The effect of dietary lipid saturation and antioxidant source on the nutrient digestibility of lamb finishing diets

Abstract

________________________________________________________________________________ AbstractThe influence of a synthetic or natural antioxidant and lipid saturation on the apparent digestibility of nutrients in a standard lamb finishing diet was investigated. The four dietary treatments consisted of the same basal diet, providing 187 g CP-, 355 g NDF-and 71 g EE per kg DM, but differing in supplemental lipid source (30 g/kg of either saturated beef tallow or unsaturated soybean oil) and type of antioxidant included (125 g/ton of either a synthetic or natural antioxidant). The digestibility study was conducted over a period of 12 days (including a 4-day adaptation to the faecal collection bags). Twenty-eight S.A. Mutton Merino lambs (45.1 ± 3.0 kg) were randomly allocated to the four dietary treatments (n = 7 lambs/treatment). Composite feed, feed refusal and faecal samples of individually penned lambs were collected for chemical analysis. The apparent digestibility coefficients, digestible nutrient and available energy content were calculated accordingly. The DMI of the lambs did not differ significantly between the various experimental diets. The inclusion of unsaturated soybean oil reduced the apparent digestibility of NDF in the diet. The apparent digestibility of NDF seems to be higher when a natural antioxidant was included in the diet. The comparatively negative effects of the unsaturated lipid source and synthetic antioxidant on the apparent digestibility of NDF were associated with a significantly lower digestible NDF content in the experimental diet. Accordingly, soybean oil resulted in a significantly lower ME content in the diet. However, estimating ME from DE with a constant factor of 0.8 probably underestimates the ME content of diets supplemented with lipids rich in unsaturated fatty acids. The latter are known to reduce methane production, and hence, energy losses. _______________________________________________________________________________________

Effects of dietary beef tallow on performance, rumen fermentation, carcass traits and meat quality of growing lambs

“…In agreement with the current results, previous studies using grain-based diets and BT at 40 g/kg DM have shown that the added fat did not affect growth performance and ruminal fermentation in finishing beef cattle (Guerrero et al, 2016;Lopez et al, 2016). Moreover, in finishing lambs, saturated beef tallow (30 g/kg DM) has been shown not to affect DMI (Booyens et al, 2013). Steers fed diets based on steam-flaked corn and supplemented with 0 and 40 g BT/kg DM also had similar rumen pH values, VFA molar proportion and ammonia N concentrations (Montgomery et al, 2008).…”

The effect of dietary lipid saturation and antioxidant type on the performance of finishing lambs

“…From the results (Table 1) it would seem that lipid saturation and antioxidant type had no-significant (P >0.05) influence on the dry matter intake (DMI) of the lambs. This was expected due to the similar dietary nutrient composition, especially NDF content (Booyens et al, 2013). It was evident that a lipid x antioxidant interaction (P <0.05) occurred for the metabolizable energy intake (MEI) of lambs.…”

“…As the inclusion of an unsaturated lipid source has a negative effect on fibre digestibility due to its antimicrobial (Palmquist & Jenkins, 1980) and coating (Firkins & Eastridge, 1994;Harris, 2003) effect, it could result in less energy being lost as heat in the rumen -resulting in more energy being available for productive purposes by the animal. The reduced production of ruminal CH 4 within the unsaturated treatment, as reported by Booyens et al (2013), could also contribute to the nonsignificant differences recorded. Therefore, both the heat increment of fermentation, as well as CH 4 production was probably reduced by the unsaturated lipid source, resulting in the non-significant differences.…”

“…In contrast with the natural antioxidant, the inclusion of unsaturated soybean oil in the diet containing a synthetic antioxidant resulted in a significantly lower (P <0.001) MEI. This lower energy intake of the lambs could probably be explained by the negative effect of an unsaturated lipid source on fibre digestion and the ME content of the experimental diets, as recorded by Booyens et al (2013). The non-significant (P >0.05) effect of the unsaturated lipid on the MEI of lambs when a natural antioxidant was included in the diet is difficult to explain.…”

“…This could be attributed to the lower (P <0.05) ME content of the unsaturated soybean oil diet (Booyens et al, 2013), and non-significant (P >0.05) differences in DMI and ADG between lipid sources. From Table 1 is it clear that the source of antioxidant did not influence (P >0.05) the efficiency of ME utilisation by the experimental lambs.…”