Protein utilization during energy undernutrition in sheep sustained by intragastric infusion

Abstract

The effect of body fat content on the protein metabolism of energy-restricted sheep has been studied in two experiments. In the first experiment, six Suffolk-cross wether sheep, three weighing about 39 kg and three of about 61 kg, were given progressively increasing amounts of casein-N from 0 to 3000 mg N/kg metabolic body weight (W0.75) daily with constant energy, 91 kJ/kg W0.75 daily, from a high-propionic acid mixture of volatile fatty acids (VFA). In the second experiment, two lean and two fat sheep of similar body weights were given progressively increasing amounts of casein with the same VFA mixture. All the animals attained a positive N balance when they were in negative energy balance. N balance was not affected by body fatness of the magnitude studied, although lean animals utilized increasing levels of standard VFA (acetate-propionate-butyrate 65:25:10, molar proportions) infusion for N accretion more efficiently than fat animals. Endogenous energy was utilized for protein accretion with an efficiency of 0.56. Supply of glucogenic VFA equivalent to 28 mmol glucose/kg W0.75 reduced fasting N excretion by 39%. Fasting heat production decreased from 335 to 300 kJ/kg W0.75 with the infusion of casein and glucogenic VFA. It is argued that fasting induces additional heat losses due to raised protein metabolism and is unsuited as a baseline for dietary assessment.

Effects of a high-protein, low-energy diet in finishing lambs: 1. Feed intake, estimated nutrient uptake, and levels of plasma metabolites and metabolic hormones

“…Ørskov et al (1979) and Hovell et al (1983) demonstrated that high PERs supplied by an intragastric infusion regimen caused sheep to attain positive N balance while in negative energy balance. Chowdhury et al (1990) reported similar results for cattle. These data suggested that endogenous fuel reserves (fat depots in particular), could serve to sustain lean tissue accretion in situations where feed energy is limiting, provided that ruminants were supplied with tissue-available protein.…”

Effects of a high-protein, low-energy diet in finishing lambs: 2. Weight change, organ mass, body composition, carcass traits, fatty acid composition of lean and adipose tissue, and taste panel evaluation

“…While Chowdhury et al (1997b) found that sheep receiving intragastric infusions could exhibit positive N balance while in negative energy balance, Iason and Mantecon (1993) concluded that enhanced protein deposition, fuelled by internal fat depots in energy-deprived but proteinsupplemented ruminants, can only occur in boverfatQ animals. However they left open the definition of doverfatT.…”

Effect of nutrition on muscle protein turnover in callipyge and normal lambs

“…They indicated that freezing callipyge chops for 8, 20, or 42 had similar calpastatin activity to fresh nomnal chops, but shear force values were similar in fresh normal lambs and frozen callipyge lambs for 8,20, or 42 d before aging. Chowdhury et al (1997) studied the effect of body fat content on protein metabolism of energy restricted sheep, and reported that all animals attained a positive nitrogen balance when they were in negative energy balances. Nitrogen balance was not affected by body fatness to the magnitude expected, although lean animals utilized increasing level of standard volatile fatty acids.…”

“…Nitrogen balance was not affected by body fatness to the magnitude expected, although lean animals utilized increasing level of standard volatile fatty acids. Endogenous energy was utilized for protein accretion with an efficiency of 0.56 (Chowdhury et al, 1997).…”

“…It has also been shown, using intragastrically nourished sheep, that infusion of volatile fatty acids to provide additional exogenous energy (250 kj/kg metabolic body weight, daily, had little effect on nitrogen balance when protein was infused in progressively increasing amounts (Chowdhury et al, 1997).…”