Interaction of flint corn grain processing and urea source, and the inclusion of calcareous marine algae in finishing diets for Nellore cattle: effects on growth performance, carcass traits, and nutritional characteristics

Abstract

Global population growth has intensified the demand for productive and environmentally sustainable livestock systems. In this context, Lithothamnium calcareum, a calcareous marine algae, has emerged as a natural buffering agent to improve ruminal fermentation and reduce methane emissions. Thus, the objective of this study was to evaluate the effects of L. calcareum supplementation on feedlot performance, carcass traits, nutrient digestibility, nitrogen metabolism, urinary and fecal pH, and enteric methane emissions in Nellore heifers during the finishing phase. Thirty-six heifers with an initial body weight (BW) of 270 ± 7 kg were allocated in individual pens and distributed in a randomized complete block design. The experimental diets were formulated with a 25:75 forage-to-concentrate ratio (DM basis) and provided ad libitum, with daily adjustments to control feed refusals. Two treatments were evaluated: 1) Sodium bicarbonate (1.8% DM in the diet, providing 110 g/heifer/day), and 2) Calcareous marine algae (supplemented with 60 g of L. calcareum /heifer/day). The experiment lasted 96 days, including 12 days of dietary adaptation followed by 84 days on the finishing diet. Refusals were collected and quantified daily to estimate dry matter intake (DMI), by calculating the difference between the amount offered and refused. BW was measured on days 0, 13, 41, 69 and 96, before the morning feeding. Enteric methane (CH₄) emissions were measured using the sulfur hexafluoride (SF₆) tracer gas technique during three distinct periods of the experiment: days 21 to 25, 49 to 53, and 77 to 81. Fecal and urine samples were also collected during three periods (days 27–32, 55–60, and 83–88). Data was analyzed using the MIXED procedure of SAS 9.4. There were no significant treatment effects on feedlot performance (P ≥ 0.560), carcass traits (P ≥ 0.681) and apparent total tract digestibility (P ≥ 0.212). Urine pH was significantly lower for heifers consuming calcareous marine algae (P ≤ 0.001) compared to those receiving sodium bicarbonate. Fecal N excretion (53.82 vs. 47.87 g/day; P = 0.079) tended to be lower in heifers fed with calcareous marine algae. Heifers fed diets supplemented with calcareous marine algae showed a tendency for an 8.2% reduction (P = 0.075) in enteric methane emissions compared to those receiving sodium bicarbonate. In summary, L. calcareum proved to be a viable natural alternative to sodium bicarbonate in finishing diets for Nellore heifers, maintaining performance and carcass traits, with potential to enhance ruminal microbial activity and reduce enteric CH₄ emissions, although further studies are needed.