THE RELATIONSHIP BETWEEN BLOOD PLASMA CHOLESTEROL AND MILK PRODUCTION PARAMETERS IN CZECH PIED COWS – PRELIMINARY RESULTS

Gustav Chládek, Ladislav Máchal, Andrzej Hibner, Piotr Nowakowski

ABSTRACT

Czech Pied dairy cows were observed one day each month for the period of 12 months (12 test days). All the cows were in the first phase of lactation, i.e. up to 100 days after calving. The mean number of lactation was 2.8, the cows were on average 54.8 days after calving and the mean concentration of cholesterol in blood plasma was 3.93 mmolˇdm^-3 (149.4 mgˇ10^-1dm^-3). During the first 100 days of lactation milk yield amounted to 2 581 kg with 3.91% fat, 3.48% protein and 4.85% lactose. Despite high values of correlation obtained within single test day, relations for the entire year between blood plasma cholesterol concentration and milk production parameters did not reveal strong relationships (from –0.013 to +0.259). However, the graphic polynomial expression showed that cholesterol concentration tended to have negative relationship with milk fat or milk lactose content. The relationship between cholesterol and milk yield was mainly negati

Key words: Czech Pied, cows, cholesterol, milk production, milk fat, milk protein.

INTRODUCTION

The Czech Pied cattle breed belongs to the group of breeds originated from Simmental cattle. The breeds of the same origin (Fleckvieh, Slovak Pied) are major dairy breeds in some European countries (Austria, Germany). In other countries (Slovakia, Poland) they play an important role in milk production. Milk production in dairy cattle breeds in the Czech Republic and Poland has significantly increased during the recent years. Top sub-populations of high- producing cows have become the subject of scientific research - especially production and reproduction parameters have been analysed [3, 5].

Increased milk production leads to higher nutritional requirements of cows. Energy, its quantity and structure, play the key role in cow’s nutrition. Cholesterol is an important indicator of energy supply in lactating cow’s organism [14]. According to Jagoš et al. [6] physiological values of blood plasma cholesterol in cattle range between 2.6 mmolˇdm^-3 and 5.2 mmolˇdm^-3, while Kraft and Dürr [8] presented a slightly different physiological range, 2.0 to 4.5 mmolˇdm^-3.

The relationship between cholesterol concentration in blood plasma and milk production was analysed by Chládek et al. [4], who observed Holstein dairy cows for the period of 12 months (12 test days). The mean milk yield was 33.8 kg, milk protein content 2.96%, milk fat content 4.02% and cholesterol concentration in blood plasma 3.44 mmolˇdm^-3. Authors concluded that the coefficients of the correlation between cholesterol in blood plasma and milk production parameters did not reveal a clear tendency in the relationships. However, the graphical expression showed the tendency towards a positive relationship between blood plasma cholesterol and milk yield and a negative relationship between blood plasma cholesterol and milk protein content. No relationship between blood plasma cholesterol and milk fat content was found due to the high variability of fat content in milk.

Ruegg et al. [12] observed relations among body condition score, milk production and the concentration of serum urea nitrogen and cholesterol in high-producing Holstein dairy cows in early lactation. They repeatedly analysed data on a group of dairy cows from 4 to 87 days after calving. The results showed an increase in daily milk yield from 28.2 kg to 42.9 kg while blood plasma cholesterol increased from 98.7 to 386.3 mgˇ10^-1dm^-3. The concentration of cholesterol was inversely related to the degree of loss in body condition and may reflect the availability of body energy sources. Cows with a higher body condition score at calving showed a greater body condition loss after calving and had lower cholesterol values.

Belibasakis [1] studied the effect of nutrition on milk yield and milk composition. He presented some milk production characteristics and blood plasma cholesterol concentrations found in three experimental groups of cows. An insignificant increase in cholesterol concentration in blood plasma (from 248.5 to 280.5 mgˇ10^-1dm^-3) was accompanied with an insignificant decrease of milk fat content (from 3.6 to 3.4%) and milk protein content (from 3.4 to 3.3%), while milk yield practically did not change (from 26.04 kg to 26.35 kg of daily milk yield).

Lean et al. [11] dealt with time series cross-correlation analyses of post-parturient relationships among serum metabolites and yield variables in Holstein cows. They found significant negative relationship between milk yield and blood plasma cholesterol (observed on the same day). They supposed that serum cholesterol might be eliminated into milk or, more likely, that alternations in metabolism required for increased milk yield resulted in lower blood cholesterol. The positive relationships between milk yield and cholesterol concentrations 3 to 9 days later may be due to alterations to the partitioning of metabolites rather than being a direct result of hepatic lipidosis. Kudláč et al. [10] studied the effects of retained placental membranes on the metabolic profile of cows. He monitored blood plasma cholesterol concentration in cows from 2 to 50 days after calving that came from a herd with average milk production 4 300 kg. Cholesterol values ranged from 2.78 mmolˇdm^-3 (2 to 5 days after calving) to 4.37 mmolˇdm^-3 (30 days after calving).

