Presynchronization with prostaglandin F2α and gonadotropin-releasing hormone simultaneously improved first-service pregnancy per artificial insemination in lactating Holstein cows compared with Presynch-14 when combined with detection of estrus

This study aimed to determine the effect of 2 simple breeding strategies combining artificial insemination (AI) after detection of estrus (AIED) and timed AI (TAI) on first-service fertility in lactating Holstein cows. Weekly, lactating Holstein cows (n = l,049) between 40 and 46 d in milk (DIM) were randomly assigned to initiate 1 of 2 breeding strategies for first service: Presynch-14 and PG+G. Presynch-14 is a presynchronization strategy with 2 PGF_2α treatments 14 d apart with the last PGF_2α 14 d before the initiation of the Ovsynch protocol. Cows treated with PG+G receive a simpler presynchronization program that uses PGF_2α and GnRH simultaneously 7 d before Ovsynch. In both treatments, cows detected in standing estrus by tail chalk at any time ≥55 DIM were inseminated, and treatment was discontinued (n = 525). Cows completing treatment received TAI from 78 to 84 DIM (n = 526). In a subgroup of cows that received TAI, blood was collected (n = 163) to assess circulating concentrations of progesterone, and ultrasonographic evaluations of ovaries were performed on the day of first GnRH of Ovsynch (n = 162) and PGF_2α of Ovsynch (n = 122). The proportion of cows that received TAI was greater for PG+G compared with Presynch-14 (63.5 vs. 31.9%), which increased DIM at first service for cows treated with PG+G compared with Presynch-14 (75.5 ± 0.4 vs. 68.7 ± 0.4). For cows receiving TAI, the ovulatory response to first GnRH of Ovsynch (73.8 vs. 48.8%) and the proportion of cows with functional corpora lutea (92.6 vs. 73.1%) were greater for PG+G than Presynch-14. Cows treated with PG+G had greater overall pregnancy per AI (P/AI) 42 ± 7 d after AI (40.2 vs. 33.6%) and calving per AI (32.1 vs. 25.2%) than Presynch-14. For cows receiving AIED, treatment did not affect P/AI 42 ± 7 d after AI. However, for cows receiving TAI, PG+G increased P/AI compared with Presynch-14 (44.6 vs. 35.2%). Overall, cows receiving TAI had greater P/AI 42 ± 7 d after AI (42.5 vs. 31.5%) and calving per AI (34.1 vs. 23.7%) and decreased pregnancy loss (16.8 vs. 25.2%) than cows receiving AIED. In summary, PG+G increased the proportion of cows receiving TAI and the DIM at first service, P/AI, and calving per AI compared with Presynch-14 when both TAI programs were combined with AIED.     

Prostaglandin F2α and gonadotropin-releasing hormone administration improve progesterone status, luteal number, and proportion of ovular and anovular dairy cows with corpora lutea before a timed artificial insemination program

The objective of this research was to increase the proportion of cows with at least 1 functional corpus luteum (CL) and elevated progesterone at the onset of the timed artificial insemination (TAI) protocol. Postpartum Holstein cows in one herd were stratified by lactation number at calving (September 2009 through August 2010) and assigned randomly to 2 treatments: 1) Presynch-10 (n=105): two 25-mg injections of PGF(2α) (PG) 14 d apart (Presynch); and 2) PG-3-G (n=105): one 25-mg injection of PG 3 d before 100-μg GnRH (Pre-GnRH) injection, with the PG injection administered at the same time as the second PG injection in the Presynch-10 treatment. Cows were enrolled in a TAI protocol [Ovsynch; injection of GnRH 7 d before (GnRH-1) and 56 h after (GnRH-2) PG injection with AI 16 to 18 h after GnRH-2] 10 d after the second or only PG injection. Blood samples for progesterone or estradiol analyses were collected on median days in milk (DIM): 36, 39, 50, 53 (Pre-GnRH), 60 (GnRH-1), 67 (PG), 69 (GnRH-2), and 70 (TAI). Ovarian structures were measured by ultrasonography on median DIM 53, 60, 67, 69, and 6 d post-TAI to determine follicle diameters, ovulation response to GnRH, or both. Although progesterone concentration did not differ between treatments before Pre-GnRH injection, the proportion of cows with at least 1 CL tended to be greater for PG-3-G than Presynch-10 cows, and more PG-3-G cows ovulated after Pre-GnRH injection than ovulated spontaneously in Presynch-10. Further, the diameter of follicles that ovulated tended to be smaller in PG-3-G than in Presynch-10 cows after Pre-GnRH injection. At GnRH-1, the proportion of cows with progesterone ≥1 ng/mL, the number of CL per cow, and the proportion of cows with at least 1 CL were greater for PG-3-G than Presynch-10. Neither follicle diameter nor percentage of cows ovulating after GnRH-1 differed between treatments. At PG injection during the week of TAI, progesterone concentration and the proportion of cows with progesterone ≥1 ng/mL tended to be greater for PG-3-G than Presynch-10, and PG-3-G had more CL per cow than Presynch-10. No ovarian characteristics differed between treatments after GnRH-2, including progesterone concentration, number of CL per cow, and total luteal volume 7 d after GnRH-2. Many of the previous ovarian traits were improved in both ovular and anovular cows after PG-3-G compared with Presynch-10. Pregnancies per AI at d 32 and 60 were only numerically greater for PG-3-G than for Presynch-10 cows, largely because of differences detected during months without heat stress. We concluded that the PG-3-G treatment increased ovulation rate and luteal function 7 d before the onset of Ovsynch, resulting in improved follicular synchrony and predisposing potentially greater pregnancies per AI in lactating dairy cows.     

