Postpartum Beef Cows Research Articles

Preovulatory estradiol and the establishment and maintenance of pregnancy in suckled beef cows1

In postpartum beef cows, GnRH-induced ovulation of small dominant follicles decreased pregnancy rates and increased late embryonic/fetal mortality. In Exp. 1, single ovulation reciprocal embryo transfer (ET) was used to examine the relationship between preovulatory serum concentrations of estradiol at GnRH-induced ovulation in donor and recipient cows and establishment and maintenance of pregnancy. Suckled beef cows (n = 1,164) were administered GnRH (GnRH1, 100 μg) on d -9 (GnRH1), PGF(2α) on d -2, and GnRH2 (GnRH2, 100 μg) on d 0 (CO-Synch protocol) either with (donors; n = 810) or without (recipients; n = 354) AI. Single embryos (n = 394) or oocytes (n = 45) were recovered from the donor cows (d 7; ET) and all live embryos were transferred into recipients. Serum concentration of estradiol at GnRH2 was positively correlated with follicle size at GnRH2 (r = 0.45, P < 0.01) and progesterone at ET (r =0.34, P < 0.01). Donor cows with greater estradiol at GnRH2 were more likely to yield an embryo than an unfertilized oocyte (P < 0.01). Donor and recipient cows were retrospectively divided into 4 groups [low estradiol (<8.4 pg/mL) or high estradiol (≥8.4 pg/mL)] based on serum concentration of estradiol at GnRH2. Pregnancy rate at d 27 for low-low (n = 78), low-high (n = 80), high-low (n = 91), and high-high (n = 101) groups (donor-recipient, respectively) was 45, 65, 43, and 61% respectively (P < 0.02). Because recipient cows with greater estradiol concentration at GnRH2 had greater pregnancy rates in Exp. 1, the objective of Exp. 2 was to evaluate the effect of estradiol supplementation on pregnancy rate. Ovulation was synchronized in suckled beef cows (n = 600) using the CO-Synch protocol with the insertion of a controlled internal drug release (CIDR; intravaginal progesterone supplement) from d -9 until d -2. Approximately one-half of the cows (n = 297) received an injection of estradiol cypionate (ECP; 0.5 mg intramuscularly) 24 h before AI. Compared with the no treatment (Control) cows, ECP treatment increased (P < 0.01) pregnancy rates of cows induced to ovulate smaller dominant follicles (<12.2 mm). In conclusion, GnRH-induced ovulation of small dominant follicles was associated with reduced serum estradiol, fertilization rate (donor cows), and pregnancy establishment (recipient cows). Furthermore, ECP supplementation during the preovulatory period increased pregnancy rates in cows induced to ovulate smaller dominant follicles.

Determination of the appropriate delivery of prostaglandin F2α in the five-day CO-Synch + controlled intravaginal drug release protocol in suckled beef cows1

The objective of this experiment was to determine if 2 doses of prostaglandin F(2α) (PGF) administered concurrently at controlled intravaginal drug release (CIDR) removal was an efficacious method for delivery of PGF in the 5-d CO-Synch + CIDR protocol. Postpartum beef cows (n = 2,465) from 13 herds in 8 states were enrolled in the 5-d CO-Synch + CIDR protocol and assigned to receive 2 doses of PGF (25 mg/dose) 8 h apart with the initial injection given at CIDR insert removal (8h-PGF), 2 doses (25 mg/dose) of PGF delivered in 2 injection sites, both administered at CIDR insert removal (Co-PGF), or a single 25-mg dose of PGF at CIDR insert removal (1x-PGF). Cows were fixed timed-artificially inseminated (FTAI) 72 h after CIDR removal concurrent with GnRH administration. Estrus-cycling status (54% cyclic) was determined by evaluation of progesterone in 2 blood samples collected before CIDR insertion. Determination of pregnancy was performed by transrectal ultrasonography 39 ± 0.1 d after FTAI and at least 35 d after the conclusion of the breeding season. Fixed timed-AI pregnancy rates were greater (P < 0.05) for the 8h-PGF (55%) than the 1x-PGF (48%) treatment, with the Co-PGF (51%) treatment intermediate and not different (P > 0.10) from the other treatments. Contrast analysis demonstrated that cows receiving 50 mg of PGF (8h-PGF and Co-PGF) had greater (P < 0.05) FTAI pregnancy rates than those receiving 25 mg (1x-PGF). Pregnancy rates to FTAI were greater (P < 0.05) in cyclic (55%) than noncyclic (47%) and greater (P < 0.05) in multiparous (≥3 yr of age; 54%; n = 1,940) than primiparous cows (40%; n = 525). Luteolysis after PGF treatment was assessed in a subset of cows (n = 277) and treatment tended (P = 0.09) to affect the proportion of cows having luteolysis. The percentage of cows that had luteolysis was least in the 1x-PGF treatment (89%) and greatest in the 8h-PGF treatment (97%), with the Co-PGF treatment (94%) being intermediate. Breeding season pregnancy rate (88%) did not differ (P > 0.10) among treatments but was greater (P < 0.01) in multiparous (90%) than primiparous (78%) cows. In summary, 50 mg of PGF was required in the 5-d CO-Synch + CIDR protocol to maximize pregnancy rates; however, pregnancy rate did not differ when 50 mg of PGF was administered simultaneously with CIDR removal or split with 25 mg administered at 0 and 8 h after CIDR removal.

