Decompositions of triangle-free 5-regular graphs into paths of length five

A Pk-decomposition of a graph  G is a set of edge-disjoint paths with k  edges that cover the edge set of  G. Kotzig (1957) proved that a 3-regular graph admits a P3-decomposition if and only if it contains a perfect matching. Kotzig also asked what are the necessary and sufficient conditions for a (2k+1)-regular graph to admit a decomposition into paths with 2k+1  edges. We partially answer this question for the case k=2 by proving that the existence of a perfect matching is sufficient for a triangle-free 5-regular graph to admit a P5-decomposition. This result contributes positively to the conjecture of Favaron et al. (2010) that states that every  (2k+1)-regular graph with a perfect matching admits a P2k+1-decomposition.