Effects of conjugated linoleic acid on glucose tolerance test and blood glucose changes of Holstein cows during transition period

Conjugated linoleic acid (CLA) is a generic term for a group of 18-carbon fatty acids with a conjugated double bond that influence a range of biological processes. Pro-inflamatory cytokines have been shown to contribute in insulin resistance process and CLA can inhibit some pro-inflamatory cytokines production. The effect of CLA on milk fat depression caused uses it as a nutritional strategy to improve negative energy of dairy cows. The aim of this study was to evaluate glucose tolerance test and blood glucose changes of dairy cows fed conjugated linoleic acid (CLA) from -21 to or -42 days (d) relative to parturition.
Seventy five multiparous dairy cows were allocated to one of four treatments: feeding palm oil (75g/d) from -21 d to d (C21) or d (C42) relative to parturition, feeding rumen protected CLA (75g/d) from -21 d to d (CLA21) or d (CLA42) relative to parturition. Rumen protected CLA provided 7.5 g/d each of trans-10, cis-12 CLA and cis-9, trans-11 isomers. Glucose tolerance tests (GTT) was carried out on five cows from each group by infusing 0.25 g/kg of BW of glucose (iv) through milk vein at 14 and 30 d after parturition. Blood samples were collected from the milk vein of opposite side of glucose infusion at −20, −10, 0, 5, 10, 20, 30, 40, 60, 80, 100 and 120 minutes (min) relative to infusion and plasma glucose level determined after centrifuge. Area under curve at 60 and 120 min, glucose clearance rate and time to reach half concentration of glucose were calculated as GTT indices. To evaluate blood glucose and insulin changes after parturition blood samples were taken via coccygeal venipuncture from a subsample of 8 cows per treatment at just after calving and 10, 21 and 42 d postpartum. Milk yield was recorded daily and milk samples to determine milk constitutes were taken weekly.
Feeding rumen protected CLA had no significant effects on GTT indices. Differences between GTT indices were significant at 14 and 30 d postpartum (P˂0.05) that was indicative of improvement of insulin sensitivity as days in milk increased. Blood glucose concentration was higher at parturition and 10 d after parturition in CLA fed cows than palm fed cows while blood insulin concentrations were the same among treatments (P˂0.05). CLA fed cows had less milk fat content and yield than palm fat fed cows (P˂0.05). Feeding rumen protected CLA during transition period increased milk yield during early lactation (P˂0.05). Extending rumen protected CLA or palm fat feeding to 42 d postpartum couldn’t increase milk yield compared to 21 d postpartum.
Results of this experiment showed that adding CLA supplementation to dairy cows ration during transition period resulted in increased blood glucose concentration at early lactation and increased milk yield without any negative effects on GTT indices as indicators of insulin resistance situation.