The objective was to examine the effects of presynchronization and bovine somatotropin (bST) on pregnancy rates to a timed artificial insemination protocol in lactating dairy cows. Lactating Holstein cows (n = 543) were assigned randomly in a 2 x 3 factorial experiment in which cows received a presynchronization treatment or not, and were treated with bST (500 mg) at 63 +/- 3, 73 +/- 3, or 147 +/- 3 d postpartum. The latter group was used as a control. Presynchronization treatment consisted of two injections of PGF2alpha (25 mg) given 14 d apart, with the second injection of PGF2alpha being administered 12 d before initiation of the timed artificial insemination protocol. All cows received GnRH (100 microg) at 63 +/- 3 d postpartum, an injection of PGF2alpha (40 mg) 7 d later, a GnRH injection at 48 h after PGF2alpha and were inseminated 16 to 20 h later. Cows were resynchronized if determined to be nonpregnant at ultrasonography at 32 d after insemination with a GnRH injection (100 microg), an injection of PGF2alpha (40 mg) 7 d later, and a GnRH injection at 48 h after PGF2alpha and were inseminated 16 to 20 h later. Cows were examined for pregnancy at 32 d and reexamined at 74 d after insemination. No differences in pregnancy rates were observed between cows receiving bST treatment at 63 +/- 3 d postpartum or at 73 +/- 3 d postpartum. An interaction between presynchronization and bST treatment indicated that pregnancy rates were increased for cows treated with bST when cows were presynchronized. When anestrous cows were excluded from the analyses, both an effect of bST and of presynchronization were observed, indicating that bST increased pregnancy rates regardless of presynchronization treatment and that presynchronization also increased pregnancy rates independently of bST treatment. Presynchronization and bST treatment may be used to increase first-service pregnancy rates to a timed artificial insemination protocol.
The objectives of these experiments were as follows: (1) to determine the association between circulating concentrations of pregnancy-associated glycoproteins (PAG) and late embryonic mortality (EM) in lactating dairy cattle following fixed-time artificial insemination (TAI) on d 0 or timed embryo transfer (TET) on d 7, (2) to identify a circulating concentration of PAG on d 31 below which late EM would be likely to occur, and (3) to identify when during gestation (d 31-59) late EM is occurring. Cows were diagnosed pregnant on d 31 of gestation based on presence of a fetal heartbeat and reconfirmed to be pregnant on d 59 of gestation. Late EM occurred when a cow had a viable embryo on d 31 of gestation but not on d 59 following TAI or TET. Only pregnant cows on d 31 were included in the analysis (TAI-maintained, n=413; TAI-EM, n=77; TET-maintained, n=238; TET-EM, n=47). Cows that were pregnant at d 31 of gestation and maintained the pregnancy until d 59 had significantly higher circulating concentrations of PAG at d 31 of gestation compared with cows that experienced late EM between d 31 and 59 of gestation in both TAI and TET. To conduct a more stringent test of the effectiveness of a single circulating PAG concentration (d 31) to predict EM, a receiver-operating characteristic curve was generated to identify a PAG concentration on d 31 that would predict EM with ≥95% accuracy in cows that received TAI or TET. Based on positive and negative predicative value analysis, a circulating concentration of PAG below 1.4 ng/mL (TAI; minimal detectable level 0.28 ng/mL) and 1.85 ng/mL (TET) was 95% accurate in predicting EM (between d 31 and 59) at d 31 of gestation, respectively. Following TET, embryonic loss was tracked by Doppler ultrasound, progesterone, and PAG from d 24 to 59 of gestation, with more than 50% of the loss occurring between d 31 and 38 of gestation. In summary, circulating concentrations of PAG on d 31 of gestation may provide a good marker for predicting EM between d 31 and 59 of gestation, and the data suggest that this model could help predict which cows will undergo late EM.
