PhD

The scope and potential of broiler rabbit production as an alternate source of meat appears to be tremendous taking into account the unique biological attributes of rabbits. However breeding experiments utilising temperate breeds like Newzealand White and Soviet Chinchilla under the humid tropics of the state revealed heavy pre – weaning mortality, high incidence of diseases, sub optimal growth and reproduction. Indirect selection for diseases resistance has been proposed as the most viable approach and immune responsiveness has been suggested as one of the best indicators of disease resistance.
Serum gammaglobulin (SG) level, Frossman antibody titer to SRBC, antibody reponse to BRBC, delayed type hypersensitivity (DTH) responses to intradermal injection of phytomitogen PHA – M, and contact sensitivity to DNCB challenge were assessed among 135 breeding rabbits below one year of age and belonging to Newzealand White and Soviet Chinchilla breeds. The effects of breed, sex, sire and body weight on the above immune traits were analysed. Heritability estimates were made for each of the above traits. Association of diseases like coccidiosis, mange and adult mortality with each of the above immune traits was worked out. Association of maternal immune trait status with litter traits was assessed. This research approach was aimed at developing an alternate breeding strategy in the indirect selection for disease resistance, growth and viability.
SG level ranged from 9.13 to 84.70 mg/ml with a mean of 28.59 mg/ml. Soviet Chinchilla breed had a significantly (P= 0.048) higher SG level with a mean of 29.51 mg/ml compared to 27.25 mg/ml in Newzealand Whites, differences among males and females were not significant.
Sire effects was not significant on SG levels and haritability estimate was 0.1259. Adult body weight had no significant effect on SG level among broiler rabbits. Association of SG level with litter size at birth was not significant. But SG level had a highly significant effect on the litter size at weaning. Correlation of SG level with pre – weaning mortality (- 0.430) was highly significant (P < 0.01) and negative litter weight at birth and at weaning were significantly correlated with SG level among broiler rabbits. No significant association could be observed between SG level and the incidence of mange and adult mortality. But a higher SG level among broiler rabbits was found to be significantly (P = 0.0440) associated with the incidence of naturally occurring coccidiosis.
Presence of Frossman’s antibodies to SRBC was confirmed in adult rabbit sera. The Forssman antibody titer (1 + loge) ranged between 1.693 and 5.159 with a mean of 2.776. Breed and sex effects were not significant on Frossman antibody titer to SRBC. Effect of sire on this trait was not significant and the heritability estimate was 0.360.
Frossman antibody titer had no significant effect on adult body weight, or litter traits among broiler rabbits. Correlations of Frossman antibody titer of the dam with the litter weight at birth, litter weight at weaning and pre – weaning mortality were not significant. No significant associations could be observed between Frossman antibody titer incidence of mange, coccidiosis and adult mortality.
Pre – immunisation titer to BRBC among broiler rabbits was zero indicating the absecnce of Feossman antibodies to BRBC. Antibody titres to BRBC (1+ loge) were 4.594, 4.425 and 4.311 respectively at the first, second and third week post immunisation. The highest antibody response was at the first week, which began to decline gradually. The influence of breed and sex on the antibody response to BRBC were not significant during the first, second and third week post immunisation. Sire effect was highly significant on the antibody response to BRBC during the first, second and third week post immunisation in Newzealand White rabbits. The effect of sire on antibody responses to BRBC was not significant during the first and third week post immunisation in Soviet Chinchilla breed though it was significant during the second week post immunisation. The heritability estimates of antibody responses to BRBC were 0.9200, 0.9400 and 0.9067 respectively during the first, second, and third week post immunisation. The correlations of adult body weight with antibody responses to BRBC during the first, second and third week post immunisation were (-) 0.244, (-) 0.224 and (-) 0.216 respectively. The correlations were highly significant and negative.
Antibody responses to BRBC during the first, second and third week post immunisation was not significantly associated with litter traits among broiler rabbits. The incidence of naturally occurring coccidiosis, mange and adult mortality was not significantly associated with antibody response to BRBC.
