Bovine Fertility and Control of Herd Infertility

Phil Rogers MRCVS <>
Grange Research Centre, Dunsany, Co. Meath, Ireland

Herd Fertility Indices

PR | SC | PPI / CFSI | CCI | SR | NDO | HDR | 18-24 d returns | Empty cows | Modern Indices | Effect of Herd Size on Fertility Indices  Intervention Levels v Herd Size

Herd Infertility

Heat detection | Heat duration | First postpartum oestrus | Suckler cows | Cystic ovaries | Fertilisation rate & calf loss | PD | Best blood samples | Blood tests | Repeat Breeders (Causes | Actions) | NDO, Silent Heats (Causes | Actions)

General comments

DMI & Min/Vit supply | Multiple Mineral Deficiencies
Single Mineral deficiency (Cu injection | Iodine via water or skin) | Ultrasound & ovarian structure | Acknowledgements

Indices to assess the severity or otherwise of a reported problem of "herd infertility"

Assessment index

"Normal" background (very good to good)

Slight problem

Moderate problem

Severe problem

% pregnant to a given service1





Services/Conception of all served cows2





Calving to Service Interval (days)3





Days Open (calving to conception)4





% Submission rate of all calved cows5





% NDO (Non-Detected Oestrus)6





% Heat Detection Rate7





% 18-24 day return intervals8





% Needing 3 services





% Needing 4 services


12.4- 6.4



% Culled as empty/year9


10.1- 7.2



  1. PR% (Pregnancy Rate) to a given service is calculated separately for 1st, 2nd, 3rd, 4th services, or for all services as: (100 X number of dams pregnant (confirmed, or assumed) to that service / number of dams given that service). As a guide to herd fertility, the % pregnant to 1st service is most useful, as it may identify problems early on. If a PD was not made and if a dam has not been seen in heat by 56 days after the last service, she is assumed to be pregnant to that service. A PR based on veterinary PD by ultrasound or palpation per rectum is more accurate than a PR based on 56-day non-return rates, as some of the latter may not have conceived (and been subsequently missed, or become anoestrous), or they may have conceived, lost the pregnancy and then been missed.
  2. S/C (Services/conception) for all served dams = (Total services / Total number of dams pregnant, or assumed pregnant on 56-day non-return). Data for any dams culled or dead within 56 days of last service, or before PD or subsequent calving, are excluded.
  3. CFSI (Calving to First Service Interval) in days (Postpartum Interval): The mean interval is calculated for all calved dams which were served, including those sold or dead during the period of the analysis.
  4. CCI (Calving to Conception Interval) in days (Days Open): The mean interval is calculated for all calved dams which were pregnant, or assumed pregnant (on 56-day non return), including those sold or dead after a positive PD.
  5. SR% (Submission Rate) = (100 X number of dams served, or seen in heat but not served, in a 3-week period early in the breeding season / number of dams eligible for breeding in that period). Note: In this definition, "Eligible dams" = ALL CALVED DAMS, as in some herds, some dams may be served before 30 days postpartum; in Moorepark, 4% are served pre-30 days postpartum). Genuine anoestrus as well as poor heat detection can reduce this index.
  6. NDO% (Non-Detected Oestrus) = (100 X number of dams calved 42 days or more but not served / number of dams calved 42 days or more). Genuine anoestrus as well as poor heat detection can increase this index.
  7. HDR% (Heat Detection Rate) = (100 X number of services) / (number of services + number of missed heats). The number of missed heats is assumed as 1, 2 or 3 for each return interval of 36-53, 54-72 and 73-96 days respectively. This index can be reduced by embryonic loss or fertilisation failure, followed by genuine anoestrus.
  8. Normal (18-24 day) returns: With good heat detection, 60-65% of returns should be 18-24 days. A high % repeats at intervals <18 days, with a low % at 18-24 day repeats, suggests poor heat detection and presentation for service of dams that are not in heat. A high % of long repeats (>24 days), with a low % <18 days suggests over cautious heat detection and failure to inseminate dams which are actually in heat (but are missed). A high % of long repeats can also occur with loss of the embryo due to infection etc, or with anoestrus (after one or more normal heats).
  9. Culling of pregnant dams!: 8-12% of dams culled as empty are pregnant at slaughter. All dams should be pregnancy-tested early. At the very least, dams should be pregnancy-tested before culling to ensure that they are empty.

