Effects of nitrates and nitrites on the depletion of liver vitamin A stores and carotens utilization in growing-finishing pigs

Abstract

Three trials were conducted using one hundred thirty Hampshire, Yorkshire and Hampshire x Yorkshire pigs to study the effects of nitrates (KNO3) and nitrites (KNO2) in rations on the depletion of liver vitamin A stores and the utilization of carotene in growing-finishing pigs. In Trial I, 50 Yorkshire x Hampshire pigs were allotted to five ration treatments to study the effects of nitrates and nitrites on the depletion of liver vitamin A stores. Prior to the start of the trial the pigs were fed a balanced ration receiving supplemental vitamin A until they reached an average weight of 100 pounds. In Trial II and III, 80 Hampshine and Yorkshire pigs were assigned to five ration treatments to study the effects of nitrates and nitrites, respectively, on the utilization of carotene in growing-finishing pigs. The sources of vitamin A activity for both trials were beta-carotene (3,300 I.U./kg.) for Treatments 1 through 4 and vitamin A palmitate (1,100 I.U./kg.) for Treatment 5. Criteria used to evaluate the experiments were liver vitamin A values (mcg./gm.), plasma vitamin A values (mcg./100 ml.), methemoglobin (gm./100 ml.), hemoglobin (gm./100 ml.), hematocrit (per cent) and the performance (lb.). The feeding of 3% nitrate or 0.3% nitrite significantly (P <.01) depressed gains with or without vitamin A and carotene supplementation. Neither nitrate nor nitrite showed a significant effect on liver vitamin A stores, plasma vitamin A and methemoglobin, regardless of vitamin A source fed. The addition of 3% nitrate to the diet of pigs receiving supplemental carotene or vitamin A did not effect liver vitamin A stores, plasma vitamin A and methemoglobin levels. Plasma vitamin A levels were signifi- cantly reduced (P<.05) by the feeding of 0.3% nitrite receiving either supplemental carotene or vitamin A. Ration containing 0.3% nitrite with vitamin A or carotene supplementation significantly increased (P <.01) methemoglobin values. Nitrate (3% NO3) or nitrite (0.3% NO₂) fed to pigs receiving supplemental vitamin A tended to show a faster depletion rate of liver vitamin A stores and a reduction of plasma vitamin A when compared to nitrate or nitrite-fed pigs receiving supplemental carotene. Hemoglobin and hematocrit remained relatively consistent for the entire trials.