Efeitos do óleo de soja sobre a digesta omasal e os ácidos graxos do leite em vacas leiteiras alimentadas com dietas à base de cana-de-açúcar
Júlia Travassos da Silva1, João Paulo Pacheco Rodrigues2, Ricardo Marostegan de Paula3, Giselle Priscila Costa4, Cassiano Fernandes Lobo5, Andréia Ferreira Machado6, Luciana Navajas Rennó7, Marcos Inácio Marcondes8
1 - Universidade Federal de Viçosa
2 - Universidade Federal de Viçosa
3 - Universidade Federal de Viçosa
4 - Universidade Federal de Viçosa
5 - Universidade Federal de Viçosa
6 - Universidade Federal de Viçosa
7 - Universidade Federal de Viçosa
8 - Universidade Federal de Viçosa
2 - Universidade Federal de Viçosa
3 - Universidade Federal de Viçosa
4 - Universidade Federal de Viçosa
5 - Universidade Federal de Viçosa
6 - Universidade Federal de Viçosa
7 - Universidade Federal de Viçosa
8 - Universidade Federal de Viçosa
RESUMO -
Foram avaliados os efeitos de níveis crescentes de óleo de soja (OS) em dietas à base de cana-de-açúcar no perfil de ácidos graxos na digesta omasal e no leite, com foco no ácido linoleico conjugado (CLA). Oito vacas Holandesas multíparas fistuladas, com peso corporal 574 ± 19,1 kg e 122 ± 6,9 d em lactação foram distribuídas em dois quadrados latinos 4×4 balanceados para efeito residual. As dietas foram formuladas com concentrações crescentes de OS (g/kg de matéria seca (MS)): controle (0 g/kg), baixo (BOS, 15,7 g/kg), médio (MOS, 44,3 g/kg) e alto (AOS, 73,4 g/kg). A concentração de 11trans-18:1, 9cis,11trans-18:2 CLA e 9cis,11trans-18:2 CLA na digesta omasal aumentou linearmente com a adição de OS. Foi detectado 10trans,12cis-18: 2 CLA no leite nos tratamentos MOS e AOS. A suplementação superior a 15,7 g de OS/kg de MS diminuiu a produção de leite e gordura sem resposta aditiva no rendimento de 9cis,11trans-18: 2 CLA.
Palavras-chave: ácido linoleico conjugado, suplementação, gordura
Effects of soybean oil on omasal digesta and milk fatty acids in dairy cows fed sugarcane-based diets
ABSTRACT - The effects of increasing levels of soybean oil (SBO) in sugarcane-based diets on omasal digesta and milk fatty acids profile, focusing on conjugated linoleic acid (CLA), were evaluated. Eight rumen-cannulated multiparous Holstein cows averaging 574 ± 19,1 kg body weight and 122 ± 6,9 d in milk were used in a replicated 4×4 Latin square design balanced for residual effects. The diets were formulated with increasing concentrations of SBO (g/kg of dry matter (DM)): control (0 g/kg), low (LSBO; 15,7 g/kg), medium (MSBO; 44,3 g/kg) and high (HSBO; 73,4 g/kg). The concentration of 11trans-18:1, 9cis,11trans-18:2 CLA, and 9cis,11trans-18:2 CLA in omasal digesta increased linearly with the addition of SBO. 10trans,12cis-18:2 CLA in milk was detected in MSBO and HSBO diets. The SBO supplementation greater than 15,7 g SBO/kg DM decreases milk and fat yield without additive response on 9cis,11trans-18:2 CLA yield.Keywords: conjugated linoleic acid, supplementation, fat
Introdução
In recent years, the demand for healthy food by consumers has strongly increased, particularly in relation to dairy products. The nutraceutical potential of some fatty acids (FA) mainly associated to conjugated linoleic acids (CLA) has been receiving focus by the scientific community. Studies demonstrate that CLA have positive effects on human health, such as their anti-carcinogenic activity. Therefore, studies that evaluate nutritional strategies to increase the CLA concentration in milk are needed. The use of vegetable oils in ruminants’ feeds has been intensely studied as a strategy to increase the concentrations of CLA in meat and milk. However, data with cows fed tropical forages such as sugarcane are scarce.Based on the hypothesis that soybean oil (SBO) supplementation increases the flow of biohydrogenation intermediates to the omasum and milk CLA, this study aimed to investigate the inclusion of SBO at higher levels than conventional on ruminal lipid metabolism and milk FA profile of cows fed sugarcane-based diets. Given the lack of milk FA studies with sugarcane our objective was to find optimum levels of SBO inclusion to increase milk CLA of cows fed this forage.Revisão Bibliográfica
