Efeitos da suplementação lipídica sobre o desempenho e metabolismo de vacas leiteiras em pastejo

Abstract

The milk production system in most of the world has pasture as the basis of feeding. However, the use of pasture can promote a variation in diet composition that does not meet the nutritional requirements of lactating cows, resulting in greater energy requirements due to the high levels of production of dairy cows. Thus, lipid supplementation comes to increase the energy density of diets without the need to increase the amount of concentrate. Since, supplements rich in fermentable carbohydrates in large quantities can lead to metabolic disorders. Although studies on the use of lipids in dairy cow diets have been conducted, the answers are not yet fully understood. In addition, the degree of saturation, source, and dose of lipids can influence responses, as well as dietary and physiological characteristics of the animals. Thus, a meta-analytical approach of multiple experiments may increase the power of the test to quantify the response of lipid supplementation and its sources of variation. Therefore, our objective was to investigate how lipid supplementation affects the performance and metabolism of grazing dairy cows. A meta-analytic approach was developed to elucidate the responses of lipid supplementation and its sources of variation, using a data set of treatment means from 18 articles. The studies were found in the Web of Science and Science-Direct databases, and manually added, the following search words "dairy cows, fatty acids and pasture" were used. The criteria adopted for inclusion of papers were (1) grazing cows; (2) all papers have control (no lipid supplementation) versus treatment (with lipid supplementation); (3) presence of mean scatter variable. A data set was created using 18 peer-reviewed published papers. Effects were compared by gross mean difference (GDM) between diets with lipid supplementation and control diets (no lipid supplementation), weighted by the inverse of variance. Lipid sources were divided into 6 groups: unsaturated fat protected from ruminal degradation (16%); saturated fat protected from ruminal degradation (13%); saturated fat (11%); seeds (10%); and free fat (5%). Ethereal extract (EE) intake levels were classified as: <400 g EE/cow/day, 401-500 g EE/cow/day, 501-800 g EE/cow/day, and >800 g EE/cow/day. The effect of lactation stage (early and mid) on the response to lipid supplementation was also evaluated. In general, fat addition had no effect on total DM (P = 0.54) and concentrate DM (P = 0.90). In contrast, pasture CMS decreased by 1.30 kg/day (P = 0.10, DMB = -2.85 to 0.24 kg/day 95% confidence interval, 95%CI). Total CMS decreases by 3.24 kg/d (P<0.01) when inclusion is greater than 800 g/cow/d. Lipid supplementation reduced on average milk fat content by -1.62 g/kg milk (P = 0.03, DMB = -3.10 to -0.14 95% CI), increased milk protein production by 0.03 kg/day (P<0.01, DMB = 0.01 to 0.05 kg/day 95% CI) and lactose production by 0.04 kg/day (P = 0.07, DMB = -0.01-0.07 kg/day 95% CI). Lipid supplementation on average increased C18:2 cis 9, trans 11 content by 2.24 g/kg fatty acids (GA) in milk (P <0.01, DMB = 0.60- 3.87 g/kg GA 95% CI). The best sources of lipids to increase milk production of pastured cows are oilseeds and protected saturated fatty acids and fatty acids. Positive responses to lipid supplementation occurred only in pastured cows at an early stage of lactation. The optimal amount of total ether extract for best responses for pasture cows is between 501 to 800 g EE/cow/day, with a mean marginal productive response was 1.70 kg milk/kg of EE supplemented. Our findings may contribute to improve recommendations for lipid supplementation in diets for pastured dairy cows.