The effects of acute and chronic protein depletion and accretion on plasma concentrations of insulin-like growth factor-1, fibronectin and total protein for ruminants nourished by intragastric infusion of nutrients

Energy: Protein Ratio in Ruminants: Insights from the Intragastric Infusion Technique

Simple Summary

One key question that has confounded nutritional scientists for years is how the ruminant responds metabolically with respect to energy and nitrogen utilisation when no exogenous energy is consumed. Fasting metabolism studies using the intragastric infusion technique (IIT) showed this to be a glucose-deficient state characterised by elevated nitrogen excretion and heat production. However, modern feeding systems continue to adopt fasting as the basis for measuring utilisation efficiency of nutritionally balanced diets, giving rise to the false concept of greater feed utilisation below than above energy maintenance. Another IIT finding was that given the animal’s genetic capacity for protein accretion and provided a rumen undegradable protein is fed, ruminants do not catabolise amino acids as an energy source but instead retain these to attain substantial gains in tissue protein deposition, fuelled by endogenous energy reserves. This suggests that endogenous fat reserves could be used to retain body protein when feed supplies are scarce or of poor nutritive value and questions the need to use high-energy diets in the finishing pre-slaughter period. Moreover, body protein and body fat deposition were also shown to be negatively correlated, contradicting current feeding systems which assume that nitrogen retention is always negative in an underfeeding situation.

Abstract

Studies on energy:protein ratio in ruminants are constrained by rumen fermentation since it governs nutrient metabolism and the ratio of energy:protein yielding nutrients available for absorption. By circumventing rumen fermentation, the total intragastric infusion technique (IIT) allowed objective quantification of maintenance energy and protein requirements, volatile fatty acid utilisation efficiency, efficiency of energy utilisation for maintenance (K_m) and growth (K_f) and the origin of N retention responses to independent variation of energy and protein intake. This review outlines the key IIT findings and whether they are reflected in current feeding systems with implications for different production systems worldwide. Maintenance energy requirements are similar to those derived from comparative slaughter but maintenance N requirements are significantly lower. No differences in utilisation efficiency exist between acetic, propionic and butyric acids. At low energy intakes, endogenous energy reserves are utilised to retain amino acids and fuel substantial tissue protein gains. The use of fasting metabolism to measure the utilisation of nutritionally balanced diets is questioned since it is a glucose-deficient state. Inter-species differences in glucose metabolism appear to exist, suggesting that glucose requirements may be higher in cattle than sheep. The difficulty in predicting nutrient requirements, particularly protein, with any one technique is highlighted.

Supplementation of rangeland primiparous Bos indicus x Bos taurus beef heifers during lactation. 1. Effects on dam milk production and liveweight, bull calf growth, live carcass characteristics and metabolic hormone concentrations

The practice of feeding replacement-breeding bulls on high energy diets after weaning to meet liveweight (LW) and carcass expectations between 18 and 24 months of age negatively affects reproductive potential. This experiment reports upon the effects of an alternative management strategy aimed at improving calfhood nutrition in rangeland-reared bulls to enhance LW and live carcass characteristics at 2 years. Following artificial insemination (AI cohort; n = 26), or natural mating, subsequent to the addition of bulls at 39 d post-AI (NM cohort; n = 36), primiparous Santa Gertrudis heifers grazing rangeland pastures with bull calf progeny were allocated at parturition to receive either nil supplement (control; CON) or provided with unrestricted access to a pelleted vegetable protein meal-based supplement containing 35% CP (SUPP) until weaning at 199 ± (SD) 26 d. The mean estimated pellet consumption by SUPP heifers during lactation was 2.6 ± (SEM) 0.5 kg DM daily. Grazing diet quality measurements indicated nutritional restriction of CON heifers until at least 115 d of lactation. This was confirmed by lower blood urea nitrogen concentrations at 88 d (P < 0.001) and greater mean NEFA (P < 0.001) concentrations. Rainfall during mid-lactation subsequently improved grazing diet quality; thus the CON heifers experienced moderate nutritional restriction across lactation, but sufficient to reduce milk yield by 1.6 kg/d (P < 0.001) and maternal LW at weaning by 18.4 kg (P < 0.001). Bulls reared by SUPP heifers were 17.5 kg heavier at weaning (P = 0.001) and had elevated IGF-I and leptin concentrations between 4 and 4.5 months of age (P < 0.05). Effects on metabolic hormones during calfhood were cohort specific, with greater concentrations of IGF-I confined to AISUPP bulls and NMSUPP bulls demonstrating greater concentrations of leptin. Bulls were amalgamated at weaning and grazed common pastures without supplementation until the experiment concluded at 675 d. Pre-weaning plane of nutrition did not affect the LW, carcass fat depth, IGF-I or leptin concentrations of bulls after weaning. Mean eye muscle area (EMA) was greater in SUPP compared to CON bulls (68.5 ± 0.9 cm²vs 65.2 ± 0.9 cm²; P < 0.05) and AISUPP bulls tended to have greater EMA (P = 0.06) than AICON bulls from 495 d of age. Thus when primiparous heifers experience moderate nutritional restriction during lactation, supplementation may have persistent effects upon increasing carcass muscle characteristics of bull progeny.

