Journal of the NACAA
ISSN 2158-9429
Volume 10, Issue 2 - December, 2017

Editor: Lee Stivers

Prevalence of Genetic Defects in Market Show Hogs in Utah

Dallin, J. , Extension Assistant Professor , Utah State University
Heaton, K. , Extension Professor, Utah State University
Greenhalgh, L., Extension Associate Professor, Utah State University
Perkins, D., Extension Assistant , Utah State University


As genetic testing advances become commercially available, livestock producers benefit by learning about the advantages and applications. Genetic testing has become especially important in the prevention of Porcine Stress Syndrome (PSS) and Rendement Napole (RN), both of which can lead to poor pork quality. The negative effects of PSS and RN on pork quality result in economic losses in the pork industry and need to be addressed. In 2016 we gathered tail hairs from 150 market show hogs from thirteen counties in the State. We found that 49% of the hogs tested had a genetic defect (PSS and/or RN) that could lead to poor meat quality. Due to the magnitude of this finding, we held a series of workshops to share information gained in this study to educate producers on how they can prevent PSS and RN.


Junior livestock projects provide excellent opportunities for education and positive agricultural experiences for 4-H youth. As genetic testing advances become widely available to livestock producers, youth benefit by learning the benefits and applications of genetic testing. Porcine stress syndrome (PSS), which springs from the Halothane (HAL) gene, is an inherited neuromuscular disorder in pigs that is triggered by stressful situations, such as exercise, fighting, marketing, vaccination, castration, parturition, and hot weather. The symptoms exhibited by pigs experiencing PSS include muscle and tail tremors, labored and irregular breathing, blanching and reddening of the skin, rapid rise in body temperature, collapse, muscle rigidity and eventual death. (Stradler & Conaster, n.d.) In addition, Rendement Napole (RN) is a gene found to cause low ultimate pH and water holding capacity (WHC) in pork. Low water holding capacity results in poor quality meat, referred to as Pale Soft Exudative (PSE) grade meat, which causes dry meat with low palatability when cooked. Unlike the porcine stress syndrome (PSS), the RN- gene appears completely dominant. This dominance implies that a copy of the RN- gene inherited from even just one parent can cause poor meat quality. The negative effects of the RN gene on pork quality result in economic losses in the pork industry (Du, 2004).

In 2016, over 1,000 4-H youth participated in Market Hog projects throughout Utah (Dallin, 2016). This article will review our 2016 findings from 150 sampled market hogs that were tested from thirteen counties in the State. Through scheduled presentations, we will be able to use our findings to educate 4-H youth, market hog producers, and USU Extension Faculty on the importance of selecting animals that do not have these genetic flaws and are therefore more likely to produce higher quality meat.



A total of 205 samples were collected at random from hogs shown at 11 Utah junior livestock shows—representing a total of 13 counties. County agents were mailed sample cards with instructions on how to collect hairs from the tails of swine to be tested; youth had the opportunity to help with sample collection in many of the counties. Tail hairs were pulled from each of the sampled hogs using pliers or a similar tool; they were then placed in a hair sample card to be sent in for testing. Of the 205 collected samples, 150 were randomly selected for testing. A total of $9,000 dollars ($60/hog) was spent on testing for Porcine Stress Syndrome (PSS) and Rendement Napole (RN). Genetic testing was performed by Geneseek, a Neogen Corporation.

Findings were then presented to producers across the state in two state-wide workshops conducted in central areas of Utah.



Of the 150 pigs that were tested, approximately 49% of the pigs had a genetic defect that could lead to poor meat quality, or other issues. Findings for the total sample are found in Table 1.


Table 1. The percentages of hogs carrying the Halothane (HAL) and Rendement Napole (RN) gene in 11 Utah counties’ junior livestock shows.

HAL (%)

RN (%)

















These findings are alarming because the negative effects caused by the HAL and RN gene are completely avoidable. The results of this study also show the significant need for market hog genetic education. By utilizing boars that are found to be stress and RN free, producers can greatly reduce the chance of their pigs having either the HAL gene or the RN gene. Eventually producers could eliminate this gene from their herds.



Porcine Stress Syndrome (PSS) is an inherited neuromuscular disorder in swine that is linked to the Halothane (HAL) gene. PSS is triggered by stressful situations and can cause many undesirable symptoms and eventually death (Stradler & Conaster, n.d.).

