**5. Accurate detection of estrus in dairy cow**

Estrous detection rate may contribute to low fertility results because of the low detection rate [102]. Van Vliet and Van Eerdenburg [103] reported that cow factors might also be contributing to low detection rates. Due to the relatively small size of the average dairy herds in several European countries (<50 cows) and the year-round calving pattern, the chances of having more than one cow in estrus simultaneously are somewhat limited. In this way, they cannot stimulate the intensity and length of each other estruses [103]. Another point of concern is the short duration of estrus. A previous study [103] showed that a substantial number of animals (40%) showed estrous signs for less than 12 h. The mean duration of estrus was 13.7 h in their study, in which they observed the cows every 2 h for 30 min. Others found that the high-yielding dairy cows (46.4 ± 0.4 kg milk/day) had a shorter duration of estrus (6.2 ± 0.5 h vs. 10.9 ± 0.7 h), fewer standing events (6.3 ± 0.4 vs. 8.8 ± 0.6), and shorter standing time (21.7 ± 1.9 s vs. 28.2 ± 1.9 s) than lower-producing dairy cows (33.5 ± 0.3 kg milk/day) measured at the same conditions [104].

The short duration of estrus on modern dairy farms emphasizes the importance of correctly determining the optimum time for artificial insemination [105]. Simple observation of the herd in the morning before and after milking, at midday, and late in the evening for 30 min is greatly recommended to determine estrus accurately under usual management circumstances. The use of traditional aids such as tailhead markings with chalk, paint, or crayon (the pin bones and the tailhead are painted), pressure-sensitive mount detectors using a colored fluid that fills a container when pressure is applied (these devices are fixed with adhesive to the hair over the midline just in front of the tailhead), camera-based recognition system for pressure-sensitive devices [106], estrous detection strip (applied to the sacrum) with a reflective strip which can be detected with an overhead camera [107], and/ or detector animals (vasectomized or surgically altered bulls or androgenized nonlactating cull cows, heifers, or freemartin heifers with chin-ball marking harness) [108] may contribute to detect estrus accurately in the field. The recent development of a pressure-sensitive device is that when a certain threshold on mounts is reached, a light is activated on the device. Different flashing light patterns can determine whether a cow is in suspect heat, standing heat, or when it is ideal for AI [108]. Recently developed activity meters (activity behavior is classified as lying, standing, walking, active, or inactive/resting/) such as leg bracelets, neck collars, or ear tags [48], and/or electronic pressure-sensitive mount detectors [109] may improve the accuracy of estrous detection. The combined use of monitoring of estrous behavior and one or more estrous detection aids may enhance its efficiency. Similarly, combined use of biosensor data of animal activity with in-line monitoring of milk yield, milk flow rate, milk temperature, and electrical conductivity of milk [110, 111], in-line progesterone measurement [112, 113], and/or ruminating time and eating time (eating bouts) may increase the accuracy of estrous detection in the farm [48].

It is essential to emphasize that when standing heat is used as a predictor for ovulation (26.4 ± 5.2 h), only a limited number of cows display standing heat (58%), especially when few animals are in estrus at the same time. The onset of mounting behavior shown in 90% of estruses is the best predictor for ovulation (30.0 ± 5.1 h); however, its limitation is that it cannot yet be assessed by estrous detection aids [114].

There are several other methods to detect estrus, for example, direct electronic sensing of the odors of estrous pheromones [115, 116], continuous measurement of vaginal temperature and conductivity [117], ventral tail base skin surface temperature [118], rumen reticular temperature [119], or external auditory canal temperature [120]; however, they need further developments before introducing them into the daily practice.

## **6. Determining the optimal time for artificial insemination**

The mean duration of an estrous cycle in dairy cows is 21 days (between 18 and 26 days), and ovulation occurs 25–32 h after the onset of standing heat [108]. According to Roelofs et al. [114], the duration between the onset of estrus and ovulation is 29.3 ± 3.9 h, while the onset of the first standing estrus and the time of ovulation is 27.6 ± 5.4 h [121]. Since the chances for pregnancy after artificial insemination (AI) are much higher when ovulation occurs within the survival time of sperm [105], it is essential to inseminate the cow within 12 h after the onset of estrus, namely during the last half of standing heat; therefore, the a.m./p.m. rule was developed as a guide for AI. This guideline recommends that cows observed in estrus in the morning should be inseminated in the afternoon, and cows observed in estrus during the afternoon should be inseminated the following morning [105]. In contrast, if we inseminate the cows at a similar time each day or employ an inseminator service, there is no need to follow the a.m./p.m. rule if heat detection is accurate, the insemination technique is good, and semen fertility is high on the farm [122–124].

