Interrelationship between body condition and metabolic status in ewes

SmallRuminant Research, 6 ( 1991 ) 15-24

15

Elsevier Science Publishers B.V., Amsterdam

Interrelationship between body condition and metabolic status in ewes R.M. Caldeira a a n d A. Vaz Portugal b,* aFaculdade de Medicina Veterindria, R. Gomes Freire, 1199 Lisboa Codex, Portugal bEsta¢~o Zoot~cnica Nacional, Fonte Boa, 2000 Santarbm, Portugal (Accepted 9 January 1991 )

ABSTRACT Caldeira, R.M. and Vaz Portugal, A., 1991. Interrelationship between body condition and metabolic status in ewes. Small Rumin. Res., 6:15-24. Blood samples were collected in four groups of mature, dry, non-pregnant ewes showing different body condition (BC) scores. In the first experiment, animals were fed differently to achieve four stabilized body weights and BC. In the second, only groups with highest and lowest weights and BCs were maintained on the experiment. The high group was fed to allow a gradual decrease to the lowest mean weight and BC, while the low group was fed to achieve the opposite. Free fatty acids (FFA), triglycerides (1"$), total cholesterol (TCh), phospbolipid (Phi) concentrations and enzymatic activities of glutamic-oxaloacetic transaminase (GOT) and glutamic-pyruvictransaminase (GPT) were determined in serum. Ewes were weighed and assessments of BC made weekly. Change of mean BC scores from 0.64 to 3.93 and from 4.14 to 1.00 took 24 and 46 weeks, respectively. Ewes with stabilized but different BC score had similar FFA, Tg, TCh, Phi concentrations, and GOT, GPT enzymatic activities. BC was related to small differences. For the increasing BC state (IBC), concentrations and activities had all increased gradually except FFA which decreased. For the decreasing BC state (DBC), mean FFA and Tg concentrations greatly increased at the beginningof food restriction, but gradually decreased afterwards. Phi and TCh concentrations remained constant while GOT and GPT activities decreased after food restriction; gradually increasing afterwards as animals were loosing BC. Results demonstrate that animals in the same BC may be in different metabolic states. Concentrationsof FFA are a good predictor of animal energy status, GOT and GPT activities are good indicators of mobilization of body protein reserves when animals are in negative energy balance.

INTRODUCTION

Seasonal changes in pasture yield and quality occur in many areas including Portugal. This alternation in grass availability to grazing ruminants (Casu and Nardone, 1988) is counteracted by the animal's physiological mechanisms of mobilization and deposition of body reserves or, stated in another way, by changes in body condition (BC). Drought conditions restrict animal productivity and make metabolic adaptation responsible for production level *To whom correspondence should be addressed.

0921-4488/91/$03.50 © 1991 Elsevier Science Publishers B.V. All fights reserved.

16

R.M. CALDEIRAAND A. VAZ PORTUGAL

and efficiency at which the animal maintains its physiological parameters (Vaz Portugal, 1988 ). BC scoring is a suitable parameter to evaluate adjustment in animal requirements to available feeds in a practical and simple way (Russel et al., 1969; Guerra et al., 1972; Teixeira, 1987). Knowledge of metabolic mechanisms in physiological animal adaptations to the environment is important to the best utilization by sheep of local forage resources and to provide a correct alimentary supplementation of the animal's physiological requirements. The purpose of this trial was to evaluate blood parameters in order to characterize metabolic pathways utilized by ewes to change their BC, to distinguish different metabolic states in animals on the same BC score and to compare live weight (LW) and BC as predictors of the nutritional status of animals. MATERIAL AND METHODS

