Directory UMM :Data Elmu:jurnal:S:Small Ruminant Research:Vol38.Issue3.Nov2000:

Macromineral pro®le in the plasma of Nubian goats

as affected by the physiological state

Muna M.M. Ahmed

a,*

, A. Khalid Siham

b

, M.E.S. Barri

c a_{Institute of Environmental Studies, P.O. Box, 321, Khartoum, Sudan}

b_{University of El Azhari, Khartoum, Sudan}

c_{Central Veterinary Laboratories, Soba, P.O. Box, 8608 Khartoum, Sudan}

Received 18 August 1999; accepted 14 June 2000

Abstract

A total of 65 Nubian dairy goats were selected to represent a combination of age and physiological status. Changes in some plasma concentrations underlying different physiological states were monitored. There were young and adult animals, pregnant animals, all with more than 50 days after kidding, divided into subgroups according to gestation, ®rst, second or third pregnancy. Lactating animals up to 50 days after kidding were divided into subgroups according to parity (®rst, second or third) and stage of lactation (early or mid). The last category consisted of animals grouped according to yield (high or low). Data analyses have shown that calcium (Ca) levels were lowest (P<0:05) during ®rst early lactation, while those of

phosphorous (P) were lowest (P<₀:_{05) in second pregnancy and also in early lactations compared with mid-lactations}

(P<0:05). Magnesium (Mg) levels increased (P<0:05) with age and number of pregnancies. The order was second, third

and ®rst. Irrespective of parity, mid-lactations showed higher (P<₀:_{05) Mg levels than early ones. Sodium (Na) plasma levels}

decreased (P<0:05) progressively with age and from ®rst to third pregnancy; and decreased (P<0:05) during ®rst and third

mid-lactations compared with ®rst or second early lactation, and as well as with second mid-lactation. Potassium (K) plasma levels were lower (P<0:05) in early than mid-lactations. Except for Mg, the type of milk yield had no signi®cant effect on

minerals under study. Minerals in the diet of animals kept under different management practices must be regarded among other essential nutrients. Physiological status might modify its requirement to these elements.#2000 Elsevier Science B.V. All rights reserved.

Keywords:Nubian goat; Macrominerals in plasma; Physiological state

1. Introduction

Nubian goats are among the best known dairy breeds in Africa especially in Sudan where they comprise 47% of the total goat population, which is estimated at 15 million heads (AOAD, 1990). This breed plays an important role in the life of many Sudanese families as a favorite household animal kept

for milk. It is raised under the traditional system, usually roaming freely during the day, scavenging in towns then con®ned and fed household wastes and concentrates at night. Sudanese Nubian goats may reach up to 85 cm at wither height, males weigh-ing 50±70 kg and females 40±60 kg. Kiddweigh-ing interval is 22817 days with multiple births being fairly proli®c. High proportion of singles (60%) occurs, while twin and triplet percentages are 30 and 3, respectively (El Naim, 1979). Weight at birth is *_{Corresponding author. Fax:‡249-11-773805}

2.5 kg for males and 2.1 kg for females. Lactation length is147 days and milk yield 1.5±2.0 kg per day, 150±200 kg per lactation. Calcium (Ca) is a structural component of the skeleton, it is essential for the activity of enzyme systems including those necessary for the transmission of nerve impulses and for con-tractile properties of muscles, and is also involved in blood coagulation (McDowell et al., 1993). In growing animals net retention of Ca occurs in the body, while in adults the amount ingested equals that lost if metabolic requirement is met (Church and Pond, 1988). Absorp-tion ef®ciency is well known to fall with age which partly relates to the decline in Vitamin D stores (Robert, 1989). Growth requirement of 7-months old West African dwarf goats gaining 100 mg per day was found to be 127 mg Ca/kg body weight (BW) per day for maintenance only and 380 mg Ca/kg BW for growth and maintenance (Adelye and Akinsoyinu, 1984), for Swiss-type goats, the require-ment was 10.7 g Ca/kg gain and 1.25 g/kg milk (Pfef-fer and Keunecke, 1986).