Due to the potential nutraceutical properties of milk fatty acids (FA), studies evaluating changes in milk FA profile encompassing alterations in dairy cows’ diets have been made in recent years (Shingfield & Wallace, 2014). The CLA isomers have shown effects on human metabolism and health. Studies demonstrated that the intake of 9cis,11trans-18:2 CLA by humans is beneficial and reduces the risk of diseases such as cancer, obesity and immune disorders (Kanwar et al., 2016). Dairy products are an important source of CLA to human nutrition. A better understanding of rumen biohydrogenation of polyunsaturated FA (PUFA) is the key to increase CLA concentration in milk. The use of plant oils such as SBO to feed cows generally is constrained to levels up to 60 or 70 g of ether extract (EE) per kg of dry matter (DM) to avoid deleterious effects on fibre digestibility (NRC, 2001). In this way, studies evaluating the effects of vegetable oils, in general do not use to reach levels of fat higher than the recommended (Prado et al., 2015). Besides the small volume of data evaluating high levels of vegetable oil, it is well known that the forage type and ratio in the diet affects the response to fat supplementation in ruminal lipid metabolism and milk FA composition (Sterk et al., 2012). Diets with sugarcane have limitations in energy intake as consequence of the high indigestible fraction of neutral detergent fibre (NDF) (Oliveira et al., 2011). Thus supplementation with vegetable oils can be an alternative to increase the energy intake of dairy cows fed sugarcane. However, there is a lack of research about strategies to alter rumen lipid metabolism and milk FA using SBO with different kinds of forage and feeding systems. Indeed, data about ruminal lipid metabolism and milk FA from cows fed tropical forages such as sugarcane and fat levels in the diet are limited in the literature.Materiais e Métodos
Eight rumen-cannulated multiparous Holstein cows averaging 574 ± 19,1 kg body weigth (BW) and 122 ± 6,9 d in milk (DIM) were used. Milk yield was 22,5 ± 1,22 kg/d at the beginning of the study. Cows were grouped in a replicated 4×4 Latin square design balanced for residual effects. The experimental period lasted 21 d, being 14 d for acclimation followed by sampling period from d 15 to 21. Diets were formulated with increasing SBO concentrations (g/kg of DM): control (0 g/kg), low (LSBO; 15,7 g/kg), medium (MSBO; 44,3 g/kg), and high (HSBO; 73,4 g/kg; Table 1). Cows were milked twice a day and had free access to the diets and water. Samples of feeds and orts were collect from d 15 to 19 of each period, when infusions of 8 g/d of Co-EDTA (766 mg of Co/d) were performed four times daily from d 13 to 18 of each period. The omasal fluid was collected according to the technique described by Leão (2002), and calculated based on the double marker method proposed by Faichney (1975). The markers concentrations and omasal flow were estimated by filtering 500 mL, separating in particle and fluid phases. Samples of feeds, orts and omasal digesta were oven-dried at 55°C for 72 h and grounded through 2- and 1-mm screens for further analyses. The DM, organic matter (OM) and crude protein (CP) content of feeds, orts, omasal digesta and milk were determined according to AOAC (2005).The FA profile of the feeds was evaluated by method described by Folch et al. (1957). The PUFA biohydrogenation rate (BHR) was calculated as BHR = 100 × (ƩPUFAi-ƩPUFAf)/ƩPUFAi, where ƩPUFAi = intake of PUFA (g/d) and ƩPUFAf = omasal flow of PUFA (g/d).Resultados e Discussão
