Risk factors affecting metaphyseal irregularities in the radius and ulna of growing Newfoundland dogs.

The main objective of this study was to study risk factors affecting metaphyseal irregularities (MI) in the distal radius and ulna of growing Newfound- land dogs. Risk factors studied included the genetic effects, effects of litters, BW, circumferences of the dis- tal radius and ulna (CDRU), and total serum alkaline phosphatase (ALP) concentrations. The study included 118 Newfoundland dogs (60 females, 58 males), derived from 32 litters. Body weight, separated on sex and MI, was fitted to the Gompertz function. Occurrence of MI differed significantly between sexes, with 55% of males and 35% of females affected (P = 0.03). Growth curves for the 2 groups of dogs, with and without MI, diverged after 60 to 70 d, and dogs with irregularities were heav- ier at maturity than dogs of the same sex without irreg- ularities. In univariate analysis, the litter effect was a significant predictor of MI, explaining 32% of total variability of the MI incidence, but the genetic effects were not significant. However, the latter were signifi- cant in bivariate analysis of MI and BW. In the bivariate analysis, the effects of litter on MI and BW were signifi- cantly correlated at all observational points except at birth, 180 d, and 536 d. Total ALP concentrations de- creased with increasing age, and differences between groups diminished with increasing age, indicating a negative effect of total ALP on MI. Correlation between MI and total ALP concentrations of litters was esti- mated in a bivariate analysis. This correlation was sig- nificant and ranged between −0.34 and −0.62. Similarly, the genetic relationship between total ALP and MI from 120 d of age onward varied between −0.31 to −0.60. However, correlations were only significant at 356 d of age (genetic correlation = 0.60; P = 0.01). The mean CDRU increased from 90 d of age toward a peak at 180 d. Thereafter, CDRU declined and stabilized at about 1 yr of age. The mean CDRU between the groups of dogs with and without MI diverged most at 90 d of age, then was nearly stable until 180 d and gradually declined until 356 d, when the CDRU began to equalize. Metaphyseal irregularities and CDRU levels of litter were significantly correlated. Litter effect was a sig- nificant predictor of MI. The effects of litters and the genetic effects on BW and MI were correlated at most phases of the growth of the dog. Similar, but lower, correlations were found for CDRU and MI, and total ALP and MI.