Curvas de lactação e consumo de vacas F1 Holandês x Zebu em pastejo e em confinamento

• Autor(a) principal: Santos, Stefanie Alvarenga
• Data de Publicação: 2011
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/1766
• topic: Consumo; Curva de lactação; Vacas mestiças; Consumption; Lactation curves; Crossbred cows; CNPQ::CIENCIAS AGRARIAS::ZOOTECNIA::NUTRICAO E ALIMENTACAO ANIMAL::AVALIACAO DE ALIMENTOS PARA ANIMAIS

This study was constituted by three experiments, which was described in four chapters. In the first study, the objective was to evaluate the effect of different forage sources on the performance of crossbred dairy cows in tropical conditions. The experiment was carried out on the Experimental Farm of the Agricultural Research Company of Minas Gerais, in Felixlândia- MG, Brazil. Twelve crossbred F1 Holstein x Gir cows were allocated to a 4x4 Latin square, balanced for residual effect, and each experimental treatment was assigned to one group of three cows. The experiment consisted of four treatments and five experimental periods of 21 days, with 14 days of adaptation and 7 days of data collection. The treatments were sorghum silage, corn silage, fresh sugarcane and sugarcane silage treated with 1% calcium oxide. The three markers method was used (LIPE ®, titanium dioxide and iADF) to estimate the individual intake and the apparent digestibility of the feed for the cows in each group. The data were subjected to analysis of variance and compared by a Tukey test at 5% probability using the PROC GLM of SAS, version 8.0 for Windows software. The dry matter intake (DMI) and organic matter intake (OMI) were highest (P<0.05) for cows consuming corn silage (P<0.05) and lower for those consuming sorghum silage, fresh sugarcane and sugarcane silage. The DMI of fresh sugarcane was lower than those of corn silage and sorghum silage (P<0.05). There was a decrease in the DMI when cows were fed sugarcane silage (P<0.05). The dry matter digestibility (DMd) and organic matter digestibility (OMd) of corn silage, sorghum silage and fresh sugarcane were statistically equal (P>0.05) and all were higher than that of the sugarcane silage-based diet (P<0.05). The milk yield from cows fed corn silage and sorghum silage were similar (P>0.05) and higher than the milk yields from cows fed sugarcane silage and fresh sugarcane, which were similar to each other. There was a higher content of non-esterified fatty acids (P<0.05) in the plasma of cows fed sugarcane silage. Nitrogen balance was greatest for cows fed corn and sorghum silage, followed by fresh sugarcane and then sugarcane silage (P<0.05). We conclude that the sugarcane silage-based diet provides a low intake, low digestibility, low efficiency of nitrogen utilization and high mobilization of body reserves in F1 Holstein x Gir cows. This mobilization supports a milk production similar to cows fed fresh sugarcane. Corn silage and sorghum silage provide satisfactory cow performance and nitrogen utilization, even with a high forage:concentrate ratio. In the second study, the purpose was to develop lactation, feed intake and weight change curves for F1 crossbred Holstein x zebu (HZ) cows under grazing conditions. The experiment was carried out at the Research Farm at the Empresa de Pesquisa Agropecuária de Minas Gerais (EPAMIG), in Felixlândia-MG-Brazil. Eighteen F1 cows were used, divided into three treatments; six were Holstein x Gir (HGI), six were Holstein x Guzerat (HGU), and another six were Holstein x Nelore (HNE), which had recently calved, distributed into simple, random samples under the feeding conditions of Brachiaria decumbens pasture plus concentrate with 22% of CP. To estimate individual feed intake at pasture, two indicators were used: titanium dioxide to estimate fecal DM excretion, and the indigestible acid detergent fiber (iADF) to estimate individual pasture intake. The original model for the prediction DMI from the NRC (2001) was not adequate to explain the data for DMI under tropical grazing conditions (P = 0.1407), though the model structure, when reparametrized, was adequate (P < 0.001). After reparametrization, the following final equation was obtained: DMI (kg/d) = (0.6089*FCM + 0.0244 *BW0.75) + (1 e(-0.2919*[WL+5.5772])), where FCM is fat corrected milk yield. BW is body weight, and WL is week of lactation. The modified model by Jenkins and Ferrell (1984) and the model by Wood (1967) showed similarities for the accurate prediction of milk production of F1 HZ cows on pasture, when compared to the original model by Jenkins and Ferrell (1984). The model by Wood (1967) showed uniform dispersion around the x-axis, and so it was used to estimate the parameters for each genetic group, as follows: HGI = 17.2667*t0.0652*e-0.00424t; HGU = 18.1470*t0.0332*e-0.00408t; and HN = 14.2836*t0.1059*e-0.00552t. The NEFA contents varied according to different genetic groups (P < 0.001), producing three different equations, as follows: HGI = 657.42 + 3.6957*t 32.4659*t1/2 0.1352*t3/2; HGU = 664.73 + 3.6957*t 32.4659*t1/2 0.1352*t3/2; and