Changes of luteinizing hormone and progesterone for dairy cows after gonadotropin-releasing hormone at first postpartum breeding

Gonadotropin-releasing hormone administered at breeding enhances fertility of dairy cows, so a study was designed to evaluate the mechanism for enhanced fertility following administration of gonadotropin-releasing hormone at first postpartum breeding. Twenty-four cows were assigned randomly to one of two treatments, 100 micrograms of gonadotropin-releasing hormone intramuscular or saline vehicle intramuscular at insemination. Blood samples for luteinizing hormone assay were taken at 2-h intervals prior to breeding and .5-h intervals for 3 h after insemination. Composite morning milk samples for progesterone assay were collected for 30 days after insemination or until next estrus. Cows given gonadotropin-releasing hormone had higher luteinizing hormone concentrations in blood serum following treatment than cows given saline, 13.2 versus 3.0 ng/ml. There was no relationship between luteinizing hormone and subsequent conception. Progesterone for cows that became pregnant was higher throughout sampling days. Mean progesterone concentrations were 4.6 versus 2.2 ng/ml in pregnant and nonpregnant cows during the first 4 days after insemination. Cows treated with gonadotropin-releasing hormone that conceived had higher progesterone than other cows, and that was evident at the first 4 days postbreeding.     

Dynamics of gonadotropin release following ovariectomy and injection of gonadotropin-releasing hormone in early postpartum dairy cows

The influence of the ovary and of injection of low doses of gonadotropin-releasing hormone on secretion and gonadotropin-releasing hormone-induced release of gonadotropins in early postpartum cows was examined in a 2 x 2 factorial design (6 cows/group). Twelve cows were ovariectomized 2 d postpartum (calving = d 0; groups 1 and 2) and 12 cows were left intact (groups 3 and 4). Groups 1 and 3 received gonadotropin-releasing hormone (5 micrograms) every 120 min for 70 h from d 6 to d 9; groups 2 and 4 received saline by the same regimen. All animals received 50 micrograms gonadotropin-releasing hormone on d 9. Mean concentrations of FSH were higher following ovariectomy compared with those of intact cows 6 to 8 d postpartum, whereas no differences in FSH were observed between cows receiving gonadotropin-releasing hormone or saline during this period. Concentrations of LH were similar in intact and ovariectomized cows on d 6 to 8 but were increased in cows receiving gonadotropin-releasing hormone compared with cows receiving saline. Ovariectomy did not alter the gonadotropin-releasing hormone-induced release of gonadotropins on d 9. Injection of gonadotropin-releasing hormone on d 6 to 8 resulted in a decreased gonadotropin-releasing hormone-induced release of gonadotropins on d 9. It was concluded that removal of ovarian influence resulted in increased secretion of FSH but did not affect gonadotropin-releasing hormone-induced release of LH and FSH during the early postpartum period.     

Fertility of postpartum dairy cows after administration of gonadotropin-releasing hormone and prostaglandin F2 alpha: a field trial

Our objective was to examine further the potential profertility effects of gonadotropin-releasing hormone and prostaglandin F2 alpha in postpartum Holstein cows. Reproductive performance was monitored in 843 cows milked thrice daily. One group of cows (n = 218) was untreated, while three groups received either 100 micrograms gonadotropin-releasing hormone administered once between d 11 and 25 (n = 211); 25 mg prostaglandin F2 alpha given once between d 11 and 25 (n = 215); or 25 mg prostaglandin F2 alpha given once between d 25 and 40 postpartum (n = 190). No profertility effects were detected in cows, regardless of their health status during the periparturient period, except cows given gonadotropin-releasing hormone between d 11 and 18 had shorter intervals to first estrus and to first service than controls. Cows with reproductive disorders (abnormal health status) in the concurrent lactation had longer intervals from calving to conception after receiving gonadotropin-releasing hormone between d 18 and 25 or prostaglandin F2 alpha between d 33 and 40. Abnormal health status adversely affected every reproductive trait measured. Early postpartum treatments with either hormone failed to improve reproductive performance of dairy cows, in contrast to several reports of profertility effects for gonadotropin-releasing hormone, and a few reports for prostaglandin F2 alpha.     

