ISSN 1313 - 8820Volume 6, Number 1

March 2014

2014

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Editors and Sections

Genetics and Breeding

Atanas Atanasov (Bulgaria)Nikolay Tsenov (Bulgaria)Max Rothschild (USA)Ihsan Soysal (Turkey)Horia Grosu (Romania)Bojin Bojinov (Bulgaria)Stoicho Metodiev (Bulgaria)

Nutrition and Physiology

Nikolai Todorov (Bulgaria)Peter Surai (UK)Zervas Georgios (Greece)Ivan Varlyakov (Bulgaria)

Production Systems

Dimitar Pavlov (Bulgaria)Bogdan Szostak (Poland)Dimitar Panaiotov (Bulgaria)Banko Banev (Bulgaria)Georgy Zhelyazkov (Bulgaria)

Agriculture and Environment

Georgi Petkov (Bulgaria)Ramesh Kanwar (USA)Martin Banov (Bulgaria)

Product Quality and Safety

Marin Kabakchiev (Bulgaria)Stefan Denev (Bulgaria)Vasil Atanasov (Bulgaria)

English Editor

Yanka Ivanova (Bulgaria)

2014

ISSN 1313 - 8820 Volume 6, Number 1March 2014

Biological fertility and milk yield in Bulgarian Dairy Synthetic Population sheep according to breeding line

1 2 3N. Stancheva *, I. Dimitrova , S. Georgieva

1Agricultural Institute, 3 Simeon Veliki, 9700 Shumen, Bulgaria2Department of Genetics and Breeding of Agricultural Crops, Faculty of Agronomy, University of Forestry, 10 Kliment Ohridski, 1756 Sofia, Bulgaria 3Department of Genetics, Breeding and Reproduction, Faculty of Agriculture, Trakia University, 6000 Stara Zagora, Bulgaria

Abstract. The aim of the study is to determine the parameters of the biological fertility and milk production of sheep breed Dairy Synthetic Population from herd of the Agricultural Institute, Shumen. The survey covers 851 ewes born in the period 2004 – 2008. Biological fertility of ewes is dependent on the order

st rdof lambing, and is the lowest on the 1 (1.24) and the highest on the 3 lamb (1.52). In animals from line 51 (a cross breed with Chios) it is the highest on 2.5 years old –1.56, on 3.5 years old – 1.67, on 4.5 years old – 1.90, as fertility of the sheep of the leading pure-bred lines is 1.27, 1.42 and 1.49. The average milk

st nd yield for standard 120-day milking period of sheep in the flock is the highest in animals from line 51 and on the 1 lactation it is by 23.7% and on the 2 by 15.07% 2higher than in pure-bred lines. The value of the heritability (h ) of the studied traits is low to medium.

Bulgarian

Keywords: sheep, milk breed, biological fertility, dairy productivity

AGRICULTURAL SCIENCE AND TECHNOLOGY, VOL. 6, No 1, pp , 201417 - 20

Introduction Material and methods

Bulgarian Dairy Synthetic Population sheep (BDSP) was The survey covers 851 ewes from SPBM, born during 2004 – registered as a breed in 2005 and is now the most widespread in 2008 in the herd of Agricultural Institute, Shumen. Based on Bulgaria. The majority of the studies performed until now are related available information from the stud-book pure-breeding lines were to the parameters defining the productivity in the various stages of set in the herd (27, 522, 913, 942, 976, 1254, 3156, 6988, 8265 and the creation of a population (Dimov, 1995; Lazarov et al., 2002; 88550) and experimental group with Chios blood (51). Studied are Nedelchev et al., 2003; Raicheva et al., 2003; Stancheva, 2003; the following traits: biological fertility to third lambing and milk yield Boikovski et al., 2005b). Other studies are aimed at identifying the for a standard 120-day period on the 1st and 2nd lactations and, effect of several factors (order of lactation, year of birth, linear which were monitored and recorded by standard methods and differentiation, breeding age, type of udder and method of guidelines laid down in the Instructions for performance monitoring calculation) on the variability of phenotypic parameters of milk yield and rating of sheep BDSP (2003, 2013). The results obtained are and biological fertility (Djorbineva et al., 1995; Boikovski et al., processed by the methods of variation statistics. Variance 2003а, 2003b, 2005a, 2006; Stancheva et al., 2006; Ivanova and assessments have been established which reflected the influence of Raicheva, 2008; Hinkovski et al., 2008; Raicheva and Ivanova, the factors involved in it and F – tests of reliability on each too. The 2010; Raicheva and Ivanova, 2011a, b). values of the coefficients of heritability on the productive traits

