Effects of dietary protein digestion kinetics on sow body condition loss and litter performance during lactation: A meta-analysis

Abstract

Over the last decades, litter size has increased considerably in modern hybrid sows. This raises concerns over body tissue mobilisation during lactation. Recent evidence suggests that protein tissue mobilization is specifically associated with reduced milk production, affecting litter weight gain, and with impaired ovarian function, affecting sow subsequent reproductive performance. Therefore, efficient utilization of dietary protein for milk production is critical during lactation. A meta-analysis was performed to investigate the role of dietary protein digestion kinetics in lactating sow weight loss, litter weight gain and nitrogen loss to the environment. Data were obtained from 17 peer reviewed publications between 1993 and 2019, including 63 different groups of sows fed with 59 different lactation diets. These publications were selected for their research focus on dietary crude protein concentration in relation to sow body weight loss and litter weight gain during lactation. Percentages of slow, fast and resistant protein in the total protein of the diets were estimated based on previously established in vitro protein degradation characteristics of the used ingredients. Results showed that higher total crude protein reduced sow weight losses and estimated body protein losses during lactation (β = -0.07 kg · (g/kg) ⁻¹, P = 0.01; β = -0.02 kg · (g/kg) ⁻¹, P < 0.01, respectively). An increase in the percentage of slow protein in total protein was associated with decreases of sow total weight loss (β = -1.85 kg/%, P < 0.01), estimated body protein loss (β = -0.33 kg/%, P < 0.01), while the percentage of fast protein in total protein was estimated to increase sow weight loss and estimated body protein loss during lactation (β = 0.46 kg/%, P = 0.03; β = 0.09 kg/%, P = 0.01, respectively). The percentage of resistant protein in total protein did not affect sow body losses but showed a negative relationship with litter weight gain during lactation (β = -0.80 kg/%, P < 0.01). Sow nitrogen loss to the environment during lactation was increased with a higher crude protein in the diet (β = 13.9 g· (g/kg) ⁻¹, P < 0.01), but not affected by protein digestion kinetics. This meta-analysis suggests that a high percentage of slow protein reduces sow body protein mobilization during lactation, probably due to a more sustained and prolonged amino acid delivery to the circulation than with fast protein, and therefore improves utilization of dietary amino acids rather than use them as energy source.