Revisiting the Timing of Insemination at Spontaneous Estrus in Dairy Cattle

Cows show spontaneous estrus over 8-20 h but become refractory to the bull about 10-12 h before ovulation. This indicates that ovulation occurs 10-12 h after the end of estrus behavior, yet spermatozoa from the bull ejaculate need to undergo maturation and capacitation for 6 to 8 h in the female reproductive tract before they are capable of fertilization. Traditionally, the onset of estrus has been considered the best timing for artificial insemination (AI) in cattle, that is, 6 to 24 h from the first signs of estrus. However, recent findings suggest this interval should be reduced to 16 to 6 h before ovulation, bringing it closer to the end of estrus. In this review, the end of estrus rather than its onset is proposed as the best guide for AI timing in dairy cattle, and physiological indicators of late estrus are discussed such as relaxation of the intravaginal part of the uterus, a lower cervical mucus viscosity and a softer pre-ovulatory follicular consistency as simple cues indicating a cow is ready for service.

When is a cow in estrus? Clinical and practical aspects

Good detection of estrus is critically important in dairy husbandry. Incorrect detection of estrus is related to loss of profit due to extended calving intervals, milk loss, veterinary costs, etc. Detection of estrus remains a major problem despites enormous progress in the knowledge of reproductive physiology of the cow and in development of estrus detection aids. To achieve good estrus detection, many factors have to be taken into account. On one hand a cow has to express estrus and on the other hand the farmer has to detect it. Combined action of several hormones causes physiological changes that lead to ovulation and an environment in the uterus that allows sperm to fertilize the egg. Besides these internal actions, a number of external changes can be observed. When using visual observations, time of the day and time spend on observation have a great impact on detection rates. Many devices are available to aid in estrus detection, such as pedometers, mount devices, temperature, and hormone measurements. Expression of estrus can be influenced by many factors. Heritability, number of days postpartum, lactation number, milk production, and health are known to influence estrus expression. Environmental factors like nutrition, season, housing, herd size, etc. also play a role in estrus expression. To evaluate estrus detection, record keeping is very important; a number of formulas can be used to assess detection efficiency. Besides the farmer, the veterinarian and inseminator can play an important role in estrus confirmation and good insemination strategy. In the end, the time of ovulation and the age of the egg at sperm penetration is critical for conception. Therefore, emphasis in research needs to be on the timing of insemination relative to ovulation, and thus on the detection of ovulation.

Effects of insemination-ovulation interval on fertilization rates and embryo characteristics in dairy cattle

The objective of this study was to examine effects of the interval between insemination and ovulation on fertilization and embryo characteristics (quality scored as good, fair, poor and degenerate; morphology; number of cell cycles and accessory sperm number) in dairy cattle. Time of ovulation was assessed by ultrasonography (every 4h). Cows were artificially inseminated once between 36h before ovulation and 12h after ovulation. In total 122 oocytes/embryos were recovered 7d after ovulation. Insemination-ovulation interval (12h-intervals) affected fertilization and the percentages of good embryos. Fertilization rates were higher when AI was performed between 36-24 and 24-12h before ovulation (85% and 82%) compared to AI after ovulation (56%). AI between 24 and 12h before ovulation resulted in higher percentages of good embryos (68%) compared to AI after ovulation (6%). Insemination-ovulation interval had no effect on number of accessory sperm cells and number of cell cycles when corrected for embryo quality. This study showed that the insemination-ovulation interval with a high probability of fertilization is quite long (from 36 to 12h before ovulation). However, the insemination-ovulation interval in which this fertilized oocyte has a high probability of developing into a good embryo is shorter (24-12h before ovulation).

