Efecto de la relación proteína y energía sobre los niveles de amonio ruminal y nitrógeno ureico en sangre y leche, de vacas doble propósito del piedemonte llanero, Colombia

Abstract

Summary

The effects of five diets with different protein to energy ratios (CP:ME) on rumen ammonia (RA) and blood (BUN) and milk úrea nitrogen (MUN) in dual-purpose cows were evaluated in the piedemonte of Colombia. Five rumen fistulated cows were assigned to five treatments using a 5 x 5 Latin Square design. All animals received a basal diet consisting of Brachiaria decumbens forage forage ad libitum and 900 g of ground rice (treatment 1); treatment 2 was identical to treatment 1 plus 39 g of urea; treatment 3 was identical to treatment 1 plus 84 g urea; treatment 4 was identical to treatment 2 plus 1200 g of sugar; and treatment 5 was identical to treatment 3 plus 934 g of sugar. The ratio between crude protein and metabolizable energy (CP:ME) was 26, 66, 103, 27 and 50 g /Mcal for treatment 1 to treatment 5, respectively. The highest concentrations of RA, BUN and MUN were observed in treatment 3 (p < 0.01), which provided the highest amount of CP and resulted in the highest CP:ME ratio. Treatments 5 and 2, with intermediate amounts of CP and CP:ME ratios, resulted in intermediate levels of RA, BUN and MUN. The levels of RA, BUN and MUN varied considerably across the day and ranged from 4.3 to 22.9, 4.8 to 13.8 and 3.6 to 16 mg/dl, respectively. The highest levels of RA, BUN and MUN occurred 3 to 6 hours after the first feeding of the day. There was a close positive relationship between MUN and BUN (MUN = 0.901*BUN, R² = 0.70). It can be concluded that the levels of BUN and MUN are closely related to the CP concentration and the CP:ME ratio in the diet. These metabolites represent a useful tool to monitor and adjust the use of supplements for dual-purpose cows fed diets based on low-quality grasses in the Llanero foothills of Colombia.