Nitrogen utilisation by dairy cows fed diets differing in crude protein level with a deficit in ruminal fermentable nitrogen

Abstract

excreted by ruminants is of endogenous origin (metabolic losses) and some corresponds to dietary nitrogen (undigested or unused nitrogen). These losses of dietary nitrogen could be reduced by increasing the efficiency of dietary nitrogen use. However, INTRODUCTIONImprovements in the management of effluents from animal production systems have been recommended to limit environmental damage. Some of the nitrogen Abstract -We studied the efficiency of nitrogen utilisation by dairy cows, using three diets differing in the crude protein (CP) level but with similar deficits (10 g . kg -1 dry matter, DM) in ruminal fermentable nitrogen. There was no difference in milk yield from the cows offered the three diets (130, 145 and 160 g CP . kg -1 DM). The milk protein content differed between the two most extreme diets (28.9 vs. 29.9 g . kg -1 , P < 0.05), resulting in higher protein yields for the highest CP treatment (P < 0.01). The efficiency of nitrogen utilisation, calculated as the proportion of ingested nitrogen recovered in the milk, was significantly higher for the 130 g CP . kg -1 DM diet than for the other two diets (0.37 vs. 0.33 and 0.32 respectively, P < 0.01). The different diets also resulted in different levels of nitrogen excretion into the environment (237, 270 and 330 g N . d -1 , P < 0.01). Hepatic deamination of the amino acids may have generated additional energy to enable the animal to make use of the additional nitrogen in the diet, resulting in an increase in plasma urea concentration.nitrogen balance / dairy cow / utilisation / milk / urine Reprod. Nutr. Dev. 42 (2002) 545-557 545

Low degradable protein supply to increase nitrogen efficiency in lactating dairy cows and reduce environmental impacts at barn level

“…On the other hand, the amount of N excreted in faeces was not significantly modified (P = 0.36, Table 3). This observation is consistent with the literature for diets varying in CP concentration (Castillo et al, 2000;Monteils et al, 2002;CantalapiedraHijar et al, 2014). As already mentionned by Kebreab et al (2001), the proportion of N excreted in faeces in relation to N intake increased (from 26% to 38%) when animals were fed diets with lower amounts of highly degradable protein.…”

“…When both PDIN and PDIE supplies are reduced, the decrease in milk and milk protein yields is generally more important, (e.g. −2 kg/ day and −13% to 18% nitrogen in milk; Monteils et al, 2002;Cantalapiedra-Hijar et al, 2014). In the present study, PDIE concentrations of the diets were deliberately maintained equivalent between treatments even if a small reduction in PDIE supply came from the decrease in DM intake.…”

“…Two strategies could then be used to reduce N excretion: 1/improve protein use efficiency by decreasing metabolisable protein supplies in relation to energy from the diet (PDIE/UFL, milk feed unit, 1 UFL = 7.106 MJ of net energy for lactation; INRA, 2007); 2/favour urea reuse by a deficit in degradable protein in the diet ((PDIN-PDIE)/UFL). A decline of PDIE intake was shown to reduce milk yield (Cantalapiedra-Hijar et al, 2014) and milk protein concentration (Monteils et al, 2002) with a curvilinear response (Vérité and Delaby, 2000). On the other hand, reducing PDIN available for microbes stimulates urea reuse for microbial synthesis (Reynolds and Kristensen, 2008), resulting in lower N excreted in urine without affecting protein synthesis and animal performance (Cutullic et al, 2013), but with a risk of decreasing microbial activity.…”

Influence of rumen protein degradability on productive and reproductive performance in buffalo cows

“…Dietary proteins and their digestibility in the rumen affect blood (BU) and milk (MU) urea concentration [1][2][3][4][5]. Overfeeding proteins has been associated with a decline in fertility in most [6][7][8][9], but not all [10] studies.…”

Desempenho de vacas leiteiras sob pastejo suplementadas com níveis de concentrado e proteína bruta

“…Resultados semelhantes aos deste trabalho foram observados por Monteils et al (2002) que não encontraram diferenças significativas na produção de leite quando compararam dietas com 13,0; 14,5 e 16,0% de PB. Pereira et al (2009) estudaram o efeito da utilização de 6 kg de concentrado com diferentes teores de PB (15,2; 18,2 ou 21,1%) para vacas mestiças em lactação sob pastejo rotacionado de capim-elefante, e não observaram diferenças entre os tratamentos, quanto ao consumo de MS na dieta total, produção de leite e os componentes: proteína, lactose e gordura, sugerindo o nível de 15,2% PB no concentrado como o mais indicado na alimentação de vacas leiteiras.…”