Nine rumen-fi stulated cows were used in a completely randomized design replicated three times to evaluate three monensin (0, 150 and 300 mg/animal/day) and three concentrate levels (25, 50 and 75%) in a 3x3 factorial arrangement. Twenty-one day subperiods were used, the fi rst sixteen for diet (Tifton hay+concentrate) adaptation. Monensin decreased DMI only in 50%-concentrate diet (P<0.05) and did not infl uence total VFAs concentrations. For ruminal pH, molar% of VFAs, and NH 3 -N concentration collected 7 times/day, the responses to high level of monensin were higher in low-forage diets (P<0.05). Responses to low level of monensin were higher in high-forage diets (P<0.05).

Efeito da somatotropina bovina recombinante (rBST) sobre o desempenho produtivo e reprodutivo de vacas da raça Holandesa RESUMOAvaliaram-se os efeitos da aplicação de rBST sobre o desempenho produtivo e reprodutivo de vacas da raça Holandesa no início da lactação. Foram avaliadas 41 vacas, dos 60 aos 150 dias de lactação, distribuídas em um delineamento inteiramente ao acaso, em três tratamentos: 1-sem aplicação de rBST (controle); 2-aplicação de rBST 60 dias após o parto (rBST-60); 3-aplicação de rBST 100 dias após o parto (rBST-100). A aplicação de rBST aumentou a produção de leite e a produção de leite corrigida a 4% de gordura em 14,0 e 13,2%, respectivamente, quando administrada aos 60 dias pós-parto. Não se observou efeito da aplicação de rBST sobre a porcentagem e a produção de gordura do leite nem sobre o período de serviço, número de serviços por concepção e taxa de gestação aos 150 dias de lactação. O uso do rBST também não afetou o ganho de peso dos animais durante o período avaliado. A aplicação de rBST aos 60 dias de lactação proporcionou maiores pico de produção e persistência da lactação, sem, no entanto, influenciar o desempenho reprodutivo. A aplicação de rBST aos 100 dias de lactação não aumentou a produção de leite e o desempenho reprodutivo das vacas.Palavras-chave: vaca leiteira, curva de lactação, produção de leite e gordura, reprodução, somatotropina ABSTRACTThe effects of recombinant bovine somatotropin (rBST) on production and reproductive parameters of Holstein dairy cows, from 60 to 150 days of lactation were evaluated. Forty-one cows were assigned to treatments: 1-no rBST application (control), 2-rBST application 60 days post calving , and 3-rBST application 100 days after calving (rBST-100), in a completely randomized design. The rBST application 60 days post calving significantly increased milk production (14%) and corrected milk production (13%). No effects of rBST administration on milk fat production (% and kg/day), days open, number of services/conception and pregnancy rate and on cow weight gain were observed. The rBST application 60 days after calving increased milk production peak and lactation persistence but did not change the reproductive performance. The rBST application at 100 days after calving did not increase milk production or the reproductive performance of cows.

R e s u m o : * P rofessor Assistente Doutor. ** P rofessor L iv r e Docente. D epartam ento de Produ ção A n im a l da Facu ldade de M edicina V eterin ária e Zootecnia da USP. *** Engenheiro Agrônom o.Pesquisador C ien tifico do In stitu to de Zootecnia da Secretaria da A gricu ltu ra, São P au lo.

No abstract

Forty-eight primiparous and pregnant Holstein cows at 202 (+/-59) days in milk and average daily milk production (DMP) of 22 (+/-5.3) kg at the beginning of the trial were used to study the possibility of identifying animals that are more responsive to recombinant bovine somatotropin (rbST). Animals were housed in free-stall barns, milked three times a day and fed a total mixed ration. Animals were injected with one dose (500 mg each) of rbST every 21 days during a 105-day total period (five doses in all). Daily milk production was recorded to measure average apparent response (AAR) and peak of apparent response (PAR). Average apparent response was defined as the average increase in milk production, expressed as kilogram per cow per day, for days 0-18 after dosing, as compared to the average production calculated for days -1, -2, -3, 19, 20 and 21 after dosing. Peak of apparent response was calculated as the increase in milk production for each day from 0 to 18 days after dosing as compared to the average production for days -1, -2 and -3. There was a positive linear correlation (r = 0.608; p = 0.0001) between AAR for the first 21 days and AAR for the total 105-day period (AATR). A correlation coefficient was calculated between each individual PAR value and AATR. The highest correlation coefficient (r = 0.511; p = 0.0002) was observed for days 8, 9 and 10, and therefore these days were considered the best estimates for calculating AAR when DMP records are not available. Also, high somatic cells count had a negative impact on milk yield response to treatment (p = 0.0162).