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.
In the Northern Hemisphere, from June to September and in the Southern Hemisphere from December to March, there are periods of reduced fertility (sub-fertility) in dairy cows that are described as ...summer infertility. Several factors contribute to sub-fertility during this time, such as ambient temperature, humidity and photoperiod. During the warm season there is a reduction in feed intake that may compromise the energy balance of the cow and/or induce an imbalance in the activity of the hypothalamo-hypophyseal-ovarian axis. These factors reduce the reproductive performance of the cow and compromise the quality of oocytes, embryos and corpora lutea. This paper reviews current knowledge on the metabolic and endocrine mechanisms that induce summer infertility and describe their effects on follicle, oocyte and embryo development in dairy cows.
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.
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.
Summer heat stress is a main factor related to low conception rate in high producing dairy herds in warm areas worldwide. We assessed the impact of several climate variables on conception rate in ...high producing dairy cows in northeastern Spain by examining 10,964 inseminations. The temperature–humidity index (THI) was compared with maximum temperature in terms of its efficiency at predicting conception rate. The following data were recorded for each animal: herd, lactation number, insemination number, insemination date, inseminating bull, and AI technician along with climate variables such as mean and maximum temperatures, rainfall, mean and maximum THI for individual time points Days 7 to 1 before insemination, the day of insemination and 1, 2 and 3 days after insemination. Averages were also established for the following periods: from 7 days before insemination to the insemination day, from 3 days before insemination to the insemination day and from the insemination day to 3 days postinsemination. Based on the odds ratios, the likelihood of conception rate increased significantly by factors of 1.48, 1.47, 1.5, and 1.1 for the respective maximum THI classes <70, 71–75, 76–80, and 81–85 only on Day 3 before AI, while on the insemination day, it increased by factors of 1.73, 1.53, 1.11, and 1.3 for the respective maximum THI classes <70, 71–75, 76–80, and 81–85. In a subsequent logistic regression excluding mean and maximum THI, the effectiveness of temperature at predicting conception rate was evaluated. Although high, the fit of the second logistic regression model was slightly lower than that of the full model (
P
=
0.88 versus
P
=
0.98, respectively) and the information provided by the THI model. The likelihood of conception rate increased significantly by factors of 1.5, 1.2, 1.0, 1.0 for the respective maximum temperature classes <20, 21–25, 26–30, 31–35
°C on Day 1 after AI. The choice of the THI or temperature to monitor the farm environment would have to depend on the particular farm and situation. In our study conditions, the use of maximum temperature alone gives a new point of view regarding the information provided by the THI variables.
This report reviews the clinical applications of routine ultrasound in gestation control programmes for dairy herds. Emphasis is placed on identifying risks of late embryo/early foetal loss of ...non-infectious cause by monitoring ovarian structures (as opposed to uterine contents), indicators of pregnancy loss and twin pregnancies. Suggestions are provided to appropriately manage a cow at risk of pregnancy loss during the late embryonic/early foetal period. This review identifies gaps in our current knowledge of the aetiology of pregnancy loss and spontaneous embryo/corpus luteum reduction. Two areas of the implantation-placentation window of gestation in particular need urgent attention: the roles in pregnancy loss of immune-endocrine interactions and the physiological status of the embryo/corpus luteum. The latter issue and consecutively endocrine interactions could be successfully addressed by incorporating Doppler ultrasonography into routine ultrasound procedures.
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.
This study sought to examine the impact of the presence of two co-dominant (ovulatory) follicles at the time of artificial insemination (AI) on the ovulatory response to GnRH given in a fixed-time AI ...protocol. The study population comprised 622 lactating dairy cows: 306 (49.2%) with a single follicle, 198 (31.8%) with two bilateral follicles (one follicle per ovary) and 118 (19%) with two unilateral follicles (same ovary). Based on odds ratios, cows with two bilateral or unilateral follicles were less likely (by factors of 0.09 and 0.11, respectively) to undergo ovulation failure compared with cows with one follicle (P = 0.01 and P = 0.02, respectively); the likelihood of ovulation failure decreased 0.75 times with every one-mm increase in follicle diameter for cows with a single follicle, whereas individual follicle diameter was not related to ovulation failure in cows with two bilateral follicles (P = 0.001). The likelihood of double ovulation decreased 0.7 times with every one-mm diameter difference between the larger and smaller follicle for all cows with two follicles (P = 0.001), whereas cows with two unilateral follicles showed a higher (P < 0.05) double ovulation rate than cows with two bilateral follicles. In 116 (58.6%) of the cows with two bilateral follicles, only the larger follicle ovulated in 59.5% cows, whereas only the smaller one ovulated in the remaining 40.5% cows. In these cows, a one-mm size difference between the larger and the smaller follicle gave rise to a 1.12-fold increase in the ovulation failure rate for the larger follicles (P = 0.0001). Cows with two bilateral follicles were more likely (by a factor of 1.5) to conceive than cows with one follicle (P = 0.001). Significant right-left differences were not found in cows with two bilateral follicles, whereas the right ovary was more active than the left in the remaining cows. Our results indicate that cows with two co-dominant follicles at AI show different ovulation patterns to those with one dominant follicle. A higher rate of ovulation failure was observed among cows with one follicle than cows with two follicles, whereas the conception rate was higher for cows with two bilateral follicles than for the remaining cows. In cows with two follicles, double ovulations along with ovulation of the smaller follicle were related to the least size difference between the larger and smaller follicle.
