until preventive measures succeeded in controlling the disease in the 1970s and 1980s. During the last 5-6 years an increasing number of cases have been observed in some Scandinavian countries. A total of 187 GBS isolates from mastitis cases were collected from 119 animals in 34 Norwegian farms in the period from April 2007 to November 2010. 133 (71%) of the isolates were from farms with automated milking systems. The strains underwent typing of capsular polysaccharides (CPS) and surface proteins, and were analyzed by multi-locus variable repeat assay (MLVA) to investigate the epidemiological relationship of strains within and between farms. The GBS strains were differentiated into 12 types by CPS and surface protein analysis, with CPS types V (54%) and IV (34%) predominating. MLVA was superior to CPS and protein typing for strain differentiation, resolving the 187 strains into 37 types. In 29 of 34 farms all GBS strains had identical MLVA profiles specific for each farm. However, in one farm represented with 48 isolates, four MLVA variants with differences in one repeat locus were observed during the almost 3-year long collection period. Similar variations were observed at four other farms. This might reflect the stability of repeat loci under in vivo conditions. Farms with automated milking systems were overrepresented in this material. In conclusion, the five-loci MLVA allowed rapid high-resolution genotyping of the bovine GBS strains within and between farms.     

Evaluation of Ewe Performance in 795 Selected Sheep Flocks in South-Eastern Norway

A study of ewe performance was undertaken in 795 sheep flocks based on data from the Norwegian Sheep Recording System. Herd level data included in the annual report for 1998 were used as the basis for the study. Average flock size was 75.3 ewes. The material was considered as representative of the better and more motivated sheep farmers in the mountain valley regions in south-eastern Norway. The average number of lambs born per ewe, inclusive (and exclusive) of barren ewes, was 1.89 (2.02), and of autumn lambs (those surviving from birth in the spring to autumn) 1.60 (1.66). The average autumn weight of the lambs corrected to 145 days of age was 42.4 kg, giving an overall performance of 67.9 kg lambs live weight per ewe. When including artificially reared lambs, overall performance was 70.4 kg per ewe. Artificial rearing of lambs, mostly triplets which had been removed from the ewe, was practised on 395 of the farms. In the 74 flocks with a rate of artificial rearing of more than 10% of all lambs, overall performance per ewe was 13.3 kg higher than in flocks with no artificial rearing. Total lamb mortality from birth to autumn recording, including stillborn lambs, was 12.44%. Mortality had a skewed distribution, some flocks having very high mortality figures. The arithmetic means (and medians) for mortality were as follows: 2.75 (2.29)% stillbirths, 2.93 (2.30)% died during the indoor feeding period, 0.88 (0.00)% at spring pasture, and 6.16 (4.40)% at summer pasture. In regression models using Proc Genmod in SAS^®, it was found that average number of autumn lambs per ewe was negatively associated with the rate of barren ewes, late lambing date (flock average day in year when lambing took place), and total lamb mortality. The corrected autumn weight of the lambs was positively associated with the average number of lambs born per ewe and non-fertility rate, and negatively associated with flock size and total lamb mortality. The Dala breed had a positive effect on number of autumn lambs per ewe, and Spæl breed a negative effect on corrected autumn live weight of the lambs.     

Electronic feed stations for feeding concentrates to pregnant ewes on commercial sheep farms

ABSTRACT

The aim of this study was to investigate the use and capacity of electronic feed stations (EFS) on commercial sheep farms. The study was conducted on four commercial farms and the numbers of pregnant ewes per EFS were 36, 70, 72 and 80, respectively. Each farm was visited once and behavioural observations were carried out. In addition the date and time for both entering and leaving the EFS and the amount of concentrates dispensed at each visit for extracted. The vast majority of the ewes used the EFS regularly. The number of rewarded visits per ewe per day varied from 3.2 to 5.9, whereas the number of unrewarded visits ranged from 6.0 to 21.5 per ewe per day. We conclude that feeding concentrates to groups of pregnant ewes in EFS function satisfactory, but the design of the entrance and exit gate still have to be improved considerably.     

