DES MOINES, Iowa — A federal judge has struck down the third attempt by the Iowa Legislature to stop animal welfare groups from secretly filming livestock abuse, finding once again that the law passed last year violates free speech rights in the U.S. Constitution.Farmers argue intruders could track in disease and want to unfairly portray their livestock practices, while animal welfare groups say producers don't want the public to see how farm animals are treated.Significant portions have been struck down by courts while a few provisions that enhance the penalties for trespassing in farms and meat production facilities have survived.The advocacy groups said the decision is important to farm and food processing plant workers placed in unsafe working conditions who are now protected under free-speech rights to record evidence, for advocates fighting to expose poor living conditions and treatment of dogs at breeding farms known as puppy mills and for animals raised for food."The ability to investigate and document how our food is made is critical in ensuring a just and transparent food system that holds companies and government institutions accountable," said David Muraskin, the food project litigation director for Public Justice, a Washington-based nonprofit law firm that represented grassroots advocacy group Iowa Citizens for Community Improvement in the lawsuit."