Midterm 3 - Lecture 21

Question 1

7 advantages of controlling the estrous cycle in livestock

Answer 1

1. Saves time and labour in detecting estrus for AI
2. Group management of breeding animals
3. Group management of gestating animals and “batch” parturition
4. Avoid losses of young by providing care and supervision
5. Uniform groups of young
6. Disease control
7. Reproductive Technologies

Question 2

What are 3 ways that the estrous cycle can be hormonally manipulated?

Answer 2

1. Prolong the Luteal Phase with Progestins
2. Shorten the Luteal Phase with PGF2a
3. Control Follicular Development & Ovulation

Question 3

What are 3 options for prolonging the luteal phase with progestins?

Answer 3

1. CIDR - Controlled Internal Drug Release Device
2. PRID - Progesterone Releasing Internal Device
3. Melengesterol Acetate (MGA) - oral progestin

Question 4

How is plasma progesterone absorption profile affected following CIDR insertion?

Answer 4

• plasma P4 increases

Question 5

What is the protocol for using CIDR?

Answer 5

• 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

Question 6

What is the protocol for using MGA?

Answer 6

• 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

Question 7

What 2 ways of prolonging the luteal cycle are used in cows?

Answer 7

1. CIDR
2. MGA

Question 8

What is the protocol for using oral progestin altrenogest (aka the way to prolong luteal phase in pigs and horse)?

Answer 8

• 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

Question 9

How is the luteal phase shortened?

Answer 9

• administer PGF2a or analogue to cause the CL to regress; only effective if administered after 5 days into estrus

Question 10

What is the common protocol for using PG (aka an analogue of PGF2a)?

Answer 10

• 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

Question 11

What is meant by ‘sows experience strong lactational anestrous’?

Answer 11

• 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

Question 12

How is parturition induced in sows?

Answer 12

• 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

Question 13

Equine - Seasonality

Answer 13

• 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

Question 14

When is an artificial photoperiod induced for a mare?

Answer 14

• Starts Dec 1st
• 16 light: 8 dark
• ovulation occurs 35-60 days after start of exposure
• breeding season starts around Feb. 15th

Question 15

Light Masks

Answer 15

• new technology
• results comparable to conventional barn lighting approach
• tricks hypothalamus into thinking it is spring by stimulating the visual system