Browsing by Subject "Plasma urea nitrogen"

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    Variation and estimation of nitrogen utilization efficiency in a crossbred pig population
    (2022) Berghaus, Daniel; Rodehutscord, Markus
    Efficient utilization of dietary nitrogen (N) in pork production is of increasing concern. Previous studies revealed that a genetic basis for N utilization efficiency (NUE) might exist, but to assess the potential of breeding for improved NUE, the between-animal variation of a large number of animals needs to be known. The standard method to determine N retention (NR) in balance trails is laborious and not feasible for the required numbers of animals. However, correlations between protein utilization and blood urea nitrogen (BUN) concentration have been shown to exist and body protein turnover is subject to hormonal control. Hence, the objective of the present thesis was to quantify NR of growing pigs at two different growth stages by N balance and to determine the impact of body protein turnover on NUE. In addition, equations for the estimation of NR were established, using performance data and blood metabolite concentrations, which were applied to evaluate the variation in NUE of a F1 crossbred population. Over a period of 2.5 years, a total of 508 crossbred pigs (German Landrace x Pietrain) from 20 different boars was investigated from the 11th week of life until slaughter. The pigs were housed individually throughout the experimental period and a two-phase fattening was performed. All animals received the same diet for ad libitum intake which was formulated to contain 90% of the recommended lysine concentration so that marginal lysine supply was the limiting factor for protein retention and pigs were allowed to express their full genetic potential of NUE. In both fattening phases, daily feed intake was recorded for each animal in a five-day sampling period (SP), and blood samples were taken from the jugular vein at around 13:00 h on three consecutive days for determination of BUN, cortisol, and insulin-like growth factor 1 (IGF-I) concentration. Additionally, in both SP, N balance was performed in the same experimental barn on a randomly selected subsample of 56 barrows. The barrows were housed in metabolism crates for six days, two days for adaption and four days for quantitative collection of feces and urine. Simultaneously, their body protein turnover was determined using the end-product method after a single oral dose of 15N-labeled glycine. Based on the N balance results, models for estimation of NR were obtained by multiple regression of performance data and blood metabolite concentrations. The significance of the variables was validated using a bootstrapping method to avoid overfitting the models to the observed data. The goodness of fit of the equations was assessed using the coefficient of determination and the root mean square error. The N balance results revealed a high protein retention potential of the animals, which did not differ on average between the two SP. However, large differences in NR were observed between individuals and NR was strongly correlated with N and lysine intake. NUE was also at a high level and varied considerably between individuals. The mean NUE was significantly higher in SP1 than in SP2 and a moderate correlation was observed between NR and NUE. The mean body protein turnover did not differ between the SP and no correlation with NUE was observed. In estimating NR, the model with the best goodness of fit included the variables initial body weight, average daily gain, average daily feed intake, N intake, BUN, cortisol, and IGF-I concentration. This model was used to estimate NR for all animals and subsequently calculate their NUE. Describing NR as a linear function of lysine intake across both SP showed an average marginal efficiency of lysine utilization for protein retention of 67%. Despite a wide variation in NUE within the offspring of the same boars, significant differences were found between the offspring groups of the boars. Under the prevailing circumstances of marginal lysine supply, the NR of fattening pigs could be estimated from performance data and blood metabolite concentrations with satisfying accuracy. This provides a fast and reliable alternative to performing N balance studies, reducing the experimental effort considerably in studies with large numbers of animals. Although lysine supply was the limiting factor for protein retention, only about 70% of the variation in NR could be explained by the level of lysine intake. The remaining part of the variation was likely caused by differences in the intermediary lysine utilization or differences in the lysine content of the retained body protein between individuals. About 50% of the variation in NUE could be explained by differences in the level of NR, implying that pigs with higher protein retention potential utilized dietary N more efficiently. However, this was not accompanied by differences in body protein turnover. Phenotyping of the F1 crossbred population revealed a large variation between individuals and a significant boar effect, indicating the possibility of improving NUE through breeding measures.