Effect of Change of Body Condition Score on Embryo Quality and Yield in Postpartum Beef Cows.

Effect of Change of Body Condition Score on Embryo Quality and Yield in Postpartum Beef Cows.

Comparison of long- versus short-term CIDR-based protocols to synchronize estrus prior to fixed-time AI in postpartum beef cows

This experiment was conducted to compare pregnancy rates in postpartum beef cows resulting from fixed-time AI (FTAI) after treatment with controlled internal drug release (CIDR)-based protocols to synchronize estrus. Cows assigned to the Show-Me-Synch (n=167) protocol received a CIDR from d 0 to 14, and prostaglandin F2α (PGF2α) on d 30. Cows assigned to 7-d CO-Synch+CIDR (n=177) received a CIDR and gonadotropin releasing hormone (GnRH) on d 23. On d 30, CIDRs were removed and PGF2α was administered. Blood sampling occurred on d −10 and 0 of treatment to determine estrous cyclicity status (progesterone ≥0.5ng/mL estrous cycling). Treatments were balanced on age, DPP and BCS. Estrous detection was performed using HeatWatch from PGF2α to FTAI. Artificial insemination was performed at predetermined fixed times (72h, Show-Me-Synch; 66h, 7-d CO-Synch+CIDR) and all cows were administered GnRH at FTAI. This experiment was conducted over a two year period; no differences were found between years so the data were pooled for further analysis. Pregnancy rate resulting from FTAI did not differ (P>0.10) between technicians or AI sires. Pregnancy rate resulting from FTAI was similar between treatments (P=0.20); however, cows that exhibited estrus prior to FTAI had a higher pregnancy rate (P<0.01) than for those that did not. Pregnancy rate at the end of the breeding period was similar between treatments (P=0.28). In summary, FTAI pregnancy rates were similar among postpartum beef cows following treatment with either a short- or long-term CIDR-based estrous synchronization protocol.

Effects of supplements with increasing glucogenic precursor content on reproduction and nutrient utilization in young postpartum range cows

Altering nutrient utilization in young postpartum beef cows from milk production to body weight gain has potential to improve reproductive performance. A 2-year study conducted at the Corona Range and Livestock Research Center from February to July in 2003 (n=33) and 2004 (n=26) evaluated responses of 2- and 3-year-old postpartum beef cows grazing native range to 2 supplements with increasing glucogenic potential (GP). Supplements were fed at 1135g∙cow−1∙day−1 twice weekly for approximately 70days postpartum and provided 1) 341g CP, 142g ruminally undegradable protein, 57g GP (GP57), or 2) 341g CP, 151g RUP+80g propionate salt (NutroCAL, Kemin Industries, Inc.), 121g GP (GP121). Supplement×year interactions were observed for days to first estrus (P=0.04) and 24-h milk production at ~60days postpartum (P=0.04). Cows fed GP57 took longer to return to estrus in 2004 than in 2003, while cows fed GP121 returned to cyclicity in similar days postpartum regardless of year. Cows fed GP57 produced more milk in 2004 than 2003, but cows fed GP121 produced similar amounts of milk regardless of year. Cows had similar (P=0.61) glucose half-lives after glucose tolerance test at ~55day postpartum (77 and 68±12min for GP57 and GP121, respectively). Young cows fed GP121 exhibited consistent milk production and return to estrus regardless of the effects of year.

