Canon LXXXVIII.

No one may drive any beast into a church except perchance a traveller, urged thereto by the greatest necessity, in default of a shed or resting-place, may have turned aside into said church.  For unless the beast had been taken inside, it would have perished, and he, by the loss of his beast of burden, and thus without means of continuing his journey, would be in peril of death.  And we are taught that the Sabbath was made for man:  wherefore also the safety and comfort of man are by all means to be placed first.  But should anyone be detected without any necessity such as we have just mentioned, leading his beast into a church, if he be a cleric let him be deposed, and if a layman let him be cut off.

Ancient Epitome of Canon LXXXVIII.

Cattle shall not be led into the holy halls, unless the greatest necessity compels it.