Levande vikt vid olika åldrar och sambandet med bröstomfång och mankhöjd hos SRB och SLB
Live-weight at different ages for Swedish Holsteins (SLB) and for the Swedish Red and White Breed (SRB), and the correlation to heart girth and height at withers.
The aim of this investigation was to study the live-weight changes and mature weight for the Swedish Red and White Breed (SRB) and for Swedish Holsteins (SLB), and to estimate the correlations between body weight and body measurements such as heart girth and height at withers, respectively. The material used was from one of the experimental dairy herds (Jälla) of the Swedish University of Agricultural Science. It included recordings on 293 dairy cows with information from 7142 weight occasions and recordings on 275 dairy cows with information of 557 heart girth measurements and 560 measurements of height at withers. The registrations were done during 1993-2002.
There was a large variation in live weight between cows in different ages and lactation stages. SLB cows were on average over all lactations 45 kg heavier than SRB. The difference between the highest and lowest body weight within each breed was 450 kg, respectively. Calving interval (12- or 15 months interval), weighing occasion, selection line (high- or low milk fat content) and year and season had a significant influence on body weight.
The live-weight increased with increasing lactation number. This was especially clear for the first 3 lactations. The difference between lactation 3 and 4 was small. For lactations 5 and 6 any general conclusion was more difficult to make due to the low number of cows (2 to 16 cows depending on weight occasion). Possibly a tendency for a lower weight in lactation 6 could be seen. In general, the live weight was highest before calving. After calving it decreased a few weeks (8-12 weeks) and then increased again until next calving.
The heart girth increased with age of cow and SLB cows were on average bigger than SRB cows. The corrected means for heart girth from the lactations 1-8 were for the SRB breed 190-203 cm and for the SLB breed 200-209 cm. Lactation number and selection line significantly influenced heart girths. Height at withers was relatively constant during the different lactations for both breeds. A corrected average for height at withers during the lactations 1-8 were for SRB 131-134 cm and for SLB 141-143 cm. Significant effects of year and season, selection line and the interaction between calving interval and selection line was obtained. A regression analysis of body weight on heart girth showed that for each cm increase of the hearth girth the body weight of SRB increased with 6.0 kg and for SLB with 6.1 kg. The regression analysis of body weight on height at withers showed that for each cm increase of height at withers the body weight increased with 8.3 kg for SRB and 7.2 kg for SLB.
The high milk fat selection line was slightly smaller in heart girth (6.6 ? 6.8.cm in the first three lactations) compared with the low fat line and weighed on average 90 kg less than the low fat line. This weight difference is larger than can be calculated from the regression analysis of body weight on heart girth which would correspond to a weight of about 40 kg. This might strengthen the hypothesis that the high line, mobilize more from their fat deposits to produce their milk.
The correlations between body weight and the two conformation traits over the 6 lactations were calculated by breeds separately as well as jointly. The highest correlations were obtained for body weight and heart girth (0.83-0.84). The correlations between body weight and height at withers were lower (0.53-0.0.64). The correlation increased only marginally when using both hearth girth and height at withers. The correlation between heart girth and height at withers varied between 0.58 and 0.60.