AbstractTreatments A and B, based on complete rations, and a conventional control (C) were compared in a completely randomized design including 8 preliminary days and 3 successive 28-day comparison periods with 17 cows (13 Holstein and 4 Brown Swiss). Both complete rations incorporated 60% basal concentrates, principally ground maize, soybean meal, wheat middlings and cane molasses, and 40% grass hay, but differed in the coarsely chopped hay in A and ground hay (9.5 mm screen) ¡n B. Formulation specified 13% crude protein and 1.58 Mcal of net energy for lactation/kg of dry matter (DM). Each was fed to two groups of three cows, ad libitum in period 1 and restricted in periods 2 and 3 in late afternoon. During the hottest hours these animals rested under shade, which reduced thermal stress. Five control cows grazed rotationally at 2.5 animals/ha in gramineous swards of good quality, with individual supplementation of basal concentrates according to milk yield. Late in period 1, DM intake (DMI) of A and B reached maxima of 22 and 23 kg per per. Mean results for A, B and C, respectively, during 84 days were: daily DMI, 16.2, 16,4 and 6.0 kg (excluding pasture herbage), and as a percentage liveweight (LW), 2.96, 2.98 and 1.09; LW, 548, 552 and 550 kg; daily milk yield, 17.7, 16.5 and 16.0 kg; 4% fat corrected milk (FCM), 15.0, 13.7 and 14.0 kg; milk fat percentage, 3.00, 2.87 and 3.19; FCM/concentrates DMI ratio, 1.55, 1.39 and 2.34. One cow of B died of acute bloat in period 2, possibly because of insufficiency of effective fiber in the rumen. Complete ration A appears promising as a possible alternative for intensified dairying in Puerto Rico.
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