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2013
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Forfattere
Håvard Steinshamn Ragnhild Aabøe Inglingstad Andrea Criscione Bernardo Valenti Marit JørgensenSammendrag
The objective of the present study was to examine the effect of grazing on different pasture types and hay feeding on dairy goat’s milk casein composition in early and late grazing season. Eighty goats were grouped according to genotype at the αS1-casein locus and number of lactations and randomly divided into two groups (Early and Late) with approximately 8 weeks difference in kidding dates. Goats within each of the two groups were further allocated to four forage treatment groups accounting for genotype and lactation number: R, forest rangeland pasture; C, cultivated pasture; HH, high quality hay; HL, low quality hay. The goats in Early were subjected to forage treatments in early grazing season, while the goats in Late received the forage treatments 8 weeks later. There was a strong effect of genotype but no genotype by diet interaction on casein content and composition. Goats grazing R yielded less milk (1.6 vs. 2.2 kg/d, P<0.001) with higher milk fat content (48 vs. 38 g/kg, P<0.001) than goats on C. Pasture type had no effect on total protein or casein content. However, milk from goats on R compared to C had lower content of αs1-casein (2.57 vs. 3.82 g/L, P<0.01) and κ-casein (4.51 vs. 5.22 g/L, P<0.05) but higher content of β-casein (13.1 vs. 11.7 g/L, P<0.001). Grazing compared to hay gave similar milk yield with higher content of total casein (24.2 vs. 21.0 g/kg, P<0.001), αs2-casein (3.48 vs. 3.04 g/L, P<0.001) and β-casein (12.4 vs. 11.7 g/L, P<0.01). Grazing compared to hay feeding improved the milk casein composition important for cheese making, while cultivated pasture were superior to rangeland.
Sammendrag
Traditionally, Norwegian dairy goats graze on diverse forest or alpine rangeland during summer, and these pastures are important both as a feed source, and for keeping the traditional image of goat milk being produced on local “natural” resources. Simultaneously, the grazing goats keep the landscape open. The quality of goat milk often declines during summer, with increased problems with free fatty acids (FFA) in the milk. This seems to coincide with the latter part of the grazing season, when goats generally also are in a later lactation stage, which also can cause problems with FFA. To elucidate the effects of pasture quality on milk production and quality we conducted an experiment where we grouped eighty goats according to genotype and lactation. They were randomly divided into two groups with approximately 8 weeks difference in kidding date and start of feeding experiment in Early (beginning of July) and Late (end of August) grazing season on improved cultivated pasture (PC) or rangeland (PR). Grazing was compared with hay of high (HH) or low (HL) quality. We used n-alkanes and long chained alcohols found in plant waxes as markers to estimate diet composition, and dosed the animals with the even-chained alkane C32 to estimate intake. Grazed plants were analysed also for feed quality. The forage intake was generally high, on average 1.2, 1.9, 2.1 and 1.6 kg DM day-1 per goat for PC, PR, HH and HL, respectively. The intake in the cultivated pasture the diet was predominantly timothy (Phleum pratense) in early season, while meadow fescue (Festuca pratensis) and couch grass (Elytrigia repens) dominated in 2nd period. In the rangeland, the diet was diverse and consisted of ferns, sedges, blueberry (Vaccinium myrtillis) and birch (Betula pubescens) in early summer. In late summer the diet was particularly diverse, coinciding with a general decline in plant quality. R yielded less milk (1.6 vs. 2.2 kg d-1) and lower milk protein content (32 vs. 33 g kg-1), but higher milk fat (48 vs. 38 g kg-1) and DM content (122 vs. 114 g kg-1) than C. Milk content of free fatty acids (FFA) was not affected by pasture type. The effect of pasture type on milk yield and milk constituents were similar in early and late grazing season. Grazing resulted in similar milk yield but higher milk fat (43 vs. 35 g kg-1), protein (32 vs. 30 g kg-1) and DM (118 vs. 107 g kg-1) content and lower content of FFA (0.25 vs. 0.31 mEq L-1) than hay feeding.
Forfattere
Margarita Novoa-Garrido Lise Aanensen Vibeke Lind Hans Jørgen S. Larsen Søren Krogh Jensen Håvard SteinshamnSammendrag
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