The concept of protein stores and its implications in diet

Diet selection in pigs: dietary choices made by growing pigs following a period of underfeeding with protein

Forty pigs (half each of females and entire males) were used in anad libitumfeeding experiment from weaning to 33 kg live weight (LW). In period 1 to 16 kg LW, the pigs had either food L (134 g crude protein (CP) per kg) or food H (278 g CP per kg) alone. The aim was to delay the growth of pigs on L and create two groups of pigs with different body compositions. At 16 kg LW, eight pigs were killed and their empty bodies chemically analysed. The pigs given L had 1·06 (s.e. 0·08) kg more lipid and a lower protein: ash ratio in their empty body than pigs on H; growth rates, from 9 to 16 kg LW, were 386 (L) and 591 (H) (s.e.d. 17)g/day. Both aims were thus achieved.

In period 2 the pigs previously given L (no. = 16) or H (no. = 16) in period 1, were given L alone (no. = 4), H alone (no. = 4) or a choice between L and H (no. = 8) to 33 kg LW when the choice-fed pigs were killed and their empty bodies chemically analysed. The objective of the experiment was to test the idea that pigs previously given a food deficient in CP, when given a choice between foods, one of high and one of low, protein content will select a diet of a composition that allows them to correct the effects of the previous mis-feeding. The pigs given L alone in period 2 grew more slowly, and ate more per day, than those given H alone, with no effect of the food given in period 1. Of those given H alone in period 2, the pigs previously given L grew faster, and were more efficient, than those previously given H.

The protein contents (g CP per kg food) of the diets selected by the choice-fed pigs were significantly affected by both sex (228 for malesv.181 for females; s.e.d. 15) and the food given in period 1 (233 for L and 175 for H; s.e.d. 15) with no significant interaction between these factors. The pigs from L grew faster (1039v.780 (s.e.d. 70) g/day) had a higher daily food intake (1420v.1319 (s.e.d. 71) g/day) and were more efficient (0·736v.0·595 (s.e.d. 0·034) g gain per g food) than those from H. At 33 kg LW lipid weights were similar for the two period 1 treatments (L had 0·40 (s.e. 0·54) kg more lipid than H); females had 1·79 (s.e. 0·54) kg more lipid than males.

It is concluded that, where pigs are given a choice between foods of low and high protein contents, they will select a diet of a composition such that the effects of previous mis-feeding are corrected. Giving pigs a choice between an appropriate pair of foods allows them to select a diet of a composition suitable for their needs.

The effects of food protein content on the performance of pigs previously given foods with low or moderate protein contents

An experiment was conducted to study the ability of the pig to recover from the effects of a period on a food deficient in crude protein (CP). Forty young pigs were given free and continuous access to foods with either 150 (L) or 252 (M) g CP per kg in period 1 of the experiment, from 6·3 kg to 13·4 and 12·3 kg live weight respectively. These live weights were expected to give equal lipid-free empty body weights. In period 2, four males and four females from each of the period 1 treatments were given access to either M or a food with 377 g CP per kg (H) to a live weight of 30 kg, when the 32 pigs were killed.

Pigs on L took 11 (s.e. 0·6) days longer to complete period 1, and had, at the end of this period, 0·20 (s.e. 0·03) kg less protein and 1·20 (s.e. 0·06) kg more lipid in their bodies than the M pigs, at a common ash weight. In period 2, pigs from L grew at a faster rate (750v.633 (s.e.d. 20) g/day), ate food at the same rate (1115v.1085 (s.e.d. 35) g/day) and converted food more efficiently (0·676v.0·585 (s.e.d. 0·016) g gain per g food) than those from M. At 30·3 kg live weight the pigs from L had corrected their protein deficit relative to ash and reduced their fatness, so that they had the same protein: ash ratio and only 0·47 (s.e. 0·12) kg more lipid in their bodies than those from M. This was the result of a higher rate of gain of protein and water, a lower rate of lipid gain and similar rate of ash gain by the pigs from L than those from M. In the first 7 days of period 2 the pigs from L gained weight at 1·4 times the rate of those from M. In the final 7 days there was no significant effect of period 1 treatment on growth rate. The pigs from L given food H in period 2 were more efficient than those given M in period 2 (food conversion efficiency (FCE) values of 0·884 and 0·791 respectively; s.e.d. 0·027), but this difference was reversed in the final 7 days (FCE values of 0·521 and 0·603 respectively). t I is concluded from these results that a period of eating a food of low protein content produces a reduced protein: ash and an increased lipid: ash ratio in the body and reduced growth rate and efficiency. When subsequently pigs are given a food of sufficiently high protein content, the protein: ash and lipid: ash ratios return to normal. The repletion of labile protein reserves, with their associated water, leads to a substantial increase in the rate of live-weight gain. The lower lipid content of the gain leads to a high efficiency. The duration of these effects depends on the protein content of the food given.

