use of ultrasound to determine body composition of ...

Proceedings, Western Section, American Society of Animal Science Vol. 55, 2004 USE OF ULTRASOUND TO DETERMINE BODY COMPOSITION OF BEEF COWS NUTRIENT RESTRICTED DURING EARLY TO MID-GESTATION L.R. Miller, S.I. Paisley, J.D.C. Molle, E.J. Scholljegerdes, S.L. Lake, R.L. Atkinson, V. Nayigihugu, W.T. Small, S.P. Ford, W.J. Means, K.R. Underwood, S.A. Thompson, and B.W. Hess Department of Animal Science, University of Wyoming ABSTRACT: One hundred-sixteen multiparous Angus × Gelbvieh cows (initial BW = 571 ± 63 kg, BCS = 5.4 ± 0.7) were blocked by BW, assigned to one of 18 pens, and received one of two dietary treatments from d-31 to 125 of gestation (Exp. 1). Control (C) cows were fed native grass hay fortified with vitamins and minerals at recommendations for a mature cow to gain 0.72 kg/d for the first 120 d of gestation. Nutrient restricted (NR) cows were fed one half C minerals and vitamins, and millet straw at 68.1% of NEm requirements. Along with BW and BCS, ultrasound measurements of ribeye area (REA), 12th rib fat thickness at the 12th rib (BF), and percent i.m. fat of the LM (IMF) were collected every 14 d. In Exp. 2, 96 cows from Exp. 1 were re-blocked according to BW and BCS and assigned to one of 16 pens. Control cows continued to be fed as in Exp. 1, while NR cows were realimented with the target of achieving BCS similar to C cows by 60-d prepartum. Body weight and BCS were measured every 14 d, whereas REA, BF, and IMF were measured every 28 d. A subset of cows from Exp. 1 (n = 20) and Exp. 2 (n = 10) were harvested to determine correlations between ultrasound and carcass measurements of REA (r = 0.49, P = 0.006), BF (r = 0.85, P < 0.001), and IMF (r = 0.69, P < 0.001). In Exp. 1, treatment × day of sampling interactions were noted (P ≤ 0.001) for all variables. Body weight, BCS, BF, IMF, and REA were reduced (P < 0.05) by d-59, 45, 59, 73, and 73 of gestation, respectively. In Exp. 2, BW and BF remained less (P < 0.002) for NR than C cows throughout the realimentation period. Cow BCS and REA were lower (P ≤ 0.03) for NR versus C cows until d-164 of gestation, but were similar (P = 0.11 and P = 0.58, respectively) by d-192 of gestation. Ultrasound may be a useful technology to predict changes in body composition associated with a beef cow’s nutritional plane. Key words: Nutrient Restriction, Ultrasound, Beef Cow INTRODUCTION Beef cows grazing rangelands in the western United States may consume low-quality forage during early to midgestation (DelCurto et al., 2000), and thus may experience periods of undernutrition (NRC, 1996). Maternal nutrient deficiencies during critical times of pregnancy can permanently affect development of fetal tissues (Barker, 1995). Furthermore, calf birth weight has been reduced when their dams were fed on a low plane of nutrition from midgestation through early lactation (Freetly et al., 2000). Beef cow producers may curtail the possibility of cows experiencing nutrient deficits by implementing feed supplementation practices. The BCS system (Wagner et al.,

