The association of ovum pickup (OPU) and in vitro embryo production (IVP) has been widely used to improve bovine reproduction. However, previous reports have indicated the occurrence of low fertility associated with summer heat stress. In the present work, we hypothesized that different categories of Holstein cattle [heifers (H), high-producing cows in peak lactation (PL), and repeat-breeders (RB)] would respond differently to OPU and IVP during the summer, because of their different metabolisms. This experiment was conducted on 2 commercial dairy farms in southeast Brazil in summer 2009. Cattle (n = 36/category) started a protocol to synchronize follicular wave emergence: 2 mg of estradiol benzoate (Sincrodiol®, OuroFino, Minas Gerais, Brazil) + 50 mg of progesterone (OuroFino) + 150 μg of D-cloprostenol (Sincrocio®, OuroFino) i.m. + a norgestomet ear implant (Crestar®, Intervet, São Paulo, Brazil) on Day 0, implant removal and OPU on Day 5. Respiration rate (RR), rectal temperature (RT), and cutaneous temperature (CT) were recorded on Day 0. Semen from a single Holstein bull previously tested was used in IVP, and oocytes from slaughterhouse were submitted to IVP as a quality control. Statistical analyses were done using PROC GLIMMIX of SAS (SAS Institute, Cary, NC, USA). The average and maximum environmental temperature and humidity were 30 and 39.8°C and 61 and 88%. Heifers were on average 15.7 months old; PL and RB cows had 112.8 ± 5.4a v. 422.8 ± 27.6b days in milk, milk production of 32.8 ± 0.9a v. 21.7 ± 1.1b kg, and number of insemination of 0.9 ± 0.1a v. 6.8 ± 0.3b; P < 0.0001; mean ± SE). Heifers and cows had different RR (H = 11.2 ± 0.3a, PL = 18.2 ± 0.6b, RB= 18.5 ± 0.4b breaths/min; P < 0.0001), RT (H = 38.7 ± 0.1a, PL = 39.56 ± 0.2b, RB = 39.32 ± 0.1b; P < 0.0001), and CT (H = 31.3 ± 0.2a, PL = 33.2 ± 0.3b, RB = 32.9 ± 0.3b; P < 0.0001). At OPU, heifers had greater number of follicles than PL cows, but they were similar to RB cows (H= 18.5 ± 1.9a, PL = 12.4 ± 1.1b, RB = 17.2 ± 2.0a; P = 0.04). Heifers had also greater number of oocytes (H = 9.6 ± 1.6a, PL = 5.0 ± 0.9b, RB = 8.8 ± 13ab; P = 0.03) and viable oocytes (H = 7.6 ± 1.5a, PL = 3.6 ± 0.8b, RB = 6.8 ± 1.2ab; P = 0.05) recovered from OPU than PL cows and similar to RB cows. However, at IVP, heifers had greater rates than both other categories (cleavage at Day 3: H = 47.8%a, PL = 31.1%b, RB = 35.4%b, P = 0.008; blastocyst at Day 7: H = 21.0%a, PL = 4.1%b, RB = 3.8%b, P < 0.0001) and more grade I embryos (H = 1.3 ± 0.4a, PL = 0.3 ± 0.2b, RB = 0.5 ± 0.2b, P = 0.04). The quality control had 80.7% cleavage and 45.4% blastocyst rates. The differences found among heifers and cows are probably related to their metabolism under heat stress, compromising oocyte number and quality. Also, although RB had similar number of viable oocytes than heifers, these oocytes are probably compromised, leading to poorer results at IVP, as observed.
Fazendas Santa Rita e Campestre, Vida Reprodutiva, LMMD, SAMVET, VITROGEN, OuroFino Saúde Animal, FAPESP (proc09/00938-3).
Impacts of heat stress on blood metabolic in different periods of lactation and pregnancy in Holstein cows