Embryonic ability to prolong the interoestrous interval in virgin and repeat breeder heifers

Effect of energy balance profiles on metabolic and reproductive response in Holstein and Swedish Red cows

This study examined the effect of two feeding levels during the antepartum and postpartum period on reproductive performance and blood metabolites (glucose, non-esterified fatty acids (NEFA), insulin) in primiparous Holstein and Swedish Red (SRB) cows, in order to identify possible differences in the way these breeds respond to negative energy balance after calving. A total of 44 cows (22 Holstein, 22 SRB) kept in a loose housing system were included in the study. The control group (HE, n = 23) was fed a diet for high-producing cows (target 35 kg/d energycorrected milk, ECM). A lower feeding intensity (LE, n = 21) was achieved by giving -50% concentrate to target 25 kg/d ECM. Diets were implemented 30 days before expected calving and the cows were monitored for 120 days postpartum. Milk yield and composition, dry matter intake (DMI), live body weight and body condition score (BCS) were assessed to calculate the weekly energy balance (residual feed intake). Blood sampling started before diet implementation and was repeated every 2 weeks until Day 60 postpartum and then once monthly until Day 120. Plasma was kept at -20 °C until analysis for glucose, insulin and NEFA concentrations. Mixed linear models were used to analyse data (SAS 9.3; PROC MIXED). Holstein cows had lower mean energy balance than SRB cows (-4.7 ± 1.4 and -0.9 ± 1.4 MJ, respectively; p = 0.05). SRB cows had higher (p<0.001) BCS (3.3 ± 0.1) than Holstein cows (2.7 ± 0.1) and also higher plasma glucose concentrations from Day -30 to Day 120 relative to parturition (4.1 ± 0.1 and 4.2 ± 0.1 log ; mg/100 ml, respectively; p < 0.05). Overall, breed or diet had no effect on NEFA blood plasma concentrations. However, plasma NEFA concentration levels tended to be higher (p = 0.09) in SRB cows than in Holsteins at Day -14 before calving, indicating higher mobilisation of lipid from adipose tissue already before calving. In contrast, Holstein cows had higher NEFA at Day 14 postpartum than SRB cows (p < 0.05). There were no significant effects of diet or breed on reproductive performance (% pregnant at first AI, days open). However, commencement of luteal activity within 21d postpartum was affected (p < 0.05) by the interaction of breed and diet. These results suggest that Holstein cows prioritise milk production to a larger extent than SRB cows, resulting in a less balanced metabolic profile.

The effects of raising post-oestrus progesterone concentrations on luteal activity in post-partum dairy cows

In order to investigate the rationale of manipulating post-ovulation progesterone (P4) concentrations, luteal activity was measured in 10 Holstein-Friesian cows treated with a progesterone-releasing device (CIDR, 1·9 g P4) inserted on the morning of day 2 post-oestrus for a period of 7 days and compared with 10 untreated control animals. Milk samples were collected daily during afternoon milking from 7 days pre- to 24 days post-oestrus and P4 concentrations were measured using enzyme-linked immuno-sorbent assay (ELISA). The milk P4 profiles were used to assess the effects of early post-oestrus P4 elevation on five intervals of the luteal phase. In the treated (T) and control (C) animals, the mean interval from oestrus to P4 rise (≥3 μg/l), was 2·38 (s.e. 0·18) and 4·90 (s.e. 0·28) days, respectively, (P < 0·01). The mean interval from oestrus to the attainment of peak P4 concentrations was not significantly different (P > 0·05) between the T (14·75 (s.e. 1-62) days) and С (14·30 (s.e. 0·70) days) animals, with cows in the T group showing a more variable (F7 9 = 4-30, P < 0·05) interval to the occurrence of the peak. The interval from peak P4 to corpus luteum (CL) regression (when P4 fell below ≥3 μg/l) was not significantly different between the T (4·13 (s.e. 1·30 days) and С (5·60 (s.e. 0·88) days) groups. Furthermore, CIDR insertion did not alter luteal phase length, number of days with P4 concentrations ≥3 μg/l (T = 16·50 (s.e. 0·80) v.C = 15·00 (s.e. 0·47) days) or the interval from oestrus to CL regression (T = 18·88 (s.e. 0·79) v.C = 19·90 (s.e. 0·41) days). We conclude that treatment with CIDR 2 days after oestrus successfully increased the availability of P4 to cows without significantly affecting luteal phase characteristics.

