Hormonal Growth Promotants and Farm Animal Growth Flashcards
Types of hormonal growth promotants (HGP)
• Estrogen → mimic the effects of the naturally occurring hormone estrogen
• androgenic →mimic the effects of the naturally occurring hormone testosterone
• Progentins
• combination implants
Why growth promotants are used in farm animals?
• to promote great
• to reduce greenhouse gas
• to manage the breeding cycles of heifers/cows
• to control estrus in feedlot heifers
How the HGPs are administered to the animals?
All HGPs are administered as subcutaneous implants (behind the ear), except for melengestrol acetate which supplied as a feed additive
Steroid hormones are not approved for…
Dairy cows, veal calves, pigs, or poultry
Which HGP products are approved in Canada?
ONLY APPROVED FOR BEEF
Natural
• progesterone
• estradiol - 17b
• testosterone
Synthetic
 • Melengestrol acetate
•Zeranol
• trenbolone acetate
Are hormonal growth implants safe?
Yes →
- Estrogen is synthesized by humans
- other common food for human has more estrogenic activity than beef from implanted cattle
Androgens in ruminants ( trenbolone acetate)
- 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
Estrogen in ruminants
- 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
Sex hormone: mode of action
- 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
Mode of Action of HGPs
- 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
Synovex
Synovex choice = trenbolone acetate and estradiol
Target animals are feedlot cattle
Synovex-C = for calves
Synovex-S = steers
Synovex-H = heifers
Compudose
- no withdrawal period
24mg Estradoil 12-B (with oxytetracyline)
Revalor
Revalor-S = steers (300-450kg)
Revalor-H = feedlot heifers
Revalor-G = Grass-fed cattle
Ralgro
- 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
STEER-oid
STEER-oid (20mg oestradoil benzonate and 200mg progesterone)
HEIFER-oid (20mg oestradoil benzonate and 200mg testosterone)
Finaplix
NOT AVAILABLE IN CANADA LEGALLY
Finaplix-S = 140mg trenbolone acetate for steers
Finaplix-H = 200 trenbolone acetate for heifers
Considerations to use HGP implants in cattle
- Age
- Sex
- Breed (some breeds have more aggressive impact strategies)
- Weight
- Effectiveness duration
- Some implants have withdrawals
- class of the animal
Implant response differences
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
Possible undesirable side effects of repeated HGP
- 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
Progestins
- 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
Melengestrol acetate (MGA)
- 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
MGA - Safety
- 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
