Study on the loss of accuracy of AC-method for milk yield control in sheep

D. Dimov*, P. Zhelyazkova, A. Vuchkov

Department of Animal Sciences, Faculty of Agronomy, Agricultural University, 4000 Plovdiv, Bulgaria (Manuscript received 30 June 2017; accepted for publication 5 September 2017)

Abstract. The aim of this study was to investigate the loss of accuracy of AC-method for milk yield control in sheep under the conditions of threefold milking per day. Test day milk yield records of 113 ewes raised on sheep farm of the Agricultural University in Plovdiv collected according to official A4 method were used. Two breeds were raised at the university experimental farm: White Maritza (49 ewes) and Patch Faced Maritza (64 ewes). Predicted milk yield data on test day were simulated using different prediction coefficients (calculated at morning, noon or evening milk recording). Database includes 2577 predicted milk yield records on test day. The loss of accuracy using AC method is accumulated in two ways: by milk yield prediction coefficients on test day and milk yield calculations during milking period. Loss of accuracy (LA1) in prediction of test day milk yield by prediction coefficients varies from 10.02% to 12.74% according to type of milk recording (morning, noon or evening). Three factors such as level of test day milk yield, type of milk recording and animal have larger influence on LA1, 27.70%, 21.99% and 19.32%, respectively, of total variation. Loss of accuracy (LA2) in the calculated total milked milk per milking period on the basis of predicted test day milk yield according to the morning, noon and evening milk recordings compared with A4 method are 7.04%, 8.03% and 6.05%, respectively. Depending on the type of milk recording on the test day (morning, noon and evening), 46.88% to 56.15 % of the observations of LA2 fall within the scope of ±5%. Rank correlations in the ranking of ewes in all years and different designs of AC method have high values from 0.891 to 1.000.

Classification and regression tree analysis in modeling the milk yield and conformation traits for Holstein cows in Bulgaria

A.Yordanova1*, S. Gocheva-Ilieva1, H. Kulina1, L. Yordanova2, I. Marinov3

1Department of Applied Mathematics and Modeling, Faculty of Mathematics and Informatics, Plovdiv University Paisii Hilendarski, 24 Tzar Asen, 4000 Plovdiv, Bulgaria
2Department of Mathematics and Informatics, Faculty of Economics, Trakia University, 6000 Stara Zagora, Bulgaria
3Department of Animal Science – Ruminants and Dairy Farming, Faculty of Agriculture, Тrakia University, 6000 Stara Zagora, Bulgaria

Abstract. In the field of livestock breeding the investigation of the factors that influence to the highest degree the efficiency (e.g. milk yield) is essential for determining the conditions for the improvement of the overall production results. To extract relevant information from the data the appropriate mathematical methods are very useful. The aim of this work is to demonstrate the capabilities of the method of Classification and regression trees (CART) for statistical data processing including data of ordinal and nominal type. For a sample of 97 observations of cattle from 4 farms in Bulgaria, two decision trees are built for studying dependence of the 305 days milk yield for Holshte in cows with respect to 13 independent variables – 12 conformation traits and farm. The model with 12 independent variables for conformation traits describes 48% of the data and identifies the main factors for quantities of milk – udder width, locomotion, stature and chest width with normalized importance 100%, 48.1%, 41.2% and 39%, respectively. The second model includes the farm where the cattle are reared as 13th independent variable and this expanded model accounts for 70% of the data. Following the obtained rules for both models, predictions for new data could be made before end of lactations.

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Effect of season, lactation period and number of lactation on mastitis incidence and milk yields in dairy cows

T. Penev1*, Zh. Gergovska2, I. Marinov2, V. Kirov3, K. Stankov4, Y. Mitev1, Ch. Miteva1
1Department of Applied Ecology and Animal Hygiene, Faculty of Agriculture, Trakia University, 6000 Stara Zagora, Bulgaria
2Department of Animal Science, Faculty of Agriculture, Trakia University, 6000, Stara Zagora, Bulgaria
3Department of Animal Sciences, Faculty of Veterinary Medicine, University of Forestry, Sofia, Bulgaria
4Department of Management, Faculty of Economics, Trakia University, 6000, Stara Zagora, Bulgaria
Abstract. The aim of the present study was to study the effect of the season, period and number of lactation on mastitis incidence and milk yields in dairy cows. The climate in Bulgaria implies the presence of seasonal variations in mastitis prevalence in dairy cows, reared in free-stall barns all the year round: spring – 5.33%, summer – 4.9%, autumn – 4.2% and winter – 4.5%. The mastitis incidence during the lactation periods increased gradually from calving to the 120th lactation day. For the first 120 days of lactation, the mastitis incidence attained 26%. The reduction in milk yields after the lactation peak was associated with gradual decliine in cows affected by mastitis to 1.7% during the last month of lactation. With increasing the number of lactations, mastitis incidence also increased: 23.3% in 1st lactation cows, 26.7% in 2nd lactation cows, 48.9% in 3rd lactation cows and 43.3% in cows in fourth or subsequent lactation. The highest daily milk yield at the peak of lactation (34.05 kg) was established in cows affected by mastitis after the 180th lactation day, followed by cows with mastitis between the 60th and 180th lactation days (32.54 kg), and third came healthy cows (31.98 kg). The lowest daily milk yield at the peak of lactation was demonstrated in cows affected by mastitis in the first 60 days of the lactation (29.39 kg). It was proved that cows with exceptionally high milk yields in the beginning of lactation were more prone to mastitis at a later stage due to weakened systemic resistance and consequent disease. Cows with relatively lower milk yield during the lactation period (7580.3 kg) were more resistant to environmental factors, therefore were not affected by mastitis and produced highquality milk with lower costs vs those with highest milk yields affected by mastitis after the 180th day. These cows produced more milk (7607.9 kg) within a 305- day lactation, but the treatment costs could be hardly compensated. Cows in which mastitis occurred until the 60th and between the 60th and 180th lactation day, produced 7215.5 and 7484.1 kg milk, respectively. The average milk yield per lactation of healthy cows was by 137.83 kg higher than that of cows with mastitis. A statistically significant reduction in milk fat (Р < 0.05) and milk protein (Р < 0.001) between healthy and diseased cows was observed.

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Effects of days open on the milk yield and the duration of the concurrent lactation in Bulgarian Murrah buffaloes

A study assigning 1021 lactations of 313 Bulgarian Murrah buffalo cows with milk yield recorded on the farm of Agricultural Institute – Shumen during
the period 1967-2001 was initiated with the objective to estimate the effect of days open on the milk yield and the duration of the concurrent lactation. Using
linear LS-analyses, significant antagonistic effect of days open on 305-day milk yield and especially on complete days in milk was established. Service period of
three to five months is expected to be the most beneficial for the balance between reproductive efficiency and productive performance, at preferable lactation
duration.

Effects of days open on the milk yield and the duration of the concurrent lactation in Bulgarian Murrah buffaloes

P. Penchev, Y. Ilieva, Tz. Peeva