Effect of Intake of Pasture on Concentrations of Conjugated Linoleic Acid in Milk of Lactating Cows

Abstract

We examined the effect of intake of fresh pasture on concentrations of conjugated linoleic acid in milk fat. Sixteen Holstein cows were paired and divided into either the control group or the grazing group. The study involved initial, transition, and final periods. During the initial period, all cows consumed a total mixed diet. Cows in the control group were fed the total mixed diet throughout the study, and cows in the grazing group were gradually adjusted to a diet consisting of intensively managed pasture. Performance of cows in the grazing group was significantly reduced from that of cows in the control group during the final period (dry matter intake, 19% less; milk yield, 29.6 vs. 44.1 kg/d; and live weight, 40 kg less). During the initial period, when both groups were consuming a total mixed diet, concentrations of conjugated linoleic acid in milk fat were similar (X = 5.1 mg/g of milk fat). As the grazing group was gradually adjusted to pasture, concentrations of conjugated linoleic acid in milk gradually increased. During the final period, when cows in the grazing group were consuming a diet consisting of pasture only, conjugated linoleic acid concentrations in the milk fat were doubled (10.9 vs. 4.6 mg/g of milk fat). Furthermore, results showed the individual consistency of the milk fat content of conjugated linoleic acid over time but also demonstrated substantial variation among individual cows within treatment groups. Overall, this study indicated that the concentration of conjugated linoleic acid in milk fat is enhanced by dietary intake of fresh pasture.

The management of the transition from hay- to pasture-based diets affects milk fatty acid kinetics

“…The decrease in SFA and increase in MUFA and PUFA observed in both rapid and progressive transition milks are in line with reference data obtained in controlled conditions (Kelly et al 1998;Khanal et al 2008). Since changes did not occur in the daily concentrate supplementation, the changes in the milk FA profile during transition from hay to pasture could be related to the higher PUFA content in fresh grass (Elgersma et al 2006) in comparison to hay.…”

“…All the cows showed similar trends in milk FA kinetics, but with different FA concen-trations before and after diet change. The individual variability was broader when cows were grazing than when they were fed with hay and concentrates, confirming literature data (Kelly et al 1998;Khanal et al 2008). Differences in cow fresh herbage intake and in cow grazing selection of plant species, or plant parts richer or poorer in PUFA may explain the broader variability of the milk FA profile of pasture-fed cows (Coppa et al 2011b;Khanal et al 2008), especially on highly biodiverse upland pastures.…”

“…Similar results were obtained by Biondi et al (2008) in a study of ewes and by Khanal et al (2008) in a study of cows after an abrupt diet transition from, respectively, a vetch hay (Vicia sativa) and concentrate ration to a vetch and oat pasture diet, and an abrupt transition from a total mixed ration (TMR) to a perennial ryegrass pasture diet and vice versa. CLA and PUFA concentration changes in milk were studied by Kelly et al (1998) and by La Terra et al (2010) on cows transferred gradually from a TMR to pasture feeding in controlled and on farm conditions, respectively; however, FA kinetics were not investigated in these studies. Reference data have mainly been obtained by monitoring abrupt diet changes in controlled experimental conditions; little is known concerning ordinary farming conditions in which transitions from a winter diet to full grazing diet are usually gradual and variously managed.…”

Alimentation des vaches laitières et composition en acides gras du lait

“…Parmi les fourrages, l'herbe fraîche est le plus riche en C18:3n-3, si bien que le lait de vaches qui pâturent peut contenir jusqu'à 1 voire 2% de C18:3n-3 (Kelly et al 1998 ;Dhiman et al 1999), soit 2 à 4 fois plus qu'un lait produit par des vaches consommant des fourrages conservés.…”

Scientific appraisal of the Irish grass-based milk production system as a sustainable source of premium quality milk and dairy products

“…Irish cows are predominantly fed pasture for the majority of the lactation, which influences milk composition, processability and the sensory characteristics of the milk, which in turn determine the quality of Irish dairy products (O'Brien and Guinee, 2016). Studies on cows offered significant quantities of grazed grass (Kelly et al, 1998;Coakley et al, 2007;Wyss et al, 2010;Butler et al, 2011;O'Callaghan et al, 2016) revealed that their milk contained increased levels of the unsaturated fatty acids, conjugated linoleic acids (CLAs), vaccenic acid, and omega-3 fatty acids, which are considered beneficial to human health, compared to the milk produced by cows on other diets, such as grass silage and concentrate-based diets. This was considered a positive and important finding as unsaturated fatty acids are believed to be better for human health (Haug et al, 2007).…”