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Abstract. In this paper it is shown that a partial sign symmetric P -matrix, whose digraph of specified entries is a symmetric n-cycle with n ≥ 6, can be completed to a sign symmetric Pmatrix. The analogous completion property is also established for a partial weakly sign symmetric P -matrix and for a partial weakly sign symmetric P 0 -matrix. Patterns of entries for 4 × 4 matrices are classified as to whether or not a partial (weakly) sign symmetric P -or weakly sign symmetric P 0 -matrix specifying the pattern must have completion to the same type of matrix. The relationship between the weakly sign symmetric P -and sign symmetric P -matrix completion problems is also examined.

OBJECTIVE To assess the presence of suspected pigment-associated deafness in North American yaks (Bos grunniens). ANIMALS 12 North American yaks, including 11 with the homozygous piebald Royal pigmentation phenotype and 1 with the heterozygous piebald Trim phenotype. PROCEDURES Hearing was assessed using the brainstem auditory evoked response (BAER) on yaks restrained in the head gate of a grooming chute. RESULTS Five of the Royal yaks and the Trim yak had hearing in both ears. Six Royal yaks were affected; 3 were deaf in 1 ear and 3 were deaf in both ears. CLINICAL RELEVANCE For the first time, probable sensorineural deafness has been confirmed to be present in Royal yaks. The disorder is assumed to be congenital and associated with white pigmentation, based on the pattern of occurrence in other species.