A high dose of initial GnRH increased ovulatory response and fertility in Holstein heifers subjected to a progesterone based 5-d CO-Synch protocol.

The objectives of this study were to investigate the effect of presynchronization or dose of GnRH on ovulatory response to initial GnRH, estrus expression and reproductive outcomes in Holstein heifers subjected to a progesterone based 5-d CO-Synch protocol. Heifers were fitted with a collar-mounted automated activity monitoring system on Day -5 and were assigned randomly to one of three groups: 1) G100 (n = 111), a 5-d CO-Synch plus PRID protocol with administration of 100 µg of GnRH at the time of PRID insertion (Day 0), 500 µg of cloprostenol (PGF) at the time of PRID removal (Day 5) and again 24 h later (Day 6); 2) G200 (n = 112), same as G100 except 200 µg GnRH was administered on Day 0; 3) P10 (n = 111), PRID + PGF on Day -5 followed by a 5 d CO-Synch with administration of 100 µg of GnRH on Day 0, PGF at the time of PRID removal (Day 5) and again 24 h later (Day 6). Approximately 72 h after PRID removal (Day 8), all heifers were timed-inseminated (TAI) and concurrently 100 µg of GnRH was administered to those not exhibiting estrus. All inseminations were done by one technician using either sex-sorted (n = 265) or conventional (n = 69) frozen-thawed semen. Transrectal ultrasonography was done to determine ovarian cyclicity and normalcy of the reproductive tract, ovarian dynamics and pregnancy. All heifers were cyclic and ovulatory response to initial GnRH was greater (P < 0.01) in G200 (51.8%) and P10 (47.7%) compared to G100 (27.9%). Estrus expression rate tended to be greater (P = 0.08) in G100 (93.7%) compared to G200 (85.7%) and intermediate in P10 (89.2%). Expression of estrus was associated positively with P/AI at 45 d post-TAI (P < 0.01; 70.2 vs. 31.4% for heifers expressing or not expressing estrus). Heifers in the G200 group had greater P/AI at 30 (P < 0.01) and 45 (P = 0.01) d post-TAI (79.5 and 75.9%, respectively) compared to those in G100 (63.1 and 60.4%) or P10 (64.0 and 62.2%) groups. Pregnancy loss did not differ among treatment groups (overall 3.9%). Results indicate that increasing the dose of the initial GnRH from 100 to 200 µg resulted in increased ovulatory response and improved P/AI in Holstein heifers subjected to a progesterone based 5-d CO-Synch protocol. Although heifers presynchronized with a combination of PRID and PGF had an increased ovulatory response to the initial GnRH, P/AI did not differ from the standard progesterone based 5-d CO-Synch protocol.

Relationships between early postpartum nutritional and metabolic profiles and subsequent reproductive performance of lactating dairy cows.

The objective of this study was to examine the relationship between early postpartum nutritional and metabolic profiles in lactating dairy cows and subsequent pregnancy to first artificial insemination (AI), pregnancy by 150 d in milk (DIM) and pregnancy loss after first AI. A blood sample was collected between 2 and 14 (median = 9) DIM from 869 lactating Holstein cows to determine serum concentrations of metabolites, minerals, and liver enzymes. Associations between analytes and fertility were determined using an adjusted odds ratio (OR). Overall, pregnancy to first AI, pregnancy by 150 DIM and pregnancy loss after first AI were 37.9, 65.8 and 11.2%, respectively. Compared to cows pregnant to first AI, non-pregnant cows had higher (P < 0.05) serum concentrations of aspartate aminotransferase (AST; 92.3 ± 1.6 vs. 84.6 ± 2.0 U/L), non-esterified fatty acid (NEFA; 0.73 ± 0.02 vs. 0.54 ± 0.02 mmol/L), and haptoglobin (0.77 ± 0.04 vs. 0.60 ± 0.05 g/L), and lower (P < 0.05) serum concentrations of Mg (0.86 ± 0.02 vs. 0.89 ± 0.02 mmol/L) and cholesterol (2.1 ± 0.03 vs. 2.4 ± 0.04 mmol/L). Cows non-pregnant by 150 DIM had lower (P < 0.05) serum concentration of Mg (0.86 ± 0.02 vs. 0.88 ± 0.02 mmol/L) and higher serum concentration of haptoglobin (0.82 ± 0.1 vs. 0.63 ± 0.09 g/L) than cows pregnant by 150 DIM. Cows that lost their pregnancy after first AI had greater serum concentrations of haptoglobin than those that did not undergo pregnancy loss (1.1 ± 0.09 vs. 0.5 ± 0.05 g/L; P < 0.01). The odds of pregnancy to first AI (OR; 95% confidence interval [CI]) decreased with increased serum concentrations of AST (OR = 0.99; 95% CI = 0.98-1.00), NEFA (OR = 0.54; 95% CI = 0.37-0.79) and haptoglobin (OR = 0.80; 85% CI = 0.66-0.96) and increased with inreased concentrations of Mg (OR = 3.24; 95% CI = 1.09-9.62) and cholesterol (OR = 1.24; 95% CI = 1.02-1.54). Increased serum concentrations of Mg (OR = 3.06; 95% CI = 1.02-9.20) and haptoglobin (OR = 0.92; 95% CI = 0.69-0.97) were associated with greater and lower odds of pregnancy by 150 DIM, respectively. Only increased concentrations of haptoglobin (OR = 1.58; 95% CI = 1.13-2.20) were associated with increased odds of pregnancy loss after the first AI. In summary, greater early postpartum serum concentrations of AST, NEFA and haptoglobin were associated with reduced fertility, but the opposite was observed for serum concentrations of Mg and cholesterol. In addition, serum concentrations of haptoglobin were positively associated with pregnancy loss.

