Impact of increasing dietary crude protein content on urinary nitrogen excretion and milk nitrogen secretion of lactating sows

Abstract Text:

The objective of the current study was to evaluate the effect of increased dietary crude protein (CP) content on urinary nitrogen (N) excretion and milk N secretion during lactation. In total, 36 sows from 1^st to 5^th parity were included in the experiment from parturition until weaning at d 28. Sows were allotted to 6 different treatments, with dietary CP contents of 149, 164, 174, 183, 193, and 208 g/kg DM, while dietary contents of SID lysine, methionine, threonine, and tryptophan were kept constant by including crystalline amino acids (AA). Sows were fed individually according to Danish recommendations, except for the recommended content of dietary CP. On d 2 postpartum, litters were equalized to 14 piglets and weighed on d 2, 10, and 17 to calculate milk production. Sows were fitted with urinary catheters on d 3, 10, and 17 and urine was collected three times during a 6 h period each week to estimate the daily urine production and N excretion. Additionally, milk samples were collected on d 3, 10, and 17 to estimate the daily secretion of N in milk. Fixed effects of week, treatment and the interaction were tested using a mixed model. Overall, there was no effect of treatment on N content in urine (P > 0.10) or the amount of urine (P > 0.10). However, excretion of urinary N tended (P < 0.10) to be lowest for sows fed 164 g CP/kg DM (20.5 g N) and highest (1.5 to 1.8 fold higher) for sows fed 193 and 208 g CP/ kg DM, respectively. The urinary N excretion averaged 28 g/d and did not change as lactation progressed (P > 0.10). Milk protein content increased with increasing dietary CP content, from 4.8 to 5.4% (P < 0.05). Milk production was comparable among treatments (P = 0.09) and ranged from 10.7 to 12.7 kg/d. The milk N secretion increased from 76 g/d on d 3 to 109 g/d on d 17, but it was not affected by dietary treatment (P > 0.10). In conclusion, the highest milk protein content was observed at 208 g CP/kg DM, whereas the lowest urinary N excretion was observed at 164 g CP/kg DM.

Keywords: milk protein, nitrogen loss, nutrition.