The effects of dietary supplementation with lysine and methionine on body and tissue composition in the pig

A feeding trial was conducted on 24 individually-fed pigs given either a diet containing plant protein with insufficient Iysine and methionine or the same diet with optimal Iysine and methionine levels. Supplementation of the diet with synthetic amino acids significantly improved daily live-weight gain, feed conversion, nitrogen balance, loin eye muscle area and total yield of lean muscle.

Pigs receiving insufficient Iysine and methionine were characterized by lower haemoglobin and creatinine values accompanied by a decreased level of glutamic oxaloacetic transaminase.

There were highly significant differences in the blood and liver Iysine levels of the two treatments, and significant differences in the fresh muscle and in the pressed muscle juice Iysine levels.

The ratios between liver and blood Iysine levels and between dietary or muscle Iysine levels and % of nitrogen retention were calculated and found to be the same on both treatments.

The accumulation of Iysine in liver and muscle was linearly related to the blood Iysine level and to N retention and Iysine intake.

Indicator amino acid oxidation responds rapidly to changes in lysine or protein intake in growing and adult pigs

There is disagreement about the adaptation time required when using the indicator amino acid oxidation (IAAO) technique. Our objective was to establish the adaptation time required to obtain a plateau in indicator (L-[1-(14)C]-phenylalanine) oxidation in response to a test diet using growing and adult pigs. Four barrows (20 kg) and 4 sows (240 kg) were surgically implanted with venous catheters for isotope infusion. Growing Pigs: After 7 d of adaptation to an adequate lysine intake of 8.8 g/d, phenylalanine oxidation in growing pigs was 9.38 +/- 1.25% of the infused dose. At 2, 3, 4, or 6 d after reducing lysine intake to 3.8 g/d, and then increasing it back to 8.8 g/d, phenylalanine oxidation was 16.94 +/- 0.84% (P < 0.05) and 9.70 +/- 0.80% (P < 0.05), respectively, with no significant effect of days of adaptation to diet. Adult Pigs: After 14 d of adaptation to an intake of 200% of the amino acid maintenance requirement, phenylalanine oxidation in sows was 4.23 +/- 0.45% of dose. Changing the intake to 100 and 50% of the maintenance requirement, increased (P < 0.05) phenylalanine oxidation to 5.95 +/- 0.26 and 7.90 +/- 0.26%, respectively, with no significant effect of time (1, 2, 5, 6, 9, and 10 d) after diet change. The CV for repeated phenylalanine oxidation measurements within pigs and diets was 13.5% for growing and 8.8% for adult pigs. This demonstrates that the IAAO requires <2 d of adaptation regardless of age, dietary challenge (individual amino acid or total protein) or direction (increase or decrease) of change, and that the measured oxidation rate (% of dose) is highly repeatable.

