Bovine Breeding management

Question 1

Dairy calves reproduction

Answer 1

Year-round for constant income stream and milk production

Question 2

Life cycle of the dairy cow

Answer 2

Birth → milk fed @ 1-60d → Breed @ 12 m → Calving at 21-23m (2y)
305d lactation → bred 60d post calving → 9m gestation → 60d dry period

Question 3

Breeding management for dairy cattle

Answer 3

Females raised as replacements for milk
Male calves raised for beef

Question 4

Breeding management for beef cattle

Answer 4

Primary source of income for calf crop
Some offspring raised as replacements

Question 5

1 producer reported reason for cows leaving the herd

Answer 5

Infertility (poor production then clinical mastitis)

Question 6

Bovine estrous cycle

Answer 6

Begins with OV (D21 of previous cycle is d0 of next cycle)
OV 24-30 hrs after onset of estrus (LH surge)

Question 7

What does estrus behavior depend on?

Answer 7

↓ in P4 and ↑ in E2

Question 8

Transition from diestrus to estrus

Answer 8

P4 declines to remove neg feedback on GnRH (LH ↑)
↑ estrodiol from DF = ↑ pulse frequency of LH (OV)

Question 9

Standing estrus

Answer 9

Primary and most definitive sign of estrus in cattle
Coincides with LH surge, OV 28 hrs later

Question 10

Secondary signs of estrus

Answer 10

Tail chalk
↑ activity and vocalization
Mucus discharge
Mounting and dismounting

Question 11

Benefits of artificial insemination

Answer 11

↑ genetic diversity of the herd
Speeds up genetic improvement of the herd
Safer than housing bulls on site
More accurate insemination/ calving dates
Cost savings

Question 12

Time of AI

Answer 12

Estrus commences with LH peak
AI 12 hrs after observation of first mount

Question 13

What is the goal of AI?

Answer 13

To inseminate before OV
Sperm requires 6-8 hrs for capacitation

Question 14

AI breeding too early

Answer 14

Nonviable sperm by the time of OV

Question 15

AI breeding too late

Answer 15

Nonviable oocyte by the time of capacitation of sperm

Question 16

Estrus (heat) detection rate

Answer 16

% of cows detected in estrus / eligible to be in estrus

Question 17

Conception rate

Answer 17

% of cows pregnant / cows inseminated

Question 18

Pregnancy rate

Answer 18

% of all eligible cows dx pregnant during estrus cycle or synchronization breeding period
PR = HD x CR

Question 19

Estrus synchronization

Answer 19

Injections of GnRH or PGF2a @ time of OV
Management tool
Reduces labor associated with estrus detection

Question 20

When is Estrus synchronization possible?

Answer 20

If cows are cycling
P4 determines cycle length and estrus behavior

Question 21

Ovsynch protocol

Answer 21

Timed artificial insemination (TAI)
Initial injection of GnRH = OV of dominant follicle
Enables insemination @ a predetermined period after parturition based on timed OV

Question 22

Importance of GnRH synchronization

Answer 22

GnRH induce LH surge needed for OV (reset cycle)

Question 23

Cow response to Ovsynch

Answer 23

OV first GnRH greater response
Lack of synchronization = poor fertility in program

Question 24

Use of bulls with estrus synchronization

Answer 24

PGF @ bull turnout or PGF 5d after bull turnout
Bull to female ration 1:15 to 1:25
Small pasture or lot, BSE

Question 25

Pregnancy Dx in dairy herds

Answer 25

Routine herd visits
Early preg dx using US
Decisions for open cows to allow re-insemination

Question 26

Pregnancy dx for beef herds

Answer 26

Whole herd, once annually
Coincides with weaning of calves

Question 27

Challenges with beef programs

Answer 27

Cows aren’t cycling
Failure of head detection after PGF
Failure of protocol compliance
Cows/ heifers not @ appropriate stage of cycle @ injections

Question 28

Why wouldn’t cows be cycling?

Answer 28

Starting too early postpartum
Poor nutrition = neg energy balance