REVIEW: Potential Effects of Vitamins A and D on Marbling Deposition in Beef Cattle

Professional Animal Scientist, Jun 2005 by Pyatt, N A, Berger, L L

Abstract

Seasonal variation in cattle grading Choice exists with percentages of carcasses grading higher in the spring and gradually declining throughout the summer with a low in October. Various nutritional or pharmacological agents have been shown to affect adipose conversion in vitro and in vivo. High (5 to 50 µM) levels of dietary fat-soluble vitamins, especially retinoic acid (RA) and 1,25-dihydroxyvitamin D^sub 3^ (D^sub 3^), inhibit adipocyte development, specifically bovine marbling, while lesser (≤10 nM) levels actively stimulate this deposition. This review was conducted to highlight the regulatory effects of vitamins A and D on adipocyte differentiation and offer a potential explanation for seasonal fluctuation in beef quality grades. Serum retinal concentration was negatively correlated with beef marbling index. Steers consuming diets containing low vitamin A concentration exhibited less serum retinal and produced greater marbling scores compared with steers consuming high vitamin A diets. Seasonal variation in quality grade may be explained by previous intake of vitamin A from lush forages and/or vitamin D synthesis from long day sun exposure. Cattle placed in the feedlots in spring or early summer are commonly grazed on lush forages, fed during the long day-length months and marketed in the fall, coinciding with seasonal lows for quality grade. Excessive circulating levels of vitamins A and D diminished adipocyte hyperplasia, lessened marbling score, and may partially explain seasonal depressions in carcasses grading Choice. Further research is necessary to elucidate the timing and dietary level of vitamins A and D during the finishing period and their relationship to high quality beef production.

(Key Words: Vitamin A, Vitamin D, Beef Cattle, Marbling, Adipocyte Differentiation.)

Introduction

With an escalating number of cattle being marketed in value-based pricing systems (Schroeder et al., 2002), quality grade and marbling become increasingly important in obtaining carcass premiums for beef producers. Numerous factors, including regulation of lipogenesis, genetics, age, nutrition, management, and environment, affect rate of marbling deposition. Seasonal variation in percentage of cattle grading Choice is well documented (Kreikemeier et al., 1998; Anderson et al., 2001; USDA, 2004); however, little information has been volunteered to explain such patterns. Adipocytes grow by proliferation in cell number (hyperplasia) and enlargement of cell size (hypertrophy). Intramuscular adipose tissue has greater adipocytes per gram of tissue, smaller cell diameter, and correspondingly lesser cell volume than subcutaneous depots (Smith and Grouse, 1984; Miller et al., 1991; May et al., 1994). Cianzio et al. (1985) indicated the number of adipocytes per gram of tissue is more closely correlated to marbling score than to diameter of the adipocytes. Those researchers concluded that hyperplasia is more important than hypertrophy for beef marbling expression. Therefore, it is imperative that the positive and negative regulatory systems for the proliferation and differentiation of adipocytes be well defined (Kawada et al., 1996). Various nutritional or pharmacological agents influence adipose conversion in vitro and in vivo (Kawada et al., 1996). Kawada et al. (1990) revealed that many vitamins (A, B, C, D, E, and K) affect terminal differentiation of adipocytes and the regulatory system for energy preservation and BW. Researchers have reported high (5 to 50 µM) levels of dietary fat-soluble vitamins, especially retinoic acid (RA) and 1,25-dihydroxyvitamin D^sub 3^ (D^sub 3^), inhibit the development of adipose tissue, specifically bovine marbling, while lesser (1 pM to 10 nM) levels actively stimulate this deposition (Sato et al., 1980, Sato and Hiragun, 1988; Kawada et al., 1990). These data necessitate further investigation regarding the mechanism by which stimulation and inhibition of adipocyte differentiation is occurring. Variability in circulating levels of RA and D^sub 3^ may be linked to patterns of beef quality. This review was conducted to highlight the regulatory effects of vitamins A and D on adipocyte differentiation and offer a potential explanation for seasonal fluctuation in beef quality grades.

Review and Discussion

Seasonality of Performance and Quality Grades. Environmental factors, such as temperature, relative humidity, snow, wind, rain, and mud, affect energy requirements, feed intake, animal performance, and composition of gain. Seasonal variation in cattle feeding profitability, performance factors, and market and input prices has been well documented (Muhamad et al., 1983; Jones et al., 1997; Kreikemeier and Mader, 2004). Changes in feed and cattle costs, as well as fed-cattle price dictate the length of time that cattle are fed (Van Koevering et al., 1995). Fluctuations in price spreads suggest relative variation in consumer demand and cattle (quality) supply entering the food chain. Seasonal variation in percentage of cattle grading Choice is well documented (Figure 1) (Kreikemeier et al., 1998; Anderson et al, 2001; USDA, 2004). In general, the percentages of carcasses grading low Choice or better are greater in the spring, peaking around March and April. Subsequently, a gradual decline in percentages of Choice and Prime carcasses occurs throughout the summer and early fall months, with a low in September or October. In November and December, carcass quality grades start to improve, and the cycle is repeated. Quality grade variation is considered small, nearly 8 to 10%; however, even slight changes in beef supply can have a dramatic effect on fed-cattle price and grid-market spreads. Choice-Select spread patterns reflect quality grade supply. Spreads are narrow, averaging $3 to $4/45.4 kg when abundant supplies of Choice cattle are available in the spring (Lawerence, 2003). Similarly, Choice-Select spread widens, approximately $10 to $12/45.4 kg, when beef supplies are short in the fall (Lawerence, 2003). Little research has been done to elucidate why seasonal quality grade variation exists.