Assessment of the productive traits of SPBM animals showed studied were calculated (Harvey, 1990). that Agricultural Academy herds are the best for ram producing and the most consolidated herds of the breed. The reached biological fertility (144–150%), average milk yield for 120 day milking period (in Results and discussionAgricultural Institute, Shumen–133.0 l; in Institute of Animal Science, Kostinbrod –116.2 l; in Institute of Agriculture, Karnobat –111.5 l) in Biological fertility of ewes is dependent on the order of lambing, herds of Agricultural Academy satisfy the requirements for breed st rdand the lowest is on 1 (1.24) and the highest on 3 lambing (1.52) at (Instructions for performance monitoring and rating SPBM sheep –

evidence of differences between ages (P≤0.05, P≤0.001) (Table 1). 2003, 2013) (Raicheva et al., 2010b). Results for maximum milk The results of a test herd were slightly lower than those found in our yield indicate the genetic capabilities of the sheep to a higher milk

stprevious study for sheep on 1 lamb (1,335) and close to the same production. In mentioned flocks was observed minimum milk yield in ndon 2 lamb (1.41) (Boikovski et al., 2003b). Analysis for biological the range of 70–75 l, which is the reason future breeding work to be

fertility at different ages, depending on the breeding line (Table 2) aimed at increasing milk production.stshows that at 2.5 years of age (the 1 lamb) is the highest among The aim of the study was to investigate the parameters of the

ewes of line 51 (with Chios blood) – 1.55 lambs against 1.33 lambs main breeding traits (biological fertility and milk yield for 120 day for animals of pure-bred SPBM lines. The available differences are period) in sheep from BDSP of the herd of Agricultural Institute, mathematically proven to breeding lines 522, 1254, 3156, 8265 (P≤Shumen, in the period after its establishment.

17

* e-mail: nevqna_68@abv.bg

18

0.05) and lines 913, 942 and 88550 (P≤0.01). The highest biological fertility in pure-bred lines had BDSP ewes originating from the 27 –

1.50 lambs (P≤0.05 compared to line 88550) and 976 – 1.33 lambs. Variation of the trait, as is to be expected, is high, which is illustrated by the values of the variation coefficient (from 30.94 to 36.12).

ndBiological fertility on 3.5 years (2 lamb) was again the highest in ewes from line 51 and it exceeded by 17.55% (CV=1.67 against CV=1.42) observed in pure-bred BDSP sheep for evidence of

differences to line 522 (P≤ 0.05). High fertility had animals from

Table 1. Overall average and coefficient of variation of thetrait biological fertility in BDSP ewes

Note: The significant differences are indicated by the sameletters

№

1

2

3

at 2.5 years, number

at 3.5 years, number

at 4.5 years, number

550

390

178

0.43

0.49

0.53

34.82

34.83

35.20

ab1.24 ad1.42 bd1.52

Biological fertility n Mean SD CV

Table 2. Biological fertility of BDSP ewes by breeding lines

Note: The significant differences are indicated by the same letters: a–z – +++; a–e – ++; f–z – +

Fertility

Line

27

51

522

913

942

976

1254

3156

6988

8265

88550

total

10

18

72

42

67

24

51

151

45

21

49

550

35.14

32.87

34.60

32.33

35.38

36.12

35.07

34.66

35.56

33.80

30.94

34.82

37.03

29.54

35.71

34.45

35.59

36.46

35.75

34.51

32.38

33.73

35.82

34.829

5

10

21

11

11

8

13

62

15

9

13

178

37.27

38.84

33.59

47.27

33.79

37.64

24.79

33.95

33.68

33.88

36.74

35.20

gj1.20fg1.90

1.52

1.46

1.55

1.38hij1.77i1.48

1.53

1.56fh1.31

1.52

8

12

50

34

42

14

35

121

23

13

38

390

1.25f1.67f1.34

1.47

1.38

1.29

1.37

1.45

1.57

1.54

1.34

1.42

j1.50abfhci1.56fg1.24c1.17a1.16

1.33h1.26g1.25

1.29i1.19bj1.14

1.24

at 2.5 years

n n nMean Mean Mean CV CV CV

at 3.5 years at 4.5 years

with evidence of differences to 976 (Р≤0.05), 88550, 522, 3156, 913 thoroughbred breeding lines 6988, 8265, 913 and 3156.(Р≤0.01) and 942, 1254 lines (Р≤0.001). Intra-linear dairy milk yield There are similar results for 4.5 years (on third lamb). Ewes