The optimal time for artificial insemination (AI) after the onset of increased activity measured by pedometers is between 5 and 17 h [114], while according to Maatje et al. [125] and Yoshioka et al. [126], it is between 6–17 h and 10–18 h, respectively. When neck-mounted collars were used to detect estrus, the highest pregnancy rates were reached for primiparous and multiparous cows when they were inseminated between 13–16 h and 9–12 h after the onset of estrus, respectively [127]. At the same time, this difference between primiparous and multiparous cows could not be confirmed by Roelofs et al. [114]. When pressure sensing devices were used to detect estrus, the optimal time for AI felt between 4–12 h [109] and 12–18 h [128] after the onset of estrus, respectively. In comparison, artificial insemination had proven to be the most effective when cows were inseminated at 12 h after the onset of estrus [129].

According to Van Eerdenburg et al. [130], cows (*n* = 100) were detected with a scoring system in estrus. Of these animals, 50% showed standing heat (58% reported by Roelofs et al. [131]), and only 64 of the 100 cows achieving a score of >50 were presented for insemination; 98% did indeed ovulate. The other 36 were <45-day postpartum and were not inseminated [132]. The milk yield, parity, follicular size, and ovulation time were not correlated with the estrous behavior score. The animals that ovulated 0–24 h after the first ultrasonographic examination scored more than twice the number of points (188 versus 65 points) as those that ovulated 24–48 h after the first scan (*P* = 0.045). If ovulation occurred >48 h after AI, only 15% of the cows became pregnant (**Figure** 2). Cows that did not show overt signs of estrus and thus scored <100 points in the scoring system had a high chance of ovulating after 24 h and should therefore be inseminated again or given GnRH (or agonist) at the time of insemination [132].

*Importance of Monitoring the Peripartal Period to Increase Reproductive Performance in Dairy… DOI: http://dx.doi.org/10.5772/intechopen.105988*

**Figure 2.**

*Pregnancy rates at Day 28 concerning ovulation time after AI. Ovulation time <0 indicates that the cow had ovulated before the initial ultrasonographic examination adapted from [132].*

Ultrasonography can also detect ovulation, since it is characterized by the abrupt disappearance of the large ovulatory follicle [132, 133]. The duration between the onset of the increased number of steps and ovulation can be 29.3 ± 3.9 h. In contrast, the period between the end of the increased number of steps and ovulation is 19.4 ± 4.4 h, measured by a pedometer. Pedometers may detect estrus accurately (83%) and appear to be a promising tool for predicting ovulation in dairy cows [131], while monitoring P4 alone is not sufficient to predict ovulation [134].

A progesterone (P4) assay of plasma or milk as an indication of true estrus clearly demonstrated that 7–22% of cows showing estrus had abnormal levels of P4 at the time of AI [135]. Bulman and Lamming [136] found that 15% of cows were inseminated during inappropriate stages of the follicular phase. However, a further 15% were inseminated during the luteal phase, while according to O'Connor [137] up to 15% of the cattle presented for insemination are really not in heat. When such cows are inseminated, they do not conceive, or it leads to abortion if they have been pregnant [135]. The number of artificial inseminations performed at the wrong time in the practice can be reduced by performing ultrasonographic examination [132, 133] or by using different diagnostic kits such as on-farm milk progesterone tests [138], in-line progesterone measurements [113, 139], or on-farm heat detection kits for detecting lactoferrin in cervical mucus [140] or by measuring the electrical resistance of vaginal fluid [137].

To eliminate the requirement for estrous detection and to optimize the timing of insemination relative to ovulation, different fixed timed artificial insemination (TAI) protocols were introduced into daily practice (**Table 3**). The TAI protocols may provide similar pregnancy rates per AI when compared with those of classical reproductive management systems, based on estrous detection and hormonal therapy when necessary. However, before selecting any protocol, it is always very important


#### **Table 3.**

*Fixed-timed artificial insemination (TAI) protocols.*

*Importance of Monitoring the Peripartal Period to Increase Reproductive Performance in Dairy… DOI: http://dx.doi.org/10.5772/intechopen.105988*

to compare the results with the traditional methods used on the dairy farm. When estrous detection on the farm is good, PGF2α treatment and AI at the observed estrus are recommended [155], while when estrous detection is poor, TAI protocols may be recommended. Recently published reviews [156–161] and meta-analyses [162–164] may contribute to selecting from an economic and management point of view the most suitable and most effective TAI protocol(s) for our dairy farm.