Phosphorous (P) is a component of phospholipids which are important in lipid transport and cell mem-brane structure. It functions in energy metabolism and forms a constituent of several enzyme systems. Increasing uptake of P by tissues (uterus in pregnancy, mammary gland in lactation and bone in growing animals) with a ®xed level of P in the diet, is predicted to cause decreasing P concentration in extracellular ¯uid, saliva and ruminal ¯uid (Symonds and Forbes, 1993).

P requirements in pregnant and lactating German Alpine goats were at least 3 g/kg dry matter (DM) in the ration per day (Barhoum et al., 1987). Goats milking between 0.8 and 2.0 kg per day were found to be in positive Ca and P balance when receiving 7.7± 21.6 g Ca oxide and 6.6±13.5 g P oxide when sources of Vitamin D was provided (Haenlein, 1980). Mag-nesium (Mg) is required for normal skeletal develop-ment and one of the commonest enzyme activator (McDowell et al., 1993). Lactation requirements, depending on breed, were found to be 0.13±0.87 g/ kg milk (Kessler, 1991). Dairy goat requirements were 3.5 g/kg BW, and supplies of 238 mg Mg per day were too low for milk production (Haenlein, 1980).

Sodium (Na) and potassium (K) are considered together because as electrolytes, they play a vital role in maintaining osmotic pressure and acid±base

bal-ance. The daily requirement of Na was found to be 1.74 g Na/kg DM (Ivandija, 1987). Growth require-ment was 1.6 g Na/kg BW over the range from birth to 31 kg BW requirements (Pfeffer and Keunecke, 1986). K requirement for lactating goats was esti-mated to be 0.7% of the ration DM in early lactation, and also appears to increase under stress (Ademosum et al., 1992). Both ions were found to ¯uctuate only slightly during pregnancy and lactation (Mbassa, 1991). Except for common salt, mineral supplementation of goat feed is usually ignored even under improved management systems. The present study was thus initiated with the objective to study changes in some macrominerals namely, Ca, P, Mg, Na and K under different physiological states in the plasma of Nubian goats, kept under good intensive management system.

2. Materials and methods

2.1. Animals

Animals used were in a ¯ock of purebred Nubian goats. They had the typical characteristics of the Nubian breed. They had large body size (70±75 cm at wither height), head was convex with pronounced running nose and long pendulous ears. Black being the dominant color with gray ears, light marbling found in some animals. Body weight ranged from 40 to 60 kg, chest was fairly deep, legs were long and well parti-tioned, udder well developed.

A total of 65 animals were used in this experiment. A combination of age and pregnancy or lactation as divided into groups as follows:

1. Young animals at 4±6 months of age. 2. Adult animals at 10±12 months of age.

3. Pregnant animals more than 50 days before kidding, grouped according to the number of gestation:

3.1. ®rst pregnancy at 1±3 years of age; 3.2. second pregnancy at 2±3 years of age; 3.3. third pregnancy at 3±4 years of age.

4. Lactating animals up to 50 days after kidding, grouped according to parity and stage of lactation: 4.1. ®rst early lactation (1±3 years);

4.4. second mid-lactation (2±4 years); 4.5. third early lactation (4±6years); 4.6. third mid-lactation (4±6 years). 5. Milking animals grouped as:

5.1. high yielders; 5.2. low yielders.

Each group or subgroup consisted of ®ve animals.

2.2. Feeds

The animal feeds consisted of roughage and con-centrate diet (50:50) offered ad libitum and 0.3 kg alfalfa hay offered weekly per animal. The roughage wasSorghum bichlore and the concentrate consisted of 50% molasses, 10% cotton seed cake, 36% wheat bran, 3% urea and 1% common salt. The animal had free access to clean water but no salt lick. The animals were kept in an open shed enclosure 20 m20 m fenced with thatch ®tted together with wire at a height of 2 m.