Bovine embryo transfer recipient synchronisation and management in tropical environments

Numerous studies have shown that it is possible to manipulate follicular and luteal dynamics, thereby eliminating the need for oestrus detection in embryo transfer (ET) programmes. Fixed-time ET (FTET) protocols are based on the use of gonadotrophin-releasing hormone (GnRH) and prostaglandin (PG) F or progesterone/progestogen (P4)-releasing devices and oestradiol. The FTET protocols increases the proportion of recipients transferred, and therefore pregnancy rates, compared with the use of PGF followed by ET 7 days after oestrus. Furthermore, the addition of equine chorionic gonadotrophin (eCG) to the P4 and oestradiol-based FTET protocols results in an even higher proportion of recipients transferred, and thus higher pregnancy rates. The beneficial effect of eCG treatment may be related to increased growth of the dominant follicle and increased plasma P4 concentrations during the subsequent luteal phase. In Bos taurus × Bos indicus recipients, pregnancy rates were positively correlated with the diameter of the corpus luteum (CL) and the number of CL at ET. When repeat-breeder Holstein cows were used as recipients, FTET protocols increased number of recipients transferred and pregnancy rates compared with the traditional PGF-based synchronisation protocols. In conclusion, the use of FTET protocols eliminates the need for the detection of oestrus and results in a greater proportion of recipients transferred and satisfactory pregnancy rates. Thus, FTET optimises the use of recipients, reducing labour and animal handling and facilitating the use of ET.

Effect of fixed-time embryo transfer on reproductive efficiency in high-producing repeat-breeder Holstein cows

The aim of the present study was to compare a synchronization of time of ovulation protocol for fixed-timed embryo transfer (FTET) with the usual administration of a single dose of prostaglandin associated with detection of estrus. Also, the effect of the presence of CL at the beginning of FTET protocol was evaluated. Lactating Holstein cows (n=651) with three previous artificial inseminations were classified according to presence or absence of a corpus luteum (CL). Cows with a CL were randomly assigned to two additional treatments and submitted to embryo transfer after detection of estrus (PGF-Estrus) or FTET (FTET-CL). Cows without CL were allocated to the FTET-NoCL treatment. On a random day of the estrous cycle (Day 0), cows in the PGF-Estrus treatment (n=229) were treated with 150 microg d-cloprostenol (PGF) i.m. followed by detection of estrus from Day 1 through Day 5 after PGF. Embryos were transferred 6-8 days after estrus detection. Cows in the FTET-CL (n=208; presence of CL) and FTET-NoCL (n=214; absence of CL) treatments received a norgestomet ear implant plus 2mg estradiol benzoate (EB) and 50mg progesterone i.m. on Day 0. On Day 8, the implant was removed and 400 IUeCG, 150 microg d-cloprostenol and 1mg estradiol cypionate i.m. were administered. No detection of estrus was performed and Day 10 was arbitrarily considered as the estrus day. Ultrasonographic exams were performed in all recipients and only cows with a single CL> or =15 mm or multiple CL received a fresh or frozen-thawed embryo on Day 17. Pregnancy was diagnosed by ultrasonography at 30 and 60 days of pregnancy. When FTET and PGF-Estrus were compared, the proportion of cows receiving an embryo (recipients transferred-to-treated rate) was greater in the FTET-CL (75.0% (156/208) than in PGF-Estrus (34.5%, 79/229; P<0.0001) treatment. Pregnancy rate (60 days) was also greater in FTET-CL (29.3%, 61/208) when compared to PGF-Estrus (16.2%, 37/229; P=0.001). However, no differences were found in pregnancy loss [PGF-Estrus=11.9% (5/42), FTET-CL=9.0% (6/67); P=0.62] and circulating progesterone concentration at embryo transfer [PGF-Estrus=4.02+/-0.52 ng/mL (n=25), FTET-CL=3.33+/-0.32 ng/mL (n=27); P=0.25] among these treatments. The presence of CL at the beginning of FTET protocol resulted greater transferred-to-treated rate [FTET-CL=75.0% (156/208) vs. FTET-NoCL=61.2% (131/214); P=0.003], but showed no effect on pregnancy rate at 60 days [FTET-CL=29.3% (61/208) vs. FTET-NoCL=22.9% (49/214); P=0.13], pregnancy loss [FTET-CL=9.0% (6/67) vs. FTET-NoCL=2.0% (1/50); P=0.15] and circulating progesterone concentration at ET [FTET-CL=3.33+/-0.32 ng/mL (n=27) compared to FTET-NoCL=3.44+/-0.40 ng/mL (n=2 9); P=0.82]. In conclusion, the protocol for synchronization of time of ovulation using norgestomet ear implant, EB and eCG increased recipients transferred-to-treated and pregnancy rates in high-producing repeat-breeder Holstein cows. Also, recipients without CL at the beginning of the time of ovulation synchronization treatment resulted in similar pregnancy rate as recipients with CL submitted to FTET protocol. Thus, the suggested protocol allowed the performance of FTET, without the need for detection of estrus, simplifying the reproductive management and increasing the reproductive efficiency in repeat-breeder Holstein recipients.

