Effects of replacement of alfalfa silage with corn silage and supplementation of methionine analog and lysine-HCl on milk production and nitrogen feed efficiency in early lactating cows

The objective of this experiment was to study effects of replacement of alfalfa silage with corn silage in diets with sufficient metabolizable protein (MP) and balanced metabolizable lysine and methionine on milk production and nitrogen feed efficiency in early lactating cows. Thirty-six cows were blocked by similar body weight at calving, parity and predicted transmitting ability of milk yield, and randomly assigned into 3 dietary treatments from calving to 15 wk postpartum. Dietary treatments included 1) alfalfa silage diet (AF, 186 g/kg CP), 2) a diet replacing alfalfa silage with corn silage and supplemented with rumen undegradable protein and 2-hydroxyl-4-methylthino-butanoic acid (HMB) (CS-M, 160 g/kg CP), 3) CS-M + lysine−HCl (CS-ML, 160 g/kg CP). Metabolizable protein was similar among treatments and approximate 110 g/kg of DM. Metabolizable Met and Lys were 2.2 and 6.3% of MP in AF; and were 2.5 and 6.2% of MP in CS-M; and were 2.5 and 6.9% of MP in CS-ML. Dry matter intake, MP intake, body weight and body condition score were not affected by treatments. Nitrogen intake was less (∼ 100 g/d) in CS-M and CS-ML than AF, but milk yield, milk protein percentage and yield were similar among treatments. The percentage and yield of milk fat and milk fat corrected milk were greater in AF and CS-ML than CS-M. From 8 to 15 wk postpartum, CS-M had a moderate milk fat depression (milk fat < 30 g/kg). Compared with AF, CS-M and CS-ML had greater nitrogen feed efficiency and less milk urea nitrogen. Concentrations of lysine and leucine in blood were greater in CS-M and CS-ML, and valine tended to be greater in CS-M and CS-ML than AF. Overall, the replacement of alfalfa silage with corn silage in the diet with adequate MP and balanced metabolizable lysine and methionine could improve nitrogen feed efficiency without compromising milk production in early lactation. In addition, unbalanced ratio of metabolizable Lys to Met could depress milk fat percentage and yield.