---
kind: "section"
citation: "21 C.F.R. § 558.342"
title: "21"
number: "558.342"
heading: "Melengestrol."
url: "https://uscodex.org/cfr/21/558.342"
---

# §558.342. Melengestrol.

- (a) **Specifications.**
  - (1) **Dry Type A medicated articles containing 100 or 200 milligrams (mg) melengestrol acetate per pound.**
  - (2) **Liquid Type A medicated article containing 500 mg melengestrol acetate per pound.**
- (b) **Sponsor.** See sponsors in [§ 510.600(c)](/cfr/21/510.600.md?p=c) of this chapter for use as in [paragraph (e)](#e) of this section.
  - (1) **No.** 054771 for use of products described in [paragraph (a)(1)](#a-1) of this section:
  - (2) **Nos.** 016592, 051311, 054771, and 058198 for use of product described in [paragraph (a)(2)](#a-2) of this section.
- (c) **Related tolerances.** See [§ 556.380](/cfr/21/556.380.md) of this chapter.
- (d) **Special considerations.**
  - (1) Type B or C medicated feeds may be manufactured from melengestrol acetate liquid Type A articles or Type B or C medicated feeds which have a pH of 4.0 to 8.0 and bear appropriate mixing directions as follows:
    - (i) **For liquid feeds stored in recirculating tank systems—** Recirculate immediately prior to use for no less than 10 minutes, moving not less than 1 percent of the tank contents per minute from the bottom of the tank to the top. Recirculate daily as described even when not used.
    - (ii) **For liquid feeds stored in mechanical, air, or other agitation type tank systems—** Agitate immediately prior to use for not less than 10 minutes, creating a turbulence at the bottom of the tank that is visible at the top. Agitate daily as described even when not used.
  - (2) A physically stable melengestrol acetate liquid Type B or C feed will not be subject to the requirements for mixing directions prescribed in [paragraph (d)(1)](#d-1) of this section provided it has a pH of 4.0 to 8.0 and contains a suspending agent(s) sufficient to maintain a viscosity of not less than 300 centipoises per second for 3 months.
  - (3) Liquid or dry combination Type B or C medicated feeds containing melengestrol acetate and lasalocid must be labeled in accordance with [§ 558.311(d)](/cfr/21/558.311.md?p=d).
  - (4) Liquid or dry combination Type B or C medicated feeds containing melengestrol acetate and monensin must be labeled in accordance with [§ 558.355(d)](/cfr/21/558.355.md?p=d).
  - (5) Liquid combination Type B or C medicated feeds containing melengestrol acetate and tylosin must be manufactured in accordance with [§ 558.625(d)](/cfr/21/558.625.md?p=d).
  - (6) Liquid melengestrol acetate may not be mixed with oxytetracycline in a common liquid feed supplement.
- (e) **Conditions of use—**
  - (1) **Cattle.**
  - (2) Melengestrol may also be used in combination with:
    - (i) Oxytetracycline as in [§ 558.450](/cfr/21/558.450.md).
    - (ii) Ractopamine as in [§ 558.500](/cfr/21/558.500.md).
    - (iii) Tylosin as in [§ 558.625](/cfr/21/558.625.md).
    - (iv) Zilpaterol as in [§ 558.665](/cfr/21/558.665.md).

## Notes

### Amendments

[42 FR 28535, June 3, 1977]

### Authority

Authority: 21 U.S.C. 354, 360b, 360ccc, 360ccc-1, 371.

### Source

Source: 40 FR 13959, Mar. 27, 1975, unless otherwise noted.

### Amendments

[42 FR 28535, June 3, 1977]