1. First make sure that your i.p injection is accurately done with no possible leak to the gut. This is just to ensure about the correctness of the procedure.

2. Make sure that Rotenone concentration is maintained in an acceptable range in your solution, which I think is normally something around 10 nm to 1 μm. But you would need to make sure about the right concentration.

3. Then, alternating to lower doses of Rotenone may be helpful, though most papers refer to even higher doses per kg (somewhere around 2.75-3 mg/kg/day). Try the low dose (1.5 mg/kg), and then the moderate dose (2.5 mg/kg).

Mature male rats with normal weight treated with 2-3 mg/kg i.p Rotenone typically should stay alive even with aggravating symptoms up to 4 weeks! But please note that mortality occurs in Rotenone-induced PD.

4. Examine a rather different approach such as injecting animals with around 2.5 mg/kg of i.p Rotenone in 48 hours, instead of the typical 24 hours. This depends on the type, timing and the amount of the pre-treatment you use in your experiment.

I should add that Rotenone injection typically develops bradykinesia, postural instability, and/or rigidity in a significant and progressive manner. If you think that your animal mortality rate remains the main obstacle, you may want to consider other methods to induce PD in your rats.

Examples of other ways to induce PD in rats:

a) Deguelin at around 6 mg/kg/day (which apparently is the closest chemical agent to Rotenone in terms of similarity of effects).

b) 6-hydroxydopamine (6-OHDA)-induced PD model

c) Lipopolysaccharide (LPS)-induced PD model

d) MPTP (1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine) induced PD model

e) S-adenosyl-l-methionine (SAM)-induced PD-like neuropathology

f) and I have seen a few papers using a specific virus (for example, Japanese encephalitis virus or JEV) to induce PD-like neuropathology.

You may get more information by looking for these methods in related papers.

I definitely agree with trying relatively lower doses and spacing out injections like what was suggested. If this does not lower to an acceptable mortality rate, you may try another compound,

MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine), that works similarly to rotenone.

Article Protocol for the MPTP mouse model of Parkinson's disease

Have you had any autopsy done on the animals to determine the cause of mortality? It may be revealing to see if there was a direct toxic effect on intraperitoneal tissues.

Good luck!