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					MILK UREA AND LACTOSE AS INDICATORS OF THE PROTEIN AND ENERGY STATUS IN LACTATING EWES AND GOATS

Bedő, Sándor Nikodémusz, Etelka
Institute of Animal Husbandry Gödöllő University of Agricultural Sciences Gödöllő, Hungary

Nagy, Zoltán
Délborsod Co-operative for Fish and Sheep-Farming Gelej, Hungary

Seregi, János
Experimental Farm of the University of Veterinary Sciences Üllő-Dóra Major, Hungary
—————————————————————————————————————————————— — ABSTRACT The concentrations of urea and lactose in the milk of 10 Pleven F 1 x East-Friesian ewes and 9 Saanen goats, under grazing and stable conditions, respectively, were monthly determined during 5 and 7 months of lactation. Blood samples were also taken and analysed for plasma urea and glucose. Milk yields were recorded. The staple diet for ewes consisted of a milking concentrate, maize grains and grazing grass. Goats were fed a milking concentrate and alfalfa or meadow hay. The levels of urea in milk and plasma correlated fairly in both species during lactation. Milk urea showed a significant (P < 0.001) diurnal variation in goats, whereas this trend was devoid in ewes. Lactose correlated positively with milk yield and plasma glucose in both species. Milk yield, lactose and urea in milk of ewes varied in positive correlation with the P:E ratio and in negative correlation with the NDF content of the grazing forage. Similar relationships were found in goats, but to a lower extent, since the P:E ratio and NDF content in their diet varied relatively less. —————————————————————————————————————————————— —

INTRODUCTION
Milk and blood urea analyses have extensively been used as an indicator of the protein nutritional status in cattle (Oltner and Wiktorsson, 1983: Magdus et al., 1988; Carlsson and Pehrson, 1994). In particular the ratio between protein and energy (P:E) is a valuable measure (Oltner and Wiktorsson, 1983). Glucose concentration in blood may indicate the energy status in ruminants (Rowlands, 1980; Andersson and Lundström, 1984; Miettinen and Huhtanen, 1989). Since glucose plays an important role in the secretion of milk and approximately 85 percent of lactose synthesised from glucose (Kállai and Kralovánszky, 1975), lactose may serve as an indirect indicator of the energy status (Bedő et al., 1997).

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This study was aimed to evaluate the use of milk urea and lactose as indicators of the proteinenergy status in lactating ewes and goats.

MATERIAL AND METHODS
The experiments were carried out with 10 Pleven F1 x East-Friesian ewes and 9 Saanen goats, under grazing and stable conditions, respectively, during 5 and 7 months of lactation. The staple diet for ewes consisted of a milking concentrate, maize grains and grazing grass. Goats were fed a milking concentrate and alfalfa or meadow hay. Nutrient composition of feeds were determined according to Weender-analysis. The NDF fraction was determined by the method of Goering and Van Soest (1970). Ewes and goats weaned in late February and early March, respectively. After the suckling period, animals were machine-milked twice daily. Evening and morning milk samples were individually taken and milk yields recorded at 4-week intervals. Milk samples were analysed for solid composition, including urea, and somatic cell counts using a Foss-Electric System 4000. Blood samples were also taken and analysed for urea and glucose by spectro-photometry using REANAL test kits of cat. No. 11532 and 07239, respectively. Circulating leukocyte count was also determined.

RESULTS AND DISCUSSION
Ewes produced daily an average 1.1  0.6 litres of milk with an average fat and protein percentage of 6.0 1.7 percent and 5.9 0.7 percent, respectively. The daily milk yield of goats averaged 2.0 0.6 litres, with a fat and protein content of 4.2 1.2 percent and 3.4 1.1 percent, respectively. Urea in milk and plasma correlated fairly (Figure 1) in ewes (r=0.88, P < 0.05) and goats (r=0.59 P > 0.10), supporting reported data for cattle (Oltner and Wiktorsson, 1983; Magdus, 1988; Miettinen and Juvonen, 1990). Corresponding levels for MU (11.4 1.8 mmol; 10.8 1.7 mmol per litres) and PU (7.4 1.6 mmol; 7.2 1.7 mmol per lit) were comparable. The concentration difference between PU and MU was due to the different methods of urea determination. The urea concentrations in plasma and milk of goats were lower in month 1 of lactation than later in lactation, similar to previous reports for dairy cows (Bruckental et al., 1980; Carlsson et al., 1995). The urea levels in plasma and milk of ewes took peaks in month 2 of lactation, then the values decreased but with an increase during the last month. A somewhat similar variation has been reported for ewes by Tadich et al. (1994).

