Heat stress has consequences on both the physiology and reproductive performance of cows, but the most dramatic effect for dairy producers is the decrease produced in fertility. The effects of heat ...stress on fertility include an increased number of days open, reduced conception rate, and larger number of cows suffering different types of anestrus. Once becomes pregnant, heat stress affects also the reproductive success of the cow through its direct effects on the ovary, uterus, gametes, embryo, and early fetus. This article reviews current knowledge of the effects of heat stress on fertility in dairy cows and the hormonal strategies used to mitigate these effects at the farm level. Administration of GnRH at the moment of artificial insemination can improve the conception rate. Breeding synchronization protocols for fixed-time insemination may reduce the calving conception interval and the number of services per conception. Progesterone-based protocols seem resolve better the reproductive disorders related to a hot environment (anestrus) than GnRH-based protocols. The use of combinations of GnRH, eCG, and hCG in progesterone-based protocols can improve results. Progesterone supplementation during the late embryonic and/or early fetal period would be useful in curtailing pregnancy losses, mainly in single pregnancies, whereas a more positive effect of treatment with GnRH than progesterone has been found in twin pregnancies. Melatonin therapy is emerging as a promising strategy to improve the natural reproductive performance of cows suffering conditions of heat stress.
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.
Equine chorionic gonadotropin (eCG) is a member of the glycoprotein family of hormones along with LH, FSH and thyroid‐stimulating hormone. In non‐equid species, eCG shows high LH‐ and FSH‐like ...activities and has a high affinity for both FSH and LH receptors in the ovaries. On the granulosa and thecal cells of the follicle, eCG has long‐lasting LH‐ and FSH‐like effects that stimulate oestradiol and progesterone secretion. Thus, eCG administration in dairy cattle results in fewer atretic follicles, the recruitment of more small follicles showing an elevated growth rate, the sustained growth of medium and large follicles and improved development of the dominant and pre‐ovulatory follicle. In consequence, the quality of the ensuing CL is improved, and thereby progesterone secretion increased. Based on these characteristics, eCG treatment is utilized in veterinary medicine to control the reproductive activity of the cow by i) improving reproductive performance during early post‐partum stages; ii) increasing ovulation and pregnancy rates in non‐cyclic cows; iii) improving the conception rate in cows showing delayed ovulation; and finally, iv) eCG is currently included in protocols for fixed‐time artificial insemination since after inducing the synchrony of ovulation using a progesterone‐releasing device, eCG has beneficial effects on embryo development and survival. The above effects are not always observed in cyclic animals, but they are evident in animals in which LH secretion and ovarian activity are reduced or compromised, for instance, during the early post‐partum period, under seasonal heat stress, in anoestrus animals or in animals with a low body condition score.
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Temperature gradients in female reproductive tissues seem to influence the success of key processes such as ovulation and fertilization. The objective of this study was to investigate ...whether pre‐ovulatory follicles are cooler than neighbouring uterine tissue and deep rectal temperatures in lactating dairy cows under heat stress conditions. Temperatures within the pre‐ovulatory follicle, on the uterine adjacent surface and 20 cm deep within rectum, were measured using fine thermistor probes within 45 min after sunrise (dawn). Cows were selected from synchronized groups for fixed‐time insemination during the warm period of the year. Five cows under direct sun radiation and 11 cows in the shade were included in the study. None of the cows in the sun area ovulated within 24 hr, whereas 10 of the 11 cows in the sun area ovulated. Four of the 10 ovulating cows became pregnant. In the ovulating cows, follicular temperatures were 0.74 and 1.54°C significantly cooler than uterine surface and rectal temperatures, respectively, whereas temperatures in the uterine area were 0.80°C significantly cooler than rectal temperatures. No significant differences among temperatures were found in non‐ovulating cows. Follicular size was similar for ovulating and non‐ovulating cows. Environmental temperatures in the shade area were 6.4°C significantly lower than those in the sun area. Results of this study indicate that pre‐ovulatory follicles are cooler than neighbouring uterine tissue and deep rectal temperatures and those temperature gradients were not found in cows suffering ovulation failure.
The biological and economic impacts of pregnancy loss in dairy herds are well recognized. This review examines clinical aspects of late embryonic/early fetal loss of non-infectious cause in the dairy ...cow. The period of interest spans from shortly after observation of at least one embryo with a heartbeat upon pregnancy diagnosis, at around Day 28 of pregnancy (late embryonic period), until approximately Day 60 of pregnancy (early fetal period). This last time point is when pregnancy is firmly established and beyond which the risk of pregnancy loss is greatly reduced. We particularly focus on the role of the clinician in managing a pregnancy and discuss findings to predict the viability of a pregnancy, available therapies for expected pregnancy problems and possible implications of the newer technologies.
•Clinical ultrasound management of pregnancy in dairy cattle.•Evaluation of ovarian structures opposed to uterine contents.•The clinician as a possible risk factor for pregnancy loss.•The matter of twin pregnancies.•Predicting the viability of a pregnancy.
