Effect of dairy cow breed on milk fatty acid composition under grazing conditions

PALLADINO, R.A., BUCKLEY, F., PRENDIVILLE, R., MURPHY, J.J., CALLAN, J., AND KENNY, D.A.

Irlanda

Congreso; Agriculture Research Forum, Ireland; 2009

Irish Grassland and Animal Production Association

Introduction. Dietary intake of omega-3 polyunsaturated fatty acids (n-3 PUFA) and conjugated linoleic acid (CLA) has been recognized as having potential positive effects on human health (Lock and Bauman, 2004). Furthermore, alteration of the fatty acid (FA) composition of milk through targeted manipulation of dairy cow diets can be achieved (Dewhurst et al., 2006). Although breed effects on the FA composition of milk have previously been reported (Kelsey et al., 2003), most work to-date has been conducted under high input TMR based systems. Furthermore, little is known on the effects of heterosis on concentrations of FA in milk. The objective of this study was to examine whether differences in milk FA concentration exist between two contrasting breeds of dairy cow and their F1 hybrid managed under a grazing based production system. Materials and Methods. Eighty-one spring-calving dairy cows (27 Holstein Frisian, 27 Jersey and 27 Holstein X Jersey cross) with a mean ± SD calving date of February 12th ± 16.4 d were used. Cows were managed under a predominantly perennial ryegrass (Lolium perenne L.) pasture. Two experimental periods were evaluated (June and July). Individual milk yields (kg) were recorded daily and milk fat, protein and lactose concentrations were recorded on one successive evening and morning, one day per week. Milk fat was extracted and methylated using an adaptation of the method reported by Christie (1982). Data were analyzed by ANOVA and mean differences were separated using the PDIFF command of SAS (adjusted by Tukey test). Cow was used as a random effect and the statistical model include terms for breed, period and its interaction. Results. There was no interaction for any of the variables studied and thus data were pooled across the two periods. Holstein Friesian cows had the highest milk yield, Jersey the lowest with the crossbred animals intermediate (P<0.01). Conversely, milk fat and protein were highest for Jersey, lowest for Holstein and the crossbred animals intermediate (P<0.01). Differences were found for n3:n6 ratio (P<0.05), C18:2 n6, and the ∆9 desaturase index (P<0.01) with all higher for Holstein animals. CLA tended to be higher in Holstein possibly as a consequence of a higher ∆9 desaturase activity (Table 1). Conclusion. The results of this study show that under the grazing conditions employed here, Holstein dairy cows produced more milk with a higher content of CLA potentially due to a higher activity of the ∆9 desaturase enzyme in mammary gland. There was no evidence for heterotic effects on any milk related variables measured.