The association of circulating prepartum metabolites, minerals, cytokines and hormones with postpartum health status in dairy cattle.

The objectives were to evaluate differences in circulating prepartum metabolites, minerals, cytokines and hormones based on postpartum disease category and determine critical circulating concentrations of prepartum analytes associated with postpartum disease in 229 cattle from 11 commercial dairies in Alberta, Canada. Blood was collected at 8.8 ± 2.1 d prepartum and analyzed for a wide array of analytes. Cattle were categorized as healthy (n = 76) or as having inflammatory (INF; n = 28), metabolic (MET; n = 34) or inflammatory and metabolic (INFMET; n = 91) postpartum diseases. The prepartum circulating concentrations of Cu were lesser (0.84 vs. 0.90 µg/mL; P = 0.02) and concentrations of Mo (19.1 vs. 16.5 ng/mL; P = 0.04) and NEFA (0.27 vs. 0.18 mmol/L; P = 0.01) were greater in INFMET cattle compared with healthy cattle. The critical threshold for Cu, Mo and NEFA prepartum concentration that predicted INFMET was ≤ 0.81 µg/mL (sensitivity 45.5% and specificity 74.3%), ≥ 9.91 ng/mL (sensitivity 70.0% and specificity 52.7%) and ≥ 0.19 mmol/L (sensitivity 62.2% and specificity 79.7%), respectively. Regardless of differences in the prepartum circulating concentrations of Cu, Mo and NEFA among healthy cattle and those with postpartum disease, the use of these analytes to predict the incidence of postpartum diseases was limited.

Effect of initial GnRH and time of insemination on reproductive performance in cyclic and acyclic beef heifers subjected to a 5-d Co-synch plus progesterone protocol.

