Stiftung Tierärztliche Hochschule Hannover Die ontogenetische ...

Studie II: Shift of the CoM in growing dogs
Mölsa et al., 2010; Kim et al., 2011; Voss et al., 2011) and, as this and one previous
study examining dogs between PW4 and PW15 show (Biknevicius et al., 1997), this
is true from early on in life. Therefore, in puppies and adult dogs, the forelimbs
consistently support a greater proportion of the body weight than the hindlimbs. At
the end of this study, at PW51, load distribution of the dogs studied herein was
comparable with adult individuals of the same breed (Abdelhadi et al., 2013).
Variation in how much the fore- vs. the hindlimbs support in adult dogs, however,
is related to morphological differences among breeds (i.e., the antero-posterior
distribution of body mass). Sighthounds such as Greyhounds or Borzoi show lower
vertical force ratios compared to other breeds such as Labrador Retriever,
Rhodesian Ridgeback or Rottweiler (Bertram et al., 2000; Mölsa et al., 2010; Kim et
al., 2011; Voss et al., 2011). Thus, depending on morphology, the specific position of
the whole-body CoM varies in adult dogs. Similarly, morphological variation due to
growth results in changes in the weight-supporting characteristics of fore- vs.
hindlimbs in mammals (Grand, 1977; Turnquist and Wells, 1994; Kimura, 1987;
Kimura, 2000; Grand and Barboza, 2001; Shapiro and Raichlen, 2006; Young, 2012;
this study). Both, vertical force and stance time ratios evaluated in the current study
indicate a net cranial shift of the CoM in growing dogs. This is in contrast to the
previous studies, which consistently reported a net caudal shift of the CoM and thus
a relative decrease in forelimb and conversely an increase in hindlimb loading with
age (Grand, 1977; Turnquist and Wells, 1994; Kimura, 1987; Kimura, 2000; Grand
and Barboza, 2001; Shapiro and Raichlen, 2006; Young, 2012).
At least two observations may explain the net cranial translation of the CoM in
growing dogs. First, the postural index (i.e., withers or pelvic height divided by the
sum of the segment lengths) decreases more in the hindlimbs than the forelimbs
(from 1.17 to 1.07 and 1.31 to 1.24 between PW11 and PW51, respectively; D.
Helmsmüller, unpubl. data). Therefore, similar to growing horses (Grossi and Canals,
2010), older dogs have relatively more erect hindlimbs than when they are younger.
The increasingly erect hindlimbs result in a postural change of the body that is
consistent with a net cranial translation of the CoM.
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