Twenty five mature, dry, non-pregnant Merino Precoce ewes were divided before the start of the trial, based on their BC, into four groups with mean BC scores of I ( n = 7 ) , 2 ( n = 5 ) , 3 ( n = 6 ) and 4 ( n = 7 ) (Russel et al., 1969). During the first two months, animals were fed to maintain constant BC and LW, which were recorded weekly. When BC and LW were considered stabilized, blood was collected (20-25 ml) from all animals by venipuncture with no additive. After this, only groups 1 and 4 were kept on the trial. Group 1 was fed a diet formulated to provide twice maintenance requirements and group 4 was fed 30% of maintenance requirements (ARC, 1980). Feed allowance was adjusted regularly in relation to LW changes so that te same proportions of maintenance requirements were kept. BC scoring (Russel et al., 1969) and LW changes were recorded weekly, prior to feeding, by two assessors. During both periods of BC variation, three blood samples were collected from each animal (Table 1 ). Diets were composed mainly of corn silage supplemented with a concentrate mixture. The nutritive values of feeds were: corn silage m 25.9%0DM, 8.8% CP/DM and 9.8 MJ ME Kg DM; concentrate mixture m 84.4% DM, 12.5% CP/DM and 10.5 MJ ME Kg DM. The N:ME ratio ( 1.25 g N/MJ ME) was similar in both diets which were offered once daily at 16.00 h, while blood samples were taken at 09.00 h. A vitamin-mineral mixture was provided to animals during the entire trial. Before the start of the trial, ewes were sheared and an antihelminthic was administered. Serum concentrations of free fatty acids (FFA), triglycerides (Tg), total cholesterol (TCh), phospholipids (Phl) and enzymatic activities of glutamic-oxaloacetic transaminase (GOT) and glutamic-pyruvic transaminase ( GPT ) were determined with commercial kits (FFA, Boehringer 450459-E; Tg, Boehringer 701882; TCh, Boehringer 237574; Phi, Bio-M6rieux 61491; GOT, Biotrol A-03010; GPT, Biotrol A-03020). For the estimation of Phl

OVINEBODYCONDITIONAND METABOLICSTATUS

17

TABLE 1 Body condition (BC) and live weight (LW) ( m e a n + S D ) of ewes on stabilized (SBC), increasing (IBC) and decreasing (DBC) BC

Item

I st Sample

2nd Sample

3rd Sample

4th Sample

1 0.64+0.24 43.9 +4.13

49 2.11 +0.28 54.1 +2.46

91 2.79_+0.22 61.4 _+3.21

168 3.93_+0.19 72.4 _+4.36

91 3.17+0.26 62.1 +6.27

210 1.92+0.34 53.0 +7.36

322 1.00+0.35 41.5 +5.36

Group 1 IBC S day BC LW Group 2 SBC S day BC LW Group 3 SBC S day BC LW Group 4 DBC S day BC LW

1 1.95 + 0.45 53.0 +4.18 1 2.71 +0.19 60.6 + 7.07

1 4.14+0.24 67.2 +5.95

SD, standard deviation; S day, sampling day.

concentration, the serum quantity utilized was doubled in relation to kit procedures, while for Tg estimation 0.04 ml of serum, 0.01 ml of standard and 1.00 ml of reagent solution were utilized. Changes to kit standard procedures were made since concentrations of these metabolites in sheep serum are different from those in human serum, to which kits were standardized. RESULTS AND DISCUSSION

Variation in BC scores and LW of groups 1 and 4 are in Fig. 1. Animals starting with mean BC of 0.64 took 24 weeks to reach BC 3.93, while on group 4 the animals required 46 weeks for similar BC change (from 4. l0 to 1.00). This difference in time required for a similar magnitude of BC variation, although in opposite directions, may indicate the existence of a metabolic adaptation to food restriction for animals of group 4 and a kind of compensatory growth in group 1 animals, which had been on a previous feed restriction, as discussed by O'Donovan (1984). Regression equations between LW and BC score are in Table 2, indicating mean LW differences of 6.9, 8.7 and 8.6 kg per unit difference in BC score which agrees with Peart (1970) and MLC ( 1983 ), but are less than recorded by Russel et al. (1969 ) and Teixeira (1987 ). Differences may be explained

18

R.M.

CALDEIRA

AND

/-

70

!

A.

VAZ

PORTUGAL

Group 4 BC

s

65

I

Group LW

4

Lf3 I 3 0

6o

0 2 Q3

55 ~_j I Group 1

Group 1 .

.

.

.

.

.

.

BC

. . . .

