Seasonal variation in retinol concentration of goat milk associated with grazing compared to indoor feeding

Author: V. Fedele, R. Rubino, S. Claps, P. Manzi, S. Marconi and L. Pizzoferrato
Year: 2004
Issue: 5
Volume: 34
Page: 148 - 150

Forty-five Siriana dairy goats were divided into three groups and assigned to three feeding treatments: i) grazing (G), ii) grazing plus 600 g of mixed barley and chickpeas grain per day (GBC), iii) grazing plus 600 g of mixed maize and broad beans per day (GMB). These grazing groups were compared to a control group (I) of 15 Siriana goats fed indoors a pasture hay plus 600 g of a commercial concentrate per day. Retinol concentrations of milk samples were determined and correlated with the herbage intake. Feeding treatments influenced all trans and total retinol concentrations significantly. Milk from treatment G contained the highest all-trans and total retinol concentrations, while milk from treatment I had the lowest values. The increase in total retinol concentration in milk of 20% and 30%, respectively, corresponded with the increase in green herbage intake, from zero in the I treatment to 381.7 g DM/day in the GBC and GMB treatments and 568.7 g DM/day in G treatment. From spring to winter the ratio between total retinol concentration and milk production (R/MP) showed an opposite trend in comparison to milk production: the more the milk production decreased, the more the R/MP ratio increased. The differences observed in summer and winter between grazing treatments were probably due to different herbage intake. The mean ingested herbage intake of the GMB group was 28% less than that of the G group, and 36% less than the GBC group. This low intake caused the R/MP ratio to decrease by 41% and 62% in the G and the GBC groups, respectively. In the spring the herbage intake was higher (ca. 39%) than in the other two seasons, but no differences were observed between treatments. The influence of feeding treatment observed on milk retinol concentration could be due to a difference in retinol precursor concentration in the animal diet and/or a difference in bioavailability of the precursors in the animal body.

Keywords: dairy goat, feeding treatment, Retinol
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