Influence of different lipid supplements and frequencies supply on microbial protein synthesis in beef heifers

Abstract

Increasing the energy density of the diet by adding lipid sources is a nutritional strategy that is used for finishing cattle, which leads to satisfactory performance. The use of lipids in ruminant diets has been recommended because by reducing methanogenesis the energy efficiency is improved. There are several ways to provide lipids to the diet, which includes grain, oil and calcium salts. According to Allen (2000) the main problem of using lipids rich in unsaturated fatty acids (UFAs) in diets for ruminants is their effect on intake and, consequently, on ruminal digestibility of the fibrous fraction. Also, diets rich in cereal grains cause a pH decrease in the rumen, which inhibits lipolysis and biohydrogenation. To avoid the negative effects just described, the lipid supplement in the form of protected fat has been recommended for ruminants because it is considered an inert ruminal fat source (Harvatine and Allen, 2006). However, the use of fat supplementation is more typical for feedlot cattle than for grazing cattle. In addition, there are only few data on effects of fat supplementation on grazing cattle (Brokaw et al., 2001; Krysl et al., 1991). Likewise, reducing the fat supplementation frequency for grazing cattle, due to great territorial extension in some cases, may enhance logistic management in the farm. Thus, the objective of this study was to evaluate the effects of different lipid sources supplemented daily or thrice weekly on microbial protein synthesis of grazing heifers.