Don Alonzo Taylor

American author. He appears to have only written two books which are historical horse stories set in the days of the pioneers. Apparently the books are based on stories which Taylor used to tell his children about his own childhood, and were collated by his daughter in later years. Both stories followed the same characters, including a feisty grey trotter called Sam. Both have very nice illustrations and the first in the series is still in print.

Old Sam Series:
Short historical series about the pioneer lifestyle seen through the eyes of two young boys, based on the author's own childhood. Much non-horsy content, although the horse Sam is a major character.

1) OLD SAM THOROUGHBRED TROTTER
aka OLD SAM DAKOTA TROTTER
(FOLLETT [USA] 1955)
ILLUSTRATED BY LORENCE BJORKLAND
Reprinted more then once in hardback by original publisher.
Reprinted a couple of times in paperback by Bethlehem Books under the title OLD SAM DAKOTA TROTTER.
The latest edition (2008) is still in print.
SUMMARY: Cousins John and Lee and their families set off west to make a new home on the prairies. Amongst their horses is Sam, a crippled grey thoroughbred trotter they rescued from being shot when he was injured. Despite Having a limp, Sam is a colourful and lively character who always seems to be at the centre of various adventures. This culminates in Sam recapturing his trotting heydey when the children secretly enter him in the Fourth of July trotting race!
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2) OLD SAM AND THE HORSE THIEVES
(FOLLETT [USA] 1967)
ILLUSTRATED BY LORENCE BJORKLAND
SUMMARY: Horse thieves strike and take Sam. The boys set out to find him and help the sheriff catch the thieves.

Collector's Info:
The first book was recently re-issued under the alternative title and is still in print: it can be bought new from both the USA and the UK (via Amazon). Second-hand copies of both the paperback and to a slightly lesser extent the hardback are quite easy to find in the USA.