F. López-Gatius

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.

Factors affecting pregnancy loss from gestation Day 38 to 90 in lactating dairy cows from a single herd.

The present study was designed to establish whether factors such as previous estrus synchronization, corpus luteum and embryo number at the time of pregnancy diagnosis, changes in body condition score, milk production, clinical disease (mastitis or lameness) and the inseminating bull affect pregnancy loss from 38 to 90 days of gestation. We derived data from 601 pregnant lactating dairy cows from a single herd. Pregnancy diagnosis was performed by ultrasonography between Day 38 and 44 following insemination. We also recorded corpus luteum and embryo number at this time. Pregnancy loss was defined as a negative pregnancy diagnosis on the second palpation per rectum undertaken between 90 and 96 days after insemination. Data were analyzed using multiple logistic regression methods. Cows that had an additional corpus luteum were eight times less likely to miscarry. The risk of pregnancy loss was 3.1 times higher in cows bearing twins. A one unit reduction in body condition score from previous partum to 30 days postpartum resulted in a 2.4-fold increase in pregnancy loss. We noted a higher incidence of pregnancy loss in cows inseminated using semen from one of the six bulls used. This particular bull led to a 3.4-fold increase in the rate of pregnancy loss. Logistic regression analysis showed no significant effects of previous estrus synchronization, milk production, clinical disease, body condition at previous partum or at pregnancy diagnosis, or body condition change between previous partum and pregnancy diagnosis. Our findings indicate a positive relationship between the presence of an additional corpus luteum and the maintenance of gestation. Risk factors for pregnancy loss were twin pregnancy, reduced body condition after previous parturition and the inseminating bull.

Effects of body condition score and score change on the reproductive performance of dairy cows: a meta-analysis

A meta-analysis was conducted to evaluate the effects of body condition score (BCS) at parturition and at first AI, and of body condition change during the early lactation period on the variables pregnancy rate at first AI and number of days open in dairy cattle. Inclusion criteria for the publications were: comparison of at least two groups of animals of different categories of BCS or change (independent variables) and consideration of pregnancy rate at first AI or number of days open (dependent variables). Fifteen papers were selected and 23 excluded. Data corresponding to 7733 cows from 11 studies described in 10 papers were included in the analysis of pregnancy rate at first AI, and those derived from 4529 cows from 11 studies described in 10 papers were used to analyze effects on the number of days open. Analyses were stratified according to study design and milk production characteristics. We defined low, intermediate and high categories of BCS for values lower than 2.5, from 2.5 to 3.5, or higher than 3.5, respectively. The categories of body condition change were increase (gain in score), slight loss (0-0.5 point loss), moderate loss (0.6-1 point loss), and severe loss (over 1 unit loss). Intermediate body condition at parturition and at first AI, and a slight loss during the early lactation period were used as reference categories. The effects of body condition on the variable pregnancy rate at first AI were highly heterogeneous, while all the studies considering the number of days open presented homogeneous results. A clear association between body condition category and pregnancy rate at first AI was detected only when the effect of a low score at parturition was analyzed: pregnancy rate at first AI significantly decreased by about 10% in cows delivering in poor condition. Animals with a high BCS at parturition showed a significant reduction in the number of days open of 5.8 or 11.7 when compared with animals with an intermediate or low body condition, respectively. In animals in the high body condition category at first AI, the variable days open showed a significant drop of 11.9 or 24.1, compared to animals in the intermediate or low categories, respectively. A severe loss in score during early lactation was related to a significant (10.6) increase in the number of days open, while a slight or moderate body condition change, either loss or gain in score, was not significantly related to the variable days open. We found that the number of days open was a good indicator of the effects of BCS or change in score on reproductive performance in dairy cattle. The variable pregnancy rate at first AI, however, yielded heterogeneous results among studies.

Study of the functional anatomy of bovine oviductal mucosa

The oviducts of 31 cyclic cows were examined to study the structure and nature of the oviductal mucosa. The general distribution of spermatozoa within the oviductal mucosa was studied in five additional cows. The oviductal infundibulum is an asymmetric funnel‐shaped structure surrounding the ostium. It is divided along the free boarder of the mesosalpinx and presents one wide and one narrow side. The mucosa of the wide side possesses a system of low interconnected cords that converge distally forming primary folds. The folds on the narrow side start sharply from the free margin and fuse toward the ostium abdominale. Areas between folds throughout the lumen of the oviduct show a high degree of complex organization. Interfold spaces are occupied by secondary and small interconnected folds which join to form a system of cul‐de‐sacs. In the infundibulum, these cul‐de‐sacs open toward the ovary, while cul‐de‐sacs present in the caudal isthmus and in the UTJ open toward the uterus. Marked variations were observed in the oviductal epithelium depending on the oviductal segment, basal or apical areas of the folds, and phase of the oestrous cycle. Near to the time of ovulation, numerous spermatozoa were found in the periphery of the caudal isthmus within pockets of basal interfold areas, as well as within pockets and cul‐de‐sacs of the tubo‐uterine junction. Individual spermatozoa were also observed in peripheral areas of the ampullary‐isthmic junction and ampulla. The topography of the oviduct provides a complex system of regulation which may influence not only the passage of gametes and/or embryos, but also movement of fluid within the oviductal canal. Anat Rec 260:268–278, 2000.

