Saturation Ratio of Supplemental Dietary Lipid on Production Performance of Holstein Cows

ABSTRACT

Two experiments were conducted to evaluate the effect of supplemental lipid varying in proportion of unsaturated and saturated fatty acids on lactation performance and milk composition. All diets (45% chopped alfalfa hay and 55% concentrates) contained 12% whole cottonseed (as-fed) and were fed as a TMR. Treatments were no supplemental lipid (control, 3% total fatty acids, DM basis) or the addition of 2% supplemental lipid from tallow, yellow grease, or a blend (60% tallow:40% yellow grease). In Exp. 1, 48 cows were assigned to their treatment diets beginning wk 4 and ending wk 18 of lactation. In Exp. 2, 4 cows that completed Exp. 1 were enrolled in a 4 × 4 Latin square with 2-wk periods to further study the effects of saturation ratio of the supplemental lipids on milk composition. In Exp. 1, no treatment effects were observed for DMI, milk production, or milk composition; however, 4% fat-corrected milk tended to increase and fat yield increased for lipid-supplemented treatments. In Exp. 2, DMI, milk production, and percent and yield of milk fat increased in lipid-supplemented treatments. Digestible energy intakes tended to increase when yellow grease was the lipid source compared with tallow. In both experiments, milk fatty acid composition was affected by supplemental lipid as well as the source of supplemental lipid. No effects on lactation performance were evident due to the differences in the unsaturated to saturated fatty acid composition of the supplemental lipid source.

Key words: dairy cow, fatty acid, milk production

INTRODUCTION

Lipids are commonly fed to dairy cows to support higher levels of milk production in early and midlactation and to replenish adipose stores in mid- to late-lactation without substantially reducing the amount of forage in the diet (Pantoja et al., 1994). Tallow and yellow grease are rendered lipids commonly fed to dairy cows. Rendered lipids are relatively inexpensive on an energy basis; therefore, maximizing their use as an energy source is of interest when balancing diets for dairy cows (Onetti et al., 2001).

It was suggested that oilseeds or rumen-available lipids be fed at a level to provide 3% of dietary DM as fatty acids (FA; Coppock and Wilks, 1991). In California, whole cottonseed (WCS) is typically fed to lactating cows because it is a good source of protein, fiber, and lipid. Rendered lipids often complement oilseeds as the main source of lipid in the diet. Production performance of cows in early lactation fed WCS with either tallow or yellow grease as the supplemental lipid had not been previously studied.

Despite the benefits, dietary lipid can reduce DMI and have detrimental effects on rumen fermentation an effect that was attributed to the amount of unsaturated FA and the degree of unesterified FA contained in the lipid (Jenkins and Jenny, 1989; Eastridge and Firkins, 1991). However, Avila et al. (2000) demonstrated that rumen fiber digestion and microbial growth were similar for diets containing either 2% tallow or 2% yellow grease as supplemental lipid. In addition, yellow grease was fed in numerous studies from our lab with no detrimental effect on animal performance (DePeters et al., 1987, 1989; Cant et al., 1991; Joy et al., 1997). In these studies the level of lipid supplementation did not exceed 4% and diets were adequate in fiber concentration to promote rumen function.

The objective was to determine the effects of saturation ratio of supplemental dietary lipid on feed intake, milk yield, content and yield of milk components, BW, and BCS of early lactation Holstein dairy cows.

MATERIALS AND METHODS

Experimental Design, Cows, and Diets

Experiment 1: Lactation Study. Forty-seven multiparous lactating Holstein cows were assigned to 1 of 4 treatments differing in supplemental lipid source, beginning the fourth week of lactation following parturition. Consideration was given to date of calving and previous 305-d milk yield equivalent when assigning each cow to a treatment. All cows were fed the control diet during wk 2 and 3 of lactation. At the beginning of wk 4 of lactation, cows were assigned to their respective treatment diets until the end of wk 18 of lactation. The study was conducted from October 1994 to April 1996.

All diets (45% chopped alfalfa hay and 55% concentrates) contained 12% whole linted cottonseed (as-fed basis) and were fed as a TMR. Treatments were no supplemental lipid (control, 3% total FA, DM basis) or the addition of 2% supplemental lipid from only tallow only, yellow grease, or a blend of 60% tallow and 40% yellow grease. The FA composition of the lipid supplements was described previously (Avila et al., 2000). Unsaturated to saturated FA ratios (U:S) for the lipid sources were 1:1 for tallow, 2.5:1 for yellow grease, and 1.5:1 for the blended lipid. The supplemented lipid replaced a portion of the corn and barley; diets were not isoenergetic.

Cows were housed in outdoor corrals with covered free stalls and a concrete exercise area. Animal care was reviewed and approved by the Animal Care and Use Administrative Committee of the University of California, Davis. Cows had free access to water and were fed twice daily after each milking using individual feeding gates to measure feed intakes (American Calan Inc., Northwood, NH). Quantity of feed offered and orts were recorded at each feeding and subsequently adjusted for appetite to allow for approximately 5% refusal (as fed basis).