This study evaluated the effect of initial GnRH and timing of AI in a 5-d Co-synch plus CIDR (device containing 1.38 g of progesterone) protocol on pregnancy per AI (P/AI) and pregnancy loss in beef heifers. A secondary objective was to determine if the effect of initial GnRH on reproductive performance was influenced by cyclicity. Crossbred beef heifers (n = 1068; 301-514 kg of body weight, and 13-15 mo of age) at three locations were assigned to either a 5-d Co-synch plus CIDR protocol with (CIDR5G) or without (CIDR5NG) an initial injection of 100 µg of GnRH at CIDR insertion (Day 0). All heifers received a single dose of 500 µg of cloprostenol at CIDR removal (Day 5) and were divided into two groups to receive GnRH and TAI at either 66 or 72 h (Day 8) after CIDR removal. All heifers were inseminated by one technician with frozen-thawed semen from 1 of 4 sires available commercially. Transrectal ultrasonography was performed on Day 0 to determine cyclicity (presence of CL) and normalcy of the reproductive track, and 27 d after TAI to determine pregnancy status. Non-pregnant heifers (n = 470) were assigned to either a CIDR5G or a CIDR5NG protocol with TAI at 72 h after CIDR removal. Twelve days after second AI, heifers were exposure to bulls for 20 d and pregnancy diagnoses were performed approximately 30 d after second TAI and 60 d after bulls were removed to diagnose bull pregnancies and determine pregnancy loss rate. The percentage of acyclic heifers was 20.3%. Overall P/AI after first TAI was 55.6% (594/1068) and did not differ between CIDR5G and CIDR5NG (56.1 vs. 55.1%), or between TAI66 and TAI72 (55.8 vs. 55.4%). However, cyclic heifers were more likely to become pregnant than acyclic ones (59.3 vs. 41.2%; P < 0.01). Moreover, acyclic heifers subjected to the CIDR5NG had fewer P/AI than those subjected to CIDR5G (P < 0.01). Overall P/AI after resynchronization was 55.1% and did not differ between CIDR5G and CIDR5NG (51.3 vs. 59.0%). Overall pregnancy loss after first and second TAI were 3.0% (18/594) and 3.9% (8/205), respectively. When pregnancy loss data were combined, synchronization protocol (4.1 vs. 2.3% for CIDR5NG and CIDR5G; P = 0.01), cyclicity (5.8 vs. 2.9% for acyclic and cyclic; P = 0.03) and the interaction between synchronization protocol and cyclicity (P = 0.04) were significant. The overall cumulative pregnancy at the end of the breeding season was 94.2% (1006/1068); acyclic heifers were less likely to be pregnant at the end of the breeding season (88.4 vs. 95.8%; P < 0.01). In summary, the initial GnRH administration in a 5-d Co-synch plus CIDR protocol that includes a single PGF treatment is necessary in acyclic beef heifers to optimize P/AI, but not in cyclic heifers. Moreover, omission of initial GnRH was associated to greater pregnancy losses, particularly in acyclic heifers. Timing of AI did not affect P/AI.

Accuracy of a cow-side test for the diagnosis of hyperketonemia and hypoglycemia in lactating dairy cows.

The objective of this study was to evaluate the use of a cow-side device (FreeStyle Precision Neo™) to diagnose ketosis and hypoglycemia based on measures of blood ß-hydroxybutyrate (BHBA) and glucose. Eleven commercial dairy farms were visited and blood samples were taken from Holstein cows between 2 and 14days in milk, yielding 441 samples for BHBA analysis and 308 samples for glucose analysis. Concentrations of BHBA and glucose were measured in two ways, 1) using the cow-side device with whole blood immediately after sampling and 2) serum samples analyzed with a standard laboratory assay (Animal Health Laboratory, University of Guelph, Canada). The accuracy of the device was determined by comparing the results to the laboratory method as well as the ability to diagnose ketosis (BHBA ≥1.2mmol/L) and hypoglycemia (glucose <2.5mmol/L). The concordance correlation coefficient (CCC), Bland-Altman plot and Kappa coefficient were calculated to evaluate agreement between the 2 methods using SAS (version 9.3). The CCC was 0.92 for BHBA and 0.56 for glucose measurements. The 95% confidence intervals of the Bland-Altman plot encompassed 97% and 95% of the mean difference between methods for BHBA and glucose measurements, respectively. The Kappa coefficients were 0.78 for BHBA and 0.23 for glucose measurements. These results indicate that the cow-side device is accurate for rapid measurement of blood BHBA and diagnosis of ketosis on farms but is not accurate for measurement of blood glucose concentrations and diagnosis of hypoglycemia.

Relationship between circulating progesterone at timed-AI and fertility in dairy cows subjected to GnRH-based protocols.

