The results of growth performance and carcass trait measurements of male Landrace pigs are presented in Table 3
. The average daily gain (ADG) was not affected by the experimental diets; however, the control group (CON) exhibited a lower ADG compared with experimental groups. The average daily feed intake (ADFI) was not affected by the diet. These results are consistent with recent studies investigating the effects of dietary protein level on growth performance and carcass traits in crossbred pigs [13
]. Furthermore, the carcass traits, e.g., back fat, muscle area and liver and belly fat weights, were not influenced by the different experimental diets, except the hot carcass weight (Table 3
Selected meat quality parameters of the longissimus
muscles of pigs are presented in Table 4
. A number of studies have demonstrated that IMF and subcutaneous fat content might be manipulated independently through dietary means. For example, feeding a low protein diet increases the level of IMF with much smaller effects or no effects on subcutaneous fat content in pigs [9
]. Inadequate dietary protein and/or lysine limit protein synthesis and increase the amount of energy available for fat deposition, resulting in higher IMF. In contrast, the IMF level in the Landrace pigs of the present study was not affected by the reduced protein level or by the use of linseed or sunflower seed oil in the diet. The IMF content ranged between 1.2% and 1.4% (Table 4
). One possible explanation for unaffected IMF contents could be the smaller difference of protein level in the diets (19.4%–19.6% HPD) vs.
15.0%–15.7% in the RPD groups compared with other studies (10%–13% low protein vs.
18%–23% for the high protein diet) [13
]. No significant effects were observed between the different diets for muscle color (L*, a*, and b*), consistent with the results of recent studies by Alonso et al.
] and Guo et al.
]. However, one other study detected higher L*, a* and b* color values in the longissimus
muscles of pigs fed low protein diets due to higher IMF contents and higher concentrations of 12:0 and 14:0 in the muscle, which makes the IMF less translucent and leads to a greater color saturation [19
]. Neither reduced protein level nor dietary vegetable oil supplementation affected shear force (WBSF), pH value or cooking loss of the longissimus
muscle (Table 4
). Our results indicate that the pigs of all diet groups were in good condition pre-slaughter, resulting in normal pH development with a tendency toward better water holding characteristics in the muscles of HPD-LO pigs (lower drip loss). The lack of significant differences in IMF contents between the dietary treatments can contribute to the similar shear forces measured in the longissimus
muscle (Table 4
). Additionally, comparable muscle shear force seems to be a reflection of a uniform growth and development pattern, indicating similar sizes of muscle fibers and IMF contents.
The effects of dietary PUFA supplements, mainly linseed, rapeseed or sunflower seed oils, cake or seeds, on pig performance and fatty acid composition of tissues have been investigated intensively. It is known that feeding a linseed diet increases the n
-3 PUFA content and decreases the n
-3 fatty acid ratio in all tissues, whereas feeding sunflower seed leads to an increase in the n
-6 PUFA contents due to the direct incorporation of the dietary PUFA into pig tissues [7
]. The single fatty acid concentrations of the longissimus
muscle in pigs are shown in Table 5
, and the selected total fatty acid concentrations are presented in Figure 1
. The muscle fatty acid concentrations of the present study appeared to be significantly affected by the diet, resulting in significantly higher n
-3 FA concentrations (up to 113 mg/100 g muscle) in linseed oil-containing high- and reduced protein diets, compared to sunflower seed oil diets; only docosahexaenoic acid (22:6n
-3, DHA) was not significantly increased. In most of the previous studies, the use of n
-3 PUFA-rich vegetable oils showed no or only small effects on the intramuscular DHA level [7
]. Feeding linseed oil-containing HPD- and RPD diets significantly decreased the concentration of single and total n
-6 PUFA in longissimus
muscle of pigs compared with the sunflower seed oil-containing fed groups and the control group (Table 5
and Figure 1
). Consequently, the high level of n
-3 PUFAs, which are beneficial for human nutrition, and the lower level of n
-6 PUFAs in pigs fed linseed oil-containing diets caused a beneficially low n
-3 PUFA ratio in the muscle compared with sunflower seed oil containing diets and the control diet. The n
-3 PUFA ratio was 1.8:1 in muscle of pigs fed linseed oil containing HPD- and RPD diets, which corresponds to the n
-3 PUFA ratio recommended by the German Nutrition Society (≤5:1) [23
]. The concentrations of single saturated and total saturated fatty acids (SFA) were not affected by either the protein content or the type of oil supplement (Table 5
and Figure 1
). Other studies showed that feeding a low protein diet with an increased IMF level resulted in elevated concentrations of 14:0, 16:0 and total SFAs, as a reflection of the higher IMF contents [19
]. Additionally, oleic acid (18:1cis
-9), the most abundant fatty acid in pig muscles, and total monounsaturated fatty acids (MUFAs) were not affected by the different dietary treatments.
Total fatty acid concentrations (longissimus muscle) of Landrace pigs fed different diets.