Effect of Herd Size on Fertility Indices: More recent statistical analysis of cow fertility in Ireland (O'Farrell KJ & Harrington D (1999) Reproductive performance targets: the effect of herd size. Irish Vet J 52(8):440-441) show that the indices of suspicion of, and for intervention to solve, herd fertility problems relate to herd size. Coincidental or random events in one or two cows in smaller herds greatly increase the error factor in deciding if there is a herd problem or not. The next table shows the "Cut-off" Points (?) and Intervention Levels (I) above or below which a fertility problem may exist (at 95% confidence level) for different herd sizes:

Herd size (n)

Preg. rate %1
? ... I

(n) Serves / conception1
? ... I

CSI days

? ... I

CCI days

? ... I

Submission rate2 %
? ... I

Infertile rate3 %
? ... I

? ... I










<30 <20

>3.13 >4.76

>76 >82

>94 >99

<53 <43

>24 >33

<39 <35


<40 <33

>2.38 >3.03

>75 >80

>94 >98

<62 <55

>18 >28

<41 <38


<48 <43

>2.08 >2.38

>75 >79

>93 >97

<69 <65

>16 >20

<20 <10


<50 <46

>1.96 >2.13

>75 >79

>93 >97

<71 <68

>15 >18

<30 <22


<52 <48

>1.92 >2.04

>75 >79

>93 >97

<73 <70

>15 >17

<37 <33

NOTES: CSI = Calving to service interval; CCI = Calving to conception interval; HDE = Heat detection efficiency; 1Same for 18-24 day repeats; 2Same for heat detection rate (%); 3Same for non-detected oestrus (%)



Teagasc can not help to investigate/prevent cases of SPORADIC infertility. Vet examination / treatment of the problem cows is the best solution in such cases.

Most outbreaks of dairy herd infertility involve more than one causal factor. As the severity increases, professional investigation is more likely to identify the cause(s) and to suggest solutions. Probably >85% of outbreaks are due mainly to managemental and other factors and <15% of outbreaks are due mainly, or in part, to mineral imbalances. If natural service is used, it is crucial to eliminate bull factors as possible causes.

CYSTIC OVARIES: Cows with breeding problems often have ovarian cysts. In Holsteins, the mean incidence of cystic ovaries is 5% but incidence within a herd varies from 1-30%, depending on the breed and the calving history. Cows with periparturient problems (milk fever, dystocia, twins, retained placenta or metritis etc) have a high incidence of cysts. 70% of cysts are follicular and 30% are luteal. 70% occur within 45 days postpartum and 70% of these recover spontaneously.

GOOD HEAT DETECTION (>90%) is essential to high cow fertility to AI: Faulty heat detection, resulting in failure to present cows for service at the correct time, is the biggest single cause of "low fertility" in herds inseminated by AI. Great vigilance is needed to detect 90% of cows in heat. Many farmers miss 20-40% of their cows in heat. Some miss >50%, especially if labour is scarce. Heat detection is more difficult in suckler- than in dairy- cows.

The mean duration of heat in dairy herds is about 9 hours but the range is very wide (2-18+ hours). Oestrous cows stand to be mounted by others several times, but only for a few seconds each time. Thus, cows stand to be mounted (the "standing heat") for only a matter of minutes in the 2-18 hour heat period.

