Performance and metabolite profile of dairy cows fed tropical grasses and concentrates containing crude protein with low or high degradability

Abstract

-Ten Holstein-Zebu crossbred cows distributed into two simultaneous Latin squares (5 × 5) as a 2 × 2 factorial arrangement formed by chopped sugarcane or elephant grass silage, both with high or low protein degradability supplements and a corn silage as a control treatment, were compared using orthogonal contrasts. The studied variables were the performance, plasma concentrations of urea-N, glucose, and creatinine, urine-N and milk urea-N, and the nychthemeral variation in NH 3 -N in the rumen fluid of dairy cows. Nutrient intake, milk production, and milk composition were affected by the treatments. The total mixed ration containing elephant grass silage combined with rumen undegradable protein (RUP) provided balanced amounts of carbon and nitrogen in the rumen. This effect may explain the 18% increase in milk yield compared with the other treatments. The diurnal pattern of ruminal NH 3 -N was interpreted with a sinusoid model. In general, cows fed elephant grass silage exhibited higher concentrations of blood plasma and milk urea-N than animals fed sugarcane. The cows that consumed elephant grass silage with rumen degradable protein concentrate showed a higher milk urea-N compared with animals that consumed elephant grass silage with the RUP concentrate. The use of diets based on corn silage leads to a better use of nitrogen compounds because these diets resulted in lower levels of urea-N in the plasma, urine, and milk at the same level of milk production compared with diets containing elephant grass silage or chopped sugarcane as roughages. In sugarcane-based diets, even greater nitrogen losses in the urine are observed, despite the presence of readily fermentable carbohydrates in the diet.

Productivity and physiological response of lactating Holstein cows to sugarcane supplementation and evaporative cooling under heat-stress

“…Perhaps the higher diet CP concentration with the sugarcane diet contributed to the increased MUN concentration. A similar finding was reported by Gomes et al (2016), who observed a higher concentration of MUN in dairy cows with diets based on sugarcane compared with diets based on maize silage at the same level of milk production. Gomes et al (2016) also found better use of N with diets based on maize silage, with a R : C ratio of 780 : 220 g/kg, due to lower N-urea losses in plasma, urine and milk compared with a sugarcane-based diet (R : C ratio of 600 : 400 g/kg) or with a diet based on elephant-grass silage (R : C ratio of 760 : 240 g/kg).…”

“…A similar finding was reported by Gomes et al (2016), who observed a higher concentration of MUN in dairy cows with diets based on sugarcane compared with diets based on maize silage at the same level of milk production. Gomes et al (2016) also found better use of N with diets based on maize silage, with a R : C ratio of 780 : 220 g/kg, due to lower N-urea losses in plasma, urine and milk compared with a sugarcane-based diet (R : C ratio of 600 : 400 g/kg) or with a diet based on elephant-grass silage (R : C ratio of 760 : 240 g/kg). Santiago et al (2013), using urea and ammonium sulphate levels (9 : 1 w/w) in the diet of dairy cows based on sugarcane as roughage, found that up to 12 g/kg of natural sugarcane could be supplied without affecting performance, but with less efficiency in the use of nitrogen ingested.…”

“…Gomes et al . (2016) also found better use of N with diets based on maize silage, with a R : C ratio of 780 : 220 g/kg, due to lower N-urea losses in plasma, urine and milk compared with a sugarcane-based diet (R : C ratio of 600 : 400 g/kg) or with a diet based on elephant-grass silage (R : C ratio of 760 : 240 g/kg). Santiago et al .…”

“…A similar finding was reported by Gomes et al . (2016), who observed a higher concentration of MUN in dairy cows with diets based on sugarcane compared with diets based on maize silage at the same level of milk production. Gomes et al .…”