25-26. breeding management of cattle + estrous cycle manipulation

describe the reproductive life cycle of the cow

1. birth

2. puberty

3. VWP 1 (2-5 months)

4. breeding / conception — first calving

   • 21-24 months of age

5. calving

6. VWP

   • in general, 50-80d post-calving

7. breeding(s) / conception-gestation-calving

repeat as often as possible (every 12-14 mos.)

natural breeding — problems with too many males

• purchase cost

• feed / management costs

• fighting — inefficiency, injury, facility damage

natural breeding — problems with too few males

• overuse — injury, loss of libido, weight loss

• open females

• delay in conception

• unrealistic reliance on performance of individual bull

  • BSE extremely accurate in determining non-fertile bulls but is limited in its ability to pinpoint bulls with low fertility

bull:cow ratio (stocking rate)

• mature bull (>2 yrs old): 1 bull for 20-30 cows / breeding season

• young bull (<2 yrs old):

  • 1 bull for 15-20 cows / breeding season

  • or 1 cow per month of age (e.g. 15 cows for one 15 month old bull)

• monitor & adjust as necessary

advantages of artificial insemination

• superior genetics

  • milk production, conformation, calving ease, fertility

• farm safety

• sex semen

• consistent fertility

• disease control

• economy of scale

disadvantages of artificial insemination

management plays a disproportionately large role in determining success of AI program for dairy herds, and management is complicated

what are two keys to a successful AI breeding program (assuming quality semen)?

1. heat (estrus) detection

   • AI submission rates (heat detection rate)

   • accuracy

2. technical performance

   • semen handling

   • AI timing & technique

what defines a cow in estrus?

standing to be mounted by a male or female

factors limiting heat detection

• chronic pain / lameness

• social issues (remixing)

• environmental issues (flooring, heat stress, stocking rate, open access to sexually active group)

• metabolic issues related to high milk production

  • ↑ dry matter intake, ↑ hepatic blood flow, ↑ metabolism of steroid hormones → ↓ estrus duration

estrus detection aids

• mount detectors

  • tail chalk, estrotect, kamar

• activity monitors

• gomerized or androgenized animals

• progesterone assay

• hormonal manipulation of the cycle to increase size of sexually active group (# of cows in estrus)

  • prostaglandin-F2α can be used to synchronize estrus

most common causes of estrus detection problems

• people

• transition period problems

• facilities

• lameness

• milk yield

• heat stress

estrus detection problems — what to look for

• stocking density of pens

• personnel & time available

• methods of heat detection

• BCS changes from calving to 30 & 60 DIM

• cyclicity status

  • ultrasound or blood (progesterone)

• incidence of disease

• early lactation performance

how to assess estrus detection accuracy

• progesterone assay

  • cows in estrus should have ↓ P4

• ↓ % of cows with short inter-service intervals

  • high proportion of cows re-inseminated <18 d after prev. insemination indicates problem with accuracy

• pregnancy / AI (P / AI or conception rate)

where should semen be placed?

uterine body (past cervix)

• cervical deposition will result in retrograde loss of sperm

ways to improve AI management

• use professional trained technicians

• transition cow management (nutrition, bunk space, minimize pen moves)

• minimize impact of heat stress

• improve AI service rate (estrus detection)

what is a voluntary waiting period?

• planned length of time set aside between calving & onset of efforts to inseminate cows; determined by the producer

• in general, 50-80 days post-calving (days in milk)

estrus / heat detection rate (EDR)

• percent of eligible cows that are inseminated in one or more 21d periods

  • cow is classified as eligible if she has passed VWP, is not pregnant, and is not classified as a reproductive cull

• = number of cows detected in estrus or inseminated / number of eligible cows to be in estrus

  • evaluated at 21d intervals

• aka service, submission, or insemination rate

pregnancy per artificial insemination (P/AI)

• aka conception rate (CR)

• = number of pregnant cows / number of inseminated cows

21 day pregnancy rate

• percentage of eligible cows that became pregnant within a given timeframe

• = number of pregnant cows / number of eligible cows to become pregnant

  • typically evaluated at 21d intervals

goals for EDR / service or submission rate

≥ 65%

goals for 1st service P/AI or conception rate

45-55%

goals for 21-d pregnancy rate

≥ 30%

when is the optimal insemination time?