By disturbing the cow, many factors (collection for milking, strangers or dogs nearby etc) may disrupt standing heat. Such breaks in standing heat occur in 30-40% of cows. Also, 10-15% of cows come in heat at night and may be gone off heat in the morning. Lame cows, especially those with pain in the hind feet or low-back, may refuse to stand to be mounted. Mild heats in such cows, even if tail-painted, may be missed.

THE FIRST POSTPARTUM OESTRUS (day 16 to 30) may be silent and only 30% of cows may stand to be mounted at that heat. By day 21 after the start of the breeding season, 70-80+% of ALL CALVED DAMS should have been served (or seen in heat but not served). By day 40 postpartum, >90% of dairy cows should have been seen in heat at least once. In any 3-week period in the breeding season, up to 16% of cows calved <42 days may be served.

Note: If >20% cows are bred <50 days postpartum, non-return rate may drop by 10-15%. Heat may occur in 4-8% of pregnant cows. Insemination at that heat may cause abortion and delayed calving index.

SUCKLER COWS have longer intervals from calving to first observed oestrus and from calving to conception than dairy cows.

FERTILISATION RATE AND EMBRYONIC/FOETAL/CALF LOSS: Fertilisation rate to AI averages about 90% but the CALVING RATE to a single service averages about 50%, i.e. about 10% of services and 45% of conceptions and do not progress to a viable pregnancy. National calf losses (embryos/foetuses/neonates) are about 47+5% of fertilised ova. Estimates of the timing of those losses are:

Percentage embryonic, foetal and calf losses and total losses

Day post-insemination

Loss %

Loss %

Total loss %

Embryo d 8- 18

27.0 (25-29)

Embryo d18- 50

9.5 ( 8-13)

Embryo d50- 90

3.5 ( 3- 5)


Embryonic loss to d90



40.0 (36-44)

Abortion (90-259 foetus)

2.0 ( 1- 3)

Stillbirth (259-calving)

3.0 ( 2- 4)


Abortion + stillbirth loss


5.0 ( 0-10)

Early postnatal loss  

2.0 ( 0- 4)


Abortion + perinatal loss


7.0 ( 0-10)

Total calf loss (embryo+foetus+perinatal)    

47.0 (42-52)

PREGNANCY DIAGNOSIS (PD): Dairy cows should be tested for pregnancy at 4-6 weeks post-insemination. PD at 7-8 weeks reduces its value. The earlier empty cows are detected and re-served, the better. Ultrasound PD, is excellent to detect foetal heartbeats at 25-45 days post-insemination. PD by rectal palpation is best done at 35-56 days. Manual PD may cause 10% embryonic/ foetal loss; loss after skilful ultrasound PD may be as low as 3-5%.

BEST BLOOD SAMPLES: To investigate mineral/nutritional causes of herd infertility (anoestrus, repeat breeders), blood-test the cows during the breeding season, or 0-2 months before the start of breeding. To investigate fertility problems in maiden heifers (delayed puberty, anoestrus, repeat breeders), sample the group of problem heifers.

Prepartum samples are of little value; they may under-estimate the mineral status postpartum, as most dairy cows get supplemented compound feed postpartum. Supplemented cows often have higher trace-element mineral status postpartum than cows prepartum. Note that Mg, Co and I status of cows can fall within days of removal of Mg, Co and I supplements.

Autumn samples, or those taken in late summer, may be of little relevance to breeding problems which may have arisen in the previous April to June.

BLOOD TESTS: If mineral deficiency is suspected, 10 heparinised samples should be tested for Cu, Se, I + Mg and 10 sodium fluoride samples for P. If nutritional inadequacy is suspected, 10 heparinised samples should be analysed for protein, albumin, globulin, bHB, urea, GLDH, Hb and ketone and 10 oxalate-fluoride samples for glucose.

If minerals are only marginally deficient in blood during (or close to) the breeding season, further supplementation with those minerals is unlikely to improve fertility.


