The objective of this trial was to evaluate the effect of starch sources and processing used in diets on performance and nitrogen metabolism of lactating Holstein dairy cows fed sugar cane as forage. Five multiparous lactating Holstein cows, cannulated in the rumen and proximal duodenum, were used in a 5 × 5 Latin square. Cows were fed a 40:60 forage concentrate ration (40% fresh sugar cane and 60% concentrate) and differ only on processing or mainly starch source: cracked corn; finely ground corn; flaked corn at 310 g/L; flaked corn at 360 g/L or cassava scrapings. The in vitro starch hydrolysis rate of cassava scrapings was higher than others sources of starch in this trial. The flaked corn showed higher hydrolysis rate of starch than ground corn. Average values for total percentage of hydrolyzed starch were 93.5, 85.6, 83.7 and 37.8% for the cassava scrapings, flaked corn at 310 g/L, flaked corn at 360 g/L and ground corn, respectively. There was no difference for dry matter intake, milk protein and fat contents, microbial synthesis and plasma glucose concentration. Cassava scrapings decrease daily fat and protein productions and fat corrected milk production, with mean values of 0.40, 0.45 and 12.48 kg/day; 0.68, 0.64 and 19.74 kg/day; 0.57, 0.62 and 17.37 kg for cassava scrapings, flaked corn and ground corn, respectively. Average values of ruminal ammonia were lower with flaked corn or cassava scrapings, showing more active fermentation of these starch sources. Although of highest rate of starch hydrolysis, cassava scrapings altered protein metabolism with a reduction in microbial protein synthesis.
blood parameters; cassava scrapings; flaked corn; grain processing; microbial synthesis; milk production