2.3. Blood sampling

Blood was collected by jugular veni-puncture into heparinized vacutainers. The plasma separated was stored atÿ20₈C pending the analysis of Ca, P, Mg, Na and K. Colorimetric determination of plasma levels of Ca, P and Mg was carried out according to the methods described by Trinder (1960), Varley (1967) and Norbert (1982), respectively. Na and K determi-nations followed the methods by Wooton (1974). Blood samples were collected 2 h after feeding which was at 10.00 h and before milking. The milking goats were hand milked once during the afternoon (14.00 h). Milk yield was 1.5±2.0 kg.

2.4. Results

2.4.1. Plasma calcium (Ca) and phosphorous (P) levels

Chemical analysis of feed stuffs offered to the goats during the experimental period is shown in Table 1. Average values with standard deviations, the range of plasma Ca and P, minimum and maximum levels are shown in Table 2. Plasma Ca and P levels of all groups of animals at different physiological states were within the normal range. For Ca levels, young animals had

signi®cantly higher values than adults, whereas the opposite was true for the P levels. While Ca levels seemed not to be affected by number of parities, P levels decreased (P<0:05) during second pregnancy, followed by third and ®nally ®rst pregnancy. Both Ca and P plasma levels tended to increase during mid-lactation compared with early mid-lactation, irrespective of number of parities. A decrease (P<₀:_{05) in Ca level} could be detected during mid-lactation. Furthermore, P plasma levels showed (P<₀:_{05) decreases during} ®rst, second and third mid-lactations compared to early lactations. No signi®cant changes could be observed between high and low yielders in both Ca or P levels.

2.4.2. Magnesium (Mg) plasma levels

The average values with standard deviations, range of plasma Mg, minimum and maximum levels are shown in Table 2 Mg plasma levels increased (P<0:05) in old animals (10±12 months) compared to young (4±6 months). Also Mg levels increased (P<0:05) with number of parities, the order was second followed by third and ®rst pregnancy. Irrespective of parity, mid-lactation showed higher (P<0:05) Mg levels than early lactation. Mg levels were lower (P<0:05) in high yielders compared to low ones.

2.4.3. Sodium (Na) and potassium (K) plasma levels The average values with standard deviations, range of plasma Na and K, minimum and maximum levels

Table 1

Chemical analysis of feedstuffs offered to the goats during the experimental perioda

Composition, DM basis (%) Concentrate Sorghum straw Dry matter 88.4 95.6

Ash 6.2 7.8

Crude protein 19.6 5.8 Crude fiber 4.3 39.0 Ether extract 2.1 0.25 Nitrogen free extract 56.2 40.8 Calcium 0.22 (0.28±0.82) 0.12 Phosphorous 0.19 (0.61±0.38) 0.01 Magnesium 0.11 (0.12±0.18) 0.05 Sodium 1.03 (0.09±0.18) 0.002 Potassium 0.19 (0.50±0.8) 0.42

a_{Figures in parentheses show adequate levels required in the}

are shown in Table 3. While Na plasma levels seemed to be affected by age, K levels were not. There was a decrease (P<₀:_{05) in Na plasma levels in adult} animals (10±12 months) compared to the young

(4±6 months), then there was a decrease (P<0:05) in Na plasma levels with increase in number of parities (®rst to third pregnancy). Although stage of lactation seemed not to have a signi®cant effect on Na plasma

Table 2

Average values (nˆ5), standard deviations (S.D.) and ranges of plasma calcium, phosphorus and magnesium levels (mg/100 ml) for Nubian goats at different physiological states

Physiological state Age Calcium level (mg/100 ml) Phosphorus level (mg/100 ml) Magnesium level (mg/100 ml) Mean S.D. Range Mean S.D. Range Mean S.D. Range Young 4±6 months 10.5a _{1.4 9.6±12.9 6.0}c _{1.3 4.5±7.1 2.4}b _{0.4 2.1±3.2}

