Oestrus detection and insemination with correct timing in farm animals is the main determinant of reproductive efficiency. The average duration of estrus in cattle is 12-18 hours, and ovulation occurs 10-12 hours after the end of estrus. This narrow time window is critical for successful pregnancy. In this article, estrus physiology, detection methods, insemination timing and synchronization protocols are discussed in the light of current literature.
Economic Importance
Every 10% improvement in estrus detection increases pregnancy rate by 5-8%. Each missed estrus results in a 21-day delay and approximately 500-1000 TL in economic loss (Senger, 2012).
VetKriter Estrus Calendar
Calculate the estrus and optimal insemination time after the last estrus date.
Estrus Calendar1. Physiology of the Estrus Cycle
1.1 Estrus Cycle in Cattle
Cattle are polyestrous animals and show regular cycles throughout the year. The average cycle length is 21 days (range 18-24 days). The cycle is divided into four phases (Senger, 2012):
2-3 days
- Corpus luteum regression
- Follicle development
- Estrogen increase
- Behavior change begins
12-18 hours
- mating acceptance
- LH peak
- Maximum estrogen
- Insemination time
3-4 days
- Ovulation (end of estrus +10-12 hours)
- CL formation begins
- progesterone increase
- Metestrus bleeding
14-15 days
- CL active
- high progesterone
- pregnancy window
- Luteolysis if not pregnant
1.2 Hormonal Regulation
| hormone | Source | Peak Time | Function |
|---|---|---|---|
| GnRH | hypothalamus | proestrus | Stimulates the release of FSH and LH |
| FSH | pituitary | proestrus | Stimulates follicle development |
| Estrogen (E2) | follicle | estrus | Anger behavior triggers LH surge |
| LH | pituitary | Beginning of estrus | Triggers ovulation |
| Progesterone (P4) | Corpus Luteum | diestrus | Maintains pregnancy, suppresses anger |
| PGF2α | uterus | end of diestrus | Luteolysis (CL regression) |
2. Estrus Symptoms and Detection
2.1 Primary and Secondary Symptoms
Standing Reflex (Standing Heat)
The cow allows other cows to mount her and stands still. This is the most reliable indicator of anger.
- Riding other cows (most common)
- Restlessness, constant movement
- bellowing, making noise
- Vulvar swelling and redness
- Clear, stringy mucus discharge
- tail lift
- Decrease in feed consumption and milk yield
- Chinese eye (swelling around the eyes)
- Hair loss on the back and tail root
Silent Heat
Some cows (especially high-yielding cows, under heat stress or with metabolic problems) have very mild or no signs of estrus. this situation is called silent heat and can reduce the detection rate to below 50%. Activity tracking systems are effective in solving this problem.
2.2 Estrus Detection Methods
| Method | Detection Rate | Advantage | Disadvantage |
|---|---|---|---|
| visual observation | %50-70 | low cost | Requires time, the night is missed |
| Activity tracking (pedometer/collar) | %80-95 | 24/7 monitoring, automatic alert | Investment cost |
| Riding detector (Kamar, Estrotect) | %70-85 | Cheap, easy application | Could be false positive |
| bull/search bull | %85-95 | high accuracy | Security risk, disease transmission |
| Progesterone test (milk/blood) | %95+ | objective, precise | Laboratory required, cost |
| Ultrasound (follicle tracking) | %95+ | Determining ovulation time | Experts and equipment required |
2.3 Optimal Observation Times
Estrus activity is more intense at night and early in the morning. At least per day 3 times, 20-30 minutes observation recommended:
morning
05:00-07:00
(before feeding)
noon
12:00-14:00
(after milking)
evening
18:00-20:00
(after feeding)
3. Insemination Timing
3.1 AM/PM Rule
For traditional insemination timing AM/PM rule commonly used (Trimberger, 1948):
Morning Heat Detection
same day evening by seed
(after 8-12 hours)Evening Estrus Detection
the next day morning by seed
(after 12-16 hours)3.2 Optimal Insemination Window
Sperm can remain alive in the female genital tract for 24-48 hours. The oocyte can only be fertilized 6-12 hours after ovulation. Therefore, insemination, ovulation 12-24 hours ago should be done (Roelofs et al., 2010).
