ORIGINAL ARTICLE Effect of pearl millet silage ammoniated with urea on lamb production and metabolic performance G. G. P. Carvalho 1 | P. M. D. Freitas 1 | E. M. Santos 2 | G. G. L. Ara ujo 3 | J. S. Oliveira 2 | A. J. V. Pires 4 | C. M. A. Maranh ~ ao 5 | T. C. G. C. Rodrigues 1 | J. E. Freitas J unior 1 | L. M. A. Rufino 6 | C. S. Rodrigues 7 | L. C. Leite 8 | M. L. G. M. L. Araujo 1 1 Federal University of Bahia, Salvador, BA, Brazil 2 Federal University of Paraiba, Areia, PB, Brazil 3 Embrapa Semi arido, Petrolina, PE, Brazil 4 State University of Southwest Bahia, Itapetinga, BA, Brazil 5 State University of Montes Claros, Jana uba, MG, Brazil 6 Federal University of Par a, Castanhal, PA, Brazil 7 Federal Institute Baiano, Salvador, BA, Brazil 8 Federal University of the Reconcavo of Bahia, Cruz das Almas, BA, Brazil Correspondence G. G. P. Carvalho, Federal University of Bahia, Salvador, Bahia, Brazil. Email: gleidsongiordano@yahoo.com.br Abstract The objective of this study was to determine the effect of diets containing pearl millet silage ammoniated with urea on the intake, digestibility, production perfor- mance, and nitrogen metabolism of lambs. Thirty-two uncastrated mixed-breed lambs at 4 to 5 months of age, with an average initial body weight of 17.39 Æ 2.16 kg, were distributed into four treatments in a randomized block experimental design with eight replicates. Experimental diets consisted of pearl mil- let silage ammoniated with urea during ensiling at the levels of 0, 20, 40, and 60 g/ kg dry matter (DM). Increasing urea levels in the pearl millet silage led to a linear decrease (p < .05) in the intakes of DM, organic matter, and total digestible nutri- ents by the lambs. Total and average daily weight gains decreased linearly (p < .05) with the addition of urea to the silage. Intake and digestibility of crude protein, nitrogen intake, urine urea nitrogen, plasma urea nitrogen, microbial synthesis, and microbial efficiency had a quadratic response (p < .05) to the urea levels in the silage. Pearl millet silage ammoniated with urea reduces dry-matter intake and daily weight gain in lambs. Urea is not recommended for use in the ensiling of pearl millet. KEYWORDS chemical additive, feedlot, Pennisetum glaucum, sheep, weight gain 1 | INTRODUCTION The use of preserved forages is an alternative in tropical regions, where forage production is typically seasonal due to long periods of drought. This seasonality compromises the production performance of small ruminants, which cannot gain weight satisfactorily and are thus slaughtered at a late age. As stated by Santos et al. (2016), pearl millet (Pennisetum glau- cum [L.] R.) can play an important role as a feed source for ruminants in arid and semiarid regions of the world because of its high toler- ance to droughts. This forage plant is an option for silage making, as it is a short-cycle (60 to 90 days) annual summer grass; has an effi- cient regrowth ability; and has the ability to develop during short rainy seasons in regions with low precipitation (400 mm annually). Because of these features, pearl millet is considered a crop with potential to produce 60 t of green matter and 20 t of dry matter per hectare. This would depend on the cultivation system of the region, which may be succession planting or include off-season crops. Despite its favourable agronomic characteristics, at the moment of ensiling, pearl millet may have a dry-matter content below recom- mended levels, which may cause nutrient losses in the form of efflu- ent or gases originating from undesirable fermentation (Ward, Redfearn, Mccormick, & Cuomo, 2001). Ammoniation is a chemical process that can be adopted to pre- serve forage while maintaining its high moisture. This process improves the nutritional value of the forage by providing non-protein Received: 9 November 2016 | Revised: 8 January 2018 DOI: 10.1111/gfs.12352 Grass Forage Sci. 2018;1–9. wileyonlinelibrary.com/journal/gfs © 2018 John Wiley & Sons Ltd | 1