Milk and plasma urea nitrogen on crossbreed cows

Esta pesquisa objetivou, inicialmente validar o emprego de kits comerciais colorimétricos enzimáticos (KITS URÉIA CE) também para leite. Foram coletadas 35 amostras de leite e cada uma subdividida em cinco alíquotas, das quais duas foram remetidas a laboratórios de referência (LR) e as demais analisadas por meio de KITS URÉIA CE. Antes da análise, porém, cada uma destas foi submetida a centrifugação (2300 x g durante 30 min) ou precipitação com ácido acético glacial associada à centrifugação ou precipitação com ácido tricloroacético a 25% seguida de filtração (TCA). Os dois LR obtiveram resultados diferentes (P > 0,05) mas altamente correlacionados (r= 0,95). Os teores de NUL determinados nas alíquotas submetidas aos três procedimentos referidos acima apresentaram altas correlações entre si e com os LR, porém apenas os resultados obtidos empregando-se o procedimento TCA foram equivalentes aos encontrados por um dos LR (P 0.05), but were highly correlated (r=0.95) with each other. MUN values from TCA, ACET and CENT were highly correlated among each other and the LRs but only the samples submitted to TCA procedure presented equal results (p < 0.05) to the one of the LR. Hence, the TCA technique was used in the subsequent step of this study, in which 10 farms located in the surroundings of Viçosa-MG were utilized. For each farm it was reserved one day to collect the milk samples during the morning milking (only healthy cows with less than 30 days after calving). Following, blood samples of dry and healthy cows, with expected calving greater than 20 days, were collected. As soon as the morning milking finished, one sample of milk bulk was collected in each property and the information about the groups of lactation or dries cows (food, number of cows and milk production) were recorded. In only one of the farms samples from lactation cows (n = 35) were also collected immediately after the morning milking. The results showed that only six of the 33 groups of cows obtained MUN average values between 12 and 16 mg/dL and three others showed MUN greater than 16 mg/dL. Despite of this, in six farms all groups of cows (n=15) presented MUN average values much lower than 12 mg/dL and in the others farms eight groups showed similar values. When the 33 groups of cows were arranged in four categories according to milk production (A: ³ 25Kg; B: 20-25Kg; C: 15-20Kg and D:£ 15Kg) the MUN average values calculated for each one of them and the respective intervals were 17.35 ± 3,79, 8.28 ± 4.18, 7.29 ± 4.29 and 6.25 ± 3.65 mg/dL. It was also observed that in seven farms where the MUN values of the samples of bulk milk were lower than 12mg/dL 95,2% (20/21) of the productions groups presented similar behavior in relation to MUN average values. Three other farms showed MUN values in bulk milk samples higher than 16mg/dL and had at least one feeding group with MUN average elevated. From ten farms, only one presented PUN average values in dry cows superior to 16 mg/dL and other eight presented values lower than 12 mg/dL. This study concludes then that ,in crossbreeding milking herds, only groups of cows with daily milk production greater than 20 mg/dL require attention in relation to excess of protein the diet and its effects. The majority of lactating and dries cows groups showed respectively MUN and PUN values very low demonstrating inadequacy in terms of protein diet. In these farms, the milk samples collected from bulk milk were also characterized by the very low MUN values that were presented.Conselho Nacional de Desenvolvimento Científico e Tecnológic