The HAL gene became more prevalent as the demand for leaner, heavier muscled pigs grew. As breeders selected for leaner, improved muscled pigs, they unknowingly selected for the HAL gene because stress carrier and stress positive pigs tend to have less backfat and more muscling (Worwood, 2007). Despite the leanness and muscling of stress carrier (heterozygous) and stress positive (homozygous) pigs, there are many negative traits associated with the HAL gene and PSS. Besides the obvious threat of losses from PSS caused deaths, the HAL gene can also lead to poor meat quality in pork. Hogs with PSS are more likely to produce pale, soft, and exudative (PSE) pork than those who are stress free.

The HAL gene is not a completely recessive gene, meaning that heterozygous stress carrier pigs can also exhibit traits of PSS. Although stress carriers are much less likely to suffer sudden death from PSS than stress positive pigs, they are more likely to exhibit poor meat quality (Worwood, 2007).

The Rendement Napole (RN) gene is also found to lead to PSE, and poor overall meat quality in swine. The poor quality is caused by low pH and low water holding capacity in pork with the RN gene (Moeller et. al, 2003). There are two alleles for the RN gene, one dominant mutant allele (RN-) and one recessive normal allele (rn+). The RN- gene appears completely dominant, meaning that just one copy of the RN- gene inherited from one parent can cause poor meat quality (Heaton et al., 2016). The negative effects of the RN gene on pork quality leads to economic losses in the pork industry, and can have a negative impact on the public support of junior livestock shows (Du, 2004).

Some recessive genes can be additive, and such is the case with PSS and RN. Research has found that the detrimental effects on pork quality are amplified in pigs with both the PSS and RN gene. Pigs with both genes can have even poorer meat quality than pigs with one gene or the other (Hamilton et. al, 2000).

Since the majority of swine are artificially inseminated and it is not economically viable for producers to test all of their sows for the RN and HAL genes, producers should utilize genetic testing performed on boars to reduce the chance of hogs carrying the HAL or RN gene. Boar stud services perform genetic testing on their sires before collecting and selling their semen. These results are available from the producer. Eighteen percent of sires on a boar stud website, selected at random, were found to have the HAL gene and be stress carriers ( By knowing and understanding indicators for animals that are carriers of PSS and RN-, producers are able to genetically select non-carriers for breeding stock. This helps to eliminate PSS and RN- altogether. As an end result, consumers who purchase 4-H market hog projects at a premium will receive a high-quality product in return. Providing preventative genetic testing should correlate with a greater positive consumer response.

Two state-wide workshops were conducted to educate producers on our findings; each workshop was well attended with 19 and 21 participants. Survey results collected from the workshops indicated that 67.5% of participants learned more about genetic testing and how it could help their operation. Many of those who said they didn’t learn more were already aware of genetic testing and its uses. This finding suggests that the workshops were an effective way of disseminating our findings to the public. In short, 4-H junior livestock projects are a great vehicle for conducting educational workshops that will help minimize the economic losses caused by the HAL and RN gene and help prepare 4-H youth to be better producers.



A Cut Above SiresYork, NE. (n.d.). Retrieved February 23, 2017, from

Dallin, J. (2016). Utah 4HOnline Market Swine Annual Report. Retrieved from

Du, W. (2004). Rendement napole gene and pork quality. Retrieved February 2016, from

Hamilton, D. N., Ellis, M., Miller, K. D., McKeith, F. K., & Parrett, D. F. (2000). The effect of the halothane and rendement napole genes on carcass and meat quality characteristics of pigs. J Anim Sci , 78 (11), 2862-7.

Heaton, K., Howard, K., & Dallin, J. (2016). Genetic testing for defects and performance measures in junior livestock show hogs. Retrieved February 2016, from http://extension.usu .edu/files/publications/publication/AG_Swine_2016-01pr.pdf.

Moeller, S. J., T. J. Baas, T. D. Leeds, R. S. Emnett, and K. M. Irvin. (2003). Rendement Napole gene effects and a comparison of glycolytic potentialand DNA genotyping for classification of Rendement Napole status in Hampshire-sired pigs12. Journal of Animal Science 81:402-410. doi:10.2527/2003.812402x

Stradler, K., & Conaster, G. (n.d.). Porcine stress syndrome and its effects on maternal, feedlot and carcass quantitavie and qualitative traits. Retrieved August 2015, from

Worwood, D. (2007). Swine artificial Insemination for beginners: selecting the right boar. Retrieved February 2017, from AG_Swine_2007-01pr.pdf.