•The likelihood of ovulation increased with increasing follicle diameter in cows with one follicle.•Individual follicle size was not related to ovulation failure in cows with one ovulatory follicle in each ovary.•Cows with two unilateral follicles showed a greater likelihood of double ovulation than cows with two bilateral follicles.•The conception rate was higher for cows with two bilateral follicles compared with two unilateral or a single follicle.
This study was designed to determine the effects of twinning on the subsequent reproductive performance and productive lifespan of high milk-producing dairy cows. The data analyzed were taken from ...complete reproductive records for 4861 Holstein Friesian cows comprising a commercial herd, including data for 12 587 calving events from April 1, 2001 to March 31, 2012. The twinning rate was 5.6%, and 9.6% of the cows delivered twins at least once during their life. Conception rates before Days 90, 120, and 300 postpartum were 20.8%, 36.9%, and 74.5%, and 34.2%, 51.8%, and 85.0% for cows delivering twins and singletons, respectively. Cox regression analysis revealed that twinning reduced the chances of conception before Day 90 by a factor of 0.76. Also, the median calving to conception interval was significantly longer for cows calving twins (134 ± 4.5 days) than for cows delivering singletons (108 ± 0.8 days; P < 0.001). Moreover, in cows in which conception was successful, the risk of abortion was higher for cows that calved twins than for those calving singletons (13.7% vs. 10.3%, respectively; P = 0.01). Culling rates before Days 90, 120, and 300 postpartum were 15.6%, 16.1%, and 28.6%, and 7.6%, 8.7%, and 15.9% for cows calving twins and singletons, respectively. Cox regression analysis of the factors affecting the culling rate before Day 300 postpartum revealed a 1.41 times greater hazard ratio of culling for cows calving twins than cows calving singletons. Further, mean productive lifespan was almost 300 days shorter for primiparous twinners (N = 48, 602 ± 493 days) than for nontwinners (N = 2592; 899 ± 581 days; P < 0.01), and 200 days shorter for secundiparous twinners (N = 126, 914 ± 429 days) than for nontwinners undergoing at least two lactations (N = 1936, 1101 ± 522 days; P < 0.01). Kaplan-Meier survival curves for productive lifespan differed between primiparous twinners and non-twinners (P < 0.001), and between secundiparous twinners and nontwinners having at least two lactations (P = 0.017). Differences in culling patterns for twinners and nontwinners were not restricted to the subsequent lactation but continued as long as 800 days after first calving, strongly suggesting long-term negative effects of twinning. As an economic implication of our findings, we suggest that twin embryo reduction at the moment of pregnancy diagnosis could be a profitable strategy to cut twinning rates and abolish their detrimental effects on subsequent reproductive performance and productive lifespan.
Contents
The aim of this study was to determine the effect of melatonin treatment during the early dry‐off period on subsequent reproductive performance and milk production in high‐producing dairy ...cows under heat stress conditions. In experiment I, addressing the pharmacokinetics of melatonin treatment in lactating dairy cows, doses of untreated, 3, 6, 9 or 12 implants/animal (18‐mg melatonin each implant) were given as subcutaneous implants on gestation day 120–20 multiparous lactating dairy cows (four cows/dose group). Experiment II was performed during the warm season on 25 heifers and 114 high milk‐producing Holstein‐Friesian cows. Animals were randomly assigned to a control (C) or melatonin group (M). Animals in the M group received nine implants (heifers) or 12 (cows) of melatonin on day 220 of gestation. In experiment I, cows in the 12 implants group showed a higher maximum melatonin concentration (Cmax) and area under the concentration curve from treatment day 0 to day 49 (AUC0–49d) than those in the remaining groups, among which there were no significant differences in this variable. In experiment II, the likelihood of repeat breeding syndrome (<3 vs ≥4 AIs per cow) and pregnancy loss (first trimester) were 0.36 and 0.19 times lower in treated than control animals, respectively. Plasma prolactin levels decreased significantly (p = 0.01) after melatonin treatment and recovered during the postpartum compared to control cows. No significant effects on milk production were observed in the subsequent lactation. Significant differences in days open between groups (means 123 ± 71.9 and 103 ± 43, respectively, for C and M; p = 0.02) were registered. In conclusion, melatonin treatment in the early dry‐off period improves the reproductive performance of dairy cattle, reducing the number of days open, repeat breeding syndrome and pregnancy loss.
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