Risk factors for postpartum ovarian cysts and their spontaneous recovery or persistence in lactating dairy cows

Cystic ovarian disease is a major cause of reproductive failure and economic loss for the dairy industry. Many cysts that develop during the early postpartum period regress spontaneously. However, it is difficult to decide at what point it would be more cost effective to treat ovarian cysts than to wait for spontaneous recovery. The objective of this study was to analyze risk factors for the development of the ovarian cystic condition during early and late postpartum, and for its persistence or recovery during the pre-service period in lactating dairy cows. Using multiple logistic regression, we analyzed data derived from 873 lactating dairy cows from a single herd. An ovarian cyst was diagnosed if it was possible to observe a single follicular structure with an antrum diameter > or = 25 mm in the absence of a corpus luteum in three sonograms performed at 7-day intervals. The cystic condition was denoted as early if the cyst was diagnosed 43-49 days postpartum, and late if detected 57-63-day postpartum. Spontaneous cyst regression before 60-day postpartum was regarded as early cystic recovery. For the early cystic group, there were no significant effects of lactation number, body condition score on prepartum Day 60, at parturition or on postpartum Day 30, or of body condition loss from parturition to 30-day postpartum. Cows calving in summer were 2.6 times more likely to develop ovarian cysts than those giving birth in winter. The risk of having a cyst was 1.9 times higher in cows with an abnormal puerperium. A 1-kg increase in milk yield raised the risk of cysts by a factor of 1.05. A 1-unit increase in body condition score (scale from 1 to 5) from prepartum Day 60 to parturition increased the risk of cyst development 8.4 times. Milk production and lactation number were negatively correlated with spontaneous early cyst recovery. A 1-kg decrease in milk production increased the probability of cyst recovery by a factor of 1.06, and a 1-unit drop in lactation number was associated with a 1.4-fold increased probability of cyst recovery. For the late cystic group, there were no significant effects of abnormal puerperium and body score data, except for a prepartum change in body score. Calving season (Odds ratio: 2.3), lactation number (Odds ratio: 1.36), increased milk production (Odds ratio: 1.05) and increased body condition score during the prepartum period (Odds ratio: 4.3) were all related to an increased risk of ovarian cysts. The probability of having a late cyst was 36.6 times greater in cows with early cysts. These findings suggest that it would be profitable to treat multiparous cows having cysts very early in the postpartum period, while treatment of primiparous cows should be delayed, at least until the end of the pre-service period, to provide the opportunity for spontaneous recovery.

SITE OF SEMEN DEPOSITION IN CATTLE: A REVIEW

The breeding of cattle using conventional artificial insemination methods involves the deposition of semen in the uterine body. However, it has been recently proposed by several authors that the site of semen deposition be changed to the uterine horns. This suggestion is based on 2 facts: the acceptance that the major preovulatory sperm reservoir may be the uterotubal junction rather than the cervical canal, and the lack of accuracy by inseminators in depositing semen. In over 50% of cases, inseminators were not sufficiently trained to deposit semen into the uterine body, so that intracervical insemination was often performed resulting in reduced fertility. The advantage of deep uterine insemination, whether bicornual or unicornual, is that it favors the deposition of semen nearer to the uterotubal junction and thus reduces the incidence of cervical deposition. This review updates the literature on the ideal site of semen deposition, including cervical, uterine body, cornual and intraperitoneal. Also analyzed are the effects of right vs. left side activity of the female reproductive tract on the optimum site of semen deposition as it affects fertilization. Finally, the question of whether the clinical training of inseminators should be reevaluated is discussed.

Clinical use of human chorionic gonadotropin in dairy cows: An update

Human chorionic gonadotropin (hCG) has a potent luteinizing hormone (LH)-like effect in cattle that extends the life span of the corpus luteum (CL) and increases progesterone synthesis, induces ovulation throughout the estrous cycle, promotes the formation of accessory corpora lutea when applied in the early luteal phase, and modifies follicular wave dynamics increasing the frequency of three-wave dominant follicular cycles. As hCG acts on ovarian cells independently of the pituitary gland and its effect is longer lasting than that produced by endogenous LH release, use of hCG rather than gonadotropin-releasing hormone (GnRH) could be targeted at populations of subfertile cows. This review describes the clinical use of hCG to improve the reproductive performance of dairy cows. In addition, we describe recent developments in the therapeutic use of hCG and studies addressing the benefits of including hCG in estrus and ovulation synchronization protocols. Our review ends with a critical discussion of how earlier findings related to ovarian responses to hCG treatment can be interpreted in the light of recent advances in the clinical applications of hCG.