| Insemination Time | Pregnancy Rate | Description |
|---|---|---|
| Onset of estrus (0-4 hours) | %40-50 | Early – sperm may age |
| Mid-estrus (4-12 hours) | %55-65 | optimal time |
| End of estrus (12-18 hours) | %50-60 | still good |
| Post-estrus (18-24 hours) | %30-40 | Late – oocyte may age |
| Post-estrus (>24 hours) | <%20 | It's too late |
4. Estrus Synchronization
4.1 Why is Synchronization Necessary?
Estrus synchronization enables mass insemination by bringing estrus in a group of animals to the same time. Advantages:
- Reduces or eliminates the need for estrus detection
- Fixed time artificial insemination (FTAI) possibility
- labor productivity
- Grouping of births
- Acceleration of genetic progression
4.2 Common Sync Protocols
| protocol | Application | Pregnancy Rate | Usage |
|---|---|---|---|
| ovsynch | GnRH (0) → PGF2α (7) → GnRH (9) → FTAI (10) | %35-45 | lactating cows |
| Cosynch | GnRH (0) → PGF2α (7) → GnRH+FTAI (9) | %30-40 | Single transaction reduction |
| Presynch-Ovsynch | PGF2α (0) → PGF2α (14) → Ovsynch (26) | %45-55 | Highly productive herds |
| Double-Ovsynch | Ovsynch → 7 days → Ovsynch | %50-60 | Heifers, first insemination |
| CIDR + PGF2α | CIDR (0-7) → PGF2α (7) → FTAI (9-10) | %45-55 | anoestrus cows |
Practical Knowledge
The Ovsynch protocol is the most widely used FTAI protocol. However, its effectiveness is lower in heifers and during the early postpartum period. In such cases, Presynch or Double-Ovsynch protocols should be preferred.
5. Reproduction in Sheep and Goats
5.1 Seasonal Polyestria
Sheep and goats are short-day seasonal polyestrous animals. In the northern hemisphere, the breeding season is generally between September and February.
- Cycle length: 16-17 days
- Estrus duration: 24-36 hours
- Ovulation: At the end of estrus
- Ovulation number: 1-4 (by race)
- Insemination: Mid-end of estrus
- Cycle length: 18-22 days
- Estrus duration: 12-48 hours
- Ovulation: in the middle of estrus
- Ovulation number: 1-4
- Insemination: mid-estrus
5.2 Off-Season Breeding
Various methods can be used for off-season breeding in sheep and goats:
- Ram/buck effect: Introducing the male to the flock during the anestrous period
- Melatonin implant: Short day effect simulation
- Progesterone + eCG: Sponge/CIDR + gonadotropin
- Light program: Day length control with artificial lighting
6. Reproductive Performance Indicators
| Parameter | Target (Cattle) | Acceptable | problematic |
|---|---|---|---|
| Estrus detection rate | >70% | 50-70% | <50% |
| First insemination pregnancy rate | >50% | 40-50% | <40% |
| Insemination per pregnancy | <2.0 | 2.0-2.5 | >2.5 |
| Volunteer waiting period | 50-60 days | 60-80 days | >80 days |
| calving interval | 365-380 days | 380-400 days | >400 days |
7. Resources
- Roelofs, J., et al. (2010). When is a cow in estrus? Clinical and practical aspects. Theriogenology, 74(3), 327-344.
- Senger, P. L. (2012). Pathways to Pregnancy and Parturition (3rd ed.). Current Conceptions, Inc.
- Trimberger, G. W. (1948). Breeding efficiency in dairy cattle from artificial insemination at various intervals before and after ovulation. Nebraska Agricultural Experiment Station Research Bulletin, 153.
- Wiltbank, M. C., & Pursley, J. R. (2014). The cow as an induced ovulator: Timed AI after synchronization of ovulation. Theriogenology, 81(1), 170-185.