Genetic analysis of postpartum measures of luteal activity in dairy cows

The objective of this study was to estimate genetic parameters for measures of luteal activity during the first 60 d postpartum. Analyses were made with different sampling intervals to investigate the possibility of combining progesterone measurement with routinely performed milk recording. Progesterone level in milk as an indicator of female fertility when selecting sires in a progeny-testing scheme was also examined. Data were collected from 1996 to 1999, and comprised 1,212 lactations from 1,080 British Holstein-Friesian cows at 8 commercial dairy farms in the United Kingdom. Milk samples for progesterone analysis were collected thrice weekly. Mixed linear animal models were used to analyze the data. Heritability for the percentage of samples with luteal activity during the first 60 d postpartum (PLA) was 0.30 and decreased with more infrequent sampling to 0.25, 0.20, and 0.14 for weekly, twice-monthly, and monthly sampling, respectively. Measures of PLA had a high negative genetic correlation with prolonged anovulation (−0.53 for monthly sampling, < −0.87 otherwise) and a moderate positive genetic correlation with persistent corpus luteum in the first estrus cycle (>0.65 if at least twice-monthly sampling). Genetic correlations with interval from calving to commencement of luteal activity were close to −1 for all PLA measurements and the selection index calculations showed that monthly progesterone sampling could be used with high accuracy (0.80 with 50 daughters per bull) to predict breeding values for commencement of luteal activity. Progesterone analysis at the time of regular milk recording could thereby be used to select for an early interval from calving to commencement of luteal activity and, at the same time, a decreased frequency of prolonged anovulation during the postpartum period.     

Relationships among body condition score,milk constituents,and postpartum luteal function in Norwegian dairy cows

Relationships among body condition score (BCS), milk constituents, and resumption of postpartum luteal function were studied in 162 lactations of first- and second-parity Norwegian dairy cows. Milk components included acetone, lactose, fat, protein, urea, and ratios of fat to protein and fat to lactose. Milk progesterone concentrations were used to determine intervals from calving to first luteal response (> 5 ng/ml). Intervals to first luteal response were divided into categories of early (< or = 24 d) or late (> 24 d) responses. Higher BCS were observed during wk 4 and 5 postpartum among both first- and second-parity cows with early compared with delayed luteal responses. Second-parity cows with early onset of luteal function also had higher BCS from wk 6 through 12, whereas first-parity cows with early onset of luteal function had higher BCS from wk 13 through 15. Higher acetone levels from wk 2 through 4 postpartum were associated with late luteal response in second-parity cows. Greater milk lactose content during wk 1, 2, 3, 6, 7, and 8 postpartum and higher fat fractions during wk 4 postpartum were related to early luteal response in second-parity cows. Relationships between milk constituents and onset of luteal function were less evident and occurred later postpartum among first-parity cows than among second-parity cows. Measures of weekly milk composites obtained during the early postpartum period and BCS were closely associated with postpartum resumption of luteal function. Acetone and lactose values in milk from the first 4 wk postpartum predicted postpartum luteal function in second-parity cows at a sensitivity of 0.84 and specificity of 0.86.     

Inducing ovulation early postpartum influences uterine health and fertility in dairy cows

The objective of the current study was to evaluate the effect of GnRH early postpartum on induction of ovulation, uterine health, and fertility in dairy cows. Holstein cows without a corpus luteum (CL) at 17 ± 3 DIM were assigned randomly to receive i.m. GnRH (n = 245) at 17 ± 3 and 20 ± 3 DIM or remain as controls (n = 245). Ovaries were scanned by ultrasonography twice weekly totaling 4 examinations. Ovulation was characterized by the appearance of a CL ≥20 mm at any ultrasound or CL <20 mm in 2 consecutive examinations. Clinical and cytological endometritis were diagnosed at 35 DIM. Compared with control, GnRH increased ovulation up to 3.5 d after the last treatment (78.7 vs. 45.0%) and did not affect the prevalence of clinical endometritis (23.9 vs. 18.6%) or cytological endometritis (30.9 vs. 32.8%). Prevalence of clinical endometritis increased in cows that had calving problems (32.6 vs. 15.9%) and metritis (40.6 vs. 15.8%). Metritis increased prevalence of cytological endometritis (50.7 vs. 23.5%). Treatment with GnRH did not affect pregnancy per artificial insemination at 32 (37.6 vs. 38.6%) or 74 d after artificial insemination (35.0 vs. 31.5%), but reduced pregnancy loss (6.8 vs. 18.1%). No overall effect of GnRH treatment on hazard of pregnancy was observed; however, an interaction between GnRH treatment and ovulation showed that GnRH-treated cows that ovulated had increased hazard of pregnancy by 300 DIM compared with GnRH-treated and control cows that did not ovulate (hazard ratio = 2.0 and 1.3, respectively), but similar to control cows that ovulated (hazard ratio = 1.1). Gonadotropin-releasing hormone early postpartum induced ovulation without affecting uterine health, but failed to improve pregnancy per artificial insemination or time to pregnancy, although it reduced pregnancy loss.     

