Effect of reducing starter feed crude protein content with different volumes of milk on the performance of calves

Abstract

The objective was to evaluate the influence of decreasing crude protein (CP) of the starter feed content according to increasing age on the development of dairy calves during the pre-weaning, weaning and post-weaning phases. Sixty crossbred heifers were randomly assigned at 4 days of age to one of six treatments: 4 L/d and starter feed with fixed CP (4L_FCP), 4 L/d and starter feed with decreasing CP (4L_DCP), 6 L/d and starter feed with fixed CP (6L_FCP), 6 L/d and starter feed with decreasing CP (6L_DCP), 8 L/d and starter feed with fixed CP (8L_FCP) and 8 L/d and starter feed with decreasing CP (8L_DCP). Animals submitted to the FCP treatment received 18% PB in the starter feed throughout the experiment, while those included in the DCP treatment received 25% PB in the starter feed from day 4 to day 24, 18% from day 25 to day 45 and 14% from day 46 to day 66. The animals had free access to water and starter feed and their consumption was measured daily, in addition, they were submitted to 3 digestibility tests, in which samples of feces, urine, blood and ruminal fluid were collected. At 67 days, gradual weaning began and at 73 days the animals were weaned and submitted to blood and ruminal fluid collection. At 74 days, the animals began to have access to corn silage and remained in the experiment until 80 days of age, when blood and ruminal fluid were collected again. In addition, body measurements and body weight were measured weekly since the beginning of the experiment and at 66 and 80 d the animals were submitted to ultrasonography of the mammary gland, to evaluate the influence of the treatments. In general, animals that received 8 and 6L/d had higher performance, digestibility, feed efficiency and N utilization than 4L/d, but at weaning, 4L/d animals had a higher ADG (607 g/d for 4 L, 545 g/d for 6 L and 293 g/day for 8 L). Body weight was higher in animals that consumed starter feed with CP fixed in the starter at 66 d (73.1 kg for FCP and 68.4 kg for DCP) and at weaning (77.4 kg for FCP and 71.2 kg for DCP). Post-weaning feed efficiency was higher in DCP animals (655 g/kg) compared to FCP animals (364 g/kg), in addition to the intake and excretion of N in feces, at 66 d it was higher for animals that consumed FCP (37.8 g/d for ingestion and 1.76 g/d for N in feces) when compared to those that consumed DCP (31.7 g/d for N intake and 1.31 g /d for N stools). The efficiency of N use and the serum concentration of IGF -I and glucose were lower for 4 L/d animals. For blood urea nitrogen (NUS), at 80 d we observed higher concentrations of NUS for all milk volumes; compared to starter feed at 24 (20.8 mg/dL), 66 (18 mg/dL), 73 (22.8 mg/dL) and 80 d (27.7 mg/dL) FCP animals had higher concentrations of NUS than DCP (17.6 mg /dL at 24 d, 12.5 mg/dL at 66 d, 11.8 mg/dL at 73 d, 21.1 mg/dL at 80 d). Acetic, propionic and butyric acids increased in relation to days, respectively. In addition, the concentrations of butyric and acetic acid in animals that received 4L/d were higher when associated with FCP (9.33 µmol/mL for butyric acid and 43.9 µmol/mL for acetic acid) than with DCP (5.73 µmol/mL for butyric acid and 30.8 µmol/mL/mL for acetic acid). In the mammary gland, the animals had better parenchyma deposition at 80 d (67.4 pixels/mm²) compared to 66 d (71.7 pixels/mm²). Regarding milk volume, 4 L/d (64.9 pixels/mm²) was better than 8 L/d (75.1 pixels/mm²) and 6 L/d (69.3 pixels/mm²) did not differ from 4 or 8 L. Animals of FCP treatments (67 .2 pixels/mm²) had better results compared to DCP animals (72.1 pixels/mm²). It can be concluded that animals that consume 6 L/d have shown a good performance, in addition to reducing costs and bringing less harm to the animals at the time of weaning. In relation to the starter diet, the animals submitted to the FCP strategy presented higher consumption and better performance in relation to the DCP animals. However, DCP animals had lower fecal N excretion at 66 d, and better EF post-weaning, proving to be an effective alternative to decrease N excretion, and that there is a potential for improvement in animal performance with the use of this strategy that should be better explored. Keywords: