1Department of Animal Sciences, Faculty of Agriculture and Natural Resources, Arak University, Arak, Iran
2Department of Animal Sciences, College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran
Performance, digestibility of nutrients, microbial nitrogen flow (MNF) and nitrogen efficiency (NE) in early lactating Holstein cows were investigated by diet supplementation with sodium caseinate (CN). Multiparous lactating Holstein cows (n = 15) with an average body weight of 638 kg and 21 days in milk were assigned to a completely randomized design (five cows per treatment) and fed a basal diet with different CN levels (treatments 1, 2, and 3, contained 0, 50, and 100, g/d/head CN, respectively). The study lasted 49 days (first 14 days for adaptation and the last 35 days for collection of data). There were no statistical differences in dry matter intake, milk yield, milk lactose yield, and protein yield with CN supplementation. 3.5% fat corrected milk yield was increased by CN supplementation (P<0.05). Digestibility of ADF was increased by CN supplementation (P<0.05). The higher level of CN affected MNF was estimated by spot urine sampling technique (P<0.05). Predicted N excretion through urine was affected (P<0.05); however, there was no effect of CN supply on predicted N excretion through faeces. In conclusion, the results indicated that although supplementation with CN improved MNF, negligible effects on performance of the cows were observed. Furthermore, increased milk urea nitrogen (MUN) concentration and predicted urine N excretion revealed the lower NE in early lactating dairy cows supplemented with CN compared with control treatment.