Association between energy balance and luteal function in lactating dairy cows

Our objective was to determine the relationship between energy balance and secretion of progesterone in lactating dairy cows. Eight primiparous and 24 multiparous lactating Holstein cows were studied from parturition to 100 d postpartum or conception. Cows calved normally and remained healthy throughout the study. All cows were fed ad libitum a total mixed diet formulated to satisfy requirements for maintenance and lactation. Intake of feed and production of milk per cow were measured twice daily. Body weight was determined weekly. Daily energy balance was determined by subtracting energy required for maintenance and lactation from intake of energy. Concentrations of progesterone were determined in milk sampled every 3rd d. For at least 4 successive d postpartum, 81% of cows were in negative energy balance. Variation in energy balance was explained largely by intake of energy. Duration of luteal phases was not associated with energy balance. Energy balance within 9 d postpartum was correlated positively with concentration of progesterone within second and third postpartum luteal phase. Postpartum interval to nadir and magnitude of nadir of energy balance interacted to reduce progesterone within second and third postpartum estrous cycles. Thus, in lactating cows, secretion of progesterone is reduced by spontaneous caloric deficit and is modulated by timing and magnitude of maximal caloric deficit. Spontaneous caloric deficit is a potential source of infertility in lactating dairy cows.     

Gonadotropin-releasing hormone and prostaglandin F2 alpha for postpartum dairy cows: estrous, ovulation, and fertility traits

A study of 234 Holstein cows was conducted to determine if early postpartum treatments of gonadotropin-releasing hormone, prostaglandin F2 alpha, or both would alter frequency and occurrence of estrus and ovulation as well as subsequent fertility. Cows in groups 1 and 2 received gonadotropin-releasing hormone (200 micrograms) between 10 and 14 d postpartum, and cows in groups 3 and 4 received saline. Ten days later, cows in groups 2 and 3 received prostaglandin F2 alpha (25 mg), and cows in groups 1 and 4 received saline. Treatment with gonadotropin-releasing hormone reduced intervals to first ovulation and first detected estrus as well as increasing the proportion of cows with three or more ovulations before first service from 57% for saline-treated controls to 83%. Treatment with prostaglandin F2 alpha reduced intervals to second and third ovulation and shortened the first estrous cycle. Treatments for cows in groups 1 and 3 increased the proportion of cows having estrous cycles of normal duration. Interval from calving to conception was reduced by 43 to 48 d for cows with an abnormal puerperium treated with either gonadotropin-releasing hormone or prostaglandin F2 alpha compared with controls (group 4) and by 27 to 29 d overall in all cows in groups 1 and 3. Cows with normal or abnormal puerperium in groups 1 and 3 required 26 to 41% fewer services per conception than controls. We conclude that treatments of gonadotropin releasing hormone or prostaglandin F2 alpha, but not the treatment combination, improved fertility of dairy cows, especially those that experienced puerperal problems.     

Effect of progesterone on magnitude of the luteinizing hormone surge induced by two different doses of gonadotropin-releasing hormone in lactating dairy cows

