References

• AOAC, 1990. Official Methods of Analysis. 15th ed. Association of Official Analytical Chemists, Arlington, VA, USA.
   Google Scholar
• Avondo, M., Bonanno, A., Pagano, R.I., Di Grigoli, A., Giambalvo, D., Alicata, M.L., 2007. Goat intake, diet selection and milk quality as affected by grazing time of day. Options Méditerranéennes, Serie A: Séminaires Méditerranéennes 74:67–71.
   Google Scholar
• Baumont, R., Prache, S., Meuret, M., Morand-Fehr, P., 2000. How forage characteristics influence behaviour and intake in small ruminants: a review. Livest. Prod. Sci. 64:15–28.
   Google Scholar
• Bava, L., Rapetti, L., Crovetto, G.M., Tamburini, A., Sandrucci, A., Galassi, G., Succi, G., 2001. Effects of a non forage diet on milk production, energy, and nitrogen metabolism in dairy goats throughout lactation. J. Dairy Sci. 84:2450–2459.
   Google Scholar
• Bonanno, A., Di Grigoli, A., Alicata, M.L., Tornambè, G., Avondo, M., Pagano, R.I., Giambalvo, D., Stringi, L., Di Miceli, G., 2007. Effect of stocking rate on selective behaviour and milk production of Girgentana goats grazing a ryegrass and berseem clover mixture. Options Méditerranéennes, Serie A: Séminaires Méditerranéennes 74:351–357.
   Google Scholar
• Bonanno, A., Fedele, V., Di Grigoli, A., 2008. Grazing Management of Dairy Goats on Mediterranean Herbaceous Pastures. In A. Cannas and G. Pulina (eds.) Dairy Goats Feeding and Nutrition. CAB International, Wallingford, UK, pp 189–220.
   Google Scholar
• Brun-Bellut, J., 1996. Urea recycling in the rumen of dairy goats: effects of physiological stage and composition of intake. Small Ruminant Res. 23:83–90.
   Google Scholar
• Cabiddu, A., Branca, A., Decandia, M., Pes, A., Cantucci, P.M., Masoero, F., Calamari, L., 1999. Relationships between body condition score, metabolic profile, milk yield and milk composition in goats browsing a Mediterranean shrubland. Livest. Prod. Sci. 61:267–273.
   Google Scholar
• Cannas, A., Pes, A., Mancuso, R., Vodret, B., Nudda, A., 1998. Effect of dietary energy and protein concentration on the concentration of milk urea nitrogen in dairy ewes. J. Dairy Sci. 81:499–508.
   Google Scholar
• Dove, H., Mayes, R.W., 1991. Use of plant wax alkanes as marker substances in studies of the nutrition of herbivores: a review. Aust. J. Agr. Res. 42:913–952.
   Google Scholar
• Fedele, V., Claps, S., Rubino, R., Calandrelli, M., Pilla, A.M., 2002. Effect of free-choiche and traditional feeding systems on goat feeding behaviour and intake. Livest. Prod. Sci. 74:19–31.
   Google Scholar
• Ferguson, J.D., Chalupa, W., 1989. Impact of protein nutrition on reproduction in dairy cors. J. Dairy Sci. 72:746–765.
   Google Scholar
• FIL-IDF, 1964. Determination of the casein content of milk. International Standard FIL-IDF 29. International Dairy Federation ed., Brussels, Belgium.
   Google Scholar
• FIL-IDF, 1993. Determination of total nitrogen in milk. International Standard FIL-IDF 20B. International Dairy Federation ed., Brussels, Belgium.
   Google Scholar
• Giaccone, P., Todaro, M., Scatassa, M.L., 2007. Factors associated with milk urea concentrations in Girgentana goats. Ital. J. Anim. Sci. 6 (Suppl. 1):622–624.
   Google Scholar
• Guo, K., Russek-Cohen, E., Varner, M.A., Kohn, R.A., 2004. Effects of milk urea nitrogen and other factors on probability of conception of dairy cows. J. Dairy Sci. 87:1878–1885.
   Google Scholar
• Hadjigeorgiou, I.E., Gordon, I.J., Milne, J.A., 2001. The intake and digestion of a range of temperate forages by sheep and fibre-producing goats. Small Ruminant Res. 39:167–179.
   Google Scholar
• Harmeyer, J., Martens, H., 1980. Aspects of urea metabolism in ruminants with reference to the goat. J. Dairy Sci. 63:1707–1728.
   Google Scholar
• Hof, G., Vervoorn, M.D., Lenaers, P.J. Tamminga, S., 1997. Milk urea nitrogen as a tool to monitor protein nutrition of dairy cows. J. Dairy Sci. 80:3333–3340.