from line 51 exceed by 27.69% (1.90 and 1.49) pure-bred ones with variation of standard 120-day period on this age had moderate to

significant difference for lines 27 and 88550 (P≤0.05). At that age

with good fertility are sheep from lines 1254 (P≤0.05 compared to 88550, 3156 and 27), 8265, 942, 6988 and 522. During our study a wide variation in the fecundity of sheep of different ages was shown as a coefficient of variation and standard deviations were high and similar in value.

st The average milk yield (Table 3) of the flock in the 1 lactation for a 120-day period (95.41 l) was lower than established in our previous study (108.4 l) (Boikovski et al.,2006), which we believe is a result of the impact of the selection and non-genetic factors. Comparing sheep lactation by linear membership shows the superiority of line 51 by 23.7% (117.12 l against 94.71 l) compared to pure-bred lines. The differences are mathematically proven to 88550, 3156, 6988

(P≤0.05), 942, 522, 913, 8265 (P≤0.01) and 1254 lines (P≤0.001). According to dairy control data, ewes from line 51 superior to pure-bred ones by 23.7% (0.967 l versus 0.789 l) and to average daily milk

styield. The lowest milk yield on 1 lactation was detected in sheep of

1254 line – 75.66 l (P≤0.05, P≤0.01, P≤0.001). Milk yield variation on breeding lines is characterized by high values of variation coefficient (21.86 to 33.34%).

nd On 2 lactation, the average milk yield was the highest in line 51 ewes (15.07%) compared to pure-bred line (108,15 l against 93,98 l)

with proven differences to 1254 (Р≤0.05) и 942 lines (Р≤0.01). From the leading herd lines with the highest milk yield was 27 (110,25 l),

Table 3. Milk yield on ewes from the SPBM sheep bybreeding lines

Note:The significant differences are indicated by thesame letters: A–Z +++; a–j – ++; k–z – +

st1 lactation nd2 lactation

Line

27

51

522

913

942

976

1254

3156

6988

8265

88550

total

10

17

76

44

65

20

56

155

38

19

54

554

31.91

25.92

27.74

24.39

21.86

29.17

33.34

25.14

30.23

26.56

29.17

27.77

8

13

57

35

51

19

41

134

32

13

47

450

13.17

33.58

23.83

30.99

32.25

30.44

24.25

27.70

26.02

15.42

25.82

25.77

AabcdkB110.25oi108.15blf94.07d88.57ApfgChi79.35k92.90Blmeno84.32cmg92.85ec99.34nh97.69ap91.00

94.41

95.10cbdiFejg117.12Cd93.97Ee95.02Ac93.97b97.40ABCDEahbF75.66Di99.65aj94.84hg88.42Bb98.33

95.41

Milk yield for 120 days, l

n nMean Mean CV CV

Milk yield for 120 days, l

19

ndvery high values (СV=13.17 to СV= 33.58%). Of the 2 lactation, milk yield of ewes from line 51 exceeds by

Variance analysis shows fairly high influence of the father on 15.07% those of pure-bred BDSP lines with evidence of differences st milk yield at 1 lactation (P≤ 0.001) (Table 4). Similar effects have compared to lines 1254 (P≤0.05) and 942 (P≤0.01). The value of the

nd inheritance of the studied traits, subject to selection in this herd are birth year on milk yield on 2 lactation. This effect is less marked for st low to medium. The main reason for this can be identified targeted milk yield on 1 lactation and biological fertility on 2,5 years (P≤0.05).

selection, strict adherence to selection limits and implementation of Low hereditary variance of biological fertility was established on 2 st "selection press".2.5 years (h =0.064 on 1 lamb) and on the following ages (3.5 and

4.5 years) with zero values (Table 5). The studies generally show low and close to zero heritability of fertility (Boikovski,1995; Laleva and

Acknowledgment

Research was part of the project 501/22 от 05.12.2012 (2012–2014) "Development of DNA markers (CAST, MSTN) for fattening ability and meat quality in Synthetic Population Bulgarian Milk, Karakachanian and Copper Red Shumen sheep breeds" financed by the Ministry of Education, Youth and Science, Republic of Bulgaria.

