Resumen

MANTEROLA, H.B. et al. Effects of two carbohydrate sources on nitrogen capture and on productive performance in dairy cows. Arch. zootec. [online]. 2013, vol.62, n.240, pp.491-499. ISSN 1885-4494.  https://dx.doi.org/10.4321/S0004-05922013000400002.

The objective of this study was to determine if the supplementation with two carbohydrate sources that have different degradation rates, reduces the ammonia production by ruminal bacteria by increasing the nitrogen capture in dairy cows grazing high protein contents pastures. Four dairy cows fitted with ruminal cannulas were randomly assigned to four treatments, corresponding to different proportion of corn:oat: T0 (control): grazing without supplementation; T1: 80:20; T2: 50:50 and T3: 20:80. Pasture consisted of perennial ryegrass (Lolium perenne) with 23 % crude protein and 14,4 MJ^*kg^-1, and the effects were measured on ruminal ammonia concentration, blood ammonia and urea, and milk production and composition (protein, fat and urea). Energy supply was made similar by changing the amount given. A 4 x 4 latin square design was used. The supplementation with carbohydrate sources independent of treatments, significantly reduced ammonia concentration (p<0,05) and no significant effects among supplemented treatments were found (19.8, 13.1, 10.6 and 14.6 mg^*dL^-1 for T0, T1, T2 and T3 respectively). No significant differences (p>0,05) were found neither for plasma ammonia and urea nor for milk production, milk fat and protein, milk energy and milk urea content. It is concluded that supplementation with mixtures of corn and oat grains to dairy cows grazing ryegrass pastures with high protein content reduces rumen ammonia concentration but do not affect milk production, milk components and milk urea.

Palabras clave : Milk urea; Supplementation.

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