45 I

0

,

i

,

i

4

,

8

i

12

,

i

,

i

,

16 20

i

24

,

i

28

,

i

i

32

,

i

,

36 40

~h

44

Time (Weeks) Group Group

I - Increosing body condition 4 - Decreasing body condition

Fig. 1. Variation in body condition (BC) scores and live weight (LW) of groups 1 and 4. TABLE2 Linear regressions between live weight (y) and body condition (BC) (x) during stabilized (SBC), increasing (IBC) and decreasing (DBC) body condition BC

n ~

SBC

25

IBC

82

DBC

130

y= a + bx

a = 39.73 b = 6.95 a=36.78 b = 8.72 a=34.23 b = 8.65

r

0.90* 0.93* 0.87*

SE2

CI a

1.87 0.69 1.04 0.38 1.18 0.44

(35.85-43.60) (5.53-8.36) (34.74-38.81) (7.98-9.47) (31.92-36.53) (7.79-9.52)

~n, size of sample; 2SE, standard error; 3CI, Confidence interval, *Significance level P< 0.05.

by subjectivity of BC evaluation, genetic differences in body size, and/or differences in gastro-intestinal contents (Russel et al., 1969; Evans, 1978; JarAge, 1988). On stabilized BC (SBC), mean serum values were similar among different BC (Table 3). Using covariance analysis, BC was responsible for small differences, suggesting that the metabolic status of an animal on maintenance diet depends on its BC. Mean serum concentrations and activities of FFA, Tg, TCh, Phi, GOT and GPT in SBC, IBC and DBC are in Tables 3, 4 and 5.

Free fatty acids In line with Bassett ( 1974, cited by Gregory, 1980) and Doiz6 et al. ( 1983 ), levels of FFA were characteristically low in SBC and IBC, when there was no

OVINE BODY CONDITION AND METABOLIC STATUS

19

TABLE3

Body condition (BC), live weight (LW), free fatty acids (FFA), triglycerides (Tg), total cholesterol ( T C h ) , p h o s p h o l i p i d s ( P h i ) , glutamic-oxaloacetic transaminase ( G O T ) and glutamic-pyruvictransaminase ( G P T ) during stabilized BC state Parameter

Group 1

SD

2

3

4

7

5

6

7

0.64 a 43.9 a 0.54 b 0.52 0.19 a 0.22 1.24 0.01 26.67 a 4.14

1.95 b 53.0 b 0.22 a 0.23 0.23 b 0.22 1.34 0.01 24.25 a 4.00

2.71 c 60.7 c 0.28 a 0.28 0.23 b 0.22 1.45 0.01 24.50 ~ 4.00

4.14 d 67.2 d 0.19 a 0.20 0.22 b 0.22 1.39 0.01 43.71 b 4.14

No. of ewes

BC L W (kg)

FFA (mmol/l) FFA corr ~ Tg ( m m o l / 1 ) Tg corr TCh (mmol/l) Phi ( m m o l / l ) GOT (U/I) GPT (U/I)

0.28* 5.49* 0.17* 0.03* 0.21 0.00 12.81" 0.80

*Significant effect P < 0.05; SD, Standard deviation. Means in the same line with different superscripts differ significantly ( P < 0.05 ). tcorr, by covariance for FFA and Tg. U / I , International enzymatic units per litre.

mobilization of fat reserves, while high values of FFA were typical during DBC (Pothoven and Beitz, 1975; DiMarco et al., 1981; Heitmann et al., 1986). During DBC, the FFA concentrations gradually decreased reflecting a direct relationship between amount of mobilizable fat reserves and FFA blood concentration (Bines and Morant, 1983; McNiven, 1984). A decreasing blood level of albumin, typical of underfeeding (Rrmrsy and Demigne, 1981 ), may also be related to those decreasing FFA values, as albumin is the FFA carder in blood and so a low level of albuminaemia restrains FFA release by adipocytes (Vernon and Peaker, 1983 ).