Adult 10±12 months 9.8a _{2.8 6.8±13.2 6.4}c _{0.6 5.5±7.0 2.8}a _{0.3 2.4±3.1}

Pregnancy

First 1±2 years 10.6a 2.5 7.3±13.7 6.3c 0.9 5.3±7.4 2.2b 0.1 2.9±3.0 Second 2±3 years 11.2a 3.1 9.3±14.8 2.3a 3.1 1.7±3.7 3.5c 1.3 2.5±5.0 Third 3±5 years 10.6a 2.9 7.3±11.8 4.1b 2.1 2.8±6.8 2.9a 0.1 2.9±3.0

Lactation

First early 1±3 years 6.3b _{3.3 3.2±11.5 4.4}b _{1.0 3.1±5.4 2.4}b _{0.2 2.1±2.6}

Second early 2±4 years 9.0a 0.6 8.2±9.8 4.0b 0.7 3.3±5.0 2.2b 0.2 2.1±2.6 Third early 4±6 years 8.8a 1.8 5.8±10.3 5.1b 1.9 3.5±7.8 2.3b 0.4 1.9±2.7 First mid 1±3 years 10.2a 1.3 8.8±12.1 6.7c 1.5 4.6±8.3 4.6d 0.1 3.8±5.0 Second mid 2±4 years 9.3a 1.8 6.4±12.2 6.9c 2.6 4.7±11.2 4.6d 0.1 3.7±4.8 Third mid 4±6 years 11.0a 1.1 10.0±12.1 8.3c 1.2 7.0±10.2 4.5d 0.5 3.7±4.8 High yielder 9.9a _{1.0 8.3±11.2 5.3}b _{1.5 4.1±7.8 2.4}b _{0.7 1.4±2.3}

Low yielder 8.7a _{1.9 5.8±10.3 5.9}b _{0.6 5.1±6.6 3.2}c _{0.7 2.3±4.0} a,b,c,d_{Values are mean of ®ve animals. Values within the same column bearing different superscripts vary atP<0:05.}

Table 3

Average values (nˆ5), standard deviations (S.D.) and ranges of plasma sodium and paotssium levels (mg/100 ml) for Nubian goats at different physiological states

Physiological state Age Sodium level (mg/100 ml) Potassium level (mg/100 ml)

Mean S.D. Range Mean S.D. Range Young 4±6 months 140d 15.8 124±160 4.2a 0.4 3.1±6.0 Adult 10±12 months 150c 4.7 144±155 4.3a 0.4 3.9±5.5

Pregnancy

First 1±2 years 157a 5.8 153±166 4.4a 0.6 3.6±5.0 Second 2±3 years 129b 5.0 126±134 5.1a 0.4 4.8±5.4 Third 3±5 years 117e 13.6 106±132 4.9a 0.5 4.4±5.3

Lactation

First early 1±3 years 134d _{22.6 105±162 3.7}b _{0.6 3.2±4.7}

Second early 2±4 years 133d _{4.8 129±139 3.5}b _{0.4 3.1±4.0}

Third early 4±6 years 142d _{13.6 106±148 3.5}b _{0.5 3.0±4.4}

First mid 1±3 years 125b _{1.7 123±127 5.1}a _{0.5 4.4±5.6}

Second mid 2±4 years 131d 17.6 102±147 5.2a 1.2 4.4±7.3 Third mid 4±6 years 128b 3.4 123±132 4.8a 0.7 4.2±6.0 High yielder 152c _{13.1 134±170 3.6}b _{0.3 3.2±4.1}

levels, second and third mid-lactation showed the lowest (P<0:05) levels. On the other hand, K plasma, in response to stage of lactation, showed increases (P<0:05) with mid compared with early lactation. Plasma K levels changed only slightly with age and parity. Both Na and K plasma levels did not show signi®cant changes due to the type of yield (high or low).

