What’s the impact of a phosphorus deficiency in beef herds?
Phosphorus supplementation in acutely deficient pastures will increase feed intake over the growing season when both energy and protein are adequate and P has become the primary limiting nutrient. Because P supplementation of deficient cattle significantly increases feed intake, cattle numbers must be adjusted to maintain sustainable long-term carrying capacity.
Phosphorus deficiency results in poor appetite and feed intake, poor growth, high breeder mortality rates, reduced fertility and milk production, bone breakage and, in severe cases, bone deformities and peg leg.
Maintaining phosphorus reserves is particularly important for breeder cows when they’re lactating and/or are in the last trimester of pregnancy. Extra phosphorus is required for milk production and for the bones and tissues of the developing foetus. When there’s insufficient phosphorus in the diet, it’s mobilised from the bones, which can increase bone fragility and injuries in stock being handled.
Indicators of phosphorus deficiency
The main pathway of P excretion from the body is faeces. Chemical analysis of faecal P can be a guide if P intake is very low or high, but not in marginal deficiency situations. However, P supplementation must be removed at least two weeks prior to sampling for an accurate measure, which could be highly impractical.
Pasture samples can provide an indication of phosphorus levels, but the animals’ daily grazing selection could mean the samples may not accurately represent the actual plants consumed.
Aim to evaluate the P status of a paddock in normal seasons – avoid exceptionally good or poor years.
Clinical signs of P deficiency such as peg leg are most evident in dry/drought years but the productivity gains apply to all seasons.
Bones are extremely useful indicators of an existing phosphorus deficiency, however, the tests require either a bone biopsy or an X-ray – neither of which are cost-effective or practical for commercial properties.
Supplementing cattle with phosphorus has many benefits, including:
Increased live weight gains
- Feed intake can increase significantly, resulting in improvements in growth rates of young cattle by up to 60kg/year and empty breeder cows weights by more than 100kg/year.
- Sale cattle are able to be sold earlier and/or at heavier weights, as well as at higher values.
- Cattle will grade better and achieve lower ossification scores compared with unsupplemented stock.
Improved reproductive performance
- Replacement heifers attain their critical mating weight sooner and shorter joining periods are achievable, which enhances productivity in young breeders.
- Conception rates in first-calf cows increase, as they’re able to maintain their ideal body weight.
- The increased pasture intake of breeders improves body condition, ensuring increased milk production and weaner weights, better re-conception rates and weaning rates.
Reduced mortality rates
- Mortality rates decrease following phosphorus supplementation. This is directly related to better feed intake and improved body reserves leading into the dry season.
- Higher birth weights and improved milk supply lead to increased calf survival.
Providing phosphorus supplementation where the pastures are deficient not only increases productivity and profitability, but it also ensures better animal wellbeing outcomes.