Analysis of factors affecting milk yield of Ankole cows grazed on natural range pastures in Uganda

Effects of seasonal rainfall (RF) and maximum temperature (T_m) variations on milk yield of Ankole cows grazed solely on range pastures were investigated. The resulting changes in herbage growth (HG), herbage yields (HY), herbage crude protein (CP_h) and neutral detergent fibre (NDF_h), as well as body condition score (BCS) of ten milking cows taken every two weeks were analysed for their correlation with milk yield (MY). Results showed that MY was significantly correlated (P = 0.05) with BCS and NDF_h, but not with RF and CP_h. The correlation with T_m, HY and HG were not significant.

Multiple linear regression analysis showed that milk yield increased with body condition and declined with herbage yield according to the model: MY = 3.70*BCS–3.90*HY–6.67. This implied that throughout most of the year, cows depended on mobilisation of body reserves built in the wet season to meet the requirements for milk production. As herbage matured, milk yield declined because cows could not maintain the dietary quality needed for optimal digestion and feed intake. Cows fed to maintain good body condition yielded more milk. Therefore, to minimise maturity, appropriate stocking rates should be applied to maintain young herbage and sustain milk yield.