3. Discussion

Chemical analysis of the ration fed to the goats at different physiological states revealed that, except for sodium, other macrominerals were shown to be lower than those recommended by NRC (1981) for goats. Hence, adequate levels required for pregnancy and lactation were not attained. It has been shown that Ca plasma levels tended to decrease with age while that of P tended to increase. As was pointed out earlier, the percentage of Ca and P in the body and their propor-tion in the skeleton increases throughout the parental and postnatal life as ossi®cation of the skeleton pro-gresses to maturity. However, since it is a metaboli-cally active tissue with continuous turnover and remodeling both in growing and mature animals, elaborate controls exist to maintain a relatively con-stant Ca concentration in the plasma. Blood P home-ostasis is more complicated than blood Ca because blood P is in equilibrium not only with bone P but also with several organic compounds (Church and Pond, 1988). In the present study, there was a tendency for Ca and P plasma levels to decrease in early lactation compared to mid-lactation. This could be related to the excretion of both elements into milk which was high-est during early lactation (Toverud et al., 1976; Bal-lantine and Herben, 1989).

The signi®cant decrease in Ca plasma level during ®rst early lactation observed in this study was similar to that obtained in Black Bengal goats (Uddin and Ahmed, 1984). Also the signi®cant decreases in P plasma levels obtained during early lactation were in agreement with those of Anges and Tozzi (1986). Ca and P lost during early lactation were regained in the same ratio with advancement of lactation by bone mobilization (Sherman and Quin, 1926). The signi®-cant differences obtained in P plasma levels between parities could be related to the complicated blood P

homeostasis during pregnancy. The non-signi®cant changes in both Ca and P levels obtained in high or low yielders would point to the fact that these elements are not affected by the genetic make up of the animals. In the current study, plasma magnesium (Mg) level decreased signi®cantly in young animals during ®rst pregnancy and early lactations. Similar results were obtained by Breibart et al. (1960). Low plasma Mg level in young animals was due to the fact that uptake of Mg by young animals was more rapid than in adult ones. Furthermore, it has been found that the exchange of Mg was ®ve to ten times greater in young than in old animals (Breibart et al., 1960). Since young animals have more water content than young, more water ions are adsorbed on the surface of bone crystal resulting in low Mg ions in the blood (Fontenot et al., 1989).

During pregnancy, plasma Mg level decreased sig-ni®cantly, this could be related to the physiochemical changes that took place in the blood during pregnancy which favored the passage of Mg from the mother to the foetus (Watchorn and McCane, 1932). Mg plasma levels were also observed to decrease in early lacta-tions but increased in mid-lactalacta-tions. Similar observa-tions were obtained by Mbassa (1991) which were associated with the high amounts of Mg being secreted into milk during early lactation with concomitant decrease in plasma Mg level in the blood.

In the present study plasma Mg level in high yielder goats was signi®cantly lower than in low yielder goats. According to Todd's (1976), high yielding cows might secret 12 mg/100 ml into milk in 1 day, which was equivalent to the total Mg in extracellular ¯uid.

Plasma Na concentrations decreased signi®cantly with age. Similarly, it was shown that in individual tissues, Na content usually declines with age, in part at least owing to a decrease in extracellular volume (Toel et al., 1960). A signi®cant decrease in Na level was also observed during mid-lactations, according to Underwood (1981), reduction of Na is most likely to occur during lactation as a consequence of losses of this element in the milk. In contrast to Na, K plasma levels decreased in early rather than mid-lactation which could be due to the maintenance of a constant ratio of Na to K in the extracellular ¯uid (Church and Pond, 1988).

system, this study showed that during pregnancy, demand of foetus for elements such as P and Mg resulted in decreased levels of these elements in the maternal blood. Similarly, the demand of milk reduced Ca, P, Mg and K and necessitated the mobilization of these elements from their original sites to be secreted into the milk.

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