LG stands for "linkage group". It seems the Chicken Genome Sequence group (Hillier et al., 2004) allocated several linkage groups (alleles or genes which tend to be inherited together) to the microchromosomes (tiny chromosomes typical of birds and reptiles), in this case called "linkage group E64" and "linkage group E22....". There are a load more microchromosomes which are the ones numbered 28-31 and 33-38 which haven't yet had their sequences resolved (Burt, 2007).
**References:**
* Burt, D.W. (2007) Emergence of the Chicken as a Model Organism: Implications for Agriculture and Biology. Poultry Science. 86 (7), 1460 –1471. Available from: [Accessed: 8 February 2012].
* Hillier, L.D.W., Miller, W., Birney, E., Warren, W., Hardison, R.C., Ponting, C.P., Bork, P., Burt, D.W., Groenen, M.A.M. & Delany, M.E. (2004) Sequence and comparative analysis of the chicken genome provide unique perspectives on vertebrate evolution. Nature. 432 (7018), 695–716.