The objectives of this retrospective study were: 1) to investigate the effect of plasma progesterone (P4) concentrations at the time of timed-AI (TAI) on fertility, and 2) to examine risk factors associated with plasma P4 concentrations that impair fertility in lactating dairy cows subjected to GnRH-based protocols. Data from 872 lactating Holstein cows that had, or had not been presynchronized prior to a 7-day GnRH-based TAI protocol were examined. However, data from only those cows (n = 697; 79.9%) that ovulated after second GnRH were analyzed. Plasma P4 concentrations were determined using a solid-phase radioimmunoassay. Transrectal ultrasonography was used to determine cyclicity at first GnRH treatment, ovulation after first and second GnRH treatments, and pregnancy status at 32 and 60 d after TAI. Parity, days in milk (DIM) and BCS were also recorded. Plasma P4 concentrations at TAI ranged from 0.0 to 9.94 ng/mL (overall mean ± SEM, 0.32 ± 0.02 ng/mL) and 41 (5.9%) cows had P4 ≥ 1.0 ng/mL at TAI. The percentage of cows diagnosed pregnant at 32 and 60 d after TAI was 45.1 and 41.6%, respectively, and pregnancy loss from 32 to 60 d after TAI was 7.6%. Plasma P4 concentrations at TAI affected (P < 0.01) P/AI at 32 and 60 d, but did not affect (P > 0.1) pregnancy loss. No cows with plasma P4 concentrations >0.80 ng/mL became pregnant. However, ROC curve analysis revealed that the optimal P4 threshold at TAI for P/AI at 32 d was ≤0.50 ng/mL, with a sensitivity and specificity of 94.9 and 20.9, respectively. The percentage of cows with plasma P4 concentrations >0.50 ng/mL was 15.8% (110/697). Furthermore, a significant (P < 0.05) quadratic relationship between plasma P4 concentrations at TAI and P/AI at 32 d was observed. The maximum predicted probability of pregnancy was 0.54 at a P4 concentration of 0.26 ng/mL. Based on the odds ratios (OR), cows with P4 ≤ 6.2 ng/mL at PGF were 2.3 times less likely to have P4 > 0.50 ng/mL at TAI compared to cows with P4 > 6.2 ng/mL (OR = 0.44; 95% CI = 0.27 to 0.71; P < 0.01). Also, cyclic cows subjected to presynchronization were less likely to undergo luteal regression than non-presynchronized or acyclic cows (OR = 5.3; 95% CI = 1.77 to 16.27; P < 0.01). In summary, plasma P4 concentrations >0.50 ng/mL at TAI resulted in significantly reduced fertility. As elevated plasma P4 concentrations at TAI were more frequent in cows with lower P4 at PGF or those subjected to presynchronization, both groups are most likely to benefit from an additional PGF treatment prior to TAI.

Diameter of the ovulatory follicle at timed artificial insemination as a predictor of pregnancy status in lactating dairy cows subjected to GnRH-based protocols.

Ovulation of an early-stage dominant follicle induced by exogenous GnRH reportedly results in a reduced ovulatory follicle size and fertility in beef and dairy cattle. Objectives were to examine factors associated with ovulatory follicle diameter and the relationship between ovulatory follicle diameter and pregnancy per artificial insemination (P/AI) and pregnancy loss in lactating dairy cows subjected to GnRH-based programs for timed artificial insemination (TAI). A total of 1048 ovulations from 1576 breedings of cows that had or had not been presynchronized and subjected to a 5- or a 7-day GnRH-based protocol with or without progesterone supplementation between initial GnRH and PGF2α were analyzed. Ultrasonography was used to determine cyclicity, ovulation, and pregnancy status and to measure diameter of the ovulatory follicle at the time of TAI. Mean (±standard error) diameter of the ovulatory follicle was 16.4 ± 0.1 mm (range, 11-25 mm; n = 1048); the most common diameters were 15 (n = 170), 16 (n = 169), and 17 mm (n = 170). Multiparous cows and those subjected to a 7-day protocol had larger ovulatory follicles (P < 0.05). On average, multiparous cows that did not ovulate after the initial GnRH had the largest ovulatory follicles (17.0 ± 0.1 mm; n = 290), whereas all cows that ovulated after the initial GnRH and were subjected to a 5-day GnRH-based protocol had the smallest ovulatory follicles (15.6 ± 0.2 mm; n = 207). The associations between ovulatory follicle diameter and P/AI at 32 and 60 days after TAI were not significant. However, a significant linear relationship between ovulatory follicle diameter and pregnancy loss between 32 and 60 days after TAI was observed, with an increased (P < 0.05) probability of pregnancy loss in cows with an ovulatory follicle greater than 20 mm in diameter. In summary, the diameter of the ovulatory follicle preceding TAI was affected by interactions between ovulatory response to initial GnRH and parity and between ovulatory response to initial GnRH and the length of ovulation synchronization protocol. Ovulatory follicle diameter was not associated with P/AI at 32 or 60 days, but large ovulatory follicle size was identified as a predictor of pregnancy loss in lactating dairy cows subjected to GnRH-based protocols for TAI.