lucerne and conception

LUCERNE AND CONCEPTION – HELP OR HINDER?

(A REVIEW OF THE LITERATURE) MURRAY LONG

The recent good seasons has seen Lucerne stands rejuvenated and once again supplying unequalled quality feed during the summer months. It has also raised the question of what effect grazing Lucerne during joining has on conception rates with some very low conception rates being reported in recent seasons when ewes were joined on predominant Lucerne pasture. We have suspected and warned breeders that the higher protein levels present in Lucerne seems to interfere with the embryo implant process in the uterus, especially in conjunction with artificial breeding programs but what else could be affecting conception. The fertility problems caused by many species of clover containing oestrogen-mimicking compounds are well known however in Lucerne, concentrations of phyto-oestrogens are affected by environment and the presence of stress and disease resulting in plenty of contradictory information that continually confuses producers. Do not confuse the ‘Clover Disease’ effect on reproduction with that caused by Lucerne.

Lucerne produces coumestrol, a phyto-oestrogenic compound that is known to influence the number of multiple ovulations in sheep and other ruminant species. The highest concentration of this compound is found in Lucerne at the budding stage when environment and nutrition can have significant effects on the growth of the plant. Other stress factors such as pest and disease are also shown to increase coumestrol production in Lucerne, with the plant containing minimal coumestrol unless affected by foliar disease, aphids or fungal pathogens. The ability of Lucerne to resist these outside stresses is affected by humidity, age of the stand, nutrition and temperature and consequently all these can have an effect on the levels of coumestrol in the Lucerne plant.

That is about where the agreement stops in relation to the effect of Lucerne on fertility; little wonder there is much confusion on this topic. Many countries have conducted research on this topic with results ranging from high ovulation rates to markedly decreasing ovulation or halting oestrus altogether. It is possible however that low concentrations of coumestrol in sheep grazing on lucerne have deleterious effects without any visible clinical signs. The trials in many cases however are conducted on fresh lucerne pasture with no mention or evidence of any stress factors involved and conversely several of the studies use pelleted Lucerne or Lucerne hay which could increase the concentration of any coumestrol present. The extreme finding in one study conducted in Spain indicated almost half of the ewes fed a Lucerne based diet showed anatomical changes within the reproductive tract that were permanent if exposure to coumestrol was prolonged. This study also showed smaller ovaries from ewe lambs fed on Lucerne silage however no subsequent difference in ovarian activity was observed.

Research conducted in NZ found a negative linear relationship between coumestrol content of pelleted lucene and the number of ewes with multiple ovulations; feeding a Lucerne pellet diet just 7 days prior to ovulation reduced multiple ovulations markedly. Multiple ovulations were reduced from an average 40.8% to just 4.1% when ewes were fed a diet containing 100ppm of coumestrol. Removing the feed subsequently showed no lasting effects. Further studies have shown that this depression of ovulation rate can be overcome by injection with PMSG indicating a cancelling of any influence on ovulation in an AI program, also suggesting that coumestrol interferes with the release of FSH from the Pituitary gland. A group of ewes fed pellets containing no coumestrol, increased average ovulation rate from 1.43 to 1.83 following an injection of 750iu PMSG whereas ewes on pellets containing  100ppm coumestrol  increased ovulation from 0.98 to 1.53 following the same level of injection with PMSG. There is evidence that high levels of coumestrol actually affect the incidence of oestrus, therefore halting it altogether.

These findings tend to confuse producers who use short term ‘flushing’ on Lucerne prior to joining where research consistently indicates increased ovulation rates when this practice is carried out. However you may suspect that Lucerne carrying a fungal infection or under stress from pathogens would contain some them off Lucerne during joining and if there is stress in the Lucerne stand, don’t flush with that Lucerne. There is no doubt that Lucerne under stress produces coumestrol and this will affect ovulation rate and incidence and result in poor conception. Even without coumestrol, the higher levels of protein in Lucerne will potentially cause problems during joining but will result in higher conceptions if used for flushing only. Poor nutrition, insect attack and leaf fungal infections on Lucerne seems to be the greatest contributor leading to high levels of phyto-oestrogens so if pasture is heavily diseased or nutritionally run down, join ewes away from these stands and after mating, given a few weeks, they can be moved back to the Lucerne. The effect can be diluted by having a grass/Lucerne mix which has been shown to reduce the effect of the phyto-oestrogen. The jury will continue to be out on this one but it does seem from the literature that it is not the Lucerne itself that is the problem but the health status of the Lucerne stand in relation to disease, growth stage, fungal and insect attack and nutrition that causes the Lucerne to generate the problem.

One other area related to medics that research has shown to significantly reduce fertility is a problem caused by a fungus (Fusarium spp.) that produces an oestrogenic compound, Zearalenone, which significantly causes reproductive problems. It has been found in badly stored grain and medic pastures and is preserved once the pasture is made into hay or silage or can be produced by mould associated with mouldy fodder. Sheep are very sensitive to Zearalenone with only 1mg/ day before mating reducing ovulation rates by 20%. Many fertility problems in commercial flocks, especially in Victoria, are now being investigated in relation to this fungus after ruling out clover oestrogens. A vaccine is may become available to counter the effect of Zearalenone.

Let’s hope we get enough rain to have to manage any problems with Lucerne!

 

References:

 DPI Victoria Note Number AG0737,

Dept Ag WA Farmnote 41/2005,

 NZ Journal of Ag Res 22 (1979) 411-416,

IBERS Legumes and Fertility Review 2011/8,

Proc NZ Soc Animal Prod. Vol 40,pp44-49,

J Animal Sc. 1995, 73, 1509-1515