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Supplementation of Cows Grazing Tropical Grass Swards with Concentrates Varying in Protein Level and Degradability

Department of Animal Science, University of Puerto Rico, Mayaguez 00709

ABSTRACT

Twelve Holstein and Brown Swiss cows participated in a replicated and balanced 3 x 3 Latin square experiment with 4-wk periods to test three commercial concentrate feeds as supplements to grazing at 4 cows/ha on mixed grass herbage of 6.94% mean CP. Available herbage DM was estimated at 27.5, 21.7, and 15.1 kg/cow per d in successive periods. Excessive rainfall had adverse effects in periods 2 and 3. Treatments were concentrates with 18, 15, or 15% CP with Protek (protein treated by a propietary process) as fed. Mean overall results were daily concentrate intake, 7.44 ± 1.37 kg; daily milk yield, 17.3 ± 4.8 kg; percentages of milk fat, SNF, and protein, 3.18 ± .80, 8.58 ± .28, and 2.94 ± .27; FCM per concentrate DM, 2.33 ± .41; and daily BW loss, .28 ± .53 kg. Differences among treatments were small and unimportant. Concentrate allowances were intended to satisfy NE₁ needs, but the anticipated contribution from pasture was overestimated. Energy rather than protein was deemed first limiting to animal performance, and neither CP higher than 15% in the concentrate nor protein protection was useful under these conditions.

¹ Present address: Escuela Nacional de Agricultura, Apartado Postal 2139. San Salvador, El Salvador.