|
Oestrogens in pasture, hay and silage | AG0737 |
Kevin Reed, Hamilton
October, 2001 |  |
To view the Adobe Acrobat file, you will need the Adobe Acrobat reader. |  PDF 35 kb | |
This Agriculture note explains oestrogens, their affect on reproductive performance of cattle and sheep, and current research efforts.
Introduction
Poor reproductive performance by sheep and cattle can be caused by their consumption of oestrogenic hormones (oestrogens). Oestrogenic hormones may be produced either by pasture legumes (plant oestrogens or phytoestrogens), or by soil-borne fungi that live on pasture plants or on dead and decomposing organic matter/litter at the base of pasture. The latter are called fungal oestrogens or mycoestrogens. In Victoria, mycoestrogens may be more widespread than phytoestrogens but the most serious problems recognised to date have been related to phytoestrogens in subterranean clover.
Oestrogens and infertility
Infertility has often been recorded in sheep grazing on swards dominated by oestrogenic legume cultivars. This is associated with the breakdown of sperm transport in the uterus. Cysts form in the uterus and cervix and the uterus does not contract normally at parturition. Dystocia and other reproductive problems have been observed. These problems are usually referred to as clover disease. Sheep are affected but reports regarding cattle are rare. Problems with sheep have been particularly severe in WA, SA and NSW.
Phytoestrogens in pasture, hay and silage
Phytoestrogens produced in clovers include formononetin, daidzein, biochanin A and genistein.
Red clover
Phytoestrogens are commonly high in red clover but Australian plant breeders have developed low oestrogen cultivars that are safe to use with breeding livestock. These are the public cultivars Redwest and Redquin. Red clover cultivars that contain oestrogen include Grasslands Pawera, Grassland Hamua, Grasslands Colenso and Quinequali.
Subterranean clover
Sheep infertility has also occurred from grazing on subterranean clover. New improved cultivars of subterranean clover developed within the National Annual Legume Improvement Program (NAPLIP), emerge from plants that have been carefully screened for oestrogens. Only clover that is low in oestrogen is released. However several old public cultivars of subterranean clover contain high oestrogen concentrations, especially Yarloop, Dwalganup, Dinninup, Geraldton and Tallarook.
It is important to buy only certified seed because uncertified seed has often been highly contaminated with these cultivars. For example, uncertified "Woogenellup" seed has often contained a high proportion of Dinninup or Dwalganup. Woogenellup, Seaton Park and Clare have also shown slight oestrogen activity in ewes. Uterine cysts formed depending on the level of oestrogen intake.
In the high-oestrogen cultivars of subterranean clover, oestrogen concentration is increased by nutrient deficiency (low phosphorus and low sulphur), by disease (eg red leaf virus in sub clover) and by waterlogging and drought or moisture stress. If such clover is conserved as hay or as well-made silage, their oestrogenic potency is maintained.
Medicago species
Coumestan phytoestrogens may be produced in Medicago species - both annuals and lucerne. In medics, the concentration of coumestans is increased by fungal disease.
Mycoestrogens in pasture, hay and silage
Several fungal species (especially Fusarium spp.) produce the oestrogen, zearalenone. Zearalenone and substances that it breaks down to, zeranol and talerenol, elicit significant oestrogenic activity. The fungi that produce zearalenone have been found in poorly stored grain, as well as in New Zealand pasture, and have been shown to cause reproductive problems in pigs, cattle and sheep.
New Zealand workers found that Fusarium growth was greatest during the drier months, summer and autumn. They have found that ewes are particularly sensitive to zearalenone. An intake of 1 mg/day before mating can reduce ovulation rates by 20%. New Zealand workers report that zearalenone ingestion shortened the oestrus cycle, lengthened the period of oestrus, reduced the number of eggs shed per oestrus, and reduced the proportion of eggs fertilised. Zearalenone has also been detected in pasture hay, and in well made silage that did not contain any significant population of the zearalenone-producing fungi commonly found with mouldy fodder.
That is, the zearalenone found in pasture can be preserved in the hay and silage conserved from it. On farms, they found evidence that grazing sheep ingest zearalenone in amounts sufficient to reduce reproductive performance. This has been demonstrated by the high levels of zearalenone metabolites detected in the urine of ewes in flocks with histories of low lambing percentage. New Zealand workers have also detected zearalenone residues in the blood and urine of cattle - in herds with low conception rates. This is of interest in Tasmania and Victoria where, in the past, infertility syndromes in cattle have proved to be unassociated with clover oestrogens.
Zearalenone Research
Victorian research
At the Pastoral and Veterinary Institute, Hamilton, research workers have detected zearalenone in most pastures sampled across south-west Victoria during autumn-winter surveys conducted in 1999 and 2000. Zearalenone concentration exceeded 1 mg/kg on 20% of pastures in the random surveys (Table 1). New Zealand workers suggest that when zearalenone levels exceed 1 mg/kg, sheep fertility may be affected. At this stage we have not documented conclusive proof that zearalenone in Victorian pasture has been a cause of poor fertility.
Table 1. Zearalenone concentration in Victrian and New Zealand pasture: proportion of pastures (%) within designated bands.
Zearalenone mg/kg dry matter | SW Victoria | New Zealand |
| 2000 | 1992 | 1993 |
0 - 0.29 | 44 | 24 | 8 |
0.3 - 0.9 | 29 | 51 | 69 |
1.0 - 2.9 | 19 | 22 | 21 |
>3.0 | 8 | 11 | 10 |
No. of pastures | 59 | 372 | 494 |
New Zealand research
Research in New Zealand has shown that (1) fodder crops including brassicas and chicory provided a low risk of zearalenone ingestion provided they were kept free of weeds; (2) vaccine treatment of ewes may overcome the effects of zearalenone and raise ovulation rate; and (3) a fungicide applied to pasture may raise pregnancy rate. Research is needed before vaccine treatment or fungicide application can be recommended in Victoria.
Analysis for Zearalenone in your pasture and fodder samples
Pasture and fodder samples can be tested for zearalenone at the Department of Primary Industries, Pastoral and Veterinary Institute, Hamilton. For further information re: collecting and transporting samples telephone (03) 5573 0900.
The advice provided in this publication is intended as a source of information only. Always read the label before using any of the products mentioned. The State of Victoria and its employees do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this publication.
|
