After parturition the energy demand for milk production is greater then the energy provided from the diet. The cow mobilises therefore body tissues to compensate for the energy loss. Live weight and body condition scores decreases as a consequence of the mobilisation.
The aim of this study was to analyse the relationship between body condition score, live weight and subcutaneous fat depth measured by ultrasound and the changes during the lactation. Possible differences between Swedish Holstein (SLB) and Swedish Red and White Cattle (SRB) were also investigated. The relationship between the measures mentioned and reproduction such as the number of days from calving to first luteal activity and to the first ovulatory oestrus was analysed.
The study was based on observations on cows from the experimental dairy herd (Jälla) of the Swedish University of Agricultural Sciences. Body condition scoring and measurements of live weight and subcutaneous fat were performed during the period 1997 to 2002. The body condition scoring was performed according to a method described by Edmonsson et al. (1989). A total of 211 cows were included in this study of which 88 were SLB and 123 SRB. The latter breed has since 1985 been selected for either high (SRB-high) or low (SRB-low) milkfat yield but with the same total quantity of milk energy. These SRB lines were handled as separate groups in the analyses. The data set included 4036, 639 and approximately 1260 live weight registrations, body condition scores and ultrasound measurements, respectively.
Body condition score (BCS) and subcutaneous fat depth differed significantly between breed and selection lines. The parity number had no effect on these measures. The unadjusted mean BCS was 3.18, 3.10 and 2.82 for SRB-low, SRB-high and SLB respectively. SRB-low had the highest unadjusted mean BCS from week 1 to 36 after calving compared to SRB-high and SLB. SLB and SRB-low decreased in BCS with approximately 20 %, whereas SRB-high decreased with 5 %. SLB had significantly higher BSC during week 36 compared to the BCS from week 4 until week 16 after calving.
The unadjusted mean for the subcutaneous fat depth was 0,44 cm, 0,49 cm and 0,41 cm for SRB-low, SRB-high and SLB respectively. The difference between two different body locations for measuring the fat depth was small. Fat tissue was mobilised from calving until week 16. SLB and SRB-high gained fat until week 36 after calving and regained weight to approximately the same level as at calving, whereas SRB-low did not succeed to regain the weight. However, it consistently had higher BCS and fat measures.
Breed and selection line and parity had a significant effect on live weight. The unadjusted mean for live weight was 670 kg for SLB, 653 kg for SRB-low and 620 kg for SRB-high. SLB had a higher weight than both the SRB selection lines during the lactation. Further on SRB-high weighed more than SRB-low. Both breeds lost weight after calving and the decrease went on until 16 weeks of lactation. With higher parity number cows were heavier.
The residual correlation between the ultrasound measurements at two different body locations varied between 0.70 and 0.90. The result indicated that a measurement at one body location is enough to get a reliable value of the subcutaneous fat depth. The residual correlation between the subcutaneous fat depth and BCS and body weight respectively varied between 0.35- 0.64 and between 0.26-0.47 during week 1 until week 16 after calving. The residual correlations between changes of body condition score, weight and subcutaneous fat were negative between different periods during the lactation. This indicates that cows mobilises body tissue in early lactation and gain fat and weight in later lactation.
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