If we don't see any clinical signs, and may not get any obvious results from supplementation, when and why should we recommend supplementation to the producers?
Selenium is the most common trace element deficiency seen in the Lower Hunter, however, both copper and selenium deficiencies have been widely diagnosed. In non supplemented cattle we see the GSHPX levels bouncing along below or near the accepted normal range 40-300 and it takes very little changes in pasture conditions to push these stock into the clinically deficient zone. The importance of selenium in the immune system is well documented. That said, I have not recognised white muscle disease in this area and clinical manifestations of selenium deficiency are often left to the "real believers", or as some would say, the imagination.
My first involvement with selenium trials in the lower Hunter was with a dairy supplementation trial run by Diane Ryan in 1985.-44% of dairy herds were shown to have low selenium levels from vat samples and 12 herds were selected to take part in the trial- I was involved with one of those herds.
The results indicated that low selenium may be involved with RFM's and increased mastitis levels - but the results seemed marginal and inconclusive.
Subsequently I looked at selenium levels and low fertility levels in a small dairy which produced encouraging results with supplementation.
I have tried copper and selenium supplementation in a vealer group with no obvious benefits in weight gain, so for many years I let selenium take a back seat.
Copper is the other trace element we see we see as causing possible problems in the Lower Hunter. The difference is that copper deficiency is usually obvious with yellow coat colour, ill thrift and possibly scouring (Figure 1). Supplementation will produce a visual response.
A couple of years ago I was asked to look at a group of vealers that weren't doing very well. Blood tests collected on 24 November 2010 revealed marked selenium deficiency with GSHPx levels averaging 9.5 U/gHb (range 2-30). One of 11 blood copper levels was below the normal range. These weaners were treated with barium selenate, the long acting product-reported to last for 18 months. We retested these vealers on 16 March 2011. GSHPx levels at this time averaged 191 U/gHb, a marked improvement.
An issue with previous supplements, oral pour-on or injectable, is the length of action - probably 4 to 6 weeks. Due to the seasonal variation of selenium levels in the pasture, the short-acting ones may not be effective when required, unless they are continually retreated.
These young cattle appeared to respond to treatment. The breeding stocks were also supplemented. It was apparent that the calves of treated cows also had adequate GSHPx levels. A sample of cows showed average GSHPx levels of 135 U/gHb while their one month old calves averaged 110. As you can see their young calves had very good selenium levels.
We started to look at selenium levels in three low fertility beef herds, supplementing these, and comparing pregnancy rates the following year. These were also very encouraging. This data has been put together by veterinary students and titled "Will Selenium supplementation improve the reproductive performance in beef cattle". This will be made available at a later date.
When the opportunity arose I looked at selenium levels in other clinical cases.
In October 2012 I looked at selenium levels in a severe pinkeye outbreak in vealers still on the cows-we bled 11 cows and calves and bulked the samples for cost reasons. Tests showed that the calves averaged 9 U/gHb while the cows averaged 8. This property also lost about 10 very good well grown calves from theileria.
The following year, after selenium supplementation of the breeders, no losses from Theileria or pink eye were reported. A blood sample taken from a calf that look a bit "doughy" gave a selenium level of 339, and the lab reported "Theileria negative but some evidence of regeneration on smears". The cow had a level of 250 U/gHb. Is this evidence that the immune system has defended against a theileria attack?
However, when I started looking at selenium levels in other theileria cases I questioned why some local bred calves were affected and others were not? I also continued to see calves in excellent condition with very low selenium levels and sometimes poor claves with very low selenium levels.
In a case investigated by a private veterinarian, looking at cattle on improved pasture and generally in good condition but with dull coats, the blood results showed copper normal levels but low selenium levels (averaging 6U/gHb).
This property also lost very good calves with theileria and pasteurella.- multiple disease problems with very low selenium a common factor. Is some other stress, or challenge involved and the low selenium levels are affecting the immune system?
Many products now contain selenium as an additive - drenches, vaccines. I have seen GSHPx levels in goats up to 400 with no clinical signs-the levels were high due to the selenium in the drenches and vaccines -they were getting continually topped up but were unaware of the selenium levels. Herein lies the danger.
Case report, possible selenium intoxication
Recently I investigated deaths in a mob of 140 steers. They were doing it tough nutritionally. Paddocks low in feed [very short rye and kikuyu] and cattle poor (Figures 2,3). Cattle had been brought to the yards to rotate paddocks. They were given Multimin, Flukazole and Cydectin LA.
The stock were moved into the new paddock and started to die the next day - there were 20 dead when I was asked to look at the problem. Total deaths were 50, over 4-5 days. The GSHPx from a live animal and a dead one were: GSH PX U/gHb 199 [live] 240 [dead].
The liver felt firm and rounded edges and haemorrhages in heart - very similar to green cestrum poisoning (Figures 4, 5). Two selenium pellets were found in the reticulum. A range of samples collected including fresh liver for selenium levels.
The striking lesion is the periacinar hepatic necrosis, which is commonly caused by ingested toxins such as that contained in green cestrum and the blue green algae group. The wet concentration of liver selenium was 145umol/kg = 11.4mg/kg and 102umol/kg =8mg/kg. Dry weight is roughly 3 times thisi.e.. about 30 mg/kg. These concentrations are consistent with acute toxicity.
Values of 20-30 mg/kg (probably dry weight though it is not stated) are given for liver selenium in sheep with chronic selenosis. It is also claimed that "clinical illness is evident at blood levels of 3 mg/kg".
It was concluded that there was marked hepatic necrosis which was multifocal periacinar, acute and severe with replacement haemorrhage. Liver selenium concentrations were within the toxic range.
This was a bit of a jolt and a reminder that selenium can be toxic. I am still to get some information on these deaths but note the circumstances - poor cattle in drought and already treated with Se pellets - the manager also unaware of selenium in the products given.
An article in the Australian dairy farmer December 2013, shows that the Irish are all over this selenium supplementation. Is selenium - enriched milk the next best thing? So how much of a good thing can you have? Selenium on your weet-bix?