ReferencesDjorbineva,1997; Boikovski et al.,2001; Stantcheva, 2003;

Boikovski S, 1995. Study on the effect of the applied methods of Stantcheva et al., 2005; Slavov et al., 2008; Staikova and breeding and mating in sheep from different productive direction. Stantcheva, 2013). Low heritability could be explained by a Thesis for DSc, Sofia, 493 (Bg).conservativeness trait, conducted an intensive selection before the Boikovski S, Stefanova G and Georgieva D, 2001. Heritability and first mating and the overwhelming influence of environmental

st Repeatability of the Traits in Sheep from Blackhead Pleven Breed conditions. Heritability values for milk yield are moderate on the 1 2 nd Depending on the Type and Mating. Bulgarian Journal of Agricultural lactation (h =0.543) and zero for ewes for the 2 time as a result of

st Science, 7, 511-520.the high level of ongoing selection, compliance selection limits for 1 Boikovski S, Stancheva N, Stefanova G and Dimitrov D, 2003a. lactation and the influence of non-genetic factors.Influence of Some Factors on Biological Prolificacy in Sheep from The Newly Created Milk Sheep Breed. Bulgarian Journal of Agricultural Science, 9, 3, 391-395.

Conclusion Boikovski S, Stancheva N, Stefanova G and Dimitrov D, 2003b. Influence of Some Factors of the Milk Composition and the Yield of

Biological fertility at 2.5 years was 22,4% (1.556 to 1,271) Trait of Sheep from The Newly Created Milk Sheep Breed. Bulgarian higher in ewes of line 51 (with Chios blood) compared to animals Journal of Agricultural Science,9, 2, 243-249. from pure-bred SPBM lines with proven differences with breeding Boikovski S, Stancheva N, Stefanova G and Dimitrov D, 2005a.

Milk Composition of the Sheep from Newly Created Milk Sheep lines 522, 1254, 3156, 8265 (P≤0.05) and lines 913, 942 and 88550 Breеd. Bulgarian Journal of Agricultural Science, 11, 5, 619-632. (P≤ 0.01). Biological fertility of ewes at 3,5 years from line 51 Boikovski S, Stancheva N and Stefanova G, 2005b. The Newly exceeds by 17.55% (1.667 to 1.418) observed in sheep SPBM with Created Milk Sheep Breed, „Eyro - Klima” Shoumen, 222 (Bg).

proven differences compared to line 522 (P≤0.05).Boikovski S, Stefanova G and Stancheva N, 2006. Milk Yield for

Ewes from line 51 on 4,5 years old are superior by 27,69% milking period in the Sheep from the Newly Created Milk Breed in

(1,900 versus 1,488) pure-bred ones from BDSP significantly Bulgaria. Bulgarian Journal of Agricultural Science, 12, 1, 145-152.

different for lines 27 and 88550 (P≤0.05). Dimov D, 1995. Results of the study on applied breeding schemes st The average sheep milk yield of the herd on 1 lactation for a for creating dairy sheep. Thesis for PhD, Sofia,145 (Bg).

standard 120-day period is higher in ewes from line 51, exceeding Djorbineva M, Dimitrov T, Mihailova G, Dimitrov I and Ivanov I, 23.7% pure-bred BDSP. The differences are mathematically proven 1995. Variability of milk productivity, milk composition and quality in to 88550 lines, 3156, 6988 (P≤0.05), 942, 522, 913, 8265 (P≤0.01) sheep of Stara Zagora Breed and crossbreds by East Frisian Rams and 1254 lines (P≤0.001). at second lactation. Animal Science, 3-4, 83-86 (Bg).

Table 4. F–test of significance of the variance analysis of biological fertility and milk yield in BDSP sheep

