Hormonal Growth Promotants and Farm Animal Growth

Question 1

Types of hormonal growth promotants (HGP)

Answer 1

• Estrogen → mimic the effects of the naturally occurring hormone estrogen
• androgenic →mimic the effects of the naturally occurring hormone testosterone
• Progentins
• combination implants

Question 2

Why growth promotants are used in farm animals?

Answer 2

• to promote great
• to reduce greenhouse gas
• to manage the breeding cycles of heifers/cows
• to control estrus in feedlot heifers

Question 3

How the HGPs are administered to the animals?

Answer 3

All HGPs are administered as subcutaneous implants (behind the ear), except for melengestrol acetate which supplied as a feed additive

Question 4

Steroid hormones are not approved for…

Answer 4

Dairy cows, veal calves, pigs, or poultry

Question 5

Which HGP products are approved in Canada?

Answer 5

ONLY APPROVED FOR BEEF

Natural
• progesterone
• estradiol - 17b
• testosterone

Synthetic
 • Melengestrol acetate
•Zeranol
• trenbolone acetate

Question 6

Are hormonal growth implants safe?

Answer 6

Yes →
- Estrogen is synthesized by humans
- other common food for human has more estrogenic activity than beef from implanted cattle

Question 7

Androgens in ruminants ( trenbolone acetate)

Answer 7

• synthetic androgen mimics testosterone
• strongly anabolic
• weakly androgenic
• get anabolic effects without aggressive behaviour
• best combined with estrogen for additive response
• TBA implant is most effective when use in conjunction with high-energy rations. Therefore it is typically used as the “terminal” implant in the finishing phase in the feed lot

Question 8

Estrogen in ruminants

Answer 8

• ruminants are unique in that estrogens are actually anabolic
• increases average daily gain and feed efficiency
• increase in lean tissue deposition
• reduce fat and marbling

Question 9

Sex hormone: mode of action

Answer 9

• cross cell membrane
• bind to steroid receptor in cytosol
• both enter the cell nucleus
• promote DNA transcription/ mRNA production
• mRNA attaches to cytoplasmic ribosomes and transplanted by RNA polymerase
• Proteins synthesized in cytosol

Question 10

Mode of Action of HGPs

Answer 10

• estrogenic HGP work in indirect manner by stimulating to secrete GH and IGF-1
• androgenic HGP work in direct fashion by binding with muscle cell receptor to increase protein synthesis
• combination of estrogenic and androgenic HGP work via additive effects to increase growth
• Synthetic hormones increase protein synthesis by reducing the degradation of protein rather than synthesis of protein

Question 11

Synovex

Answer 11

Synovex choice = trenbolone acetate and estradiol
Target animals are feedlot cattle

Synovex-C = for calves
Synovex-S = steers
Synovex-H = heifers

Question 12

Compudose

Answer 12

• no withdrawal period
  24mg Estradoil 12-B (with oxytetracyline)

Question 13

Revalor

Answer 13

Revalor-S = steers (300-450kg)
Revalor-H = feedlot heifers
Revalor-G = Grass-fed cattle

Question 14

Ralgro

Answer 14

• Ralgro Magnum for feedlot cattle
• Can be used in calves, heifers, and steers
• non steroidal estrogenic growth promotant but acts like a steroid by binding to estrogen receptor

Question 15

STEER-oid

Answer 15

STEER-oid (20mg oestradoil benzonate and 200mg progesterone)
HEIFER-oid (20mg oestradoil benzonate and 200mg testosterone)

Question 16

Finaplix

Answer 16

NOT AVAILABLE IN CANADA LEGALLY
Finaplix-S = 140mg trenbolone acetate for steers
Finaplix-H = 200 trenbolone acetate for heifers

Question 17

Considerations to use HGP implants in cattle

Answer 17

• Age
• Sex
• Breed (some breeds have more aggressive impact strategies)
• Weight
• Effectiveness duration
• Some implants have withdrawals
• class of the animal

Question 18

Implant response differences

Answer 18

Sex: steers > Heifers > Bulls
Maturity: Growing > Finishing > Suckling
Paradox:
- greatest response observed in TBA in helifers
- greatest response observed with estrogen in steers
- implants are not approved for use in bulls (implants will reduce testicular development, semen quality)
- Do not implant a bull calf until its castrated

Question 19

Possible undesirable side effects of repeated HGP

Answer 19

• aggressive implant strategy increase the risk of lower quality grade
• Markets that demand leaner beef and more retail product are the best met by a more aggressive implant strategy
• high quality markets demand either less aggressive implant stategies or longer feeding periods and heavier weights
• reproductive processes including signs of estrus, vaginal or rectal prolapse, development of the udder in heifers
• Reduce marbling and tenderness
• Increase DFD
• heavy hide weight

Question 20

Progestins

Answer 20

• progesterone, MGA
• increase growth rate and feed efficiency of cycling heifers by reducing estrus behaviour
• increases half life of estrogens when administered in combination
• it can increase growth rate by increasing protein accretion in the ruminant without increasing aggressive behaviour

Question 21

Melengestrol acetate (MGA)

Answer 21

• a synthetic progesterone
• administered in feed (0.4mg/head/day)
• Improves ADG and Feed efficiency
• approved for heifers only (>181 kg) → use only in heifers being fed for slaughter
• can also be used to synchronize heifers
• withdrawal 48h prior to slaughter
• do not use in dairy cattle
• Do not feed to heifers with other hormone drugs

Question 22

MGA - Safety

Answer 22

• Does not increase cancer risk
• protects against endometrial hyperplasia and endometrial carcinoma in estrogen-treated post-menopausal women
• does not increase risk of circulatory disease
• Does not impair adrenal function
• Has no immunological effects
• Causes no important change in liver function
• Does not harm fertility, pregnancy, or lactation in treated women
• Does not harm child development in treated lactating women
• MGA accumulated in liver and fat tissues