MILK UREA AND LACTOSE AS INDICATORS OF THE PROTEIN AND ENERGY STATUS IN LACTATING EWES AND GOATS
Bed, Sándor Nagy, Zoltán
Nikodémusz, Etelka Délborsod Co-operative for
Institute of Animal Husbandry Fish and Sheep-Farming
Gödöll University of Agricultural Sciences Gelej, Hungary
Experimental Farm of the
University of Veterinary Sciences
Üll-Dóra Major, Hungary
The concentrations of urea and lactose in the milk of 10 Pleven F1 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.
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 (Bed et al., 1997).
This study was aimed to evaluate the use of milk urea and lactose as indicators of the protein-energy 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).
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.
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).
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.
Figure 4. Variation in milk yields of ewes and goats and in dietary P/E ratio during lactation
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 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.
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