Deficiency of phosphorus is usually primary and is widespread under natural conditions. It is characterized by pica, poor growth, infertility, and osteodystrophy in the later stages. Post parturient haemoglobinuria is also associated with phosphorous deficiency in cattle.
Aetiology: The phosphorus deficiency is usually primary, which is exacerbated by the excess of calcium and deficiency of vitamin D. Low phosphorus and excess levels of iron or aluminium or calcium in soils predispose incidences of phosphorus deficiency. Heavy leaching by rain, and drought conditions also contribute to low levels of phosphorus in soil.Secondary phosphorus deficiency is of less importance. The deficiency of vitamin D and excess of calcium in diet may contribute to phosphorus deficiency, particularly when the phosphorus intake is marginal. The presence of phytic acid in plant tissues is an important cause of secondary phosphorus deficiency in pigs. Supplementation of magnesium to prevent lactation tetany may precipitate hypophosphataemia in dairy cows when availability of phosphorous is low.
Clinical findings: Nearly 80-85% of phosphorus in the body is found in skeleton, where it provides strength to bones in combination with calcium. Bone also acts as the reservoir of phosphorous. Phosphorus is essential for broad range of enzymatic activities, transfer of genetic information, various buffering systems, maintenance of integrity and structure in the form of phospholipids and most importantly mineralization of bones and teeth. The signs observed in phosphorus deficiency are the outcome of the disturbance in one or many of these functions.
Primary phosphorus deficiency in cattle causes failure to reduced growth and rickets in young calves. Mature cattle show reduced feed intake, low milk yield and infertility accompanied by anoestrus, sub-oestrus, and irregular oestrus. The sexual maturity is delayed. Osteomalacia and reduced bone weight are also found in adult cattle.Unthriftiness, failure to gain body weight, reduced feed intake, allotriophagia,abnormal stance and locomotion, rough hair coat, and reduced bone weight have been noted in cattle suffering from phosphorus deficiency. The animals have narrow chest with weak ribs, and small pelvis. Stiffness in forelegs causes characteristic lameness referred to as ‘styfsiekte’ or ‘creeps’ or ‘pegleg’. High-yielding cows may become recumbent in early lactation and are unable to stand. Osteophagia is common in phosphorus deficient cattle and may be associated with outbreak of botulism. Sheep and horses in phosphorous deficient areas are of poor stature and show perverted appetite.
Diagnosis: Phosphorus deficiency is diagnosed on the basis of phosphorus content in diet, pasture and drinking water. Total phosphorus intake by an animal can be determined by estimation of the mineral in faeces. Bone ash concentration and calcium and phosphorus contents in ribs are good estimates of phosphorus and calcium status in an animal serum inorganic phosphorus concentration below 4 mg/dl in cattle indicates hypophosphataemia due to phosphorous deficiency.
Treatment and prevention: Deficiency of phosphorus can be treated by dietary phosphorus supplements such as bonemeal, di-calcium phosphate, di-sodium phosphate, sodium pyrophosphate. However, use of phosphorus supplements in the diet is not without risk. Complicated cases of parturient paresis with hypophosphataemia in cattle can be treated by intravenous administration of sodium acid phosphate (30 g in 300 ml distilled water).Phosphorus deficiency in grazing animals can be prevented by supplementing diets with phosphorus or by adding phosphate supplements in drinking water. An intake of phosphorous @ 0.36-0.4% of dry matter is recommended for dairy cattle. But this level may vary depending upon stage of production cycle, and under different grazing systems. Breed of cattle, feeding practices, possible interactions between nutrients and parasitism also influence phosphorus requirement. Many dairy farmers supplement rations with excess phosphorus to improve milk yield, but studies have shown that over supplementation of phosphorus did not improve milk production or reproductive performance of dairy cows. Excess feeding of phosphorus to livestock is also looked with environmental concern, since high phosphorous levels in manure may pose problem of environmental pollution.