Midterm 3 - Lecture 21 Flashcards
7 advantages of controlling the estrous cycle in livestock
- Saves time and labour in detecting estrus for AI
- Group management of breeding animals
- Group management of gestating animals and “batch” parturition
- Avoid losses of young by providing care and supervision
- Uniform groups of young
- Disease control
- Reproductive Technologies
What are 3 ways that the estrous cycle can be hormonally manipulated?
- Prolong the Luteal Phase with Progestins
- Shorten the Luteal Phase with PGF2a
- Control Follicular Development & Ovulation
What are 3 options for prolonging the luteal phase with progestins?
- CIDR - Controlled Internal Drug Release Device
- PRID - Progesterone Releasing Internal Device
- Melengesterol Acetate (MGA) - oral progestin
How is plasma progesterone absorption profile affected following CIDR insertion?
- plasma P4 increases
What is the protocol for using CIDR?
- CIDR inserted and removed after 7-8 days
- 1 day prior to CIDR removal PGF2a injection causes CL to regress - if present
- cows/heifers will come into heat over the next few days
What is the protocol for using MGA?
- feed MGA for 14 days
- CL regresses while oral progestin maintains anestrus
- 1st estrus after MGA withdrawal animal is less fertile so breeding is skipped
- bull introduced 14 days after MGA withdrawal to breed on 2nd estrus
What 2 ways of prolonging the luteal cycle are used in cows?
- CIDR
- MGA
What is the protocol for using oral progestin altrenogest (aka the way to prolong luteal phase in pigs and horse)?
- Altrenogest added to feed for 14-18 days
- CL regresses while oral progestin maintains Luteal phase
- Female comes into heat 3-7 days after withdrawal and can be bred
How is the luteal phase shortened?
- administer PGF2a or analogue to cause the CL to regress; only effective if administered after 5 days into estrus
What is the common protocol for using PG (aka an analogue of PGF2a)?
- 1st injection with PG
- 2nd injection with PG 14 days later
- by doing this twice, you should be able to catch all of the herd (animals that don’t respond on the 1st injection will be caught by the second)
- inevitably wasting some produce by injecting on day 14 bc some animals will already be undergoing luteolysis on their own
What is meant by ‘sows experience strong lactational anestrous’?
- a sow will not return to estrus while nursing a full litter
- following an appropriate lactation period (3-4 weeks) removal of the litter will result in a return to estrus 4-7 days later
How is parturition induced in sows?
- administer PGF2a (or analogue) after 111 days of gestation; sows farrow ~8-24 hrs later
- allows for better use of labour to supervise farrowing
- creates batches to synchronized sows at weaning that will come into estrus together
Equine - Seasonality
- seasonal polyestrous (long day breeders)
- 90% of mares are seasonal
- in the Northern Hemisphere:
Cyclic: april - sept
Transition to anestrus: oct-dec
Deep anestrus: jan-feb
Transition to cyclicity: mar-april
When is an artificial photoperiod induced for a mare?
- Starts Dec 1st
- 16 light: 8 dark
- ovulation occurs 35-60 days after start of exposure
- breeding season starts around Feb. 15th
Light Masks
- new technology
- results comparable to conventional barn lighting approach
- tricks hypothalamus into thinking it is spring by stimulating the visual system