1988) has been adopted by the beef industry as a method to assess a cow’s plane of nutrition by subjectively evaluating her body energy reserves. On a one-to-nine scale, differences from BCS 1 to 4 are primarily the result of variation in energy stored as muscle protein whereas changes from BCS 5 to 9 are mostly related to external body fat (Mathis et al., 2002). Due to the subjectivity of the BCS systems, however, ultrasound measurements may also be used in commercial cow operations to aid in the assessment of cow energy reserves. Ultrasound measurements can provide estimates of some body energy reserves in a fast, inexpensive, and repeatable fashion. Ultrasound technology has been successfully employed to as a management tool in the feedlot (Houghton and Turlington, 1992; Smith et al., 1992; Greiner et al., 2003) and replacement female sectors (Tait, Jr. et al., 2004) of the beef industry. Although Bullock et al. (1991) demonstrated that ultrasound measurements can be used to predict cow body energy reserves, this technology has yet to be fully exploited to evaluate changes in body energy reserves in mature beef cows maintained on various planes of nutrition. The first objective of this study was to determine the correlation between ultrasound and carcass measurements of beef cows. The second objective was to evaluate BW, BCS, and ultrasound measurements of ribeye area, 12th rib fat thickness, and percent i.m. fat in pregnant beef cows fed various planes of nutrition. MATERIALS AND METHODS All procedures were conducted in accordance with an approved University of Wyoming Animal Care and Use Committee. In Exp. 1, on d 31 of gestation, 116 multiparous, Angus × Gelbvieh cows (initial BW, 571 ± 63 kg; initial BCS, 5.4 ± 0.7) were stratified by weight, assigned to one of nine blocks, and allotted to one of two pens within each block (5 to 7 cows/pen). Control cows were fed native grass hay (12.1% CP, 70.7% TDN on a DM basis) fortified with vitamins and minerals at NRC (1996) recommendations for a mature cow to gain 0.72 kg/d during the first 125 d of gestation. Nutrient Restricted cows were fed one half the Control minerals and vitamins, and millet straw (9.9% CP, 54.5% IVDMD) to provide 68.1% NEm and 86.7% of metabolizable protein requirements during the first 120 d of gestation (NRC, 1996). Feed intake was adjusted every 14 d based on average pen weight. Body weight was measured and BCS measurements were calculated as the average of three trained individual’s estimates on d 31, 45, 59, 73, 87, 101, and 115 of gestation. Ribeye area, 12th rib fat, and percentage i.m. fat were measured on d 31, 45, 59, 73, 87, 101, and 115 of gestation

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via ultrasound using the "New" Aloka SSD-500 with 17.2-cm transducer (Aloka Co., Ltd, Wallingford, CT). Images were collected on Beef Image Analysis (BIA) software (Designer Genes Technologies, L.L.C.). In Exp. 2, 96 cows from Exp. 1 were re-blocked according to BW and BCS. Cows were assigned to one of 16 pens (5 to 7 cows/pen). Control cows were fed the same diet as in Exp 1. Nutrient restricted cows were fed the Nutrient Restricted hay, Control minerals and vitamins, and a cornbased supplement (Table 1) to achieve a BCS equal to the Control cows by d 220 of gestation. Body weight and BCS were measured on d 136, 150, 164, 178, and 192 of gestation. Ribeye area, 12th rib fat thickness, and percentage i.m. fat were measured on d 136, 164, and 192 of gestation via ultrasound as in Exp. 1. A subset of cows from Exp. 1 (n = 20) and Exp. 2 (n = 10) were slaughtered at the end of each experiment. Cows were withheld from feed over night, slaughtered using normal industry procedures, and chilled at 2 to 4˚C for 48 h. Fortyeight hours postmortem, the left side of each carcass was ribbed between the 12th and 13th ribs and 12th rib fat and ribeye area measurements (Boggs et al., 1998), and marbling scores (USDA, 1989) were recorded. These values were used to determine correlations between live animal ultrasound estimates and actual measurements of ribeye area, 12th rib fat, and percentage i.m. fat. All data were analyzed using the GLM procedures of SAS (SAS Inst. Cary, NC) using a model for a split-block design. Dietary treatment was the main plot tested against the treatment × block interaction (error a), with the period and treatment × period interaction as the subplot tested against residual error (error b). RESULTS AND DISCUSSION Ultrasound and carcass measurements were moderately to highly correlated and significant. Carcass measurements versus ultrasound-predicted ribeye area, 12th rib fat thickness, and percent i.m. fat were all positively correlated with r-values of 0.49, 0.85, and 0.69, respectively. In their review of the literature, Houghton and Turlington (1992) found that correlation coefficients for actual vs. ultrasound-predicted ranged from 0.20 to 0.94 for ribeye area, 0.55 to 0.96 for 12th rib fat thickness, and 0.21 to 0.91 for percentage i.m. fat. Smith et al. (1992) attributed their moderately low correlation coefficient for ribeye area (r = 0.43) to improper placement of the transducer, poor image resolution, or inaccurate interpretation of the image. The potential for error caused by improper placement of the transducer cannot be eliminated, but we suspect that poor images resulting from insufficient surface contact in the cows with lower BCS may explain our moderate correlation coefficient for ribeye area. Bullock et al. (1991) reported a high correlation coefficient (r = 0.79) for 12th rib fat thickness for cows ranging in mean BCS from 2.9 to 7.1. The slightly higher correlation coefficient (r = 0.85) noted herein could be attributed to more uniform BCS for the cows on this study (BCS ranged from 4.1 to 6.7). Harada et al. (1985; as cited by Houghton and Turlington, 1992) reported correlation coefficients of 0.78 and 0.24 for percentage i.m. fat in serial scans of Japanese black bulls. These researchers attributed the

