Assessing phosphorus overfeeding in dairy cows

• Faecal total phosphorus (TP) from dairy cows consists of a largely insoluble fraction and a soluble P fraction (SP), which mainly represents excess P. The soluble fraction increases proportionately with increased P feeding as excess P is mainly excreted with the faeces in soluble form. Determination of the acid-soluble P fraction in faeces has been suggested as a useful tool to identify excessive P feeding. The overall aim of this licentiate thesis was to gain a better understanding of how different fractions of faecal samples can be used as tools to map P (over)feeding in dairy cows. Paper I studied faecal excretion of different P fractions in 42 dairy cows fed a wide range of rations with varying P content ranging from approximately 70% up to 190% of their requirement. Faecal excretion of TP and SP was determined. The slope of the regression indicated that there was a significant relationship between actual measured SP and indirectly calculated regulated P. TP and SP were correlated and it was suggested that they can both serve as markers of P overfeeding Paper II screened intake and faecal excretion of P on Swedish commercial dairy farms, with special emphasis on comparing farms with organic (N=14) and conventional (N=15) production systems. In each herd, intake of P and other nutrients in feeds was determined for 10 cows in varying stages of lactation. Milk yield and faecal content of P (TP and SP) were also determined for these cows. The results indicated that cows in both management systems consumed more P than they required. However the level of overfeeding was higher for cows in conventional systems. Pooling faecal samples from lactating cows improved the correlation between faecal P concentration and calculated P requirements. SP and TP appeared to be equally good in reflecting P intake relative to predicted requirement. It was shown that slurry samples could be used to evaluate P feeding on herd level. In conclusion, this thesis showed that P overfeeding is greater in conventional dairy herds than in organic dairy herds and that both SP and TP in faecal samples can be used as markers of P overfeeding in dairy cows.

Subject headings

LANTBRUKSVETENSKAPER  -- Husdjursvetenskap -- Husdjursvetenskap (hsv//swe)

AGRICULTURAL SCIENCES  -- Animal and Dairy Sience -- Animal and Dairy Science. (hsv//eng)

Publication and Content Type

vet (subject category)

lic (subject category)