Triglycerides Mean Tg serum concentrations during SBC, IBC and DBC followed nearly the same pattern as FFA (Reid et al., 1979; Mazur et al., 1987) reflecting a metabolic relationship. The high value of sample 2 during DBC may be due to a hepatic failure to oxidize all mobilized FFA to ketone bodies and/or acetate, converting the remaining FFA (mainly esterified) to Tg (Mayes, 1976 cited by Reid et al., 1979; Mamo et al., 1983 cited by Mazur et al., 1987; Rrmrsy et al., 1986). Lower values of samples 2 and 3 in the IBC state may be due to high insulin

20

R.M. CALDEIRAAND A. VAZPORTUGAL

TABLE4 Body condition (BC), live weight (LW), free fatty acids (FFA), triglycerides (Tg), total cholesterol (TCh), phospholipids (Phi), glutamic-oxaloacetic transaminase (GOT) and glutamic-pyruvic transaminase ( G P T ) during increasing BC state Parameter

Sample 1

SD 2

3

4

7

7

7

7

0.64 a 43.86 a 0.54 c 0.19 b 1.24 a 0.01 b 26.67 ~ 4.14 ~

2.11 b 54.07 b 0.32 b 0.14 a 1.37 b 0.01 a 29.86 ~ 5.33 b

2.79 c 61.36 c 0.17 ~ 0.14 ~ 1.17 a 0.01 b 41.86 b 3.86 ~

3.93 a 62.36 a 0.22 a 0.23 ¢ 1.52 ¢ 0.01 c 44.60 b 7.57 ~

No. of ewes

BC LW (kg) FFA ( m m o l / I ) Tg ( m m o l / I ) TCh (mmol/1) Phi ( m m o l / l ) GOT ( U / l ) GPT ( U / l )

0.23* 3.61" 0.15* 0.04* 0.16" 0.00" 7.98* 0.79"

*Significant effect P < 0.05; SD, Standard deviation. Means in the same line with different superscripts differ significantly ( P < 0.05 ). U / l , International enzymatic units per litre.

TABLE5 Body condition (BC), live weight (LW), free fatty acids (FFA), triglycerides (Tg), total cholesterol (TCh), phospholipids (Phi), glutamic-oxaloacetic transaminase (GOT) and glutamic-pyruvic transaminase ( G P T ) during decreasing BC state Parameter

Sample 1

SD 2

3

4

6

6

6

6

4.08 d 67.42 d 0.21 a 0.22 a 1.36 0.01 45.67 b 4.00 ~

3.17 ¢ 62.08 c 0.81 d 0.28 b 1.22 0.01 16.00 ~ 2.83 ~

1.92 b 53.00 b 0.63 c 0.22 a 1.39 0.01 33.8(P b 7.00 b

1.01Y 41.50 a 0.38 b 0.21 a 1.45 0.01 83.83 c 11.83 ¢

No. o f ewes

BC LW (kg) FFA (mmol/1) Tg (mmoi/1) TCh (mmol/1) Phi ( m m o l / l ) GOT ( U / l ) GPT ( U / l )

*Significantly effect P < 0.05; SD, Standard deviation. Means in the same line with different superscripts differ significantly ( P < 0.05 ). U/1, International enzymatic units per litre.

0.30* 6.41" 0.27* 0.05* 0.24 0.00 34.02* 2.58*

OVINE BODY CONDITION AND METABOLIC STATUS

21

concentrations for a long period after feeding (R6m6sy et al., 1986), which directs gluconeogenic substrates to muscle and fat tissues (Brockman and Laarveld, 1986 ), stimulates synthesis of lipoproteins (R~m~sy et al., 1986 ) and lipoprotein lipase activity (Chilliard, 1985), increasing the circulating Tg uptake and therefore decreasing its serum concentration. Higher values in the last sample of IBC may be explained by body fat accumulation with intake reduction, anticipation of FFA mobilization and reesteriflcation to Tg (Doiz6 et al., 1983).