The SBO decreased quadratically (P<0.05) the OM and EE intake, with greatest decrease from MSBO to HSBO diet (Table 2). The SBO quadratically increased (P<0.05) the BHR of PUFA with lower increases between the MSBO and HSBO diet (Table 2). In the present study, the decrease in the intake and increase in BHR of PUFA may be related to the decrease in the fractional rate of passage of iNDF (Rodrigues et al., 2016). Mostly FA with 18 carbons flowing to the omasum increased linearly (P<0.05) when SBO increased except for C18:0 and 9,12cis-18:2 CLA which were quadratically (P<0.05) affected and unaffected (P>0.10), respectively (Table 2). The 11trans-18:1 formed in the rumen is the main precursor of 9cis,11trans-18:2 CLA isomer synthesized by the ∆9-desaturase enzyme in the mammary gland (Corl et al., 2001). Thus, the increase in 11trans-18:1flow to the omasum is the main objective when supplementing fat to increase CLA contents in ruminant products (Shingfield & Wallace, 2014). The additive effects of SBO inclusion were linear and increased about 8-times the flow of 11trans-18:1to the omasum when comparing the control to HSBO diet. Nevertheless, the increase in 9cis,11trans-18:2 CLA in milk fat did not follow the response of 11trans-18:1 flow to the omasum. It is important to note that the use of Co-EDTA as a fluid marker leads to a lower activity of ∆9-desaturase activity as observed by Shingfield et al. (2008). The SBO addition linearly decreased (P<0.05) the DI of 9cis,11trans-18:2 CLA (Table 2). The decrease in DI 9cis-18:1 and 9cis,11trans-18:2 CLA was consequence of increase in the flowing of substrates to the omasum without increase in products. Wang et al. (2015) observed increase in 9cis,11trans-18:2 CLA in milk and ∆9-desaturase mRNA expression in mammary gland supplementing SBO at similar levels (25 g/kg of diet DM) to LSBO diet. In our study the LSBO diet promoted the CLA production without greater milk fat depression (MFD). Soybean oil decreased (P<0.05) milk fat concentration. The concentration of 9cis,11trans-18:2 CLA in milk increased linearly (P<0.05). The SBO increased quadratically the 9cis,11trans-18:2 CLA yield (P<0.05). The presence of 10trans,12cis-18:2 CLA in milk was observed only in HSBO diet. Fatty acids derived from de novo synthesis were linearly decreased (Table 2). The 10trans,12cis-18:2 CLA flow to the omasum leads to an important decrease in milk fat with no increase in CLA yield. Bauman & Griinari (2003) demonstrated the direct effect of 10trans,12cis-18:2 CLA increase in milk and the occurrence of MFD and decrease in the de novo synthesis of FA in the mammary gland. The 9cis,11trans-18:2 CLA concentration in milk fat and daily yield of that isomer together may indicate that the increase of milk CLA concentration is more associated with MFD than the increasing in its synthesis in the mammary gland.Conclusões
In conclusion, the addition of SBO proved to be a feasible alternative to increase rumen outflow of 11trans-18:1. However increasing the 9cis,11trans-18:2 CLA contents in milk the SBO supplementation to levels between 4.43 and 7,34g SBO/kg, DM provided low efficiency of usage of substrates to produce 9cis,11trans-18:2 CLA in the mammary gland. In order to increase the yield of 9cis,11trans-18:2 CLA without great decrease in the intake and milk and fat production of dairy cows fed sugarcane-based diets, SBO supplementation at 15,7 g SBO/kg DM is recommended.Gráficos e Tabelas