Vojtíšek et al. [15] examined the effect of fatty acid salts (C16-C18) in the diet of cows after parturition as a source of increased energy addition and their effect on some characteristics of metabolism, reproduction and milk production. Maximum daily milk yield during the first 100 days of lactation was 22.4 kg FCM in the control group and 24.4 kg FCM in the experimental group. Blood plasma cholesterol concentration was 3.1 mmolˇdm^-3 (23^rd day of lactation) and 4.8 mmolˇdm^-3 (107^th day) in the control group and 3.8 mmolˇdm^-3 (23^rd day) and 6.1 mmolˇdm^-3 (107^th day) in the experimental group.

The aim of the present study was to describe changes in the relationship between blood plasma cholesterol and milk production traits in Czech Pied cows in the course of a year.

MATERIALS AND METHODS

Groups of Czech Pied cows (n = from 20 to 23 per month) in early lactation (20 to 100 days after calving) were chosen for observation each month during the course of one year. The cows came from one dairy herd with an average milk yield of 6 000 kg per cow, per lactation. All the cows were housed in the same cowshed with a tethered system and straw bedding. The all year around diet consisted of feeds typical for that region (maize and grass silage, grain meal, extracted meal, minerals and vitamins) and the ration was calculated according to recommendations of Sommer et al. [13]. The diet was not served as TMR and the concentrated feed was fed according to the milk yield.

Each cow was blood sampled (from vena subcutanea abdominis) in the morning. On the same day blood samples were centrifuged to separate blood and cholesterol concentration was assessed colorimetrically using Bio-La-tests. Other milk production parameters were adopted from the database of milk recording (A₄), where the samples were analysed for milk fat, protein and lactose content using Milkoscan 255 AB. Cholesterol values were compared to milk traits which were calculated as averages for the 100 days of lactation.

Trends in the relationships between blood plasma cholesterol and milk production parameters were described by coefficients of correlation.

Changes in milk production, milk fat, protein and lactose content and plasma cholesterol concentration in a course of time were graphically expressed as a polynomial of the second or third degree.

RESULTS AND DISCUSSION

Mean values of blood plasma cholesterol concentration and some milk production parameters during the first 100 days of lactation are presented in Table 1. The number of cows in the groups ranged from 20 to 23 while the average number was 21.2 cows per group and month. Blood plasma cholesterol concentration was, on average, 3.93 mmolˇdm^-3 with maximum and minimum values of 4.67 and 2.75 mmolˇdm^-3, respectively. The mean number of days after calving was 54.8 with a minimum of 49.5 days and a maximum of 66.4 days. The milk yield for the first 100 days of lactation ranged from 2 418 to 2 830 kg, with a mean of 2 581 kg. Milk fat content was on average 3.91% while the highest fat content was 4.27% and the lowest was 3.62%. The mean milk protein content was 3.48% with a maximum of 3.87% and a minimum of 3.16%. Milk lactose content ranged from 4.70 to 5.01% with a mean value of 4.85%.

Coefficients of correlation between traits are shown in Table 1. The coefficient of correlation for the whole set of data (12 months) between blood plasma cholesterol concentration and number of lactation was –0.013, with the values ranging from the minus 0.217 to +0.781 for the single months results. The coefficient of correlation between cholesterol and days after calving was +0.259 for the whole population, with the range from –0.202 to +0.911 in different months of the year. Relation between cholesterol and milk production was –0.089 (range from –0.746 to +0.470 in separate months). General coefficients of correlation between blood plasma cholesterol and milk components were as follows: for milk fat –0.176 (minimum value –0.616 and maximum +0.297), for milk protein +0.100 (minimum –0.758 and maximum +0.599) and for lactose content –0.079 (minimum –0.393 and maximum +0.431).

Graphical expressions of changes in blood plasma cholesterol concentration and milk production parameters, including their polynomial trends, described by equations, were presented as: plasma cholesterol concentration and milk fat content (Fig. 1) and plasma cholesterol concentration and lactose content (Fig. 2). Polynomial equations were very good fitted during the yearly pattern for both: milk fat (R² = 0.90) and lactose content in milk yield per 100 days (R² = 0.81). Cholesterol was negatively related to lactose and fat milk contents. Observed trends were much smoother and better fitted to test results in the period of summer season feeding (from May to September) when compared to patterns observed during winter season feeding (October to April). Cholesterol level was quite stable during summer season test days with lower values towards the autumn.

