Rofleponide palmitate

The objectives of this experiment were to determine the effects of replacing metabolizable Lys from porcine blood meal (PBM) with rumen-protected (RP) Lys (RPL) on lactation performance, ECM/DMI, N use efficiency (NUE; milk N/N intake), nutrient partitioning, metabolic heat production (HP), and metabolites in dairy cows. Holstein cows (n = 64) with a mean ± SD lactation of 3.30 ± 1.01, milk yield 51.5 ± 6.2 kg/d, and milk protein 3.38 ± 0.47% were enrolled at 87 ± 18 DIM. Cows and bins (16 cows/8 bins per treatment) were randomly assigned. Before enrollment, cows were allowed 2 wks to acclimate to bins followed by a 1-wk covariate period to establish baseline measurements. Cows were then assigned to 1 of 4 diets for 12-wks: PBM as the primary source of metabolizable Lys (PBM), or to a diet that replaced 33% (RPL33), 66% (RPL66), or 100% (RPL100) of the metabolizable Lys from PBM with RPL (n = 16/group). Methionine supply was maintained by RP Met (RPM) supplementation across all treatments. With only RPL and RPM supplemented, the RPL33, RPL66, and RPL100 diets were formulated to either meet or supply 27, 70, and 114 g/d less MP, respectively, than the estimated requirement. Lactation performance and DMI were recorded daily, while urine, and blood samples were collected during the covariate and wk-12 of the treatment period. Individual CO₂, O₂, and CH₄ gas exchanges were measured every day using head chamber (GreenFeed), and used to calculate respiration quotient (RQ), net carbohydrate (COXnet) and fat oxidation (FOXnet), and metabolic HP. Replacing PBM with RPL did not affect BCS, BW or net energy balance; however, it tended to linearly reduce DMI and ECM. Increasing replacement of PBM with RPL linearly decreased the yields of milk, protein, and lactose; however, fat yield was not affected across treatments. Intake of N and milk and urinary N output decreased linearly with increasing replacement of PBM with RPL. Although DMI and ECM yield tended to decrease linearly, the feed efficiency (ECM/DMI) or NUE remained unaffected across treatments. Replacing PBM with RPL did not affect the CH₄ production (g/d), yield (g/kg of DMI), and intensity (g/kg of ECM yield). Replacing PBM with RPL linearly increased the RQ and COXnet, while FOXnet declined linearly, accompanied by linear reductions in metabolic HP. Concentrations of BUN tended to decrease linearly; whereas concentrations of creatinine in blood tended to increase linearly with increasing replacement of PBM with RPL. These results indicate that increasing replacement of PBM with RPL reduces milk and protein yields linearly even under moderate MP limitation, emphasizing the need to maintain adequate MP supply while optimizing Lys and Met balance in mid-lactation high-producing dairy cows.