The influence of supplemental feed protein concentration on growth and carcass characteristics of Short Horn Zebu bulls grazing natural pastures

In Uganda, beef production is mainly based on local cattle breeds like the Short Horn Zebu (SHZ) which graze unimproved natural pastures. Sole grazing on natural pastures cannot meet the annual nutrient requirements of SHZ due to seasonal variability in quantity and quality of the pastures resulting in delayed attainment of market slaughter weight. In order to meet the nutrient requirements of SHZ and hence to shorten the time to attain market weight, we evaluated the effect of providing ad libitum supplements of varying crude protein (CP) levels (90, 110 and 130 g CP kg⁻¹ dry matter (DM)) on the performance and carcass characteristics of grazing SHZ bulls. Ninety-six SHZ (6 ± 2 months old) were allocated to one of four treatment diets including the control T1 (sole grazing), T2, T3 and T4 grazing plus a supplement containing 90, 110 and 130 g CP kg⁻¹ DM, respectively. Crude protein of natural pastures ranged between 103.9 to 158.4 g kg⁻¹DM. Dry matter intake (DMI) varied with month (P<0.001) and increased (P<0.001) level of protein supplementation. For supplemented groups, the supplement contributed more than 75% of DMI even though supplement intake did not vary (P>0.05) with level of CP in supplement. However, CP intake of animals increased with level of CP of the supplement offered. Final live weight and average daily weight gain (ADG) increased (P<0.001) with level of CP in supplement. Feed conversion ratio (FCR) varied (P<0.01) with level of CP in the supplement (13.7 for T4 vs 18.5 for T1). The supplement with 110 g CP kg⁻¹ DM resulted in higher α-linoleic acid and ratio of n6:n3 polyunsaturated fatty acids (PUFAs) in meat compared to meat from unsupplemented cattle. It is concluded that providing grazing SHZ cattle with a supplement containing 110 g CP kg⁻¹ DM improves feed intake, ADG, carcass yield and carcass composition.