inability to consistently measure percentage i.m. fat on the premise that i.m. fat is a very mobile energy reserve that is highly affected by environment. Our findings, combined with previous research would imply that the use of ultrasound is an acceptable method of tracking changes in cow 12th rib fat, percentage i.m. fat, and ribeye area. However, there are limitations to the use of correlation coefficients in the reporting of ultrasound accuracy (Houghton and Turlington, 1992). Two limitations that potentially explain the observed results would be that populations with larger than normal variations will produce high correlations, and correlation coefficients do not necessarily reflect the bias associated with consistently over or underestimating measurements (Houghton and Turlington, 1992; Greiner et al., 2003). Houghton and Turlington (1992) also suggest that there is potential that position of the hanging carcass influences measurements, therefore influencing the perceived accuracy of ultrasound. Exp. 1 Treatment × period interactions were noted (P ≤ 0.001) for all variables. By design, BW of Nutrient Restricted cows was less than that of Control cows by d 59 of gestation, and remained lower (P < 0.001) for the duration of the restriction period (Table 2). Body condition score was also reduced (P < 0.001) by d 45 of gestation and remained lower (P < 0.001) for the duration of the restriction period (Table 2). Freetly et al. (2000) noted similar reductions in cow BW and BCS with nutrient restriction during mid to late gestation. Lalman et al. (1997) and Buskirk et al. (1992) noted that each unit change in BCS corresponded with a 33 kg and 40 kg change in BW, respectively. Additionally, the NRC (1996) suggests that more weight is associated with a change in BCS for cows with a BCS > 5. In the current study, Control cows would have changed 122 kg in BW for each unit change in BCS, whereas Nutrient Restricted cows would have changed 108 kg for each corresponding unit change in BCS. Some of the discrepancy between BW and associated BCS change in our study could be attributed to the increased weight gain associated with pregnancy. In a companion abstract, Vonnahme et al. (2004) reported that Control cows had heavier fetuses than Nutrient Restricted cows. Estimated weights increases associated with the gravid uterus (Ferrell et al., 1976; Prior and Laster, 1979) ranged from 3.66 to 8.22 kg for this same period. A large proportion of the weight change for the Nutrient Restricted cows can be attributed to the loss in internal organ mass. In a companion paper, Molle et al. (2004) reported that Nutrient Restricted cows had reduced weights of the rumen, omasum, heart, pancreas, liver, and kidney. Therefore, apparent associations between changes in BW and BCS in our study may not have been similar to previous reports because of the confounding influence of the gravid uterus and (or) the mass of visceral tissue. Twelfth-rib fat, percentage i.m. fat, and ribeye area were reduced (P ≤ 0.05) for Nutrient Restricted cows by d 59, 73, and 73 of gestation, respectively (Table 2), and tended to be different (P ≤ 0.10) on d 45 and 59 for 12th rib fat and percentage i.m. fat, respectively. Reduced fat cover over the 12th rib occurring sooner than reduced i.m. fat or ribeye area

