Produção de leite de vacas F1 Holandês x Zebu em pastagens de marandu e tifton 85, suplementadas com concentrado proteico de diferentes degradabilidades

Abstract

This work aimed to evaluate the yield and nutritive value of two tropical grasses in a rotational grazing system and the productive potential of dairy cows on these pastures, supplemented with protein concentrate of different degradabilities. For analysis of the diets, we used 36 F1 Holstein x Zebu cows, with average of 65 days of lactation, an average initial weight of 514 kg distributed into a completely randomized design with 6 replicates per treatment in a factorial 2 x 3 x 3, being two grasses (marandugrass and Tifton 85), three types of concentrate supplementation (2 kg of protein concentrate with low rumen degradability, 2 kg of protein concentrate with high rumen degradability, and without providing concentrate feed ) and three grazing periods. As for the evaluation of grassland, it was used a randomized block design with three replications in a factorial 2 x 3 x 3, i.e., two grasses, three blocks and three periods. The area was divided into 32 paddocks of 2,324 m2, 16 for each grass. There was no difference in the heights of the canopy in the pre and post grazing between the grasses. The forage dry mass did not present differ between species in the pre grazing, but it was different in the post one, when the Tifton 85 had lower values than the marandugrass. In the post-grazing, there was higher proportion of stem and leaf blade in Tifton 85, and dead mass in marandugrass. The ashes values of the whole plant and leaf blade were higher for the marandugrass. The Tifton 85 showed the highest values of NDF, hemicellulose and NDIN of leaf blade. There was no difference between the ADF and EE of the whole plant. The Tifton 85 had highest CP and hemicellulose values. However, the marandu presented the lowest values of ADF and ADIN. The average live weight of the animals in the beginning and at the end of the experiment did not differ, with average of 537 kg. The production values of milk, lactose, total solids and solids not fat (SNF) were higher for animals that received supplementation, and there was no difference between concentrates. The values of fat, protein and SNF were higher during April. The supplementation improved quality of milk, regardless of the potential of fodder degradability and the type of grass. The average days open of all the cows used in the assay was 125.5 days. The Tifton 85 and marandugrass for F1 H/Z cows can be used to get the same production and quality of milk in grazing rotated with 30 days of rest. The Tifton 85 had higher carrying capacity. Protein sources independent of its degradability can be used to supplement F1 H/Z cows to pasture, with no difference in the quantity and quality of milk.