The mean pre – injection skin thickness was 2.140 mm in Newzealand White and 2.224 among Soviet Chinchilla breed. The mean PHA responses at 24, 48 and 72 hours post injection were 2.259, 1.544 and 0.778 mm respectively. Breed effect was not significant on the pre – injection skin thickness or on the PHA responses at 24, 48 and 72 hours. The effect of sex was highly significant in the skin thickness with males having a thicker skin compared to females. The effect of sex on PHA responses at 24, 48 and 72 hours was highly significant with a female superiority for DTH responses to PHA – M. The effect of sires was not significant on pre – injection skin thickness. Sire effects were highly significant on the PHA responses at 24 and 72 hours and approaching near significance at 48 hours in Newzealand White rabbits. However, sire effect was not found to be significant on the PHA responses at 24, 48 and 72 hours post injection among Soviet Chinchillas. Heritability esimates for pre – injection skin thickness, PHA responses at 24, 48 and 72 hours were 0.7637, 0.8600 and 0.6370 respectively.
Adult body weight was not significantly associated with the skin thickness and the PHA responses at 24, 48 and 72 hours. Litter size at birth was significantly less in thick skinned does, though weaning litter size was significantly higher in them. PHA responses at 24, 48 and 72 hours had no significant effect on litter size at birth and at weaning or any other litter traits. Pre – injection skin thickness and PHA responses at 24 and 72 hours were not significantly associated with the incidence of mange, coccidiosis and adult mortality. But reduced PHA response at 48 hours significantly pre – disposed the rabbits to body mange.
Contact sensitivity to DNCB at 24, 48 and 72 hours post challenge averaged 3.585 mm, 1.796 mm and 1.085 mm respectively. Breed and sex had no significant effect on the contact sensitivity to DNCB at 24, 48 and 72 hours post challenge. Sire effect on contact sensitivity to DNCB at 24, 48 and 72 hours post challenge was not significant in Newzealand White rabbits. Among Soviet Chinchillas also effect of sire was not significant on contact sensitivity to DNCB at 24 and 72 hours, though highly significant at 48 hours. Heritability estimates for contact sensitivity to DNCB at 24, 48 and 72 hours post – challenge were, 0.3820, 0.5490 and 0.3039 respectively. Contact sensitivity to DNCB at 24, 48 and 72 hours post challenge was not significantly associated with adult body weight, litter size at birth and litter size at weaning. Contact sensitivity of the doe at 24 hours post challenge was positively correlated with pre – weaning mortality and litter weight at birth.
Lowered contact sensitivity to DNCB at 24 hours had a highly significant effect on the incidence of naturally occurring body mange among rabbit. The incidence of mange was near significant level among broiler rabbits with a lowered contact sensitivity at 48 hours post challenge also. No significant association could be observed with contact sensitivity to DNCB at 24, 48 and 72 hours on the incidence of coccidiosis and adult mortality. Correlations between serum gamma globulin level and Frossman antibody titer to SRBC (0.271) was highly significant correlations of Frossman antibody titer with antibody response to BRBC during the first, second and third week post immunisation was also highly significant.
Pre – injection skin thickness had a highly significant negative correlation with PHA responses at 24, 48 and 72 hours. Correlations among PHA responses at 24, 48 and 72 hours were highly significant. Similarly correlation among contact sensitivity reactions at 24, 48 and 72 hours post challenge were highly significant. PHA responses at 24, 48 and 72 hours had significantly high correlations with contact sensitivity to DNCB at 24, 48 and 72 hours post challenge.
Prospects of utilising maternal serum gammaglobulin level as a marker in indirect selection for enhanced pre – weaning survivability and growth appears to be promising. Though increased SGlevel was found to be associated with the incidence of coccidiosis, further researches on the coccidial species and host defenses are before establishing a coccidiosis resistance phenotype associated with this trait. The differences in sire effects among the two breeds for antibody response to BRBC and PHA responses are suggestive of the genetic structure of the two breeds, especially the Soviet Chinchilla colony developed from few animals. The significant negative correlation of adult body weight with antibody responses are indicative of lower antibody responses in heavier rabbits. Strong negative correlations between PHA responses and pre – injection skin thickness and a significant effect of contact sensitivity at 24 hours on reducing the litter size at weaning appear to suggest that a low maternal cell mediated immunity might enhance pre – weaning survivability of the kits. Significantly higher incidence of mange among rabbits with a lowered PHA response at 48 hours post injection and contact sensitivity at 24 hours post challenge suggest of an enhanced cell mediated immune response conferring mange resistance.