The Challenges in Growing-Fattening Swine

By: Dr. Ko-Hua Tso, scientific expert, Dr. Bata Ltd.

Fattening pigs, also known as finishing pigs, play a crucial role in the swine industry, which involves raising pigs to the desired market weight and affecting meat quality [1]. Efficient fattening pig management is essential for several reasons:

1. Economic efficiency [2]: Efficient pig fattening management directly influences the economic viability of pig production. Well-managed fattening results in higher growth rates, improved feed conversion, and reduced production costs.
2. Quality pork production [3]: Proper management ensures the production of high-quality pork with desirable characteristics such as marbling, tenderness, and flavor. This is essential for meeting consumer preferences and demands.
3. Disease infection [4]: Disease outbreaks can significantly impact pig production. Effective management practices, including biosecurity measures, help prevent the spread of diseases and reduce the need for costly treatments.
4. Optimal feed utilization [5]: Fattening pigs convert feed into muscle mass efficiently. Proper nutrition management is essential for maximizing growth rates and minimizing feed costs.
5. Meeting market standards [6]: Fattening pigs to meet market standards is crucial for success in the pork industry, including achieving the desired weight, carcass composition, and quality specifications demanded by consumers and processors.

Hence, there are some challenges that pig farmers need to face at this stage of pig production.

Here are some key challenges and the importance of effective management:

1. Transportation and management stress [7]:
   1. Moving pigs from one location to another, such as during transportation to a new farm or to a processing facility, can cause significant stress.
   2. Rough handling, including using electric prods or excessive force, can cause stress and fear. Besides, the loud noises and unfamiliar surroundings during transportation can lead to fear and anxiety among pigs.
2. Social stress [8]:
   1. Pigs are social animals. Disruptions in their social hierarchies, such as mixing unfamiliar pigs, can lead to aggression and stress.
   2. Overcrowding in pens can also cause social stress, as pigs compete for feed and water, leading to dominance behaviors and stress-related injuries.
3. Environmental stress:
   1. Temperature changes [9]: Sudden changes in temperature, both hot and cold, can stress pigs. Heat stress, in particular, can reduce feed intake and growth rates.
   2. Poor ventilation [10]: Inadequate ventilation in animal houses can lead to poor air quality, the accumulation of gases like ammonia, and increased humidity, all of which contribute to stress.
   3. Inadequate housing [11]: Lack of space, uncomfortable flooring, and insufficient bedding material can cause physical discomfort and stress in pigs.
4. Nutritional stress [12,13]:
   The best growth, meat percentage, and feed consumption are the top goals of your feeding strategy for growers and finishers. Hence, poor-quality or imbalanced feed can lead to nutritional stress, affecting growth rates and overall health in grower-fatteners.
5. Disease and infection stress:
   During the growing and finishing stage, digestive disease in pigs significantly impacts the swine industry, including reduced feed intake, decreased feed conversion rates, and increased medication costs [14]. The most critical enteric pathogens during the fattening phase are Lawsonia intracellularis, Brachyspira hyodysenteriae, and Salmonella spp. These pathogens are responsible for porcine proliferative enteropathy (PPE), swine dysentery (SD), and porcine salmonellosis (PS), respectively [15,16]. These diseases occur in growing and finishing pigs and are characterized by fecal-oral transmission [17,18]. The simultaneous presence of these bacteria is not uncommon in the case of diarrhea around the world [17,19]. Besides, the subclinical infection in pigs of these diseases not only causes growth retardation but also prevents pigs from being marketed on schedule and continues to shed the pathogen, leading to an increase in the pathogen infection pressure in the environment.

Figure 1. Incidence of pathogens in enteric disease in pigs related to age (modified from [20,21]).

