Changes in plasma progesterone levels in the caudal vena cava and the jugular vein and luteinizing hormone secretion pattern after feeding in lactating and non-lactating dairy cows

Effects of progesterone concentrations and follicular wave during growth of the ovulatory follicle on conceptus and endometrial transcriptome in dairy cows

Objectives were to evaluate the effects of follicular wave and progesterone concentration on growth of the ovulatory follicle, conceptus elongation, uterine IFN-τ concentration, and transcriptome of conceptus and endometrium of pregnant cows on d 17 of gestation. Nonlactating nonpregnant Holstein cows were assigned randomly to one of 3 treatments: ovulation of a first-wave follicle (FW, n = 15); ovulation of a first-wave follicle and progesterone supplementation (FWP4, n = 12); and ovulation of a second-wave follicle (SW, n = 19). Ovulation of a first- or second-wave follicle was achieved by initiating the Ovsynch protocol (d -9 GnRH, d -2 and -1 PGF_2α, d 0 GnRH and artificial insemination, d 0.7 artificial insemination) on d 0 or 6 of a presynchronized estrous cycle, respectively. Cows in FWP4 received 3 intravaginal inserts containing progesterone at 12, 24, and 48 h after the first GnRH injection that were removed on d -2. Cows were killed on d 17 for collection of the reproductive tract. Transcriptome was evaluated by microarray using the Affymetrix Bovine Array. Orthogonal contrasts were built to assess the effects of progesterone concentration during follicle growth (FW vs. FWP4 + SW) and follicular wave (FWP4 vs. SW). Progesterone concentrations (LSM ± SEM) from d -9 to -2 were greater for SW, followed by FWP4 and FW (5.38 ± 0.24, 4.26 ± 0.28, and 1.17 ± 0.27 ng/mL). Diameter of the ovulatory follicle (FW = 19.6 ± 0.6; FWP4 = 15.6 ± 0.6; SW = 15.2 ± 0.5 mm) and concentrations of estradiol from d -2 to 1 (FW = 4.05 ± 0.33; FWP4 = 2.73 ± 0.35; SW = 2.48 ± 0.30 pg/mL) were greater for FW compared with FWP4 and SW. Progesterone concentrations from d 3 to 16 were greater for FW compared with FWP4 and SW. A total of 28 singleton conceptuses were collected (FW, n = 8; FWP4, n = 8; SW, n = 12) and only intact conceptuses were included in the analyses of length (FW, n = 8; FWP4, n = 6; SW, n = 12). Although conceptuses were longer for FW compared with FWP4 and SW (FW = 16.6 ± 2.3; FWP4 = 9.8 ± 2.2; SW = 9.6 ± 2.0 cm), treatment did not affect the amount of IFN-τ in uterine flushing. Transcriptome of conceptuses and endometrium of pregnant cows was not extensively affected by follicular wave (8 and 1 differentially expressed transcripts) or concentration of progesterone during follicle growth (0 and 3 differentially expressed transcripts), showing that these factors did not affect conceptuses and endometrium transcriptome in pregnancies that are maintained to d 17.

Profiles of prostaglandin F2α metabolite in dairy cattle during luteal regression and pregnancy: implications for corpus luteum maintenance†

Mechanisms of bovine corpus luteum (CL) maintenance during the second month of pregnancy have not been adequately investigated, despite significant reproductive losses. In the first month, interferon-tau is believed to suppress oxytocin-stimulated prostaglandin F2α (PGF) production, yet there are conflicting reports of circulating PGF metabolite (PGFM). In this study, characterization of PGFM and P4 occurred through continuous bihourly blood sampling in cows undergoing CL regression (day 18-21, n = 5), and during the first (day 18-21, n = 5) and second month (day 47-61; n = 16) of pregnancy. Cattle in the second month were assigned to control (n = 8) or oxytocin treatment (n = 8; three pulses to mimic luteolysis) to evaluate if oxytocin receptors were active. All cows but one (which had elevated PGFM prior to oxytocin treatment) maintained the pregnancy. Basal PGFM concentrations were low (11.6 ± 0.7 pg/mL) in the first month but increased 2.54-fold in the second month. Few (0.26 ± 0.12 pulses/day) PGFM pulses with low peak concentrations (28.8 ± 3.1 pg/mL) were observed during the first month of pregnancy, similar to cows not undergoing regression. However, in the second month, frequency (1.10 ± 0.26 pulses/day) and peak concentration (67.2 ± 5.0 pg/mL) of PGFM pulses increased, displaying similar frequency but lower peak PGFM than seen in regression (1.44 ± 0.14 pulses/day; 134.5 ± 18.9 pg/mL). Oxytocin treatment increased likelihood of PGFM pulses post-treatment and increased peak concentration (89.7 ± 10.1 pg/mL) in cows during the second month. Thus, cows have more PGFM pulses during second than first month of pregnancy, possibly induced by endogenous oxytocin, indicating suppression of PGF production is an important mechanism for CL maintenance during first but not second month of pregnancy.

Progesterone profiles in the caudal vena cava and jugular vein in response to pulsatile luteinizing hormone stimulation induced by GnRH treatment during the mid-luteal phase in lactating dairy cows

The aim of this study was to examine whether increased frequency of luteinizing hormone (LH) pulses influences luteal progesterone (P₄) secretion by measuring progesterone concentrations at the secreted (caudal vena cava) and circulating levels (jugular vein) in lactating dairy cows. Cows received six intravenous administrations of 2.5 μg of GnRH (gonadorelin acetate, n=4) or 2 ml saline (n=3) at 1-h intervals on 12.4 ± 0.4 (mean ± SE) days after ovulation. Blood samples were collected from the caudal vena cava and jugular vein every 12 min for 12 h (6 h before and after treatment). During the 6 h after treatment, frequency of LH pulses (5.3 ± 0.3 and 3.0 ± 0.0 pulses/6 h) and mean LH concentration (0.50 ± 0.06 and 0.38 ± 0.05 ng/ml) were greater (P<0.05) in GnRH-treated cows than in saline-treated cows. Mean P₄ concentration and amplitude of P₄ pulses in the caudal vena cava during the 6 h after treatment were greater (P<0.05) in GnRH-treated cows than in saline-treated cows, but the frequency of P₄ pulses was not different between the groups. Mean P₄ concentration in the jugular vein during the 6 h after treatment was also higher (P<0.05) in GnRH-treated cows than in saline-treated cows (7.0 ± 1.3 and 5.4 ± 0.9 ng/ml). These results indicate that the increased frequency of LH pulses stimulates progesterone secretion from the functional corpus luteum and brings about higher P₄ concentrations in the circulating blood in lactating dairy cows.