A comparison of claw conformation and claw horn structure of two sheep breeds, and their relationship to footrot incidence
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This study compared claw conformation (length of dorsal border (DB), diagonal length (DL), dorsal angle (DA), heel height (HH), hardness) and claw horn structure (number of horn tubules, diameter of tubules medullary cavity (TC), thickness of tubules cortex (TX) and average and total horn tubules zone) of two sheep breeds. Heritabilities for these parameters were estimated and the relationship to the incidence of footrot investigated. In total, front and hind claws of 240 sheep of the two breeds Merinoland (ML; n = 142) and Rhoen sheep (RH; n = 98) were examined four times in monthly intervals. Animals were screened for footrot every second week during the study period. DL and DB, were greater in ML than in RH (P<0.05) and greater in front than in hind claws (P<0.05). Front claws had greater HH and DA than hind claws (P<0.05) with the values being superior in ML compared to RH (P<0.05). Only in ML front and hind claws differed in their hardness (P<0.05). Only 14% of ML animals were footrot-positive. These animals showed higher values in DA (P<0.01) and HH (P<0.05) and shorter DL than footrot-negative ones. Heritability estimates were on a moderate level for DL (0.29-0.53) and HH (0.15-0.25), whereas lower values were estimated for DB (0.04-0.15) and DA (0.08-0.19). Hardness was not found as a possible selection trait. Regarding the claw horn structure, TC, TX and average and total tubules zone were lower in ML than in RH (P<0.05). In RH hind claws had larger average (P<0.05) as well as total (P<0.05) tubules zone than front claws. Parameters of claw horn structure showed moderate heritabilities (0.36-0.57). In conclusion, the results indicated the possibility to select sheep on the basis of morphological parameters of claw conformation and claw horn structure for an improved claw quality. However, the low incidence of footrot-positive animals did not allow drawing conclusions on the relationship between the observed parameters and the incidence of footrot.