Nutrient utilization and plasma mineral level in sheep fed diets with different calcium and phosphorus ratios with ragi (Eleusine coracana) straw as a roughage source

Three experimental diets (CP: 20.0%; TDN: 65-67.0%) were formulated using wheat bran, groundnut cake, yellow maize and calcium carbonate to achieve different levels of Ca and P ratios in the concentrate mixture, and fed to 3 groups of sheep of 9 in each group for 150 days period. The diet comprised wheat bran and groundnut cake, which is the normal feeding practice with small holding livestock farmers, diet 2 additionally contained required quantity of calcium carbonate to increase the Ca level, whereas diet 3 contained similar ingredients with part of wheat bran replaced strategically with yellow maize grain to reduce the P level. Weighed quantity of concentrate mixture was offered to each animal to meet 75% of the protein requirement and ragi straw was offered ad lib. as dry roughage source. The intake of concentrate and straw (DM) was in the ratio of 35: 65 in all the 3 groups. The ratio of Ca and P in three concentrate mixtures was 1 : 5.6, 1 : 2 and 1 : 1 for groups 1, 2 and 3, respectively. However, when the total dry matter intake through both concentrate and ragi straw was taken into account, the Ca : P ratios were 1 : 1.01, 1 : 0.76 and 1 : 0.52 for groups 1, 2 and 3, respectively, which was due to higher proportion of P as compared to Ca in concentrate mixtures and more Ca and less P in ragi straw (Ca: P - 1 : 0.05). The DM intake did not differ amongst the groups and the nutrient utilization (DM, CP, EE, NDF) was significantly higher in sheep fed concentrate mixture with Ca : P ratio of 1 : 1 (group 3). Providing excess P with low Ca in concentrate mixture (groups I and 2 - Ca : P, 1 5.6, 1 : 2) resulted in significantly more excretion of P, Mg, Cu, Zn and Co through faeces. The plasma mineral level of P was significantly higher after 150 days of feeding in group 3 fed concentrate mixture having Ca : P ratio of 1 : 1 with a net ratio of 1 : 0.52 in the total DM consumed. The values of other minerals (Ca, Mg, Cu, Zn) did not vary significantly among the groups and the interaction between group and period was also not significant. It was concluded that feeding of concentrate mixture having more of wheat bran/groundnut cake as practiced under field conditions contributed to higher P intake, resulting in its higher excretion in dung besides affecting the utilization of other nutrients. Decreasing the P level in the concentrate mixture through the addition of other energy source like maize and corresponding increase in Ca level through inclusion of calcium carbonate was found to be advantageous.