Modulation of bone mineral content in replacement gilts in response to a depletion and repletion protocol

To limit the use of mineral phosphates, there is an increased interest to feed phosphorus (P) levels allowing maximized growth, without fulfilling the higher requirement for maximised bone mineralisation to growing pigs. In some contexts of production, replacement gilts are raised with fattening pigs until 80-100 kg BW. Considering that bone mineralization of replacement gilts should be maximized to expect a high lifetime breeding performance, it was hypothesized that after a depletion period that render them more efficient to use Ca and P, they can recover bone mineralisation when fed a repletion diet. From 58-95 kg BW, twenty-four Swiss Large White gilts were fed either a finisher control diet (C; 2.1 g digestible P/kg) or a finisher low P diet (L; 1.2 g digestible P/kg). From 95-140 kg BW, half of the gilts from each finisher diet were randomly assigned to either a C diet or a high P diet (H; 3.5 g digestible P/kg), resulting in four treatments: LC, CC, LH and CH. The Ca:dig. P ratio was 3.3, 3.1 and 2,9 for C, L and H diets, respectively. Whole body bone mineral content (BMC) as well as body composition of pigs were measured on each gilt at two-week intervals by dual energy X-ray absorptiometry. Data were analyzed as a randomized complete block design with PROC MIXED of SAS. Diet did not affect growth performance during the entire experiment. At 95 kg, gilts fed L showed a reduced BMC (8.7%; P<0.001) compared to the gilts fed C. At 140 kg, BMC of gilts fed LC were similar to CC, but lower than LH (2989 and 3133 vs 3314 g; P<0.001) while BMC of gilts fed LH and CH were not different (3314 vs 3356 g). These results show the important potential to limit dietary digestible P concentration during the fattening period without revealing detrimental effects on growth performance and they confirm the ability of replacement gilts to recover their bone mineralisation by 140 kg BW by increasing BMC efficiency. Finally, a high dig. P content between 95-140 kg BW allowed to further increase bone mineralisation, but required the use of dietary phosphates. 

Key words: replacement gilts, repletion, depletion, phosphorus, calcium, bone mineralization.

Published in the proceedings of the Animal Nutrition Conference of Canada 2020. For information on the event, past and future editions, check out https://animalnutritionconference.ca/.