Caracterização de pastos, consumo e desempenho de vacas em pastagens de Pennisetum sp

Abstract

The study was conducted at IPA’s Itambé Experimental Station, rainforest region of the state of Pernambuco, Brazil, to evaluate the structural characteristics, productivity and influence of forage quality of Pennisetum sp. genotypes on the consumption and milk production of crossbred cows (5/8 Holstein-Zebu), supplemented with sugar cane in the drought period. For the forage, randomized blocks design with subdivided plots in time were used, in which the plots were the clones (IRI–381, Venezuela–AD, Elephant B, Hexaployd and HV–241), and the subplots were the periods of evaluation (08 to 24/12/2005, 25/12/2005 to 09/01/2006, 10 to 25/01/2006, 26/01 to 10/02/2006 and 11 to 25/02/06). For the animals, a system of rotational stocking (36 days of rest period of the grass and four days of grazing) was used in a double Latin square 5 x 5, with five periods of assessment of 16 days each, being eight days for adjustment and eight for collection, and five clones. Regarding the chemical composition of the forage,randomized blocks with subdivided plots in time were used, in which the plots were the clones and the subplots were the periods of collection. There was no effect of interaction (P>0.05) clone x period of the year for any of the structural and productive characteristics of pastures. There was difference (P<0.05) for the average height and the total mass of pre-grazing forage, with emphasis on the clones IRI–381, Venezuela–ADand Hexaploid (1.92, 1.88 and 1.86 m and 11,761; 11,842 and 11,921 kg of DM/ha, respectively). The leaf blade/stem ratio of the clones varied (P<0.05) only in pre-grazing, with the Venezuela–AD value 0.46 outpacing all others, which averaged 0.38. There was no difference (P>0.05) for the accumulation rate of total mass of forage, being the average of clones 105.0 kg of DM/ha/day. The genotypes of Pennisetum sp. did not affect (P>0.05) neither milk production nor the consumption of sugar cane with urea and ammonium sulfate, being the averages 3.6 kg of milk/cow/day and 7.6 kg of DM/cow/day, respectively. The estimated consumption of elephant grass using both the agronomic and cow milk production methods was of low accuracy. The consumption of NE and CP was a limiting factor in milk production of cows. The genotypes of Pennisetum sp. were different to the levels of MM, NDF, TCH and TDN, with HV–241 hybrid and Venezuela–AD clone presenting the highest and the lowest nutritional value,respectively. The structural characteristics and productivity of elephant grass pastures were influenced by periods of the year. The elephant grass clones IRI–381, Venezuela–AD and Hexaploid stood out for mass of stem productivity, leaf blade and total mass of forage, and show promise for use under grazing conditions in the rainforest region of the state of Pernambuco.