Minimum Effects of Sampling Time on the Apparent Digestibility of Nutrients and Blood Protein Catabolites in Light Lambs

SIMPLE SUMMARY: Nowadays, animal nutritionists are more aware of how expensive and limited protein is in animal feedings. Understanding the role of sampling time in evaluating the nutritional status of small ruminants could be helpful to assess more efficiently dietary crude protein content. However, faeces or blood samples to analyse dietary changes are taken at indistinct times of the day, depending on the availability of the technicians. Thereby, this study was designed to evaluate the effect of sampling time (8:00 a.m., 12:00 p.m., and 4:00 p.m.) on some apparent nutrient digestibility and blood catabolites related to nutritional status. Our findings revealed that one sample of faeces or blood in the morning enables the optimal evaluation of the impact of crude protein variations in diet formulations. ABSTRACT: This experiment aimed to evaluate the effects of sampling time on organic matter (OM), crude protein (CP) and phosphorous (P) apparent digestibility and plasma urea and creatinine concentration in growing and finishing male Ripollesa lambs fed different CP concentrations in the diet. Twenty-four male Ripollesa lambs with 14.5 kg body weight (BW) were randomly assigned to two groups differing in CP content in the growing (14 to 19 kg of BW) and finishing (19 to 25 kg of BW) phases (20% vs. 18% CP and 19% vs. 17% CP, respectively). Faeces collected from the rectum and blood samples collected from the jugular vein were taken at 8:00 a.m., 12:00 p.m., and 4:00 p.m. During the growing period, the OM, CP and P apparent digestibility were higher in the lower CP diet (p < 0.05), but only P was affected by the sampling time, being highest at 8:00 a.m. (p < 0.05) compared to other sampling hours. During the finishing period, there were no differences in these digestibility coefficients between diets or sampling times (p > 0.05). Sampling time did not affect (p > 0.05) plasma urea concentrations either in the growing or finishing period. Plasma creatinine concentrations did not differ (p > 0.05) between lambs receiving 18% or 20% CP diets, but during the finishing period, it was lower at 4:00 p.m. in lambs fed 17% CP (p < 0.05) than those offered 19% CP. Overall, the results suggest that the collection schedule to evaluate the protein nutritional status can be shortened through one spot sample of faeces or blood in the morning.