Effect of glucose supply on fasting nitrogen excretion and effect of level and type of volatile fatty acid infusion on response to protein infusion in cattle

Two experiments were carried out on cattle nourished entirely by intragastric infusion, to determine the extent to which glucose or a glucose precursor determines the response to protein infusion in energy-undernourished animals. In order to determine the requirement for glucose in 1-year-old fasting cattle, glucose was infused at increments to supply 0, 1·5, 2·5, 3·5, 4·5, 5·5 and 6·5 g/kg metabolic body weight (W0·75) and the effects on plasma β-hydroxybutyrate and N excretion were measured. At 5·5 g glucose/kg W0·75plasma β-hydroxybutyrate was reduced to a basal level of 1·65 mmol/l and fasting N excretion reduced from 529 to 280 mg N/kg W0·75. No further reduction was observed with the higher level of 6·5 g glucose/kg W0·75. In the second trial, three steers were used in a 3 × 3 Latin square design and infused with a volatile fatty acid mixture of 65, 27 and 8 mol acetic, propionic and butyric acids respectively/100 mol, either at an estimated maintenance energy level of 450 kJ/kg W0·75and supplying a calculated glucose equivalent level of 13·0 g/kg W0·75(M1A), or at 1·5 × maintenance supplying a glucose equivalent of 20 g/kg W0·75(M1·5A). Another mixture infused at the maintenance energy level contained 49, 43 and 8 mol acetic, propionic and butyric acids respectively/100 mol but with a glucose equivalent of 20 g/kg W0·75(M1P). Casein was infused at each of these energy treatments to supply 0, 200, 400, 800, 1600 and 2500 mg N/kg W0·75daily, and N balance and blood metabolites were measured. N retention increased linearly (r0·98) with casein infusion. The coefficients for N retention were 0·55, 0·57 and 0·64 for M1A, M1·5A and M1P respectively. The mean efficiency of N utilization was 0·58. The results suggest that provided the glucose need is met there is no relationship between energy supply and efficiency and level of protein retention. However, the results also indicate that glucose requirement in cattle may be higher than that previously observed in sheep.

Localization of insulin-like growth factor I (IGF-I) in the chicken liver after fasting and refeeding: demonstration by using antigen retrieval immunohistochemistry

Immunohistochemical localization of insulin-like growth factor-I (IGF-I) was investigated in the liver of fasted and refed chickens by using an antigen retrieval method. The present study is the first one showing the localization of IGF-I in the chicken liver. Immunoreactivity for IGF-I was detected on the paraffin sections of livers from the fed and refed chickens after the treatment with the antigen retrieval agent. A moderate number of cells showing IGF-I immunoreactivity were scattered in the parenchyma of the liver from fed chickens. These cells were relatively large and polygonal in shape and seemed to be hepatocytes. Reaction products were observed as a granular structure in the cytoplasm of IGF-I-immunoreactive hepatocytes. The number of immunoreactive hepatocytes was increased in the liver from refed chickens compared with fed chickens. Diffuse reaction products as well as granular ones were observed throughout the cytoplasm of IGF-I-immunoreactive hepatocytes of livers from refed chickens. There are, however, no regular patterns of the distribution of immunoreactive hepatocytes in the parenchyma of both fed and refed chickens. In the liver of the fasted chickens, clear immunoreactivity for the peptide was not observed. These data show that IGF-I is located in the chicken hepatocytes and influenced by the nutriture.