The immediate effects of abrupt diet composition changes in young pigs

Forty pigs (twenty males and twenty females) were weaned at 4 weeks of age into individual cages, and their weights and feed intakes measured daily. From weaning to 16 kg live weight they were given free access to a feed with either 134 (L) or 278 (H) g crude protein (nitrogen x 6.25)/kg fresh weight. During this period pigs on feed L grew at a slower rate and converted feed less efficiently than pigs on feed H. At 16 kg live weight they were introduced to a 6 d period of feeding when, on successive days, they were given feeds L, H, L, H, L and H (if previously fed on L) or feeds H, L, H, L, H and L (if previously fed on H). For pigs previously given access to feed L the live-weight gain was 1061 v. 575 g/d on the days when H or L was given; the feed intake was 1078 v. 1027 g/d respectively. For pigs previously given access to feed H, the live-weight gain was 655 v. 610 g/d and the feed intake 844 v. 1071 g/d on the days when H or L were given. The interactions between the feed given previously and the feed given for the 3 d of the subsequent 6 d period were highly significant for both live-weight and feed intake. These rapid changes in feed intake and growth rate suggest that the metabolism of young pigs is extremely flexible, with a rapid rate of response to a change in the protein content of their feed.

Compensatory nitrogen retention in growing pigs following a period of N deprivation

1. Semi-synthetic diets, with dried microbial cells (Pruteen) as the nitrogen source, were used to measure N retention in 50 kg pigs given different combinations of N intake involving periods of deprivation and enhanced supply. 2. Metabolic faecal N losses were 1.92 g/d (1.26 g/kg dry matter eaten) and endogenous urinary losses were 3.96 g/d for pigs given an N intake of 6.9 g/d. 3. Compensatory N retention averaging 4.2 g extra N/d was observed in pigs given enhanced N supply by diets providing 31.0, 60.4 and 93.4 g N/d. In some instances enhanced N retention was maintained for 22 d. 4. Pigs given enhanced N supply by extravagant N intake did not maintain the compensatory response which had been evident initially.

Effect of high-fat and high-protein diets on toxicity of parathion and dichlorvos

Growing male rats that weighed 120 +/- 5 g were kept for 30 days on the following synthetic diets: high protein diet (HPD), 59% casein; high fat diet (HFD), 50% saturated fat; and normal diet (ND), 19% casein, 10% saturated fat, and 60% sucrose. Other essential dietary ingredients were included in all the diets. All animals were injected at the end of the 30-day period with parathion [10 mg/kg intraperitoneal (ip) injection as a single dose] or dichlorvos (30 mg/kg ip as a single dose) to compare the effect of dietary pretreatments on mortality from parathion and dichlorvos. A lower dose of parathion (7.5 mg/kg) and dichlorvos (20 mg/kg) was employed in another set of experiments to compare the spontaneous regeneration of plasma and red blood cell (RBC) cholinesterase (ChE) activity at 2 hr, 1 day, 3 days, and 5 days after administration of parathion or dichlorvos. The effect of these diets on hepatic microsomal oxidases was also determined. Results showed that diets per se did not affect initial plasma and RBC ChE activity. The HPD and HFD significantly protected against mortality from parathion but not from dichlorvos. Hepatic microsomal cytochrome P-450 and aminopyrine demethylase activity were unchanged, but aniline hydroxylase activity was increased significantly by HPD and HFD. Parathion oxidase in hepatic microsomes was significantly increased in rats fed HFD only. For the HPD, spontaneous regeneration of ChE diminished in RBCs in parathion-intoxicated rats and in plasma and RBCs of dichlorvos-intoxicated rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Labile protein reserves and protein turnover

The concept of a labile protein reserve is based on the relatively slow establishment of a new equilibrium in the rate of nitrogen excretion after an abrupt change in dietary supply. The evidence reviewed shows that a majority of this nitrogen is derived from or deposited in skeletal muscle proteins. The rates of synthesis and degradation of total body protein are rapid in large animals (man and swine) and are correlated with heat production. The rate of protein synthesis in skeletal muscle greatly exceeds the rate of growth and is sensitive to nutritional status. The rate exceeds the rate of degradation in response to the ingestion of an adequate diet so that tissue proteins are accumulated, but it decreases below the rate of degradation under conditions of deprivation. In this latter state, proteins of skeletal muscle supply amino acids for energy or for the synthesis of other more essential proteins, e.g., milk proteins during lactation. Thus, we conclude that the labile protein reserve is a product of the normal, dynamic metabolism of protein.