Timed artificial insemination: current challenges and recent advances in reproductive efficiency in beef and dairy herds in Brazil

Beef and dairy productivity depends directly on the reproductive efficiency and genetic gain of the herd, which can be related to the appropriate use of biotechnologies, such as timed artificial insemination (TAI). When considering variations in synchronizations protocols, longer or shorter periods of progesterone (P4) device treatment could provide benefits to fertility. However, our studies evidenced that protocols with six (J-synch), seven, eight and nine days of P4 device treatment had similar pregnancy per AI (P/AI). In cyclic cows, the early prostaglandin (PGF) administration, moving from the day of P4 device removal to two days earlier, which results in four handlings of cows, or the administration of one extra dose of PGF at the onset of the protocol and a single PGF on the day of P4 device removal (three handlings) are both efficient to induce early luteolysis, reducing serum P4 concentrations and, therefore, stimulating LH pulsatility, which improves growth of the dominant follicle and results greater P/AI when compared with protocols with the administration of PGF only on the day of P4 device removal. Resynchronization is another valuable tool to reduce the interval between AI. Traditional Resynch is initiated at pregnancy diagnosis (28 to 32 days after TAI) and the interval between AI is around 40 days; Resynch 22 and Resynch 14 respectively initiates 22 and 14 days after the previous AI in all cows (unknown status of pregnancy) and reduces the interval between AI to 32 and 24 days. The novelty about Resynch 14 is the need to use of Doppler ultrasonography for pregnancy diagnosis [ evaluation of corpus luteum (CL) vascularization]. Similar P/AI after Resynch 22 and 14 were found in Nelore cows. In dairy cattle, reproductive management is carried out throughout the year, thus, it is important to adapt the reproductive management to few established days of the week. Therefore, traditional Resynch and Resynch 25 were set to start 32 and 25 days after previous TAI, respectively. The hastening of reproductive age of Nelore heifers aims to reduce age at first calving and increase productivity. Factors such as age, weight, body condition score (BCS), uterine score (USC), average daily weight gain (ADG), withers height/depth of rib relationship (dRIB) and subcutaneous fat thickness (SCFT) were associated with an increase in the success of gestational establishment at TAI and can be used to select the heifers that are more suitable for reproduction. These technologies can contribute to improve the national production of kilograms of meat and liters of milk per hectare, and consequently improve livestock profitability.