A Bayesian meta-analysis of the effects of administering an intra-vaginal (CIDR) device in combination with other hormones on the reproductive performance of cycling, anoestrous and inseminated cows

AIMS

To evaluate the effectiveness of treatment programmes that included controlled internal drug-releasing (CIDR) devices containing progesterone (P4) in improving synchrony of oestrus, and conception and pregnancy rates in cycling, anoestrous and inseminated dairy cows, using meta-analysis. To describe the difference in response between cycling and anoestrous cows to CIDR-based synchrony programmes.

METHODS

Scientific papers written in the English language between 1989 and 2002 that investigated the effects of treatment programmes including CIDR devices on reproductive performance in dairy heifers or lactating dairy cows were identified using a computerised literature search. The criteria for inclusion incorporated evidence that treatment allocation was completely randomised; the population studied was lactating dairy cows; and that data were available on submission, conception and pregnancy rates and their associated measures of variability. Reproductive outcomes from 25 synchrony trials (total n=11,058 cows) were analysed. Summary measures of the effect of treatment on reproductive outcome were assessed using fixed- and random-effects Bayesian meta-analysis models.

RESULTS

Treatment programmes including a CIDR device increased the risk of submission in cycling cows (predicted Bayesian RR=2.86, 95% credible interval=1.46-5.67). Compared with controls, synchrony programmes including CIDR devices in cycling dairy cows had no effect on the risk of conception to first service post-treatment (predicted Bayesian RR=1.00, 95% credible interval=0.80-1.24). Compared with controls, synchrony programmes including CIDR devices had no effect on the risk of pregnancy throughout the mating period (predicted Bayesian RR=1.02, 95% credible interval=0.89-1.17). In anoestrous cows, CIDR treatment had no effect on the risk of conception to first service post-treatment and no effect on the risk of pregnancy throughout the mating period, compared with anoestrous, untreated controls (predicted Bayesian RR=0.91 and 0.97, respectively; 95% credible interval=0.68-1.26 and 0.59-1.60, respectively).

CONCLUSION

The results of this meta-analysis showed that synchrony programmes using CIDR devices combined with other hormones reliably enhanced submission rates in lactating dairy cows. The relatively small number of trials with data suitable for analysis and the heterogeneity of results at the individual trial level limited our ability to confirm either a beneficial or deleterious effect of treatment on conception or pregnancy rates. Further randomised, controlled trials to evaluate the effectiveness of this form of reproductive therapy in commercial dairy farms are needed.

