Gradual-release nitrogen supplementation in late gestation : effects on maternal performance, physiology, metabolism, and offspring early development in beef cattle

Abstract

In tropical beef systems, late gestation often coincides with forage shortages, challenging maternal–fetal nutrition. Therefore, this study aimed to evaluate slow-release nitrogen supplementation as a strategy to improve maternal metabolism and fetal development in cows fed low-quality forage. Thirty-three pregnant Brahman cows were used. From days 180 to 270 of gestation, one of three diets were randomly assigned to cows: (1) Control (CON; basal diet), (2) regular protein (REG; soybean meal + urea, 40% CP), or (3) Slow-release nitrogen-based supplement (SRN, Timafeed Boost, Roullier Group, Saint-Malo, France; 40% CP). Cows were housed individually and fed twice daily until calving. After calving, cow–calf pairs grazed pasture with creep feeding until weaning. Statistical differences were considered when P < 0.05. At 270 days of gestation, body weight (BW) and empty BW were greater in REG and SRN than CON (P < 0.01). Total average daily gain (ADG) and empty body gain increased with supplementation (P < 0.01), whereas gestational tissue ADG was unaffected (P = 0.23). Maternal tissue mobilization occurred across groups but was less pronounced in REG and SRN (P < 0.01). Both supplementation programs increased feed intake, total-tract apparent digestibility, and nitrogen balance (P < 0.01). Plasma glucose, IGF-1, and citrulline were greater in supplemented cows, whereas urea was highest in REG, intermediate in SRN, and lowest in CON (P ≤ 0.01). REG also increased the sum of nonessential and glucogenic amino acids (P ≤ 0.05). Calf birth weight was not affected by supplementation programs (P = 0.13), but by weaning, calves from supplemented dams were heavier than those from CON (P = 0.04). In conclusion, protein supplementation during late gestation, either conventional or SRN-based, improved maternal performance, and supported greater postnatal calf growth under tropical conditions.