Levels of concentrate and rumen undegradable protein in the diet of lactating cows / Níveis de concentrado e de proteína não degradável no rúmen na dieta de vacas em lactação

AUTOR(ES)
DATA DE PUBLICAÇÃO

2009

RESUMO

The modern consumer increasingly choose quality products, and industry, seeking to adapt to this new trend, has sought to reward the producer by milk quality, especially with regard to its total solids composition. This way, an experiment was conducted at the Dairy Cattle Teaching, Research and Extension Unit of Animal Science Department of Universidade Federal de Viçosa, in Viçosa-MG, from May to August of 2007, to evaluate the effect of three concentrate levels and two levels of rumen undegradable protein (RUP) in the diet of dairy cows producing 30 kg of milk/day was evaluated on rumen degradation parameters, intake of diet components, digestibility, intake of digestible components, nitrogen compounds metabolism, milk production and composition. Twelve Holstein cows were allotted in two 6 x 6 Latin squares, with 17 days experimental periods. The diets were formulated in a 3 x 2 factorial arrangement, using three concentrate levels, 40, 50 and 60 %, and two RUP levels, 4.0 and 5.4 %, with fixed 10 % rumen degradable protein (RDP) level, on dry matter (DM) basis, resulting in six treatments. Fish meal was used as RUP source and corn silage as roughage. The results were evaluated using SAS PROC MIXED (SAS, 1999), adopting 5 % as the critical level of probability for type I error, with the comparisons among means performed using orthogonal contrasts. There was no interaction between concentrate levels and RUP levels on milk production and composition. The ordinary feedstuffs used in ruminant feeding, soybean meal and ground corn, had the greatest DM effective degradation, while fish meal had low ruminal degradation. It was observed total DM intake (DMI) increase (P<0.05) as the concentrate level was increased, with no effect (P>0.05) of RUP increase on total DMI. There was a lower intake of neutral detergent fiber corrected for ash and protein (NDFap) (P<0.05) and greater intake of non-fiber carbohydrates corrected for ash and protein (NFCap) (P<0.05), when the concentrate level was increased. Increasing the level of RUP, the NFCap intake decreased. The ether extract intake (EEI) was increased (P<0.05) both by the concentrate increase as by the RUP increase. There was a reduction (P<0.05) of the DM digestibility coefficients (DMDC), organic matter (OMDC) and total digestible nutrients (TDN) content, with supplemental RUP sources. There was no effect (P>0.05) on the digestibility coefficients of DM, OM, EE, crude protein and NFCap, when the concentrate level was increased. The TDN increased linearly (P<0.05) with the concentrate level increase, while there was a decrease of TDN (P<0.05) with increasing RUP in the diet. Regarding the intake of digested components, there was an increase (P<0.05) of digestible DM (DDM), digestible OM (DOM) and TDN intakes with the increase of concentrate level and reduction (P<0.05) of intake with RUP increase. It was observed an interaction between levels of concentrate and RUP for DEE, DNDFap and DNFCap intake. The urinary excretion of urea nitrogen and allantoin decreased (P<0.05) in treatments in which the RUP was increased, with no effect of the concentrate level on these variables. The other metabolites resulting from the metabolism of nitrogen compounds were not changed according to the level of concentrate and RUP. Linear increase (P<0.05) wasobserved on milk production, increasing concentrate ration supply and RUP level. Milk fat level reduced linearly with the increase of concentrate in the diet and the addition of RUP. However, milk fat production, in kg/day, was not altered (P>0.05) by treatments. The content and production of milk protein increased (P<0.05) with increase of concentrate level and RUP, verifying variation of 0.16 percent unit in milk protein level. Milk lactose and total solids levels were not influenced (P>0.05) by increasing levels of concentrate in the diet. However, when diet RUP level was increased from 4.0 to 5.4 %, total solids level was reduced (P<0.05), with no effect on lactose content. The content of defatted total solids was not altered by the treatments. Total and defatted total solids production was greater when the diet concentrate level was increased. There was no effect on these variables with RUP increase. Increasing levels of concentrate and RUP, using fish meal as RUP source, with stabilized RDP, promote increased milk production of high production dairy cows, reduced milk fat content and increased milk protein content.

ASSUNTO(S)

pndr composição do leite nutrição animal nutricao e alimentacao animal rup milk composition animal nutrition

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