Ovulation to the first GnRH injection of Ovsynch-type protocols is lower in cows with high progesterone (P4) concentrations compared with cows with low P4 concentrations, suggesting that P4 may suppress the release of LH from the anterior pituitary after GnRH treatment. The objectives of this study were to determine the effect of 1) circulating P4 concentrations at the time of GnRH treatment on GnRH-induced LH secretion in lactating dairy cows and 2) increasing the dose of GnRH from 100 to 200 μg on LH secretion in a high- and low-P4 environment. A Double-Ovsynch (Pre-Ovsynch: GnRH, PGF(2α) 7d later, GnRH 3d later, and Breeding-Ovsynch 7d later: GnRH, PGF(2α) 7d later, and GnRH 48 h later) synchronization protocol was used to create the high- and low-P4 environments. At the first GnRH injection of Breeding-Ovsynch (high P4), all cows with a corpus luteum ≥ 20 mm were randomly assigned to receive 100 or 200 μg of GnRH. At the second GnRH injection of Breeding-Ovsynch (low P4) cows were again randomized to receive 100 or 200 μg of GnRH. Blood samples were collected every 15 min from -15 to 180 min after GnRH treatment, and then hourly until 6h after GnRH treatment. As expected, mean P4 concentrations were greater for cows in the high- than the low-P4 environment. For cows receiving 100 μg of GnRH, the LH peak and area under the curve (AUC) were greater in the low- than in the high-P4 environment. Similarly, for cows receiving 200 μg of GnRH, the LH peak and AUC were greater in the low- than the high-P4 environment. Cows receiving 100 or 200 μg of GnRH had greater mean LH concentration in the low- than the high-P4 environment from 1 to 6h after GnRH treatment. On the other hand, when comparing the effect of the 2 GnRH doses in the high- and low-P4 environments, cows receiving 200 μg of GnRH had a greater LH peak and AUC than cows treated with 100 μg of GnRH both in the high- and low-P4 environments. For the high-P4 environment, mean LH was greater from 1.5 to 5h after GnRH treatment for cows receiving 200 μg of GnRH than for those receiving 100 μg of GnRH. In the low-P4 environment, mean LH was greater for cows receiving 200 μg of GnRH than for those receiving 100 μg of GnRH from 1 to 2.5h after GnRH treatment. We conclude that the P4 environment at GnRH treatment dramatically affects GnRH-induced LH secretion, and that a 200-μg dose of GnRH can increase LH secretion in either a high- or a low-P4 environment.     

Treatment with gonadotropin-releasing hormone after first timed artificial insemination improves fertility in noncycling lactating dairy cows

Lactating Holstein cows were assigned randomly to treatments to improve fertility after first postpartum timed artificial insemination (TAI). In Experiment 1, cows received no treatment (control; n = 9), a controlled internal drug releasing (CIDR) insert from 5 to 12 d after TAI (CIDR; n = 9), or 100 μg of GnRH 5 d after TAI (G5; n = 7). Although treatments did not affect circulating progesterone (P₄) concentrations from 5 to 19 d after TAI, there was a tendency for CIDR cows to have greater P₄ compared with control or G5 cows within 24 h after treatment. In 2 field trials, cows received either control (n = 223), CIDR (n = 218), or G5 (n = 227) treatments (Experiment 2), or control (n = 160), G5 (n = 159), or treatment with 100 μg of GnRH 7 d after TAI (G7; n = 163; Experiment 3). Treatment did not affect pregnancies per AI (P/AI) in Experiments 2 or 3; however, when data were combined to compare control (n = 383) and G5 (n = 386) treatments, P/AI tended to be greater for G5 (49.1%) than for control (45.8%) cows. This effect resulted from a GnRH treatment × cyclicity status interaction in which P/AI for noncycling cows receiving G5 was greater than for noncycling control cows (45.5 vs. 31.1%). In conclusion, treatment with CIDR inserts after TAI had no effect on P/AI, whereas treatment with GnRH 5 d after TAI improved P/AI for noncycling, but not for cycling cows.     

Intravaginal instillation of gonadotropin-releasing hormone analogues with an absorption enhancer induced a surge of luteinizing hormone in lactating dairy cows

