Author/Authors :
A.L. Goetsch?، نويسنده , , S.S. Zeng?، نويسنده , , T.A. Gipson، نويسنده ,
Abstract :
Differences between production systems based on grazing and browsing vs. use of harvested
feedstuffs in confinement largely depend on specific feedstuffs and plants available
and being consumed. Low forage nutrient ingestion should have relatively greater impact
on tissue mobilization than milk production in early than later periods of lactation, with a
transition to proportionally greater change in milk production in late lactation. However,
low body condition at kidding would limit tissue energy mobilization and restrict impact
of level of nutrient intake to milk yield and, likewise, tissue mobilization would be less
with one vs. two or three milkings per day. As lactation advances after freshening, fat and
protein levels decrease with increasing milk yield, and when production declines in mid- to
late lactation, fat and protein concentrations increase. Milk production generally peaks at a
parity of 3 or 4, thereafter declining slowly. Elevated somatic cell count alone in dairy goats
is not a valid indication of mammary infection. Extended lactations offer opportunities to
minimize or avoid seasonal fluctuations in milk production and lessen production costs. If
differences in performance between suckled and machine-milked dairy goats occur, they
may be restricted to or of greater magnitude during the suckling period compared with
post-weaning, and differences in milk yield will either be absent or less with one kid compared
with greater litter sizes. The magnitude of effects of milking frequency on milk yield
is less for goats of low vs. high production potential and with low vs. high diet quality.
Likewise, the effect of milking frequency is greater in early and mid-lactation when yield
is higher than in late lactation, along with a shorter period of peak production with one
vs. two daily milkings. Physical form of the diet can affect production and composition of
goat milk, although effects appear of smaller magnitude than in dairy cattle. When tissue
is mobilized to support milk production in early lactation, levels of C18:0 and C18:1 cis in
milk increase and levels of medium-chain fatty acids decline. Effects of elevated levels of
dietary fatty acids on specific long-chain fatty acids in milk and milk products vary with
the fatty acid profile of fat sources used.