Inger Johanne Karlengen defended her PhD thesis on December 16th 2011

Ane Gro Siri Skjelfjord

Effect of cobalt on fatty acid composition in milk of dairy cows and sows

Abstract from the thesis - PhD thesis 2011:75

Author: Inger Johanne Karlengen

Previous research revealed that supplementing excess cobalt (Co) reduces bovine milk content of monounsaturated fatty acids (MUFAs), probably mediated by the enzyme ∆9-desaturase. The general aim of this research project was to further explore the effect of Co on the desaturation of fatty acids (FAs), especially in lactating dairy cows, but also in sows. Three experiments were performed. In the first study, the main subject was to investigate the effects of excess Co on FA composition of blood plasma and milk from lactating sows (Paper I). Experimental animals were 10 lactating sows: five intramuscularly injected with saline solution (control) twice a day, and five intramuscularly injected with a Co solution twice a day (118 mg Co/d). The treatment lasted five days. Fatty acid composition of blood plasma and milk fat was determined. Cobalt had no effect on FA composition of blood plasma. In contrast, milk fat from the sows receiving Co showed a significant (p<0.05) decrease in the concentration of myristoleic acid (cis-9 14:1) and palmitoleic acid (cis-9 16:1), confirming that excess Co also lowered the ∆9-desaturation of milk fat from lactating sows.

In study 2, the objective was to determine the effect of excess Co on gene expression levels of ∆9-desaturase, FA synthase (FASN), diacylglycerol acyltransferase 1 (DGAT1) and diacylglycerol acyltransferase 2 (DGAT2) in the mammary gland of lactating dairy cows (Paper II). Seven cows were given 1.4 g Co per os twice daily for seven days, followed by a nine-day depuration period. Udder biopsies were performed three times during the experiment: before the treatment started, at the end of the treatment period, and at the end of the depuration period. Gene expression levels of ∆9-desaturase, FASN, DGAT1 and DGAT2, and FA composition of milk fat were determined. Excess Co significantly reduced (p<0.05) the concentration of all cis-9 MUFAs in milk fat, confirming a reduction in ∆9-desaturation in the mammary gland. However, neither ∆9-desaturase, FASN, DGAT1 nor DGAT2 gene expression levels were significantly affected, indicating that the effect of Co on milk FA profile observed was mediated by a reduction in ∆9-desaturase activity in the mammary gland at the post-transcriptional level.

The third study was conducted to determine what amount of Co is needed to lower the proportion of cis-9 MUFAs in bovine milk fat (Paper III). Four lactating dairy cows were used in a 4 x 4 Latin square design study. The basal diet of grass silage and concentrate mixture was supplemented with four levels of Co: 0 mg/d, 4.0 mg/d, 360 mg/d, and 5100 mg/d. The Co solutions were continuously infused into the rumen for 11 days. Milk yield and milk content of fat, FAs, protein, lactose, Co, zinc (Zn), iron (Fe) and copper (Cu) were determined. Blood plasma was analyzed for contents of FAs, Co, Zn, Fe and Cu. Feed intake and total tract digestibility of the feed components were also determined. Cobalt affected the proportion of some FAs in blood plasma, but the effects were relatively small in magnitude. With few minor exceptions, only the highest level of Co (5100 mg/d) significantly lowered the MUFA proportion in milk fat. Oleic acid (cis-9 18:1) was reduced as much as 38% compared to that with the lowest Co level. However, the highest level of Co also lowered feed intake and milk yield.

The main conclusion from the present studies is that excess Co also lowers the proportion of MUFAs in sow's milk, and that this effect of Co in dairy cows is probably mediated by posttranscriptional reduction of ∆9-desaturase activity. Moreover, the amount of Co needed to suppress ∆9-desaturation in bovine milk is so high that the normal levels of Co in rations for dairy cows do not significantly affect milk FA composition.

Updated: 25.01.12
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