Reduced response to an estrous induction program in postpartum beef cows treated with zilpaterol and gaining body weight

In beef cows, reduced energy intake delays first ovulation postpartum and is associated with lesser insulin, IGF-I and leptin concentrations. However, the close relationship among these hormones mask their individual roles in the reinitiation of ovarian activity. A β-adrenergic receptor agonist (βAR) was used to increase body condition score (BCS) and yet reduce body fat and leptin serum concentration to determine the specific role of leptin in the postpartum ovarian activity. Beef cows (n=77) with BCS 3.1±1.4 received 2kg/day of feed containing 0 or 0.15mg/kg of zilpaterol (a synthethic βAR), for 33 days. Estrus was induced with a progestin implant applied for 9 d and cows in estrus were bred by artificial insemination (AI). Zilpaterol administration increased (P<0.05) daily weight gain, muscle depth and BCS, with no changes in back fat depth, reducing fat to muscle ratio (P<0.05). At the time of AI, insulin (38%) and IGF-I (26%) concentrations were less in zilpaterol-treated cows (P<0.05), but leptin concentration was unaffected. Ovulation rate and animal with luteal activity after estrus induction were also reduced by 35% (P=0.05) and 56.5% (P=0.007), respectively, in zilpaterol-treated cows. Logistic regression estimates for BCS (P=0.016) and IGF-I concentration (P=0.03) were positively related with the occurrence of luteal activity. In addition, whilst back fat (P=0.009) had a positive effect on luteal activity, leptin concentration did not show a significant relationship. In conclusion, despite an increase in body weight and a positive change in BCS, the reduction in insulin and IGF-I concentrations, associated with βAR treatment, reduced the response to induction of estrus. However only IGF-I, but not leptin or insulin, significantly influenced the odds for the occurrence of luteal activity after estrous induction in cattle with poor BCS.

Influence of inducing luteal regression before a modified fixed-time artificial insemination protocol in postpartum beef cows on pregnancy success1

Most fixed-time insemination protocols utilize an injection of GnRH at the beginning of the protocol to initiate a new follicular wave. However, the ability of GnRH to initiate a new follicular wave is dependent on the stage of the estrous cycle. We hypothesized that administering PGF(2α) 3 d before initiating a fixed-time AI protocol would improve synchrony of follicular waves and result in greater pregnancy success. Therefore, our objective was to determine whether inducing luteal regression 3 d before a fixed-time AI protocol would improve control of follicular turnover and pregnancy success to fixed-time AI. Multiparous crossbred cows at 3 locations (n = 108, 296, and 97) were randomly assigned to 1 of 2 treatments: 1) PGF(2α) [25 mg; intramuscularly (i.m.)] on d -9, GnRH (100 μg; i.m.) and insertion of a controlled internal drug-releasing device (CIDR) on d -6, PGF(2α) (25 mg; i.m.) and CIDR removal with PGF(2α) (25 mg; i.m.) at CIDR removal on d 0 (PG-CIDR) or 2) GnRH (100 μg; i.m.) and insertion of a CIDR on d -5 and CIDR removal with PGF(2α) (25 mg; i.m.) at CIDR removal and 4 to 6 h after CIDR removal (5-d CIDR). Cows were time-inseminated between 66 and 72 h (PG-CIDR) or 70 to 74 h (5-d CIDR) after CIDR removal, and GnRH was administered at the time of fixed-time AI. At location 1, ovulatory response to the first injection of GnRH was determined by ultrasonography at the time of GnRH and 48 h after GnRH administration. Among cows with follicles ≥10 mm in diameter, more (P = 0.03) PG-CIDR-treated cows ovulated after the initial GnRH injection (88%, 43/49) compared with the 5-d CIDR-treated cows (68%, 34/50). Pregnancy outcome was not influenced by location (P = 0.96), age of the animal (P = 1.0), cycling status (P = 0.99), BCS (P = 1.0), or any 2-way interactions (P ≥ 0.13). However, pregnancy success was influenced by synchronization protocol (P = 0.04). Pregnancy outcome was greater (P = 0.04) for the PG-CIDR protocol (64%) compared with the 5-d CIDR protocol (55%). In summary, control of follicular turnover was improved by inducing luteal regression 3 d before initiation of a fixed-time AI protocol, and pregnancy success was improved with the PG-CIDR protocol compared with the 5-d protocol.

Effect of Ovulatory Follicle Size and Estradiol Supplementation During the Preovulatory Period on Pregnancy Rates in Postpartum Beef Cows.

Effect of Ovulatory Follicle Size and Estradiol Supplementation During the Preovulatory Period on Pregnancy Rates in Postpartum Beef Cows.

