Performance by spring and fall-calving cows grazing with full, limited, or no access to toxic Neotyphodium coenophialum-infected tall fescue.

Replacing toxic, wild-type Neotyphodium coenophialum-infected tall fescue (E+) with nontoxic, N. coenophialum-infected tall fescue (NE+) has improved cow performance, but producer acceptance of NE+ has been slow. The objective was to compare performance by spring- and fall-calving cows grazing either E+ or NE+ at different percentages of the total pasture area. Gelbvieh×Angus crossbred cows (n=178) were stratified by BW and age within calving season and allocated randomly to 1 of 14 groups representing 5 treatments for a 3-yr study: i) Fall-calving on 100% E+ (F100); ii) Spring-calving on 100% E+ (S100); iii) Fall-calving on 75% E+ and 25% NE+ (F75); iv) Spring-calving on 75% E+ and 25% NE+ (S75); and v) Spring-calving on 100% NE+ (SNE100). Groups allocated to F75 and S75 grazed E+ until approximately 28 d before breeding and weaning, then were then moved to their respective NE+ pasture area for 4 to 6 wk; those allocated to F100, S100, and SNE100 grazed their pastures throughout the entire year. Samples of tall fescue were gathered from specific cells within each pasture at the time cows were moved into that particular cell (∼1 sample/mo). Blood samples were collected from the cows at the start and end of the breeding season. Stocking rate for each treatment was 1 cow/ha. Forage IVDMD, CP, and total ergot alkaloid concentrations were affected (P<0.05) by the treatment×sampling date interaction. Hay offered, cow BW, and BCS at breeding, end of breeding, and at weaning were greater (P<0.05) from fall-calving vs. spring-calving. Cow BW at weaning was greater (P<0.05) from F75 and S75 vs. F100 and S100. The calving season×NE+ % interaction affected (P<0.05) calving rates. Preweaning calf BW gain, actual and adjusted weaning BW, ADG, sale price, and calf value at weaning were greater (P<0.05) from fall-calving vs. spring-calving and from SNE100 vs. S75 except for sale price which was greater (P<0.05) from S75 vs. SNE100. Cow concentrations of serum prolactin at breeding and serum NEFA at the end of breeding were affected (P<0.05) by the calving season×NE+ % interaction. Serum Zn and Cu concentrations from cows were affected (P<0.05) by calving season. A fall-calving season may be more desirable for cows grazing E+, resulting in greater calving rates, cow performance, and calf BW at weaning, whereas limited access to NE+ may increase calving rates, serum prolactin, and NEFA concentrations during certain times in the production cycle, particularly in spring-calving cows.

Links between phytoplankton and bacterial community dynamics in a coastal marine environment.

Bacteria and phytoplankton dynamics are thought to be closely linked in coastal marine environments, with correlations frequently observed between bacterial and phytoplankton biomass. In contrast, little is known about how these communities interact with each other at the species composition level. The purpose of the current study was to analyze bacterial community dynamics in a productive, coastal ecosystem and to determine whether they were related to phytoplankton community dynamics. Near-surface seawater samples were collected in February, May, July, and September 2000 from several stations in the Bay of Fundy. Savin et al. (M.C. Savin et al., Microb Ecol 48: 51-65) analyzed the phytoplankton community in simultaneously collected samples. The attached and free-living bacterial communities were collected by successive filtration onto 5 microm and 0.22 microm pore-size filters, respectively. DNA was extracted from filters and bacterial 16S rRNA gene fragments were amplified and analyzed by denaturing gradient gel electrophoresis (DGGE). DGGE revealed that diversity and temporal variability were lower in the free-living than the attached bacterial community. Both attached and free-living communities were dominated by members of the Roseobacter and Cytophaga groups. Correspondence analysis (CA) ordination diagrams showed similar patterns for the phytoplankton and attached bacterial communities, indicating that shifts in the species composition of these communities were linked. Similarly, canonical CA revealed that the diversity, abundance, and percentage of diatoms in the phytoplankton community accounted for a significant amount of the variability in the attached bacterial community composition. In contrast, ordination analyses did not reveal an association between free-living bacteria and phytoplankton. These results suggest that there are specific interactions between phytoplankton and the bacteria attached to them, and that these interactions influence the composition of both communities.

Plankton diversity in the Bay of Fundy as measured by morphological and molecular methods.

Phytoplankton have traditionally been identified based on morphological characteristics. However, identifications based on morphology are time-consuming, require expertise in taxonomy, and often fail to distinguish differences among the multitudes of minute, nondescript planktonic organisms. Molecular techniques, which have revealed new insights into bacterial and picoplankton communities, may also enhance our knowledge of the diversity among communities of larger plankton. We compared plankton identifications and community assessments based on the two types of techniques (morphological vs molecular) for surface seawater samples collected on 2 May, 31 July and 25 September 2000 from several sampling stations in the Bay of Fundy. Phytoplankton captured in surface bucket samples were quantified and identified based on morphology. DNA was extracted from plankton communities (5-100 microm in diameter) collected by filtration, and 18S rRNA gene fragments were amplified with primers specific for eukaryotes. Denaturing gradient gel electrophoresis (DGGE) was used to develop DNA profiles of eukaryotic phylogenetic diversity and to select cloned 18S rDNA fragments for sequencing. Both morphological and molecular methods showed great community diversity. However, the communities identified with the two different types of techniques were starkly different. Morphological abundances and taxon richness were lowest in the May samples, whereas the number of DGGE bands was highest in May and July. Morphological identifications showed a succession of dominant organisms through time. Whereas neither diatoms nor dinoflagellates were dominant in May, diatoms and a few dinoflagellates were dominant in July and September. In contrast, few 18S rDNA sequences were related to rDNA sequences of known identity, and furthermore, few diatoms were identified in the molecular analyses. Molecular phylogenetic analysis indicated the presence of many novel organisms, several of which were most closely related to other unidentified sequences from diverse marine environments representing new lineages. Our results support the ideas that we are just beginning to uncover the diversity of eukaryotic marine organisms and that there may be many more ubiquitous, microeukaryotic plankton than previously realized. Our results suggest that both types of methods capture only a portion of the community. Morphological methods may be more adept at capturing the phototrophic organisms within the community. However, just as for bacteria and picoplankton, molecular techniques can enhance our understanding of plankton diversity, particularly by detecting previously unidentified organisms.