Experiment 1 evaluated pregnancy rates when estradiol cypionate (ECP) was used to induce ovulation as part of a timed artificial insemination (TAI) protocol in comparison to Ovsynch for lactating dairy cows in Florida (n = 371) and Texas (n = 321). Cows were presynchronized with two injections of PGF2, (25 mg, im) given 14 d apart with TAI protocols beginning 14 d after the second injection of PGF20. The TAI protocols consisted of an injection of GnRH (100 microg, im) followed by PGF2alpha 7 d later. Then, cows either received an injection of GnRH (Treatment I, Ovsynch) at 48 h after PGF2alpha and inseminated 16 to 24 h later or received an injection of ECP (1 mg, i.m.) at 24 h after PGF2alpha, (Treatment II; Heatsynch) and inseminated 48 h later. In Florida, pregnancy rates after TAI were 37.1 +/- 5.8% for Ovsynch compared with 35.1 +/- 5.0% for Heatsynch. In Texas, pregnancy rates were 28.2 +/- 3.6% for Ovsynch and 29.0 +/- 3.5% for Heatsynch. Overall pregnancy rates did not differ between Ovsynch and Heatsynch treatments. In Experiment 2, estrus and ovulation times were determined in lactating dairy cows submitted to the Heatsynch protocol. Frequencies of detected estrus and ovulation after ECP were 75.7% (28/37) and 86.5% (32/37), respectively. Mean intervals to ovulation were 55.4 +/- 2.7 h (n = 32) after ECP and 27.5 +/- 1.1 h (n = 27) after onset of estrus. Estrus occurred at 29.0 +/- 1.8 h (n = 28) after ECP. It is recommended that any cow detected in estrus by 24 h after ECP injection be inseminated at 24 h and all remaining cows be inseminated at 48 h because 75% (n = 24/32) of the ovulations occurred between > or = 48 h to < or = 72 h after ECP. Synchronization of ovulation and subsequent fertility indicated that estradiol cypionate could be used to induce ovulation for successful timed insemination.
The objectives were to evaluate the effects of feeding diets with 2 levels of negative dietary cation-anion differences (DCAD) during the last 42 or 21 d of gestation on performance and metabolism in dairy cows. The hypothesis was that extending feeding from 21 to 42 d and reducing the DCAD from -70 to -180 mEq/kg of dry matter (DM) would not be detrimental to performance. Holstein cows at 230 d of gestation were blocked by parity prepartum (48 entering their second lactation and 66 entering their third or greater lactation) and 305-d milk yield, and randomly assigned to 1 of 4 treatments arranged as a 2 × 2 factorial. The 2 levels of DCAD, -70 or -180 mEq/kg of DM, and 2 feeding durations, the last 21 d (short) or the last 42 d (long) prepartum resulted in 4 treatments, short -70 (n = 29), short -180 (n = 29), long -70 (n = 28) and long -180 (n = 28). Cows in the short treatments were fed a diet with DCAD of +110 mEq/kg of DM from -42 to -22 d relative to calving. After calving, cows were fed the same diet and production and disease incidence were evaluated for 42 d in milk, whereas reproduction and survival was evaluated for 305 d in milk. Blood was sampled pre- and postpartum for quantification of metabolites and minerals. Reducing the DCAD linearly decreased prepartum DM intake between -42 and -22 d relative to calving (+110 mEq/kg of DM = 11.5 vs. -70 mEq/kg of DM = 10.7 vs. -180 mEq/kg of DM = 10.2 ± 0.4), and a more acidogenic diet in the last 21 d of the dry period reduced intake by 1.1 kg/d (-70 mEq/kg of DM = 10.8 vs. -180 mEq/kg of DM = 9.7 ± 0.5 kg/d). Cows fed the -180 mEq/kg of DM diet had increased concentrations of ionized Ca in blood on the day of calving (-70 mEq/kg of DM = 1.063 vs. -180 mEq/kg of DM = 1.128 ± 0.020 mM). Extending the duration of feeding the diets with negative DCAD from 21 to 42 d reduced gestation length by 2 d (short = 277.2 vs. long = 275.3 d), milk yield by 2.5 kg/d (short = 40.4 vs. long = 37.9 ± 1.0 kg/d) and tended to increase days open because of reduced pregnancy per artificial insemination (short = 35.0 vs. long = 22.6%). Results suggest that increasing the duration of feeding diets with negative DCAD from 21 to 42 d prepartum might influence milk yield and reproduction of cows in the subsequent lactation, although yields of 3.5% fat- and energy-corrected milk did not differ with treatments. Reducing the DCAD from -70 to -180 mEq/kg of DM induced a more severe metabolic acidosis, increased ionized Ca concentrations prepartum and on the day of calving, and decreased colostrum yield in the first milking, but had no effects on performance in the subsequent lactation. Collectively, these data suggest that extending the feeding of an acidogenic diet beyond 21 d is unnecessary and might be detrimental to dairy cows, and a reduction in the DCAD from -70 to -180 mEq/kg of DM is not needed.
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