Effects of cloprostenol sodium at final prostaglandin F2α of Ovsynch on complete luteolysis and pregnancy per artificial insemination in lactating dairy cows

Luteolysis is a key event in Ovsynch programs of lactating dairy cows. Studies indicate that as many as 20% of cows treated with a Presynch/Ovsynch program have delayed or incomplete luteolysis using dinoprost tromethamine. Cows must have complete luteolysis to have a chance to become pregnant. Dinoprost tromethamine has a short half-life of approximately 7 to 8 min. Cloprostenol sodium is more resistant to endogenous metabolism and is maintained in circulation for a longer time (half-life = 3 h). The objective was to determine if cloprostenol sodium could increase the percentage of cows with complete luteolysis and subsequent pregnancy per artificial insemination (P/AI) in lactating dairy cows compared with dinoprost tromethamine when administered within a presynchronization plus Ovsynch program for first artificial insemination (n = 652) and an Ovsynch resynchronization program for second or later AI (second+; n = 394). Blood samples were collected daily for 5 d beginning at the PGF_2α of Ovsynch in a subset of cows (n = 680) for first and second+ AI to measure circulating concentrations of progesterone (P₄) and estradiol (E₂). Complete luteolysis was defined as cows with functional corpus luteum (CL) at time of treatment and serum concentrations of P₄ <0.5 ng/mL at 56, 72, and 96 h after treatment. Percentage of cows with functional CL that had complete luteolysis after treatment was not greater for cloprostenol sodium compared with dinoprost tromethamine in first (79 vs. 80%, respectively) or second+ AI (70 vs. 72%, respectively). In addition, mean serum concentrations of P₄ were not less for cows treated with cloprostenol sodium following treatment. Pregnancy per AI of cows treated with cloprostenol sodium tended to be greater than dinoprost tromethamine for first (40 vs. 35%; respectively) but not second+ AI (23 vs. 21%, respectively). Cows with greater serum P₄ concentrations at time of PGF_2α of Ovsynch had a greater probability of undergoing complete luteolysis after PGF_2α of Ovsynch and pregnancy at 39 d after timed AI (i.e., 50% pregnant at 8 vs. 28% pregnant at 4 ng/mL P₄). Serum concentrations of E₂ at 56 h after PGF_2α of Ovsynch were a positive predictor of pregnancy at 39 d after timed AI. In summary, cloprostenol sodium tended to improve P/AI. Cows with greater serum concentrations of P₄ at time of PGF_2α of Ovsynch had a greater chance of luteolysis and pregnancy.     

