Effects of dietary energy level on productivity of growing yearling male Bonsmara, Nguni and Brahman cattle during summer months

Abstract

A study was conducted to determine the effect of dietary energy level on DM intake, growth rate, feed conversion ratio (FCR), live weight and physiological responses of yearling male Bonsmara, Nguni and Brahman cattle during the summer season. The experimental diets were isonitrogenous but with different dietary energy levels. A complete randomized design was used in all the experiments. The dietary treatments were ME10 (10 MJ ME/kg DM), ME12 (12 MJ ME/kg DM) and ME13 (13 MJ ME/kg DM). Dietary energy level had no affect (P>0.05) on feed intake and live weight of Bonsmara, Nguni and Brahman cattle. Dietary energy level also had no effect (P>0.05) on growth rates of Bonsmara and Nguni cattle; however, it affected (P<0.05) growth rate in Brahman cattle. Brahman cattle on Diet ME13 had higher (P<0.05) growth rates than those on ME12 and ME10 diets. Breed had an effect (P<0.05) on some performance parameters of the cattle. Bonsmara cattle had higher (P<0.05) DM intakes per metabolic weight than Nguni and Brahman cattle in all the dietary treatments. However, Nguni and Brahman cattle had similar (P>0.05) DM intakes per metabolic weight. Bonsmara cattle had higher (P<0.05) growth rates than Nguni and Brahman cattle in all the dietary treatments, the least being Nguni cattle. Feed conversion ratios were similar (P>0.05) between cattle breeds fed Diets ME12 and ME13; however, breed affected (P<0.05) FCR when the cattle were fed on a low energy diet of 10 MJ ME/ kg DM. Bonsmara and Nguni cattle had similar (P>0.05) FCR values when fed on Diet ME10. Similarly, Nguni and Brahman cattle on Diet ME10 had similar (P>0.05) FCR values. Bonsmara cattle had better (P<0.05) FCR values than Brahman cattle when fed on Diet ME10. Bonsmara cattle had similar (P>0.05) DM intakes, growth rates and FCR in all the dietary treatments with increase in ambient temperature. Brahman cattle had similar (P>0.05) feed intake with an increase in ambient temperature for all the dietary energy levels. Growth rates were higher (P<0.05) in Brahman cattle fed a high energy diet (ME13) than those fed on low energy diets (ME10 and ME12). Feed conversion ratios were also improved (P<0.05) with an increase in dietary energy levels at high ambient temperature. Generally, a diet high in energy level had improved FCR of the cattle with an increase in ambient temperatures. Dietary energy level had no effect (P>0.05) on nutrient digestibility and body temperature of the cattle. Cortisol level was similar (P>0.05) in both Bonsmara and Nguni cattle fed diets differing in energy levels; however, dietary energy level had an effect (P<0.05) on the cortisol level of Brahman cattle. Cortisol level was better (P<0.05) in Brahman cattle fed on diets low in energy (ME10 and ME12) than those fed on a diet high in level (ME13). It is concluded that dietary energy level had no effect (P>0.05) on feed intake, digestibility and live weight of yearling Bonsmara, Nguni and Brahman cattle during summer months. However, dietary energy level had effect on growth, FCR and Cortisol level of growing cattle. Similarly, cattle breeds responded differently to increase in dietary energy level.