Effect of the interval between estrus onset and artificial insemination on sex ratio and fertility in cattle: a field study

We have carried out a field trial in cattle to study the effect of the interval between the onset of estrus and AI on sex ratio and fertility. Data were obtained from 716 cows that had been inseminated at different times between 8 and 44 h from the visual detection of estrus. Before analyzing the data, it was grouped in three intervals considering the time between estrus onset and AI (8-18, 18-30, and > or = 30 h). Our results show that the percentage of calved females (73.05%) is significantly superior for early inseminations (8-18 h), and it decreases 1.85% per hour from the onset of estrus. Delayed AIs (> or = 30 h) produce a significant deviation of the sex ratio towards the males (72.06%); nevertheless, fertility (percentage of successful pregnancies) diminishes significantly, from 66.19% (8-18 h) to 45.35% (> or = 30 h). In conclusion, variations in the interval between the onset of estrus and AI modify sex ratio. However, we must consider its effect on fertility.

Comparison of the breeding performance of cows in cold and warm loose-housing systems in Finland

Finland's cold loose-housing systems for dairy cows were compared with the more traditional warm loose-housing systems regarding the number of days from calving-to-first-service, the first-service-pregnancy risk and the repeated-service-conception hazard. 3131 calvings registered during the indoor periods in 1996 and 1997 on 208 farms were modelled using multilevel survival analysis and logistic regression in a retrospective cohort study. Compared to cows in a warm loose-housing system, cows in a cold loose-housing system had the same period from calving-to-first-service, a significant 6% lower first-service-pregnancy risk and the same repeated-service-conception hazard.

Automated electronic systems for the detection of oestrus and timing of AI in cattle

For the majority of dairy herds where artificial insemination (AI) is practiced, the limiting factor toward obtaining efficient reproductive performance is the failure to detect oestrus in a timely and accurate manner. Periodic visual observation has been the dominant method used to identify cows in oestrus. New approaches are being developed to provide automated systems of detection of oestrus using electronic technology. The goal of an oestrus detection program should be to identify oestrus positively and accurately in all cycling animals and consequently to identify animals not cycling. The ultimate goal should be to predict the time of ovulation, thus allowing for insemination that will maximize the opportunity for conception. Unfortunately, most studies designed to evaluate the optimal time of AI generally contained two technical deficiencies: inadequate numbers of cows for valid statistical comparisons and inaccurate knowledge of the onset of oestrus because of low frequency of visual observations and/or efficiency of methods used for the detection of oestrus. Studies using pedometry and a pressure sensing radiotelemetric system will be reviewed as each have independently obtained an optimal time of AI of 5 to 17 h after either the increase in locomotive activity or following the first standing event associated with the onset of oestrus.

Effect of time of artificial insemination on pregnancy rates, calving rates, pregnancy loss, and gender ratio after synchronization of ovulation in lactating dairy cows

In order to assess the optimal time of artificial insemination (AI) in relation to ovulation, lactating dairy cows (n = 732) from herds with rolling herd averages of 9980 to 11,800 kg from three milkings per day were randomly assigned to five groups by stage of lactation and parity. Ovulation was synchronized by administration of GnRH followed 7 d later with PGF2 alpha followed 2 d later with a second treatment with GnRH. Cows were inseminated at 0, 8, 16, 24, or 32 h after the second injection of GnRH (ovulation occurs between 24 and 32 h after GnRH). Pregnancy diagnoses were performed by ultrasound at 25 to 35 d post-AI. Pregnancy rates per AI were similar for the groups inseminated at 0, 8, 16, and 24 h and lower for the group inseminated at 32 h. A significant quadratic effect of treatment suggests that the middle time periods (8, 16, and 24 h) may produce the greatest pregnancy rate per AI. However, the group inseminated at 0 h had lowest pregnancy loss, and the group inseminated at 32 h tended to have the greatest pregnancy loss compared with that of the other groups. The calving rate was similar between the groups inseminated at 0, 8, 16, and 24 h and lower in the group inseminated at 32 h. The time of AI also appeared to affect gender of calf: cows bred at 0 and 32 h having a higher percentage of female offspring. In conclusion, there appears to be substantial flexibility in the time of AI after the second injection of GnRH, and lower reproductive rates were observed only when AI was after the time of ovulation.

