Effect of stocking rate and cow lactation stage on nitrogen balance of dairy cows in two periods of supplementation at pasture under Galician conditions (NW Spain)

Resumo

The effect of stocking rate (SR), low vs. high (L, 4.0 vs. H, 5.2 cows ha-1), and cows’ lactationstage (LS), early vs. middle (E, 31 vs. M, 140 days in milk) was studied on N-balance of cows(n = 72). N inputs (grass, silage and concentrate) and N outputs (milk and body weightgain) were evaluated in two periods, with medium (P1) vs. low (P2) level of supplementationat pasture. N inputs and N outputs were higher (P<0.001) in cows at E (189±14 and 121±9g N cow-1 d-1) than at M lactation stage (163±2 and 105±5 g N cow-1 d-1). Supplement intakewas higher (P<0.05) in H than in L stocking rate groups (10.4±0.2 vs. 9.2±0.9 kg DM cow-1d-1). N inputs, N outputs and N excretion were no different for SR treatments. N inputsand N outputs (g N cow-1 d-1) were higher (P<0.001) in P1 (237±8 and 140±10), with highersupplementation, than in P2 (114±19 and 86±8). N excretion was also higher (P<0.001) in P1than in P2 (479±67 vs. 68±24 g N cow d-1), but no differences were found between cows atboth LS and SR. N surplus was the highest in cows at E lactation stage and H stocking rat