Rachitic Rosaries and Rib Nodules

by 5m Editor
7 January 2011, at 12:00am

Rib nodules found on pig carcasses at a processing plant were more likely to have been caused by previous injury than nutrient deficiency, according to Drs Steve S. Dritz and Jerome C. Nietfeld of Kansas State University in a paper presented at the Swine Profitability Conference 2010.

Nutrition problems associated with calcium and phosphorus metabolism is the most common metabolic nutritional disease we encounter, write Drs Dritz and Nietfeld. Typically, these problems are associated with gross errors in diet formulation or feed manufacturing. For example, cases we have encountered include lack of vitamin D included in the vitamin premix, erosion of a hole in the salt storage bin into the monocalcium phosphate bin, and lack of providing supplemental inorganic phosphorus when switching from a base mix to a premix programme. Also, we have encountered vertebral breakage associated with stunning that did not appear to affect production parameters and appeared to have been caused by feeding a withdrawal diet lacking an inorganic phosphorus source (Dritz et al., 2000).

Recently, the higher cost of vitamins and inorganic phosphorus sources has lead to lowering of nutrient margins of safety in many swine diet formulations. Also, this has driven the use of higher levels of the supplemental enzyme phytase in diets to increase the availability of phosphorus. With the use of dried distillers grains (DDGS) and phytase, many grow finish diets currently lack supplemental inorganic phosphorus supplementation. Since phytase is an enzyme, it is susceptible to inactivation and degradation overtime if exposed environmental conditions such as heat and humidity during extended storage times.

Finally, due to the expression of phytase activities that vary across sources there is a greater potential of errors in premix or diet formulation. Therefore, the risk of calcium and phosphorus nutritional disorders has increased in the past few years.

Case Description

This case is based on an email provided to us that was sent to all producers supplying pigs to a US packing plant. Excerpt from the email:

Subject: Rachitic Rosaries (Rib Nodules) & Nutrient Deficiencies
We have several carcasses everyday with rachitic rosaries, which are abnormal nodules that occur on the rib bones when moderate deficiencies of calcium, phosphorus and vitamin D3 occur in the diets. Pictures are attached that show these rachitic rosaries (rib nodules).
This past week, we have been monitoring carcasses with rachitic rosaries. Rachitic rosaries are indicative of decreases in growth rates and feed conversion, and they also result in a substantial loss in carcass value due to the damage that occurs to the ribs and belly when these rib bone nodules are removed.
Check the formulation of your swine diets to make sure that adequate levels of calcium, phosphorus and vitamin D3 are present in all diet phases.

Pictures provided with the email message

Since we were unfamiliar with the term rachitic rosaries, we did a brief literature search and found that the term is a description of rickets lesion from the human literature. The term is based on a clinical presentation of multiple enlarged ends of the ribs at the costochondral junction (Nield et al., 2006). Thus, the enlarged ends provide a beaded (rosary) type appearance of the costochondral junction on palpation or radiographs.

A brief review of the pathology of rickets indicated that rickets is a disorder of the developing skeleton with macroscopic lesions most prominent at sights of rapid growth, especially the growth plates of long bones and costochondral junctions of the large middle ribs (Maxie, 2007).

These lesions form as a result of defective mineralisation of cartilage matrix at the growth plates and in newly formed osteoid. The cartilage matrix continues to proliferate with the lack of mineralisation and leading to the beaded nodular appearance. This reference indicated that the lesions are best appreciated on radiographs and that lesions may vary considerably within the same animal.

Therefore, since we were unable to discern if the costochondral junction was involved, we requested samples from several carcasses be sent to the KSU Veterinary Diagnostic Laboratory. A radiographic, gross and histopathologic evaluation of these samples was performed.

Gross and radiographic evaluation of representative rib samples from pigs with rib nodules

KSU Radiologist Comments

Note that all lesions are mid-shaft, suggestive of compressive forces causing a fracture. Additionally, there is no evidence that these lesions are infected or any kind of infective process associated with them. All of these lesions are suggestive of bony callus formation associated with fracture healing. Especially, with poor stability of the fracture, the callus size will be increased. Finally, bone density appears normal and there is even some evidence of calcification in the cartilaginous portion of the ribs. Metabolic disease associated with diet would be expected to be more diffusely distributed.

Next, several ribs were dissected and split using a band saw, with care taken to include the nodular lesions and the costochondral junction.

As indicated, none of the bony nodules is associated with the costochondral junction. Also, there is a clear demarcation of the mineralisation zone for the cartilaginous matrix at the growth plate. Finally, in agreement with radiographic evaluation, the cortical bone thickness appears normal.

Microscopic Evaluation

Sections of costochondral junction consist of normal cartilage that gives rise to bony spicules that form the primary spongiosa adjacent to the growth plate. The primary spongiosa is normally remodeled and the secondary spongiosa is formed normally. In the cartilage portion of the costochondral junction, the resting chondrocytes give rise to proliferating chondrocytes which become arranged into rows that progress and mature as they progress towards the costochondral junction. The mature chondrocytes then become normally mineralised to form the primary spongiosa.

The nodules involving the ossified portion of the bone contain areas where the continuity of the bone spicules is disrupted and fibrous connective tissue fills the space between the bone spicules. The fibrous tissue and the bone on either side of the fibrous tissue are disorganized and sometimes contain small nodules of disorganised cartilage. These areas represent calluses and are the result of a previous fracture that is in the process of healing.

Due to the lack of costochondral junction involvement and microscopic indications of normal growth plate development at the costochondral junction our assessment was that these nodules are not associated with rickets.

We believe a likely cause is a traumatic event a number of weeks prior to slaughter is responsible for these lesions. Although, we cannot fully rule out a marginal calcium or phosphorus deficiency that may have lead to osteoporosis and bone weakness during a prior period of growth. In marginal cases of deficiency, bones or areas that consist predominately of cancellous bone, rather than trabecular bone are first affected. Thus, the first signs are often seen in vertebrae, ribs and other flat bones. Due to the preferential mobilisation from specific bones serving as a reservoir to mitigate these marginal deficiencies, they may not have an impact on production parameters similar to the case we have observed previously with the vertebral fractures.

Literature Cited

Dritz, S.S., M.D. Tokach, J.M. Sargeant, R.D. Goodband and J.L. Nelssen. 2000. Lowering dietary phosphorus results in a loss in carcass value but not decreased growth performance. Swine Health and Production 8:121-124.
Maxie, M.G. 2007. Bones and joints. In: Jubb, Kennedy & Palmer's 'Pathology of Domestic Animals', 5th Edition. Vol. 1: 75-81.
Nield, L.S. P. Mahajan, A. Joshi and D. Kamat. 2006. Rickets: Not a disease of the past. Am. Fam. Physician. 74:619-26, 629-630.

Further Reading

- You can view other papers presented at the Kansas Swine Profitability Conference 2010 by clicking here.

December 2010
Sponsored content