الفهرس | Only 14 pages are availabe for public view |
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. |