Table 1. Clinical and pathological symptoms of the main pig enteric bacterial disease. (modified from [20-22])

1. E. coli

Escherichia coli is a common cause of post-weaning diarrhea in piglets but usually does not affect grower-finishers [23,24]. However, in some field cases, it is still observed that eleven-week-old pigs showed the causative agent to be an E coli-producing shiga-like toxin [25]. Difference with weaning piglets, no pigs developed neurological signs or other conditions usually associated with edema disease. No significant difference between clinically affected and unaffected groups was observed in mortality or growth performance [26].

1. Diarrhea [27]: Fattening pigs experience watery or mucohemorrhagic diarrhea. The diarrhea can be severe, leading to dehydration and electrolyte imbalances. However, the feces in fattening pigs are not as watery as in younger pigs.
2. Dehydration [28]: Dehydration is a common symptom in fattening pigs due to fluid loss from diarrhea. Dehydrated fattening pigs exhibit signs of weakness, lethargy, and sunken eyes.
3. Loss of appetite [29]: Fattening pigs have reduced appetite in feed and water. However, their feed intake drops less dramatically than that of weaned pigs.
4. Lethargy and weakness [30]: Fattening pigs become lethargic and weak, exhibiting reduced activity levels. The weakness can be observed but not as severe as in weaned pigs.

Figure 2. Eleven-week-old grower-finishers with severe watery diarrhea caused by E. coli [25].

2. Clostridium perfringens (Necrotic Enteritis)

Infection with C. perfringens type C occurs worldwide, causing fatal necrohaemorrhagic enteritis mostly in neonates, even if cases of clostridiosis can be observed until 3 weeks of age [20]. The disease can spread rapidly in a herd, and mortality in affected piglets from non-vaccinated herds can reach 100%. There are only a few cases of growing-fattening pigs, but the symptoms are much milder than those of suckling piglets [31]. The symptoms mainly present appetite reduction, weakness, watery diarrhea, and dehydration in grower-finishers [26].

3. Lawsonia intracellularis:

Porcine proliferative enteropathy (PPE) is an enteric disease affecting weaned and growing pigs and is attributed to the intracellular bacterium L. intracellularis [32]. The clinical manifestations of PPE include anorexia, diminished growth rate, and persistent diarrhea [26]. In finishing pigs, this disease may escalate to severe melena and sudden death, resulting from acute hemorrhage in the affected intestines [32]. The primary pathological hallmark of PPE is the hyperplasia of immature crypt cells in the ileum or colon epithelium. This intestinal infectious disease is characterized by thickening the aboral small and proximal large intestinal mucosa due to enterocyte proliferation [33]. Porcine proliferative enteropathy [34,35] can manifest in two distinct clinical presentations: chronic diarrhea and stunted growth in growing-finishing pigs, known as porcine intestinal adenomatosis (PIA), or acute hemorrhagic diarrhea leading to mortality in gilts and finishing pigs close to market age, referred to as proliferative hemorrhagic enteropathy (PHE). The disease is distributed worldwide and is an economic concern for the pig industry. The occurrence of L. intracellularis was reported in various countries throughout the world, with prevalence ranging between 48% and 100% [36]. In European latest survey indicated that out of the 144 herds sampled in Germany, Denmark, Spain, the Netherlands, and the United Kingdom, 90.3% contained at least one positive fecal sample. Of the 6450 nurseries, growing, and finishing pigs of the previously mentioned herds, 26.2% of the animals tested positive in fecal samples [37]. On the other hand, Taiwanese latest survey indicated that 61 pig farms had 62.3% positive rates of L. intracellularis and the individual positive rates of L. intracellularis were 2.62% and 23.1% in growing and pre-market pigs [38].

1. Chronic diarrhea [32]: In weaned piglets, L. intracellularis infection can lead to chronic persistent watery diarrhea. However, in fattening or finishing pigs, the symptoms can escalate to more severe manifestations, including acute hemorrhage and severe melena.
2. Weight loss and poor growth [32]: Infected fattening pigs exhibit poor body weight gain and growth rates due to reduced feed intake caused by intestinal inflammation and discomfort.
3. Rough hair coat [39]: Pigs affected by L. intracellularis have a rough or unkempt hair coat, indicating their overall health status.
4. Subclinical infections [40]: Some fattening pigs do not show obvious clinical signs but still have subclinical infections. These pigs present reduced feed efficiency and fail to reach their growth potential without exhibiting severe symptoms.

