THE EFFECT OF SELENIUM SUPPLEMENTATION DURING THE EARLY POST-MATING PERIOD ON EMBRYONIC SURVIVAL IN SHEEP

The effect of selenium (Se) supplementation of ewes with blood Se conc entrations ranging between 100-200 ng/ml on embryonic survival during the early post-mating period (days 15-35) was studied in 4 trials. In the 1st 2 trials 137 ewes were used in 1991 and 118 in 1992. After bei ng mated as a single flock these ewes were stratified randomly into 3 groups. One group served as a control, the 2nd was injected with 1 me Deposel (containing 50 mg Se as Ba selenate) and the 3rd group injecte d with 1 me containing 1 mg Se as Na selenite. During 1991, supplement ation was administered immediately after the mating period. It was pos tponed by 14 days in 1992. Parenteral Se supplementation reduced (p < 0.10) the number of ewes that lambed by > 19 % during 1991 but not dur ing 1992. The number of ewes producing twins was unaffected. In Trials 3 and 4 there was a consistent indication that parenteral Se suppleme ntation of pregnant ewes between 15-35 days after mating resulted in a reduced (22-40 %) embryonic survival rate, although significant (p le ss than or equal to 0.10) differences were only observed after the poo ling of treatments receiving parenteral Se supplementation. Drenching of ewes with 50 mg Se as Na selenite resulted in a similar tendency. B iochemical appraisal of the blood, kidney and liver Se status of ewes failed to reveal toxic levels. The possible mechanisms involved in imp aired embryonic survival are unclear. Supplementation of ewes during t he 1st month of pregnancy with parenteral Se preparations is not recom mended.