Small Ruminant Research ELSEVIER Small Ruminant Research 20 ( 1996) 47-51 Influence of dietary protein content and digestibility on milk yield and blood constituents in lactating goats G.H. Pailan, H. Kaur” Dairy Catfle Nutrition Division, National Dairy Research Institute, Karnal 132 001, India Accepted 10 April 1995 Abstract Eighteen crossbred (Alpine X Beetal) lactating goats were divided into three equal groups on the basis of milk yield and lactation number. Goats of groups I and II were fed 100% CP requirements with RDP to UDP ratio of 75 : 25 and 60: 40, respectively. Group III goats were fed 85% CP compared with the other two groups with 60: 40 ratio of RDP to UDP. All groups were offered isoenergetic diet. DM intake per 100 kg body weight (BW) was significantly reduced in group III. Group II produced significantly more milk compared with I and III. Milk composition was not influenced by dietary treatments except milk fat which was reduced in group II. Blood glucose level remained unaffected but plasma protein concentration was decreased in group II goats. Increased milk yield with reduced feed cost per kilogram milk production in group II suggested that feeding the same amount of CP with less RDP resulted in better performance. Feeding even 15% less protein containing 60% UDP maintained the milk production in group III. Keywords: Goat; Protein degradability; Milk production; Blood metabolites 1. Introduction New protein requirement systems for ruminants (ARC, 1980; NRC, 1989) have been proposed in order to overcome the limitations of the CP system. Since all dietary CP is not transformed to microbial protein in the rumen, efforts have been made to determine actual amino acid requirements of ruminants. Feeding less degradable protein to lactating cows (Oldham et al., 1982; Forster et al., 1983; Sloan et al., 1988; Susmel et al., 199 1) was found to improve their performance. NRC ( 1989) has recommended 1520% reduction in CP requirements of dairy cattle when UDP content in the diet was increased and RDP content was decreased. However, N requirements of dairy goats are not well * Corresponding author. 0921.4488/96/$15.00 0 1996 Elsevier Science B.V. All rights reserved SSDIO921-4488(95)00766-O known (Morand-Fehr and Sauvant, 1978; Haenlein, 1980). Hence, there is a need to find out the optimum dietary RDP to UDP ratio and amount of CP which can lead to increase in milk production without affecting cost of milk production. The present study was con- ducted to find effects of varying dietary protein content and degradability on milk yield, milk composition and certain blood metabolites in lactating goats. 2. Materials and methods Eighteen lactating, crossbred goats were divided into three equal groups on the basis of milk yield and lac- tation number such that milk yield at the start of the experiment averaged 2.08 + 0.04, 2.13 k 0.04 and 2.03 k 0.03 kg day- ’ in groups I, II and III, respec-