Mortality associated with gastric ulceration in swine

Abstract

On a large swine operation, necropsy revealed that 39 of 146 (27%) pigs during one week in April and 37 of 137 (27%) pigs during one week in June died from hemorrhage due to gastric ulceration. Contributory factors may have been feed withdrawal one day per week and feeding finely ground pellets.

The purpose of this study on a large pig farming operation was to investigate the mortality rate associated with gastric ulceration in the finishing stage and determine the prevalence of subclinical gastric lesions in the pigs at the time of slaughter.

This large agricultural corporation has a history of deaths due to gastric ulcers. The sow inventory is approximately 100 000, with farrowing, breeding-gestation, and nurseries located together. Pigs are moved at 20 to 25 kg body weight to grower-finisher barns, which are either company-owned or contract facilities. The corporation owns 520 grower-finisher curtain-sided finishing barns, each of which has the capacity to hold 1150 pigs.

The grower-finisher barns are clustered together in groups of 8, with one person managing each cluster of buildings. An 8-building cluster of barns is emptied, cleaned, and then restocked at one time. Pigs are fed a finely ground ration ad libitum. However, as the heaviest pigs reach market weight, the feed is withdrawn for an 18- to 24-hour period, during which selection, weighing, and marketing of the heaviest pigs takes place. This is done to ensure that pigs shipped to slaughter have an empty stomach.

Mortality is recorded on a weekly basis and the cause of death as determined by the herdsman is also entered into the computerized record system. The causes of death loss are categorized generally as digestive disorders (including gastric ulceration and gastrointestinal torsion), respiratory disease, and other (including unknown).

The operation was visited twice, during the last week of April and the second week of June. Production records were examined. Confirmation of the causes of death as noted by the herdsmen was done by visiting 49 of the 65 sites. Eight 8-building grower-finisher complexes were visited on each date. During the visits, gross postmortem examinations were performed on all pigs that had died recently at each site.

In addition, a slaughterhouse check was performed at the visit in June to assess the prevalence of subclinical lesions. Stomachs were selected on a consecutive basis from the abattoir and incised along the greater curvature. The pars oesophagea was examined for evidence of lesions, including parakeratosis, erosions, and ulceration. A score of 0, 1, 2, or 3 was attributed, based on the gross morphological appearance of the pars oesophagea and a scoring system similar to that of Mackin et al (5).

The grower-finisher pig inventory for the company-owned units was 503 321 pigs on the last week of April and 617 589 pigs on the second week of June. The total death loss for the week in April was 1219 (0.24% of all pigs at risk), and the week in June, 1372 (0.22% of all pigs at risk). Mortality attributed to digestive disorders, as classified by the herdsmen, was 573 pigs during the last week of April and 543 pigs for the first week of June (47% and 49% of all deaths, respectively).

Total death loss from January 1st (week 1) until the 2nd week of June (week 23) was 36 812 pigs, or an average of 1600 pigs/wk. The average weekly inventory of grower-finisher pigs during this 23-week period was 544 531 pigs. If we assume that the average length of time that a pig remained in the grower-finisher area was 16 wk, mortality in the grower-finisher barn was 4.6%; this figure included animals that were culled and those that were destroyed.

Postmortem examination of 146 pigs in the week of April revealed that 39 pigs (27%) died from hemorrhage due to gastric ulceration. Similarly, during the week of June, necropsy of 137 pigs showed that 37 animals (27%) had died as a result of hemorrhage from a gastric ulcer. The second most common cause of death, as determined by gross inspection, was pneumonia, accounting for 11% of deaths in the April study and 28% of deaths in the June investigation (see Table 1).

Table 1.

A total of 1021 stomachs were examined at slaughter. More than half had erosive lesions of the pars oesophagea, and only 6.2% were classified as normal (Table 1).

Overall, the approximately 4.6% mortality in the grower finisher area during the first 23 wk of the year is higher than industry targets. Death due to gastric ulceration appeared to be a major contributor to this high mortality. Approximately 25% of mortality was attributable at necropsy to severe blood loss caused by gastric ulceration. The annual economic loss attributable to gastric ulceration for this company was estimated to be over 2.3 million dollars (US).

