The effect of phosphorus restriction during the weaner-grower phase on compensatory growth, serum osteocalcin and bone mineralization in gilts

Minimizing phosphorus (P) outputs from pig facilities has become an important objective of legislators, producers and nutritionists. Dietary manipulations provide the opportunity to reduce the environmental impact of pig production. Several studies have demonstrated the effects of compensatory growth when growing pigs were subjected to protein restriction, resulting in substantial reductions in nitrogen excretion. However, there is a scarcity of information on the compensatory effects of dietary P and calcium (Ca) restriction on pig growth performance and bone mineralization. The hypothesis was that dietary P and Ca restriction would adversely affect growth performance, serum osteocalcin concentration and bone mineralization at 50 kg BW. However upon realimentation with a high P and Ca diet the negative effects on the aforementioned variables would be influenced (50 to 100 kg BW). Ninety-six female pigs with an initial BW of 10.0±1.6 kg were assigned to 4 dietary treatments to determine the effects of restricting dietary P level during the weaner-grower (approximately 10 to 50 kg BW; d 0 to 59) and finisher (approximately 50 to 100 kg BW; d 59 to 131) periods on growth performance, serum osteocalcin concentration, bone development and calculated P utilization. The dietary treatments were: (1) 4.0 g total P (tP)/kg from d 0 to 131 (LL); (2) 4.0 g tP/kg from d 0 to d 59 and 6.0 g tP/kg from d 59 to 131 (LH); (3) 6.0 g tP/kg from d 0 to 131 (HH) and (4) 6.0 g tP/kg from d 0 to 59 and 4.0 g tP/kg from d 59 to 131 (HL).

During the weaner-grower period (d 0 to 59), pigs offered high P diets had higher daily gain (P<0.001), feed intake (P<0.05), P intake (P<0.001), bone ash (P<0.05) and serum osteocalcin concentration (P<0.05) compared to pigs offered low-P diets. Pigs offered LH,HH and HL diets had higher average daily gain compared to pigs offered LL diet from d 59 to 131 (P<0.01). Pigs offered LL diet had a lower carcass weight compared to pigs offered LH, HH and HL diets on d 131 (P<0.05). Pigs offered LL diet had a lower bone ash (P<0.05), bone P (P<0.01) and bone calcium (P<0.05) concentration than pigs offered LH, HL and HH diets on d 131. Pigs offered LH diet had higher concentration of osteocalcin compared to pigs offered LL (P<0.01), HH (P<0.05) and HL (P<0.05) diets on d 88 and 108.

In conclusion, compensatory effect occurred in growth performance and bone mineral concentration at the termination of the finisher stage when high P was introduced at the initiation of the finisher stage, following consumption of a low-P diet during the weaner-grower stage. However, pigs offered LH diet did not surpass the level of growth performance or bone mineralization achieved by pigs offered HH diet.