Differential gene expression in anterior pituitary glands from anestrous and cycling postpartum beef cows1

Oligonucleotide microarrays (GeneChip Bovine Genome Arrays, Affymetrix Inc., Santa Clara, CA) were used to evaluate gene expression profiles in anterior pituitary glands collected from 4 anestrous and 4 cycling postpartum primiparous beef cows to provide insight into genes associated with transition from an anestrous to a cycling status. Tissues were collected 40 to 61 d after calving from anestrous cows and from cyclic cows between d 7 and 13 of the estrous cycle (luteal phase) from d 54 to 77 after calving. Hybridization signals were normalized across arrays, and genes with mean differences in expression that were at least 1.5-fold apart and with a minimum difference in mean signal intensity of 10 were compared. Based on these criteria, 47 transcripts were increased (P < 0.025) and 31 transcripts were decreased (P < 0.025) in pituitary gland tissue from cycling compared with anestrous cows. Few transcripts identified in this analysis were associated previously with reproductive function. To provide greater detail on the influence that stage of the estrous cycle (i.e., collection during the luteal phase) might have on the differences detected in gene expression, quantitative real-time PCR was used to compare gene expression in anterior pituitaries of anestrous cows with an additional independent set of anterior pituitary glands collected at 4 different stages of the estrous cycle: 0.5 to 2 d (n = 9), 5 to 6.5 d (n = 5), 11.4 to 13.7 d (n = 5), and 17.9 to 19 d (n = 6) after the onset of estrus. Gastrin-releasing peptide, the gene that exhibited the largest fold increase in expression in the microarray experiment, and IGFBP3 mRNA were expressed at greater (P < 0.004) amounts in samples from the different stages of the estrous cycle than in samples from anestrous cows. In addition, expression of IGFBP3 mRNA was proportional to serum progesterone concentrations throughout the estrous cycle (P < 0.05). Expression of versican mRNA was decreased (P = 0.03) in samples from the different stages of the estrous cycle compared with anestrous cow samples. Results identified numerous genes that may be involved in the transition from anestrous to cycling status, providing novel insight into mechanisms regulating reproductive function.

The use of insulin to improve fertility of timed-inseminated postpartum suckled beef cows

The objective of this work was to evaluate the effect of insulin alone or in association with equine chorionic gonadotropin (eCG) on the fertility of postpartum beef cows subjected to synchronization. A total of 340 cows was subjected to fixed time artificial insemination. In the trial 1, the cows were subjected to temporary weaning (TW), while in the trial 2 the same protocol was tested without TW. The addition of an insulin injection to a progesterone/eCG-based protocol without TW increased the pregnancy rate of beef cows with body condition score (BCS) equal to or lower than 2.5. Insulin had no effect on cows submitted to TW or with BCS equal to or higher than 3.0.

Comparison of Long-term CIDR-based Estrous Synchronization Protocols on Estrous Response and Pregnancy Rates in Postpartum Beef Cows

Estrous synchronization and artificial insemination allow beef producers to maximize genetic improvement in their operations. However, many beef producers have been reluctant to incorporate this technology into their program due to the management requirements it entails. Therefore, any improvements to decrease time and/or labor inputs may increase the use of such technology. The CIDR-Select protocol is an effective method of synchronizing estrus in beef cows. This protocol involves 14 days treatment with a CIDR progesterone insert, GnRH treatment 12 days after CIDR removal, and treatment with prostaglandin F2alpha seven days after GnRH. The entire protocol requires over 33 days, from initial CIDR insertion to detection of estrus and insemination. Reducing the interval from CIDR removal to GnRH treatment would shorten the protocol and potentially make it more attractive for use by producers, providing effectiveness was maintained. The objective of this experiment was to characterize the estrous response and subsequent fertility of postpartum beef cows following synchronization utilizing the CIDR-Select protocol, in which the interval from CIDR removal to GnRH treatment was reduced from 12 to two days.

