PhD

Survivability and better performance of pigs under tropical stress have been
reported to be significantly influenced by immune responses. Immune response -traits
under genetic control offer potential possibilities for exploited in commercial pig
production. The present research project on the utilisation of porcine immune responses
by estimating the magnitude of humoral and cell' mediated immune responses in Desi and
Large White Yorkshire attempted to evaluate the genetics of immune responses and to
identify the association between the immune response traits and economic traits. The
immune response traits were studied in 150 piglets aged between two to three months, 75
each belonging to Desi and Large White Yorkshire of both sexes and sired by eight sires
each. The immune response traits studied were antibody response to sheep red blood cells
(SRBC), delayed type hypersensitivity (DTH) to intradermal injection of PHA-M and
lymphocyte transformation response to BCG. The economic traits recorded were litter
size at birth, litter weight at birth, litter size at weaning, litter weight at weaning, weaning
mortality and the occurrence of diarrhoea and pneumonia.
Naturally occurring antibodies to SRBC could not be detected in both the breeds.
Peak antibody response to SRBC was obtained at day 7 post immunisation with a mean
titre of 4.830. Heritability estimates of antibody response to SRBC were 0.8969 ± 0.4235,
0.9187 ± 0.4893 and 0.8174 ± 0.4893 respectively at 7th day, 15th day and 21st day post-
immunisation. Litter size at birth and weaning had no significant influence on antibody
response. Similarly, antibody response to SRBC among piglets was not influenced by the
incidence of diarrhoea, pneumonia and pre-weaning mortality to a significant level.

DTH responses to intradermal injection of PHA peaked at 24 hours post injection
with a mean value of3.39 mm. The mean pre injection skin thickness was 3.508 mm and
3.012 mm among Large white Yorkshire and Desi pigs respectively. This difference was
found to be significant (P<0.05) and this difference was due to the significant breed
difference confounding with body weight classes. The effect of breed on PHA responses
at 24, 48 and 72 hours were not significant. Sex of the pig also did not influence the
PHA responses significantly. The body weight classes did not influence the DTH
response to PHA significantly. Sire effect was not significant on the pre injection skin
thickness. But the DTH response at 24 hours was influenced by the sires in both Large
White Yorkshire and Desi pigs to a highly significant level (P post injection also DTH responses were influenced by sires to a significant level
(P<0.05). The heritability estimates for pre injection skin thickness and DTH responses
at 24, 48 and 72 hours were 0.5173 ± 0.4179,0.8136 ± 0.5643,0.6816 ± 0.5187 and
0.7134 ± 0.5283 respectively. The litter .size at weaning was not influenced by the initial
skin thickness. DTH responses to PHA at 24, 48 and 72 hours had no significant
influence on the litter size at birth and weaning. PHA responses at 24, 48 and 72 hours
were not influenced significantly by the incidence of diarrhoea, pneumonia and pre-
weaning mortality.
The analysis of lymphocyte transformation and stimulation index to BCG on zero
day was around one indicating that there was not marked increase in the lymphocyte
multiplication in PPD stimulated samples. The stimulation index on 15th day was 6.0161
in Large White Yorkshire and 6.3340 in Desi. This index further increased to 6.1070 and
6.5920 on so" day and began to decline from 45th day with a mean value of 6.0020 in
Il

Large White Yorkshire and 5.9890 in Desi pigs. The effect of breed, sex and body
weight class of piglets was not found to influence the stimulation index significantly.
Sire effect was not significant or/the pre inoculation index while it was highly significant
on 15th, 30th and 45th day in Large White Yorkshire and Desi. The estimates of
heritability on is", 30th and 45th day stimulation index were 0.5171 ± 0.2893,0.6289 ±
0.3817 and 0.4983 ± 0.2583 respectively. Litter size at birth and weaning was not found
to have any significant influence on the LT response to BCG.
Correlation analysis among different immune response traits revealed that
antibody response to SRBC at 7, 14 and 21st day had highly significant positive
correlation. Similarly, the correlation between PHA responses at 24, 48 and 72 hours
were also highly significant and positive. PHA responses at 24 hours and LT responses
at 15th day was also positive and significant. LT responses at 15th and 30th day were
also significant and positive. The association between LT responses during different time
. ,
intervals were always positive and significant. PHA responses were always negatively
correlated with initial skin thicknesss to a significant level.
Antibody response at 7, 15 and 21 st day had a significantly high negative
influence on the body weight at weaning. There was a significant decrease in pre-
weaning mortality associated with LT response at 15th day.