Our objectives were to evaluate circulating LH concentrations after intravaginal (IVG) instillation of GnRH analogs in lactating dairy cows. In 2 experiments, lactating Holstein cows (experiment 1: n = 32; experiment 2: n = 47) received the experimental treatments 48 h after the first of 2 PGF_2α treatments given 12 h apart and 7 d after a modified Ovsynch protocol (GnRH at ?7 d, PGF_2α at ?24 h, PGF_2α at ?56 h, GnRH at 0 h). In experiment 1, cows were stratified by parity and randomly allocated to receive the following treatments: 2 mL of saline IVG (SAL, n = 6), 100 µg of gonadorelin (Gon) i.m. (G100-IM, n = 5), and 100 (G100, n = 7), 500 (G500, n = 8), or 1,000 µg of Gon IVG (G1000, n = 7). In experiment 2, treatments were SAL (n = 8), G100-IM (n = 8), G1000 (n = 7), 1,000 µg of Gon plus 10% citric acid (CA) IVG (G1000CA, n = 8), 80 µg of buserelin IVG (B80, n = 8), and 80 µg of buserelin plus 10% CA IVG (B80CA, n = 8). In both experiments, blood was collected every 15 min from ?15 min to 4 h, and every 30 min from 4 to 6 h after treatment. Data for area under the curve (AUC), mean LH concentrations, and time to maximum LH concentration were analyzed by ANOVA with (mean LH only) or without repeated measures using PROC MIXED of SAS (version 9.4, SAS Institute Inc., Cary, NC). The proportion of cows with a surge of LH was evaluated with Fisher's exact test using PROC FREQ of SAS. In both experiments, LH concentrations were affected by treatment, time, and the treatment by time interaction. In experiment 1, the AUC for LH and maximum LH concentration were greatest for the G100-IM treatment and were greater for the G1000 than for the SAL and G500 treatments. The proportion of cows with an observed surge of LH was 100 and 0% for cows that received Gon i.m. and IVG, respectively. In experiment 2, the AUC and maximum LH concentrations were greater for the G100-IM, G1000CA, and B80CA treatments than for the other IVG treatments. The proportion of cows with a surge of LH differed by treatment (SAL = 0%, G100-IM = 100%, G1000 = 14%, G1000CA = 88%, B80 = 13%, and B80CA = 100%). For the treatments with a surge of LH, time to maximum concentration of LH was the shortest for the G100-IM treatment, intermediate for the G1000CA treatment, and the longest for cows in the B80CA treatment. In conclusion, Gon (up to 1,000 µg) absorption through intact vaginal epithelium after a single IVG instillation was insufficient to elicit a surge of LH of normal magnitude. Conversely, IVG instillation of 1,000 µg of Gon and 80 µg of buserelin with the addition of citric acid as absorption enhancer resulted in a surge of LH of similar characteristics than that induced after i.m. injection of 100 µg of Gon.     

Effects of dystocia on postpartum adrenocortical function in dairy cows

Postpartum adrenocortical responses to adrenocorticotropic hormone in cows after normal (n = 10) and difficult (n = 52) parturition were investigated. The post-partum adrenocortical function of cows was affected by type of parturition (spontaneous parturition, forced extraction of fetus, caesarean section calving with or without attempted forced extraction, and total fetotomy) and day after calving (d 1, 4, and 8; d 0 = day of parturition). Cows after normal calving did not show enhanced or depressed adrenocortical function postpartum. Adrenocortical function was enhanced, compared with cows calving normally, for cows with dystocia that had a caesarean section after forced extraction was attempted and in cows in which calves were already dead and total fetotomy was performed. Cows with dystocia assisted with forced extraction by one to two people and cows that had caesarean sections without forced extraction did not show higher plasma glucocorticoid concentrations before or after adrenocorticotropic hormone administration than did cows with normal calving. Results indicate that dystocia requiring caesarean section following unsuccessful extraction or total fetotomy enhanced postpartum adrenocortical function in cows.     

Effects of d-cloprostenol dose and corpus luteum age on ovulation, luteal function, and morphology in nonlactating dairy cows with early corpora lutea

