Diarrhea causes significant economic impact on the success of the swine industry in the country. This is always common in many piglets leading to poor growth rate associated with a low and variable feed intake before and after weaning, the experts said.

Piglets are believed to be susceptible to enteric pathogens and at a younger age or before weaning, the most common disease is diarrhea. It usually occurs after a 3-to 4-day latency period and peaks around one week after weaning. It causes high mortality that affects swine production.

This problem was one of the primary reasons why the Philippine Carabao Center (PCC), thru its Animal Health Unit, conducted a study titled, “Comparative Gene Expression of Swine Leukocyte Antigen (SLA) in Diarrheic and Non-Diarrheic Cases in Pigs (Sus scrofa, LARGE WHITE AND NATIVE BREEDS) at Post-Weaning and Pre-Weaning Using Real Time Polymerase Chain Reaction.”

The study was under Swine Genomics Project 2 of PCC, Philippine Council for Agriculture, Aquatic, and Natural Resources Research and Development (PCAARRD), Bureau of Animal Industry (BAI), and ASBAP.

According to the study, swine leukocyte antigens (SLA), the swine major histocompatibility complex (MHC), codes for a series of extremely polymorphic cell-surface glycoproteins which are critically involved in acute rejection and control of immune responses towards diseases.

It further stated that the SLA region becomes an obvious candidate for marker-assisted selection because of its association and polymorphism which have been reported with variation in the swine immune responses to different diseases.

Studies on the MHC of pigs, the study averred, would be a useful reference for the culling of livestock with altered immune responses and selection of animals with disease resistance which can be associated with production and reproductive performance.

Methodologies used

“We collected blood samples from 20-headpost-weaned piglets that are six to eight-week old. Ten of the animals were diarrheic post-weaned piglets which composed of five native breeds and five Large White and the other 10were non-diarrheic post-weaned piglets which were represented by five native breeds and five Large White breeds served as negative control,” Mary Rose D. Uy, lead researcher of the study, explained.

She also said that 20 pre-weaned piglets (Large White and Native), which were about 2 to 4 weeks of age, were used in the study. The 10 non-diarrheic piglets which were composed of five native breeds and five Large White were used as negative control, while the other 10 comprised of five native breeds and five Large White diarrheic piglets were assigned as positive control.

She further said that they also obtained samples for RNA extraction of SLA type 1 (SLA-1) and SLA type 2 (SLA-2) genes from the blood of diarrheic and non-diarrheic post-weaned and pre-weaned piglets. These samples were reversely transcribed into complementary cDNA (cDNAs) before amplification that applied the primer SLA-1*13XX (which targets the SLA-1 gene with a 217 bp) and SLA-2*w08XX (which recognizes the SLA-2 gene with a 126 bp). Amplified products were analyzed by real-time polymerase chain reaction (qPCR).

Gene expression levels were computed based on comparative CT method. These were tested statistically using Students’ T-test.

As revealed in the study, the use of quantitative PCR allowed the researcher to view the entire reaction and product being generated throughout all stages of the reaction. In its simplest and cheapest form, qPCR employed the DNA-binding dye, SYBR green.

 “We examined the SLA gene because it is one of the candidate markers in the immune response of pigs in a particular disease,” Uy said.

Aside from Uy, the other researchers of the study were Jeffrey Niel P. Aquino, Dr. Gemerlyn G. Garcia, Dr. Claro N. Mingala, Joan Carla F. Sampang, and Dr. Reginaldo V. Abuyuan.

Correlation analysis

Results of the study showed that the expression levels of SLA-1 in post-weaned piglets were slightly in piglets experiencing diarrhea, however, the statistical result showed no significant differences. In SLA-2 genotype, the expression levels between diarrheic and non-diarrheic post-weaned piglets had also no significant differences.

On the other hand, in pre-weaned piglets expression level of SLA-1 in diarrheic Native and Large White were significantly higher than that of the non-diarrheic piglets (P<0.0399). SLA-2 expression level was not significantly different in non-diarrheic and diarrheic native and Large White piglets.

Correlation analysis showed negative relationship in the expression of SLA-1 and SLA-2 in diarrheic and non-diarrheic Native and Large White piglets. The data gathered demonstrated that SLA-1 and SLA-2 accompany diarrhea in Native and Large White piglets in terms of their CT values which were significantly different (P<0.0094).

“SLA type 1 apparently mediates or triggers immune responses of pigs to diarrhea at pre-weaning,” Uy declared.

The study aimed at quantifying and determining the difference in the expression of SLA-1 and SLA-2 gene expression in a course of diarrheic and non-diarrheic conditions in post-weaned and pre-weaned piglets.

“Results of the study showed that pre-weaned piglets are seen to have higher expression of SLA gene compared to the post-weaned. Higher expression happens when piglet has been infected, which means it has immune response against certain disease and it is expressed more in the pre-weaning piglets in several folds,” she added.

Importance

“The data that were gathered will serve as a reference in improving the health status of farm animals and in increasing productivity. Information regarding SLA genes and their products are useful tools in deciding for the elimination of livestock with altered or weak immune responses and in the selection of animals with disease resistance,”she explained.

Further studies on the identification of pathogen-causing diarrhea in piglets and its association on immune responses of MHC classical I genes should be made.Moreover, regulation mechanisms involving SLA entail elaborate investigation and a significantly higher number of experimental animals is needed.