A search for copyright renewal was done at copyright.gov. There were no renewals for Saddle and Bridle; only post-1977 original registrations for later copies of the magazine. There's no evidence that copyright continues to be claimed on this material.
Note that it may still be copyrighted in jurisdictions that do not apply the rule of the shorter term for US works (depending on the date of the author's death), such as Canada (70 years p.m.a.), Mainland China (50 years p.m.a., not Hong Kong or Macao), Germany (70 years p.m.a.), Mexico (100 years p.m.a.), Switzerland (70 years p.m.a.), and other countries with individual treaties.