Insulin-like growth factor and growth hormone receptor in postpartum lactating beef cows

The objective of this study was to evaluate the plasma concentrations of insulin-like growth factor-I (IGF-I), and the mRNA hepatic expression of IGF-I and of the growth hormone receptors GHR and GHR 1A, in postpartum beef cows. Four Angus and four crossbred (Angus x Nelore) postpartum suckled beef cows were used. Liver and blood samples were collected every 10 days, from calving to 40 days postpartum, for gene expression and for β-hydroxybutyrate and IGF-I assays, respectively. Samples for progesterone assay were collected every other day, from day 10 to 40 postpartum. Three cows ovulated before 40 days postpartum. IGF-I concentration was higher in Angus x Nelore than in Angus cows. There was no difference in the expression of GHR, GHR 1A and IGF-I according to breed or ovulatory status. IGF-I concentrations were higher in crossbred cows, but have not changed according to postpartum ovulatory status. Moreover, changes in postpartum IGF-I concentrations are not associated with changes in liver GHR, GHR 1A and IGF-I mRNA expression in either breed.

Factors affecting preovulatory follicle diameter and ovulation rate after gonadotropin-releasing hormone in postpartum beef cows. Part II: Anestrous cows1

There is large variation in dominant follicle diameter at the time of GnRH-induced ovulation in the CO-Synch protocol [a first GnRH injection on d -9 (GnRH1), followed by PGF(2alpha) on d -2, and a second GnRH injection (GnRH2) with timed AI on d 0], and the reason for the presence of small dominant follicles at GnRH2 is not known. Our hypothesis was that ovulatory response to GnRH1 and progesterone exposure [controlled intravaginal drug-releasing insert (CIDR; EAZI-Breed, Pfizer Animal Health, New York, NY)] would affect ovulatory follicle size at GnRH2 in anestrous cows. This study used a 2 x 2 factorial arrangement of treatments in which anestrous suckled beef cows (n = 55) either ovulated (Ov1+) or failed to ovulate (Ov1-) after GnRH1 and either received (CIDR+) or did not receive (CIDR-) a 7-d CIDR treatment (from GnRH1 to PGF(2alpha)), resulting in the following treatment groups: Ov1+CIDR+, Ov1-CIDR+, Ov1+CIDR-, and Ov1-CIDR- (n = 9, 17, 11, and 18, respectively). The Ov1+ cows had larger follicles at GnRH2 (12.3 vs. 11.0 mm; P = 0.04), a decreased proportion of small follicles within cows that ovulated to GnRH2 (2/16 vs. 14/23; P = 0.003), and a similar growth rate of the ovulatory follicle from d -5 to 0 (d 0 = GnRH2; 1.1 +/- 0.06 vs. 1.1 +/- 0.07 mm/d; P = 0.99) compared with Ov1- cows. Administration of a CIDR had no effect on follicle diameter at GnRH2 (11.8 vs. 11.2 mm; P = 0.3), proportion of small ovulatory follicles at GnRH2 (7/19 vs. 9/20; P = 0.6), and follicular growth rate from d -5 to 0 (d 0 = GnRH2; 1.2 +/- 0.07 vs. 1.1 +/- 0.07 mm/d; P = 0.76). Administration of a CIDR, but not ovulation to GnRH1, increased follicle growth from d -2 to 0 (d 0 = GnRH2; P = 0.03 and 0.9, respectively). Large follicles (>11 mm) had a similar growth rate from d -5 to 0 (d 0 = GnRH2; P = 0.44) compared with small follicles (1.1 +/- 0.07 vs. 1.2 +/- 0.07 mm/d), but the large ovulatory follicles were larger at d -5 compared with small ovulatory follicles (P < 0.001). Follicle diameter was positively correlated with serum concentrations of estradiol at GnRH2 (r = 0.622; P < 0.0001). In summary, ovulation to GnRH1, but not CIDR administration, resulted in increased dominant follicle diameter at GnRH2 in anestrous suckled beef cows. Large follicles were already larger 5 d before GnRH2 but grew at a rate similar to small follicles; follicle size was positively correlated with serum concentrations of estradiol at the time of GnRH-induced ovulation.

Metabolic and luteal function in winter‐calving Spanish beef cows as affected by calf management and breed

