Effects of Dietary Protein Solubility on Nitrogen Losses from Lactating Dairy Cows and Comparison with Predictions from the Cornell Net Carbohydrate and Protein System

Abstract

This experiment determined the effects of dietary protein solubility on amount, form, and route of nitrogen loss in lactating Holstein dairy cows, and the ability of the Cornell Net Carbohydrate and Protein System (CNCPS) to accurately predict rumen microbial yield, serum urea N (SUN), milk urea N (MUN), and fecal N. Eighteen multiparous Holstein cows were assigned randomly to one of three dietary treatments that were similar in crude protein (17.7%) content but differed in their content of soluble intake protein (SIP). Dietary contents of SIP, as % of total CP were 30, 36, and 48%. The experimental period was 21 d, and total N balance collections were done during the last 5 d. As dietary content of SIP increased, excretion of urinary N increased quadratically, and it was the primary route of N excretion. Urinary excretion of purine derivatives (PD) responded quadratically as dietary SIP content increased. The CNCPS predicted a quadratic decrease in total metabolizable protein (MP) supply. No effect of dietary content of SIP was detected on MUN and SUN. The CNCPS predicted a quadratic decrease in SUN and MUN as dietary SIP increased. Results from this study indicated that changing the dietary content of SIP altered routes of N excretion in dairy cows, but had no effect on total N balance. The CNCPS did not adequately predict changes in SUN and MUN for cows fed diets varying in SIP.

Effect of pasture allowance and supplementation with maize silage and concentrates differing in crude protein concentration on milk production and nitrogen excretion by dairy cows

“…The range of intakes in the current experiment are within the ranges reported by Haig et al (2002) and Leonardi et al (2003) for cows in mid to late lactation (b 190 DIM) offered diets balanced at an overall CP concentration of 160 to 180 g/kg DM and is comparable to the N intake value (618 g/d) reported by Mulligan et al (2004) for grazing dairy cows fed a high protein diet in mid-lactation. The lower CP content of the concentrate offered on the LC treatment had the effect of reducing N intake and PDIN supply compared to the HG and HC treatments even though herbage constituted a large proportion of the diet on all treatments.…”

Evaluation of feeding value of forage soybean silage as a substitute for wheat bran in sheep

“…In this experiment, although SIP and DIP contents of forage soybean silage were higher than those of wheat bran (Table 1), there was no difference in fecal N excretion between both diets. This result was inconsistent with result of Haig et al (2002). Van Soest (1994) described that as the concentration of acid detergent insoluble protein (ADIP) increased, total tract N digestibility decreased.…”

Effect of dietary crude protein level and degradability on ruminal fermentation and nitrogen utilization in lactating dairy cows1

“…Broderick (2003) reported that excretion of urinary purine derivatives increased as dietary CP was increased from 15.1 to 16.7% of diet DM, but no further increase was noted with an 18.4% CP diet. Haig et al (2002) found urinary purine derivatives excretion increased quadratically as RDP (expressed as soluble intake N) concentration of the diet increased. Crude protein concentration or degradation most often does not affect microbial N flow (Windschitl and Stern, 1988a;Calsamiglia et al, 1995;Cunningham et al, 1996).…”