REPEAT BREEDER COWS (mean service/conception rate >1.67, esp. >1.99)

Farmers often report a "repeat breeder problem" when none exists. In healthy cows, the number of serves needed per conception relates directly to the conception rate (CR%): 









% of healthy cows that need

2 services

3 services

4 services



















Many authorities dismiss the term "repeat breeder" as meaningless because it includes some healthy cows. At conception rates of 70, 60 and 50%, respectively, 2.7, 6.4 and 12.5% of healthy cows need 4 services to conceive (see table, above). Bearing that in mind however, for practical purposes, we define a "repeat breeder" as a female that needs 4 or more services to conceive. If >12.5% of cows need 4 or more services, the herd has a moderate to severe subfertlity problem.

1. Errors of management Poor heat detection, mainly in large herds where AI or hand-mating is used (low submission rate, cows bred too early or too late); pain/stress (lameness(1), general stress, Cu injection close to breeding(2)); [(1) Lame cows rarely stand to be mounted and have longer calving to conception intervals. (2) Cu injections during breeding, or within 1 month before it, can drop conception rates by 15-25 points. Oral Cu, bullets or boluses are safer close to breeding];
2. Seasonal factors Lush spring grass high in NPN(3); low intake of lush grass often undersupplies energy and true protein at a time of maximum milk yield (especially in winter and on the second round of spring grazing), see also nutrition faults below; problem improves later in the season); [(3) Drs. Michael Diskin and Joe Sreenan noted a 15-25 point drop in conception rates in some herds at 3-8 weeks after turnout to herbage high in N (especially NPN). Conception rates were normal (about 65%) before turnout. Blood urea levels were very high. Feeding 600-700 g of a protein feed with low rumen-degradability (for example fish-meal) during that time returned conception rates to normal. In any case, the problem usually improved spontaneously after 2 months at grass. For details, contact Belclare (phone 093-55455). Intensive dairy farms use high levels of N-fertiliser. Cows usually graze paddocks within 15-25 days after N is applied, i.e. before the N can be converted into true plant protein. Such herds (i.e. most intensive herds) usually show high blood- or milk- urea on such grass. This is normal for intensive Irish herds and analysis of blood/milk for urea in such herds is pointless when the herds are on lush grass];
3. Female factors Metabolic stress/nutrition faults pre- and/or post- calving (poor body score at calving; fat cow/fatty liver syndrome; high milk yield, negative energy balance and rapid weight loss pre-breeding; excessive NPN/high blood urea; ketosis, hypoglycaemia); age (heifers versus cows); infection (Leptospira, BVD/IBR, VD (Campylobacter (Vibrio) etc), possibly Salmonella, etc); intercurrent disease; metritis after dystocia or retained foetal membranes (heifers; twins; periparturient disorders);
4. Male factors Bull: Sire variation (some sires have 15% better conception rates than others); stock bull: 5% are totally infertile and 30% may be subfertile; check bull for infection (Campylobacter (Vibrio), BVD etc); testis/semen quality; bull health (especially libido, feet and back and service ability); too many cows (>50/per bull);

AI: time of AI (best at 18 hours after heat onset if low-fertility bulls used); operator effects (especially in DIY-AI; semen and straw storage; best to inseminate into the uterus); poor cow restraint (use a good crush, not the milking parlour);

5. Toxicity Plant (oestrogen’s etc), chemical (F, Se, I etc));
6. Severe mineral-vitamin deficiency Se, I, Co, Cu; possibly P, Mg, Mn. Some authors claim that severe Vit A, b-carotene or Vit E deficiency reduces fertility, but this is controversial).


1. Analyse ACCURATE records (cow identity, calving problems, date of calving, heat, service, bull and inseminator used, dates stock bull was with herd, number of cows/bull, pregnancy diagnosis; separate analysis for maiden heifers, first calvers and older cows) to quantify the problem and identify the problem times or subgroups.

