Uréia para vacas leiteiras no pós-parto: desempenhos produtivo e reprodutivo

Abstract

RESUMO -Quinze vacas mestiças (Holandês-Zebu) com peso médio de 511,8 kg foram distribuídas ao acaso em quatro tratamentos, sendo quatro animais nos tratamentos 1, 2 e 4 e três animais no tratamento 3. Os tratamentos foram constituídos de dietas à base de volumoso (silagem de milho) e concentrado (60:40), fornecidas individualmente e à vontade, e definidos como: T 1 =0,0; T 2 =0,7; T 3 =1,4 e T 4 =2,1% de uréia, correspondendo às concentrações de 2,08; 4,01; 5,76 e 8,07% de proteína bruta na forma de compostos nitrogenados não-protéicos (NNP), respectivamente. As médias do consumo de matéria seca foram de 16,04; 16,49; 11,64; e 11,93, em kg/dia, e 3,29; 3,09; 2,47; e 2,35, em % PV, e as da produção de leite corrigida para 3,5% de gordura, de 21,18; 24,92; 20,63; e 18,83 kg/dia, para as concentrações de NNP de 2,08; 4,01; 5,76; e 8,07, respectivamente, e reduziram com o aumento de NNP nas rações. As médias dos teores plasmáticos de uréia e N-uréia foram de 46,33 e 21,59 mg/dL e não foram influenciadas pelos teores de NNP das dietas. O número de ondas de crescimento folicular por ciclo estral, a emergência da primeira e segunda ondas de crescimento folicular e o diâmetro máximo do folículo ovulatório não foram influenciados pelas concentrações de NNP nas rações. A primeira ovulação e o primeiro estro no pós-parto foram observados aos 55±23 e 81±36 dias, respectivamente, e não foram influenciados pelas concentrações de NNP nas dietas.Palavras-chave: dinâmica folicular, pós-parto, uréia Urea for Postpartum Dairy Cows: Productive and Reproductive PerformanceABSTRACT -Fifteen crossbred cows (Holstein-Zebu) from EPAMIG-Leopoldina Experimental Farm with an average weight of 511.8 kg were allocated into an experiment in a complete randommized design, in four treatments, with four animals in the treatments 1, 2, and 4 and three in the treatment 3. The treatments were cosntituted of diets with corn silage and concentrate (60:40) and were fed individually and ad libitum and their contents in percentage of urea were: T 1 =0.0; T 2 = 0.7; T 3 = 1.4 and T 4 =2.1 corresponding to the 2.08; 4.01; 5.76 and 8.07% of crude protein in the form of non-protein nitrogen (NNP), respectively. The average dry matter intake (DMI) expressed in kg/day and in the percentage of body weight were: 16.04; 16.49; 11.64; 11.93 and 3.29; 3.09; 2.47 and 2.35, respectively. The milk production for 3.5% of fat were: 21.18; 24.92; 20.63 and 18.83 kg/day for the NNP concentrations of 2.08; 4.01; 5.76 and 8.07, respectively and decreased with the increase of NNP concentrations in the rations. The mean plasma concentrations of urea and N-urea were: 46.33 and 21.59 mg/dL, and were not affected by the concentrations of NNP in the diets. The number of follicular waves per cycle and the emergency of the first and second follicular waves and its diameter were not affected by the concentrations of NNP in the diets. The first estrus and ovulation occurred on days 55±23 and 81±36, respectively and were not affected by the NNP concentrations of the diets.

Urea in sugarcane-based diets for dairy cows

“…The PUN level in the cows receiving sugarcane with 12 g UAs/kg (14.31 mg/dL) was similar to that observed by Rangel et al (2008), in cows receiving sugarcane with the same UAs level, without effect on intake. The PUN value in this study was, however, smaller than values observed in studies in which intake reduced as UAs were increased (from 19.90 to 23.08 mg/dL) (Silva et al 2001a,b;Oliveira et al, 2001;Oliveira et al, 2004). The lower PUN value observed in the present study in relation to those of Silva et al (2001a,b), Melo et al (2003) and Oliveira et al (2004) is possibly related to the nature of the dietary carbohydrates present in the sugarcane, which are mostly soluble in neutral detergent, especially those rich in sugars, of higher rumen degradation rate in relation to the amylaceous fractions, and the ones insoluble in neutral detergent, which are typical in silages of corn and sorghum (Lanzas et al, 2007).…”

“…The PUN value in this study was, however, smaller than values observed in studies in which intake reduced as UAs were increased (from 19.90 to 23.08 mg/dL) (Silva et al 2001a,b;Oliveira et al, 2001;Oliveira et al, 2004). The lower PUN value observed in the present study in relation to those of Silva et al (2001a,b), Melo et al (2003) and Oliveira et al (2004) is possibly related to the nature of the dietary carbohydrates present in the sugarcane, which are mostly soluble in neutral detergent, especially those rich in sugars, of higher rumen degradation rate in relation to the amylaceous fractions, and the ones insoluble in neutral detergent, which are typical in silages of corn and sorghum (Lanzas et al, 2007). A higher rumen degradation rate of the fraction of sugars propitiates greater synchrony with the rate of rumen ammonia availability through urea, allowing for lower accumulation of rumen ammonia (Nocek & Russell, 1988).…”

“…This result is consistent with Rangel et al (2008), who, utilizing the same levels of urea in the sugarcane, but with a lower roughage:concentrate ratio in relation to the present study, also did not observe effect on the performance of dairy cows with production above 20 kg/day. However, it is not in line with other researchers, who observed linear decrease in the milk yield of cows fed increasing levels of urea (up to 21 to 24 g/kg DM of the diet), but utilizing corn or sorghum silage or a mixture of corn silage and forage cactus as exclusive source of forage (Silva et al, 2001a;Melo et al, 2003;Oliveira et al, 2004).…”

“…This result is consistent with Rangel et al (2008), who did not observe effect of the source of nitrogen (soybean meal vs. urea) and of the level of UAs in the sugarcane (4, 8 and 12 g/kg of sugarcane, as fed) on the intake of dairy cows with milk production above 20 kg/day. However, it contradicts other researchers who observed linear decrease in the DMI of dairy cows with increase in urea up to the level between 21 and 24 g/kg DM of the diet, but utilizing corn or sorghum silages or a mixture of corn silage and forage cactus (Silva et al, 2001a,b;Melo et al, 2003;Oliveira et al, 2004). In spite of the elevated level of urea in the diet (up to 30 g/kg DM), the absence of effect on intake is probably related to the pool of ammonia in the blood circulation, which probably remained at thresholds lower than the necessary to cause malfunctioning of the body tissues by energy deficit, especially the brain tissue, with consequent reduction of intake (Detmann et al, 2007).…”

“…However, the addition of up to 20 g urea/kg DM in the diet to diets based on corn or sorghum silage has been show to decrease intake and performance of dairy cows (Melo et al, 2003;Oliveira et al, 2004).…”