Strategies to predict and minimize differences in field fertility in bulls

• Ano de defesa: 2021
• Autor(a) principal: Silva, Mateus Anastacio da
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Biblioteca Digitais de Teses e Dissertações da USP
• Palavras-chave em Português: Bovino; Cattle; Espermatozoide; GnRH; IATF; Oviduct; Oviduto; Pregnancy; Prenhez; Semen; Sêmen; Sperm; TAI
• Link de acesso: https://www.teses.usp.br/teses/disponiveis/11/11139/tde-12112021-123002/

Two studies were carried out aiming to adjust timed-artificial insemination (TAI) protocols to increase pregnancy per AI (P/AI) of Nelore bulls of lower fertility and to predict the field fertility of Holstein bulls. In the first study, Nelore cows (n = 1133) underwent a TAI protocol, starting on Day -10, with insertion of an intravaginal progesterone device (P4, 1.0 g) and treatment with estradiol benzoate (EB, 2.0 mg). On Day -2, the P4 device was removed, and cows received cloprostenol sodium (PGF, 0.5 mg), eCG (300 IU) and estradiol cypionate (EC, 1.0 mg). On Day -0.5 or 0 cows were subjected to GnRH treatments (G-16 = GnRH 16 h before AI or G0 = GnRH at AI). On Day 0 cows were inseminated and assigned to the fertility category bull treatment (H = one dose of higher fertility bull semen [n = 3]; L1 = one dose of lower fertility bull semen [n = 3]); L2 = two doses of semen from bull L [n = 3]). In addition, the sperm binding test was performed on oviduct cell aggregates. Semen from H (n = 3) and L (n = 3) Nelore bulls was used. For this, reproductive tracts of cows in slaughterhouse were collected and the region of the isthmus of the oviduct was used to collect the cells in the laboratory. Cells were cultured for 24 h to form cell explants, followed by co-incubation with sperm for 36 h. In addition, sperm motility was assessed by the CASA system and the integrity of membranes was assessed by fluorescence microscopy and flow cytometry. The fertility of bulls H and L was similar (P > 0.10), regardless of the adjustment of time of ovulation with GnRH and number of semen doses. However, despite P/AI of cows inseminated with H bulls was similar regardless of the BCS, cows with BCS < 3.0 had lower P/AI when inseminated with L bulls (BCS < 3.0: 50.5% [166/329]; BCS &#8805; 3.0: 60.6% [254/419]; P < 0.05). The number of sperm bound per mm of cell explant did not differ at 0.5 h (P = 0.10), but at 12 h, 24 h and 36 h there was a greater number of sperm/mm of H bulls (P > 0.05). H sperm had greater total and progressive motility than L sperm. The membrane characteristics analyzed did not differ between H and L groups. In the second study, semen from H (n = 3) and L (n = 4) Holstein bulls was used. The number of sperm/mm of cell aggregate was evaluated. In addition, sperm motility was assessed by CASA and the integrity of sperm membranes by flow cytometry. With 0.5 h of co-incubation there was a tendency for a greater number of H sperm bound per mm of aggregate, and from 12 h of co-incubation on the binding of sperm in aggregates was greater for H. With 24 h and 36 h the number of spermatozoa bound per aggregate was maintained, being greater for sperm from bulls H, and at 36 h there was a high correlation between field fertility and the number of sperm bound per mm of explant (r = 0.89). Out of the motility patterns evaluated by CASA, only the straight velocity was higher for bulls H. Out of the sperm membrane characteristics analyzed, L bulls had the greatest percentage of cells with intact plasma and acrosomal membranes (80.3% vs. 74.5%; P = 0.01) and greater mitochondrial potential of cells with an intact plasma membrane (P = 0.004). Thus, the BCS of cows, timing of ovulation and sperm characteristics influenced field fertility of bulls. Combined with conventional analyzes of sperm motility and membrane integrity, the lower ability to bind to oviduct cells may be the cause of lower fertility in L bulls, allowing the industry to use this technique as a new strategy for predicting field fertility of bulls.