[alpaca_fibre] Fwd: [Alpacasite] Evaluating Micron Blowout
- From: Ian Watt <alpacaconsult@xxxxxxxxxxxxx>
- To: alpaca_fibre@xxxxxxxxxxxxx
- Date: Wed, 4 Feb 2004 11:18:18 -0800
I thought I would send this out for those of you who do not subscribe =20=
to the alpaca list.
It is an interesting take on micron blowout in sheep and alpaca.
Perhaps someone might care to read it and perhaps translate it into =20
more user friendly terminology as some parts of it can be pretty heavy =20=
reading?
Regards,
Ian
ps sincere thanks to Ken Madl for the report
Begin forwarded message:
> From: "Kenneth E. Madl" <kenneth.madl@xxxxxxxxxxx>
> Date: Wed Feb 4, 2004 10:33:16 US/Pacific
> To: Alpaca Discussion Forum <Alpacasite@xxxxxxxxxxxxxxx>, Australian =20=
> Alpaca List <AustAlpacas@xxxxxxxxxxxxxxx>
> Subject: [Alpacasite] Evaluating Micron Blowout
> Reply-To: Alpacasite@xxxxxxxxxxxxxxx
>
> On Wed Feb 4, 2004, Rick Horn <alpacas@xxxxxxxxxxxxx> wrote in
> "First note from the Moderator":
>
>> You don't care about sheep or goats? Delete his posts, it's a
>> simple keystroke.
>
>
> Some people don't care about sheep or goats because they don't
> believe there's a correlation between those species (or what has
> happened in those industries) and alpacas, but they would be wrong.
>
> As an example, in Volume 50 Number 3 (Spring 2002) of "Wool
> Technology and Sheep Breeding" (which describes itself as "The
> journal for the sheep and wool industry") is an article by K. L.
> Butler and B. A. McGregor titled "A Statistical Approach for
> Evaluating Micron Blowout, with Australian Alpacas as an Example".
>
> This is their Summary:
>
> "The existence of between-sheep variability in micron blowout and
> its possible causes have caused considerable discussion and
> controversy. It appears inadequate to define micron blowout as any
> change in observed micron with age. We suggest that problems of
> interpreting heritabilities of micron blowout can be resolved by
> using models of the form
>
> MFD =3D Fixed Effects (including effects involving age)
> + ai + bi =D7 T(A)
> + Random Error (with constant variance),
>
> where the symbols ai and bi are correlated, animal-specific,
> random intercept and slope effects. Australian alpacas are used as
> an example of this approach."
>
>
> It's a technical article, and one that would be perfect for "The
> Alpaca Registry Journal", if it is ever started again.
>
>
> What's interesting is their "Comparison with Australian Merino
> Sheep":
>
> "Repeatable between-age correlations for Australian alpacas (Table
> 1) are relatively similar to between-age genetic correlations that
> have been reported for Australian Merino sheep (Atkins 1990; Table
> 2). Even allowing that repeatabilities can and do include
> environmental variation of lifelong effect, as well as genetic
> effects, it would not be unreasonable to suggest that similar
> processes could be occurring with both Australian alpacas and
> Australian Merino sheep. If anything, the deviations from one of the
> genetic correlations for Australian Merino sheep are greater than
> the deviations from one of the repeatable correlations for
> Australian alpacas."
>
> The article begins with "Micron blowout has previously been
> calculated from the mean fibre diameter (MFD) of an individual
> sheep, measured at different ages, using a contrast of the MFD value
> obtained at each age (Taylor and Atkins 1992; Cottle et al. 1993,
> 1995; Hickson et al. 1995).", and then jumps into formulas.
>
> After discussing previous methods to correlate micron blowout with
> age, they say "We suggest that the term "micron blowout" be reserved
> for increases in micron with age that can be described as
> "repeatable" within a sheep, goat or camelid where "repeatable" is
> defined in a sensible way. This sensible way would appropriately be
> a combination of micron change that is due to a combination of
> genetic variation and environmental variation with lifelong effect."
>
>
> They reach some very interesting conclusions about alpacas:
>
> "Despite the large differences between properties in the MFD
> response to age, the statistical analysis of this study showed that
> these between-property differences were dwarfed by individual alpaca
> differences in micron blowout (i.e., by the effect of differences in
> the bi's on the response of MFD to age). In fact, the between-alpaca
> variation in micron blowout is, by far, the largest effect observed
> in the data. The variation in micron blowout is far greater than the
> effects of sex, breed, fleece colour, property of origin or year on
> MFD and also far greater than the variation between alpacas of MFD
> measurements at a younger age.
>
> "Calculations show that, for a typical property, an estimated 95%
> probability range for the repeatable increase in MFD for individual
> alpacas between 0.5 and 7.5 years of age is 7.5 =B1 7.5 microns. This
> implies that repeatable alpaca-to-alpaca variation is such that many
> alpacas will not increase MFD at all from a young to an old age,
> while many other alpacas will increase MFD by about 15 microns." ...
>
> "The repeatable correlation between MFD at 0.5 years of age and
> micron blowout slope is only about 0.36. This indicates that the MFD
> of alpacas at young ages is a fairly poor indicator of the degree of
> micron blowout. This repeatable correlation between age-specific MFD
> and micron-blowout slope increases to 0.94 at old ages."
>
>
> The implications for this study are that in order to develop a
> first-class fiber industry, the mean fibre diameter (MFD) of a young
> alpaca is not that important, but rather, (as Ian Watt and others
> have pointed out in the past), what is REALLY important is that it
> does not blow out with age.
>
> Ken Madl
> Aviana Farms
>
>
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