Total cholesterol and phospholipids Serum concentrations of TCh and Phi showed significant changes only in IBC state. In the other states, values remained unchanged, reflecting a remarkable stability in concentrations, probably because of the structural role played by these metabolites, particularly in membrane composition (Green and Fleisher, 1964; McMurray and Magee, 1972; Lindsay, 1983 ). Cholesterol also functions as the precursor of steroid hormones and bile acids. Increasing TCh and Phi concentrations during the IBC state may be due to greater availability of nutrients for their synthesis. Lower TCh values in the first sample during food restriction (DBC state) may be explained by the sudden decrease of nutrient availability for synthesis and/or a decrease in 3hydroxy-3-methylglutaryl CoA reductase by excess of hepatic ketone bodies (Vernon and Peaker, 1983 ), FFA hepatic oxidation with reesterification to Tg (Puppione, 1978 ), and reduction in hepatic synthesis of cholesterol transporter lipoproteins (R6m6sy et al., 1986). Glutamic-oxaloacetic and glutamic-pyruvic transaminases Relationships existed for GOT and GPT activities and protein and energy metabolism in SBC, IBC and DBC states. GOT and GPT seem to be good predictors of level of amino acids utilization during gluconeogenesis, and therefore of body protein depletion on negative energy balances (Weber et al., 1967 cited by Howarth et al., 1968; Martin et al., 1973; Magdus et al., 1985 ). GOT and GPT activities in the DBC state support the hypothesis of less protein metabolism (mobilization and turnover) when animals have plenty of body fat reserves (period I). In the second period, the levels of these transaminase activities gradually increased suggesting a greater utilization of body protein reserves to meet animal energy requirements. Higher values of GOT and GPT in the last samples during IBC may be due to increases in body protein synthesis and turnover. Similarly, high GOT activity in group 4 of SBC may be explained by increased body protein turnover (Orskov, 1984). Correlations among different parameters of SBC, IBC and DBC (Table 6) show that BC had higher correlations than LW with serum parameters, particularly FFA, Tg, GOT and GPT. Correlation between BC and LW, in this

22

R.M. CALDEIRAAND A. VAZ PORTUGAL

TABLE 6

Correlation coefficients for all pairs o f variables during stabilized, increasing and decreasing body condition (BC) states stabilized BC (n = 21 ) BC BC LW FFA Tg TCh Phi GOT

LW

FFA

Tg

TCh

Phi

GOT

GPT

0.905**

-0.572** -0.561"*

-0.371Ns 0.237 Ns - 0.168 Ns

0.230 Ns 0.149 r~s - 0.470 r~s 0.205*

- 0 . 2 1 6 Ns - 0 . 1 9 2 Ns 0.107 ~s 0.319 Ns 0.038 Ns

0.462* 0.443 Ns - 0.177 Ns - 0 . 1 0 0 Ns - 0 . 2 4 7 Ns _0.071Ns

0.019 Ns 0.124 Ns 0.078 r~s 0.246 Ns - 0 . 1 0 8 Ns _ 0 . 0 2 8 r~s 0.063*

increasing BC (n = 21 ) BC BC LW FFA Tg TCh Phi GOT

LW

FFA

0.947**

- 0 . 3 6 0 r~s -0.401Ns

Tg 0.697** 0.724** 0.119 Ns

TCh 0.329 Ns 0.394 Ns 0.160 Ns 0.568**

Phi

GOT

GPT

0.794** 0.765** - 0 . 3 8 8 Ns 0.510" 0.306 Ns

0.576** 0.514" - 0 . 1 4 2 r~s 0.380 r~s - 0 . 1 6 7 ~s 0.553*

Phi

GOT

GPT

-0.649** -0.617"* - 0 . 4 2 0 Ns - 0.417 ~s 0.148 Ns - 0.045 r~s

-0.740** -0.650** - 0 . 4 6 9 Ns - 0.423 Ns 0.189 Ns - 0.126 Ns 0.878**

0.619"* 0.569** 0.248 Ns 0.652** 0.733** 0.390 r~s 0.194 Ns

decreasing BC (n = 18 ) BC BC LW FFA Tg TCh Phi GOT

LW

FFA

0.915"*

0.509* 0.481 r~s

Tg 0.566* 0.395 r~s 0.555*

TCh - 0 . 3 5 9 Ns - 0 . 2 2 6 Ns - 0 . 2 5 7 Ns - 0.182 Ns

0.124 Ns 0.028 Ns 0.087 Ns 0.646"* 0.170 Ns

NSnot significant. Significance level * P < 0.05, **P< 0.01.

case of non-pregnant and dry ewes, was highly significant ( P < 0.01 ) in line with Russel et al. (1969) and Teixeira (1987). ACKNOWLEDGEMENTS

This research was supported in part by Estag~o Zoot6cnica Nacional and in part by a grant from Instituto National de Investiga~o Cientifica National.

