1. The heat losses and energy and nitrogen balances of thirty-six individually-housed, entire male pigs (initial body-weight 18-30 kg) were measured over 7 d periods, when they were fed on rations containing 153, 201 and 258 gcrude protein (nitrogen x 6.25; CP)/kgdry matter (DM). The rations also contained 16,29,16,96 and 17.24 MJ metabolizable energy (ME)/kg DM so that the CP: ME values were 9-4, 1 1.8 and 15.0 g CP/MJ ME respectively. Each ration was given at three levels, 20, 35 and 50 g feed/kg body-weight per d, thus giving nine dietary treatments.The experiments were carried out at an environmental temperature of 22 (k 1)O. 2.Heat loss ( H ) increased significantly ( P < 0.01) with increase in ME intake. The rate of increase in H was not, however, influenced by the protein content of the ration. Thus, energy retention (ER) at any given level of ME intake was independent of the ration offered. From the relationship between ER and ME, estimates of the maintenance energy requirement (ME,) and the partial efficiency of energy utilization (k) were determined. ME, varied within the range 494-568 kJ/kg b~dy-weighto'~ per d, while k vaned from 0.70 to 0.76.3. Both energy and protein intakes had a significant influence upon the rates ofprotein (P) and fat ( F ) deposition, and hence body-weight gain. At any given level of feed intake P was higher and F lower the higher the protein content of the ration. However, when compared at similar levels of protein intake, both P and F were reduced the higher the protein content of the ration.4. From the multiple regression equations relating P and F to ME, individual estimates Of ME, and the energetic efficiencies of protein (kp) and fat (kF) depositions were determined. Using an overall mean k , value of 0.86, it was calculated that ME, ranged from 462 to 525 kJ/kg b~dy-weight~''~ per d while k p varied from 0.48 to 0.55. The significance of these estimates of k p are discussed in the light of their derivations and in relation to theoretical values.In assessing the energy requirements of farm animals it has been customary to partition the metabolizable energy (ME) intake into that required for maintenance (ME,) and that for production ME^). The productive component can be further partitioned into a requirement for protein deposition and a requirement for fat deposition. This procedure allows separate estimates for the energetic efficiency of protein (k,) and fat (kF) deposition to be calculated. Estimates of ME,, k , and kF are usually calculated from regression analyses where ME or ME, is related to the quantities of protein and fat deposited. Using these techniques it has been found in the pig, maintained under thermally-neutral conditions, that while values for k , remain relatively constant and close to those calculated on theoretical grounds, those for both ME, and k , vary considerably, the latter being generally lower than theoretical calculations indicate (Kielanowski, 1976;Pullar & Webster, 1977;Close, 1978;Fowler et al. 1980;Webster, 1980). These authors have prop...

1.The nitrogen balances of thirty-six individually-housed, entire male pigs (body-weight range 19-50 kg) were measured over 7 d periods when the animals were kept initially at an environmental temperature of 22O and then at loo while fed on rations containing 153, 201 and 258 g crude protein (N x 6.25; CP)/kg dry matter (DM). The respective metabolizable energy (ME) contents were 16.29, 16.96 and 17.24 MJ/kg DM. Each ration was p e n at three levels, 20,35 and SO g feed/kg body-weight per d. The animals fed on the 20 and 35 g/kg feeding level were catheterized and blood samples withdrawn on two consecutive days within the N-balance periods for the determination of blood urea (BU) concentration both before and at hourly intervals for 7 h following the morning feed.2. An increase in feed intake resulted in a significant increase in N retention (NR) at each environmental temperature. However, NR as a proportion of N intake was higher the lower the protein content of the ration. With the exception of the animals fed on the low-protein ration, NR at any given feed intake was lower at loo than at 22O and these differences were reflected in the animal's body-weight gain.3. Values for the fasting N metabolism (N,), calculated from the relationship between NR and intake of digestible N (IDN), were temperature-dependent. At 22', a constant N, value of 0,255 g N/kg body-weight0 75 per d was found appropriate, while at loo N, increased with increase in protein content of the ration from 0.380 on the low protein ration to 0.533 and 0.753 g N/kg body-weight0 75 per d on the medium-and high-protein rations respectively. 4.The efficiency of N utilization (kN) reflected the differences in the relationships between NR and IDN. At 22O the relationship was curvilinear so that kN decreased with increase in both the level of feed intake and the protein content of the ration. At 10' the relationship was linear, hence k , was independent of feed intake within rations. However, it decreased from 0.909 to 0.679 as the protein content of the ration was increased.5. The concentration of BU attained a maximal value some 3-5 h after the ingestion of the feed, with the values at loo being higher than those at 22O. BU increased as the level of protein in the ration increased but decreased with the level of feed intake when dietary protein concentration was held constant. There was a significant correlation between BU and kN, indicating that BU is a useful criterion for assessing the efficiency of N utilization.

