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J Dairy Res. 2008 Feb;75(1):48-54. doi: 10.1017/S0022029907003019. Epub 2008 Jan 29.

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

Author information

1
Dipartimento di Scienze Agronomiche, Agrochimiche e delle Produzioni Animali, DACPA, University of Catania, Via Valdisavoia 5, 95123, Italy. mavondo@unict.it

Abstract

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 ( degrees SH) increased in the PM group (respectively 3.56 v. 3.42%; P=0.01; 3.55 v. 3.22 degrees 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.

PMID:
18226306
DOI:
10.1017/S0022029907003019
[Indexed for MEDLINE]

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