Ovarian Traits After Gonadotropin-Releasing Hormone-Induced Ovulation and Subsequent Delay of Induced Luteolysis in an Ovsynch Protocol

Luteolysis, progesterone, and pregnancy per insemination after modifying the standard 7-day Ovsynch program in Holstein-Friesian and Holstein cows

Two experiments were conducted with Holstein-Friesian cows in the Republic of North Macedonia and with Holstein cows in Kansas. We hypothesized that 1 dose of PGF_2α administered on d 8 (Ov-8×1) instead of d 7 (Ov-7×1) in an Ovsynch program [GnRH-1 (d 0)-7 d-PGF_2α-56 h-GnRH-2-16 h-timed artificial insemination (AI)] would increase the proportion of cows with complete luteolysis compared with controls receiving a single dose on d 7. Cows were treated with Ov-7×1 or with Ov-8×1 in experiment 1 (n = 347), using only a single dose of PGF_2α. In experiment 2 (n = 452), a third treatment was added (Ov-7×2), in which a second dose of PGF_2α was administered on d 8. Progesterone was measured in blood samples collected before the first or only PGF_2α administration and 72 h later before insemination. Complete luteolysis was defined as having occurred when progesterone was ≥1 ng/mL before PGF_2α and ≤0.3 ng/mL 72 h later (time of AI). Follicles and luteal structures were mapped before GnRH-1 and PGF_2α administrations. The results of experiment 1 demonstrated a greater percentage of multiparous cows in OV-8×1 having complete luteal regression compared with multiparous Ov-7×1 cows, whereas treatments were equally effective in primiparous cows, as reflected in the concentrations of progesterone before AI. Furthermore, pregnancy per AI did not differ between treatments. Results in experiment 2 revealed that 99.3% of cows in the Ov-7×2 treatment receiving the second dose of PGF_2α had complete luteolysis, regardless of parity, compared with significantly fewer cows in the Ov-7×1 and Ov-8×1 treatments (91.2 and 90.6%, respectively). Neither concentrations of progesterone, which averaged <0.4 ng/mL at AI, nor pregnancy per AI differed among the 3 treatments. In both experiments, when status of luteal function before PGF_2α treatment was examined [cows with no corpus luteum (CL) before GnRH-1 but which had formed a new CL in response to ovulation after GnRH-1; cows with an older CL (the same CL that was detected before GnRH-1); or cows with both a new and an older CL], treatments did not differ in causing complete luteolysis. Furthermore, complete luteolysis in experiment 2 did not differ regardless of whether cows had 1, 2, or 3 or more CL before PGF_2α administration. Pregnancy per AI did not differ among treatments, indicating that any of the 3 treatments might produce similar pregnancy outcomes with the flexibility of applying either of the 7- or the 8-d treatments.

A phenotypical approach to the effects of production traits, parturition, puerperium and body condition on commencement of luteal activity in high yielding dairy cows

The interval from calving to commencement of luteal activity (CLA) was determined by progesterone measurements from milk samples obtained once a week until the 14th week post-partum in 513 German Holstein cows in first to third parity. Milk samples were analyzed by an "on-farm" device (eProCheck(®), Minitüb, Germany) and simultaneously by RIA. The objective of this study was to examine the effect of milk yield, protein content and body condition of a cow on the CLA post-partum. Milk progesterone concentrations of "on-farm" measurements correlated with measurements done by the RIA-method significantly (r=0.72; P<0.001). Within the analyzed herd the interval from calving until the first rise of progesterone averaged 5.6±2.4 weeks. The 100-days milk yield was not associated with CLA. Cows with a milk protein content at 1st milk recording of ≤3.5% revealed first luteal activity 1.3±0.3 weeks later than cows that had a content of >3.75% protein (P<0.01). Furthermore cows with assisted calving or dystocia presented significantly later CLA than cows which required no help during the calving process (P<0.05). The change in back fat thickness from 1st to 2nd milk recording had a significant influence on CLA (P<0.05). In conclusion the phenotypic impact of milk yield on fertility cannot be confirmed regarding to CLA. The negative energy balance after calving, caused by the high milk yields, is more detrimental for the cyclical activity as was shown by the parameters milk protein content and change in BFT.