Repeat breeding in dairy heifers: follicular dynamics and estrous cycle characteristics in relation to sexual hormone patterns

Repeat breeding occurs at an incidence of 10% in the Swedish dairy cow population. Evidence is available for a hormonal asynchrony around estrus in repeat-breeder heifers (RBH). This asynchrony seems to be the underlying cause for a series of dysfunctions such as prolonged standing estrus and delayed ovulation, leading to fertilization failure. For further determinations of repeat-breeder estrous cycle characteristics, seven strictly selected RBH and six virgin heifers (VH) were studied during 3-7 consecutive cycles, with particular attention paid to the estrous period. Follicular dynamics were studied by ultrasonography and related to estrous behavior and pattern of sexual hormones (progesterone, estradiol-17beta, and LH) in peripheral circulation. Mean group data were compared and a classification model was designed. The most prominent findings for RBH were prolonged duration of estrus, delayed LH peak, prolonged lifespan of the preovulatory follicle, and a late postovulatory rise in plasma progesterone. There was also a strong tendency for peri-ovulatory suprabasal progesterone levels in RBH. It is suspected that these deviations cause changes in the microenvironment of the preovulatory follicle, negatively affecting the final maturation of the oocyte. The heterogeneity of the RBH group underlines the multifactorial cause of the repeat-breeder syndrome. The VH formed a homogenous group with data varying within physiological limits. A classification model based on three characteristic variables managed to identify 81% of the VH and 79% of the RBH correctly. Results from this study propose that some heifers have general, consistent problems in synchronizing estrous events, displayed as varying symptoms in the course of consecutive estrous cycles. These subfertile animals could be classified as repeat-breeders.

Ovarian follicle apoptosis at the onset of standing estrus in virgin and repeat-breeder dairy heifers

There is evidence that repeat breeding in dairy cattle can be caused by both extrinsic, environmental factors and intrinsic, animal factors. In repeat-breeder heifers (RBH), disturbed endocrine patterns and estrous events result in a subsequent decreased fertility associated with delayed ovulation. Whether infertility is also due to the presence of an unsuitable follicular environment impairing normal fertilization, remains to be determined. At the onset of standing estrus, ovaries were obtained from 7 strictly defined RBH and 5 virgin heifers (VH) of the Swedish Red and White breed. Detection of apoptosis in the preovulatory and three subordinate follicle walls was done by using the TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling) technique at light microscopy level. The follicles were histologically assessed for degree of atresia. The ultrastructure of the follicle wall and recovered oocytes was studied using transmission electron microscopy. The overall degree of apoptosis in membrana granulosa and theca interna of preovulatory and subordinate follicles did not differ between RBH and VH, but the numbers of TUNEL-positive cells differed significantly between preovulatory and subordinate follicles in both RBH and VH. There was a strong relationship between density of apoptotic cells and degree of atresia. No differences in follicle wall apoptosis nor morphology were detectable, suggesting that repeat breeder heifers enter standing estrus with the same morphological prerequisites as normal animals, considering follicular structure.

Corpus luteum activity, fertility, and adrenal cortex response in lactating Carora cows during rainy and dry seasons in the tropics of Venezuela