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indicates that s.c. fat reserves were more readily mobilized than intramuscular adipose tissue or muscle energy reserves. Consistent with our observations, Bullock et al. (1991) reported decreased back fat thickness and reduced ribeye area as cow BCS decreased from 7.1 to 2.9. Our findings also support the suggestion that i.m. fat is a mobile energy reserve (Harada et al., 1985 as cited by Houghton and Turlington, 1992). Exp. 2 In our second experiement, previously restricted cows were fed to achieve a BW similar to Controls by d 220 of gestation. Cow BCS was lower (P ≤ 0.001) for Nutrient Restricted versus Control cows through d 178, but only tended to be lower (P = 0.09) on d 192, although BW remained less (P < 0.001) for Nutrient Restricted than Control cows throughout the realimentation period (Table 3). Therefore, Nutrient Restricted cows were on track to be similar in weight to Control cows by d 220 of gestation. Control cows gained 36.2 kg but only increased BCS by 0.06 units, whereas Nutrient Restricted cow BW increased 70.9 kg with 0.47 units in BCS. This would equate to one unit in BCS gain for every 603 kg gain in BW for Control cows and one BCS unit for every 151 kg increase in BW for Nutrient Restricted cows. Expected gain associated with the growth of the gravid uterus from d 115 to 192 of gestation was between 12.2 (Prior and Laster, 1979) and 17.0 kg (Ferrell et al., 1976). Thus, increased BW of cows was partially attributed to growth of the gravid uterus. Data from our companion paper (Molle et al., 2004) indicated that realimenting the Nutrient Restricted cows increased total digestive tract weight by 22.0%, which compared to a 10.9% increase for Control cows. These same cows exhibited an increase of 43.3% and 14.3% (Nutrient Restricted and Control, respectively) in the combined weights of the lung, heart, pancreas, liver, and kidney weight from d 125 to 250 of gestation. Increased BW without a concomitant increase in BCS was likely due to a combination of increased weight of the gravid uterus and increased internal organ mass, especially for the Control cows. Freetly et al. (2000) noted that cows nutrient restricted during gestation will regain BCS when realimented either during the last third of gestation or during the first 28 d of lactation. Over the course of the realimentation period, Nutrient Restricted cows in our study increased (P ≤ 0.001) in BCS. Although i.m. fat percentage did not change (P = 0.18) over the course of Exp. 2, Nutrient Restricted cows tended to have a lower (P = 0.11) percentage i.m. fat than Control cows. Likewise, 12th rib fat thickness for Nutrient Restricted cows remained less (P < 0.001) than Control cows throughout the realimentation period. Cow ribeye area was lower (P ≤ 0.001) for Nutrient Restricted versus Control cows until d 164 of gestation, but were similar (P = 0.58) by d 192 of gestation. Our findings support the contention of Harada et al. (1985; as cited by Houghton and Turlington, 1992), who suggested that i.m. fat percentage is a mobile energy reserve that is highly affected by environment. The ability of the realimented cows to regain ribeye area indicates increased gain of bodily protein reserves (Mathis et al., 2002; NRC, 1996). The inability of

the realimented cows to regain s.c. fat by d 192 of gestation was consistent with our observation that BCS tended to be lower in these cows. Buskirk et al. (1992) demonstrated that body lipid content increased to a greater degree than body protein as cow BCS increased. Thus, ultrasound measurement of back fat thickness at the 12th rib may be a sensitive estimate of a cow’s body energy reserve. IMPLICATIONS Ultrasound is a useful technology to predict changes in body composition associated with a beef cow’s nutritional plane. Utilizing ultrasound measurements to predict body energy reserves will aid producers in making informed decisions about cow nutritional management programs. LITERATURE CITED Barker, D. J. P. 1995. Fetal origins of coronary heart disease. Br. Med. J. 311:171-174. Boggs, D. L., R. A. Merkel, and M. E. Doumit. 1998. Livestock and Carcasses An Integrated Approach to Evaluation, Grading, and Selection. 5th ed. Kendall/Hunt Publishing Co. Dubuque, IA. Buskirk, D. D., R. P. Lemanager, and L. A. Horstman. 1992. Estimation of net energy requirements (NEm and NE∆) of lactating beef cows. J. Anim. Sci. 70:3867-3876. Bullock, K. D., J. K. Bertrand, L. L. Benyshek, S. E. Williams, and D. G. Lust. 1991. Comparison of realtime ultrasound and other live measures to carcass measures as predictors of beef cow energy stores. J. Anim. Sci. 69:3908-3916. DelCurto, T., B. W. Hess, J. E. Huston, and K. C. Olson. 2000. Optimum supplementation strategies for beef cattle consuming low-quality roughages in the western United States. Proc. Am. Soc. Anim. Sci. 1999. available at: http://www.asas.org/jas/symposia/proceedings. Ferrell, C. L., W. N. Garrett, and N. Hinman. 1976. Growth, development and composition of the udder and gravid uterus of beef heifers during pregnancy. J. Anim. Sci. 42:1477-1489. Freetly, H. C., C. L. Ferrell, and T. G. Jenkins. 2000. Timing of realimentation of mature cows that were feedrestricted during pregnancy influences calf birth weights and growth rates. J. Anim. Sci. 78:2790-2796. Greiner, S. P., G. H. Rouse, D. E. Wilson, L. V. Cundiff, and T. L. Wheeler. 2003. The relationship between ultrasound measurements and carcass fat thickness and longissimus muscle area in beef cattle. J. Anim. Sci. 81:676-682. Harada, H., K. Moriya, and R. Fukuhara. 1985. Early prediction of carcass traits of beef bulls. Jpn. J. Zootech. Sci. 56(3):250. Houghton, P. L., and L. M. Turlington. 1992. Application of ultrasound for feeding and finishing animals: A review. J. Anim. Sci. 70:930-941.