12-16 hours after onset of estrus (first time cow stands in heat)

how are progestogens used to manipulate the estrous cycle?

• oral or intravaginal implant

• enforce artificial diestrus & suppress ovulation by inhibiting gonadotropin release by hypothalamus

• synchronize return to estrus about 2-4 days after withdrawal

• must not have a function CL when therapy is stopped

• also used in combination with synchronization of ovulation programs in dairy and beef cows/heifers for 5-7 days

advantages of progestogens

• fair synchrony & expression of estrus

• reasonable cost

• approved for use in dairy cattle

disadvantages of progestogens

• lower fertility with AI after longer treatments

• shorter treatments require using PGF

• P/AI better when bred based on detection of estrus

• intra-vaginal implants are complicated & cause vaginitis

during what stage(s) of the cycle is prostaglandin F2α effective?

• luteolytic effect only during diestrus

  • most cows in diestrus return to estrus

• response rate is dependent on CL status

  • cows in anestrus, estrus, metestrus, and proestrus do not respond to PGF

• interval to estrus is dependent on follicular wave status

advantages of PGF2α

• estrus expression is “normal”

• similar P/AI compared to AI after non-induced estrus

• safe, approved, and inexpensive

disadvantages of PGF2α

• synchrony is relatively poor, so works best with heat detection

• only works for cycling cows in diestrus (with a mature CL)

• potent abortifacient in cattle → requires extra caution to avoid unintentional abortions

ovsynch treatment objectives

• day 0: GnRH → control onset of new follicular wave

• day 7: PGF2α → luteolysis; control lifespan of spontaneous & induced CL

• day 9: GnRH → control time of ovulation

  • cause LH surge, which induces synchronous ovulation of dominant follicle

• day 10: timed AI → control time of insemination relative to time of ovulation

  • ideally 16-20 hrs after second GnRH injection

factors affecting the success of the core Ovsynch program

• cyclic status of cows at onset of program

  • cows without a CL at start of program perform poorly

    • ↓ [P4] during growth of ovulatory follicle

• luteal tissue (new CL) formed by first GnRH injection is at metestrus/diestrus border when PGF is administered

• stage of cycle at onset of program

  • cows in late metestrus / early diestrus perform best (day 6 or 7 of estrous cycle)

advantages of ovsynch program

• no heat detection required

• same program for all cows

• all cows inseminated whenever desired at the end of VWP or when diagnosed as not pregnant

disadvantages of ovsynch program

• similar P/AI to AI following estrus (~35%)

• cost

• number of treatments

• does not work in heifers, probably because most heifers have 3 follicular waves

how to improve ovsynch program

• ensure presence of a functional mature dominant follicle & CL

• pre-synchronize cows to be on day 6 or 7 of cycle on the day of the first GnRH treatment

  • use PGF or combination of PGF & GnRH

key factors for fertility treatment success

• cow comfort, management, and health

  • calving pen and post-calving management

  • grouping post-calving (e.g. parity & stocking density)

  • diseases (e.g. lameness, metritis, pyometra, ketosis)

  • vaccination program

  • heat abatement

• AI technique (e.g. semen placement in repro tract) / technician / semen handling

• sire fertility

• cycling status of cow

• parity, DIM at AI, BCS at calving & postpartum, and level of milk production

other important considerations for timed-AI programs

• compliance issues

  • right day & time of treatments is crucial for success

  • administration technique → be precise with dose & injection location

• evaluate results

  • check DIM at first breeding