Zusammenfassung Einfluß des Phenylethanolamins Clenbuterol auf den Protein‐ und Fettstoffwechsel wachsender Ratten Es wurden Untersuchungen an weiblichen Wistar‐Ratten von unterschiedlicher Lebendmasse mit der Referenzsubstanz Clenbuterol durchgeführt, um die ernährungsphysiologische Attraktivität der β‐Agonisten zu beurteilen und um Erkenntnisse über ihren Wirkmechanismus zu gewinnen. Die stimulierenden Effekte von Clenbuterol (25 ppm in der Diät) auf den Zuwachs und die N‐Retention stiegen mit der Lebendmasse zu Behandlungsbeginn. Die ernährungsphysiologische Wirkung der β‐Agonisten scheint also bei hohem Körperfettgehalt und entsprechend geringem Proteinretentionsvermögen am ausgeprägtesten zu sein. Den Eingriff der Substanz in den intermediären Protein‐ und Fettstoffwechsel belegen direkte und indirekte Parameter. Ein gesteigerter Proteinansatz wurde im Stoffwechselversuch (N‐Bilanz) sowie durch die vergleichende Schlachtkörperanalyse nachgewiesen. Der Körperproteingehalt war tendenziell erhöht, die Serumharnstoffkonzentration nach 24 h Fasten signifikant angestiegen. Der Körperfettgehalt und der tägliche Fettansatz wurden dagegen stark reduziert, wie die Schlachtkörperanalyse und die Sektion des perirenalen Fettgewebes zeigten. Entsprechend waren die Blutspiegel an unveresterten Fettsäuren im Fastenzustand erniedrigt. Nach 14‐tägiger Verabreichung von Clenbuterol mit dem Futter (25 ppm) waren die Serumkonzentrationen an Glucose, unveresterten Fettsäuren und insbesondere an Insulin im Vergleich zur unbehandelten Kontrolle deutlich reduziert. Es wird vermutet, daß geringe Insulinspiegel, verbunden mit einer verminderten Insulinsensivität der Fettzellen (Insulinresistenz), zumindest teilweise für die antilipogenen Effekte der β‐Agonisten verantwortlich sind. Die Messung einiger relevanter NADPH‐abhängiger lipogener Enzyme (MDH, G‐6PDH, 6‐PGDH) konnte in dieser Arbeit eine Lipogenesehemmung durch Clenbuterol nicht bestätigen.

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In growing male pigs fitted with jugular catheters, changes in plasma zinc concentrations were followed up to 330 min postprandially. In pigs with normal fasting zinc values ( > 70 µg/100 ml) plasma levels decreased significantly (p < 0.05) up to 35% below, whereas in pigs with lowered fasting values plasma level increased up to 36% above the respective fasting values within 120 and 180 min after feed intake. The amount of feed administered was without effect on the postprandial decline. No dose-response relationship between the intake of graded amounts of zinc in the inorganic (ZnSO₄) or naturally bound form (barley) and changes in plasma zinc level was found.