Responses in Urea and True Protein of Milk to Different Protein Feeding Schemes for Dairy Cows

Abstract

Four multiparous Holstein cows were used in a 4 x 4 Latin square to investigate the effects of protein concentration, degradability, and quality on plasma urea concentration and milk N constituents. Diets varied in the amount and proportion of RDP and RUP relative to NRC requirements: diet 1, excessive RDP, deficient RUP; diets 2 and 3, balanced for RDP and RUP; and diet 4, excessive RDP, balanced for RUP. Diet 3 was formulated for optimal AA balance as predicted by the Cornell Net Carbohydrate and Protein System. Diets contained 34% corn silage, 19% alfalfa haylage, and 49% concentrate (DM basis). Concentrates varied in amounts of urea and soybean, corn gluten, and fish and blood meals. Concentrations of urea N and NPN in milk varied among diets: diet 1, 19 and 34 mg/dl; diet 2, 16 and 31 mg/dl; diet 3, 15 and 30 mg/dl; and diet 4, 23 and 39 mg/dl, respectively. Increases in NPN concentration were attributed to increases in the urea fraction of NPN. Intake of RUP and AA balance influenced milk true protein content; diet 1, 2.89%; diet 2, 2.90%; diet 3, 3.01%; and diet 4, 2.95%. the proportions of true protein and urea in milk are influenced by CP concentration, protein type, and protein quality.

The effects of and interactions between the maturity of grass silage and concentrate starch source when offered as total mixed rations on the performance of dairy cows

“…The MNE was more closely related to the dietary concentration than intake of CP (Huhtanen and Hristov, 2009); delaying the harvest decreased dietary CP concentration in the LGS, resulting in reduced CP supply per unit DMI and improved MNE for LGS diets. Although the EGS diets provided more CP and rumen degradable protein to the animals, the milk urea concentrations are within the range for practical diets (Oltner and Wiktorsson, 1983), suggesting that the N supply to rumen microbes or ruminant tissues or both was not in excess to the requirements as milk urea concentration is a strong metabolic indicator of N utilization (Baker et al, 1995). In addition, the reported MNE of EGS diets in the present study indicates that the utilization of N was within the expected limits in commercial herds as described by Biagini and Lazzaroni (2009).…”

Enteric and manure-derived methane and nitrogen emissions as well as metabolic energy losses in cows fed balanced diets based on maize, barley or grass hay

“…This indicates that ruminal N utilisation by the microbes was affected by feeding barley instead of maize as there is a quantitative relationship between urinary N excretion and ruminal N losses (Van Vuuren et al, 1993). The efficiency of N utilisation is high when ruminally available feed-N matches the N requirement of the ruminal microbes (Baker et al, 1995). This is further determined by the amount of fermentable OM as the second substrate required by these microbes, which is a function of the degradability of the dietary energy sources .…”

Digestibilidade aparente de dietas contendo silagem de cana-de-açúcar tratada com aditivo químico ou microbiano para cordeiros

“…Duas hipóteses corroboram com o resultado observado. Han et al (1983) sugerem que a baixa digestibilidade da cana-de-açúcar in natura está relacionada ao complexo lignina-celulose e a cristalinidade desta celulose que dificulta a digestão da FDN. Os autores também relatam que tratamentos químicos, físicos ou biológicos podem ocasionar: melhora na digestibilidade, e neste contexto, a ensilagem com ou sem aditivos pode contribuir para o melhor aproveitamento da forragem.…”