Scientific Papers

Housing and management factors and breed predisposition for haemorrhagic bowel syndrome in swine | Porcine Health Management

The aim of this study was to identify risk factor for the occurrence of HBS in Swiss finisher pigs with focus on environment and management factors as well as breed predisposition. Overall, 97 farms were investigated (48 case farms and 49 control farms), over a time period of 13 months, a representative sample population of Swiss finishing farms could be realised to find possible risk factors for the occurrence of HBS in grower-finisher pigs. Our results are unlikely to be affected by a selection bias because the farms were solely chosen based on their mortality rate caused through HBS. The time-consuming visits as well as the cooperation of the farmers to allow visits and invest their time for this project prevented a more sophisticated selection of farms and the inclusion of more farms. Furthermore, farms that had an HBS problem were not necessarily investigated when a HBS case occurred but rather having had a defined percentage of cases in the last 6 to 12 months. Environmental factors such as indoor and outdoor temperatures as well as air draft might have been different at the time of HBS cases.

After univariable analysis a total of eleven variables were significantly related to the outcome variable of being a HBS case farm and therefore put into a multivariable logistic regression model. The highest odds ratio (OR) was found for the variable pig breed, concerning the swine breeds that are found on each farm, followed by number of origins per pig group and frequency of cleaning of the distribution pipes and feed place width per animal (for finisher pigs).

A possible genetic component to HBS was suspected in different studies from the USA [4] and South Africa [14] attributing the higher frequency of HBS to the longer carcass of modern pigs. Since breeds used for meat production vary between countries in their genetic composition but also their frequency of use, no data about the correlation between Swiss pig breeds and the occurrence of HBS was available. Our study revealed a significant effect of PREMO® (Swiss Large White sire line) on the occurrence of HBS in comparison with Duroc. However, the OR of 147 should be treated cautiously because the breed specified by the farmer was not verified within the supply chain or with genetic markers and the 95% confidence interval is relatively large. Regardless, the lower boundary of the 95% confidence interval (OR = 8.19) still shows that using PREMO® is an important risk factor for HBS in Switzerland. A similar situation concerning OR and the 95% confidence interval was detected for farms having both PREMO® and Duroc in their stables. Due to lack of information on the breed of died pigs on mixed farm, no further conclusion can be drawn. However, it can be hypothesized that in mixed groups Duroc will limit the risk for HBS cases. A possible explanation for these findings could be the fact that the carcasses of PREMO® pigs are longer than those from other breeds such as Duroc and Piétrain. Furthermore, the PREMO® breed had been extensively selected for feed conversion ratio, average daily gain and lean meat percentage, although Duroc has even greater growth potential and Piétrain more lean meat than PREMO. These four characteristics (i.e. length of carcass, feed conversion ratio, average daily gain and lean meat percentage) combined could have an important effect on the digestive system as well as the abdominal structure and the available space in the abdominal cavity. These interactions could increase the risk for torsion of the intestines and death due to HBS. Another speculation is, that modern pigs in fattening systems have reached high level of performance and are therefore running at their possible limit. Minor changes in their normal environment and feeding practices can overstrain the performance of said pigs and therefore lead to problems such as HBS. The Swiss AI market already reacted to the higher HBS risk of PREMO. In the last two years the number of artificial inseminations with semen from Duroc boars in Switzerland significantly increased (almost doubled) [17].

The feeding space of pigs was detected as a risk factor for HBS in comparison to other studies neglecting to investigate this factor of animal housing [5, 18]. In the present study an additional of 1 dm of feed place width per finisher pig was linked to a decreased risk of HBS with an OR of 14.1. It might be that less space increases the stress level of pigs at feeding time, leading to the assumption that stress at feeding time as well as directly after has a significant impact on HBS occurrence. If feeding space is limited a competition over feed will be established, even if enough feed is present, stronger pigs having more access but still needing to defend their space whereas weak pigs will eat as fast as possible to get enough feed once they are at the feeding trough. This stressful behaviour can lead to more air being swallowed while feeding and therefore leading to more air in the gastrointestinal tract. Furthermore, the increased activity provoked by the stressed behaviour can cause pigs to try and go under other pigs, lifting them up and disrupting the normal feed intake as well as compressing and decompressing the abdomen in fast succession. Movement combined with gas in the stomach and intestines can increase the risk for torsion of intestines in the abdomen along the mesenteric root. Leading to the question if the minimal standard width per finisher pig should be altered to reduce stress at feeding. The minimal standard feeding space width per pig for Swiss fattening pigs (i.e. 30 cm/pig) is comparable to the ones from Sweden (i.e. 31 cm/pig). Studies from both countries from Sweden as well as from the USA have not been able to identify the feeding space width as a risk factor for HBS but was acknowledged in both studies to have a significant impact on the duration of feed intake and the activity at feeding time [5, 19]. Furthermore, the study from Sweden focuses on aggression and corresponding lesions and not causes for mortality in investigated herds.