Timing of insemination for dairy cows identified in estrus by a radiotelemetric estrus detection system

The optimal time of artificial insemination (AI) was determined from data for 2661 AI in 17 herds utilizing a radiotelemetric system for estrus detection that has the potential for continuous 24-h surveillance to monitor behavioral events associated with estrus. The system consisted of pressure-sensitive radio frequency transmitters affixed over the sacrum region of cows. The activation of the sensor sent a radiotelemetric signal to a microcomputer via a fixed antenna. Cow identification, date, time, and duration of each standing event were recorded in the software program provided with the system. Each farm selected a 3-h interval to AI for cows that were identified in estrus during the previous 24 h. Pregnancy status was determined from data for return to estrus and palpation of the uterus 35 to 75 d following AI. Standing events during estrus averaged (+/- SD) 8.5 +/- 6.6 per cow, and the number of events per estrus across herds averaged from 6.2 +/- 5.1 to 12.8 +/- 9.9 per cow. The duration of estrus ranged from 5.1 +/- 3.8 to 10.6 +/- 6.8 h across herds; the mean was 7.1 +/- 5.4 h. The interval from the first standing event to AI affected the probability of pregnancy; the highest conception rates for AI occurred between 4 and 12 h after the onset of standing activity. The probability of pregnancy was higher for cows > 100 d in milk, exhibiting > 2 standing events during estrus, and inseminated during March, April or May.

The relationship of rheological behavior of the vaginal fluid at the time of insemination to the pregnancy rate in dairy cows

The objective of this study was to determine whether rheological properties of the vaginal fluid at the time of insemination could be used as an indicator of potential fertility in dairy cows. Thixotropy and flow behavior were evaluated. Vaginal samples were collected from 347 cows at the time of insemination, within a 12- to 24-h interval after the onset of a natural estrus. Logistic regression analysis showed no significant effects of thixotropy measurements on the pregnancy rate, while flow behavior and the index of consistency (K) had a significant effect. The decrease in the consistency index (K) was related to the increase in the pregnancy rate (odds ratio = 0.99; P = 0.014), and the risk of nonpregnancy was higher (odds ratio = 0.46; P = 0.024) in cows in which vaginal fluid had a Newtonian behavior. Non-Newtonian behavior was recorded in 294 samples (85%) while 53 behaved as Newtonian fluids. For samples from all cows, the mean value of the consistency index was 310 +/- 28.2 milliPascals.second(n) (x +/- SEM) and ranged from 0 to 3881 milliPascals.second(n). In Newtonian samples, the consistency index mean was 2.6 +/- 0.6 milliPascals.second(n) and 367.6 +/- 30.4 milliPascals.second(n) for non-Newtonian samples. Of the 347 cows, 131 (38%) became pregnant. For flow behavior classification, 15 (28.3%) cows in which samples had Newtonian behavior and 116 (39.5%) cows with non-Newtonian samples became pregnant. Therefore, the highest probability of pregnancy was shown by cows in which samples had non-Newtonian behavior and the lowest consistency index values. Our data suggest that flow behavior measurements of the vaginal fluid at the time of insemination may be an indicator of potential fertility in cattle.

A case-control study to identify farm factors affecting fertility of dairy herds: univariate description of factors

OBJECTIVE

To identify farm factors which were associated with reproductive performance in dairy herds in New South Wales.

PROCEDURE

A survey was administered by face to face interview to examine the responses of producers drawn from 757 herds, which used the New South Wales Agriculture Department Dairy Herd Improvement scheme. A case-control approach was used to select a total of 126 herds from the first (top group-cases) and fourth quartiles (low group-controls) for intercalving interval.

RESULTS

We found that the estimated interval from calving to first mating was significantly different between group (P = 0.03) and that the groups significantly differed in both their target for interval to first mating (P = 0.02) and their perceived optimum time for first mating (P = 0.04). Other factors associated with a longer intercalving interval included, use of embryo transfer programs (P = 0.08), younger managers (P = 0.02), fewer breedings per day (P = 0.01), a greater number of people detecting heats (P = 0.07), but less hours spent detecting heats while handling the cows (P = 0.11), and a failure to vaccinate bulls for campylobacteriosis (P = 0.14).