2. IDENTIFY AND CORRECT THE CAUSAL FACTORS (poor heat detection, pain/stress), MALE factors (stock bull, AI/DIY-AI factors), FEMALE factors (infection, intercurrent disease; individual cow problems after dystocia/RFM, faulty nutrition/metabolic stress, toxicity and mineral supply).

If dystocia/periparturient disorders/RFM were causes of metritis, correct these by:

3. IMMEDIATE REMEDIAL ACTION: The most important routine actions are:

a. Ensure good heat detection: See Herd Fertility, 3 pages back. See also under NDO, silent heats etc, below.
b. Tail painting: See under NDO, silent heats etc, below.
c. Mineral-vitamin supplements?: If blood levels are low for Cu, Se or I (common in unsupplemented herds), P, Mg, (rare today), or feed tests show low Mn or Zn levels (very rare or rare), or soil tests show low Co and/or high Mn (common) it is advisable increase the supply of those elements precalving and before / during the breeding season. See Mineral-vitamin supplementation for high bovine fertility (below).


NDO, SILENT HEATS (bovine anoestrus, suboestrus, delayed puberty, delayed return to postpartum oestrus, low submission rates)

Short, mild heats, easily missed if tail-painting is not used, are very common. Genuine anoestrus (due to inactive ovaries) may occur but the incidence is probably low. In New Zealand, true anoestrus is about 9%. In UK, 25 and 5% of dairy cows respectively fail to cycle by 24 and 50 days postpartum.

1. Errors of management Poor heat detection is the main cause of NDO where AI/DIY-AI or hand-mating is used. Low submission rates, high rates of NDO and "anoestrus" usually are due to managemental errors (ovaries active but heat not detected). 
2. Undernutrition relative to high milk yield Negative energy balance pre-breeding is a major factor in repeats and/or NDO in high-yielding herds (ketosis; poor quality or quantity of forage, especially in winter and on the second paddock rotation); rapid weight loss (>40 kg) between calving and breeding (poor quality feed, reduced feed intake with periparturient problems, especially after twinning / dystocia / RFM, or due to pain / intercurrent problems); poor body score at calving and/or breeding may delay onset of postpartum ovarian activity;
3. Suckling Suckling delays onset of postpartum ovarian activity;
4. Severe mineral deficiency Deficiency of P, I, Co and Mn, though an uncommon cause, can cause anoestrus. Cows with severe Cu or Se deficiency may show suboestrus or anoestrus but repeat breeders are more common in these herds.


1. Analyse accurate records Quantify the problem and identify the problem times or subgroups by checking cow identity, calving problems, date of calving, heat, service, bull and inseminator used, dates stock bull was with herd, number of cows/bull, pregnancy diagnosis.
2. Correct detected faults Identify and correct the causal factors of poor heat detection, general nutrition, body condition, and mineral supply:
3. The most important routine remedial actions are good heat detection and tail painting! Ensure good Heat Detection: see Herd Fertility, 4 pages back. Moorepark data shows that NDO is related to frequency of heat detection: NDO may be 24% in herds observed 2-3 times/d, as compared with 12% in herds observed 5 times/d. If tail painting is not used, we advise close observation 5 times/d, from early morning to late evening.

Tail Painting is a routine aid to heat detection for AI/DIY-AI or hand-mating of cows at pasture. If tail painting is used, 3 observations daily (8 a.m., before evening milking and 9 p.m.) usually detect 90% of cows in heat. Up to 16% of cows (especially later-calving cows) should be served within 40 days postpartum if compact calving is desired next time.

All farmers who use AI/DIY-AI are advised to use tail-painting if herd infertility is a problem. It is important to clip the hair tightly over the tailhead before applying the paint. Paint matted into thick hair may not be dislodged by a genuine mount. The paint should be renewed weekly. The colour should be changed when heat is detected and the cow is inseminated.

