Effects of varying ruminally undegradable protein supplementation on forage digestion, nitrogen metabolism, and urea kinetics in Nellore cattle fed low-quality tropical forage1

Abstract

Effects of supplemental RDP and RUP on nutrient digestion, N metabolism, urea kinetics, and muscle protein degradation were evaluated in Nellore heifers (Bos indicus) consuming low-quality signal grass hay (5% CP and 80% NDF, DM basis). Five ruminally and abomasally cannulated Nellore heifers (248 ± 9 kg) were used in a 5 × 5 Latin square. Treatments were the control (no supplement) and RDP supplementation to meet 100% of the RDP requirement plus RUP provision to supply 0, 50, 100, or 150% of the RUP requirement. Supplemental RDP (casein plus NPN) was ruminally dosed twice daily, and RUP supply (casein) was continuously infused abomasally. Jugular infusion of [ 15 N 15 N]-urea with measurement of enrichment in urine was used to evaluate urea kinetics. The ratio of urinary 3-methylhistidine to creatinine was used to estimate skeletal muscle protein degradation. Forage NDF intake (2.48 kg/d) was not affected (P ≥ 0.37) by supplementation, but supplementation did increase ruminal NDF digestion (P < 0.01). Total N intake (by design) and N retention increased (P < 0.001) with supplementation and also linearly increased with RUP provision. Urea entry rate and gastrointestinal entry rate of urea were increased by supplementation (P < 0.001). Supplementation with RUP linearly increased (P = 0.02) urea entry rate and tended (P = 0.07) to linearly increase gastrointestinal entry rate of urea. Urea use for anabolic purposes tended (P = 0.07) to be increased by supplementation, and RUP provision also tended (P = 0.08) to linearly increase the amount of urea used for anabolism. The fraction of recycled urea N incorporated into microbial N was greater (P < 0.001) for control (22%) than for supplemented (9%) heifers. Urinary 3-methylhistidine:creatinine of control heifers was more than double that of supplemented heifers (P < 0.001). Control heifers reabsorbed a greater (P < 0.001) fraction of urea from the renal tubule than did supplemented heifers. Overall, unsupplemented heifers had greater mobilization of AA from myofibrillar protein, which provided N for urea synthesis and subsequent recycling. Supplemental RUP, when RDP was supplied, not only increased N retention but also supported increased urea N recycling and increased ruminal microbial protein synthesis.

Influence of organic phosphorus on reproductive performance and metabolic profiles of anoestrous Farafra ewes in subtropics at the end of breeding season

“…Higher plasma creatinine concentrations have also been reported during times of nutritional deprivation (Thrall et al., ). In the present study, there was no significant difference in CK between phosphorus and control ewes as the increased production of urea is not likely to be due to muscle catabolism (Batista et al., ). Values of AST and ALT were within the normal range and indicated that the animals were generally in a good nutritional status and their livers were in normal health condition.…”

Effects of Supplements with Different Protein Contents on Nutritional Performance of Grazing Cattle During the Rainy Season

“…This increase in N supply reduces the proportion of ingested N directed for survival and maintenance purposes, and increases the proportion of total N used for anabolic purposes. Consequently, it raises the overall efficiency of MP utilization (Detmann et al, 2014b; Batista et al, 2016), which increases the production of NMIC, and explains the positive linear relationship between CP concentration in supplements and the efficiency of N utilization (Table 5). …”

“…Ruminal pH values were combined in a similar manner. Rumen fluid samples for VFA analysis were pooled by animal and experimental period (equal volumes per sampling time) and analysed by high-performance liquid chromatography as described by Batista et al (2016).…”

The effect of CP concentration in the diet on urea kinetics and microbial usage of recycled urea in cattle: a meta-analysis

“…The low UUE:UER at low dietary CP concentrations demonstrates the remarkable ability of ruminants to conserve N through urea recycling mechanisms in the face of a severe N deficiency (Wickersham et al, 2009a). In addition, when N and/or energy availability is deficient, tissue protein mobilization can increase the N pool available for urea N synthesis and subsequent recycling (National Research Council (NRC), 1985;Batista et al, 2016).…”

“…Nevertheless, as described by Wickersham et al (2008), UUA includes some urea N that, subsequent to GIT entry, is excreted in the urine in forms other than urea, because the urinary excretion of label in forms other than urea is not measured by the methodology described by Lobley et al (2001). Indeed, several studies have reported that MNU:GER is frequently less than UUA:GER (Wickersham et al, 2008 and2009b;Davies et al, 2013;Batista et al, 2016) demonstrating that UUA:GER is not a measure of ruminal microbial incorporation of urea N.…”