   Google Scholar
• Jelinek, P., Gajdusek, S., Illek, J., 1996. Relationship between selected indicators of milk and blood in sheep. Small Ruminant Res. 20:53–57.
   Google Scholar
• Jonker., J.S., Kohn, R.A., Erdman., R.A., 1998. Using milk urea nitrogen to predict nitrogen excretion and utilization efficiency in lactating dairy cows. J. Dairy Sci. 81:2681–2692.
   Google Scholar
• Jonker, J.S., Kohn, R.A., Erdman, R.A., 1999. Milk urea nitrogen target concentrations for lactating dairy cows fed according to National Research Council recommendations. J. Dairy Sci. 82:1261–1273.
   Google Scholar
• Macciotta, N.P.P., Cappio-Borlino, A., Pulina., G., 2000. Time series autoregressive integrated moving average modelling of Test-Day milk yields of dairy ewes. J. Dairy Sci. 83:1094–1103.
   Google Scholar
• Mayes, R.W., Lamb, C.S., Colgrove, P.M., 1986. The use of dosed and herbage n-alkanes as markers for the determination of herbage intake. J. Agr. Sci. 107:161–170.
   Google Scholar
• Mayes, R.W., Dove, H., 2000. Measurement of dietary nutrient in free-ranging mammalian herbivores. Nutr. Res. Rev. 13:107–138.
   Google Scholar
• Mellado, M., Valdez, R., Lara, L.M., García, J.E., 2004. Risk factors involved in conception, abortion, and kidding rates of goats under extensive conditions. Small Ruminant Res. 55:191–198.
   Google Scholar
• Mitchell, R.G., Rogers, G.W., Dechow, C.D., Vallimont, J.E., Cooper, J.B., Sander-Nielsen, U., Clay, J.S., 2005. Milk urea nitrogen concentration: heritability and genetic correlations with reproductive performance and disease. J. Dairy Sci. 88:4434–4440.
   Google Scholar
• Nousiainen, J., Shingfield, K.J., Huhtanen, P., 2004. Evaluation of Milk Urea Nitrogen as a Diagnostic of Protein Feeding. J. Dairy Sci. 87:386–398.
   Google Scholar
• Nudda, A., Battaccone, G., Bencini, R., Pulina, G., 2002. Nutrition and milk quality. In: G. Pulina (ed.) Dairy sheep feeding and nutrition. Avenue Media, Bologna, Italy, pp 197–228.
   Google Scholar
• Pulina, G., Cannas, A., Serra, A., Vallebella, R., 1991. Determinazione e stima del valore energetico di latte di capre di razza Sarda. Proc. 45th Nat. Congr. SISVet., Altavilla Milicia, Palermo, Italy, 45:1779–1781.
   Google Scholar
• Roseler, D.K., Ferguson, J.D., Sniffen, C.J., Herrema, J., 1993. Dietary protein degradability effects on plasma and milk urea nitrogen and milk non protein nitrogen in Holstein cows. J. Dairy Sci. 76:525–534.
   Google Scholar
• SAS/STAT, 2004. Qualification Tools User’s Guide, Version 9.1.2. SAS Institute Inc., Cary, NC, USA.
   Google Scholar
• Schepers, A.J., Meijer, R.G.M., 1998. Evaluation of the utilization of dietary nitrogen by dairy cows based on urea concentration in milk. J. Dairy Sci. 81:579–584.
   Google Scholar
• Silanikove, N., 2000. The physiological basis of adaptation in goats to harsh environments. Small Ruminant Res. 35:181–193.
   Google Scholar
• Soryal, K.A., Zeng, S.S., Min, B.R., Hart, S.P., Beyene, F.A., 2004. Effect of feeding systems on composition of goat milk and yield of Domiati cheese. Small Ruminant Res. 54:121–129.
   Google Scholar
• St-Pierre, N.R., 2001. Invited review: Integrating quantitative findings from multiple studies using mixed model methodology. J. Dairy Sci. 84:741–755.
   Google Scholar
• Todaro, M., Scatassa, M.L., Giaccone, P., 2005. Multivariate factor analysis of Girgentana goat milk composition. Ital. J. Anim. Sci. 4:403–410.
   Google Scholar
• Van Soest, P.J., Robertson, J.B., Lewis, B.A., 1991. Methods for dietary fiber, neutral detergent fiber and non-starch polysaccharides in relation to animal nutrition. J. Dairy Sci. 74:3583–3597.
   Google Scholar
• Van Soest, P.J., Fox, D.G., 1992. Discounts for net energy and protein - fifth revision. pp 40-68 in Proc. Cornell Nutrition Conf., Ithaca, NY, USA.
   Google Scholar