OVINEBODYCONDITIONANDMETABOLICSTATUS

23

REFERENCES ARC, 1980. The nutrient requirements of ruminant livestock. Commonwealth Agricultural Bureaux, Surrey, UK, pp. 114-118. Bines, J.A. and Morant, S.V., 1983. The effect of body condition on metabolic changes associated with intake of food by the cow. Br. J. Nutr., 50:81-89. Brockman, R.P. and Laarveld, B., 1986. Hormonal regulation of metabolism in ruminants: a review. Livest. Prod. Sci., 14:313-334. Casu, S. and Nardone, A., 1988. Races ~ forte croissance et production de viande en milieu mediterraneen (High growth potential breeds and meat production in Mediterranean environment). Proc., 3rd World Congress Sheep and Beef Cattle Breeding, 19-23 June, INRA, Paris, Vol. 2, pp. 93-112. Chilliard, Y., 1985. Metabolisme du tissu adipeux, lipog6n~se mammaire et activit6s lipoprot6ine-lipasiques chez la ch~vre au cours dy cycle gestation-lactation (Metabolism of adipose tissue, lipogenesis in the mammary gland and lipoprotcin lipase activity in the dairy goat during gestation and lactation). Doctorat Th~se. Univ. Pierre et Marie Curie, Paris. DiMarco, N.M., Beitz, D.C., and Whitehurst, G.B., 1981. Effect of fasting on free fatty acid, glycerol and cholesterol concentrations in blood plasma and lipoprotein lipase activity in adipose tissue of cattle. J. Anita. Sci., 52: 75-82. Doiz6, F., Vandcrmeerschcn Bouchat, J.C., Bouckoms-Van-Dermeir, M.A. and Paquay, R., 1983. Effects of long-term ab libitum feeding on plasma lipid components and blood glucose, flhydroxybutyrate and insulin concentrations in lean adult sheep. Reprod. Nutr. D6velop., 23: 51-63. Evans, D.G., 1978. The interpretation and analysis of subjective body condition scores. Anita. Prod., 26: 119-125. Green, D.E. and Fleisher, S., 1964. Role of lipid in mitochondrial function. In: R.C.M. Dawson and D.R. Rhodes (Editors), Metabolism and physiological significance of lipids. Proc., Advanced Study Course, September, 1963, Cambridge, John Wiley Sons Ltd., London, pp. 581620. Gregory, N.G., 1980. Observations on the control of fat growth. Proc., Workshop, Univ. Leeds. Agricultural Research Council, UK, pp. 90-98. Guerra, J.C., Thwaites, C.J. and Edey, T.N., 1972. Assessment of the proportion of chemical fat in the bodies of live sheep. J. Agric. Sci., Camb., 78: 147-149. Heitmann, R.N., Sensenig, S.C., Reynolds, C.K., Fernandez, J.M. and Dawes, D.J., 1986. Changes in energy metabolite and regulatory hormone concentrations and net fluxes across splanchnic and peripheral tissues in fed and progressively fasted ewes. J. Nutr., I 16:25162524. Howarth, R.E., Baldwin, R.W. and Ronning, M., 1968. Enzyme activities in liver, muscle and adipose tissue of calves and steers. J. Dairy Sci., 51: 1270-1274. Jarrige, R., 1988. Ingestion et digestion des aliments (Food intake and digestion). In: Alimentation des bovins, ovins et caprins (Nutrition of cattle, sheep and goats), INRA (Editor), Paris, pp. 29-56. Lindsay, D.B., 1983. Growth and fattening. In: J.A.F. Rook and P.C. Thomas (Editors), Nutritional Physiology of farm animals, Longman, London, pp. 261-313. Magdus, M., Galambos, L. and Husv6tch, F., 1985. Studies on the lipid metabolism of ewes in the periparturient period. Acta Vet. Hungarica, 33: 89-100. Martin, R.J., Wilson, L.L., Cowan, R.W. and Sink, J.D., 1973. Effects of fasting and diet on enzyme profiles in ovine liver and adipose tissue. J. Anita. Sci., 36: 101-106. Mazur, A., AI-Kotobe, M. and Rayssiguier, Y., 1987. Influence de la lipomobilisation sur la s6cr~tion des triglyc6rides par le foie, chez le mouton (Effect of fat mobilization on triglyceride hepatic secretion in sheep). Reprod. Nutr. Develop., 27:317-318.

