Responses in Feed Intake, Digestibility and Nitrogen Retention in Lactating Dairy Goats Fed Increasing Amounts of Urea and Fish Meal

Abstract

Abstract Balance measurements were made on a total of 14 dairy goats of the Swedish Landrace breed during 3 experimental years. Experimental diets were composed of 40% hay and 60% concentrate mixture on a feed basis. The concentrate mixtures were unsupplemented or supplemented with urea (0.9, 1.8, 2.7 and 3.5%) or fish meal (3.9, 7.9, 11.7 and 15.8%) in increasing amounts. All diets were fed ad libitum. There was a gradual increase in buffer-soluble crude protein (BSCP) and effective rumen degradability of crude protein (EPD) in concentrates with added urea. The opposite was found in concentrates with added fish meal. EPD and BSCP in concentrate mixtures were linearly (p<0.001) related (r 2 = 0.72). Feed intake showed large between-animal variations, which were most pronounced at low and at high crude protein contents in the diet. The relative feed intake decreased significantly (p<0.01) with increasing urea and fish meal supplementation. However, milk protein production was well maintained on the fish meal diets. Organic matter digestibility was similar on all diets (73%; SD 0.7). Crude fibre (CF) digestibility varied between diets but was significantly (p<0.001) positively related to the amount of BSCP in feed organic matter in unsupplemented and fish meal supplemented diets. Significant (p<0.05) individual differences in CF digestibility were also apparent. The nitrogen balances (total N retention-milk N) were not significantly influenced by the diets fed and were, on average, 1.9 g N per day (SD 0.6). Increasing supplementation of urea was not significantly related to any increase in nitrogen accretion. Fish meal addition, on the other hand, gave a significant (p<0.05) curvilinear increase of nitrogen retention in milk.