Effect of protein supplementation on milk production and metabolism of dairy cows grazing tropical grass

Abstract

The objectives of this study were to determine if midlactation dairy cows (Bos taurus L.) grazing intensively managed elephantgrass would have their protein requirement met exclusively with the pasture and an energy concentrate, making the use of protein ingredients unnecessary, as well as to determine the dietary crude protein (CP) content that would optimize the efficiency of N utilization (ENU). Thirty-three Holstein and crossbred (Holstein × Jersey) midlactation dairy cows, producing approximately 20 kg/d, were grouped within breed into 11 blocks according to milk yield and days in milk. Within blocks, cows were randomly assigned to 1 of 3 treatments and remained in the study for 11 wk. The control treatment contained only finely ground corn, minerals, and vitamins, and it was formulated to be 8.7% CP. Two higher levels of CP (formulated to be 13.4 and 18.1%) were achieved by replacing corn with solvent-extracted soybean meal (SSBM). Pasture was fertilized with 50 kg of N/ha after each grazing cycle and averaged 18.5% CP (dry matter basis). No differences were observed in milk yield or milk fat, protein, and casein content or casein yield. In addition, pasture intake was not different among treatments. Milk urea N increased linearly as the concentrate CP content increased. Cows fed the 8.7% CP concentrate had higher ENU. In another experiment, 4 ruminally cannulated Holstein dry cows were used in a metabolism trial designed in a 4×4 Latin square. Cows were fed the same treatments described as well as a fourth treatment with 13.4% CP in the concentrate, in which urea replaced SSBM as the main N source. Ruminal volatile fatty acid concentration and microbial synthesis were not affected by levels or sources of N in the concentrate. Ruminal NH(3)N content increased as the concentrate CP content increased. Inclusion of SSBM in the concentrate did not increase production and decreased the ENU of midlactation dairy cows grazing on tropical forage. Supplementation of an 8.7% CP concentrate, resulting in a diet with CP levels between 15.3 and 15.7% of dry matter, was sufficient to meet the protein requirements of such milk production, with the highest ENU (18.4%).

Effect of dietary nitrogen source and crude protein content on nitrogen balance and lactating performance of dairy cows

“…Therefore, in this study and the study of Danes et al (2013), for cows with average milk production of 17-19, the increase of dietary CP content may not change the productive performance, whereas it can increase the diet cost and excretion of nitrogen into the environment.…”

“…For cows producing 20 l/d of milk and grazing elephant grass as pasture (18.6% CP), Danes et al (2013) studied three CP levels of concentrate (8.7%, 13.4% and 18.1% CP), and did not observe effect of CP concentrate on DMI, milk yield, and fat and crude. However, to meet the requirements of dairy cows for amino acids balancing RDP and RUP, the nitrogen sources, crude protein content, and ruminal carbohydrate digestibility may be considered in diet formulation.…”

Comportamiento ingestivo de vacas en una asociación grama nativa/Arachis pintoi en el trópico húmedo veracruzano

“…Se formó una muestra de excremento compuesta a partir de alícuotas diarias, y el contenido de Cr se determinó por espectroscopia de absorción atómica (13) . La producción de excremento se obtuvo con la fórmula: [(g de Cr dosificados)*(Tasa de recuperación)] / [Cr] en excremento; se supuso una tasa de recuperación del 82.5 %, con base en la información presentada por Danes et al (14) . from the pasture by the grazing cow, which is easily audible (11) .…”

“…A composite feces sample was made from daily aliquots and its Cr content determined by atomic absorption spectroscopy (13) . Production of feces was obtained by the formula: [(dosed g of Cr) * (recovery rate)] / [Cr] in feces; a recovery rate of 82.5 % was assumed, based on the information published by Danes et al (14) . The DM digestibility of ingested grass (extrusa) was estimated using the in situ method for 48 h of ruminal incubation (15) of extrusa esophageal samples, which were introduced as dried and ground (Wiley Mill # 4 sieve 1 mm) in triplicate into the rumen.…”

Energy supplementation for beef steers grazing tropical grass (Brachiaria brizantha, cv Marandu) managed under rotational system with different initial sward heights

“…Even in intensive tropical grazing systems based on well managed pastures, cattle ADG and milk production are far lower than animals genetic potential . Most of this limitation comes from limited energy intake, due to limitations in forage harvest capacity of the animals DANÉS et al, 2013) and rumen fill caused by fiber content and low particle fragility of grasses.…”