Effect of dose and frequency of prostaglandin F2α treatments during a 7-day Ovsynch protocol with an intravaginal progesterone releasing device on luteal regression and pregnancy outcomes in lactating Holstein cows

Our objective was to evaluate the effect of 3 different Ovsynch protocols on progesterone (P4) and pregnancies per artificial insemination (P/AI), where all cows received a P4 releasing intravaginal device (PRID) from d 0 until d 8. We hypothesized that (1) both modified PGF_2α treatments lead to decreased P4 at the second GnRH treatment (G2), resulting in greater P/AI, (2) the treatment effect is influenced by the presence of a corpus luteum (CL) at the beginning of the protocol, and (3) potential vaginal discharge caused by the PRID does not have a negative influence on fertility. Lactating Holstein cows (n = 1,056) were randomly assigned to 1 of 3 treatment groups on a weekly basis (n = 356; control: d 0, 100 µg of GnRH + PRID; d 7, 25 mg of dinoprost; d 8, PRID removal; d 9, 100 µg of GnRH). Cows in the second group (n = 353) received an Ovsynch protocol with a double dose of PGF_2α (DoubleDose: d 0, 100 µg of GnRH + PRID; d 7, 50 mg of dinoprost; d 8, PRID removal; d 9, 100 µg of GnRH). Cows in the third group (n = 347) received an Ovsynch protocol with a second PGF_2α treatment 24 h after the first one (2PGF: d 0, 100 µg of GnRH + PRID; d 7, 25 of mg dinoprost; d 8, 25 mg of dinoprost and PRID removal; d 9, 100 µg of GnRH). All cows had their ovaries scanned to determine the presence of a CL at the beginning of the Ovsynch protocol. Vaginal discharge score (VS) was evaluated at PRID removal. All cows received timed artificial insemination approximately 16 h after G2. Pregnancy diagnosis was performed via transrectal ultrasonography (d 38 ± 3 after timed artificial insemination) and rechecked on d 80 ± 7 after timed artificial insemination. Blood samples were collected on d 0, 7, and 9 of the protocol to determine P4 concentrations. Treatment affected P4 at G2. Progesterone was lower for 2PGF and DoubleDose cows compared with cows in the control group (control 0.35 ± 0.02 ng/mL; DoubleDose 0.29 ± 0.02 ng/mL; 2PGF 0.30 ± 0.02 ng/mL). Overall, P/AI did not differ among treatments. We found, however, an interaction between treatment and CL at the first GnRH treatment. Cows lacking a CL at the first GnRH treatment in the 2PGF group had greater P/AI (47.9%) compared with the same type of cows in the DoubleDose group (32.7%). We observed an effect of VS on P4 concentration at d 7. We found an increase in P4 with greater VS. Vaginal discharge score at PRID removal tended to have a positive effect on P/AI at d 38 (VS0: 36.5%; VS1: 41.3%; VS2: 49.7%). In conclusion, the addition of a second PGF treatment on d 7 and 8 of a 7-d Ovsynch protocol increased luteal regression and decreased mean P4 at G2. Cows treated with PGF_2α 2 times 24 h apart showed greater P/AI, compared with cows treated with an increased dose of PGF_2α.     

Effect of dose and timing of prostaglandin F2α treatments during a Resynch protocol on luteal regression and fertility to timed artificial insemination in lactating Holstein cows

Our objective was to evaluate the effect of a second PGF_2α treatment (25 mg of dinoprost) or a double dose of PGF_2α (50 mg of dinoprost) during a Resynch protocol on luteal regression and pregnancies per artificial insemination (P/AI) in lactating dairy cows. Lactating Holstein cows (n = 1,100) were randomly assigned at a nonpregnancy diagnosis to receive (1) Ovsynch (control: 100 µg of GnRH; 7 d, 25 mg of PGF_2α; 56 h, 100 µg of GnRH), (2) Ovsynch with a second PGF_2α treatment (GPPG: 100 µg of GnRH; 7 d, 25 mg of PGF_2α; 24 h, 25 mg of PGF_2α; 32 h, 100 µg of GnRH), or (3) Ovsynch with a double dose of PGF_2α (GDDP: 100 µg of GnRH; 7 d, 50 mg of PGF_2α; 56 h, 100 µg of GnRH). All cows received timed artificial insemination (TAI) approximately 16 h after the second GnRH treatment (G2). Pregnancy diagnosis was performed by transrectal palpation 39 ± 3 d after TAI, and pregnancy status was reconfirmed 66 d after TAI. Blood samples collected from a subset of cows in each treatment at the first PGF_2α treatment (n = 394) and at G2 (n = 367) were assayed for progesterone (P4). Data were analyzed by logistic regression using the GLIMMIX procedure of SAS (SAS Institute Inc., Cary, NC). At 39 d after TAI, GPPG cows tended to have more P/AI than control cows [35% (137/387) vs. 31% (107/349)], whereas P/AI for GDDP cows [32% (118/364)] did not differ from that for control cows. Pregnancy loss from 38 to 66 d did not differ among treatments and was 8% (30/362). The percentage of cows with complete luteal regression (P4 <0.4 ng/mL at G2) tended to differ among treatments and was greater for GPPG cows than for GDDP and control cows (94% vs. 88% vs. 88%, respectively). Overall, cows with P4 <1 ng/mL at the first PGF_2α treatment had fewer P/AI than cows with P4 ≥1 ng/mL (27% vs. 38%), whereas cows with P4 ≥0.4 ng/mL at G2 had fewer P/AI than cows with P4 <0.4 ng/mL (15% vs. 38%). We conclude that adding a second PGF_2α treatment 24 h after the first within a Resynch protocol tended to increase the proportion of cows undergoing complete luteal regression and P/AI, whereas treatment with a double dose of PGF_2α at a single time did not.     