The effect of the rainy (RS) and the dry season (DS) on fertility, corpus luteum activity, and adrenal cortex response relationships were evaluated after first service (49 +/- 6 d postpartum) in Carora cows, a dairy cattle of Venezuela raised in tropical conditions. Cows (n = 84 in RS and n = 98 in DS) were kept semistabled, had two or three calvings, body condition score 3.5 on a 5-point scale and similar milk yield (2450 +/- 560 kg of milk during the previous lactation). Cows were grouped retrospectively according to pregnancy status. A split-plot model with repeated measures over Days 5, 7, 10, 14, and 15 after insemination was used to analyze the effects of season, pregnancy status, and their interaction involving the day on: 1) serum concentration of progesterone in four treatments: RS pregnant (n = 26), RS nonpregnant (n = 24), DS pregnant (n = 24), and DS nonpregnant (n = 20) cows; 2) serum concentration of cortisol at Days 0, 10, 14, 15, and 16 postservice in the previous treatments (n = 9, 7, 6, and 8, respectively); and 3) concentrations of cortisol after 0.1 mg of adrenocorticotropin in these last four groups of cows at Day 14 postinsemination. Breeding during the DS decreased (P < 0.05) conception rate to first service and increased (P < 0.01) days in service. In addition, the DS decreased (P < 0.05) the percentages of cows with normal interestrous interval (20-22 d), expression of estrus, and (P < 0.01) luteal phase progesterone; but DS increased (P < 0.05) percentages of short and long estrous cycles, anovulatory estrus, and repeat breeding rate. Mean serum concentration of progesterone was lower (P < 0.05) at Days 10, 14, and 15 in DS nonpregnant than in DS pregnant cows, and lower during luteal phase (P < 0.05) in DS nonpregnant than RS nonpregnant cows. Serum cortisol concentration was greater (P < 0.05) at Days 10, 14, and 16 in DS nonpregnant than DS pregnant cows. A significant (P < 0.05) negative correlation (r = -0.78) between serum concentrations of progesterone and cortisol was found within DS nonpregnant cows. Concentrations of cortisol after adrenocorticotropin were greater (P < 0.05) in DS nonpregnant cows than in other groups. These results indicate that elevated concentrations of cortisol associated with the DS may decrease progesterone secreted by the corpus luteum and therefore mediate the negative effect of the DS on fertility.

Relationship of pregnancy rate to peripheral concentrations of progesterone and estradiol in beef cows

The relationship between pregnancy rate and concentrations of progesterone (P(4)) and estradiol-17beta (E(2)) in serum was examined in inseminated beef cows. Jugular blood was collected twice daily on Days 4 through 7 and Days 14 through 17 after estrus to establish patterns of secretion of P(4) and E(2). Pregnancy rate was determined by palpation per rectum at 45 d. Mean concentrations of each hormone, ratio of E(2):P(4) and regressions of hormone on day were the variables measured for each of the 2 periods. Cows were classified into low (n=26), medium (n=50) and high (n=26) groups for each variable. The relationship of pregnancy rate to each variable was tested using Chi-square analyses. Pregnancy rates to the first service decreased linearly as relative mean concentrations of E(2) increased on Days 14 through 17 (P<0.05) but were not affected by any of the other hormonal variables studied during either period. Pregnancy rates to the second service were not related to concentrations of P(4) or E(2) during the luteal phase before mating (Days 14 through 17). The effects of pregnancy on concentrations of E(2) and P(4) also were tested. On Days 14 through 17, P(4) increased slightly in pregnant cows and declined slightly in nonpregnant cows (P<0.05), but pregnancy did not affect E(2) during either period or P(4) on Days 4 through 7. In summary, pregnancy rate to the first service decreased significantly as concentrations of E(2) increased on Days 14 through 17.

Plasma levels of prostaglandin F2 alpha metabolite and progesterone in repeat breeder heifers

A detailed clinical-endocrine investigation was performed in 6 repeat breeder heifers (RBH) with the aim being to ascertain whether endocrine asynchronism exists at luteal regression and during early pregnancy. The heifers were first studied during an open cycle and then after insemination when 3 heifers became pregnant. Circulating plasma levels of PGF2 alpha metabolite were measured every 2nd h, while progesterone (P4) levels were measured every 6th h. The oestrous period and intervals between the onset of oestrus and ovulation were relatively longer, compared with what is normally seen in heifers. Plasma levels of P4 at the onset of oestrus were higher than normal, but it was concluded that the plasma levels of PGF2 alpha metabolite and P4 in RBH at luteal regression and early pregnancy were normal.