The breeders who use artificial insemination always have difficulty in identifying the fertility period of the cows through the observation of the moment in which they begin to accept mounting by bulls. This is so as the beginning and the end of the fertility cycle occurs during the night which impedes checking.
To solve the problem which implies losses, a team from the São Paulo State University (Unesp) and the University of São Paulo (USP) have perfected a hormonal treatment to synchronize the ovulation of cows and buffalo and to allow for the artificial insemination to take place at an exact time, getting rid of the need for the observation of the fertility cycle. The studies began in 1991, coordinated by the veterinary doctor Ciro Moraes Barros, of the Biosciences Institute of Unesp in the town of Botucatu. He studies the cattle breed Nelore because at least 100 million of the 150 million Brazilian cattle are of this breed or are related to it.
A mounting signal
After having studied through ultra-sound cows’ reproductive organs to see the development of the follicles – the structures of the ovary that houses an egg, he went on to research a way of synchronizing the ovulation. The study included the observation of the sexual behavior of the cattle on the São Manuel ranch belonging to Unesp in Botucatu, and on the ranch of the Brazilian Farming Company (Embrapa) in Campo Grande (MT). Barros commanded a group that remained seven days and seven nights in the corrals, with lantern in hand, in order to observe the beginning of the fertility cycle at night.
“The first item to be verified was that 30% of the Nelore cows entered into and come out of the cycle at night. Since the cowboy only carries out his observation in the field during the day, in the morning at the end of the day, he does not know that many of the cows have already passed through the cycle. “Another conclusion is that the beginning of the cycle of ovulation is similar to the European breeds: they begin to ovulate 26 hours after the first mounting. Ed Hoffmann Madureira, of the Veterinary Medicine and Zootechnology School of USP in Pirassununga, confirms this: “He used a piece of apparatus attached to the hindquartersof the cow, which , when pressured by the mounting transmits the information to a computer.” Dr. Hoffmann obtained a rate of detection of the cycle in the Nelore cattle between 40% and 60%.
The synchronization of the ovary follicles requires three injections of hormones at any moment during the cycle – which lasts 21 days. The first injection is of the liberator hormone gonadotrophin (GnRH) or one of its synthetic counterparts, which for its part liberates the luteinising hormone (LH), which starts the ovulation process. The goal is to induce another wave of follicle structures in all of the cow at the same time.
“Seven days afterwards, we apply the hormone prostaglandin (PGF), whose function is to destroy the luteous body (part of the follicles responsible for the production of progesterone), which naturally only occurs on the 17th day of the cycle”, says Barros. Between 24 and 48 hours after the application, another hormone is applied, the oestradiol benzoate (OB) or the liberator factor of gonadotrophin (GnRH), which stimulates the liberation of LH and will promote a synchronized ovulation in the majority of cows. Then, between 16 and 24 hours after the final injection, the cows are artificially inseminated.
Because of the cost, this treatment is used more often with milking cows than with beef cattle. It was costing R$ 15.00 per animal, but Barros began to use BO in the second dose in place of GnRH and the cost has fallen to R$ 10.50.Three years ago he began to test techniques to lower the cost even further. He experimented with half a dose of prostaglandin given intravulvally, which resulted in a level of pregnancy similar to that obtained with the complete dose, intramuscular introduction, though this study was restricted to only a few animals. The goal is that the treatment should be used widely both in milk and in beef cattle, since in Brazil only 5% of the cows are artificially inseminated.
With milking cows, even at a cost of R$ 15.00 per animal, the treatment is worthwhile and has been in use in the country for at least three years according to José Luiz Moraes Vasconcelos, of the Veterinary Medicine and Zootechnology School of Unesp in Botucatu, who is part of the group. He says that the delay of a day for the milking cow involves a cost of R$ 2.00 to the farmer. Consequently, a delay of 20 days implies a loss of R$ 40.00, while the alternative proposed is that of spending only R$ 15.00 in the hormonal treatment and anticipates the return to milk production.
As well as the treatment with prostaglandin, Madureira and Pietro Sampaio Baruselli, of the Veterinary and Zootechnology School of USP, are testing the synchronization with other hormones: the progestational hormones, applied by way of implants in the ear or vagina devices. “The progestational hormones show the characteristic of inducing the coming of the fertility cycle in females that have not reached this period. This is important in Brazil, where the cattle are fed almost exclusively in the pasture and are slow to enter into the fertility cycle in the postpartum.”
Buffalos in heat
Another study by the group is into the synchronization of ovulation for artificial insemination and embryo transfer for the buffalo population, which has reproductive behavior and a reply to treatment different from that of cattle. Brazil has the largest buffalo population in the West – close to 3 million heads -, which need to be improved through genetic breeding. The work, coordinated by Baruselli and Madureira has already brought a positive result: they have verified the technical viability for artificial insemination within a fixed time, without the necessity of the detection of the fertility cycle.
Ciro Barros is also studying the synchronization of the fertility cycle of the source donors, which pass through a treatment of super ovulation so as to produce more embryos. The objective is to obtain a super ovulation response that is more homogeneous and to understand why the cows produce heterogeneous embryos. The treatment planned out by Barros is for the improvement of a system developed by a group of Dutch researchers with the elimination of the observation of the fertility cycle.
“We have already managed to improve the handling, but the ovulation response continues to be the same, because the big problem of super ovulation throughout the world is the variation of the individual reaction of the cows to the treatment.” The researchers carried out experiments on 40 animals, but the variability remained the same: “Some sources produce 15 embryos and others none.” Naturally, Barros is confident of obtaining better results during this project. He says that the studies of the group are being directed towards the development of cheaper and more efficient systems, which improve the relationship cost/benefit and make themselves available to the large majority of the breeders throughout the country.
Synchronization of Ovulation for Artificial Insemination (IA) at a Pre-determined Time in Nelore Cows (nº 95/02355-0); Modality Regular line of research assistance; Coordinator Dr. Ciro Moraes Barros – Unesp-Botucatu; Investment R$ 1,170.00 and US$ 19,000.00