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The aim of this study was to evaluate effects of season and lactation status on embryo production in Holstein donors (n = 51). Data from 195 embryo collections (94 from lactating cows and 101 from non-lactating cows), at a dairy farm located in Descalvado, Sao Paulo, Brazil, in 2005, were analyzed. The superstimulation protocol included two 3-mg norgestomet ear implants (Crestar�; Intervet, Sao Paulo, Brazil) and an injection of 3 mg of estradiol benzoate IM (EB) on random days of the estrous cycle. Four days later, 500 IU FSH IM (Pluset�; Calier, Buenos Aires, Argentina) were divided into 8 decreasing doses given 12 h apart. With the seventh FSH injection, 0.530 mg IM of sodium cloprostenol (PGFα Ciosin�; Coopers-Brazil, Sao Paulo, Brazil) was given, and implants were removed with the eighth FSH injection. Twelve hours later, 250 �g IM of gonadorelin (Fertagyl�; Intervet) was given, followed by two AI 12 and 24 h later. Ova/embryos were recovered 6.5 days after the first insemination. The total number of ova/embryos, IETS grades 1, 2, and 3 (viable) and grade 4 plus unfertilized (non-viable), were analyzed by General Linear Model (GLM). Effects of donor, lactation status (lactating or non-lactating), sire, season (1: January through March, n = 56; 2: April through June, n = 37; 3: July through September, n = 50; 4: October through December, n = 52), and their interactions were included in the model. There was an effect of donor on all outcome variables (P < 0.01). There was an effect of season on the total number of ova/embryos (1: 10.2 � 1.2; 2: 6.6 � 1.0; 3: 10.0 � 1.1; 4: 11.2 � 1.2; P < 0.02) and of viable embryos (1: 3.7 � 0.5; 2: 2.4 � 0.5; 3: 5.9 � 0.9; 4: 4.4 � 0.7; P < 0.001). Lactation status influenced the total number of ova/embryos (lactating: 10.9 � 0.9 vs. non-lactating: 8.7 � 0.7; P < 0.001) and the number of non-viable embryos (lactating: 6.7 � 0.8 vs. non-lactating: 4.4 � 0.5; P < 0.01). However, there was no effect of lactation status on the number of viable embryos (lactating: 4.14 � 0.5 vs. non-lactating: 4.29 � 0.5; P > 0.10). In summary, the number of viable embryos in Holstein cows was influenced by season and donor, but not by lactation status.

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 (PGF2�, Ciosin�; Coopers Brazil, Sao Paulo, Brazil) was given IM; implants were removed with the eighth FSH injection. Twelve hours later, 250 �g 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 PGF2� 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.