Variation of ureic nitrogen in milk and blood of cows under grazing in mixed meadows during the rainy season in the Andean region
Livestock farming in the Andes is based on grazing Kikuyo grasslands (Pennisetum clandestinum Hochst. Ex Chiov.) With rye grass (Lolium perenne L.) and white clover (Trifolium repens L.). A large part of the protein is non-protein nitrogen (NNP) and rumen degradable protein (PDR), being attributed as the main cause of metabolic problems associated with excess ammoniacal nitrogen (NH4). Urea nitrogen in milk (NUL) and in the blood (NUS) are used to evaluate the degree of NH4 utilization. The purpose of this study was: 1) to evaluate the variation of NUL in grass meadows with legumes in proportions from 10 to 40%, and 2) to evaluate changes in NUS as a function of days of lactation during the rainy season. The work was carried out at 2500 m of altitude, 18oC of temperature and 1,465 mm of annual precipitation. Twenty-two 0.5-hectare pasture plots were used in which 45 Holstein Friesian cows grazed for 60 days in a system of daily rotation and ad libitum consumption. The proportion of grasses and legumes was determined by sampling using a 0.25 m2 quadrant. For NUL, samples of 100 ml of milk were taken from the herd's reception tank, and for NUS, weekly samples of 10 ml were taken from the coccygeal vein of the cows, analyzed with the enzymatic-colorimetric technique. NUL as a function of legumes was analyzed using a generalized additive model with Gaussian distribution and the identity linkage function. NUS in relation to days of lactation, by linear regression adding a quadratic parameter in the independent term to adjust the nonlinear curve, using software R version 3.4.0. The results showed a significant non-linear relationship between NUL and legumes (p 0.0198), evidencing relative stability of the NUL (~ 18 mg dl-1) between 0% to approx. 18% legumes before increasing to ~ 23 mg dl-1 between 19 and 30% legumes. The values drop again until stabilizing at ~ 20 mg dl-1 when legumes are 40%. That model explained just 26.1% of the variation in NUL. On the other hand, NUS varied significantly with the lactation stage, with an increase from ~ 10 mg ml-1 to ~ 18 mg ml-1 in the first 150 days of lactation (p 0.000601). From this point, NUS decreases to an approximate initial value> 250 days of lactation (p 0.001081). NUL and NUS would be good indicators to diagnose the quality of the diet of grazing animals.
| Main Authors: | , , , , |
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| Format: | Digital revista |
| Language: | spa |
| Published: |
Asociacion Latinoamericana de Produccion Animal
2018
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| Online Access: | https://ojs.alpa.uy/index.php/ojs_files/article/view/2626 |
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