Protein feedstuff with different intraruminal degradability in lamb fattening

The objective of this feeding experiment was to find out how higher or lower intraruminal degradability of the feed protein sources (urea, peas or soybean meal) affect the fattening performance, the carcass value and selected metabolic parameters of lambs. A total of 120 lambs (77 male and 43 female) of different genotypes (purebred Merinolandsheep, cross-breeds of Merinolandsheep ewes with different rams bred for meat) were allocated into four feeding groups. The animals were fattened and then slaughtered at a body weight of 43 kg for males and 38 kg for females. As rations components, straw and four different pelleted feed concentrates were used. The planned increase in ruminal degradability from mixture 1 (group 1) to mixture 4 (group 4) was realized by the choice of different protein sources as well as changing the proportions of the components in the mixture. In mixtures 1 and 2, soybean meal (rumen protected or unprotected) dominated as the protein source whereas in mixtures 3 and 4, peas and urea (supplement) were used as the main source of protein. The consumed feed rations varied between 14 (group 1), 15 (groups 2 and 3) and 16g RP/MJ ME (group 4). The animals in group 1 attained the highest daily weight increase of 333 g/d which was significantly higher than that of animals in groups 3 (300 g/d) and 4 (298 g/d) (p =0.03 and p =0.02, respectively). The animals in group 2 (with their daily weight increase of 325 g/d) tended to be superior to the lambs in groups 3 and 4 (p = 0.09) and p = 0.07). The feedstuff had only a slight influence on carcass value. A significant difference between the groups was noted in the amount of kidney fat. An increased amount of kidney fat was found in the carcasses of animals in group 3 (233 g) in comparison to those of animals in groups 4 (162 g; p = 0.01), 1 (181 g; p = 0.04) and 2 (204 g; p = 0.25). The amount of blood urea increased from group 1 to group 4 (7.3; 9.1; 10.7; 11.5mmol/l). The value for group 4 was significantly different from that of groups 1 and 2 (p = 0.001 as opposed to p = 0.02), while group 3 showed a higher value in comparison to group 1 (p = 0.003). The values for the liver enzymes ASAT and GLDH were above normal in all groups. The values of these enzymes tended to be highest for animals in group 4.

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