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Sheep Pasture and Red Clover – Again

by Ulf Kintzel
A while back I wrote an article for Farming Magazine “Red Clover in Sheep pasture?” in which I advocated grazing red clover even during breeding season. I wrote a similar article for Small Farm Quarterly’s winter 2013 issue “Does Red Clover Cause Infertility in Sheep?” shortly thereafter. Let’s recap the premise: It is said that red clover causes infertility in sheep when grazed during breeding season due to an estrogen-like substance called phyto-estrogen. However, I have not experienced such negative effect at all. Since red clover offers so many advantages, I just kept grazing it, including during breeding season. Yet, I always had in the back of my mind if it was a responsible thing to do, advocating grazing it while the sheep are being bred.

Red clover was the dominant grazing plant during breeding season last fall

Red clover was the dominant grazing plant during breeding season last fall

In at least one of these studies examining the influence of red clover it was suggested that the effects of this estrogen-like substance are less when the clover is higher and is in bloom. This is when I graze it on my home pasture but I have always wondered if one would need to be more careful if the clover is younger and shorter and before bloom. It so happened that during my second breeding season of the year I was pasturing my sheep on the neighbor’s field most of October and into November.
Guess what one of the incomes this farmer has from his farm. Growing medium red clover for seed production! Since I took lots of pictures during that time it is easy for me to check what the sheep ate at what dates and how the lambing percentage corresponds with that time. Leading up to the onset of breeding season I had already been grazing on his farm for 19 days. The fields I grazed were either small pieces of straight red clover or old hay fields that had been frost-seeded with this legume and then harvested. The re-growth of this legume was considerable. I would estimate that during that time the intake of red clover was never less than 50 percent. From there I moved to several pieces that were not always full with red clover and had some orchard grass and alfalfa. However, since this farmer had been doing red clovers seed for many years and since this is upstate New York, there always is red clover EVERYWHERE. From these small pieces I moved to one large parcel with 80 to 90 percent of this legume, only interspersed with some weeds and some small wheat plants that had germinated after harvest. In addition to its abundance, the red clover was also quite short. (By the way, clovers tolerate close grazing after the onset of dormancy very well). Grazing this large clover field during breeding season happened to correspond with the height of my lambing season in March but more about that later.
I use a harness with differently colored crayons during breeding season. I do this in order to know what ewes where bred at what time by which ram. This is important to me for various reasons, one being my management of my lambing season and another being the fact that I need to be able to sell groups of ewe lambs with unrelated ram lambs for breeding purpose. In short, I can’t just throw all my rams into the flock without knowing who is breeding whom and when. Once breeding season is concluded I let the flock go through the chute and mark the ewes with a dot on the wither with a spray paint designed for sheep. I use the same color spray as the crayon color. The crayon marking will disappear after some time while the spray paint will last the next five months until the sheep lamb. When I did this I noticed 16 ewes without any marking. That is eight percent of my breeding ewes and it was seemingly a worrisome sign. I did have the short red clover in the fields in the back of my mind when I ran the sheep through the chute that day and it kept being there all throughout winter.
Fast forward five months and we are in my spring lambing season. (Half the flock had already lambed in February. The lambing percentage was almost 170 percent. While that is at the lower end of my expectation, it still is a respectable result that I can live with. These sheep had grazed mostly orchard grass and white clover while breeding.) Lambing season in March started slowly. Instead of the five ewes on average per day, I had three or sometimes four sheep lambing a day. I was wondering why that was. (I figured out later that the onset of the second breeding season must have been almost exactly two cycles later than the first one and therefore a smaller percentage of ewes was coming into season the first ten days, which was the length of the first breeding season). Then, ten days later, it hit. 19 sheep and goats were lambing and kidding the same day. It so happened that our kids had school spring break and were home for a week. They were a great help. Between lambing and my regular chores, I was a bit overwhelmed. The next day I still had a large number of sheep lambing and then it tapered off a bit to the five on average I had anticipated. As it turned out, all ewes without markings from the breeding the previous fall were pregnant. The green-colored crayons I had used had not been working properly, were probably too dried out. The lambing percentage was overwhelming. As of this writing it stood at 185 percent.
However, if I select out the lambs from last year that I also let breed the same year they are born, the lambing percentage stood at 195 percent for all ewes two years and older. This does not include the still-born lambs, which would have to be added to evaluate conception rate and if and how the red clover influenced it negatively. In addition, as of this writing a single ewe seems to be empty and will not have lambs. All others were pregnant.
So I can now say with even more certainty that I have not experienced any negative effects with grazing red clover during breeding season, even when it is quite short and not blooming. In fact, the quality of the legume is quite possibly a big contributor for such tremendously good lambing percentage. I readily admit that I am still left to wonder if other breeds are perhaps easier affected. I also speculate at times if I had over the years inadvertently culled those sheep that were indeed sensitive to grazing red clover during breeding season when I culled the few sheep each year that didn’t have any lambs. However, the numbers – in some years as low as one – are just too low to think that red clover may have been the culprit.
I found this story was worth sharing. I breathed a big sigh of relief that I could let my previous articles about grazing red clover with sheep during breeding season stand. Or was that sigh of relief more about the fact that my lambing season was not negatively impacted? Whichever it was, I will graze away that red clover. It is nutritious, highly digestible, and well-liked by sheep. I will keep ignoring the inevitable future articles in the leading sheep publications that will warn me once again about the danger of grazing it during breeding season.
Re-printed in part from the spring 2016 issue of “Farming Magazine”, Ohio
Ulf owns and operates White Clover Sheep Farm and breeds and raises grass-fed White Dorper sheep and Kiko goats without any grain feeding and offers breeding stock suitable for grazing. He is a native of Germany and lives in the US since 1995. He farms in the Finger Lakes area in upstate New York. His website address is www.whitecloversheepfarm.com. He can be reached by e-mail at ulf@whitecloversheepfarm.com or by phone at 585-554-3313.

Claire Cekander


  1. Maureen Sullivan on October 18, 2016 at 1:12 pm

    I work as a nurse midwife. Estrogen surges during pregnancy. I never understood why clover, with high photo-estrogen content, would be an issue!
    Dreaming of my own flock someday.

  2. Grond The Wolf's Head on April 4, 2021 at 7:02 pm

    I am so tired of this study being used for the “soyboy” nonsense.

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