|dc.description.abstracteng||In dairy farming reproductive performance and milk yield of cows have a major impact on the operation’s economic success. As the negative correlation between milk yield and reproductive performance is widely known, the dairy industry has a strong interest in finding ways to improve the entire reproductive management in high performing dairy herds.
This can be achieved by improving estrus detection, reducing service period and days open, and increasing pregnancy rate. In addition the detection of cows that fail to conceive due to prior service is of major interest. Beside technical devices, such as pedometers and paint sticks (tail chalk), fixed-time AI protocols developed in North America are becoming increasingly important, also under German husbandry conditions.
Therefore, this dissertation includes three studies that address the following aspects:
• Implementation of a fixed-time insemination protocol on middle-sized family farms in pasture-based farming regions of Northern Germany
• Evaluation of fixed-time AI following a Presynch- or Ovsynch protocol with GnRH or hCG as ovulation-inducing agents in German middle-sized family-run or large dairy operations and
• A comparison of pregnancy diagnosis methods in dairy cows
In the first experiment, a total of 618 cows in four East Friesian dairy herds were fixed-time inseminated after following an Ovsynch-protocol as described by Pursley et al (1995). Of the 618 cows 300 were administered two PGF2a injections at an interval of 14 days, following a Presynch-regimen. For control purposes, 150 cows were inseminated when in estrus. In the second experiment, 1,509 Holstein-Friesian cows were inseminated following a Pre-or Ovsynch-regimen. A total of 526 cows were left untreated and inseminated after estrus detection. In both experiments, the ovulation was induced 16-20 hours before artificial insemination with the administration of alternating GnRH or hCG.
In both experiments, the achieved pregnancy rates after Pre- (38% experiment 1 and 39% experiment 2) and Ovsynch-treatment (41% in experiment 1 and 33% in experiment 2) were not significantly different from those in untreated cows (48% in experiment 1 and 45% in experiment 2). The use of hCG as ovulation-inducing agent resulted in both studies in significantly lower pregnancy rates (34% in both experiment) as compared with GnRH-treated cows (44% in experiment 1 and 42% in experiment 2). However, when compared to the untreated cows (48% in experiment and 45% in experiment 2) only in hCG-treated cows participating in experiment 2, significantly lower pregnancy rates were observed.
The application of Presynch resulted in a shortening of service period from 80 days (untreated animals) to 73 days in experiment 1 and from 87 days (untreated animals) to 75 days in experiment 2.
However, when bearing in mind that the individual dairy operations are not directly comparable due to different husbandry and management conditions, results may turn out different under differing conditions. Claimed benefits of fixed-time insemination the reduced workload because there is no longer a need for estrus detection as well asincreased service rates and consequently higher pregnancy rates.
Based on the present results, the substitution of GnRH by hCG cannot be recommended, even when considering lower drug costs. The same may apply to the administration of a Presynch-protocol due to the increased workload caused by the additional two prostaglandin injections.
Furthermore, when considering the use of reproductive hormones in livestock, consumer protection and animal welfare aspects should not be neglected. As part of the TAI regimen hormones are administered to synchronize and trigger physiological processes such as ovulation or luteolysis in terms of work efficiency. However, the applied dose is marginal and all hormones are metabolized within a few hours.
In the third experiment, the pregnancy diagnosis methods determination of milk progesterone and pregnancy-associated glycoprotein concentration in blood, ultrasonography and rectal palpation were compared regarding their overall reliability. For this purpose, 213 Holstein-Frisian cows were inseminated. For the determination of milk progesterone concentration, milk samples were striped on days 21, 28 and 49 p.i and stored frozen until analysis. On days 29 to 35, all animals were tested for pregnancy by ultrasound. Simultaneously blood samples from each cow were drawn from the tail vein (vena coccygealis ventralis) for the determination of pregnancy-associated glycoprotein (PAG). Both, the ultrasound examination and blood sampling were performed by an experienced veterinarian. Rectal palpation of the uterus on day 60 p.i was performed by one of three AI technicians with several years of experience. The final calving rate 280 ± 10 days after insemination was 38% (81 out 213 cows). The highest overall reliability of 97.8% was achieved when milk progesterone concentration was determined on days 21 and 28. A combination of single days resulted in overall reliabilities ranging between
87.5 % (days 21, 28 and 49) and 95.5 % (day 49). The PAG determination resulted in an overall reliability of 91.6 % followed by ultrasound with 89.2 %. Manual palpation and calving outcome agreed by 95.3 %.
In conclusion, the interval between insemination and pregnancy diagnosis must be considered critically. The earlier pregnancy determination is carried out, the greater may be the influence of the embryonic mortality. However, early detection of non-pregnant cows, in the interest of an immediate re-insemination, is desirable. Ultimately price and availability as well as producers’ preferences will determine which pregnancy diagnosis method is used on each individual dairy farm.||de