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Background: Monogastric animals like pigs need easily digestible phosphorus sources. Therefore is it necessary to add inorganic phosphorus originating from mines to a vegan diet. However, the price of phosphorus increased heavily in the last years. Moreover, phosphorus supplementation of feed causes an increase of the phosphorus content in the natural fertilizers.
As a result, especially areas with a high animal-arable land ratio are often oversupplied with minerals like phosphorus and nitrogen. The subsequent washing out of minerals into natural water resources raises their nutrient content with dramatic environmental consequences.
By adding the enzyme phytase to the porcine diet, inorganic phosphorus can be liberated from the plant phosphorus source phytate in the gastrointestinal tract. Thus, the amount of digestible phosphorus increases while expensive and limited resources of inorganic phosphorus can be saved.
Objective: The objective of this study was to test whether a greatly P-reduced diet (test group) impairs the development of fattening pigs when fed from weaning to slaughter. A standard P-reduced diet as commonly used by self-producers in Westphalia was given to the control group. All data were intended for testing the effects of the factors diet, sex and daily weight gain (above-/below-average).
Methods: During piglet rearing, animals were fed with two-phase dry feed (control group: P 5.9/4.8 g/kg, Ca 8.3/6.9 g/kg, phytase 500/500 FTU/kg; test group: P 4.5/4.5 g/kg, Ca 5.8/6.6 g/kg, phytase 1000/1000 FTU/kg). In the fattening stage, pigs were three-phase liquidly feed (control group: P 4.6/3.6/3.8 g/kg, Ca 10.3/5.3/4.7 g/kg, phytase 500/500/
250 FTU/kg; test group: P 4.0/3.4/3.4 g/kg, Ca 6.8/5.1/5.3 g/kg, phytase 1000/1000/500 FTU/kg). No inorganic phosphorus was added to the diet of the test group for animals above 40 kg body weight (BW). Fattening performance traits and index point per kg carcass weight for the assessment of the carcass quality were obtained, as well as the serum concentrations of the bone markers osteocalcin and β-crosslaps at 40 kg and 110 kg BW. After slaughtering at approximately 120 kg BW, the breaking strength and composition of metacarpi III were analyzed.
Results: The greatly P-reduced diet did not affect the carcass and fattening performance traits statistically significantly during the piglet rearing and fattening stage. Only the fattening period of the test group was statistically significantly extended by 2.3 days. Furthermore, there were statistically significant differences between the diets regarding osteocalcin concentration at 40 kg and 110 kg BW. Osteocalcin concentrations were decreased in the test group at both time points compared to the control group. Serum concentration of β-crosslaps was not influenced by the factors diet, sex or daily weight gain.
The comparison of both sexes showed that gilts had a decreased feed intake during the final stage and in the total assessment of the fattening stage. During the middle stage the gilts’ daily weight gain was decreased, so the fattening period was prolonged. On the other hand, female carcasses got a higher index point on average. Furthermore the calcium content of the metacarpi of gilts was greater (all statistically significant).
Regarding the factor daily weight gain, the pigs with above-average gain had a statistically significant higher BW at the end of piglet rearing (= beginning of the fattening stage) and at the end of the fattening stage. Thus, the required period for reaching the particular threshold weight for slaughter was less in the middle and final stages, as well as and in total.
There was a statistically significant negative correlation of the daily weight gain with the breaking strength and the dry matter of the metacarpi. Between breaking strength and distance (L) at maximal force (Fmax), there was a positive correlation. The concentration of β-crosslaps at 40 kg BW correlated positively with the concentration at 110 kg BW and with the dry matter of the bones. Serum osteocalcin at 110 kg BW correlated positively and statistically significantly with ash, calcium and phosphorus contents. There was a statistically significant positive correlation between ash and calcium and phosphorus content of the metacarpi, the latter two correlated with each other as well.
At least 13% of the pigs showed lameness and/or indications for joint diseases in the form of osteochondrosis dissecans. Animals of both the test and control diets were affected similarly, with an increased incidence in stables with restricted exercise space.
Conclusions: The great reduction of phosphorus in the diet had no negative impact on the traits of the fattening performance and carcass quality. Gait and joint abnormalities occurred in both the control and the test groups. Thus there was no direct link between these pathologies and phosphorus reduction. Further research should critically examine the lower limit of the customary practice to use P-reduced rations. The analyzed concentration of osteocalcin implied a higher content of digestible phosphorus in the test group. Thus it is tempting to speculate that the used phytase product (Natuphos 5000L®) is more efficient in liberating phosphate from phytate than originally assumed.