True Absorption of Phosphorus in Sheep Fed Corn Silage and Corn Silage Supplemented With Dicalcium or Rock Phosphate

Abstract

Eighteen male crossbred sheep were assigned to three groups and fed corn silage (CS), corn silage and dicalcium phosphate (CS-DP) or corn silage and rock phosphate (CS-RP). The rock phosphate originated from an igneous deposit located in Cargill Township in Northern Ontario. The endogenous fecal loss of phosphorus (P) was estimated by the isotope dilution method using 32P as a tracer. The total fecal P and total fecal endogenous P increased with increasing P intake. However, the percentage of endogenous fecal P was in the order: CS > CS-DP > CS-RP. The true absorption of P was 75.1, 67.3 and 48.1% for CS, CS-DP and CS-RP, respectively. The availability of P from rock phosphate supplement is much lower than that from dicalcium phosphate supplement. Key words: Sheep, phosphorus, true absorption, corn silage, dicalcium phosphate, rock phosphate

In Situ Dry Matter, Nitrogen and Phosphorous Disappearance of Different Feeds for Ruminants

“…Corn silage may supply 77 to 79% of total dietary P in nonlactating pregnant dairy cows (Martz et al, 1999). It was also reported that the true absorption of P was 80% for lactating cows (Martz et al, 1990) and 75% for sheep (Dayrell and Ivan, 1989).…”

II. Quantitative aspects of phosphorus absorptionin ruminants

“…Even though inorganic phosphates have been intensively studied (from 1957 [38] to 1998 [39]), the results are scarce for forages and concentrates. The authors who studied phosphorus digestive availability of forages have reported values of 0.70 [29], of 0.75 [35] and even 0.80 in lactating cows [40] for corn silage. In contrast, true absorption (alfalfa) for hay phosphorus was found to be only 0.55 [41].…”

“…Improvement of our knowledge of the mineral content of feedstuff [35] and of phosphorus quality [36] is the two keys for improved supplementation [31] and pollution management [37]. Despite its importance in the calculation of phosphorus supply, few experimental findings on phosphorus availability in ruminants are available.…”

The utilization of phytate-phosphorus by the transition dairy cow

“…Endogenous P reaches the intestinal contents by 1) diffusion from blood or interstitial tissue fluid, 2) as part of secretions such as saliva, 3) as a component of cells or cell fragments sloughed off from the intestinal lining, or 4) P contained in phagocytes (Kleiber et al, 1951). Even though the amount of endogenous fecal P loss is directly related to P intake (Dayrell and Ivan, 1989;Field et al, 1983;Scott et al, 1985) there is some unavoidable endogenous loss (Braithwaite, 1983;Braithwaite, 1984;Challa et al, 1989) due to continuous sloughing of cell fragments from the intestinal lining, saliva secretions, and other functions that contribute to endogenous losses. There is also an endogenous fraction that is excreted to maintain P homeostasis, representing P absorbed by the intestine in excess of the need to maintain normal blood P (NRC, 2001).…”