The number of origins per batch of pigs has not yet been described in context of HBS. Rather the influence of multiple origins per batch in relation to infectious agents as well as the transmission of such was investigated [20]. In the present study the chance to be a HBS case farm is 52 times more likely if two or more origins of pigs were given per batch as compared to having one origin only. Therefore, an infectious component to the HBS complex cannot be excluded, and investigation into infectious agents relevant to the fattening age group transmitted through faecal material should be conducted. As non-infectious causes the genetic similarity and the comparable microbiome of pigs being born in the same farm from the same sire (breed) could explain the connection found between HBS and number of origins. Furthermore, the social hierarchy of pigs is very strong leading to fights when new pigs, at the time of arrival on the farm, are mixed together, the same behaviour can be seen if pens are regularly mixed together instead of incorporating an all-in-all-out system [19, 21]. Competition at feeding time or at the feeding station can be strong in socially unstable groups leading to more stress and higher activity and might therefore be a promoting risk factor to torsion of the intestines and deaths due to HBS.

The importance of feed distribution system hygiene was described in multiple studies [3, 8, 9]. Therefore, a special focus was laid on the cleaning management, especially cleaning frequency and the used methods, of the feed distribution systems as well as feed storage containers. The used methods on the farms were investigated by multiple studies but none of those studies investigated the frequency of cleaning. Interestingly, farms which practice cleaning of the distribution pipes every six months or after every group were slightly less likely to be HBS case farms than farms with no cleaning. However, farms with a higher cleaning frequency (weekly, monthly and daily) had higher odds of being HBS case farms than farms with no cleaning. Therefore, it might be that frequent cleaning leads to an imbalance of the microflora in the feed distribution system [22]. Hence, the building of a new microflora in the feeding systems favours the growth of coliform bacteria until an adequate lactic acid bacteria flora is established [28], which might lead to a high number of coliform bacteria in the feed. Therefore, the cleaning interval of the feed distribution system can improve the feed hygiene and might reduce HBS on herd level. Furthermore, one study claimed, that the incubation of the freshly cleaned pipes with a lactic acid bacteria strain could improve the establishment of an adequate flora and therefore shortens the time of coliform overgrowth in the feed distribution system [22]. This effect could not be proven with our questionnaire, because none of the farms used an incubation strain after cleaning the feeding system. However, no significant differences between the cleaning methods (i.e. acid solution, alkaline solution, combination of acid and alkaline solution, water and barley corns) of the feed distribution system on the HBS prevalence could be detected.

Our study did not confirm previously described risk factors for HBS including liquid feeding systems [6] whey [2, 15], routine use of antibiotics [8, 9] as well as sex of the pigs [3, 16] and seasonal effect [3, 4]. Although, liquid feeding systems were used in 60.8% of all investigated farms, no statistically significant difference between case and control farms on the prevalence of HBS could be detected. In addition, including whey as component of the diet is discussed as a risk factor in multiple studies [8, 9, 12, 15] and often mentioned by practitioners, but showed no significant effect in this study. However only the usage of whey in the diet was asked by questionnaire, and therefore, no analysis of the quality or bacterial contamination of the whey was conducted. Hence, no valid conclusion can be drawn about the effect of whey on HBS, but warrants that further research is needed to exclude whey as a potential risk factor. Since the routine use of antibiotics, for example as treatment at arrival of a new group, is not allowed in Switzerland the effect of such an application could not be examined. Reason for the disallowance of routine antimicrobial use in Switzerland is the prudent use of antibiotics act aiming to reduce the bacterial resistance situation. In addition, a controversial gender effect was described for HBS revealing a higher prevalence in female pigs in a Swiss study [3] compared to a higher prevalence for castrated males and boars in a study from Great Britain [16]. In the questionnaire no information about the gender effect was available, because the farmers did not take notes of the diseased pigs’ gender. Furthermore, no seasonal effect on the occurrence of HBS could be detected in this study in comparison with an older study from Switzerland [3]. A possible explanation for this difference in findings could be the generally better stable climate and management found in fattening stables today as compared to the older study [3]. Differences in temperature and humidity can be regulated better with modern climate installations in pig stables leading to a more stable climate and therefore reduces stress in pigs. Knowledge about the tolerable difference in day and night temperature is increased and modern fattening stables often use micro climate zones to further accommodate pigs better.

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