24

R.M.CALDEIRAANDA.VAZPORTUGAL

McMurray, W.C. and Magee, W.L., 1972. Phospholipid metabolism. Annu. Rev. Biocbem,, 41: 129-160. MLC, 1983. Feeding the ewe (2nd Edn.). Sheep Improvement Services Meat and Livestock Commission, Milton Keynes, UK. McNiven, M.A., 1984. The effect of body fatness on energetic efficiency and fasting heat production in adult sheep. Br. J. Nutr., 51: 297-304. O'Donovan, P.B., 1984. Compensatory gain in cattle and sheep. Nutr. Abst. Rev., Series B, 54: 389-410. Orskov, E.R., 1984. Protein nutrition in ruminants. Academic Press, Ltd., London, 160 pp. Peart, J.N., 1970. The influence of live weight and body condition on the subsequent milk production of Blackface ewes following a period of undernourishment in early lactation. J. Agric. Sei., Camb., 75: 459-469. Pothoven, M.A. and Beitz, D.C., 1975. Changes in fatty acid synthesis and lipogenic enzymes in adipose tissue from fasted-refed steers. J. Nutr., 105: 1055-1061. Puppione, D.L., 1978. Implications of unique features of blood lipid transport in the lactating cow. J. Dairy Sci., 61: 651-659. Reid, I.M., Collins, R.A., Baird, G.D., Roberts, C.J. and Symonds, H.W., 1979. Lipid production rates and pathogenesis of fatty liver in fasted cows. J. Agric. Sei., Camb., 93: 253-256. R~m~sy, C. and Demigne, C., 1981. Les principaux aspects du m~tabolisme dy glucose et des acides amin6s chez la vache laiti~re (Principal aspects of amino acids and glucose metabolism in the dairy cow). Bull. Techn. C.R.Z.V. Th6ix, INRA (45): 27-35. R6m6sy, C., Chilliard, Y., Rayssiguier, Y., Mazur, A. and Demigne, C., 1986. Le m6tabolisme h6patique des glucides et des lipides cbez les ruminants: principales interactions durant la gestation et la lactation (Carbohydrate and lipid hepatic metabolism in ruminants: principal relationships during gestation and lactation). Reprod. Nutr. Develop., 26: 205-226. Russel, A.J.F., Doney, J.M. and Gunn, R.G., 1969. Subjective assessment of body fat in live sheep. J. Agric. Sei., Camb., 72: 451-454. Teixeira, A.J.C., 1987. Reparto de la grasa en function de la condition corporal en ovejas adultas rasa Aragonesa (Effect of body condition on fat partition in Aragonesa ewes). MSc. Thesis, Centre International de Hautes l~tudes Agronomiques Mediterrane~nnes, Zaragoza. Vaz Portugal, A., 1988. Intensive beef production. In: E.S.E. Galal, M.B. Aboul-Ela and M.M. Shafie (editors), Ruminant production in the dry subtropics: constraints and potentials, E.A.A.P. Publication No. 38, Pudoc, Wageningen, pp. 52-66. Vernon, R.G. and Peaker, M., 1983. The regulation of nutrient supply within the body. In: J.A.F. Rook and P.C. Thomas (Editors), Nutritional physiology of farm animals, Longman, London, pp. 114-174.