4. Mineral-vitamin supplements? If blood levels are low for Cu, Se or I (common in unsupplemented herds), P, Mg, (rare today), or feed tests show low Mn or Zn levels (very rare or rare), or soil tests show low Co and/or high Mn (common) it is advisable increase the supply of those elements precalving and before / during the breeding season. . See Mineral-vitamin supplementation for high bovine fertility (below).



Peak lactation usually coincides with the peak breeding season and the peak tetany season (April-June). Energy deficit is a major cause of repeat breeding and/or anoestrus in high-yielding herds. High-RBI cows need total DM intakes of 14-22+ kg/head/d at peak. DM intakes on silage + concentrates, or on the second rotation on paddocks may be seriously below the requirements for the energy lost in milk. Depending on the energy deficit, such herds may need 1-5 kg/cow/d of Summer Feeds (high in Mg and trace-elements) before/during the breeding season.

FIXED-RATE FEEDING of well balanced minerals and vitamins is the cheapest, most reliable way to supply them. For more detail, see Mineral Supplements for Dairy Cows, Mineral Supplements for Beef Cows, Control of MIneral Imbalances in Cattle and Sheep. In summary:

If MULTIPLE MINERAL DEFICIENCIES are confirmed in a problem herd, cows should be fed high-quality mineral mixes. Three types are needed:

If ONLY ONE MINERAL DEFICIENCY is confirmed (and other trace-elements are not a problem), boluses, bullets, Se injections etc may be considered.

AVOID Copper INJECTION: Note that Cu injection close to breeding may depress conception rates. Close to breeding, it is preferable to use ORAL Cu (in carrier feed, or slow-release bolus or bullet).

Iodine via the water or via skin application: See Iodine Supplements for Livestock and Iodine Supplementation of Cattle. If I deficiency alone is involved, medication of the trough water with 1.2 ml 5% tincture of I/cow/d or 80 mg potassium iodide/cow/d pre- and during the breeding season may suffice. An alternative is to spray or paint 5% tincture of I (9 ml/cow/week) on the thin skin of the pocket of the flank fold once/week pre- and during the breeding season. Lipiodol (oil-based) injection is not as reliable as oral iodine supplements. 

Ultrasound characteristics of ovarian structures



Day 1- 4. Poorly defined, irregular, grey-black, with echogenic spots all within the ovary


Day 5-16. Well defined, grey echogenic structure, with visible demarcation line between it and ovarian stroma. Sometimes protrudes from ovary


Day 17-21. Well defined, grey echogenic structure, with faint demarcation line between it and ovarian stroma. More compact and protrudes less.
FOLLICLE Uniformly non-echogenic structure with diameter >10 mm and no wall.
Follicular cysts persist for 2-5+ weeks and are due to insufficient preovulatory LH; ovulation does not occur. Nymphomania (frequent and/or prolonged heats) occurs in 75% cows calved >60 days with follicular cysts.

Uniformly non-echogenic antrum, with diameter >24 mm and wall <4 mm. Treatment by GnRH works in 53-83% but pregnancy rates are <50%.

Luteal cysts persist for up to 9 weeks. Anoestrus is the main clinical sign.

Non-echogenic antrum; diameter >24 mm; wall >3 mm but grey patches in antrum or along inner cyst wall. Treatment by prostaglandin works in >90% but pregnancy rates are about 40%. Prostaglandin may be combined with GnRH (prostaglandin, then GnRH 3-4 days later; or GnRH, then prostaglandin 9-14 days later).

See: Ribaldu et al 1994, Vet Rec 135, 452-457; O'Farrell 1995 Irish Vet J 48, 119-123 and 1999 Irish Vet J 52,440-441.

Acknowledgements: These herd fertility data are from research by Drs. Michael Diskin, John Mee, Jim Roche, Joe Sreenan et al, but especially by Kevin O'Farrell (Measurement of fertility in seasonally calving dairy herds. R & H Hall Technical Bulletin (2), 8 pp (1994) and personal communications).