NUTRIENT FLOW AND DIGESTION IN HOLSTEIN HEIFERS FED DIETS BASED ON UREA OR COTTONSEED MEAL AS MAIN CRUDE PROTEIN SOURCES

Abstract

An experiment was conducted with four Holstein heifers (160 kg body weight, BW) with cannulas installed in proximal duodenum (approximately 8 cm from the pyloric sphincter) and distal ileum, to evaluate duodenal flow and ruminal and intestinal nutrient digestion feeding cottonseed meal or 1.6 % urea based diets. Dietary treatments were the following: a) urea diet: 79.8 % steam-flaked corn, 15.7 % sudangrass, 3 % vitamin-mineral premix and 1.6 % urea; b) typical diet: 70 % steam-flaked corn, 15.7 % sudangrass, 11.4 % cottonseed meal, and 3 % vitamin-mineral premix. Both diets contained 12.6 % crude protein (CP); the urea diet contained 4.6 percentual units as non protein nitrogen (NPN). Microbial N flow to duodenum was higher (p0.10) by the dietary N source. Detergent acid fiber (FDA) flow to duodenum tended to be higher (p0.10) by the CP source. Neither intestinal digestion (percentage of duodenum flow) or rumen-intestinal digestion (percentage of intake) of dry matter (DM), OM, CP and starch were affected (p>0.10) by the source of N. These results indicate that CP source (urea or cottonseed meal) does not affect the duodenal flow and digestibility of nutrients in Holstein heifers. Amino acid digestibility of microbial and escape protein were similar, suggesting that duodenal nutrient flow in both diets may promote comparable growth rates in heifers.