Ulceration of the pars oesophagea is a common, widespread condition in finishing pigs world wide. It can be a significant cause of death in certain herds. Mortality due to bleeding from deep, erosive lesions may reach 1% or higher, with culling losses of 3% to 5% in such herds. The approximate annual mortality attributable to gastroesophageal ulcers has been estimated to be between 0.5% and 0.75% (1).

Ulceration occurs rapidly and can heal prior to slaughter, so that it is inappropriate to attempt to correlate findings at slaughter with growth performance during the previous 3 mo (2,3). However, examination of stomachs at slaughter may provide the practitioner with an indication of the prevalence of subclinical lesions in the herd.

Gastric ulceration is generally accepted to have multiple contributing causes. Often factors that are strongly associated with ulceration, such as fine particle size and pelleting of feed, are also known to improve growth rate and feed efficiency (4). Therefore, efforts to control ulceration must be weighed carefully against possible loss in performance. Before changes are implemented, the cost of gastric ulceration on a particular farm must be assessed in order to estimate the cost-benefit of a control program.

It has been estimated that in North Carolina more than 2% of grower-finisher pigs placed during the summer months died from gastric bleeding (1). The level of mortality from gastric ulceration appears to be lower on this farm than the North Carolina estimate. However, it is possible that the annual death loss attributable to ulceration might have been higher than estimated by this study if mortality had been investigated in the hottest summer months, July and August.

The level of subclinical gastric lesions is correspondingly high with over 50% of the pigs having evidence at slaughter of erosions or ulcers. This level is comparable with the highest farm prevalence of gastric lesions reported by Guise et al (6).

The slaughter data must be interpreted with caution, in that several researchers have demonstrated that feed withdrawal prior to slaughter results in a significantly higher prevalence of erosive lesions than if the animals had been slaughtered with feed in their stomachs (3,7). The fact that feed is withdrawn from all pens of pigs in the entire barn for 1 d each week, at which time the largest pigs are shipped to market, may contribute to ulcer development in the pigs that remain in the grower-finisher area.

Feeding finely ground pellets also probably contributed to the high prevalence of gastric lesions and the high mortality rate attributable to ulceration. Although both pelleting and small particle size of feed are proven factors contributing to gastric ulceration (4), a switch to coarsely-ground mash feed would be uneconomical, even if all gastric ulcer death loss was eliminated. Pelleting improves average daily gain by 5% and feed conversion by 7% (4). Reducing average feed particle size from 1000 mm to 400 mm increases feed conversion by 8%. The added feed cost associated with a change from finely ground pellets to a coarse mash far outweighs the cost of the mortality associated with gastric ulceration in this herd. However, a temporary change to a mash feed for a short period of time might help to heal ulcers and reduce losses without a significant loss in feed efficiency (2). Alternatively, research has shown that the use of a relatively small amount of coarse fiber, such as sunflower hulls, added to a finely-ground diet, can decrease the number and severity of esophagogastric lesions to the same extent, as will coarse milling of the whole diet, and minimize the detrimental effect on feed conversion (8). However, coarse particles in a pelleted ration have a negative effect on pellet quality, making the pellets fall to pieces.

The solution to the problem of gastric ulcers on this particular farming operation requires some compromise, and a great deal of diligence with respect to feed manufacture. In order to feed a finely ground product, the feed mill has to produce a pellet at the appropriate temperature for it to contain grain particles of a uniform and appropriate size. Feed production practices that incorporate flour or “fines” in pellets increase the risk of ulcers. In addition, high temperatures during pelleting might result in gelatinization of starches rendering the diet more ulcerogenic.

To decrease the proportion of pale, soft, exudative pork, it has been recommended that feed be withdrawn from hogs 12 to 24 h prior to slaughter (9). The operation in this study is unwilling to stop this practice. Therefore, it would appear to be prudent practice that during these periods of interruption in feed intake, those pigs remaining in the barns should be treated to prevent ulcers. Numerous pharmaceutical agents have been used experimentally to neutralize acid, reduce gastric secretion, and promote ulcer healing. Given the presence in the barn of pigs about to be shipped to market, mass medication would need to be limited to products that do not require a withdrawal period. Therefore, antacid preparations are likely the most suitable products for investigation. The use of sodium bicarbonate in the feed has been tried with variable results (10), but only limited information regarding water medication during periods of feed withdrawal is available.