Dose frequency of prostaglandin F2α administration to dairy cows exposed to presynchronization and either 5- or 7-day Ovsynch program durations: Ovulatory and luteolytic risks

We hypothesized (1) that neither duration of the Ovsynch program nor dose frequency of PGF_2α would change the proportion of cows with complete luteolysis (progesterone <0.4 ng/mL 72 h after PGF_2α) and (2) that the additional GnRH treatment administered as part of a presynchronization program would not alter the proportion of anovulatory cows starting the timed artificial insemination (AI) program compared with an alternative shorter presynch program including only 1 GnRH treatment. Lactating Holstein cows (n = 406) were milked 3 times daily and enrolled in a 2 × 2 × 2 factorial experiment consisting of 8 treatments before the first postpartum AI. Treatments were used to test ovulatory, luteal, and luteolytic outcomes to 3 main effects: (1) 2 GnRH-PGF_2α presynchronization programs (PG-3-G vs. Double Ovsynch), (2) 2 Ovsynch program durations [5 d: GnRH (GnRH-1)–5 d–PGF_2α–24 h–PGF_2α–32 h–GnRH (GnRH-2)–16 h–timed AI; 7 d: GnRH-1–7 d–PGF_2α–56 h–GnRH-2–16 h–timed AI], and (3) 2 PGF_2α dose frequency treatments (2 × 25 mg) 24 h apart versus 1 dose (1 × 50 mg) of PGF_2α administered 72 h before timed AI. The presynchronization treatments of PG-3-G and Double Ovsynch had no effect on the proportion of cows with luteal function at the onset of the Ovsynch treatments (87.9 vs. 86.2%). Although ovulatory responses were similar after GnRH-1 (>60%), Double Ovsynch cows tended to have greater ovulatory responses than PG-3-G after GnRH-2 (95.3 vs. 90.6%). The 2 × 25-mg doses of PGF_2α and the 1 × 50-mg dose induced luteolysis in both Ovsynch treatment durations, but the 1 × 50-mg dose was less effective in the 5-d program. More pregnancy per AI (P/AI; 49.2%) tended to occur in the PG-3-G cows in the 7-d program compared with the other treatment combinations (range: 32.4–37.4%; Ovsynch × presynch interaction). In addition, an Ovsynch × PGF_2α dose frequency interaction resulted in cows receiving the 1 × 50-mg dose in the 7-d program having the greatest P/AI (46.1%) and cows receiving the 1 × 50-mg dose in the 5-d program having the least P/AI (30.6%). We conclude that complete luteolysis was less effective in the 5-d program when the 1 × 50-mg dose was applied, but both PGF_2α dose frequencies (1 × 50 mg and 2 × 25 mg 24 h apart) effectively induced complete luteolysis in the 7-d program. Treatments producing complete luteolysis tended to be related to subsequent pregnancy outcomes.     