CONCLUSIONS

Managers of herds with poorer reproductive performance did not intend to mate cattle as soon after calving as managers with better reproductive performance, were not as active in seeking veterinary advice on reproduction, and were attempting to treat reproductive diseases and disorders themselves.

Timing of artificial insemination of dairy cows: fixed time once daily versus morning and afternoon

Nonreturn rates to professional technician service of 7240 first AI Holstein cows were calculated to evaluate differences between once daily and a.m.-p.m. AI. To determine whether management practices affected nonreturn rates, participating herd owners were surveyed for methods used for detection of estrus. Nonreturn rates for once daily and a.m.-p.m. AI were 64.6 and 65.6% for 60-d, 60.1 and 60.6% for 75-d, and 58.4 and 57.8% for 90-d nonreturn periods. Signs of estrus for AI and interval from detection of estrus to AI were related to nonreturn rates. Nonreturn rate was highest, 63.4%, when cows were in standing estrus. Nonreturn rates were lowest, 36%, when cows were bred after treatment with PGF2 alpha without being detected in estrus or bred strictly on veterinary advice based on palpation. Nonreturn rates were similar for different times of the day when once daily AI was practiced. However, AI in the midmorning may have some advantages. The highest nonreturn rate for a 3-h period was 68.2% for 0800 and 1100 h; the lowest was 54.7% for 1300 to 1600 h. Movement before observation for estrus and an observation period > 15 min improved nonreturn rates for once daily AI. Once daily AI can be used effectively with no difference from the traditional a.m.-p.m. system; results are best when AI is based on standing estrus and performed between 0800 and 1100 h.

A retrospective analysis of the effect of prostaglandin F2a on conception rates in commercial dairy herds

The objective of this retrospective analysis was to determine the effect of prostaglandin F2a (PGF2a) on conception rates in commercial dairy herds. During routine herd visits, cows were selected for palpation if they had been milking for at least 60 days and had not been observed in estrus, or if they had been inseminated at least 30 days prior to the study selection. Nonpregnant cows with a palpable corpus luteum of sufficient size were injected with PGF2a. The herdsmen were instructed to inseminate animals within 6 to 12 hours after the observed estrus. The insemination rate within 6 days of treatment was 77.6%. The conception rate for the treated animals (47.9%) was statistically the same as that for the nontreated controls (47.2%).

Effect of progesterone supplementation in repeat-breeder cattle on conception and plasma progesterone

Reposital-type progesterone (75 mg/d for cows, 40 mg/d for heifers) or saline were administered to 24 Holstein cattle to assess the effects of exogenous progesterone (P) on fertility in repeat-breeders. Treatments were administered daily from day 6 to 10 after fourth, fifth and sixth insemination. Cumulative conception rate (57.1%) for the fourth through sixth insemination was affected by lactation number, service number, plasma P (4.67 ng/ml for pregnant cows vs 4.06 ng/ml for nonpregnant cows) and corpus luteum size on days 5 and 15. Plasma P concentrations were affected by day of cycle and size of corpus luteum on both ovaries on day 15. A treatment by day interaction accounted for higher plasma P in P-treated cattle than saline-treated cattle from day 5 through 15. Administration of exogenous P during early life of the corpus luteum in the repeat-breeder increased plasma P. Higher plasma P was associated with insemination success.

Comparison of a prostaglandin-F2α-based reproductive program with an estrus detection-based reproductive program on a large commercial dairy herd