Luteolysis is a key event in cattle reproduction. A standard dose of exogenous PGF(2α) will induce full luteolysis in the majority of cows with a matured corpus luteum (CL). However, this will not occur in cows with a CL <5d old. To date, it is not known whether a larger dose will have a more potent luteolytic effect in cows during early diestrus. The objective of this study was to characterize the effect of 2 doses of d-cloprostenol (150 and 300 μg) on the progesterone concentration, luteal diameter, and ovulation rate in nonlactating dairy cattle 96 to 132 h postovulation. Twenty nonlactating dairy cows were included in the study. Each cow received 2 treatments of d-cloprostenol in 2 consecutive cycles: a standard dose of 150 μg and a double dose of 300 μg. The cows were allocated randomly to 1 of 4 groups (5 cows in each group) according to the age of the CL at the time of treatment: 96, 108, 120, and 132 h. The exact time of ovulation was known within 12h, because of twice per day ultrasound examination. The CL diameter and progesterone concentration were measured before treatment (d 0) and 2 and 4d after treatment. Within each CL age group, the effect of d-cloprostenol dose on luteolysis was determined. More cows treated with double dose tended to have full luteolysis compared with the standard dose (8/10 vs. 4/10, respectively). This effect was only apparent in cows with CL of 120 and 132 h but not in earlier CL. The interval from treatment to ovulation was shorter (3.3 ± 0.1d) in cows treated with a double dose than in cows treated with the standard dose (4.5 ± 0.4d).     

Short communication: Characterization of early postpartum estrous behavior and ovulation in lactating dairy cows using radiotelemetry

The objective of this study was to describe early postpartum estrous behavior and ovulation in lactating dairy cows using radiotelemetry. Cows (n=50) were continuously monitored for behavioral estrus with a radiotelemetric system, HeatWatch II (CowChips LLC, Manalapan, NJ), from d 14 to approximately d 49 postpartum. Blood collection for analysis of progesterone and ovarian ultrasonography were performed once weekly starting on d 14. First ovulation was associated with behavioral estrus in 5 cows and occurred at 28.2±10.8d (mean±SD; range 17 to 40d). The average duration of estrus was 6.0±4.9h (range 3 to 12.2h), and the mean number of standing events was 18.4±8.9 (range 4 to 26). Based on progesterone concentrations of ≥1ng/mL, estimated first postpartum ovulation occurred at 25.1±10.4d (range 10 to 49d) for 38 animals without evidence of behavioral estrus. The interval to estimated first ovulation without behavioral estrus was not different from the interval to first ovulation associated with behavioral estrus. Level of milk production and body condition score loss did not affect the interval to estimated first ovulation without estrus or first ovulation associated with estrus. Six animals did not show evidence of ovulation based on progesterone concentration, whereas 1 cow showed evidence of estrous behavior on the day before removal from the study. The majority of first postpartum ovulations (38/43; 88.4%) were not associated with behavioral estrus.     

Effects of treatment of anestrous dairy cows with gonadotropin-releasing hormone, prostaglandin, and progesterone

Cows anestrous at the start of a seasonal breeding period have lesser probability of breeding, lesser conception rates, and a longer interval to conception than cycling herdmates. Historically, treatment included estradiol benzoate, which is no longer available. Consequently, alternative programs are required. Hence, a study was undertaken to assess new treatment regimens for these cows. The presence or absence of a corpus luteum was determined using ultrasonography in cows (n = 2,222 from 12 herds) that were not detected in estrus by 9 d before the start of breeding. Cows were then randomly assigned to one of 4 treatments within each herd. Treatments were (1) 100 μg of gonadorelin, followed 7 d later by 500 μg of sodium cloprostenol, followed 54 to 56 h later by 100 μg of gonadorelin, followed by fixed-time artificial insemination at 13 to 18 h after the final GnRH injection (Ovsynch); (2) as for (1) but with placement of an intravaginal progesterone (P4)-releasing insert between the initial GnRH and PGF_2α (Ovsynch-56+P4); (3) as for (2) but with the final GnRH treatment delayed until 71 h after PGF_2α and P4 insert removal with fixed-time artificial insemination 0 to 5 h after GnRH treatment and with insemination of those cows detected in estrus before the second GnRH injection (Cosynch-72+P4); and (4) untreated controls (control). Day 0 was defined as the day of the second GnRH injection. Milk samples were collected from 154 and 152 cows from the Ovsynch and Ovsynch-56+P4 treatments, respectively, at d 0, 7, and 14 for P4 concentration determination. This was to test the hypothesis that inclusion of P4 would result in a greater proportion of cows having normal luteal function after treatment in these 2 groups that differed only in the inclusion of P4 in the Ovsynch-56+P4 treatment. All treatments resulted in shorter intervals from first day of breeding to conception compared with the controls. The Ovsynch-56+P4 treatment resulted in start of breeding to conception intervals 3, 6, and 16 d shorter than those of Cosynch-72+P4, Ovsynch, or controls, respectively, and the positive effect of the Ovsynch-56+P4 treatment occurred both in corpus-luteum-positive and in corpus-luteum-negative cows. The Ovsynch-56+P4 treatment resulted in fewer short interestrus intervals than did Ovsynch (i.e., <18 d; 16 vs. 31%) and more cows with elevated (>1 ng/mL) milk P4 concentrations at d 7 (88 vs. 74%) and d 14 (80 vs. 60%). It was concluded that treatment of anestrous cows before the start of breeding resulted in earlier conception than no treatment but had no effect on the final pregnancy rate. The addition of P4 to the Ovsynch program resulted in earlier conception and in more cows with normal subsequent luteal-phase lengths.     