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Lalman, D. L., D. H. Keiser, J. E. Williams, E. J. Scholljegerdes, and D. M. Mallett. 1997. Influence of postpartum weight and body condition change on duration of anestrus by undernourished suckled beef heifers. J. Anim. Sci. 75:2003-2008. Mathis, C. P., J. E. Sawyer, and R. Parker. 2002. Managing and feeding beef cows using body condition scores. New Mexico State University. Cooperative Extension Service. Circular 575. Molle, J. D. C., E. J. Scholljegerdes, S. L. Lake, V. Nayigihugu, R. L. Atkinson, L. R. Miller, S. P. Ford, W. J. Means, J. S. Caton, B. W. Hess. 2004. Effects of maternal nutrient restriction during early- to midgestation on cow and fetal visceral organ measurements. Proc. West. Sect. Am. Soc. Anim. Sci. 55:(Submitted). NRC. 1996. Nutrient requirements of beef cattle, 7th rev. ed. Natl. Acad. Press, Washington, DC. Prior, R. L., and D. B. Laster. 1979. Development of the bovine fetus. J. Anim. Sci. 48:1546-1553. Smith, M. T., J. W. Oltjen, H. G. Dolezal, D. R. Gill, and B. D. Behrens. 1992. Evaluation of ultrasound for prediction of carcass fat thickness and longissimus muscle area in feedlot steers. J. Anim. Sci. 70:29-37. Tait, Jr., R. G., G. H. House, D. R. Maxwell, M. L. Spangler, and P. B. Wall. 2004. A comparison of serially scanned replacement and feedlot Angus sired heifers for body composition traits: Ribeye area, fat cover, and percent intramuscular fat. Iowa State Univ. Anim. Industry Rep. A.S. Leaflet R1871.

USDA. 1989. Official United States standards for grades of carcass beef. Agri. Marketing Service, United States Dept. of Agriculture, Washington, D.C. Vonnahme, K. A., S. P. Ford, M. J. Nijland, L. P. Reynolds. 2004. Alteration in cotyldonary (COT) vascular responsiveness to angiotensin II (ANG II) in beef cows undernourished during early gestation. Proc. Soc. Study Reprod., Vancouver, B.C., Canada, (In Press) Wagner, J. J., K. S. Lusby, J. W. Oltjen, J. Rakestraw, R. P. Wettemann, and L. E. Walters. 1988. Carcass composition in mature Hereford cows: Estimation and effect on daily metabolizable energy required during winter. J. Anim. Sci. 66:603-612. Table 1. Realimentation supplement fed to cows d 125 through d 192 of gestation Ingredient

Ration composition, %

Corn 79.6 Soybean meal 6.1 Sunflower meal 5.3 Molasses 4.2 Safflower meal 2.6 Dried skim milk 1.6 Chemical composition ------% DM-------CP 13.2 IVDMD 77.6

Table 2. Effects of nutrient restriction on body composition of multiparous beef cows during early to mid gestation (Exp. 1) Day of gestation Measurement 31 45 59 73 87 101 115 SE P