Effects of crude protein level in concentrate supplements on animal performance and nitrogen utilization of lactating dairy cows fed fresh-cut perennial grass

Abstract

Nitrogen pollution of air and ground water from grazing cattle is of increasing concern. Although several studies have investigated mitigation strategies for nitrogen output from dairy cows fed conserved forages and concentrates, similar research on fresh-cut grass in addition to production parameters is limited. The current study, using 3dietary treatments and incorporating 2 genotypes, was designed to evaluate the effects of concentrate crude protein (CP) levels on animal production and nitrogen utilization efficiency (NUE) in lactating dairy cows. Twelve multiparous cows (6 Holstein and 6 Holstein × Swedish Red) were used in a changeover study with three 25-d periods and 3 diet treatments. Low, medium and high CP concentrate [14.1, 16.1, and 18.1%, respectively, dry matter (DM) basis] diets were fed at 32.8% DM intake combined with good-quality zero-grazed perennial ryegrass (18.2% CP, DM basis). Each period consisted of an adaptation phase (18d) housed as a single group, a 1-d adaptation phase in individual stalls, and a 6-d measurement phase with feed intake and feces, urine, and milk output recorded. We observed no significant interaction between cow genotype and concentrate CP level on any animal performance or NUE parameter. Total DM intake, milk yield and composition, and NUE were not affected by dietary treatment. However, increasing concentrate CP level increased (1) N intake by 42g/d and excretion in urine and manure by 38 and 40g/d, respectively, and (2) the ratio of urine N over manure N. Feeding high CP rather than low CP concentrate increased milk urea N (MUN) content by 3.6mg/dL and total MUN output by 1.08g/d. Crossbred cows had lower grass DM intake, total DM intake, total N intake, and energy-corrected milk yield. However, cow genotype had no significant effect on NUE or MUN parameters. Equations have been developed to predict urine N excretion using MUN output as a sole predictor or in combination with dietary CP level. The present study indicated that when grazing cows are fed good-quality pasture, feeding concentrates with a protein content as low as 14.1% may not negatively affect productivity. In addition, reducing concentrate CP concentration may be successful in reducing the urinary N excretion of lactating dairy cattle on pasture-based systems, but further research is needed to investigate the long-term effects of supplementary concentrate CP content on milk production.

Effects of dietary crude protein and tannic acid on nitrogen excretion, urinary nitrogenous composition and urine nitrous oxide emissions in beef cattle

“…Increasing dietary CP from 110.6 g/kg DM to 135.7 g/kg DM should have quantitatively increased the absorption of ruminal NH 3 and therefore consequently increased the urinary N excretion and the total N excretion. The results were in agreement with Hynes et al () who reported that increasing dietary CP levels (14.1, 16.1, 18.1% DM) increased the excretion of the total N and the urinary N in dairy cows. The results indicated that feeding cattle with rations containing the level of CP more than the requirement generally increases the urinary excretion of urea while high urea‐N percentage of the total urinary N and excess intake of CP would lead to the excess excretion of urinary N (Dijkstra et al, ).…”

“…Previous studies indicated that the dietary crude protein (CP) level had important impacts on the proportions of N in the faeces and the urine of cattle (Hynes, Stergiadis, Gordon, & Yan, ). At low dietary CP levels, the faeces are the main pathway for N excretion (Castillo et al, ) while at high dietary CP levels the urinary N excretion will be increased in cattle (Marini & Van Amburgh, ).…”

Effects of arginase inhibition via jugular infusion of Nω-hydroxy-nor-l-arginine on metabolic and immune indices in lactating dairy cows

“…In our study, the urine N production and urine N-to-total N intake ratio decreased with nor-NOHA and increased with nor-NOHA + Arg compared with control, but the difference was not significant. Furthermore, the output of urea N in milk was also reported to be another NUE indicator closely related to urinary N in animals fed concentrate diets containing different concentrations of CP (Hynes et al, 2016). In present study, the output of MUN also had a nonsignificant tendency to decrease in nor-NOHA + Arg compared with nor-NOHA alone, which partly supported the increased NUE in nor-NOHA + Arg compared with that in nor-NOHA alone.…”

Effect of grain- or by-product-based concentrate fed with early- or late-harvested first-cut grass silage on dairy cow performance

“…Although decreases in dietary CP concentration can increase the risk of restricted microbial activity in the rumen, the PBV values for all diets in this study were still above zero, the recommended minimum allowance (LUKE, 2017). The major increase in manure N excretion can be attributed to urinary N excretion, as observed by Gordon et al (1995) and in other studies with high CP diets (Hynes et al, 2016a(Hynes et al, , 2016b. According to , who reviewed a wide range of dietary treatments (n = 277), on average 84.4% of the incremental N from diets is excreted in urine when using N intake and DMI as independent variables in a bivariate model.…”