The incidence of necrotic enteritis in turkeys is associated with farm, season and faecal Eimeria oocyst counts

Abstract

Background: Specific studies on the epidemiology of necrotic enteritis in turkeys are absent in the literature. Necrotic enteritis is common in turkeys and a leading cause of use of therapeutic antibiotics. This study describes the incidence of necrotic enteritis in turkey farms, and the association between incidence and bird age, season, faecal oocyst counts, grow-out size and feed mill.

Results: Necrotic enteritis was diagnosed post mortem in 20.2 % of 545 grow-outs of commercial female and male B.U.T. 10 turkeys started during the years 2010-2016. 80 % of all cases occurred at four to seven weeks of age. Median (minimum-maximum) age at disease detection was 37 (18-115) days. Turkey age at detection was influenced by season, and varied from 33 days among grow-outs hatched in February to 42 days among those hatched in July-August. The incidence also varied with season, showing peak occurrence among grow-outs hatched during February-March and the lowest incidence in turkeys hatched in July-August. 59 % of all cases were detected in 25 % of the farms. The incidence per farm varied from below 4 to 59 %. A multilevel mixed-effects logistic regression model indicated clear impacts of farm and season on incidence, and border-line impacts of grow-out size and feed mill. Grow-outs diagnosed with necrotic enteritis had higher counts of faecal Eimeria oocysts than grow-outs without a diagnosis. This difference was particularly clear during the high-risk period at five to seven weeks of age. Necrotic enteritis was the cause of treatment with therapeutic antibiotics in 88.2 % of all cases of treatment.

Conclusions: Our data indicate that necrotic enteritis incidence in turkeys can be substantially influenced by risk factors at farm level. The incidence showed two seasonal peaks; a moderate peak in turkeys hatched in October/November and a marked peak in turkeys hatched during February/March. Mitigation measures at the farm may therefore be of particular importance during these months in farms located in the Northern temperate zone. Measures which effectively reduce counts of faecal Eimeria oocyst are likely to be among the more promising actions to take both at the farm and at population level.

Keywords: Age; Epidemiology; Feed mill; Grow-out size; OPG; Production performance.

Fig. 1

Distribution of age in days at detection of necrotic enteritis in 107 grow-outs of commercial slaughter turkeys. a All 107 grow-outs with age data. b Distributions of age at NE diagnosis per month (1 = January, 2 = February and so forth until 12 = December)

Fig. 2

Percentage of grow-outs diagnosed with NE in 13 size categories based on numbers of day-old turkeys per grow-out. Numbers of day-old birds started (grow-out size) are indicated in thousands below each bar. The number of grow-outs per size category varied from 15 (14,000–14,999 day-olds) to 90 (6000–6999 day-olds)

Fig. 3

Box plots depicting the age dynamics of faecal oocyst counts (median counts: solid black line) per week of age. Y-axis indicates log₁₀ oocysts per gram faeces (OPG). X-axis indicates age in weeks (3 to 8) of the examined turkey groups. a OPG of groups from grow-out diagnosed with necrotic enteritis (NE). NE occurrence is indicated as a dotted line (NE, arrow pointing at the line) in relative levels. The peak value at five weeks of age corresponds to detection of NE in 17.9 % of the grow-outs at that age. b OPG from grow-outs without NE diagnosis. The graphs are based on data from 39 grow-outs raised on 16 different farms