Goat intake, diet selection and milk quality as affected by grazing time of day

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.