The mean milk yield of the experimental animals was 2 581 kg per 100 days, which meant that daily production was approximately 26 kg and a predicted yield per lactation of 6 000 kg. These values were lower than those presented by Chládek et al. [4] and Ruegg et al. [12] but they were higher than the values reported by Kudláč et al. [10] and Vojtíšek et al. [15].

The cows produced milk with higher milk protein content compared to the results of Chládek et al. [4]. This difference was most likely due to the different breed of observed animals; we used dual-purpose Czech Pied cattle, while the above quoted authors observed dairy Holstein cows. On the contrary milk fat content was not as high as could be expected in dual-purpose cattle.

Our mean value of cholesterol concentration in blood plasma (3.93 mmolˇdm^-3 = 149.4 mgˇ10^-1dm^-3) and the range of values (from 2.75 mmolˇdm^-3 = 104.5 mgˇ10^-1 dm^-3 to 4.67 mmolˇdm^-3 = 177.5 mgˇ10^-1dm^-3) corresponded with results of Kudláč et al. [10] and Vojtíšek et al. [15]. The lowest mean concentration of cholesterol reported have been found by Chládek et al. [4] and Ruegg et al. [12]. Maximum values differed greatly between studies; our highest values were lower than those presented by Vojtíšek et al. [15], Belibasakis et al. [2] and considerably lower than values presented by Ruegg et al.[12]. Our mean concentration of cholesterol lay in the middle of the physiological range according to results of Jagoš et al. [6], while according to Kraft and Dürr [8] our results approached the upper physiological limit.

Our coefficients of correlation between blood plasma cholesterol concentration and milk production traits did not show a clear tendency; the relationships were better described graphically. This conclusion was consistent with results of Chládek et al. [4].

We found a significant positive relationship between blood plasma cholesterol and the number of days after calving (+0.259), in agreement with Kudláč et al. [10] and Vojtíšek et al. [15]. Our positive relationship between blood plasma cholesterol and milk protein content (+0.100) was rather exceptional; Belibasakis [1] observed a non-significant tendency towards a negative relationship and Chládek et al. [4] found the relationship to be significantly negative. This discrepancy could result from the use of different breeds between the experiments. Also, while we monitored milk yield per 100 days, Chládek et al. [4] only analysed milk production on the test days.

We found a negative relationship between blood plasma cholesterol and milk fat content (-0.176). This result corresponded with tendencies described by Belibasakis [1] and it did not strictly contradict results of Chládek et al. [4]. The relationship between blood plasma cholesterol and milk yield was negative when cholesterol concentration was higher than approximately 4.0 mmolˇdm^-3; when the concentration was lower than 4.0 mmolˇdm^-3 the relationship was positive. The negative relationship prevailed. This finding was in agreement with Vojtíšek et al. [15] but in contrast with Chládek et al. [4], which could be explained by differences in methods between experiments (a different breed and milk yield recording).

Lean et al. [11] also found a negative relationship between blood plasma cholesterol and milk yield even though they only examined the milk yield on test days. They supposed that serum cholesterol might be eliminated into milk or, more likely, that alternations in metabolism required for increased milk yield resulted in lower blood cholesterol.

Discrepancies in relations (negative or positive) between the same traits but obtained for different test days partially might be explained by the use of not the same animals in different months and by nutritional factors – not uniform during the course of observations. As stated by Kandeh et al. [7] selection for low or high serum cholesterol concentration in farm animals is possible and changes their lipid metabolism. Kronfeld et al. [9] stated that one of the best serum predictors of ration variables was cholesterol. Based on this statement not uniform feeding pattern of cows during winter season was observed in our study. Coefficients of correlation for test days during winter season showed no steady and clear trends between serum cholesterol and milk production traits.

CONCLUSIONS

Comparison of coefficients of correlation between blood plasma cholesterol concentration and milk traits obtained in separate test days of different months of the year did not suggest a clear tendency. However, based on general relations and on analysis of polynomial trends such tendencies were shown. It can be concluded that blood plasma cholesterol concentration in Czech Pied cows in the first phase of lactation had generally positive relationship with the number of days after calving and milk protein content. On the contrary, it had a generally negative relationship with milk fat, milk yield and milk lactose content.

ACKNOWLEDGEMENTS

The study was supported by MSM 432100001.

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Andrzej Hibner, Piotr Nowakowski
Institut of Animal Husbandry
Agricultural University of Wrocław
Chełmońskiego 38c, 51-630 Wrocław, Poland
Tel. (+48-71) 3205-772
e-mail: hibner@ozi.ar.wroc.pl

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