Pregnancy outcomes after change in dose delivery of prostaglandin F2α and time of gonadotropin-releasing hormone injection in a 5-day timed artificial insemination program in lactating dairy cows

We demonstrated that 50 mg of PGF_2α on d 6 successfully induced luteolysis in lactating dairy cows enrolled in a traditional 5-d Ovsynch-72 program [GnRH injection 5 d before (d 0; GnRH-1) and 56 (p.m. on d 7; GnRH-2) or 72 h (d 8; GnRH-2) after a 25-mg injection of PGF_2α (d 5 and 6 after GnRH injection); timed artificial insemination (AI) on d 8]. Our current objective was to determine pregnancy outcomes in lactating dairy cows after a 50-mg injection of PGF_2α on d 6 or a 25-mg injection of PGF_2α on d 5 and 6 in a 5-d Ovsynch program. Cows in herd 1 diagnosed not pregnant between 30 and 36 d since last AI were enrolled to receive either a 50-mg injection of PGF_2α on d 6 (1 × 50; n = 134) or a 25-mg injection of PGF_2α on d 5 and 6 (2 × 25; n = 139) after GnRH-1 (d 0), with GnRH-2 at 72 h after PGF_2α injection (d 5), concurrent with timed AI (d 8). Cows in herd 2 diagnosed not pregnant between 34 and 40 d were treated similarly: even-tagged cows received the 2 × 25 (n = 422) treatment, and odd-tagged cows received the 1 × 50 (n = 450) treatment, except that GnRH-2 was administered at 56 h. Blood collected from cows in herd 1 at d 0, 5, 6, and 8 was assayed for progesterone. Luteolysis was defined to occur when progesterone concentration was ≥1 ng/mL on d 5, and 72 h later (d 8) was either <0.5 ng/mL or <1 ng/mL. Progesterone concentrations did not differ between treatments on pretreatment d 0 and 5, but were greater in 1 × 50 than 2 × 25 cows on d 6 (4.7 ± 0.2 vs. 1.1 ± 0.2 ng/mL) and d 8 (0.43 ± 0.04 vs. 0.19 ± 0.04 ng/mL), respectively. Luteolysis was greater in the 2 × 25 versus 1 × 50 treatment when the cut point was 0.5 ng/mL, whereas no difference was detected when the cut point was <1 ng/mL on d 8. Lack of complete luteolysis was greater in cows classified as early cycle on d 0 or having a new corpus luteum after d 0 because progesterone concentration was greater on d 5 and 6 than for cows classified as late cycle on d 0 or cows having low progesterone on d 0 and 5. Pregnancy per AI at 30 to 40 d did not differ between 2 × 25 and 1 × 50 cows having luteolysis by d 8 or in all cows (37.2 vs. 33.3%) in herd 1, respectively, but differed in herd 2 (24.7 vs. 19.5%; no treatment by herd interaction). We conclude that incomplete luteolysis by d 8 was greater in 1 × 50 cows using a cut point of <0.5 ng/mL at AI. The difference in pregnancy outcome in herd 2 may have resulted from insufficient time for complete luteolysis before GnRH-2 at 56 h compared with GnRH-2 at 72 h (at AI) in herd 1.     

Effects of supplementing feedlot steers and heifers with zilpaterol hydrochloride on Warner–Bratzler shear force interrelationships of steer and heifer longissimus lumborum and heifer triceps brachii and gluteus medius muscles aged for 7, 14 and 21 d

Longissimus lumborum (LL) muscles from 117 steers plus LL, gluteus medius (GM), and triceps brachii (TB) muscles from 132 heifers were evaluated for effects of feeding duration of zilpaterol hydrochloride (Zilmax®; ZH; 7.56 g/907 kg on a dry matter basis) and aging time on tenderness. Both genders were blocked by initial weight into six blocks of four pens. Pens were assigned to treatments of control (C), or 20, 30 or 40 days on ZH, with a 3 day withdrawal. Steaks from each subprimal were vacuum aged individually for 7, 14 or 21 days, frozen, thawed, and cooked to 71 °C for Warner–Bratzler shear force (WBSF). All muscles from steers and heifers from ZH30 and ZH40 treatments had higher (P < 0.05) WBSF than those of C. The WBSF of steer LL and heifer TB from the ZH20 treatment was higher (P < 0.05) than C. There was a treatment by aging interaction (P > 0.05) for WBSF of GM steaks from heifers. Percentage of intramuscular fat had little effect on tenderness. Percentages of steer LL and heifer TB steaks with WBSF values below thresholds of either 5.0 or 4.6 kg from the ZH20 treatment were quite high, whereas percentages of heifer LL and GM muscles below 5.0 kg (67%) and 4.6 kg (57%) were low. Feeding ZH ? 20 days generally increased WBSF values, but mean WBSF values for steer LL and heifer TB were below 4.6 kg. Feeding ZH 20 ? days resulted in >40% of GM steaks with WBSF values above 4.6 kg.