Biological fertilitySources of variation

at 2.5 years at 3.5 years at 4.5 yearsstat 1 lactation ndat 2 lactation

№

1

2

3

Father line

Mother line

Year of birth

Significance of differences at: + P ≤ 0.05; + P ≤ 0.05; +++ P ≤ 0.01

n.s

n.s

+

n.s

n.s

n.s

n.s

n.s

n.s

+++

n.s

+

n.s

n.s

+++

Milk yield for 120 days

2Table 5. Heritability (h ) of biological fertility and milk yieldin BDSP sheep

n 2hTraits

Biologicalfertility

Milk yield for120 days, l

at 2.5 years

at 3.5 years

at 4.5 years

at 1st lactation

at 2 nd lactation

0.094

0.000

0.000

0.153

0.000

0.064

0.000

0.000

0.543

0.000

542

385

177

546

443

SЕ

20

EASRAB, 2003. Instructions for monitoring the signs of sheep. Raicheva Е and IvanovaТ, 2011a. A previous study on the some Sofia, 45(Bg). parameters connecting whit the milk production at early conceived Harvey W, 1990. User's grueide for LSMLML and MIXMDL, PC-2 as ewe lambs from Synthetic Population Bulgarian Milk. Journal of version, Mimeo, Ohio, USA, 91. Mountain Agriculture.Hinkovsky Tz, Raicheva Е and Metodiev N, 2008. Estimation of Slavov R, Krastanov Zh, Slavova P and Angelova Т, 2008. productivity of ewes from the Bulgarian Dairy Synthetic Population. Analysis of the genetic varians of the North-East Bulgarian merino Animal Science, 3, 35-41 (Bg). breed and in its crossing with Australian merino, Ile de France and Ivanova Т and Raicheva Е, 2008. Assessment the effect of some Booroola. Animal Science, 3, 168-171 (Bg).factors on lactation. Conference Proceedings "80 years Agrarian Staikova G and Stancheva N, 2013. Effect of different sources of Sciences in the Rhodopes", 67-71 (Bg). specific variants on signs live weight and fertility in sheep Caucasian Laleva S and Jorbineva М, 1997. Fertility of Dairy type sheep Breed. Agricultural Science (in press) (Bg).dams. Animal Science, 7-8, 5-7 (Bg). Stancheva N, 2003. Phenotypic and genotypic parameters of Lazarov V, Mihailova L and Iliev М, 2002. Creation of population of selection indices in the Newly Created Milk Sheep Population in sheep with increased milk yield. Animal Science, 6, 11-13 (Bg). Bulgaria. Thesis for PhD, Sofia, pp.188 (Bg).Nedelchev D, Raicheva Е and Petrova Y, 2003. Characteristics of Stancheva N, Boikovski S, Stefanova G and Dimitrov D, 2005. the productivity of dairy sheep crosses. Animal Science, 3-4, 111- Sources of specific variance and heritability of the live weight and the 114 (Bg). biological fecundity in sheep from the Caucasian Fine Fleece Breed.

International Scientific Conference, Stara Zagora, 3, Stock-Raicheva Е, Nedelchev D and Petrova Y, 2003. Complex score breeding, 56-61 (Bg).assessment of dairy sheep productivity. Animal Science, 1-2, 77-80

(Bg). Stancheva N, Boikovsk S, Stefanova G, Dimitrov D and Raicheva Е and Ivanova Т, 2010. Duration of lactation and milk Rusenov А, 2006. Regularities in lactation persistency of lactation production in ewes from synthetic population Bulgarian milk and possibilities for using part of lactation in tribal work in ewes from depending on the order of lactation. Animal Science, Supplement 1, Synthetic Population Bulgarian Milk. International Scientific 58-63. (Bg). Conference, Stara Zagora, 1-2, 2. Veterinary Medicine, Animal

Studies, 244-247 (Bg).Raicheva Е, Ivanova Т, Boykovski S, Stancheva N and Iliev М, 2010. Status, Problems and Perspectives in the selection and Stancheva N, Dimov G and Baycheva Е, 2013. Instructions for breeding of sheep from Synthetic population Bulgarian milk kept in monitoring the signs of sheep from Synthetic Population Bulgarian the institutes of the Agricultural Academy. Sheep news, 2, 5-8 (Bg). Milk. “Himera”, Shoumen, 28 (Bg).

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Instruction for authors

Preparation of papersPapers shall be submitted at the editorial office typed on standard typing pages (A4, 30 lines per page, 62 characters per line). The editors recommend up to 15 pages for full research paper ( including abstract references, tables, figures and other appendices)The manuscript should be structured as follows: Title, Names of authors and affiliation address, Abstract, List of keywords, Introduction, Material and methods,Results, Discussion, Conclusion, Acknowledgements (if any), References, Tables, Figures.The title needs to be as concise and informative about the nature of research. It should be written with small letter /bold, 14/ without any abbreviations. Names and affiliation of authorsThe names of the authors should be presented from the initials of first names followed by the family names. The complete address and name of the institution should be stated next. The affiliation of authors are designated by different signs. For the author who is going to be corresponding by the editorial board and readers, an E-mail address and telephone number should be presented as footnote on the first page. Corresponding author is indicated with *.Abstract should be not more than 350 words. It should be clearly stated what new findings have been made in the course of research. Abbreviations and references to authors are inadmissible in the summary. It should be understandable without having read the paper and should be in one paragraph. Keywords: Up to maximum of 5 keywords should be selected not repeating the title but giving the essence of study. The introduction must answer the following questions: What is known and what is new on the studied issue? What necessitated the research problem, described in the paper? What is your hypothesis and goal ?Material and methods: The objects of research, organization of experiments, chemical analyses, statistical and other methods and conditions applied for the experiments should be described in detail. A criterion of sufficient information is to be possible for others to repeat the experi-ment in order to verify results.Results are presented in understandable

