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RESEARCH PRODUCT

Milk quality as affected by grazing time of day in Mediterranean goats.

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We evaluated the effect of grazing time of day on goat milk chemical composition, renneting properties and milk fatty acid profile in a Mediterranean grazing system. Sixteen lactating Girgentana goats were divided into two experimental groups and housed in individual pens, where they received 500 g/d of barley grain. For 5 weeks the two groups were left to graze in two fenced plots on a ryegrass sward as follows: morning group (AM), from 9·00 to 13·00; afternoon group (PM), from 12·00 to 16·00. In selected herbage, water-soluble carbohydrates (WSC) increased in the afternoon (204 v. 174 g/kg dry matter, DM; P=0·01), whereas crude protein (CP) and linolenic acid decreased (respectively, 16·7 v. 19·8% DM; P<0·01 and 26·8 v. 30·4 g/kg DM; P<0·01). Pasture dry matter intake (DMI) was significantly higher in the afternoon (0·82 v. 0·75 kg/d; P=0·026). Fat corrected milk production (FCM), milk fat and lactose content were not affected by treatment, whereas protein and titrable acidity (°SH) increased in the PM group (respectively 3·56 v. 3·42%; P=0·01; 3·55 v. 3·22°SH/50 ml; P=0·01). In contrast, milk urea content was significantly higher in the AM group (381 v. 358 mg/l; P=0·037). The results seem to indicate that an improvement in ruminal efficiency might be obtained by shifting grazing time from morning to afternoon, as a consequence of a more balanced ratio between nitrogenous compounds and sugars. Indeed, the higher linolenic acid and the lower conjugated linoleic acid (CLA) (respectively 1·02 v. 0·90, P=0·037; 0·71 v. 0·81% of total fatty acids, P=0·022) in the milk of goats grazing in the afternoon seem to indicate a reduced biohydrogenation activity in the PM group.