PSV-14 - Determination of optimal digestible phosphorus level in lactating sows

Abstract: Optimal dietary phosphorus (P) level is important for sows, not only to maintain P homeostasis and prevent premature culling due to lameness and locomotion, but also to support growth of their offspring. The objective of this experiment was to determine the optimal level of digestible P in lactating sows for the best reproductive performance and piglet growth. A total of 550 gestating sows were enrolled using a randomized block design with sow parity and group as blocks. Sows with an entry body weight of 247.5 ± 29.1 kg were allotted to one of the five levels of digestible P (similar as standard total tract digestibility of P with consideration of phytase released P): 0.2%, 0.3%, 0.4%, 0.5% and 0.6%. A corn-soy-wheat middling based lactation diet was formulated with phytase inclusion (550 FTU/kg) and a fixed ratio between calcium (Ca) and digestible P of 2.5. All diets were formulated to have the same nutrient levels except 69 kcal net energy difference between 0.6% and 0.2% digestible P treatments due to slight difference in the ingredient composition. Experimental diets were fed approximately four days before farrowing and throughout the entire lactation (21 days). Feces were collected from 20 sows per treatment around 14 days of lactation to measure apparent total tract digestibility (ATTD) of Ca and P. Using R (version 4.0.0), performance and digestibility data were analyzed using a general linear model and a generalized linear model specifying a binomial distribution was deployed for count data. Dietary treatments did not impact sow average daily feed intake or piglet birth and weaning weights. However, dietary treatments affected piglet livability (P < 0.05) and pre-weaning morality (P < 0.01), with 0.5% digestible P having the highest livability and 0.4% digestible P having the lowest pre-weaning mortality. There was a positive linear dose effect of digestible P on probability of weaned pigs (P < 0.05). Dietary digestible P affected ATTD Ca (88.8 ± 3.1%, P < 0.01) and ATTD P (64.4 ± 6.5%, P < 0.01) in sows on d14 of lactation, with higher digestible P level leading to lower ATTD Ca and P. In conclusion, dietary digestible P level affected ATTD Ca and P during lactation. Digestible P level of 0.4% and higher led to higher piglet livability and resulted in greater probability of weaned pigs.