#### § 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) of this chapter](/on/2024-09-17/title-21/section-510.600#p-510.600(c)) for use as in [paragraph (e)](/on/2024-09-17/title-21/section-558.342#p-558.342(e)) of this section.

(c) *Related tolerances.* See [§ 556.380 of this chapter](/on/2024-09-17/title-21/section-556.380).

(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)](/on/2024-09-17/title-21/section-558.342#p-558.342(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)](/on/2024-09-17/title-21/section-558.311#p-558.311(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)](/on/2024-09-17/title-21/section-558.355#p-558.355(d)).

(5) Liquid combination Type B or C medicated feeds containing melengestrol acetate and tylosin must be manufactured in accordance with [§ 558.625(d)](/on/2024-09-17/title-21/section-558.625#p-558.625(d)).

(6) Liquid melengestrol acetate may not be mixed with oxytetracycline in a common liquid feed supplement.

(e) *Conditions of use* —

(1) *Cattle.*

| Melengestrol acetate in mg/head/day | Combination in grams/ton | Indications for use | Limitations | Sponsor |
| --- | --- | --- | --- | --- |
| (i) 0.25 to 0.5 | | Heifers fed in confinement for slaughter: For increased rate of weight gain, improved feed efficiency, and suppression of estrus (heat). | Administer 0.5 to 2.0 pounds (lb)/head/day of medicated feed containing 0.125 to 1.0 mg melengestrol acetate/lb to provide 0.25 to 0.5 mg melengestrol acetate/head/day. | 016592 054771 058198 |
| (ii) 0.5 | | Heifers intended for breeding: For suppression of estrus (heat) | Administer 0.5 to 2.0 lb/head/day of Type C feed containing 0.25 to 1.0 mg melengestrol acetate/lb to provide 0.5 mg melengestrol acetate/head/day. Do not exceed 24 days of feeding | 016592 054771 058198 |
| (iii) 0.25 to 0.5 | Lasalocid, 10 to 30 | Heifers fed in confinement for slaughter: For increased rate of weight gain, improved feed efficiency, and suppression of estrus (heat); and for control of coccidiosis caused by *Eimeria bovis* and *Eimeria zuernii* | Add at the rate of 0.5 to 2.0 lb/head/day a medicated feed (liquid or dry) containing 0.125 to 1.0 mg melengestrol acetate/lb to a feed containing 10 to 30 g of lasalocid per ton to provide 0.25 to 0.5 mg melengestrol acetate and 100 to 360 milligrams of lasalocid per head/day. See [§ 558.311(d) of this chapter](/on/2024-09-17/title-21/section-558.311#p-558.311(d)). Lasalocid as provided by No. 054771 in [§ 510.600(c) of this chapter](/on/2024-09-17/title-21/section-510.600#p-510.600(c)) | 054771, 058198 |
| (iv) 0.25 to 0.5 | Monensin, 10 to 40 | Heifers fed in confinement for slaughter: For increased rate of weight gain, improved feed efficiency, and suppression of estrus (heat); and for the prevention and control of coccidiosis due to *Eimeria bovis* and *E. zuernii* | Add at the rate of 0.5 to 2.0 lb/head/day a medicated feed (liquid or dry) containing 0.125 to 1.0 mg melengestrol acetate/lb to a feed containing 10 to 40 g of monensin per ton to provide 0.25 to 0.5 mg melengestrol acetate/head/day and 0.14 to 0.42 mg monensin/lb body weight, depending on severity of coccidiosis challenge, up to 480 mg monensin/head/day. See [§ 558.355(d) of this chapter](/on/2024-09-17/title-21/section-558.355#p-558.355(d)). Monensin as provided by No. 016592 or 058198; melengestrol acetate as provided by No. 016952, 054771, or 058198 in [§ 510.600(c) of this chapter](/on/2024-09-17/title-21/section-510.600#p-510.600(c)) | 016592 045771 058198 |

(2) Melengestrol may also be used in combination with:

(i) Oxytetracycline as in [§ 558.450](/on/2024-09-17/title-21/section-558.450).

(ii) Ractopamine as in [§ 558.500](/on/2024-09-17/title-21/section-558.500).

(iii) Tylosin as in [§ 558.625](/on/2024-09-17/title-21/section-558.625).

(iv) Zilpaterol as in [§ 558.665](/on/2024-09-17/title-21/section-558.665).

[[42 FR 28535](https://www.federalregister.gov/citation/42-FR-28535), June 3, 1977]

###### Editorial Note

#### Editorial Note:

For Federal Register citations affecting [§ 558.342](/on/2024-09-17/title-21/section-558.342), see the List of CFR Sections Affected, which appears in the Finding Aids section of the printed volume and at *[www.govinfo.gov](http://www.govinfo.gov).*