Relationship between urinary excretion of purine and creatinine derivatives and food intake in dairy cows

Abstract

Molar concentrations of purine (PD) and creatinine (CT) derivatives were measured in urine samples of 63 cows submitted to 4 levels of feeding (6.04; 10.09; 11.63 y 18.31 kg DM/d and 2.98; 5.9; 7.37 y 12.5 kg DOMR/d). Based on PD/CT ratio and dry matter intake (DMI) and degradable organic matter in the rumen, intake (DOMRI), regression equations were derived to estimate of DOMRI based on the PD/CT ratio.

Moreover, the daily excretion of PD was calculated and from that, the absortion of PD and efficiency of microbial nitrogen supply (EMNS) by food intake unit were obtained.

It was concluded that the molar PD/CT ratio in one urine sample, allows to discriminate among levels of food intake differing more than 4.05 kg of DMI, or more than 2.92 kg of DOMRI.

The quadratic regression were PD/CT = 0.25 + 0.072 DMI + 0.002 DMI² (r² = 0.720) and PD/CT = 0.25 + 0.147 DOMRI + 0.0015 DOMRI² (r² = 0.710 ). However, when they were expressed as the total of PD excreted daily (PDe), it was possible to differentiate among the 4 levels of feeding. Values of PDe by groups were I = 84.77 ± 12.19; II = 140.66 ± 7.21; III = 168.67 ± 6.45 and IV = 297.03 ± 9.72 (mmol/d) (p< 0.05).

The ± 0.928; II = 8.096 ± 0.549; III = 8.898 ± 0.491 and IV=11.573 ± 0.74 g/kg where the group IV was the only one different from the others (p< 0.05). Expressed as EMNS/kg of DOMRI was statistically equal for the 4 groups with values of: I = 13.224 ± 1.537; II = 13.846 ± 0.909; III = 14.041 ± 0.813 and IV = 16.953 ± 1.226 g/kg respectively. It is concluded that PD/CT of a urine sample in a cow has a high correlation with food intake and that PDe estimated from this ratio allows to identify differences in average food intake of 1.5 kg of DMI and of 1.47 kg of DOMRI.