Undegradable dietary protein in alpaca diets affects fibre diameter and time spent urinating K. E. Lund A , J. T. B. Milton A,C , S. K. Maloney B , K. M. M. Glover A , J. L. Vaughan D and D. Blache A,E A UWA Institute of Agriculture (Animal Production), The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia. B School of Anatomy, Physiology, and Human Biology (M311), The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia. C Independent Lab Services, PO Box 244, Serpentine, WA 6125, Australia. D Cria Genesis, PO Box 406, Ocean Grove, Vic. 3226, Australia. E Corresponding author. Email: Dominique.Blache@uwa.edu.au Abstract. There is evidence that alpacas derive most of their glucose for energy from the deamination of amino acids. Consequently, they may have an insufficient supply of amino acids to meet their requirements for fibre growth. To optimise fibre production, it may be necessary to supply alpacas with supplemental protein to meet their requirement for extra amino acids. In this study, we examined if the proportion of rumen-degradable dietary protein (RDP) to undegradable dietary protein (UDP) from canola meal influenced the fibre growth of alpacas. We hypothesised that alpacas fed at maintenance a diet containing canola meal protein high in UDP would produce more fibre and spend less time urinating than peers fed a similar amount of canola meal protein with a low proportion of UDP. Four groups of eight alpacas were fed diets with the following ratios of UDP : RDP: 0 : 100, 30 : 70, 60 : 40 or 100 : 0 from canola meal protein. The fibre growth of the animals was measured over 2 months and the behaviour of the animals in the two extreme groups (0 and 100% UDP) was measured over 5 days. The alpacas fed the 0% UDP diet produced fibre of finer diameter than the alpacas fed diets containing higher levels of UDP (P = 0.039) and the 0% UDP group also spent more time urinating (P = 0.027). This result suggests that alpacas may have a limited ability to recycle nitrogen to the fermentative chambers of their stomach when fed a diet low in UDP. Consequently, microbial protein synthesis in the fermentative chambers may have limited the supply of amino acids available to the alpacas. Received 22 December 2011, accepted 23 April 2012, published online 16 July 2012 Introduction Alpacas were introduced to Australia to establish a new fibre industry with a focus to produce large quantities of quality fibre (Fysh 2003; McGregor 2006). In sheep, most of the glucose requirement is derived from propionate and fibre production is markedly influenced by the supply of dietary protein (Black and Reis 1979; McDonald et al. 2002). There is evidence that alpacas obtain most of their glucose from the deamination of dietary amino acids rather than from propionate (Van Saun 2006). Consequently, when alpacas are fed to meet their energy requirements for maintenance they may utilise most of the amino acids absorbed from the small intestine to meet their needs for glucose, especially since they maintain a blood glucose level higher than sheep (Kaneko et al. 2008). Therefore, under these conditions, alpacas may have an inadequate supply of amino acids to meet their requirements for fibre growth and it may be necessary to supply them with supplemental protein to optimise fibre production. In ruminants, the extent to which ingested protein is degraded depends upon its solubility and the time it is retained in the rumen. The protein that enters the rumen is either degradable (rumen degradable protein, RDP) or undegradable (undegradable dietary protein, UDP) (Bach et al. 2005). In the rumen, RDP can be degraded to varying degrees from peptides through to ammonia and these products can all be utilised for the synthesis of microbial protein (Bach et al. 2005). Ammonia that is not captured for microbial protein synthesis passes from the rumen and is converted to urea by the liver. This urea can be recycled back to the rumen, either via saliva or across the rumen wall, or excreted in urine (McIntyre 1970; McDonald et al. 2002). Alpacas are thought to be particularly efficient at recycling nitrogen (N), which would be advantageous in environments where the feed that is available is of low N content (Genin et al. 1994; Genin and Tichit 1997). If there is adequate fermentable carbohydrate in the diet, the N recycled by alpacas, in the form of urea, may be the main source of N for microbial protein synthesis occurring in the first and second chambers of the alpaca stomach (fermentative chambers). Excess N, for example from RDP when there is inadequate fermentable carbohydrate for microbial protein synthesis, will CSIRO PUBLISHING Animal Production Science, 2012, 52, 959–963 http://dx.doi.org/10.1071/AN11367 Journal compilation Ó CSIRO 2012 www.publish.csiro.au/journals/an