205

EWES
13 12 MU PU 9

MU (mmol/l)

11 7 10 9 8 A M J J A S O

r = 0.88 P < 0.05

6

5

GOATS
MU 13 12 PU 9

MU (mmol/l)

11 7 10 9 8 A M J J A S O

r = 0.59 P > 0.1

6

5

M onths

Figure 1.

Variation in urea concentrations in milk and plasma of ewes and goats during lactation

Milk urea was significantly (P < 0.001) higher in evening than morning milk of goats, whereas it showed no significant diurnal variation in grazing ewes (Figure 2). The feeding may reportedly influence the serum urea level significantly in the morning, while it may not be so influential in the afternoon (Miettinen and Juvonen, 1990). The above difference may therefore be due to a relatively longer fasting period during the preceding night in case of goats, compared to ewes grazing till sunset.

206

PU (mmol/l)

8

PU (mmol/l)

8

15

MU (mmol/l)

M orning 10 Evening

5

EWES

GOATS

Figure 2. The urea concentration in the morning and evening milk of ewes and goats Lactose correlated positively with milk yield and also with plasma glucose in ewes (r=0.88; r=0.42) and goats (r=0.23; r=0.73) during lactation. The overall concentrations of lactose (4.9 0.6 percent and 4.7 0.3 percent) were comparable, but plasma glucose was lower by 39 percent in ewes (1.6 0.5 mmol per litres) than goats (2.6 0.7 mmol per litres), due to a very low initial value (Figure 3).

207

EWES
Glu Lact 2 5

1

4

r = 0.42 P > 0.1
0 A M J J A S O 3

GOATS
Glu 4 Lact 5

2

4

1

r = 0.73 P < 0.05
3 A M J J A S O

0

M onths

Figure 3. Variation in lactose and plasma glucose levels of ewes and goats during lactation

The milk production parameters varied according to the nutrient composition of feeds during lactation (Figures 4-5). Milk yield, lactose and urea in milk followed mid-lactation depressions in ewes due to the decreases in the P:E ratio and increases in the NDF content of the grazing forage. The positive correlation of these variables with the P:E ratio (r=0.94; r=0.85; r=0.59) and their negative correlation with NDF (r=-0,96; r=-0,78; r=-0,39) showed that milk production in grazing ewes was strongly affected by the aging of the grass with rising air temperature.

208

Lact (%)

Glu (%)

3

Lact (%)

Glu (%)

EWES
MY P/E 2 20

1,5

15

1

r = 0.94 P < 0.001

10

0,5 A M J J A S O

5

GOATS
MY P/E 2,5 14

2 12 1,5

r = 0.75 P < 0.05

11

1 A M J J A S O

10

M onths

Figure 4. Variation in milk yields of ewes and goats and in dietary P/E ratio during lactation

P/E (g/MJ)

MY (l)

13

P/E (g/MJ)

MY (l))

209

EWES
Lact 5,5 NDF 60

Lact (%)

4,5

40

4

r = - 0.78 P < 0.1

30

3,5 A M J J A S O

20

GOATS
Lact NDF 5 45

Lact (%)

35 4

r = - 0.69 P < 0.1
3 A M J J A S O

30

25

M onths

Figure 5. Variation in lactose level of ewe's and goat's milk and NDF content during lactation Milk yield, lactose and urea in milk also positively correlated with the dietary P:E ratio in goats (r=0.75; r=0.10; r=0.45) and negatively with NDF (r=-0.46; r=-0.69), except milk urea (r=0.61). However, the degree of correlation was lower, since the P:E ratio and NDF in the diet of goats varied relatively less, except the last month's drops. Thus, milk yield showed inconsistent decreases and urea in milk consistently increased till the last month, when both dropped. Except for a temporary decrease in mid-lactation, lactose varied little. A rather weak positive correlation was found between yields and milk urea level in ewes (r=0.28) and goats (r=0.10) over the whole period of lactation. A similar correlation has been observed in dairy cows, particularly in late lactation (Carlsson et al., 1995). Apart from the last month, this correlation was, however, definitely negative (r=-0.76) in the case of goats, suggesting a relative overfeeding. This relationship could be attributed to the variation in the P:E ratio of the diet rather

