Early lactation dairy cows are naturally in a period of a negative energy balance. Non available energy from feed intake is mobilized from body reserves. Massive mobilization of body mass in early lactation, in form of body fat, increases the risk of metabolic diseases like ketosis. Lost of milk production, lower reproductiveness and earlier exit of the dairy cow from production with high economical losses are the consequence.
Since identification of the t10,c12 conjugated linoleic acid (CLA) isomer and its capability to reduce milk fat content, the possibility for a targeted reduction of milk fat content for dairy cows existed. Conjugated linoleic acid supplementation is used with the intention to reduce the energy requirement for milk production via a reduced milk fat synthesis to disburden the energy metabolism and to improve the calculated energy balance of the early lactation dairy cow. This should be reflected in the body composition and the body fat mobilization during early lactation, but these aspects have not yet been investigated. Therefore, the aim of the present study was to investigate changes in body composition, body mass mobilization and especially the body fat mobilization, as well as the energy metabolism under conditions of a CLA induced reduction of milk fat synthesis during early lactation.
For this purpose a slaughter experiment with 25 primiparous German Holstein cows was conducted. The animals were divided into 5 groups and each group contained 5 animals. An initial group (IG) was slaughtered at 1 day in milk (DIM) and this group received no CLA supplementation. Further 10 animals were slaughtered after 42 DIM, whereby 5 of these 10 animals received from 1 until 42 DIM a CLA supplement (42/CLA group) and the remainder 5 animals received a control fat supplement (42/CON group). The remaining 10 animals were slaughtered at 105 DIM and five animals received from 1 until 105 DIM the CLA supplement (105/CLA group) and 5 animals received the control fat supplement (105/CON group). The animals of the CLA and control group received 3.5 kg pelleted concentrate per day (on dry matter (DM) basis). Either the CLA supplement (contained t10,c12 CLA and c9,t11 CLA in equal parts) or the control fat supplement (CLA’s were substituted by stearic acid) was contained in this concentrate. On the basis of analyzed CLA contents in the concentrate the animals of the CLA group consumed 6 g/d t10,c12 CLA and 6 g/d c9,t11 CLA. Additionally, the animals of the CLA and control groups were fed a partial mixed ration comprising of 38%
maize silage, 25% grass silage and 38% concentrate (on DM basis) for ad libitum consumption.
The overall performance level of the animals during the present experiment was characterized by an average daily milk yield of 25.7 kg and an average milk fat content of 3.9%. In the period from 1 until 42 DIM the average milk fat content of the animals in the CLA groups (42/CLA and 105/CLA group) was reduced by 14.1% and milk fat synthesis was numerical decreased by 9.8%. The remaining animals of the 105/CLA group showed from 42 until 105 DIM a reduction of milk fat content by 25.4% and a reduced milk fat synthesis by 17.1%.
Despite of partial ruminal biohydrogenation of the rumen protected CLA, which was indicated by the fatty acid pattern of the ileal chyme, the reduction of milk fat synthesis was obvious in CLA supplemented dairy cows.
However, the CLA induced reduction of milk fat synthesis resulted not in an improvement for the calculated energy balance in CLA fed animals and it seems, that the energy metabolism is not influenced by CLA supplementation. This could be partially explained by a numerical increase of milk yield. From 1 until 42 DIM the average milk yield for the animals in the CLA groups (42/CLA and 105/CLA group) showed a numerical increase for milk yield by 1.1 kg or 4.7%. From 42 until 105 DIM a numerical increase of milk yield by 2.7 kg or 10.4% for CLA fed animals was obvious. It could be concluded that the saved energy from milk fat synthesis is available for higher milk yield and therefore for lactose synthesis. However, the energy content of 1 g milk fat is more than twice that of 1 g lactose and it is questionable if the higher milk synthesis could totally explain the retention of the energy saved from reduced milk fat synthesis. Moreover, dry matter intake (DMI) was slightly decreased in the CLA groups compared to the control groups with approximately equal milk energy output. The consideration of the body composition and the body mass mobilization enabled deeper insights into the energy metabolism and fat metabolism of the dairy cows.
No CLA effect on the body fat content was shown. In addition to that less than 0.2% of the supplemented t10,c12 CLA-Isomer was included into the body fat of the dairy cow and in the first 42 DIM marginal amounts of the t10,c12 CLA isomer were incorporated into the retroperitoneal fat depot. In the same period the weight reduction of this fat depot was slightly reduced. Furthermore, in the CLA groups a trend for a higher body protein content was observed.
Applying the principle of the comparative slaughter technique on the body composition data for calculation of body mass mobilization, a trend for reduced body mass mobilization was shown form 1 until 42 DIM in CLA supplemented cows. This trend for lower body mass mobilization could be mainly explained by a numerical reduction of body fat mobilization of 9.8 kg during this period. The trend for a lower fat accumulation in the liver for CLA
supplemented animals could also be associated with the trend for lower body mass mobilization. Additionally, a higher protein accretion was observed for CLA fed animals from 1 until 105 DIM. This is in accordance with the tendency for higher protein content in the CLA groups. The observation of several trends in this trial could be connected to the low animal number and the general variation for data of body composition and body mass mobilization in dairy cows.
Overall, the present experiment showed for CLA supplemented dairy cows in early lactation a lower energy requirement from body mass mobilization, which was more pronounced from 1 until 42 DIM. Additionally, more energy was accreted in body protein form 1 until 105 DIM.
Moreover, slightly less energy was consumed with DMI. In association with repartitioning of the spared milk fat energy to higher milk yield and approximately equal milk energy output, with less energy mobilized from body fat and more energy retained in body protein, it can be suggested that CLA supplementation improved the utilization of the metabolizable energy (ME) in early lactation dairy cows.
Carrying on the energetically considerations with regression analysis, the results for the animals of the present trial suggested that the proportion of the ME expended for maintenance was 20% higher as in currently used energy evaluation systems. For CLA supplemented animals the ME needed for maintenance seems to be lower by 5.9%. Besides, it appears that the utilization of the ME for milk production was more efficient in CLA supplemented dairy cows. Further research on these aspects is needed in the future.
In conclusion the present experiment showed that CLA could partially relief the energy metabolism by reduction in milk fat synthesis and additionally by optimization of the energy metabolism in form of a more efficient utilization of the ME. This could reduce the risk of metabolic diseases in early lactation and makes the cow more able to tough the critical period of early lactation.