High mortality in laying hen pullets caused by crop and gizzard impactions associated with ingestion of bale net wrap

Abstract

High mortality was observed in young replacement layers. Balls of bale net wrap strings were found in the crop and/or gizzard of birds causing impaction and traumatic injury. Some birds experienced loss of portions or the entire tongue secondary to ischemic necrosis. Mortality stopped with the removal of strings from the environment.

Round straw bales are used for chopped bedding for poultry and a popular practice has been to wrap these bales with knitted polyethylene netting. Bales wrapped with net wrap instead of twine are baled much more quickly and are reported to have better integrity during handling and transport, which is an advantage in straw chopping systems used to put bedding into poultry barns (1). The net wrap must be removed from the bales before chopping for bedding otherwise short pieces of net wrap may become incorporated into the bedding. This report describes the outcome of this occurrence in a flock of replacement laying chickens.

Case description

A small commercial flock of day-old laying hen pullets was placed into 2 barns in floor pens bedded with straw; 1800 birds were placed in the east barn and 2600 birds were placed in the west barn. Prior to placement, the barns were bedded with straw blown in by a powered chopper and blower unit. The straw bales had been wrapped in net wrap (Figure 1) and the net wrap had been removed from all the bales except one; chopped straw from this bale was blown into both barns.

Figure 1.

Straw bales with bale net wrap.

The flock had a high rate of mortality due to culling, with a total mortality of 5% on day 30 after placement [normal mortality is 1% to 2% from 0 to 2 wk of age and ≤ 0.25/1000 per day during growth (2)]. The producer noticed mobility issues, crouching of the birds, and labored breathing. At 30 d of age, a submission of 7 birds was made to the Poultry Health Centre of Excellence (PHCE) in Airdrie, Alberta. Of the 7 birds, only 3 arrived at the lab alive with the other 4 dying in transit. The live birds were open mouth breathing, had increased respiratory effort, and were depressed with ruffled feathers. A small volume of clear fluid was dripping from the beaks of 2 of the live birds. All but 1 bird was below body weight target for their age [target weight for 28 d of age is 200 to 250 g (3)], with birds ranging in weight from 96 g to 235 g; all were in fair to poor body condition.

Complete postmortem examinations were performed and tissue samples including tongue, proventriculus, trachea, lung, air sac, spleen, liver, and bursa were fixed in 10% neutral-buffered formalin, trimmed into cassettes, and submitted to the Animal Health Laboratory, University of Guelph for histologic evaluation. A pooled tracheal swab was taken and submitted to Agri-Food Laboratories, Alberta Agriculture and Rural Development to be tested by polymerase chain reaction (PCR) for avian influenza (AI) matrix and avian paramyxovirus-1 (APMV-1).

At postmortem examination, 1- to 3-cm long segments of linearly twisted bale net wrap were found in the upper gastrointestinal tract of all the birds. Three birds had 2 cm diameter balls of net wrap filling the crop with string extending up the esophagus (Figure 2), and in 4 birds, the string looped around the base of the tongue. Two birds were missing their tongues entirely, likely from ischemic necrosis, and in 1 of these birds, the string was wrapped around the larynx. All 7 chickens had intussusception of the proventriculus into the gizzard and 2 birds also had 2- to 3-cm diameter balls of net wrap in the gizzard. The mucosa of the proventriculus was markedly reddened, and ulcerated and a large amount of yellow cloudy exudate was loosely adherent to the proventricular and gizzard mucosa. Three birds had cloudy air-sacs indicating airsacculitis.

Figure 2.

Crop impaction and bale net wrap string extending the length of the esophagus. Bird head to right, body to left. Black arrows indicate the location of the twisted string and ball of the net wrap.

The PCR testing was negative for AI but positive for non-velogenic APMV-1 as the flock had been vaccinated with a modified-live Newcastle disease virus (NDV)-infectious bronchitis virus (IBV) combination vaccine (Avipro ND-IB Polybanco; Lohman Animal Health International, Winslow, Maine, USA) via the drinking water 3 d before the laboratory submission. Histologic lesions included ulcerative proventriculitis with marked lamina proprial and submucosal hemorrhage and necrosis. On the ulcerated mucosal surface and within the superficial serocellular exudate were large numbers of a mixed population of bacteria (Figure 3). In addition, there were lesions of acute septicemia including mild splenic fibrinous necrosis, mild acute airsacculitis, acute mild multifocal fibrinous hepatic necrosis, hepatic heterophilia, and mild pulmonary congestion. There was mild to moderate bursal lymphoid depletion.

Figure 3.

A — Affected proventriculus. Marked proventricular mucosal effacement with superficial bacterial colonization (red arrow) and severe lamina proprial hemorrhage, edema and necrosis (red bar). Within the expanded and hemorrhagic submucosa (S) are the proventricular glands (P). B — Normal proventriculus with mucosal folds (black arrow) and narrow lamina propria (black bar). Submucosa is not visible and contains the proventricular glands (P). Hematoxylin and eosin stain. 40×.

Following the communication of results to the producer, all the straw in the barns was removed and replaced with fresh straw. Shortly after rebedding, the mortality rate decreased to normal levels.

Discussion

Trauma to the upper gastrointestinal tract from the net wrap caused significant necrosis and inflammation of mucosal surfaces and loss of organs (i.e., tongue), serving as portals of entry for bacteria which would explain the lesions of secondary septicemia seen in the liver, spleen, and air sacs. The increased respiratory effort and open-mouth breathing could have also contributed to the development of the airsacculitis. The overall poor body condition and inability or reluctance of birds to prehend feed would have contributed to the mild to moderate bursal lymphoid depletion (4).

Crop, proventriculus, and gizzard impactions have been previously described in poultry (5). Recently, foreign body ingestion and crop impaction were reported as a minor cause of mortality among backyard chickens in California (6). Crop impactions in chickens due to feathers (7), grass (8), and plastic and metal objects (9,10) have previously been reported. Litter made from grass and wood shavings has been reported to cause intestinal impactions in chickens (8,11). The authors are unaware of other published reports of ingestion of bale net wrap resulting in gastrointestinal impactions in poultry.

The provision of magnesium sulfate (Epsom salts) in the water and liquid molasses in the feed has been recommended as a way of alleviating intestinal grass impaction in larger poultry flocks (8). It is unlikely that this would be effective with the tough polyethylene material used to make bale net wrap. The basis of treatment in individual birds lies in removing the foreign body (9), but this is not possible with a commercial flock of hundreds to thousands of birds. In order to avoid foreign body injuries and crop or gizzard impactions in chickens it is important to remove those objects from a chicken barn or coop. Metal or plastic objects, strings, and even feathers can all be hazards and are readily eaten by chickens. Poor nutrition or inappropriate diets may also contribute to pica in chickens (10) but was not considered a factor in this case.

Veterinarians should be aware of the possibility of foreign bodies causing gastrointestinal obstructions, respiratory signs, and mortality in floor-raised chickens, in both backyard and commercial flock settings. Veterinarians should advise their clients to be vigilant and to ensure the chickens’ environment is free of potential hazards or change husbandry practices to discourage the eating of bedding materials. Monitoring of mortality by postmortem examinations can identify impactions earlier and allow institution of preventive measures and treatments so as to minimize further losses.