Estimates of genetic and phenotypic parameters for production, haematological and gastrointestinal nematode-associated traits in Australian Angora goats

Abstract

Genetic parameters for liveweight (LWT), greasy fleece weight (GFW), mean fibre diameter (MFD), standard deviation of MFD (MFD-s.d.), mean fibre curvature (CURVE) percentage of medullated (%MED) and kemp (%KEMP) fibres, faecal worm egg count (WEC), packed cell volume (PCV), mean corpuscular volume (MCV) mean corpuscular haemoglobin content (MCHC), circulating anti-nematode IgG (IgG) and counts of circulating eosinophils (EOS), lymphocytes (LYM), neutrophils (NEU), basophils (BASO) and monocytes (MONO) up to 18 months of age were estimated in Australian Angora goats (608 animals, 14 sires 3 years of birth). Measurements were made during a period of natural parasite challenge up to 5 months of age, or following artificial challenge with 10 000 infective larvae of Trichostrongylus colubriformis at 5.25 months of age. Year of birth had a significant impact on production and parasite-associated traits at all ages studied. Sex had a marked effect on production and erythrocyte traits. Birth type had no effect on any traits in animals older than 6 months. Maternal effects were not significant except for LWT at 3, 5 and 6 months and for IgG at 3 months. Most production traits were highly (LWT, GFW, MFD, %MED) or moderately (CURVE, MFD-s.d.) heritable (range 0.17–0.59) with only %KEMP having a low heritability (0.02–0.14). The heritability estimates (±s.e.) for CURVE are novel for goats and ranged from 0.18 ± 0.09 at first shearing to 0.44 ± 0.14 at third shearing. Heritability estimates were low for WEC (0.02–0.16) and for specific IgG during natural infection (0.14–0.15) but higher for IgG following artificial challenge with T. colubriformis (0.42 ± 0.13). Of the haematological variables NEU and all red cell traits were highly heritable (0.45–0.71), LYM and MONO were moderately to highly heritable (0.31–0.55), and EOS was weakly to moderately heritable (0.06–0.28). Strong phenotypic correlations existed between production traits. MFD was positively correlated with GFW and negatively correlated with CURVE, indicating that finer fibres have a higher crimp or wave count. WEC had consistent negative phenotypic correlations with PCV, LYM and EOS, and positive correlations with NEU. Correlations with IgG were positive up to 5 months and negative thereafter. Phenotypic correlations between WEC and LWT as well as with GFW and MFD were negative. Heritability estimates for production traits were generally consistent with other studies. Haematological and fibre curvature findings are completely novel for Angora goats. Estimates of heritability for WEC fell in mid range of published findings for other goat breeds, and these results suggest that there is some scope for breeding for worm resistance in Angoras but the response is likely to be slow.

Development of immunity in boer goats naturally infected with the nematode haemonchus contortus

“…Correlation analyses of the data showed that live weight was positively correlated with eosinophil counts. This result is in agreement with Bolormaa et al (2010) and Olayemi et al (2011) where eosinophil counts were positively associated with the live weight of Australian Angora and Cashmere goats naturally infected and followed by challenge infections with T. colubriformis. They suggested that such positive correlations between live weight and eosinophil counts may indicate resistance to infection rather than of the infection itself.…”

“…In this study MCV, MCH and RDW values dropped especially in the younger groups of goats for both sexes similar to the finding of Ameen et al (2006). MCHC values also dropped in this study in agreement with Bolormaa et al (2010). However, in this study the values of MCV and MCH were dropped but not significantly lower compared to the MCHC and RDW throughout study period.…”

“…However, the total leukocyte counts in female goats were relatively higher than male goats although this was not significant. This finding contrasts with Bolormaa et al (2010) where they reported that there were a few significant differences in leukocyte counts between male and female kids in all ages they studied.…”

“…Therefore, stool examination can be used to determine the cause of iron deficiency (Lewis et al 2001). Studies in Angora goat kids showed that the MCV values were significantly reduced after being naturally challenged with H. contortus at 5 months of age (Walkden-Brown et al 2008;Bolormaa et al 2010). They also stated that the MCV and PCV values in Angora goats were significant influence by birth type with twin-born kids having lower PCV and MCV at 3 months of age.…”

“…Reports on neutrophils, monocytes and basophil in H. contortus infected goats and sheep are scarce and their role in relation to resistance and resilience is not clear. Slight increases in monocyte and basophil values were reported in goats naturally infected and challenged with T. colubriformis while neutrophil counts declined steadily with age (Bolormaa et al 2010;Qamar & Maqbool 2012).…”