methionine: Weight gain for different methionine sources
In MaximeBSanofi/drc2:

Description Usage Format Details Source Examples

Data consist of average body weight gain of chickens being treated with one of the two methionine sources DLM and HMTBA.

1	data(methionine)

A data frame with 9 observations on the following 3 variables:

product: a factor with levels control, DLM and MHA denoting the treatments
dose: a numeric vector of methionine dose
gain: a numeric vector of average body weight gain

The dataset contains a common control measurement for the two treatments. More examples using this dataset are found under AR.2 and MM.2.

Kratzer. D. D. and Littell, R. C. (2006) Appropriate Statistical Methods to Compare Dose Responses of Methionine Sources, Poultry Science, 85, 947–954.

## Fitting model with constraint on one parameter 
met.ar.m1 <- drm(gain~dose, product, data = methionine, 
fct = AR.3(), pmodels = list(~1, ~factor(product), ~factor(product)), 
upperl = c(Inf, Inf, 1700, Inf, Inf)) 

plot(met.ar.m1, xlim=c(0,0.3), ylim=c(1450, 1800))
abline(h=1700, lty=1)

summary(met.ar.m1)