I, for one, have no idea what "relative to turnout" means in your sentence, consequently I do not know what exactly you're asking.

Week is given relative to the turnout date to pasture. Turnout is an expression in dairy farming.

My question is if at/in week 21 to 26 for all genotypes will be understood, i.e. if the minimum odds for the genotypes are in week 21 to 26 (not all in the same week), instead of giving the week for each of the genotypes.

Blick auch nicht ganz durch. Allgemein: Ich würde die präzisere, ausführliche Form wählen. Nur dazu, zum besseren Überblick, den Satz in 2 oder gar 3 Sätze aufspalten. - Wenn der Bericht so weitergeht, müsste man allerdings gucken, ob man, wenn die Ergebnisse deutlich sind, diese mal tabellarisch darstellt, um die Bezüge der Werte klarer zu machen.

I'd say in weeks 21 to 26

@3: Dieser Satz soll den quadratischen Zeiteffekt erläutern, und so kurz und präzise wie möglich wurde es verlangt. Die präzisere, ausführlichere Form wäre ja die Aufzählung mit "respectively", dies wollte ich umgehen, da für zwei der Genotypen in derselben Woche die minimalsten odds geschätzt wurden, und ich nicht weiss, ob man dann die Wochen den Genotypen zuordnen kann.

Der Knackpunkt ist für mich, wie in #2 ausgeführt, ob mit in weeks 21 to 26 for all genotypes klar ist, dass die minimal odds der 4 Genotypen sich im Zeitraum von 21 bis 26 nach dem Turnout (Weidebeginn) bewegen (je nach Genotyp in einer anderen Woche).

ja wuerde ich sagen - schliesslich steht dort doch for ALL.

Genau das ALL ist vermutlich der eigentliche Knackpunkt: "for all gentoypes" könnte ja auch bedeuten für alle Genotype im Sinne von: jeder Genotyp hätte Minima (plural) in dem besagten Zeitraum

I may have mentioned this before, but if you want people to bother to read and understand your text, you really need to write in shorter sentences.

How about:
"The risk of lameness or gait abnormalities decreased with time on pasture. For all genotypes, fitted minimum odds against lameness or gait abnormalities were found between weeks 21 to 26 from turnout (week 21 for CHBS and CHHF, week 24 for NZHF, and week 26 for CHRHxSi). The risk then increased slightly for the rest of the observation period (quadratic effect of week)."
KISS

Thanks for your ideas.
Fitted values are estimated by the statistical model, so I would skip the verb "found".
The quadratic effect not only refers to the increase in the end, that's an impression one might get with your sentences. To be short and precise enough, I tried to avoid giving the weeks for each of the genotypes. That's all my question was about.
The text also has figures, which helps the readers to understand the text.

Ok - it wasn't at all clear from your original mammoth sentence. Even with figures, people aren't going to spend ages trying to work out what you mean.
Which verb would you use for a statistical model?

"The risk of lameness or gait abnormalities decreased with time on pasture. For all genotypes, fitted minimum odds against lameness or gait abnormalities occurred between weeks 21 to 26 from turnout, with the risk increasing slightly for the rest of the observation period (quadratic effect of week)."

>What verb would you use for a statistical model?

Found would be ok, but as I wrote fitted minimum odds (fitted by the model), I'd simply say ...were in weeks 21 to 26 or between weeks 21 to 26 relative to turnout, if the latter was preferable with for all genotypes (?)