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The painting shows a fairly conventional depiction of this very common scene, with some unusual details.  The number of shepherds is rather large at nine, and the pose of the shepherd pointing at the baby Jesus while looking over his shoulder outside the picture space suggests that more are arriving. Or possibly he has seen the approaching Magi, the next arrivals in the traditional narrative.  Saint Joseph, often a rather superfluous figure in paintings of the Nativity, is shown making himself useful by carrying hay, presumably to feed the ox and ass, in the background, so filling a gap in the composition, and perhaps distracting them from joining in with the bagpipe music. The relegation of the ox and ass to a dimly-lit background is typical of 17th century compositions.A prominently placed shepherd on the left side of the group is shown playing his bagpipes. Though the shepherds sometimes carry musical instruments, often including pipes (see gallery below), they are less often shown playing them at this solemn moment, as opposed to the earlier scene of the Annunciation to the Shepherds where an angel appears to them with their flocks.  If music is shown being performed beside the crib it is more often by angels.  A charming but atypical miniature in the 15th-century Flemish La Flora Hours in Naples shows a shepherd playing his bagpipes as his two companions dance for the infant Jesus and a delighted Virgin Mary sits to one side.   Outside his painting, Domeninchino had a serious interest in musical instruments and their design, which his paintings sometimes reflect. He designed and himself constructed instruments intended to be suitable for playing ancient music.
The inclusion of the shepherd's dog, especially right by the crib, is unusual, though the shepherds very often have one in scenes of their annunciation, and sometimes bring a lamb to the crib as a gift; here the dove held by the boy in the foreground is intended to represent a gift.  In the 17th century the shepherds often crowd round the crib, as here, and Mary actively displays her child to them.  However her gesture of lifting a cloth, revealing a full view of a naked Jesus, including his penis, is unusual in art by this date.  In the late medieval period pictures of the infant Jesus often made a point of displaying his genitals for theological reasons, but in the Counter-Reformation this was discouraged by clerical interpreters of the vague decrees on art of the Council of Trent, such as Saint Charles Borromeo.
discouraged by clerical interpreters of the vague decrees on art Naples bagpipe Council of Trent Magi Charles Borromeo ancient music very common scene Annunciation to the Shepherds Counter-Reformation paintings of the Nativity left Saint Joseph