Resumo

LEMUS-RAMIREZ, Vicente; GUEVARA-ESCOBAR, Aurelio  e  GARCIA-MUNIZ, José G.. Lactation curve and weight change of grazing Holstein-Friesian cows. Agrociencia [online]. 2008, vol.42, n.7, pp.753-765. ISSN 2521-9766.

Milk production from grazing, although moderate, is an attractive option because of low capital investment and operation costs. This study characterized a non-seasonal grazing system in the Mexican central plateau, evaluating environmental effects on variables related to milk yield with 120 lactation records of New Zealand bred Holstein-Friesian cows from 2001 to 2004. Characterization included metabolizable energy needs, dry matter (DM) intake, and feed efficiency (FE) using eleven second-lactation cows recorded in fall-winter, 1996-1997. Changes in body weight were analyzed and FE was calculated using fitted values of milk, milk solids (MS), and live weight. Yield at lactation peak (Y_max) and at 305 d (Y₃₀₅) was lower in first-calf cows (19.4 and 4388 L) than in multiparous cows (23.1 L and 5331 L), although persistency (s) was similar. Among the multiparous cows (2-7 calvings), there was no difference in Y_max, Y₃₀₅, or s. In lactations beginning in spring, Y_max was reached faster, and s was lower than those beginning in fall; when lactation began in other seasons, these variables were similar. Calving season had no effect on Y_max or Y₃₀₅. Calculated DM intake was 7120 kg (18.1 kg DM cow^-1 d^-1) during the productive cycle, and FE was 73.62 kg MS Mg^-1 DM intake. On average, the cows lost 9 kg live weight from calving to day 33, but gained 24 kg by the end of the dry period. Energy concentrations (10 MJ of ME kg^-1) and crude protein (19.5%) of the sampled forage was not consistent with the productive response of the cows, likely because they consumed forage with higher energy content relative to the calculated model of ME needs.

Palavras-chave : Nutrient needs; rotational grazing; persistency; milk solids.

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