7 ESTRUS LENGTH AND INTENSITY IN BOS TAURUS (HOLSTEIN) v. BOS INDICUS (NELORE) NONLACTATING COWS

The aim of this study was to compare the length and intensity of oestrus in nonlactating Bos taurus (Holstein; n = 11) v. nonlactating Bos indicus (Nelore; n = 13) cows. The cows were kept in a single pen to allow interaction between them and were daily fed a maintenance diet according to the NRC (2000), containing 42.8% sugarcane bagasse, 45.7% corn, 3.2% soybean meal, 1.2% urea, 5.7% molasses, and 1.4% mineral salt, totaling 71% dry matter (DM) in the diet. The intake of DM per kg of body weight (BW) was 1.45%. Body condition score and BW were 3.5 ± 0.1 and 3.0 ± 0.2 (range 1 to 5), and 549.5 ± 14.3 and 625.5 ± 20.5 kg for Nelore and Holstein cows, respectively. All females had the emergence of follicular wave synchronized with an intravaginal progesterone device (Sincrogest, Ourofino Agronegocio, Sao Paulo, Brazil), 2 mg of oestradiol benzoate (Sincrodiol, Ourofino; IM) and 0.150 mg PGF2α (Sincrocio, Ourofino; IM). Ten days after initiation of the protocol, the intravaginal device was removed and another treatment with 0.150 mg PGF2α was given. Thereafter, cows were evaluated for oestrus by continuous visual observation 24 h a day for 5 days. The number of the cow that was mounting and the number of the cow that was standing was recorded for each event, as well as the time of the event. To confirm ovulation, ultrasound examination was performed between 5 and 7 days after oestrus detection. Data were analysed by Student’s t-test and Fisher’s exact test or Chi-square and data are presented as mean ± SE or percentage. Ten of 13 (76.9%) and 11 of 11 (100%) Nelore and Holstein cows, respectively, were detected in standing oestrus and ovulated (P > 0.10). On average, Holstein cows tended to start oestrus earlier than Nelore cows after device removal (40.4 ± 2.9 v. 47.7 ± 2.8 h; P = 0.09). There was no difference in intensity and duration of oestrus between Bos taurus and Bos indicus cows. Oestrus length was 14.7 ± 1.0 h (range 8.3 to 19.0 h) in Holstein cows and 12.4 ± 0.8 h (range 8.6 to 17.1 h) in Nelore cows (P > 0.10). Moreover, the average number of times that cows accepted mounts was 32.2 ± 6.1 and 36.3 ± 5.3 for Holstein and Nelore cows, respectively (P > 0.10). Only 9.1% of the mounts accepted by Nelore cows were performed by Holstein cows and only 3.8% of the mounts accepted by Holstein cows were done by Nelore cows (P < 0.05). We concluded that Bos taurus and Bos indicus cows managed under similar environment and nutritional conditions exhibit oestrus with the same intensity and duration. However, there was very little interaction during oestrus between Nelore and Holstein cows, showing a breed segregation pattern. This work was financially supported by CNPq, FAPESP, and Ourofino Agronegocio of Brazil.