Feasibility of a "leader-follower" grazing system instead of specialised paddocks with regard to integrated gastrointestinal control in small ruminant farming.

In the humid tropics, small ruminant farmers have to deal with gastrointestinal parasitic nematodes (GIN), among which anthelmintic resistant (AR) populations are rapidly spreading. Although targeted selective treatments (TSTs) are being increasingly used in breeding stock, suppressive drenchings remain the rule in younger animals, for safety and ease of implementation. Until now, the weaned animals are grazed on dedicated plots, making the selection and spread of AR parasites inevitable. Given that GINs disseminate through pastures, we compared the usual grazing system (control) to a "leader-follower" grazing system (LF) for managing the entire GIN population at the farm scale. There were no significant differences between treatments for the dam reproductive parameters and level of GIN infection nor for the pre-weaning death rate of the kids. The 70-day weight of the litter was significantly lower for LF than for control goats (9.71 vs. 11.64 kg, P < 0.05). Although they were more infested with GIN (1860 vs. 966 epg, P < 0.05), the LF weaned animals grew faster (53.4 vs. 40.8 g day(-1), P < 0.05) and their death rate was lower (4.0 vs. 7.7 %, P < 0.05). The overall animal output was estimated to 1010 [911; 1086] vs. 966 [885; 1046] kg LW ha(-1) year(-1), for LF and control grazing systems, respectively. Additionally, the LF grazing system would make the stocking rate easier to manage. Therefore, it is to be recommended as a complement of TSTs in sustainable small ruminant farming.

High-density SNP-based genetic map development and linkage disequilibrium assessment in Brassica napus L.

BACKGROUND: High density genetic maps built with SNP markers that are polymorphic in various genetic backgrounds are very useful for studying the genetics of agronomical traits as well as genome organization and evolution. Simultaneous dense SNP genotyping of segregating populations and variety collections was applied to oilseed rape (Brassica napus L.) to obtain a high density genetic map for this species and to study the linkage disequilibrium pattern. RESULTS: We developed an integrated genetic map for oilseed rape by high throughput SNP genotyping of four segregating doubled haploid populations. A very high level of collinearity was observed between the four individual maps and a large number of markers (>59%) was common to more than two maps. The precise integrated map comprises 5764 SNP and 1603 PCR markers. With a total genetic length of 2250 cM, the integrated map contains a density of 3.27 markers (2.56 SNP) per cM. Genotyping of these mapped SNP markers in oilseed rape collections allowed polymorphism level and linkage disequilibrium (LD) to be studied across the different collections (winter vs spring, different seed quality types) and along the linkage groups. Overall, polymorphism level was higher and LD decayed faster in spring than in "00" winter oilseed rape types but this was shown to vary greatly along the linkage groups. CONCLUSIONS: Our study provides a valuable resource for further genetic studies using linkage or association mapping, for marker assisted breeding and for Brassica napus sequence assembly and genome organization analyses.

Insertion site-based polymorphism markers open new perspectives for genome saturation and marker-assisted selection in wheat.

In wheat, the deployment of marker-assisted selection has long been hampered by the lack of markers compatible with high-throughput cost-effective genotyping techniques. Recently, insertion site-based polymorphism (ISBP) markers have appeared as very powerful new tools for genomics and genetic studies in hexaploid wheat. To demonstrate their possible use in wheat breeding programmes, we assessed their potential to meet the five main requirements for utilization in MAS: flexible and high-throughput detection methods, low quantity and quality of DNA required, low cost per assay, tight link to target loci and high level of polymorphism in breeding material. Toward this aim, we developed a programme, IsbpFinder, for the automated design of ISBP markers and adapted three detection methods (melting curve analysis, SNaPshot Multiplex System and Illumina BeadArray technology) for high throughput and flexible detection of ISBP or ISBP-derived SNP markers. We demonstrate that the high level of polymorphism of the ISBPs combined with cost-effective genotyping methods can be used to efficiently saturate genetic maps, discriminate between elite cultivars, and design tightly linked diagnostic markers for virtually all target loci in the wheat genome. All together, our results suggest that ISBP markers have the potential to lead to a breakthrough in wheat marker-assisted selection.