We evaluated the effect of grazing time of day on goat milk chemical composition, rennetingproperties and milk fatty acid profile in a Mediterranean grazing system. Sixteen lactatingGirgentana goats were divided into two experimental groups and housed in individual pens, wherethey received 500 g/d of barley grain. For 5 weeks the two group were left to graze in two fencedplots 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 inthe afternoon (204 v. 174 g/kg dry matter, DM; P=0.01), whereas crude protein (CP) and linolenicacid 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 bytreatment, whereas protein and titrable acidity (8SH) increased in the PM group (respectively 3.56v. 3.42%; P=0.01; 3.55 v. 3.22 8SH/50 ml; P=0.01)). In contrast, milk urea content wassignificantly higher in the AM group (381 v. 358 mg/l; P=0.037). The results seem to indicate thatan improvement in ruminal efficiency might be obtained by shifting grazing time from morningto afternoon, as a consequence of a more balanced ratio between nitrogenous compounds andsugars. Indeed, the higher linolenic acid and the lower conjugated linoleic acid (CLA) (respectively1.02 v. 0.90, P=0.037; 0.71 v. 0.81% of total fatty acids, P=0.022) in the milk of goats grazing inthe afternoon seem to indicate a reduced biohydrogenation activity in the PM group.
|Numero di pagine||7|
|Rivista||THE JOURNAL OF DAIRY RESEARCH|
|Stato di pubblicazione||Published - 2008|
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