The purpose of this study was to describe biological outcomes of two reproductive management strategies in commercial dairy cows: estrus detection with and without the use of prostaglandin-F2alpha. At regular preinsemination examinations, cows were allocated randomly to two cohorts: 1) prostaglandin cohort -- cows with palpable corpora lutea were injected with 25 mg dinoprost tromethamine and were bred by appointment 72 and 96 hours later, followed one week later by standard estrus detection practices (twice daily observation and tail chalking, with breeding approximately 12 to 24 hours later); and 2) estrus detection cohort -- cows identified as exhibiting estrus (observed estrus) were bred through the above standard procedures, without exposure to prostaglandin therapy. Age, milk production, weight, milk progesterone levels and reproductive data were collected for all cows. Although certain between-cohort effects were statistically significant, no differences could be found between the cohorts regarding standard measures of reproductive performance (average days in milk at conception (P=0.79), services per conception (P=0.48), proportion of animals failing to conceive to artificial insemination (P=0.53), and survival analysis on time to conception (P=0.30). With evidence for biological equivalence between the two reproductive strategies, nonbiological standards such as economics or ease of execution would be appropriate in choosing between the two strategies.

Nutrition and reproduction in dairy cows

Diagnosis of nutritional effects on herd fertility requires a systematic analysis of reproductive records in addition to quantifying the feeding program on the farm. Corroborative laboratory tests for specific deficiencies may be useful.

Effectiveness of rump-mounted devices and androgenized females for detection of estrus in dairy cattle

Detection of estrus was evaluated in 1124 estrous cycles for the effectiveness of rump-mounted devices and androgenized females equipped with chin-ball markers. Estrous number, location, type of detection method (compared with visual observation of estrus), and milk progesterone influenced standing behavior. Rates of disagreement with visual observation of estrus were 13.2, 17.0, and 18.5% for Kamar, Hot Flash, and the two devices used simultaneously. Frequency of observed standing behavior was greater with fourth and subsequent estrous periods. Percentage of high milk progesterone during suspected estrus for cows inseminated was 3.8% for controls, 11.0% for Kamar cattle, 18.5% for Hot Flash cattle, and 12.6% when both devices were used. Androgenized cattle equipped with chin-ball markers marked 47% of the cattle observed in estrus but no cows with high milk progesterone. Combination of rump-mounted devices and androgenized females increased the percentage of estrous detection by 1.3 to 6.2% compared with device or androgenized female used alone. Loss rates of rump-mounted devices exceeded 40%. High milk progesterone at estrus was associated with lower fertility.

Nonreturn rates of dairy cattle following uterine body or cornual insemination

In the dairy cattle industry, uncertainty still remains regarding the most desirable site of inseminate deposition to maximize AI conception rates. The effect of site of inseminate deposition on nonreturn rates was determined from 2195 cornual and 2428 uterine body-bred dairy cattle. Twelve technicians from various areas of Pennsylvania and New York were chosen on the basis of their accuracy of semen deposition in retraining sessions, average nonreturn rates, and their willingness to cooperate in the study. For a 3-mo period (June, July, and August 1988), technicians alternated weeks of cornual and uterine breeding on all dairy cattle inseminated. One-half (.25 ml) of each semen unit was deposited approximately 5.1 cm into each uterine horn for cornual insemination. No significant difference in nonreturn rates was found between horn-bred (70.8%) and body-bred (69.5%) cows. The range of differences in percent nonreturn rates for technicians was 19 and 30% for body and cornual inseminations, respectively. A significant difference in nonreturn rates was found between technicians and between months with significantly higher average nonreturn rates (6.8%) in June. Cornual and uterine body deposition of semen yielded similar results; therefore, depositing an inseminate in the uterine horns to maximize fertility is unnecessary.

Prostaglandin F2α usage in a dairy reproduction program for treatment of unobserved estrus, pyometra and ovarian luteal cysts