Pregnancy in dairy cows after synchronized ovulation regimens with or without presynchronization and progesterone

Two experiments examined pregnancy after synchronized ovulation (Ovsynch) with or without progesterone (P4) administered via controlled internal drug release (CIDR) intravaginal inserts. In experiment 1, 262 lactating cows in one herd were in 3 treatments: Ovsynch (n = 91), Ovsynch + CIDR (n = 91), and control (n = 80). The Ovsynch protocol included injections of GnRH 7 d before and 48 h after an injection of PGF20. Timed artificial insemination (TAI; 57 to 77 d postpartum) was 16 to 20 h after the second GnRH injection. Cows in the Ovsynch + CIDR group also received a CIDR (1.9 g of P4) insert for 7 d starting at first GnRH injection. Control cows received A-I when estrus was detected using an electronic estrus detection system. Based on serum P4, 44.1% of cows were cyclic before Ovsynch. Pregnancy rates at 29 d (59.3 vs. 36.3%) and 57 d (45.1 vs. 19.8%) after TAI and embryo survival (75.9 vs. 54.5%) from 29 to 57 d were greater for Ovsynch + CIDR than for Ovsynch alone. In experiment 2, 630 cows in 2 herds received TAI at 59 to 79 d postpartum after 6 treatments. Estrous cycles were either presynchronized (2 injections of PGF2alpha 14 d apart; n = 318) or not presynchronized (n = 312). Within those groups, Ovsynch was initiated 12 d after second presynchronization PGF2alpha, and used alone (n = 318) or with CIDR inserts for 7 d (1.38 g of P4/insert, n = 124 or 1.9 g of P4/insert, n = 188). Before Ovsynch, 80% of cows were cyclic. Presynchronization increased pregnancy (46.8 vs. 37.5%) at 29 d after TAI, but CIDR inserts had no effect on pregnancy in experiment 2. Overall embryonic survival between 29 and 57 d in experiment 2 was 57.7%. Use of CIDR inserts with Ovsynch improved conception and embryo survival in experiment 1 but not in experiment 2, in part due to differing proportions of cyclic cows at the outset. Presynchronization before Ovsynch enhanced pregnancy rate.     

Spatial relationships of ovarian follicles and luteal structures in dairy cows subjected to ovulation synchronization: Progesterone and risks for luteolysis,ovulation, and pregnancy

Objectives were to determine relative ovary location of follicles, GnRH-induced corpora lutea (CL), and older CL present in ovaries as part of ovulation synchronization and their associations with progesterone concentration and risk for luteolysis, ovulation, and pregnancy. Cows were exposed to a timed artificial insemination (AI) program [GnRH-1–7 d–PGF_2α (1 dose or 2 doses 24 h apart)–56 h after first or only dose of PGF_2α–GnRH-2–16 h–timed AI at 72 ± 3 d in milk]. Blood was collected to assess progesterone when ovarian structures were mapped in 694 cows before GnRH-1 and before and 48 h after PGF_2α and, in a subset of cows, size of CL (n = 599) and progesterone (n = 380) at 6 d after AI. Dominant follicles and CL in single-ovulating cows were detected more often in right than left ovaries (follicles before GnRH-1: 60.6% right and GnRH-2: 61.2% right; and CL before GnRH-1: 58.6% right and GnRH-2: 66.4% right). Dominant follicles in single-ovulating cows before GnRH-1 tended to be ipsilateral to the CL more often than contralateral (54.8 vs. 45.2%) with co-dominant follicles identified in both ovaries (19.3%). In response to GnRH-1 or GnRH-2, more left-ovary follicles ovulated contralateral to CL (left to right, 54.7%; right to left, 34.7%) than right-ovary follicles, but fewer left-ovary follicles ovulated ipsilateral to CL (left to left: 45.3%) than right-ovary follicles ovulated ipsilateral (right to right: 65.3%). Preovulatory follicles in single-ovulating cows before PGF_2α tended to be detected more often ipsilateral than contralateral to CL induced by GnRH-1 (younger CL; 56.5 vs. 43.6%), but were of equal frequency ipsilateral or contralateral to older CL present before GnRH-1. Luteolytic risk was less in cows bearing co-dominant follicles in both ovaries compared with those in either right or left ovaries. Luteolytic risk in single-ovulating cows did not differ between ovaries. Luteolytic risk was greater for cows bearing older CL (86.5%) than for cows bearing younger GnRH-1-induced CL (65.3%) or both (79.6%). Pregnancy risk at 60 d after AI was or tended to be greater in cows having both CL types compared with either younger or older CL, respectively, partly because of greater embryonic loss in the latter 2 cases. More female calves tended to be carried in right horns when conception occurred after first service, whereas the opposite greater female frequency occurred in left horns after repeat services. Right-ovary dominance is evident before and after GnRH treatment.     

