Growth and carcass characteristics of lambs fed high-concentrate diets containing different sources of non-protein nitrogen

Abstract Text: Nitrate supplements can be used as non-protein nitrogen (NPN) in ruminant diets. The interest in this NPN source is due to its capability of reducing methane emissions. Forty-four Dorper x Santa Inês lambs (initial BW 21.05 ± 2.65 kg and 79 ± 5 d old) were used in a randomized complete block design, according to initial BW and age, to determine the effects of supplementing urea or calcium nitrate on growth and carcass characteristics. Lambs were penned individually during 56 d and fed an isonitrogenous (16% CP, DM basis) total mixed ration composed of 80% concentrate and 20% coastcross hay. The experimental diets were: C (control, with soybean meal), U (1.1% urea), NEN (2.65% non-encapsulated calcium nitrate) and EN (3.0% encapsulated calcium nitrate). Diets containing nitrate were formulated to have the same content of NO^3- (DM basis). Urea was added to have the same crude protein equivalent as nitrate. In the first week of feeding a gradual adaptation period was used to avoid toxic effects of nitrate or urea. Data were evaluated using orthogonal contrasts. The first contrast was the C vs non-protein nitrogen (NPN), the second contrast was U vs calcium nitrate (U vs CN) and the third was formed by NEN vs EN. The control animals had greater (P < 0.01) ADG (389, 355, 345 and 346 g for C, U, NEN and EN, respectively) and feed efficiency (gain:feed = 0.286, 0.265, 0.269 and 0.264 for C, U, NEN and EN, respectively) compared with NPN. However, there was no difference (P > 0.05) between U vs CN and NEN vs EN. Dry matter intake (1.37, 1.35, 1.29 and 1.32 kg/d for C, U, NEN and EN, respectively) and carcass characteristics (dressing percentage, longissimus muscle area, back fat thickness and body wall thickness) were unaffected (P > 0.05) by the experimental diets. Lambs fed 2.65% non-encapsulated or 3% encapsulated calcium nitrate have similar performance and carcass characteristics of lambs fed 1.1% urea.

Keywords: calcium nitrate, urea, sheep