Optimal voluntary waiting period for highly productive cows in herds of more than 3000 milking heads

. The study showed that fertility at the first artificial insemination (AI) is 9% higher if the voluntary waiting period (VWP) is 80 days compared to 60 days. However, in the second IO, the level of fertilization in both cases remains the same and is 44%.Thus, the period of voluntary waiting for 80 days of milking provides 80% of the pregnant in our herd on the 150th day of milking, which is an excellent indicator.


Introduction
The voluntary waiting period (VWP) can be defined as the interval in a cow's postpartum period during which milk producers decide not to inseminate cows even if heat occurs.
It usually lasts about 50 days, but can vary greatly from herd to herd depending on the reproductive strategy in place.For example, the voluntary waiting period tends to be longer for herds that rely more on timing programs, or may vary depending on the number of cows, breed, and even calving season.
Dairy cows should not be bred earlier than 40-50 days after the start of lactation because their reproductive systems have not fully recovered from previous calving and conception rates are usually poor.On the other hand, for healthy cows, you should not wait more than 100 days after calving to first breed cows and risk increasing calving intervals or having too many non-pregnant cows lactating for more than 150 days.Thus, the ideal voluntary waiting period is a delicate balance between timely insemination as soon as possible after calving and uterine involution, and waiting long enough to ensure good fertilization results.
The purpose of our work is to evaluate the effectiveness of the optimal voluntary waiting period in a large herd of more than 3000 dairy cows.
To achieve this goal, we set ourselves the following tasks: to analyze the current situation in the field of insemination of cows on a dairy farm, paying special attention to the use of synchronization programs, such as the Presing-Osynch program.The main goal is to increase the success of insemination of cows while maintaining other key indicators, such as service period, pregnancy index and the percentage of pregnant cows by the 150th day of milking.
Make adjustments to the protocols of hormonal programs, specifically for the first inseminations, starting inseminations from the 80th day of milking.
Conduct weekly ultrasound diagnostics on days 35-42 of pregnancy to ensure accurate monitoring of cows' pregnancy.

Materials and methods
As part of a joint collaboration with LLC Dairy Company Genetika-Yug, we conducted research from April 2023 to September 2023 on a dairy farm in the Kalininsky district, Krasnodar Territory, on lactating cows of the Holstein breed.The experiment was carried out on 1 commercial dairy farm, without tether housing, the average milking population in the herd was 6520 heads, the milk yield was 10300 kg of milk for 305 days of lactation.
The key factor when choosing a period of voluntary housing is the ability of animals to become fertilized after the second injection of prostaglandin, the regulations for the operation of the reproduction unit on a weekly basis, animals are inseminated for the first time on the 80th day of milking.
Consistently excellent heat detection along with resynchronization schemes improve overall insemination rates and allow cows to be conceived more quickly after the 80-day voluntary waiting period ends.The injection sites are clean.
On all farms, the hormonal program "Presing-Owing" is used for the first artificial insemination.
A hormone program involves a combination of hormone therapy and time management to optimize reproductive efficiency in the herd.Pre-synchronization: On Wednesday -day zero -all cows receive initial hormonal therapy Prostaglandin F2-alpha (PGF2α) is administered to induce luteolysis (regression of the corpus luteum) in cows that are not showing signs of heat.After 2 weeks, the prostaglandin injection is repeated.After the second injection, the cows are detected in heat.In the 4th week, on Monday, we give an injection of GnRH (gonadotropin-releasing hormone), this is aimed at synchronizing the appearance of follicular waves.
We continue to identify cows in heat, in the fifth week we complete the hormonal program according to the injection schedule (Table 1), and carry out artificial insemination.All injections are performed intramuscularly, perpendicular to the neck muscles in the middle third or back of the thigh.In our case, a convenient injection site is the back of the thigh; the injection site should be clean.
The needle size is 40 mm long and 1.2 mm internal diameter (the needles are pink).Our observations are that herds with high conception rates can afford to delay the time to 1st breeding, but it is estimated that for every 10 days of delay to 1st breeding, herds will need to increase conception rates by 6-8%.In these herds, adherence to a synchronization program is imperative to ensure fertility levels justify an extended voluntary waiting period, which can be as long as 80 days per milking.A comparison of the timing of artificial insemination by numbers with the new duration of VWP 80 days and with those that were with VWP 60 days shows that most second inseminations take place in 105-130 days of lactation (previously, with VWP 60 days -in 90-120 days), but for the third artificial insemination there was almost no difference.According to the data in Tables 2 and 3, the percentage of fertility during the first insemination of cows with a voluntary waiting period of 80 days is 9% higher, during the second insemination this figure is equal, and during the third insemination it is 5% higher.We also note that the insemination index during this period is 22% lower.The percentage of pregnant women by the 150th day of milking is an important indicator in dairy farming.It reflects the percentage of cows that are already pregnant after 150 days of calving.Reproduction in industrial milk production must first of all be highly intensive.This is the only way we can maintain optimal average milking days for the herd for the best feed conversion and, therefore, maximum profitability.The minimum realistic goal for any farm is 80% pregnant by day 150 of milking.
On an ultrasound scan, at the first pregnancy test, the embryos were identified, without pathologies with normal development, according to the term (Figure 1.)

Conclusion
The study found that fertility at first artificial insemination (AI) is 9% higher when the voluntary waiting period (VWP) is 80 days compared to 60 days.However, in the second AI, the fertility rate in both cases remains the same and is 44%.Thus, the voluntary waiting period of 80 days for milking ensures in our herd 80% of pregnant women in the herd on the 150th day of milking, which is an excellent indicator.
However, if your reproduction and conception rates are suboptimal, consider establishing a voluntary waiting period, such as 60 days after calving, and address the larger management and health issues of your herd.

Fig. 1 .
Fig. 1.Pregnancy forecast by the 150th day of lactation with a new VWP of 80 days: 80%.

Table 1 .
Sexual heat synchronization scheme "Presing-oving".The study was conducted from early January to August 2023.As a result of the study, 2 groups of animals were formed, with different voluntary waiting periods of 60 and 80 days.Hormonal programs are designed in such a way that insemination occurs no earlier than the established days.During the experiment, 1646 heads were inseminated the first time and 1050 the second time, 1092 heads the third time or more, with a voluntary waiting period of 60 days.With a voluntary waiting period of 80 days -1875 goals the first time and 937 the second time, 855 goals the third time or more.