210

NDF (%)

40

NDF (%)

5

50

than to an effect of milk yield per se. This assumption was supported by the closer correlation of milk yield and milk urea level with the dietary P:E ratio. The somatic cell count in goat's milk (1041 802 x 103 cells per ml) surpassed, whereas the SCC in ewe's milk (611 843 x 103 cells per ml) was well below the threshold count of 1 million per ml. The similar counts of circulating leukocytes (7.1 2.1 x 103 and 7.9 2.0 x 103 per ml), in turn, revealed that animals were healthy. The SCCs varied in significant negative correlation with milk yields (r=-0.82, P < 0.05; r=-0.90, P < 0.001), suggesting the strong function of dilution by milk volume. The results showed that milk urea and lactose may be useful indices of the protein-energy status of lactating small ruminants, especially under grazing conditions. The negative correlation found between urea and SCC in milk of ewes (r=-0.61) and goats (r=-0.10) was also noteworthy.

REFERENCES
Andersson, L. & Lundström, K. 1984. Effect of energy balance on plasma glucose and ketone bodies in blood and milk and influence of hypoketonemia on milk production in postparturient dairy cows. In: Zbl. Vet. Med. A 31: 539-547. Bedő, S.- Nikodémusz, E.- Gundel, K. & Nagy, Z. 1997. Relations of plasma concentrations of urea, glucose and total protein to milk levels of urea, lactose and protein of grazing ewes during lactation. In: Arch. Tierz., Dummerstorf 40: 265-275. Bruckental, I.- Andersson, L. & Carlström, G. 1986. Determination of milk urea by flow injection analysis. In: J. Vet. Med. A 33: 53-58. Carlsson, J.- Bergström, J. & Pehrson, B. 1995. Variations with breed, age, season, yield, stage of lactation and herd in the concentration of urea in bulk milk and individual cow's milk. In: Acta Vet. Scand. 36: 245-254. Carlsson, J. & Pehrson, B. 1994. The influence of the dietary balance between energy and protein on milk urea concentration. Experimental trials assessed by 2 different protein evaluation systems. In: Acta Vet. Scand. 35: 193-205. Goering, H. K. & Van Soest, P. J. 1970. Forage Fiber Analyses (Apparatus, Reagents, Procedures, and Some Applications). In: Agric. Handbook. No. 379. ARS-USDA, Washington, DC. Kállai, I. & Kralovánszky, U. P. 1975. Biology of Meat and Milk Production (in Hungarian). Mezőgazdasági Kiadó, Budapest, 1975, 201-207. Magdus, M.- Fekete, S.- Frenyó, L. V- Miskucza, O. & Kotz, L. 1988. Milk production and certain parameters of energy metabolism in dairy cows fed rations of varying energy and crude protein contents and fat. In: Acta Vet. Hung. 36: 43-59. Miettinen, H. & Huhtanen, P. 1989. The concentrations of blood metabolites and the relations between blood parameters, fatty acid composition of milk and estimated ME-balance in dairy cows given grass silage ad libitum with five different carbohydrate supplements. In: Acta Agric. Scand., Stockholm 39: 319-330. Miettinen, P. V. A. & Juvonen, R. O. 1990. Diurnal variations of serum and milk urea levels in dairy cows. In: Acta Agric. Scand. 40: 289-296. Oltner, R. & Wiktorsson, H. 1983. Urea concentrations in milk and blood as influenced by feeding various amounts of protein and energy to dairy cows. In: Livestock Prod. Sci., Amsterdam 10: 457-467.

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Rowlands, G.J. 1980. A review of variations in the concentrations of metabolites in the blood of beef and dairy cattle associated with physiology, nutrition and disease, with particular reference to the concentration of metabolic profile. In: World. Rev. Nutr. Diet. 35: 172-235. Tadich, N.- Wittwer, F.- Gallo, C.& Jorquera, M. 1994. Efecto de un programa de salud en ovinos sobre la condition corporal y los valores sanguines de B-hidroxibutirato, hematocrito y urea. In: Arch. Med. Vet. 26: 43-50.

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