This study sought to establish whether treatment with the GnRH analog dephereline in the early luteal phase could be useful to improve fertility in repeat-breeder cows (>3 inseminations). Dephereline ...was given 5–7 days after insemination, and effects of both a single and elevated (2.5 times) dephereline dose on pregnancy and subsequent embryo survival determined in repeat-breeder lactating dairy cows. The study population comprised 810 cows: 399 repeat-breeder cows and 411 non repeat breeders. To determine the effects of treatment on the pregnancy rate, three study groups were established: Control, no treatment (n = 269), DEPH, single dephereline dose (100 μg) (n = 270), or 2.5DEPH, 2.5 dephereline doses (250 μg) (n = 271). Recorded pregnancy rates in these groups were 28.6% (77/269), 31.9% (86/270) and 39.1% (106/271), respectively. Binary logistic regression analysis revealed a significant effect of the interaction treatment x repeat breeder on the pregnancy rate. This meant that the single dose and control treatments led to a pregnancy likelihood of repeat-breeder cows reduced by factors of 0.47 and 0.34, respectively, when compared to the 2.5 dose treatment as reference. Treatment had no effects on non repeat breeders. Based on odds ratios, treatment given either as a single or 2.5 dose increased the probability of an additional corpus luteum (more corpora lutea than embryos) in pregnant cows by factors of 5 or 5.4, respectively. Treatment had no effect on embryo survival. Our findings support the hypothesis that dephereline treatment in the early luteal phase after AI improves fertility in repeat-breeder cows. A dephereline dose 2.5 times higher than normal led to improved pregnancy rates, thus overcoming the impacts of repeat-breeder syndrome. Importantly, both the single and 2.5 dephereline doses increased the chances of pregnant cows having an additional corpus luteum, likely favoring embryo survival.
•2.5 dephereline doses given 5–7 d post-AI increase fertility in repeat breeders.•A single or 2.5 dephereline doses increase accessory CL in pregnant cows.•Dephereline may overcome the effects of repeat-breeder syndrome.
The effects of season on the fertility of the dairy cow added to the metabolic stress of milk production are well known. We here present lactating dairy cows as a comparative model of this problem. ...This review examines the results of recent studies that have highlighted heat stress (HS) effects on pre-ovulatory follicles. From these studies, we draw information regarding the mechanisms giving rise to temperature gradients across reproductive tissues. Our review is completed by a discussion of approaches designed to reduce the negative effects of HS based on cooling strategies implemented before ovulation at or around estrus.
•Direct measurements of intra-follicular temperature.•Pre-ovulatory follicles unequivocally cooler than rectum.•Follicular cooling is a prerequisite for ovulation.•Follicular cooling correlates positively with the potential for pregnancy.
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.
This study examines the possible effects on the reproductive performance of high-producing dairy cows of progesterone (P4) given in the early luteal phase (1.55 g of P4), from Days 3 to 5 ...post-artificial insemination (AI) as compared with the time of pregnancy recognition, from Days 15 to 17 post-AI. Cows in their third day post-AI were alternately assigned on a weekly rotational basis to the following groups: control, no treatment (C: n = 351), P4 treatment started 15 days after AI (P4-D15: n = 261), or P4 treatment started 3 days after AI (P4-D3: n = 203). Based on odds ratios, cows in P4-D3 were 1.71 times more likely to conceive than control cows (P = 0.004), whereas cows in P4-D15 showed a 1.4-fold greater risk approaching significance of becoming pregnant compared with control cows (P = 0.06). Differences were not observed between treatments. In nonpregnant cows, the given treatment (D3 vs. D15) had no effect on subsequent return to estrus or AI interval and neither were any effects of treatment observed on early fetal loss rates. In contrast, in pregnant cows, the relative risk of twin pregnancy was 2.5 times higher for those in P4-D15 (P = 0.02) than the remaining cows. These findings indicate the efficacy of P4 supplementation after AI. However, when given at the time of pregnancy recognition rather than in the early luteal phase, this treatment increases the twin pregnancy rate.
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The objective of this study was to determine whether fluid drainage from the subordinate follicles by ovum pickup procedures prevents the risk of twin pregnancy without reducing the ...fertility of the cow. Lactating dairy cows with at least two follicles over 12 mm diameter located one on each ovary and selected from synchronized groups for fixed‐time insemination were assigned to a Control (n = 49) or Drainage (n = 49) group. The largest follicle was considered as the dominant follicle. Draining of all subordinate follicles (≥10 mm) was performed in the Drainage group. All drained follicles developed as a corpus luteum 7 days later. In the Control cows, the presence of two corpora lutea (55.1%) was lower (p = .003) than those in the Drainage cows (87.8%), whereas the incidence of twin pregnancies was 50% and 0% for the Control and Drainage groups, respectively (p < .001). Draining did not affect the pregnancy rate. These results indicate that puncture and drainage of the subordinate follicles at insemination may eliminate the risk of twin pregnancies and reduce the risk of subsequent pregnancy loss by increasing the incidence of additional corpora lutea.
