Crossing indigenous goats with a larger imported breed increases vulnerability to natural infection with gastrointestinal strongyle parasites

摘要

Uncontrolled crossbreeding of indigenous tropical goats with exotic breeds to increase genetic potentials for growth and body size is a common strategy for genetic improvement. However, in most cases, goats of all genotypes are managed under similar extensive or semi-intensive conditions without corresponding improvements in feeding or health care. Fitness characters such as parasite resistance are believed to be present in indigenous goats and important under typical field conditions but potentially diluted by uncontrolled crossbreeding. This study was therefore designed to compare resistance to gastrointestinal (GI) strongyle parasites in 279 Sri Lankan Indigneous (SLI) and 243 Jamnapari crossbred (JCB) kids. Kids were 4 to 6 months old and maintained under similar management on 68 farms in the Eastern Province of Sri Lanka. Body weight (BW), packed cell volumes (PCV), and fecal egg count (FEC) were determined for each goat at the start of the study in mid-July and again 7 days later. Effects of sex and time were observed for BW, and effects of sex and sex x breed interaction were present for PCV. Kids were heavier (P < 0.05) at the second sampling time, and male kids were heavier than females (10.2 +/- 0.2 versus 9.5 +/- 0.2 kg). The SLI females had greater (P < 0.05) PCV (26.3 +/- 0.3%) than SLI males, JCB females, and JCB males, which did not differ (P = 0.54; average PCV of 24.4%). Both SLI and JCB goats had relatively low levels of GI strongyle parasitism under field conditions during the dry season in Sri Lanka, but exhibited substantial within-breed variability in FEC. The sum of FEC across the two measurement times was 1,123 +/- 333 eggs per gram of feces (epg) for JCB kids and 488 +/- 107 epg for SLI kids (P = 0.03), and the breed difference in FEC was larger for females than for males (P = 0.04 for breed x sex interaction). The proportion of goats with FEC > 3,000 epg was greater for JCB goats (7.2%) than for SLI goats (1.3%), and the within-farm variance in FEC with significantly greater for JCB goats. These results indicated that, when infected, JCB goats were more severely affected than SLI goats. Phenotypic resistance to GI strongyle parasites was therefore detectable under field conditions in the dry season in Sri Lanka, indicating potential to improve both parasite resistance and production potentials in tropical goats using systematic crossbreeding and selection.