1. Growth Modifiers An S 426 Spring 2007

2. Growth modifiers General types General types 1.Antibiotics – chlortetracycline (Aureomycin), oxytetracycline (Terramycin) 2.Growth promotants – estrogen (Compudose), estrogen-like (Ralgro) 3.Feed enhancers – monensin (Rumensin), lasaloacid (Bovatec), ractopamine hydrochloride (Optaflexx)  -adrenergic agonist

3. Growth modifiers Growth promotants Growth promotants Mode of action: 1.Evidence they change hormone status of animal. 2.Probably function at site of hormone production and at the receptor sites of target cells. 3.Thought to affect mechanism which causes increased nitrogen retention in muscle. 4.Thought to “partition” nutrients into the more desirable, higher valued components (i.e. muscle) and away from the less desirable components of the carcass (i.e. fat) causing an apparent shift in the lean tissue growth.

4. Growth modifiers Growth promotants Growth promotants Mode of action: 5.Exogenous estrogenic promotants are thought to enhance protein gain through increased production of growth hormone, insulin and insulin-like growth factors. 6.Androgenic substances are thought to increase muscle growth by inhibiting the release of hormones (e.g. glucocorticoids) which cause degradation of muscle; this results in net shift in the partition of nutrients which is manifested by faster relative rates of muscle growth.

5. Growth modifiers Characteristics: Characteristics: –Implants approved for insertion Most will be absorbed –No withdrawal time –Cost per implant will range from Effects on performance: 1.5. 2.6. 3.7. 4.

6. Growth modifiers Characteristics: Characteristics: –Strategies for utilization: –Melengesterol acetate (MGA) Feed additive for suppressing heat in heifers – Feed additive for suppressing heat in heifers – Similar effects on performance Similar effects on performance Effective dose = Effective dose = Cost = Cost =

7. Growth modifiers Characteristics: Characteristics: –Melengesterol acetate (MGA) Other uses of MGA: Other uses of MGA:1.2. MGA / Lutalyse 5 ml injection of Lutalyse will cause most heifers less than 100 days pregnant to abort within 35 days (most within 14 days) Heifers can be started on MGA 7 to 10 days following Lutalyse injection

8. Growth modifiers Feed enhancers Feed enhancers –Mode of action: Increases feed conversion by Summary by Elanco: Rumensin Percent VFAs (g/T)AceticPropionicButyric 052389 3049437

9. Growth modifiers Feed enhancers Feed enhancers Considering that: –63% of energy from acetic acid is used for maintenance and production –100% of energy from propionic acid is used for maintenance and production –75% of energy from butyric acid is used for maintenance and production

10. Growth modifiers Feed enhancers Feed enhancers Study by Dr. Gill, Ok. St. Un. Reason high silage diet showed greater improvement in feed efficiency attributed to lower propionic acid level initially SilageRumensin Percent VFAs ADGFeedFeedPercent Level(g/T)AceticPropionicButyricConsum.Conver.Improve. 30 % 048.5539.5511.953.3118.775.69 5.66 3046.5045.707.853.2717.885.46 75 % 061.6024.7013.702.5218.517.40 7.74 3054.7533.7511.552.4917.086.82

11. Growth modifiers Characteristics: Characteristics: –Effective dose Rumensin: 150 mg/hd/day for less than 200 mg/hd/day for 330 mg/hd/day for Bovatec: 100-360 mg/hd/day Optaflexx: Rumensin may reduce feed intake during adaptation period May start cattle on

12. Growth modifiers Characteristics: Characteristics: –No withdrawal time Rumensin fatal to –Costs: Rumensin – Bovatec – Optaflexx –

13. Growth modifiers Effects on performance: Effects on performance: 1.5. 2.6. 3.7. 4. Strategies for utilization: Rumensin may be fed with Tylosin (rumensin 10-30 g/T + Tylosin 10g/T) Some research suggests feeding Rumensin and Bovatec on alternate days or weeks to

14. Growth modifiers Buller – steer syndrome Buller – steer syndrome Abnormal sexual behavior observed among steers Abnormal sexual behavior observed among steers Recipient of repeat mountings is referred to as a buller steer Recipient of repeat mountings is referred to as a buller steer Results in:

15. Growth modifiers Buller – steer syndrome Buller – steer syndrome Kansas survey indicates 2.2% of all steers on feed removed from pens because of this condition Represented a minimum loss of Cause: Chemistry: plasma contains more total estrogens possibly as a result of stress and growth stimulants – thus estrogen may account for a pheromone secretion partially responsible for the buller syndrome.