Characterization of overgrown toes in sow breeding herds

Feet, leg structure rank right behind reproductive failure as major identifiable reason for sow culling and reduced sow longevity.

October 5, 2021

7 Min Read
sow leg and feet.png
Iowa State University

Breeding herd mortality and replacement rates continue to be challenging areas for commercial swine producers. Breeding sow herd lameness is a major contributor to mortality challenges, feet and leg conformation and lameness. Feet and leg structure rank right behind reproductive failure as the major identifiable reason for sow culling and reduced sow longevity. 

Overgrown toes, often called digital overgrowth in scientific circles, continues to represent an increasing breeding sow herd challenge. Overgrown toes are one of the most common foot abnormalities seen and recorded on commercialized sow farms, and often lead to lameness and premature sow culling. In addition, sows with severe toe overgrowth may have impaired welfare and this in-turn could erode consumer confidence.

It has been reported that just under 10% of lactating sows had overgrown toes (KilBride et al, 2010). In another study that included 3,500-plus pregnant sows, over 25% had moderately overgrown toes, while 7% had severely overgrown toes (Boyle, 1996). Overgrown toes can negatively impact sow performance because sows spend less time eating and are quicker to lay down post farrowing when compared to sows with normal toe growth (Calderon Diaz et al., 2015). In addition, Calderon Diaz and colleagues (2015) reported that sows with overgrown toes had higher instances of slipping and weight shifted frequently. Collectively, these behaviors and postural changes indicate a sow in greater discomfort. Beyond discomfort, the actions of slipping and being quicker to lay down may be related to increased piglet crushing and greater pre-wean mortalities. Fitzgerald et al. (2012) reported that sows with overgrown toes averaged 1.5 fewer piglets born alive when compared to control sows without digital overgrowth. The overall combination of sow discomfort, lower feed intake, lower number born alive and greater piglet crushing contributes to poorer sow performance and reduced breeding herd efficiency (Lucia et al., 2000). The sow’s age/number of parities may also play a role with overgrown toes in the breeding herd. Knauer et al. (2012) reported that 8% of parity 1 sows had overgrown toes on their rear feet, but between parities 6 through 10 this number increased to 40%. Interestingly, sows culled with overgrown toes on the front feet were much lower, with 0% for parity 1 sows and approximately 5% between parities 6 through 10 (Knauer et al., 2012).

fig. 1 ISU sow leg and feet.png

Sows with overgrown toes tend to have a greater risk for developing other foot problems like cracks in the toes and lesions (Lisgara et al., 2014). Furthermore, overgrown dew claws may become concave, extremely curved or extend below the heel bulb that in-turn and contribute to increased lameness. In a study evaluating sow lesions at the harvest plant, Knauer et al. (2007) observed that 86% (n=3,158) had a lesion on at least one foot. Additionally, 52% of sows had at least one lesion on their front feet and 81% had at least one lesion on their rear feet. The same study speculated that increased rear foot lesions may be attributed to the wet environment that sows are exposed to in a gestation stall.

Another factor contributing to overgrowth toes relates to weight bearing on their feet. Approximately 80% of the sow’s weight of the sow is born by the outside (lateral) toe and the majority of the weight on that toe being placed on the heel bulb (Webb, 1984). The uneven weight distribution on the feet as well as the difference in weight distribution between the outside (lateral) and inside (medial) toes (Sasaki et al., 2015) likely contribute to the uneven toe wear that can contribute to overgrown toes in the sow breeding herd.

As the sow’s toes and dewclaws become overgrown, there is an increased risk that they may getting caught in slotted flooring and break off creating lameness issues (Pluym et al., 2013b). If a sow’s dewclaw becomes detached, the highly innervated corium (like the nail bed in humans) is exposed and results in a very painful lameness condition (Pluym et al., 2011; Pluym et al., 2013b). The risk for this occurrence increases in group-housed sow gestation settings where the biological demand increases because sows are competing for resources and increased locomotion occurs (Anil et al., 2003; Pluym et al., 2013b; Tinkle et al., 2017).

Histologically, there are differences when comparing foot and toe structure from sows’ feet with overgrown toes with sows having normal appearing toes. A variety of factors including body weight, weight distribution, trauma, fighting, housing type and the interaction among two or more factors play a role in differing foot structures that contribute to overgrown toes observed among breeding herd females (Newman et al., 2014). Newman et al. (2014) evaluated 24 Landrace x Large White F1 females to study cellular and toe structure. They defined overgrowth as claws that were greater than 50mm long. Their results indicated that of the 72 claws evaluated, 39 showed digital overgrowth while the remainder showed normal appearing toe growth. Overgrown toes ranged between 51 mm and 79 mm in length. Lateral rear claws comprised 67% of all overgrown toes. Laminitis was found in several toe tissue samples when evaluated microscopically from sows presenting overgrown toes. Inflammation was observed from 14 of the sows with overgrown toes, but total numbers were insufficient to create statistical significance.

It is clear that overgrown toes can be a challenge for commercial sow breeding herds. We know that overgrown toes can contribute to increased locomotion challenges and reduced sow performance in the breeding herd. Additionally, overgrown toes can be a welfare issues when toe overgrowth is excessive and/or when toes breakoff. This may cause injury or lameness. To date, identifying the cause for overgrown toes within commercial sow herds is challenging and is an area our research group is focusing on in the coming months. 

Sources: Derek Henningsen, Grace Moeller, Anna Johnson, Locke Karriker, and Ken Stalder, Iowa State University, who are solely responsible for the information provided, and wholly own the information. Informa Business Media and all its subsidiaries are not responsible for any of the content contained in this information asset.


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