Differential detection of <i>Ascaridia galli</i> and <i>Heterakis gallinarum</i> eggs in intestinal and caecal excreta of floor-housed laying hens: a longitudinal study

<i>Ascaridia galli</i> and <i>Heterakis gallinarum</i>, the most prevalent nematodes of chickens, inhabit the small intestine and caeca, respectively, and often co-occur. Current excreta egg count (EEC) methods do not differentiate between their eggs, and although chickens produce two distinct excreta types - intestinal excreta (IE) and caecal excreta (CE) - the distribution of eggs of these species across them remains poorly understood. Forty Hy-Line Brown laying hens (40 weeks, mean body weight (BW) 2·07 ± 0·02 kg), cleared of prior nematode infection and artificially infected with <i>A. galli</i> (n = 20) or <i>H. gallinarum</i> (n = 20) were housed in separate floor pens and monitored for 26 weeks. Assessments included clinical signs, EECs from IE, CE and mixed excreta (ME), and worm recovery from subsets of birds at 8, 14, 20 and 26 weeks. Neither infection resulted in clinical signs, but <i>A. galli</i> slightly reduced BW gain (0·5 g/week/hen) than <i>H. gallinarum</i> (2·8 g/week/hen). Egg detection aligned with worm predilection sites: <i>A. galli</i> eggs were predominantly found in IE, while <i>H. gallinarum</i> eggs were largely confined to CE. In ME samples, egg counts were reduced by 45% relative to IE for <i>A. galli</i> and 60% relative to CE for <i>H. gallinarum</i>. EECs showed a negative but non-significant association with excreta moisture content. Natural re-infection produced a stable adult worm population in both infections. These findings demonstrate that analysing IE and CE separately provides a practical, non-lethal approach for differentiating these infections, while ME appears to have limited diagnostic utility. Further studies should evaluate these patterns across broader conditions and individual variation.