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Erarbeitung einer Methode zur Bewertung des Wachstumsverlaufes von Holstein-Friesian Färsen vom zweiten Lebenshalbjahr bis zur Hochträchtigkeit

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Erarbeitung einer Methode zur Bewertung des Wachstumsverlaufes von Holstein-Friesian Färsen vom zweiten Lebenshalbjahr bis zur Hochträchtigkeit

Nora Weiß (Unbekannter Einband, Deutsch)

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Beschreibung

Devising a method for supervising the course of growth of Holstein-Friesian heifers from their second six months of life to late pregnancy The body condition of dairy cows is assessed by the BCS system according to Edmonson et al. (1989). A separate method for assessing young cattle in their growth period, though, is still lacking. The present study was aimed at working out a BCS assessment scheme adapted to heifer rearing. During the first part of the study, data on the course of growth and of fat deposition were collected from growing heifers. In the second part, the new method developed for body condition scoring had to be verified with regard to the information it provided. Scoring comprised the rearing period from age six months to the 9th month of pregnancy. Starting with the beginning of puberty in the second six months and continuing during pregnancy, a substantial increase in fat deposition is observed, so it is important in this period to ensure an optimum growth rate while counteracting adiposity, with the aid of condition scoring. Within a study period of two years, three herds of Holstein-Friesian breeding heifers reared on three farms by different methods, with a total of 1936 randomly selected head were checked for backfat thickness (BFT), live weight (LW) and sacral height (SH), and the body condition was assessed by a method specially developed for heifers. The heifers were grouped according to months of age (6 to 9 , 9 to 11, 12 to 16) and months of pregnancy (1st to 4th, 5th to 7th, late-pregnant 8th to 9th). Every examination included at least 30 heifers. Backfat thickness measured objectively by ultrasound was used as a reference method for assessing the body condition of each age group. According to the new BCS system, backfat thickness is estimated in terms of mm fat deposit by visual observation and palpation. For breeding heifers, the BCS criteria are fat deposition in the tailhead skinfold and the area between the hooks and the rump points. An analysis of the course of growth revealed differences in live weight and in the development of backfat. Except for the 6-to-9-months age group, the course of growth in sacral height was uniform for the heifers reared by differing methods in the three dairy farms. The live weight curve of the heifers of farm 1, which were raised under extra-high-intensity management, took a steeper course in the 6 to 12 months age group, whereas the growth intensity declined during the second year of life. In contrast to this, the heifers of farms 2 and 3 showed a continuous rise in live weight. Fat deposit was found to undergo substantial changes starting in the 8th to 9th month of life. Only from this age, when the heifers reach puberty, is it practical to use BFT as a measure of body condition. When pregnant, the heifers in the three farms still accomplished a growth in SH of 6 to 7 cm. The heifers of farm 1, raised at extra-high intensity in their first year in order to reach an age at first calving (AFC) of 22 months, suffered a significant decrease in BFT from the 7th month of pregnancy, a consequence of that farm’s housing, feeding and breeding management. The heifers of farm 3, also raised intensively to achieve an AFC of 24 months, showed a slight increase in BFT during the same period of observation. The prepartum live weights reached by the heifers were 583 kg (farm 1) and 600 kg (farm 3). The late-pregnant heifers had a BFT of 15 mm (farm 1) and 18 mm (farm 3). The mean SH was 144.3 cm (farm 1) and 145.7 cm (farm 3). Concerning the use of the measuring methods, it should be noted that the BFT must always be regarded as the result of growth courses of differing intensities, which must not be left out of account. Nor does the live weight reveal the heifers‘ differentiation in BFT. For a reliable control of the course of growth, therefore, one should, with heifers age 9 months and over, consider both live weight and backfat thickness. Methods to supervise the course of growth include: – Live weighing – Measurement of wither height / sacral height – Body condition scoring From the results of determining the accuracy of estimation of the body condition of growing heifers, it follows that it is possible to estimate the mean BFT for an age group of heifers, whether by exclusively examining the caudal fold cavity (visual method, S1) or the area between hooks and points of rump (visual method, S3), or by examination plus palpation of the fat deposit in the tailhead fold (palpatory method, S2), all with a high level of agreement with the BFT measured objectively by ultrasound. 49% of the variability of the heifers‘ body condition can be explained on the basis of BFT estimation by exclusively visual examination according to method S1, whereas 55% can be explained according to method S3. Additional palpation of the tailhead fold increases the coefficient of determination (R2) to 64%, thus improving BFT estimation. In the various age groups, the methods attained high correlation coefficients for repeated scorings (r= 0.75 to 0.85). Therefore, the methods can be assumed to capture the characteristics reliably. The validity of the BCS method for a single animal is relatively limited. For the assessment of groups of animals in a herd, however, this method is an important tool for checking the course of growth and feed correction. BFT estimation minimizes measurement efforts within the scope of herd examinations. For checking, and verifying the accuracy of condition estimation, the estimated data should be compared with the ultrasonic measurements in a portion of the animals at certain intervals, and the assessment criteria adjusted accordingly. With cattle difficult to assess, such as late-pregnant heifers, the estimated data should by checked against BFT measurements in a portion of the animals. The BCS as known for milk cows cannot be readily applied to growing heifers. The suggestion is that the assessment criteria established as a result of the study be used for scoring the condition of heifers. Moreover, one should not assign grades but rather estimate conditions by means of the concrete BFT in terms of mm. Weniger zeigen

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Technische Daten

Erscheinungsdatum

29.06.2018

Sprache

Deutsch

EAN

9783863879037

Herausgeber

Mensch & Buch

Sonderedition

Nein

Autor

Nora Weiß

Seitenanzahl

190

Auflage

Einbandart

Unbekannter Einband

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