This experiment aimed at evaluating the effect of calf management and breed on the metabolic and luteal function of post-partum beef cows fed at maintenance. Fifty multiparous cows, 22 Parda de Montaña (PA) and 28 Pirenaica (PI), were assigned to either suckling once-daily for 30 min (RESTR) or ad libitum (ADLIB) from the day after calving. Blood samples were collected to analyse metabolites [non-esterified fatty acids (NEFA), beta-hydroxybutyrate, total protein and urea)], insulin-like growth factor-I (IGF-I) and progesterone (P4) at different intervals. Cows from RESTR maintained their live-weight (LW) over the first 3 months post-partum, whereas ADLIB cows lost nearly 4% LW. Both genotypes showed similar LW gains during this period (p > 0.10). Calf daily gains were lower in RESTR than in ADLIB treatment (p < 0.05), but similar across breeds (p > 0.10). Milk and lactose production were lower in RESTR cows than in ADLIB (p < 0.05). Milk and protein yield were greater in PA than in PI breed (p < 0.05). Serum NEFA, total protein and urea were higher in PI cows suckling ADLIB than in the rest (p < 0.05). Cows from PI breed had greater NEFA values than PA ones on the first week post-partum (p < 0.001). Circulating IGF-I was not affected by suckling frequency, breed nor their interaction (p > 0.10). Suckling frequency, but not breed, affected the interval from calving to first ovulation (p < 0.001), being shorter in RESTR than in ADLIB cows. In conclusion, the ad libitum suckling practice improved cow milk yield and offspring gain compared to once-daily suckling for 30 min from the day after calving, at the expense of impairing the onset of cyclicity. The effect of calf management was confounded with breed on the studied blood biochemical constituents, but any of these metabolites influenced the role of endocrine IGF-I in these genotypes.

Factors affecting preovulatory follicle diameter and ovulation rate after gonadotropin-releasing hormone in postpartum beef cows. Part I: Cycling cows1

Cows induced to ovulate small dominant follicles were reported to have reduced pregnancy rates compared with cows that ovulated large follicles. The reason for the presence of small dominant follicles at the time of GnRH-induced ovulation in timed AI protocols is unknown. The objectives of this experiment were to examine the role of day of the estrous cycle at initiation of treatment on ovulation after the first GnRH injection (GnRH1) and associated effects on growth rate and final size of the ovulatory follicle at the second GnRH injection (GnRH2), serum concentrations of estradiol at GnRH2, and subsequent luteal concentrations of progesterone in suckled beef cows. Estrous cycles of cows were manipulated to be at 1 of 5 specific days of the cycle (d 2, 5, 9, 13, and 18, d 0 = estrus; n = 12 per treatment group) at the beginning of the CO-Synch protocol (GnRH1 on d -9, PGF(2alpha) on d -2, and GnRH2 on d 0). Day of the estrous cycle at GnRH1 did not affect the size of the preovulatory follicle or the proportion of cows ovulating at GnRH2 (P = 0.65 and 0.21, respectively). When all cows were included in the analysis, cows that ovulated after GnRH1 had similar follicle size at GnRH2 compared with cows that did not ovulate after GnRH1 (11.4 and 10.4 mm, respectively; P = 0.23). When only cows that could ovulate after GnRH1 (excluding cows treated on d 2) were included in the analysis, cows that ovulated to GnRH1 had a larger follicle at GnRH2 than cows that did not ovulate after GnRH1 (11.4 and 9.5 mm, respectively; P = 0.04). Follicle growth from d -5 to 0 was similar between cows that ovulated after GnRH1 and cows that did not (1.01 vs. 0.89 mm/d, respectively; P = 0.75). There was a tendency for faster follicle growth rate in cows that ovulated a large follicle (>11 mm) compared with cows that ovulated a small follicle (< or = 11 mm; 1.01 vs. 0.86 mm/d, respectively; P = 0.07). Serum concentrations of estradiol at GnRH2 and progesterone after ovulation were reduced in cows that ovulated small follicles compared with cows that ovulated large follicles (P = 0.006 and 0.005, respectively). In summary, day of the estrous cycle at initiation of synchronization did not affect ovulatory follicle size, but follicle growth rates affected the size of the follicle at GnRH2. Cows that ovulated a small follicle had reduced serum concentrations of estradiol at GnRH2 and progesterone after ovulation.

Flushing em vacas de corte no pós-parto, submetidas ao desmame precoce: desempenho reprodutivo

