Effects of rumen undegradable protein on intake, digestibility and rumen kinetics and fermentation characteristics of dairy heifers

• Autor(a) principal: Silva, Alex L.
• Data de Publicação: 2018
• Outros Autores: Detmann, Edenio, Rennó, Luciana N., Pedroso, Alexandre M., Fontes, Marta M. S., Morais, Valber C., Sguizzato, Anna L. L., Abreu, Marcelo B., Rotta, Polyana P., Marcondes, Marcos I.
• Tipo de documento: Artigo
• Idioma: eng
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: https://doi.org/10.1016/j.anifeedsci.2018.07.019; http://www.locus.ufv.br/handle/123456789/23828
• topic: Microbial protein; Nitrogen balance; RDP; RUP

The aim of this work was to evaluate the influence of increasing amounts of rumen undegradable protein (RUP) on intake, nutrient digestibility, rumen kinetics and fermentation characteristics and N use efficiency of dairy Holstein heifers. Eight rumen-cannulated Holstein heifers (initial body weight 276 ± 8.3 kg) were used in a replicate 4 × 4 Latin square design with four dietary RUP amounts in the total dietary protein, as follows: 38% of RUP (38RUP), 44% of RUP (44RUP), 51% of RUP (51RUP) and 57% of RUP (57RUP). The experimental period was 84 days, subdivided into four periods of 21 days (14 days for adaptation + 7 days for collections). Eight spot collections of faeces, urine, ruminal content and omasal digesta were performed at 9-h intervals, as follows: on 15th day samples were collected at 0600 h and 1500 h; on 16th day samples were collected at 0000 h, 0900 h and 1800 h; on 17th day samples were collected at 0300 h, 1200 h and 2100 h. Two complete rumen evacuations were performed: one on 19th day 4 h after morning feeding and another on 21st day immediately before morning feeding. Total (kg/day) and relative (g/kg of body weight) intake of dry matter, crude protein (CP), neutral detergent fibre corrected for ash and protein were not affected (P >  0.10) by dietary RUP amounts. Ruminal (P =  0.06) and intestinal (P =  0.09) digestibilities of CP presented a tendency to decrease with increasing RUP. There were no effects of dietary RUP amounts (P >  0.10) on the rates of ingestion, passage and digestion (%/h) as well on the total volatile fatty acid concentration in the rumen. Urinary N excretion presented a tendency (P =  0.08) to decrease with increasing RUP. In addition, retained N presented a tendency (P =  0.09) to increase according to dietary RUP amounts and greater values were observed for treatments 51RUP and 57RUP. Microbial protein synthesis, microbial efficiency and the efficiency of use of N for microbial synthesis decreased with increasing RUP (P <  0.05). Metabolisable protein flow presented a tendency to increase (P =  0.091) and greater values were observed for 51RUP and 57RUP. In general, urinary N excretion decreased, while the flow of metabolisable protein and RUP increased with increasing RUP levels. As a consequence of this pattern, the treatments 51RUP and 57RUP presented increases in the retained N.