Abstract:
In South Africa, Nguni cattle are one of the breeds found predominantly in extensive production systems. In this study the effect of two feedlot diets with different energy levels have been investigated using a transcriptome approach. Twenty Nguni and twenty Bonsmara bulls were fed a low or a high energy diet for 120 days and growth parameters were measured. At slaughter, L. dorsi muscle samples were collected for transcriptome analysis. Performance results showed a higher live weight, carcass weight and marbling score for all bulls fed the high energy diet compared to bulls fed the low energy diet. Diet had a greater effect on the Bonsmara compared to the Nguni according to transcriptomic and phenotypic values. A total of 73 differentially expressed genes were observed between the diets across breeds. The genes that were involved in intramuscular fat deposition (CRHR2, NR4A3, MMD) were expressed on a higher level in the bulls on the low energy diet compared to bulls on the high energy diet. Genes that were involved in muscle deposition (PITX2, Leptin, AVP) was expressed higher in the bulls on the high energy diet. Comparing the breeds revealed that 2214 genes were differentially expressed between the Bonsmara and the Nguni. At the end of the feedlot trial a higher expression of marbling genes (SIRT, ND, ADIPOQ) were observed in the Nguni, however this expression was not observed in the marbling scores recorded. Several genes (ASIP, MOGAT, SNAI3) that were involved in fat deposition were upregulated in the Bonsmara. This suggests that the Nguni was still growing at the end of the feedlot trial while the Bonsmara had reached physiological maturity. An extended feedlot period for Nguni cattle should be considered in future studies. This study provides reference data for differentially expressed genes in muscle of South African feedlot cattle.