The objective of this experiment was to evaluate the effects of short-time fat supple-mentation (flushing) on the reproductive performance (postpartum estrus, postpartum anestrus, postpartum estrus interval, calving interval, number of artificial insemination, artificial insemination interval, and pregnancy rate) of postpartum beef cows, submitted to the early weaning. Two hundred and fifty eight beef cows were used from the following genetic groups: Aberdeen Angus (n= 21), Aberdeen Angus x Canchim (n= 20), Canchim x Aberdeen Angus (n= 52), Charoles x Caracu (n= 29), Charolais (n= 18), Cachim (n= 34), Caracu (n= 35), Caracu x Charoles (n= 26) an Puruna (n= 23), with 418.1 kg of body weight and all pregnant. These animals were split into two types of treatments: flushing (30% soybean full + 70% corn) and no supplementation. There was no flushing effect on postpartum estrus percentage (82.9%), anestrus percentage (17.0%), postpartum estrus interval (100.5 days), calf birth weight (34.2 kg), number of artificial insemination (1.4), interval between the 1st and the 2nd artificial insemination (19.2 days), interval between the 1st and the 2nd artificial insemination (19.9 days), and pregnancy percentage (54.6%). The flushing reduced calving interval (391.14 vs. 399.31 days). The November period had lower postpartum estrus percentage (70.6%), anestrus percentage (29.4%), postpartum estrus interval (90.3 days), calving interval (378.3 days), number of artificial insemination (1.2), interval between the 1st and the 2nd artificial insemination (11.5 days), and pregnancy percentage (27.5%).

Comparison of short-term progestin-based protocols to synchronize estrus and ovulation in postpartum beef cows1

Two experiments evaluated short-term controlled internal drug release (CIDR) insert-based protocols to synchronize estrus and ovulation and compare differences in their potential to facilitate fixed-time AI (FTAI) in postpartum beef cows. Experiment 1 was designed to compare the 7- and 5-d Select Synch + CIDR protocols on the basis of timing and synchrony of estrus after treatment. Cows assigned to the 7-d protocol (n = 59) received GnRH [100 microg intramuscularly (i.m.)] and CIDR inserts (1.38 g of progesterone) on d 0 and PGF(2alpha) (25 mg i.m.) and CIDR removal on d 7. Cows assigned to the 5-d protocol (n = 58) received GnRH and CIDR inserts on d 2, PGF(2alpha) and CIDR removal on d 7, and a second injection of PGF(2alpha) 12 h after CIDR removal. Estrus detection and AI were performed for cows assigned to each protocol during the 144-h synchronized period. There was no difference in estrous response (P = 0.85), interval to estrus (P = 0.09), or variance for interval to estrus (P = 0.75) between treatments, nor were there differences in synchronized conception or pregnancy rates resulting from AI (P = 0.85, P = 0.91, respectively). Experiment 2 was designed to compare pregnancy rates resulting from FTAI after administration of the 7- and 5-d CO-Synch + CIDR protocols. Both treatments were administered the same as in Exp. 1; however, cows assigned to the 7-d protocol were inseminated 66 h after PGF(2alpha) and CIDR removal, and cows assigned to the 5-d protocol were inseminated 72 h after the first PGF(2alpha) injection. Cows assigned to both protocols were administered GnRH (100 microg i.m.) at AI. There was no effect of treatment (P = 0.85), technician (P = 0.20), or sire (P = 0.25) on pregnancy rates resulting from FTAI. Given these observations, the 5-d protocol provides an effective alternative to the 7-d protocol for use in facilitating FTAI; however, beef producers must carefully consider the increased labor and treatment costs associated with the 5-d protocol.

Transvaginal follicular aspiration and embryo development in superstimulated early postpartum beef cows and subsequent fertility after artificial insemination

This study was conducted to investigate in early postpartum suckled beef cows with and without FSH pre-stimulation: (i) the influence of the postpartum period on the number and quality of oocytes recovered by ovum pick-up (OPU), (ii) the overall efficiency of the OPU/IVP embryos from days 30 to 80 postpartum and (iii) if repeated OPU negatively affect fertility following a fixed-time artificial insemination protocol. After parturition suckled Angus cows ( n = 30) were divided in three groups ( n = 10 group −1). All cows were anestrous at the commencement of experimental treatments (30.0 ± 3.2 days postpartum, mean ± SD; range 25–34 days). Group 1 treatments included: dominant follicle ablation (DFA), FSH treatment and OPU procedure 5 days after DFA. A total of 9 mg FSH (Ovagen™) was administered s.c. once a day over 2 days at equal doses (4.5 + 4.5 mg). For fertility test the cows received an intravaginal progesterone treatment from Days 78 to 86 postpartum and were fixed-time artificially inseminated (FTAI) at 56 and 72 h after device removal. Group 2: as cited for Group 1 with no FSH treatment. In both groups, OPU was repeated four times (Days 35, 49, 63 and 77 postpartum) and the collected oocytes classified as viable were in vitro matured, fertilized and presumptive embryos cultured for 8 days. Group 3 (Control FTAI): cows that had not previously aspirations were FTAI as Groups 1 and 2. Pregnancy was diagnosed by means ultrasonography 39 days after FTAI. The numbers (mean ± SEM) of follicles visible and aspirated at the time of OPU in FSH-treated cows were greater ( P < 0.05) than in non-treated cows (10.6 ± 0.6 and 8.4 ± 0.4 vs. 8.0 ± 0.5 and 4.6 ± 0.3, respectively). Following FSH treatment, the number (mean ± SEM) of recovered oocytes per cow per OPU session and percentage of viable oocytes were greater in the treated ( P < 0.05) than in non-treated animals (3.0 ± 0.1 and 39.5% vs. 1.5 ± 0.1 and 30.0%). The cleavage and embryo development rates were similar ( P > 0.05) for both groups (14.8 and 6.4% vs. 16.6 and 5.5%). After FTAI the pregnancy rates were not different ( P > 0.05) among groups (70, 60 and 90% for Groups 1, 2 and 3, respectively). We can conclude that (1) FSH-treated suckled postpartum cows can be a source of oocytes for in vitro fertilization and (2) repeated DFA/OPU applied during postpartum period did not affect the subsequent fertility following FTAI.

