Growth promotants and feed enhancers

AnS 426

Growth Modifiers Two broad groups

–Agents that alter the digestive process

–Agents that modify the way the animal uses or partitions nutrients for growth

Growth modifiers General types

1. Antibiotic growth promoters2. Ionophores3. Implants4. -adrenergic agonist5. melengestrol acetate (MGA)

Antibiotic growth promoters Any medicine that destroys or inhibits

bacteria and is administered at a low, subtherapeutic dose

Main antibiotics added to cattle feed– Chlortetracycline – Oxytetracycline– Tylosin

3 to 5 % improvement in gain and FE No withdraw if fed at subtherapeutic dose

Antibiotics fed to finishing cattle for the control of liver abscesses

When fed high concentration rations, cattle that are borderline on subacute acidosis and have a few small liver abscesses gain faster and more efficiently than cattle that are not stressed and have no liver abscesses. However, managing to allow a slight amount of acidosis is difficult.

Feed enhancers

Ionophores– monensin (Rumensin)– lasaloacid (Bovatec)

Improve feed conversion– Increase efficiency of bacterial

protein and energy metabolism– Can also reduce incidence of

digestive upsets

Growth modifiers Feed enhancers

Study by Dr. Gill, OSU

Reason high silage diet showed greater improvement in feed

efficiency attributed to lower propionic acid level initially

Silage

Rumensin

Percent VFAs ADG

Feed Feed Percent

Level (g/T) Acetic

Propionic

Butyric

Consum.

Conver.

Improve.

30 % 0 48.55

39.55 11.95 3.31

18.77 5.69

5.6630 46.5

045.70 7.85 3.2

717.88 5.46

75 % 0 61.60

24.70 13.70 2.52

18.51 7.40

7.7430 54.7

533.75 11.55 2.4

917.08 6.82

VFA

Why dose changing the VFA profile affect performance:

– 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

Growth modifiers

Effective doseRumensin:

150 to 330 mg/hd/day

Bovatec:100 to 360 mg/hd/day

NO withdraw period The effects of ionophores and growth

promoting implants are additive

Protein “sparing” Ionospheres decrease the breakdown

of feed protein and thus increase bypass protein that reaches the small intestine

This has little effect on performance of feedlot cattle on high-grain diets, but it is important in growing cattle on high-roughage diets

The protein sparing effect on performance is maximized when natural protein is fed below the animals requirement

Rumensin Can be fed with tylosin or MGAFinishing Cattle

– 1 to 3 % improvement in daily gain– 6 to 8 % improvement in feed efficiency

Growing Cattle– 5 to 15 % improvement in daily gain– 8 to 12 % improvement in feed efficiency

Growing cattle on pasture– Provide in supplement or free choice mineral– Can supplement 300-400 mg/hd every other

day

Bovatec Not cleared to be fed with antibiotics or MGA

Finishing cattle– 4 to 6 % improvement in daily gain– 6 to 8 % improvement in feed efficiency

Growing cattle– 5 to 15 % improvement in daily gain– 8 to 12 % improvement in feed efficiency

Use of Ionophores in transition to finishing diet Cattle started on feed without

ionophores– more erratic feed intake patterns– more digestive problems

Use of Ionophores in transition to finishing diet Rumensin

– Feeding 100 mg/hd/d during the step-up period and then switching to 200-300

improves daily gain, feed intake, and feed efficiency compared to starting cattle on 200 -300 mg/hd/d

Bovatec – The response to stepping-up Bovatec??

Less?…Bovatec does not reduce intake as much as Rumensin early in the feeding period

Implants General types

1. Estrogen based (estradiol, zeranol, and progestrone)

2. Androgens (testosterone and trenbolone acetate or TBA)

3. Combination of estrogen and androgens

Implants No withdraw time Cost usually between $1-3 Increase ADG 5 to 30% Increase feed conversion 6 to

16%

How to Implant

1) Load Implant Gun with implant cartridge

2) Insert needle between skin and cartilage in middle third of the ear

3) Pull trigger and retract needle4) Check implant site with thumb5) Disinfect needle

1) Load Implant Gun with implant cartridge

2) Insert needle between skin and cartilage in middle third of the ear

3) Pull trigger and retract needle

4) Check implant site with thumb

5) Disinfect needle

Implants

Mode of action:1. Exogenous estrogenic promotants are thought

to enhance protein gain through increased production of growth hormone, insulin and insulin-like growth factors.

2. 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.

How Implants Work

MUSCLE

Pituitary

Protein synthesis

Protein breakdown

Growth hormone

ESTROGENS

ANDROGENS

X

Beta agonists

Implants and -adrenergic agonists

Mode of action: “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.

-adrenergic agonist

ractopamine hydrochloride (optaflexx)Feed during the last 28 to 42 days of the finishing period150-300 mg/hd/d and no withdraw

zilpaterol hydrochloride (zilmax) Feed during the last 20 to 40 days of the finishing period 60-90 mg/hd/d and has a 3 d withdraw

-adrenergic agonist Structurally similar to

catecholamines and other compounds that bind to the beta-adrenergic receptor

Agonist: Able to bind to receptor and elicit response

beta-agonists works via the β-Adrenergic Receptor

“Repartitioning” effects are due to stimulation of lipolysis and changes in muscle protein metabolism

Why do we only feed - agonists at the end of finishing? Market cattle become less

efficient during the last month of the finishing period, because the animal is depositing less muscle and more fat.

Chronic exposure to a ligand can cause desensitization of the receptor due to uncoupling or down-regulation of receptor

-adrenergic agonist

Optaflexx:Rumensin may reduce feed

intake during adaptation period

Melengestrol acetate (MGA) Similar to progesterone Suppresses estrus of intact

heifers Reduces injuries and energy loss

from riding and chasing– 3 to 7 % improves gain and feed

efficiency Effective dose 0.25-0.5 mg/hd/d Cost about 1¢/da