The Effects of Supplementing Napier Grass (Pennisetum purpureum) with Rock Phosphate and Steamed Bone Meal Compared with a Commercial Mineral Mix on Phosphorus Absorption in Cattle

Twelve Boran steers with a mean live weight of 215.8±13.9 kg were used in an incomplete Latin Square experiment to compare the apparent phosphorus (P) absorption in cattle when Napier grass (Pennisetum purpureum) was supplemented with Busumbu rock phosphate (BRP), Minjingu rock phosphate (MRP), steamed bone meal (SBM) or a commercial mineral mix (CMM). The steers were housed individually and supplemented with P at 0, 4.5 or 17.5 g P/day. Dry matter intake (DMI) and dry matter digestibility (DMD) were not affected (p>0.05) by the source of P. Live weight gains (LWG) were different (p<0.05) across the sources of P. The coefficient for apparent P absorption from the supplement (CAPA), DMD and LWG decreased linearly (p<0.05) with period. Dry matter intakes were not significantly different (p>0.05) across periods. The level of P supplementation had no significant effect (p>0.05) on DMI or LWG. However, increasing the level of P supplementation significantly increased (p<0.05) the DMD of the basal diet. There was also a significant (p<0.05) source×level interaction for CAPA. The CMM had the highest CAPA, which decreased from 106% to 74.7% with increasing level of P supplementation. For SBM, BRP and MRP, increasing P supplementation also increased CAPA. The CAPA for SBM and BRP and BRP and MRP were not significantly (p>0.05) different from each other. These results suggest that BRP has potential as a source of P for ruminants.     

Maintenance of acquired immunity to Trichostrongylus colubriformis in Merino sheep that are losing weight

SUMMARY The effect of loss of weight on maintenance of acquired immunity to Trichostrongylus colubriformis in Merino sheep was assessed in 2 experiments. Adult Merino sheep with previously acquired immunity to T colubriformis were housed in individual pens. Sheep were infected 3 times weekly with 2000 T colubriformis larvae. A diet based on chopped oaten and lucerne hay (experiment 1) or a pelleted diet based on lucerne hay and grain products (experiment 2), was offered in amounts to sustain a moderate gain in body weight, or was reduced step-wise to cause a loss in body weight. Worm egg counts were determined weekly. The reduction in feed on offer resulted in a mean weight loss of 4.0 kg over 9 weeks (experiment 1) or 4.8 kg over 7 weeks (experiment 2). Based on worm egg counts, there was no indication of a change in immunity to T colubriformis in either of the experiments. These results suggest that acquired immunity to T colubriformis in adult sheep that are exposed to infection is maintained during periods of moderate loss of weight associated with inadequate nutrition.