HNE = 607.70 + 3.6957*t 32.4659*t1/2 0.1352*t3/2. In conclusion, the model by Wood (1967) provides a better fit to the milk production data of F1 HZ cows grazing on tropical grasses, and the HGI cows have greater cumulative production at 305-d. The peak DMI, estimated by the reparametrized NRC (2001) equation, occurs during the sixthweek of lactation, when the DMI by the different genetic groups was stabilized. In the thirth study the objective was to evaluate intake, digestibility and efficiency of N use in F1 Hostein x Zebu dairy cows on grazing system. The experiment was conducted at the experimental farm of EPAMIG in Felixlândia-MG, between January and May 2008. We used 18 F1 cows, six HGI, six HGU and six HNE, which were the three experimental treatments, distributed in simple random samples under the same conditions of supply: pasture plus concentrate containing 22% crude protein (CP). To estimate the individual intake on pasture, we used two markers. Titanium dioxide was used to estimate the excretion of fecal dry matter and we used the acid detergent fiber (iADF) to estimate the individual pasture intake. There was no effect of genetic groups on intake and digestibility of nutrients (P <0.05) for any effect of multiple linear regression. All parameters of the regression equations for consumption of nutrients, except for DM and OM in% of body weight (BW) of non-fiber carbohydrates (NFC) and total digestible nutrients (TDN)% BW, were significant (P <0.05) and presented a quadratic behavior with positive critical point. The digestibility coefficients for CP, neutral detergent fiber corrected for ash and protein (NDF) and TDN content were affected by the lactation period (P <0.05), while the digestibility of DM, ether extract (EE) and organic matter (OM) presented no effect of lactation (P> 0.05). There was no effect of genotype (P> 0.05) for the parameters of efficiency of utilization of N. The excretion of urea nitrogen in urine (UNU) presented a quadratic function of days in milking (P <0.05), estimating the maximum excretion at 49 days. Since the milk urea nitrogen (MUN) and plasma (PUN), also in a quadratic behavior (P <0.05) presented peaks at 120 and 119 days, respectively. Thus, we conclude that the use of different genetic groups of Holstein- Zebu cows under tropical pastures does not promote change on intake, digestibility and nutrient utilization efficiency of N, which varied according to the milking period, presenting an general quadratic behavior for the three genetic groups. In the fourth study, the objective was to evaluate lactation, intake and body weight change curves of F1 Holstein x Zebu dairy cows in feedlot. The experiment was conducted at the Experimental Farm of EPAMIG in Felixlândia- MG, between the months of June 2008 and February 2009. We used 18 crossbred F1, six HGI, six HGU and six HNE, which were three experimental treatments and distributed in simple random samples, fed corn silage ad libitum plus concentrate with 20% CP. To estimate the intake of individual cows fed group were used three markers. The LIPE ® was used to estimate the excretion of fecal dry matter. To estimate the individual intake of concentrate fed, we used the titanium dioxide. To estimate the individual forage intake, we used the iADF. We used three models to fit the curves of lactation and weight change, as follows: Y = at be&#8722;ct (Wood,1967); Y = ate&#8722;ct (Jenkins & Ferrel,1984); Y = a+bte&#8722;ct. (Jenkins and Ferrell, 1984) with a parameter adjustment. There was no effect (P> 0.05) of genetic groups on the dry matter (DM) intake and other nutrients. The DM, organic matter, NDF, EE, and TDN intake presented a quadratic function of days in milking (P <0.05), and the same behavior observed for the digestibility of DM, OM and EE , and TDN levels (P <0.05). Lactation curves were constructed for the genetic groups, as follows: HGI =19,0764*t0,0166*e-0,00181*t; HGU =15,6232*t0,0936*e-0,00274*t e HNE =15,4655*t0,0401*e-0,00305*t,, through the mathematical model obtained by Wood (1967). The model Jenkins and Ferrell (1984) has developed an equation to estimate the weight variation of animals belonged to three groups jointly, as follows: HZE = 511,1 + 1,7925*t*e-0,0105*t . There was no effect (P> 0.05) of genetic groups on the efficiency of utilization of nitrogen compounds, but there was a significant effect of lactation period, except on microbial nitrogen compounds (MN), that was a quadratic model throughout the lactation (P <0.05). Thus, we conclude that the use of different genetic groups of Holstein-Zebu cows in feedlot does not promote change on intake and digestibility of nutrient, weight change and metabolic efficiency. The HGU Cows present a milk produce accumulated in 305 days of 4946.81 kg, with a peak of 19.80 kg of milk at 34 days, while the HGI cows have a similar performance, with peak lactation of 19.46 kg to 8 days and cumulative production of 4821.78 kg. Cows HNE underperform, with peak production of 16.47 kg at 16 days and cumulative production of 3674.98 kg.