A STUDY OF 2 GRAZING METHODS .1. MAIN PRODUCTIVE INDEXES IN DAIRY-COWS

An experiment with 84 Holstein cows with a milk yield potential of 3 8 00 to 4 500 litres of milk per lactation grazing star grass (Cynodon n lemfuensis) was carried out to compare the productive performance of d airy cows. The animals were divided into two grazing treatments: Ratio nal Voisin grazing (RVG) (36 paddocks/group and traditional rotational grazing (RG-12) (6 paddocks/group) with an initial stocking rate of 4 .7 animals/ha. Two groups of cows were used in each treatment (product ion and dry) rotating in line. Milk yield, live weight, protein and mi lk fat data were analysed according to a multiplicative model (Menchac a 1978) and the quality of the feeds, lactose, non-solid and total fat s by a linear model of ruled effects. Individual production was higher (P < 0.01) with RG-12 throughout the experiment. Treatment/year inter action indicated that in the former there was a greater milk yield (P < 0.01) than in the remaining ones and a recovery was observed in the third one. No difference in milk quality of cows in both systems were found. Milk production/grazed hectare decreased (P < 0.01) in 21.6 and 45.3% in the second and third year, respectively in respect to the fo rmer with RG-12 while with RVG production was reduced in 45.1% in the third year. It was demonstrated that regardless the treatment, Holstei ns do not express their milk yield potential with low cost systems in an intensive exploitation (high stocking rates and grazing intensities ) and have no advantages by increasing the number of subdivisions.