Effect of forage type and season on Norwegian dairy goat milk production and quality

Goat milk quality produced by goats grazing on rangeland may have inferior quality with low content of solids and high content of free fatty acids (FFA). The main objective of this experiment was to test the effect of grazing woodland or cultivated pasture on dairy goat milk production and quality in early (EGS) and late (LGS) grazing seasons. Two different hay qualities (high and low quality) were used as control feeds. Eighty Norwegian dairy goats were grouped according to genotype and lactation number and randomly divided into two groups with approximately 8 weeks difference in kidding date. The EGS and LGS feeding experiments had 8 weeks departure in time, when the goats in the two kidding groups were in the same stage of lactation, on average 132 (SD 11.5) days in milk. The goats in each group were randomly allocated to four forage treatment groups: WR, woodland rangeland; PC, cultivated pasture; HH, high quality hay; HL, low quality hay. Goats on WR yielded less milk (1.58 vs. 2.15kg/d, P<0.001) but with higher milk fat (47.7 vs. 37.6g/kg, P<0.01) and total solids content (122 vs. 114g/kg, P<0.05) than goats on PC. Milk FFA content was not affected (P>0.1) by pasture type. The effects of pasture type on milk yield and milk gross composition were similar in EGS and LGS, but milk yield (2.44 vs. 1.36kg/d, P<0.001) and milk content of FFA (0.35 vs. 0.23mEq/L, P<0.05) were higher in EGS than LGS. Grazing resulted in similar milk yield but higher milk fat (42.6 vs. 34.8g/kg, P<0.001), protein (32.3 vs. 29.6g/kg, P<0.001) and total solids (118 vs. 107g/kg, P<0.001) content and tended to yield lower content of FFA (0.23 vs. 0.34mEq/L, P=0.068) than hay diet. The milk from the goats on WR had lower (P<0.05) proportion of medium-chain fatty acids (FA), C10:0–C14:0 and C18:2c9t11, but higher (P<0.05) proportion of C18:0, C18:2c9,12 and C20:0 than on PC. Grazing compared to hay feeding resulted in milk with lower proportion of medium-chained FAs (C12:0–C14:0) and C16:0 and higher proportion of the long-chained FAs C18:0, C18:1t11, C18:2c9,t11, C18:3c9,12,15, C20:0 than hay feeding. The milk proportion of the short- and medium-chained FAs (C6:0–C14:0) and C16:0 was higher (P<0.0001) in LGS than in EGS, whilst the proportion of long chained FAs (C18:0, C18:1c9, C18:1t11, C18:2c9,12, C18:2c9t11 and C18:3c9,12,15) were lower (P<0.001). In conclusion, woodland rangeland yielded less milk than cultivated pasture but milk gross composition and content of FFA were not altered.