Rape, Ryegrass and turnips. Ewe fertility?

[exmoorromney]

I've got a field of rape, ryegrass and turnips that I'm currently trying to fatten lambs on. If I was to cash the lambs in as stores would I be able to put ewes on it before they went to ram or would the rape affect their fertility? Or how long after tupping could I run the ewes across it to clear it up?

 

[Global ovine]

There are no phyto-oestrogens to upset normal ewe fertility in those three plant species. The cause of such problems occur in plants such as Lucerne (alphalpha) when the leaf is infected with Black Spot fungi, resulting in short term ovulation depression (lowers lambing %) and Red Clover in which some cultivars are high in formanonetin, a different phyto-oestrogen, that accumulates damaging cervical tissues that interferes with sperm transport for fertilisation and causes an increase in lambing difficulties. Neither of these are in your forage mix.
None of those plants will affect embryonic mortality, so good to clean up with ewes during mating and afterwards.

If the forage mix quoted above is currently growing lambs well, ewes will definitely restore their body weight seen in their body condition score which underpins their reproductive performance.
The only problem associated with Rape is nitrite poisoning (causes red blood cells to die) but that is unlikely unless being grazed off as immature plants and also represents the bulk of the forage DM on offer.

What gives the best bang for buck? Fattening lambs in a year of high lamb prices, or ensuring a higher lambing % for next season when the price is still a guess. All prices being equal I would punt on better feeding of ewes as poorer condition affects all aspects of their performance, not just lambing %. However another 10% increase in lamb growth and another 5% increase in lambing % has traditionally had very similar profit outcomes. So when do you want to bank the money, this year or next?