210 FACTORS AFFECTING CONCEPTION RATE IN LACTATING HOLSTEIN RECIPIENTS

Abstract

This study evaluated embryo transfers from Holstein donors in lactating Holstein recipients. It was performed at the Santa Rita Farm, Descalvado, SP, Brazil, between January 2005 and January 2006. Holstein recipients were milked 3 times a day and fed with total mixed ration. Embryos were obtained by a superstimulation protocol with two 3-mg norgestomet ear implants (Crestar^®; Intervet, Sao Paulo, Brazil) and an IM injection of 3 mg of estradiol benzoate (EB) on random days of the estrous cycle. Four days later, 500 IU FSH (Pluset^®; Laboratorios Calier de Argentina) was divided into 8 decreasing doses given IM 12 h apart. With the seventh FSH injection, 0.530 mg of sodium cloprostenol (PGF_2±, Ciosin^®; Coopers Brazil, Sao Paulo, Brazil) was given IM; implants were removed with the eighth FSH injection. Twelve hours later, 250 µg gonadorelin (Fertagyl^®: Intervet, Brazil) was given IM, followed by two AI 12 and 24 h later. Ova/embryos were recovered 6.5 days after the first insemination. Recipients (n = 2543) received an injection of PGF_2± and were observed in estrus (n = 1322). Presence of CL was evaluated by rectal palpation of cows that presented heat, and embryo transfers (n = 873) were performed with a nonsurgical method 6 to 8 days after heat. Pregnancy diagnoses were performed by ultrasonography (Aloka 500, probe 5.0 MHz; Aloka) on Days 25 and 39. Embryonic mortality was considered when any recipient pregnant on Day 25 was open on Day 39. Data were analyzed by logistic regression and variables included in the model were: donor status (lactating or non-lactating), recipient CL external size classification (1 > 2 > 3), donor–recipient synchrony (-1, 0, +1), fresh or frozen embryos, embryonic development (Mo, Bi, Bl, Bx – IETS), and embryo quality (degree 1, 2, 3 – IETS). The conception rate (CR) on Day 25 was influenced by donor–recipient synchrony (-1: 37.7%; 0: 46.9%; +1: 45.6%; P = 0.053). Embryonic development (Mo: 45.6%; Bi: 41.8%; Bl: 46.9%; Bx: 43.8%), embryo quality (1: 44.2%; 2: 47.4%; 3: 42.3%), CL external size classification (CL 1: 47.9%; CL 2: 43.5%; CL 3: 30.0%), embryo condition (fresh: 45.8%; frozen: 43.1%), and donor status (lactating: 45.5%; non-lactating: 47.08%) did not affect conception rate. The CR on Day 39 was also affected by donor–recipient synchrony (-1: 29.9%; 0: 34.9%; +1: 38.2%; P = 0.021). Embryonic mortality was affected by donor status (lactating, 16.6% vs. non-lactating, 24.0%; P < 0.10). These data suggest that donor–recipient synchrony is a major factor affecting conception rate in lactating Holstein recipients.