Nutrition. Development. Dairy calves.O objetivo foi avaliar a influência da diminuição do teor de proteína bruta (PB) do concentrado de acordo com o aumento da idade no desenvolvimento de bezerras leiteiras durante as fases de pré-desmame, desmame e pós-desmame. Sessenta bezerras mestiças foram distribuídas aleatoriamente, aos 4 dias de vida, em um dos seis tratamentos: 4 L/d e concentrado com PB fixa (4L_PBF), 4 L/d e concentrado com PB decrescente (4L_PBD), 6 L/d e concentrado com PB convencional (6L_PBF), 6 L/d e concentrado com PB decrescente (6L_PBD), 8 L/d e concentrado com PB convencional (8L_PBF) e 8 L/d e concentrado com PB decrescente (8L_PBF). Animais submetidos ao tratamento PBF recebiam 18% de PB no concentrado durante todo o experimento, já os inclusos no tratamento PBD recebiam 25% PB no concentrado do dia 4 ao dia 24, 18% do dia 25 ao dia 45 e 14% do dia 46 ao dia 66. Os animais tiveram livre acesso a água e concentrado e seu consumo foi medido diariamente, além disso, foram submetidos a 3 ensaios de digestibilidade, nos quais foram amostrados fezes, urina, sangue e líquido ruminal. Aos 67 dias iniciou-se o desmame gradual e aos 73 dias os animais foram desmamados e submetidos à coleta de sangue e líquido ruminal. Aos 74 dias, os animais passaram a ter acesso à silagem de milho e permaneceram no experimento até os 80 dias de idade, quando o sangue e o líquido ruminal foram novamente coletados. Além disso, medidas corporais e peso foram aferidos semanalmente desde o início do experimento e aos 66 e 80 d os animais foram submetidos à ultrassonografia da glândula mamária, a fim de avaliar a influência dos tratamentos. De modo geral, animais que receberam 8 e 6L/d tiveram desempenho, digestibilidade, eficiência alimentar e utilização do N superior aos 4L/d, porém no desmame os animais 4L/d tiveram um maior GMD (607 g/d para 4 L, 545 g/d para 6 L e 293 g/dia para 8 L). O peso corporal foi maior nos animais que consumiam concentrado com PB fixa no concentrado aos 66 d (73,1 kg para PBF e 68,4 kg para PBD) e no desmame (77,4 kg para PBF e 71.2 kg para PBD). A eficiência alimentar no pós-desmame foi maior nos animais PBD (655 g/kg) em relação aos animais PBF (364 g/kg), além disso a ingestão e a excreção de N nas fezes, aos 66 d foi maior para os animais que consumiram PBF (37,8 g/d para ingestão e 1,76 g/d para N nas fezes) quando comparados aos que consumiram PBD (31,7 g/d para ingestão de N e 1,31 g/d para N fezes). A eficiência de uso de N e a concentração sérica de IGF -I e glicose foram menores para animais de 4 L/d. Para nitrogênio uréico sanguíneo (NUS), aos 80 d observamos maiores concentrações de NUS para todos os volumes de leite; com relação ao concentrado aos 24 (20,8 mg/dL), 66 (18 mg/dL), 73 (22,8 mg/dL) e 80 d (27,7 mg/dL) animais de PBF apresentaram maior concentração de NUS do que o PBD (17,6 mg /dL aos 24 d, 12,5 mg/dL aos 66 d, 11,8 mg/dL aos 73 d, 21,1 mg/dL aos 80 d). Os ácidos acético, propiônico e butírico aumentaram em relação aos dias, respectivamente. Além disso, as concentrações de ácido butírico e acético nos animais que receberam 4L/d foram maiores quando associado a PBF (9,33 µmol/mL para butírico e 43,9 µmol/mL para acético) do que com PBD (5,73 µmol/mL para butírico e 30,8 µmol/mL/ mL para acético). Na glândula mamária os animais tiveram maior deposição de parênquima aos 80 d (67,4 pixels/mm²) em comparação aos 66 d (71,7 pixels/mm²), animais que consumiram, 4 L/d (64,9 pixels/mm²) foram melhores que 8 L/d (75,1 pixels/mm²) e 6 L/d (69,3 pixels/mm²) não diferiram de 4 ou 8 L, já no concentrado animais PBF (67,2 pixels/mm²) tiveram melhor resultado comparados a animais PBD (72,1 pixels/mm²). Pode-se concluir que, animais que consomem 6 L/d demostraram um bom desempenho, além de diminuir custos e trazer menos prejuízos aos animais no momento do desmame. Em relação à ração inicial, os animais submetidos à estratégia PBF apresentaram maior consumo e melhor desempenho em relação aos animais PBD. No entanto, os animais PBD tiveram menor excreção fecal de N aos 66 d, e melhor FE no pós-desmame, mostrando-se uma alternativa eficaz para diminuir a excreção de N, e que existe um potencial de melhora no desempenho animal com o uso dessa estratégia que deve ser melhor explorado. Palavras-chave: Nutrição. Desenvolvimento. Bezerras leiteiras.