الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
 |  | from | 132 |  |  |
| | | from | 132 | | |
Abstract
Milk production is an energy expensive biological process. High levels of
dietary concentrates often are used to support milk production, although Kesler
and Spahr (1964) and Moore et al. (1986) concluded that an excessive
proportion of concentrate in the diet may depress milk fat percentage, reduce
fiber digestibility, cause rumen acidosis, and reduce milk yield. Therefore
feeding supplemental fat to lactating dairy cows has been of interest for many
years because fat is energy dense nutrient and used as a supplement for lactating
cows (Sundstol, 1974).
Added dietary fat is advocated in early lactation. The influence of fat
supplementation on milk production and composition was studied by several
authors (Grummer and Carroll, 1991; Thatcher and Staples, 2000). In this
respect, Palmquist and Jenkins (1980) stated that 3 to 5% total fat in the ration
may enhance milk production and be fed with no negative effects. Fats that are
insoluble or unavailable in the rumen may allow greater fat inclusion in the diet.
Dietary nutrients and nutrients from body tissues are directed to milk
production. During the same time, the uterus, ovary, and hypothalamus/pituitary
glands of the cow undergo a process of recovery and rebuilding for the
establishment of subsequent pregnancy. Unique dietary formulations targeted for the benefit of reproductive performance represents a challenging new area of
postpartum research (Thatcher and Staples, 2000).
Increased genetic selection has resulted in increased milk production in
dairy cows world-wide. At the same time reproductive performance has declined
(Macmillan et al., 1996; Mee et al., 1999; Royal et al., 2000).
The effect of dietary lipid on the reproductive performance of lactating
cows has received much less attention. Little information is available currently
comparing the response of Holstein and Jersey cows to supplemental fat.
The objective of this study was to determine the effect of dietary protected
fat (Magnapac) on milk production and reproductive performance of lactating
Holstein cows during early post-partum period.