Effect of level of dietary calcium and phosphorus on the site of absorption and utilization of phosphorus in gestating and lactating ruminants

Abstract

Two digestion trials were conducted to determine the effect of level of Ca and P on the site and extent of absorption of P in gestating and lactating ruminants. Gestating Nubian dairy nannies (n=8; 41-55 kg) with abomasal cannulas were used in the gestation feeding trial, which consisted of three 20 d dietary treatment periods. Nannies were randomly assigned to the following dietary treatments of Ca and P: 1) Ca 0.4%, P 0.3% (LCLP), 2) Ca 0.8%, P 0.3% (HCLP) and 3) Ca 0.8% and P 0.6% (HCHP) in a replicated 3x3 Latin Square designed experiment. Reassignment of diets during subsequent periods assured that animals would not consume a diet they were previously exposed to. All diets contained 0.25% chromium oxide as a digestive tract marker. Limestone and monocalcium phosphate were utilized to supply the necessary Ca and P. Six d sample periods were used to collect diets beginning on d 13 of each period, refusals beginning on d 14 and abomasal digesta and feces beginning on d 15. Blood was collected 3 h post-feeding on d 20. Nannies fed HCLP had more (P<.05) Ca passing the abomasal cannula than LCLP. Animals fed HCLP excreted more (P<.05) Ca in the feces than those fed LCLP, while increasing dietary P intake had no effect (P>.05) on fecal excretion. Increasing dietary P in the presence of elevated Ca decreased (P<.05) serum Ca. Feeding high Ca in the presence of low dietary P increased (P<.05) serum inorganic P. The lactation feeding trial consisted of two 20 d feeding periods. At parturition, nannies (n=3) from the gestation feeding trial were assigned to one of two dietary treatments of Ca and P: 1) HCLP and 2) HCHP. In addition to samples previously described, milk was collected to determine 24 h milk production and Ca and P concentrations. No differences (P>.05) were detected between dietary treatment groups because the desired P intake was not achieved. These data suggest that dietary Ca levels may be increased with increasing Ca requirements for gestation and lactation without increasing P to maintain a 1.5:1 to 2:1 ratio.