**1. Introduction**

336 A Bird's-Eye View of Veterinary Medicine

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#### **1.1 Importance of RBC in dairy cattle**

Dairy cattle production requires great intensification, which has been demonstrated to affect negatively on the reproduction. One calf by cow and year is the reproductive objective in these animals. It means that cows must get pregnant after AI, maintain the pregnancy, have parturition after 270 days approx., and wait for a period of 40-50 days to be successfully inseminated again. Nevertheless, this is not always attained and cows must be reinseminated during several consecutive cycles. In this context appears the Repeat Breeder Cow syndrome (RBC), comprising a heterogeneous group of subfertile cows, without anatomical abnormalities nor infections, that exhibit a variety of reproductive disturbances in a consistent pattern during the course of 3 or more consecutive estrous cycles of normal duration (17-25 days). Any of these disturbances may affect the delicate interplay of estrous behavior, hormone patterns, and ovarian dynamics, which in synchrony with the uterine functions finally determines the outcome of mating or artificial insemination (AI) (Bage et al., 2002). Epidemiological studies of RBC prevalence have shown disparate results, ranging from a 5% described by Ayalon (1984) in Jordan, to a 36% observed by Zambrano et al. (1982) in Cuba. Nevertheless, considering the great demands on dairy cow production (which ideally requires obtaining a calf per cow per year), RBC has an important impact on dairy cattle economics (Figure 1).

#### **1.2 Importance of RBC in beef cattle**

Beef cattle reared under extensive system usually have a deficient data record, and then it is difficult to identify this syndrome. In this case cows are considered as RBC when they do not get pregnant after being exposed to bulls during the established reproductive periods. The bull-cow interaction usually ranges from 45 to 90 days, although sometimes it lasts 6 months or it may also be permanent. Few reports on RBC exist in beef cattle (Maurer & Echternkamp, 1985; Ferreira et al., 2008).

In contrast with dairy cows, to obtain a high reproductive efficiency in beef cattle, it is necessary to get a calving interval of 365 days and an overall calving rate of 95% (Duffy et al., 2004). The cow should get pregnant around day 85 after parturition. But how many cows

Clinical Approach to the Repeat Breeder Cow Syndrome 339

calves, veterinary costs and worse reproductive indexes (longer parturition-estrus interval

The aethiology of RBC syndrome is unclear and multifactorial. The cow, the bull and several environmental/handling factors are incriminated. All of them are often overlapped and it is

Causes provoking repeat estrus in cattle are often related to maternal defects, which used to be at individual-level and make more difficult the clinical assessment and diagnosis. Age, genetic defects, genital tract infections, conformational defects, hormonal disorders, embryo mortality and nutritional defects have been reported. But usually there is no clear aethiology and several concomitant causes often appear, what makes difficult to characterize the

It has been widely reported that age impacts negatively on fertility (Hodel et al., 1995), and higher RBC rates have been described in old cows (Hewett, 1968). It is attributed to alterations in hypothalamic or pituitary hormonal levels or to inability of the ovary response (Bullman & Lamming, 1978). It has also been demonstrated the relationship between old age and low oocytes viability, what explains the fertility decline (Lanman, 1968). Studies in RBCs showed that age and breed affect the FSH and LH levels. FSH was higher in cows with six or more lactations (1.03 ± 0.12 ng/ml) and LH ranged from 1.31 ± 0.21 ng/ml in heifers and 2.19 ± 0.28 ng/ml in cows after three calves, falling to 0.94 ± 0 25 ng/ml in six or more calves (Santana et al. 2000). It is supported that fertility in dairy cattle improves after the 1st or 2nd parturition, and decreases from the 4th or 5th, but it should be taken into account the time required for uterine involution or problems associated to puerperium

Individuals inherit their parent´s genetic merit, and then chromosomal or genetic abnormalities of parent, or those that occurred during the differentiation process may compromise fertility. RBC syndrome has been described in cows with chromosomal abnormalities as translocation 1/29 or trisomy X (Roberts, 1971; Lafi & Kaneene, 1988; Bruyas et al., 1993). A study regarding Robertsonian translocation 1/29 in cattle (Rodriguez et al., 2000) informed that cows diagnosed with this chromosomal defect were classified as RBC. Few embryos (less than 10%) exhibit chromosomal or genetic abnormalities, and are usually associated with high inbreeding or aged gametes. Humblot (1986) observed higher RBC rate in Holstein and Charolais breeds than in Norman or Frisian breeds, considering

The utilization of bulls to produce bigger calves could be considered as a genetic- or management-based problem when dystocia or postpartum disease appear, and metritis,

or lower conception rate).

problem.

(Dominguez, 1989).

**2. Aethiology of RBC syndrome** 

difficult to determine the primary origin.

**2.1.1 Influence of maternal age** 

**2.1 Maternal factors involved in RBC syndrome** 

**2.1.2 Genetic factors in repeat breeder cows** 

breed as a risk factor for this syndrome.

infertility or repeat estrus are developed.

really get this objective? Studies carried out in US indicate that only between 50-70% of cows reach this goal. In Spain, the production system presents notable differences with respect to reproductive indexes. Under intensive farming, beef cows usually calve for the first time at 28 months old, while in dairy cows the first parturition occurs at 26 months old. In beef cattle exists a tendency to reduce the calving interval, in contrast with dairy cows.

Fig. 1. Evolution of the lactation curves in normal and repeat breeder cows. Note that RBCs have fewer calves per cow and therefore milk yield is also reduced.

The preovulatory follicle size is correlated with fertility in beef cattle, and it has been postulated that the implementation of management to optimize the size of the ovulatory follicle could improve the fertility (Perry & Perry, 2008). For getting good reproductive results it is recommended to select those animals that:


Then, the reproductive efficiency can be measured throughout the number of weaned calves/number of cows in reproduction x 100. This percentage ranges between 60-70%. The majority of cows that failure to get pregnant (30-40% of cows in reproduction) has infertility problems during the breeding season, and many of these cows are defined as RBC. This syndrome should be treated in beef cattle farms, since expenses may rise due to the decrease of the number of calves per season and a prolonged breeding season. If beef cows are mated for a long time (for a long season), a low production will be obtained: calves will be less heavy and then its price will be lower, the health management of different ages calves will be more difficult, and the calving interval will be longer. A higher conception rate means that a higher number of calves will be weaned, and then, a higher beef yield is obtained. The costs are the same in pregnant or open cows, but profits are different. It has been reported that dystocia provokes higher economical expenses associated with perinatal mortality of calves, veterinary costs and worse reproductive indexes (longer parturition-estrus interval or lower conception rate).