Figure 3. Ileum of pigs affected by (A) PHE with a thickened wall and blood clot in the lumen and (B) PIA complicated by secondary bacterial infractions leading to necrotic enteritis, known as regional ileitis (modified from [20]).

4. Salmonella spp.

Salmonellosis in pigs occurs mainly in weaned and grower-finisher swine raised under intensive conditions [41]. The loss of passive immunity and exposure to stressors cause the disease to occur in pigs. Other exogenous factors can influence or interact with salmonellosis. Poor response to treatment by pigs infected with S. Choleraesuis was attributed to concurrent exposure to aflatoxin in the feed [20]. Suckling pigs can be infected, while the disease is infrequently observed, presumably due to protection given by lactogenic immunity. S. Typhimurium and its monophasic variant S. 1,4,[5],12:i:- have worldwide distribution [42] and cause clinically indistinguishable diseases characterized by

1. Diarrhea [43]: Fattening pigs present diarrhea, varying in consistency from mild to severe. The feces can be watery or mucoid, but the symptoms and duration of weaned piglets are more stringent than fattening pigs.
2. Reduced feed intake [44]: Infected fattening pigs have reduced appetite and decreased feed intake. However, these clinical signs are not as dramatic as in weaned pigs.
3. Lethargy [43]: Infected fattening pigs become lethargic, exhibiting reduced activities and interest in their surroundings.
4. Dehydration [20]: Diarrhea can lead to dehydration in fattening pigs, which causes weakness and sunken eyes. However, dehydration is as severe as in younger pigs.

5. Brachyspira hyodysenteriae (swine dysentery)

Swine dysentery (SD) is a production-limiting disease in grower-finishers caused by strongly hemolytic Brachyspira species, such as B. hyodysenteriae [45,46]. The bacterium can survive in the environment for extended periods and spreads through direct pig-to-pig contact or via contaminated feces, feed, water, or equipments [46]. Swine dysentery is widespread around the world, and the prevalence significantly varies depending on farm environment (from 0% to nearly 40%) [46]. European (Denmark, France, Germany, the Netherlands, Spain, and the United Kingdom) research [47] revealed that the prevalence are from 4.2% to 45.8% for B. hyodysenteriae from 144 herds. The latest survey in Taiwan indicated that 61 pig farms have 24.59% positive rates of B. hyodysenteriae. Particularly, the positive rates of B. hyodysenteriae in growing and pre-market pigs were 1.64% and 4.43%. Besides, the results showed that the tiamulin-valnemulin antibiotic resistance gene exists in Taiwan strains, which can reduce the sensitivity of B. hyodysenteriae to tiamulin. This means that Taiwanese pig industry must find effective alternatives to antibiotics in treating dysentery [38].

1. Mild to moderate diarrhea [48]: Fattening pigs infected with B. hyodysenteriae exhibit mild to moderate diarrhea. Affected pigs develop mucohemorrhagic diarrhea and typhlocolitis, often with extensive fibrinous exudate, mucus, and blood in the large intestine.
2. Body weight loss [48]: Infected fattening pigs exhibit body weight loss due to feed intake reduction caused by the ongoing intestinal inflammation and discomfort associated with SD.
3. Rough hair coat [49]: Pigs affected by B. hyodysenteriae have a rough or unkempt hair coat, indicating their overall health status.
4. Subclinical infections [46]: Some fattening pigs carry B. hyodysenteriae without showing obvious clinical signs but still experience reduced growth performance. These subclinical infections can lead to economic losses.

Figure 4. Pig with typical diarrhea due to B. hyodysenteriae (A). Feces are characterized by mucous, blood and muco-fibrinous exudate (B) [20].

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