Antibacterial spectrum and some other characteristics of an antimicrobial factor produced by Yersinia ruckeri

Yersinia ruckeri produces an antibacterial factor which inhibits the growth of a wide spectrum of Gram-negative and Gram-positive bacteria, though not other strains of Y. ruckeri. The antibacterial factor was produced at low temperatures (4-20 degrees C), but not at 37 degrees C. The activity was lost after treatment of the supernatant with chloroform, UV-light and after boiling of the supernatant. One did not succeed in obtaining the antibacterial factor in a sterile solution.     

Associations between housing and management factors and reproductive performance in 327 Norwegian sheep flocks

Background

Housing sheep in insulated, warm buildings, which is common in Norway, involves high buildings costs, but has not been reported to improve health and performance. Few studies have dealt with the association between housing and management and reproductive performance.Data on housing and management during the indoor period from a questionnaire were merged with herd level data from the Norwegian Sheep Recording System, and the material included 327 sheep flocks. Associations between housing and management factors and reproductive performance were analyzed by means of multivariate regression models and grouped logistic regression.

Results

There was no difference in reproductive performance between warm and cold housing. Number of live born lambs born per pregnant ewe was highest in flocks with 10 or less ewes per pen, and lowest in flocks with more than 40 ewes per pen. Rate of barren ewes was lowest, and number of lambs per ewe at the end of the indoor period was highest in flocks where the sheep were regrouped according to number of foetuses (lambs) identified by scanning. A higher total number of lambs born per pregnant ewe and lambs per ewe at the end of the indoor period were found where other available housing facilities or outdoor areas were used in addition to the main housing unit in the lambing season. The rate of stillbirths was lowest on farms where sheep was the only animal production. None of the factors evaluated had any significant association with mortality of live born lambs in the indoor period. Lowest number of lambs per ewe at the end of the indoor period was found on farms where other family members/hired labour were caretakers as compared with the farmer or spouse/cohabitant, and highest numbers were found where caretakers were older than 60 years of age. Reproductive performance was lower in the Spæl Breed than the Norwegian White Sheep.

Conclusion

Housing systems per se are of minor importance, whereas management practices in the indoor period should be expected to improve reproductive performance.     

Impact of acid precipitation on freshwater ecosystems in Norway

Extensive studies of precipitation chemistry during the last 20 yr have clearly shown that highly polluted precipitation falls over large areas of Scandinavia, and that this pollution is increasing in severity and geographical extent. Precipitation in southern Norway, Sweden, and Finland contains large amounts of H⁺, SO⁼ ₄, and NO^? ₃ ions, along with heavy metals such as Cu, Zn, Cd, and Pb, that originate as air pollutants in the highly industrialized areas of Great Britain and central Europe and are transported over long distances to Scandinavia, where they are deposited in precipitation and dry-fallout. In Norway the acidification of fresh waters and accompanying decline and disappearance of fish populations were first reported in the 1920s, and since then in Sørlandet (southernmost Norway) the salmon have been eliminated from several rivers and hundreds of lakes have lost their fisheries. Justifiably, acid precipitation has become Norway's number-one environmental problem, and in 1972 the government launched a major research project entitled ‘Acid precipitation — effects on forest and fish’, (the SNSF-project). Studies of freshwater ecosystems conducted by the SNSF-project include intensive research at 10 gauged watersheds and lake basins in critical acid-areas of southern Norway, extensive surveys of the geographical extent and severity of the problem over all of Norway, and field and laboratory experiments on the effect of acid waters on the growth and physiology of a variety of organisms. Large areas of western, southern, and eastern Norway have been adversely affected by acid precipitation. The pH of many lakes is below 5.0, and sulfate, rather than bicarbonate, is the major anion. Lakes in these areas are particularly vulnerable to acid precipitation because their watersheds are underlain by highly resistant bedrock with low Ca and Mg contents. Apart from the well-documented decline in fish populations, relatively little is known about the effects of acid precipitation on the biology of these aquatic ecosystems. Biological surveys indicate that low pH-values inhibit the decomposition of allochthonous organic matter, decrease the species number of phyto-and zooplankton and benthic invertebrates, and promote the growth of benthic mosses. Acid precipitation is affecting larger and larger areas of Norway. The source of the pollutants is industrial Europe, and the prognosis is a continued increase in fossil-fuel consumption. The short-term effects of the increasing acidity of freshwater ecosystems involve interference at every trophic level. The long-term impact may be quite drastic indeed.