Symptoms of primary phosphorus deficiency are seen frequently in NSW cattle, when grazing mainly native pastures in coastal, rangelands, and more recently tablelands areas (Cohen 1972, Alcock 2007, Anon 2008, Johnson & Watt 2011). Sheep are grazed on many of these same pastures, yet there has been no clear demonstration of natural phosphorus deficiency in pasture-fed sheep (Radostits el al, 2008).
Cattle affected by phosphorus deficiency show symptoms such as:
Sheep grazing phosphorus-deficient pastures often fail to thrive, but this symptom has been attributed to the concurrent low protein content of the pasture (Radostits el al, 2008). This paper reports marked lameness in sheep on the southern tablelands of NSW, associated with low serum phosphorus.
Sixty mixed-age dorper sheep grazed a 40Ha property about 20km south of Goulburn. The flock had been established for two years on part of what had previously been a fine-wool merino grazing property. It is believed no phosphorus fertiliser had been applied to this block for more than a decade. Eight two- and four-tooth ewes were run exclusively in an eight hectare paddock since joining, and three of these showed marked progressive lameness from between two and four weeks after lambing. Each of them was rearing twin lambs. No lambs were lame, but were thought to be growing slowly due to the loss of condition and subsequent reduced milk production of their dams. The bulky unimproved pasture in this paddock was of poor quality, comprising frosted kangaroo grass (Themeda australis), mature witchgrass (Panicum capillare) and rushes (Juncus spp).
The owner had noticed lameness in one or both forelimbs, progressing to involve all four legs. Affected ewes had a back-sparing stance (rigid arched back with all four limbs drawn closer under the body), and moved with a rapid shortened stride. (photo). They sought to lie down frequently, and were reluctant to move. There were no joint swellings.
Blood samples collected from the three affected ewes in early September showed normal serum calcium and low serum phosphorus (Table 1). The possibility that black-headed dorpers may become vitamin D deficient in winter was investigated, but all three affected ewes returned results within the normal reference range.
Affected ewes were given a subcutaneous injection containing 625mg sodium oxybenzylphosphinic acid (equivalent to 100mg phosphorus, Richtafort Phosphorus/B12). A lick block containing 8% phosphorus was placed in the paddock, but was ignored by the sheep. As the ewes were familiar with hand feeding, a phosphorus/calcium supplement (DCP powder) was added to cereal grain and fed daily to the ewes. The lameness improved markedly within a week, and the ewes fully returned to normal by the time lambs were weaned at 14 weeks of age.
The nature of the lameness was not investigated other than through blood chemistry. Phosphorus deficiency in cattle and sheep causes ostemalacia. This results in osteoporosis and formation of excessive uncalcified matrix leading to lameness, associated with reduced bone density radiographically, and erosions of articular cartilage (Radostits et al, 2008).
Phosphorus level in grasses declines as they mature (Campbell, 1983). This property is in an area where phosphorus deficiency in cattle has been diagnosed (Tablelands LHPA data on file). It is likely that young dorper ewes attempting to rear twin lambs would have a higher phosphorus requirement than the small-framed merino sheep previously grazing this property. In addition, there would have been insufficient protein and energy available to these ewes from this poor quality pasture to support lactation. Catabolism of body tissues including bone resorption would increase (Ternouth and Budhi, 1996), further reducing bone density.
There has been significant subdivision of larger rural holdings in this district during the past two decades, with more than 50% of holdings now below 50.1Ha in size (Tablelands LHPA data). It is anticipated that more cases of phosphorus deficiency will be seen in the district with the increasing popularity of dorper sheep and boutique cattle breeds on these smaller holdings.