Effects of Amounts and Degradability of Dietary Protein on Lactation, Nitrogen Utilization, and Excretion in Early Lactation Holstein Cows

Abstract

Five treatment diets varying in crude protein (CP) and rumen undegradable protein (RUP) were calculated to supply a postruminal lysine to methionine ratio of about 3:1. Diets were fed as a total mixed ration to 65 Holstein cows that were either primiparous (n = 28) or multiparous (n = 37) from 21 to 120 d in milk to determine effects on lactation and nitrogen utilization. Crude protein % and calculated RUP (% of CP) of diets [on a dry matter (DM) basis] were: 1) 19.4, 40 (HPMU), 2) 16.5, 34 (LPLU), 3) 16.8, 40 (LPMU), 4) 16.8, 46 (LPHU), 5) 17.2, 43 (LPHU + UREA), which is the result of adding 0.4% of the diet DM as urea to LPHU. The corn silage-based treatment diets contained an average of 24% acid detergent fiber and 1.6 Mcal/kg net energy of lactation. Milk urea nitrogen (MUN) concentrations and body weights (BW) were used to calculate predicted amounts of urinary nitrogen (N) using the relationship: urinary N (g/d) = 0.0259 x BW (kg) x MUN (mg/dl). Cows fed HPMU had greater CP and RUP intakes, which resulted in higher concentrations of plasma urea nitrogen, rumen ammonia, MUN, and predicted urinary N. Milk yield, fat yield, fat percent, protein yield, and protein percent were not significantly different among treatments. Parity primarily affected parameters that were related to body size and not measurements of N utilization. The interaction of treatment and parity was not significant for any measurements taken. In this study, cows fed LPHU had significantly lower MUN and predicted urinary N without limiting production. These results demonstrate the potential to optimize milk production while minimizing N excretion in lactating dairy cattle.

Responses of milk urea nitrogen content to dietary crude protein level and degradability in lactatingHolsteindairy cows

“…The MUN values were significantly affected by dietary treatments (P < 0.01), with the lowest values in cows fed diet A, followed by diets B and C, and the highest in cows fed diet D. The MUN values increased with CP levels. The observation was consistent with some studies (Davidson et al, 2003;Groff and Wu, 2005;Promkot and Wanapat, 2005), while Flis and Wattiaux (2005) found that a 1% change in the dietary protein level did not cause a significant change in the MUN content.…”

“…Milk composition was not affected by increasing CP levels. The lack of responses in milk production and milk composition was consistent with others' observations that these did not change when dietary protein varied from 16.7 to 18.4% (Davidson et al, 2003), from 16.4 to 20.4% (Mulligan et al, 2004), from 16.4 to 18.0% (Wattiaux and Karg, 2004), and from 14.6 to 18.3% (Castillo et al, 2001). While some researchers observed significant differences in milk yield or composition with dietary protein from 13.1 to 17.0% (Frank and Swesson, 2002), it has been reported that milk production benefits from > 15% protein, but increasing the protein above 17% has no further effect (Groff and Wu, 2005), and dietary protein has only a low effect on milk fat and protein concentration (Sutton, 1989).…”

“…The result in Experiment 2 confirmed this viewpoint. Some researchers also observed that dietary protein degradability did not affect the urea content in blood (Blouin et al, 2002;Reynal and Broderick, 2003) or milk (Rodriguez et al, 1997), whereas Davidson et al (2003) reported that MUN was affected significantly by the varying dietary RUP level. It has been suggested that a restriction in energy supply increases MUN (Kirchgessner et al, 1986).…”

Effect of rumen-degradable protein balance deficit on voluntary intake, microbial protein synthesis, and nitrogen metabolism in growing double-muscled Belgian Blue bulls fed corn silage-based diet1,2,3

“…Plasma urea-N has repeatedly been shown to correlate positively to the level of dietary CP (Marini and Van Amburgh, 2003), RDP (Davidson et al, 2003), or OEB (Fiems et al, 1999a). Johnson and Preston (1995) found that increasing the CP level from 10 to 16% in steer diets by 2% steps caused a 1-to 3-mg increase in PUN concentrations between each CP level.…”

Parâmetros ruminais, balanço de compostos nitrogenados e produção microbiana de vacas leiteiras alimentadas com soja e seus subprodutos

“…Os primeiros 14 dias foram usados para adaptação das vacas às dietas experimentais e as coletas de dados efetuadas nos 7 dias posteriores. As vacas foram agrupadas de acordo com a produção inicial de leite (30 kg/dia), média de 160 dias de lactação, escore corporal três e meio (Edmonson et al, 1989) e na 4 a ordem de lactação, distribuída em três quadrados latinos simultâneos, cada um com quatro animais, submetidos a quatro dietas em quatro períodos.…”