A retrospective study was conducted to evaluate the outcome of 223 prostaglandin F(2)alpha (PGF) treatments given to lactating Holstein and Jersey cows over a 44-mo period. The cows were part of a commercial dairy herd. Treated cows were given PGF (25 mg i.m.) because they had not been observed in estrus or because they had been diagnosed as having a luteal cyst or pyometra. Outcome of treatments was assessed for frequency of response to treatment (the detection of estrus), time interval to detection and pregnancy outcome of breedings at PGF induced estrus. Of the 223 administrations of PGF, 70% (156 223 ) were given for unobserved estrus, 12.1% (27 223 ) were given for cystic ovarian disease and 15.2% (34 223 ) were given for pyometra. Estrus was detected in 55.3% (120 217 ) of cows over a period of 36 to 130 hours after PGF administration. Interval to estrus and response rates were not influenced by the reason for treatment. Mean time interval to response was 79.1 h. Time interval for response was affected by season (P < 0.01) housing location (P < 0.01) and lactation number (P < 0.05). Insemination was performed following 157 of the treatments. For cows treated for unobserved estrus, insemination was performed in response to estrus or at 80 h if no estrus had been previously seen. Of this group, 39.7% (58 146 ) failed to show estrus and were inseminated at 80 h. Reinsemination was required for 22.7% (20 88 ) of the cows that manifested estrus following insemination at 80 h. Overall conception rate was 41.4% (65 157 ). Cows inseminated in response to estrus had a 53.4% (47 88 ) conception rate, and appointment bred (80 h) cows had a 20.7% (12 58 ) conception rate. Factors significantly influencing conception were response to PGF administration (P < 0.05), season (P < 0.01) and lactation number (P < 0.01). It was concluded that estrus detection efficiency affects the outcome of PGF administration and that conception rates resulting from 80 h breeding when no estrus is observed may be unacceptably low.

Factors affecting calving interval in Italian Holstein-Friesian heifers

Effect of rump conformation on calving interval of 520 Italian Holstein Friesian heifers was evaluated with simultaneous adjustment for herd, year of birth, calving month, age at first parturition, and milk production. All factors, except age at first parturition, were important sources of variation. Heifers with narrow rumps at the pins had the longest calving interval. There were significant differences among the herds. Cows born between 1979 and 1981 had shorter calving intervals, probably resulting from a national plan against bovine infertility initiated in 1981. Cows calving in July had better reproductive performance. There was positive relationship between milk production and calving interval.

Interrelationships between energy balance and postpartum reproductive function in dairy cattle

Genetic improvement of dairy cows has markedly increased milk yield over the last three decades. Increased production has been associated with reduced conception rates (66% in 1951 versus 40 to 50% since 1975). Because conception rate in dairy heifers has remained higher, the metabolic demands of higher production may be related to the decline in reproductive performance in cows. During early lactation, increasing dietary intake fails to keep pace with rising milk production. The resultant negative energy balance and rate of mobilization of body reserves appear directly related to the postpartum interval to first ovulation and lower conception rate. Delays in the onset of normal ovarian activity, thus limiting the number of estrous cycles before breeding, may account for the observed decrease in fertility. Negative energy balance probably acts similarly to undernutrition and may manifest in delayed ovarian activity by impinging on pulsatile secretion of LH. Lower availability of glucose and insulin may also decrease LH pulsatility or limit ovarian responsiveness to gonadotropins. Alternatively, release of endogenous opioids in association with increasing feed intake or other lactational hormone responses may provide neural or pituitary inhibition of the pulsatile LH production that is requisite for ovarian follicular development.

Impact of site of inseminate deposition and environmental factors that influence reproduction of dairy cattle

Uterine body and cornual inseminations (n = 2127) were evaluated over a 3-yr period in Holstein and Jersey cattle. For cornual insemination one-half of each semen dose was deposited approximately 2.5 cm into each uterine horn. Conception rate was lower for cervical insemination (39.4%) than uterine body (48.1%) or cornual (49.3%) inseminations. Pregnancy site distribution was equal for both insemination techniques but cervical insemination resulted in 60% right horn pregnancies. Primary housing, service number, inseminator, lactation number, and sire affected conception rate. Older cows were least fertile (31.4%), second service conception rate was lowest (42.6%), and barn housed cattle had a 39.7% conception rate. Days open was affected by primary housing, service number, sire, site of semen placement, and twinning. Twinning increased days open by 10 d. Optimum time for insemination of lactating cows was between 6 and 12 h after the initial observation of estrus. From this study we conclude that shallow cornual insemination is as effective as uterine body insemination, and conception rate is optimized when estrus is positively assessed.