Effects of high selenium forages on reproduction in sheep

Abstract Text: High Se-containing forages grow on seleniferous soils in many parts of world and can cause acute or chronic selenosis in livestock. Anecdotal reports of decreased reproductive rates in livestock grazing seleniferous forages have been reported and it has been speculated that reproductive failure is one of the initial changes of Se poisoning.  However, there is very limited if any information in the literature on the effects on selenium on reproduction in livestock.  The objective of this research was to determine the effect of high Se forages on reproduction in ewes and rams. Ewes were randomly divided into three groups (n = 10) and fed a control alfalfa pellet (< 0.3 ppm Se) or a high Se-containing alfalfa pellet that contained either 10 or 30 ppm Se for 12 weeks. Feeding of the pellets began six weeks before exposing the ewes to rams. Each ewe was exposed to two rams twice each day for two complete reproductive cycles. After the first cycle, significantly (P < 0.05) more ewes were pregnant in the control group (10/10) than in the 10 ppm Se (6/10) and 30 ppm Se (6/10) groups. After a second cycle 9/10 and 6/10 were pregnant in the 10 and 30 ppm Se groups, respectively. In a second study rams were randomly divided into two groups (n = 10) were they were fed either a control alfalfa pellet (containing <0.3 ppm Se ) or a high Se-containing alfalfa pellet (~25 ppm Se) for twelve weeks during which time semen samples were collected weekly.  After twelve weeks of being fed high Se pellets, one testicle from each ram was surgically removed, the rams were then fed a control alfalfa pellet diet (containing < 0.3 ppm Se) and allowed to recover for eight weeks at which time the second testicle was surgically removed for histological analysis.  Rams fed the high Se-containing alfalfa pellet had a decrease in sperm motility and an increase in the percentage of abnormal sperm.  These negative effects were reversed after the rams were fed the regular alfalfa pellets for eight weeks.  None of the sheep in either study demonstrated any clinical signs of Se poisoning during the study.  In summary, high selenium feeds negatively affect reproduction in both ewes and rams.

Keywords: Selenium, Reproduction, Sheep