Estrous Sync/ Induction in Cattle

Question 1

What is the average age that a heifer will reach puberty?

Answer 1

11 months and 200kg+ of BW

Question 2

What are the 3 factors that affect the onset of puberty in cattle?

Answer 2

1) Nutrition: need to meet all nutritional requirements and ensure ideal BCS
2) Genetics: dairy breeds will show estrus at lower weights at slightly younger ages compared to beef. Beef breeds also need to be heavier (300-325kg)
3) Social Cues: the presence of a bull can advance the time of puberty- likely due to pheromones

Question 3

What age and weight should a Friesian (dairy breed) be at, for her first breeding?

Answer 3

Breed at 13-15 months, when she reaches 300kg+

note: same as a beef heifer

Question 4

What age and weight should a Hereford (beef breed) be at, for her first breeding?

Answer 4

Breed at 13-15 months, when she reaches 300kg+

note: same as a dairy heifer

Question 5

What age and weight should a Continental Beef Cross be at, for her first breeding?

Answer 5

Breed at 13-15 months, when she reaches 330kg+

note: need to be 30kg more than the Friesians and Herefords

Question 6

When should a cow be returning to estrus postpartum?

Answer 6

By day 42 (week 6) after parturition

Question 7

What are the 2 types of Anestrus?

Answer 7

1) Real Anestrus: a cow doesn’t show heat, can happen for several reasons
2) Apparent Anestrus: the cow is showing estrus but we don’t detect it or see it for some reason

Question 8

What are the 3 main reasons why a cow will be in Real Anestrus?

Answer 8

1) Failure of the Dominant Follicle to ovulate
2) Dominant Follicle forms a cyst
3) Prolonged CL maintenance

Question 9

What can be done if a cow is in Real Anestrus due to the failure of the dominant follicle to ovulate?

Answer 9

1) Insert a progesterone device into the vagina of the cow for 7-9 days

2) After this, you can do one of the following:
- Nothing
- Give eCG: because it has FSH activity and some LH activity it will encourage the DF to secrete enough estradiol leading to a surge. eCG may cause twins which can be a problem
- Give Estradiol Benzoate 24 hours after the IV device is removed: Estradiol will cause a surge of LH once progesterone has fallen

Question 10

What can be done if a cow is in Real Anestrus due to the Dominant Follicle forming a cyst?

Answer 10

1) Do nothing and allow the follicular cyst to correct itself

2) Luteinize the cyst: Give a single injection of LH, hCG or GnRH
- 7 days later, when the structure has completely luteinized, give PGF2alpha to regress it

3) Ovulate the follicle: place a progesterone device for 9-12 days, this will reduce the LH pulses
- Remove the device and 2-3 days later, estrus and ovulation will follow

Question 11

What can be done if a cow is in Real Anestrus due to prolonged CL maintenance?

Answer 11

1) Give PGF2alpha, the cow should come into estrus within the next 5 days
note: This happens when the cow has ovulated, a CL has formed, but for some reason the prostaglandin is blocked which means the CL won’t regress

Question 12

What is the normal duration of estrus in a cow?

Answer 12

Around 8 hours (this is very short)

note: 25% of cows are considered to have a low-intensity estrus, thus 1/4 of them don’t show signs of estrus

Question 13

What are the aids to good heat detection in cattle?

Answer 13

1) An active bull: this will always be the best detector
2) A stockperson with a keen/ skilled eye: this will be the second-best option

3) Kamar Heat Detectors: tube of paint placed on the back of a cow
4) Estrotect Cards: change colour when a cow has been mounted
5) Vasectomized Bull with a chin ball: very good but have to refill the paint reservoir
6) Heat watch mounted on tail head
7) Activity monitor: Dairy Master or Heat Time

Question 14

What is the definition of sub-estrus?

Answer 14

When the cow is in estrus but shows fewer estrus behaviours

Question 15

Why might a cow be in sub-estrus?

Answer 15

• Feeding and Milking
• Lameness and slippery floors
• Space for a sexual group to interact
• Stressors and disease

Question 16

Why do we Synchronize estrus in cattle? (3)

Answer 16

1) Reduce the problems of heat detection: theoretically, all the cows should be coming into heat within a tight window, this means less time is spent on monitoring and less labour
2) Shorten the breeding season, leads to a compact calving period
3) Allows us to use AI on heifers and part of the dairy herd

Question 17

What are the 3 main strategies of syncing estrus in cattle?

Answer 17

1) Induce premature CL regression through the use of PGF2alpha, If they all regress together then they should theoretically come into heat together
2) Manipulate the follicular wave population with GnRH injection, then use PGF2alpha and sync Ovulation (OvSynch, Pre-Synch, and Double Ovsynch)
3) Administer progesterone/ progestogens to regulate the time of ovulation with an intra-vaginal device

Question 18

What considerations should be taken into account when choosing an estrus synchronization technique?

Answer 18

• The goals of the farmer and their willingness to monitor estrus
• The type of animal (Heifer vs Dairy cow vs Beef cow)
• If the animal is cyclic or non-cyclic: recall that a cow doesn’t immediately cycle after parturition
• The source of the semen

Question 19

What estrus synchronization technique is used in Heifers?

Answer 19

1) 2 injections of PGF2alpha, given 11 days apart

2) Day 0: GnRH injection, insert P4 device for 7 days
Day 7: Give PGF2alpha injection and Remove P4 device
56 hours later: AI

Question 20

What estrus synchronization technique is used in Post-partum Dairy Cows?

Answer 20

1) Give a single injection of PGF2alpha, wait for signs of estrus with the use of tail paint
2) Progesterone tx in cyclic cows, or progesterone tx + eCG in anestrus cows
3) Injection of PGF2alpha to cattle with a prolonged luteal phase
4) Give progesterone, or GnRH + PGF to cattle with follicular cysts

Question 21

What estrus synchronization technique is used in Post-partum Beef Cows?

Answer 21

1) Day 0: GnRH injection, insert P4 device for 7 days
Day 7: Give PGF2alpha injection and Remove P4 device
56 hours later: AI