INFLUENCE OF CALVING SEASON ON THE INTERACTIONS AMONG REPRODUCTIVE DISORDERS OF DAIRY COWS

The objective of this study was to evaluate the influence of calving season on the interactions among reproductive disorders prior to conception and their effect on subsequent reproductive performance in dairy cows. Data from 3170 lactations of Holstein-Friesian cows that subsequently conceived were analysed by means of path analysis techniques. The cows were from nine commercial dairy herds in north-eastern Spain. Lactation incidence rates for retained placenta, metritis, ovarian cysts and repeat breeding (more than four artificial inseminations per conception) were 6·4, 3·7, 5·4 and 7·9%, respectively, and there were no differences between warm (May to September) and cool (October to April) calving seasons. However, our data show that calving season influenced the interrelationships among reproductive traits. Lactation number was not related to any of the path model variables for cows calving in cool seasons and retained placenta did not directly influence ovarian cysts or repeat breeding. In contrast, older cows that calved during warm seasons showed an increased risk of experiencing retained placenta, ovarian cysts and more days open; retained placenta was a direct risk factor for ovarian cysts and repeat breeding. Our data indicated that a cool season decreased interactions among reproductive disorders of dairy cows. Cows that calved in a cool environment could more effectively cope with reproductive disorders prior to conception and this fact was mainly observed in older cows.

Persistent ovarian follicles in dairy cows: a therapeutic approach

Anestrus is common during the postpartum period in high-producing dairy cows. In a previous investigation, we were able to diagnose persistent follicles of 8 to 12 mm in anestrous cows. This report describes 2 consecutive studies. The objectives of the first were to 1) assess the association of persistent follicles with anestrus; and 2) evaluate 2 therapeutic treatments. In the second study, we compared the effectiveness of the best treatment established in Study 1 with the Ovsynch protocol. For Study 1, anestrous cows were considered to have a persistent follicle if it was possible to observe a single follicular structure > 8 mm in the absence of a corpus luteum or a cyst in 2 ultrasonographic examinations performed at an interval of 7 d. At diagnosis (Day 0), cows were assigned to 1 of 3 treatment groups. Cows in Group GnRH/PGF (n=17) were treated with 100 microg GnRH i.m., and 25 mg PGF2alpha i.m. on Day 14. Cows in Group PRID (n=18) were fitted with a progesterone releasing intravaginal device (PRID, containing 1.55 g of progesterone) for 9 d and were given 100 microg GnRH i.m. at the time of PRID insertion, and 25 mg PGF2alpha i.m. on Day 7. Cows in Group Control (n=18) received no treatment. The animals were inseminated at observed estrus and were monitored weekly by ultrasonography until AI or 5 weeks from diagnosis. Blood samples were also collected on a weekly basis for progesterone determination. The mean size of persistent follicles on Day 0 was 9.4 +/- 0.04 mm. Progesterone levels were < 0.2 ng/mL during the first 35 d in 16 of 18 Control cows. Cows in the PRID group showed a lower persistent follicle rate (16.7% < 70.6% < 88.9%; P < 0.0001; PRID vs GnRH/PGF vs Control, respectively); a higher estrus detection rate (83.3% > 29.4% > 11.1%; P < 0.0001) and a higher pregnancy rate (27.8% > 5.9% > 0%; P = 0.02). For the second study, 145 cows with persistent follicles were randomly assigned to 1 of 2 treatment groups: cows in Group Ovsynch (n=73) were treated with 100 microg GnRH i.m. on Day 0, 25 mg PGF2alpha i.m. on Day 7, and 100 microm GnRH i.m. 32 h later. Cows in this group were inseminated 16 to 20 h after the second GnRH dose (Ovsynch protocol). Cows in Group PRID (n=72) were treated as those in the PRID group of Study 1, and were inseminated 56 h after PRID removal. Cows in the PRID group showed a higher ovulation rate (84.8% > 8.2%: P < 0.0001); a higher pregnancy rate (34.2% > 4.1%; P < 0.0001) and lower follicular persistence rate (22.2% < 63%; P < 0.0001) than those in Ovsynch. Our results indicate that persistent follicles affect cyclic ovarian function in lactating dairy cows. Cows with persistent follicles can be successfully synchronized and time inseminated using progesterone, GnRH and PGF2alpha but show a limited response to treatment with GnRH plus PGF2alpha.

Factors of a noninfectious nature affecting fertility after artificial insemination in lactating dairy cows. A review

After 80 years of the commercial application of artificial insemination (AI) in the cow, the method still has numerous benefits over natural insemination including worldwide gene improvement. The efficiency of insemination depends, among many other factors, on the delivery of an appropriate number of normal spermatozoa to the appropriate reproductive tract site at the appropriate time of estrus. The metabolic clearance of steroid hormones and pregnancy associated glycoproteins and the negative effects of different types of stress related to high milk production makes the high-producing dairy cow a good animal model for addressing factors affecting fertility. Nevertheless, extensive studies have shown a positive link between high milk production in an individual cow and high fertility. When a cow becomes pregnant, the effect of pregnancy loss on its reproductive cycle is also a topic of interest. This paper reviews the factors of a noninfectious nature that affect the fertility of lactating dairy cows following AI. Special attention is paid to factors related to the cow and its environment and to estrus confirmation at insemination. Pregnancy maintenance during the late embryonic/early fetal period is discussed as a critical step. Finally, the use of Doppler ultrasonography is described as an available research tool for improving our current understanding of the health of the genital structures and conceptus.