Estrus and Luteal Activity of Postpartum Beef Cows After Treatment with Estradiol

Multiparous Hereford × Angus postpartum cows were used to determine the effects of treatment with estradiol cypionate (ECP) on estrus and luteal activity (LA) of thin ( 1 ng/mL for 1 d) within 10 d after treatment (P = 0.52). Days to normal LA were greater (P = 0.02) for thin and moderate cows treated with ECP at 25 d after calving (74 ± 5 d) compared with control cows (61 ± 5 d), and ECP treatment tended to increase (P = 0.07) days to LA for thin cows treated at 50 d after calving. Although ECP induced estrus in beef cows during the first 50 d after calving, normal luteal function was not initiated.

Effects of feeding high-linoleate safflower seeds on postpartum reproduction in beef cows1,2

Two experiments were conducted to evaluate reproductive responses to supplemental high-linoleate safflower seeds in postpartum beef cows. In Exp. 1, 18 primiparous, crossbred beef cows (411 +/- 24.3 kg of BW) were fed Foxtail millet hay starting 1 d postpartum at 1.68% of BW (DM basis) and a low-fat control (control: 63.7% cracked corn, 33.4% safflower seed meal, and 2.9% liquid molasses; DM basis) at 0.35% of BW (n = 9) or a supplement (linoleate) containing 95.3% cracked high-linoleate (79% 18:2n-6) safflower seeds and 4.7% liquid molasses (DM basis) at 0.23% of BW (n = 9). Beginning 1 d postpartum, blood was collected every 3 d for sera. Cows were slaughtered at 37 +/- 3 d postpartum for collection of hypothalami, anterior pituitary glands, liver, ovarian follicles, and uterine tissue. By 37 +/- 3 d postpartum, dietary treatment did not influence ovarian follicular development (P >or= 0.17), hypophyseal concentrations of LH (P = 0.14), or concentrations of IGF-I in liver (P = 0.15). In contrast, anterior pituitary glands from linoleate cows contained more FSH (P = 0.02) than control cows and linoleate cows had less IGF-I in the medial basal hypothalamus (P = 0.05), preoptic area (P = 0.06), and in follicular fluid (P <or= 0.03) from follicles less than 15 mm in diameter. In Exp. 2, twenty-four 3-yr-old multiparous beef cows (initial BW 473.9 +/- 9.2 kg) were fed chopped bromegrass hay at 2.1% of initial BW starting 1 d postpartum and a low-fat supplement (control) fed at 0.6% of initial BW or a high-linoleate supplement (linoleate) fed at 0.4% of initial BW until 80 d postpartum. Cows were observed for estrus twice daily from d 30 to 80 postpartum and treated with GnRH between 40 and 45 d postpartum. Seven days after GnRH administration cows were given PGF(2alpha) and were checked for estrus and artificially inseminated until 80 d postpartum. The magnitude of GnRH-induced release of LH (P = 0.82) or FSH (P = 0.86) did not differ between treatments. However, peak serum concentrations of estradiol during proestrus after treatment with PGF(2alpha) were less (P = 0.04) in linoleate than control cows. In conclusion, fat supplementation with high-linoleate safflower seeds did not improve the development of ovarian follicles and detrimentally affected early postpartum fertility possibly because of a reduction in IGF-I concentrations in tissues essential to reproduction.