tables and figures, accompanied by the statistical parameters needed for the evaluation. Data from tables and figures should not be repeated in the text.Tables should be as simple and as few as possible. Each table should have its own explanatory title and to be typed on a separate page. They should be outside the main body of the text and an indication should be given where it should be inserted.Figures should be sharp with good contrast and rendition. Graphic materials should be preferred. Photographs to be appropriate for printing. Illustrations are supplied in colour as an exception after special agreement with the editorial board and possible payment of extra costs. The figures are to be each in a single file and their location should be given within the text. Discussion: The objective of this section is to indicate the scientific significance of the study. By comparing the results and conclusions of other scientists the contribution of the study for expanding or modifying existing knowledge is pointed out clearly and convincingly to the reader.Conclusion: The most important conse- quences for the science and practice resulting from the conducted research should be summarized in a few sentences. The conclusions shouldn't be numbered and no new paragraphs be used. Contributions are the core of conclusions. References:In the text, references should be cited as follows: single author: Sandberg (2002); two authors: Andersson and Georges (2004); more than two authors: Andersson et al.(2003). When several references are cited simultaneously, they should be ranked by chronological order e.g.: (Sandberg, 2002; Andersson et al., 2003; Andersson and Georges, 2004).References are arranged alphabetically by the name of the first author. If an author is cited more than once, first his individual publications are given ranked by year, then come publications with one co-author, two co-authors, etc. The names of authors, article and journal titles in the Cyrillic or alphabet different from Latin, should be transliterated into Latin and article titles should be translated into English. The original language of articles and books translated into English is indicated in parenthesis after the bibliographic reference (Bulgarian = Bg, Russian = Ru, Serbian = Sr, if in the Cyrillic, Mongolian =

Мо, Greek = Gr, Georgian = Geor., Japanese = Jа, Chinese = Ch, Arabic = Аr, etc.)The following order in the reference list is recommended:Journal articles: Author(s) surname and initials, year. Title. Full title of the journal, volume, pages. Example:Simm G, Lewis RM, Grundy B and Dingwall WS, 2002. Responses to selection for lean growth in sheep. Animal Science, 74, 39-50Books: Author(s) surname and initials, year. Title. Edition, name of publisher, place of publication. Example: Oldenbroek JK, 1999. Genebanks and the conservation of farm animal genetic resources, Second edition. DLO Institute for Animal Science and Heal th, Netherlands.Book chapter or conference proceedings: Author(s) surname and initials, year. Title. In: Title of the book or of the proceedings followed by the editor(s), volume, pages. Name of publisher, place of publication. Example: Mauff G, Pulverer G, Operkuch W, Hummel K and Hidden C, 1995. C3-variants and diverse phenotypes of unconverted and converted C3. In: Provides of the Biological Fluids (ed. H. Peters), vol. 22, 143-165, Pergamon Press. Oxford, UK.Todorov N and Mitev J, 1995. Effect of level of feeding during dry period, and body condition score on reproductive perfor-

thmance in dairy cows,IX International Conference on Production Diseases in Farm Animals, Sept.11 – 14, Berlin, Germany, p. 302 (Abstr.).Thesis:Penkov D, 2008. Estimation of metabolic energy and true digestibility of amino acids of some feeds in experiments with muscus duck (Carina moshata, L). Thesis for DSc. Agrarian University, Plovdiv, 314 pp.

The Editorial Board of the Journal is not responsible for incorrect quotes of reference sources and the relevant violations of copyrights.EthicsStudies performed on experimental animals should be carried out according to internationally recognized guidelines for animal welfare. That should be clearly described in the respective section “Material and methods”.

Volume 6, Number 1March 2014