Adrenal responsiveness in pre- and postpartum dairy cows.

Adrenal responsiveness was evaluated by injecting 10 multiparous dairy cows with 200 IU adrenocorticotropin between -13 and -2 days prepartum (I) and postpartum between 24 and 40 h (II) and 21 and 24 days (III). Concentrations of glucocorticoids following injection were influenced by day of injection, temperature, and minimum percent relative humidity but not by breed, breed X injection day interaction, or age of cow. Likewise differences in regressions for adrenal response and mean response (ng/ml) for the three injections were nil. Mean concentrations at peak (45, 60, and 120 min postinjection samples) adjusted for preinjection concentrations also did not differ for the three periods of injection. Mean concentrations of glucocorticoids in plasma for daily samples between -13 and -2 days prepartum were 5.3 +/- .4 (n = 61), reached a peak of 14.8 +/- .3 ng/ml the day of calving, and remained high for 2 days postpartum. Estradiol increased through prepartum sampling from 23.3 to 339.6 +/- 94.1 pg/ml the day of calving, then declined abruptly. Progestins began to decline about -5 days prepartum from mean concentration of 4.09 +/- .62 (n = 25) and attained low concentrations (.30 +/- .06 ng/ml) 2 days postpartum. Although there was a surge of glucocorticoids at parturition, this was not associated with a modification in adrenal responsiveness or with prepartum concentrations of other steroid hormones of plasma. Adrenal potential in prepartum and postpartum dairy cows appears well maintained.     

Partial feed restriction decreases growth hormone receptor 1A mRNA expression in postpartum dairy cows

Uncoupling of the growth hormone (GH) axis in early postpartum dairy cows is correlated with a decrease in liver GH receptor (GHR) 1A mRNA and a decrease in liver GH receptor protein. Postpartum recoupling of the GH axis is also correlated with GHR 1A mRNA and GHR protein. We hypothesized that dry matter intake (DMI) partially controls the increase in GHR 1A mRNA postpartum. Prepartum Holstein dairy cows (n = 11) were offered feed ad libitum. After calving, 6 cows were fed 70% of their expected DMI (feed restriction) for 14 d and 5 cows were fed ad libitum (control). Both groups were fed ad libitum after d 14. Liver was biopsied prepartum and on d 1, 7, 14, and 21 postpartum; blood was sampled throughout the experimental period. Rate of increase in postpartum milk production was less for feed-restricted cows. The GHR 1A mRNA decreased from prepartum to d 1 postpartum and subsequently increased. Rate of postpartum increase in GHR 1A mRNA was less in feed-restricted cows. Diminished GHR 1A persisted for at least 7 d after feed-restricted cows returned to ad libitum feeding. Liver insulin-like growth factor-I mRNA concentrations decreased from prepartum to d 1 as well, but were similar for feed restricted and control thereafter. We concluded that DMI partially controls GHR 1A mRNA expression in early postpartum dairy cows and that the decrease in GHR 1A in response to feed restriction persisted for at least 1 wk after ad libitum feeding was restored.