The effect of dietary inclusion of barley, unmolassed sugar beet pulp and molasses on milk production, digestibility and digesta passage in dairy cows given silage based diet

Abstract

Ten dairy cows in early lactation were given five different supplements with grass silage ad libitum according to two 5x5 Latin square designs. The supplements consisted of barley (Ba), unmolassed sugar beet pulp (SBP) and molasses (Mo) on dry matter (DM) basis as follows: (A) Ba 1000g, (B) Ba 667 g and Mo 326 g, (C) Ba 417 g, SBP 410 g and Mo 163 g, (D) SBP 983 g and (E) 656 g SBP and 326 g Mo per kg. The lower fat content of SBP and molasses than of Ba was balanced with rapeseed oil. These supplements were fed at the level of 6 kg DM/d. In addition, 1 kg of rapeseed meal was given as a protein supplement. No differences in silage DM intake between the Ba and SBP supplements were found, but inclusion of a high level of Mo depressed silage and total DM intake. Cows given SBP supplements yielded 1.1kg (P < 0.01) more milk and 32 g (P < 0.05) more protein than those given Ba supplements. Milk fat concentration was lower (P < 0.001) on SBP (46.0 g/kg) than on Ba diets (49.1 g/kg) and thus there was no difference in the yield of fat corrected milk(FCM) and milk fat between the two supplements. Inclusion of 2 kg of DM of More reduced the milk (P < 0.001), FCM, fat and protein yields (P < 0.01) compared to diets without molasses. Supplement C increased (P < 0.05) the milk yield compared to the other diets but the milk composition was not affected. The effect of supplements on the digestibility of the ration was determined using acid insoluble ash as a marker. The apparent digestibility of organic matter averaged 0.743 and was not significantly affected by the diet. Digestibility of neutral detergent fibre was higher (P < 0.001) for SBP diets (0.680) than for Ba diets (0.596). Similar differences were observed in the digestibility of other fibre components. However, the digestibility of the silage was not affected by the treatment. Feeding SBP diets resulted in lower (P < 0.001) digestibility of crude protein than did Ba diets. Metabolizable energy (ME) of SBP diets tended to be used more efficiently for milk synthesis than ME of Ba diets. Inclusion of Mo in Ba or SBP did not reduce the efficiency, although the milk yield was decreased. The passage rate of liquid was determined with CoEDTA and that of particles with Cr-labelled straw. The average mean retention time of liquid ranged from 18.0 to 19.9 h and that of particles from 36.8 to 37.7h. Neither time was affected by the treatment. The passage rate of particles from the rumen ranged from 0.045 to 0.048 and that of liquid from 0.096 to 0.104, irrespective of the diet.