Hassen, Abebe

Rouse, G. H.

Wilson, D. E.

English

Rouse, G.

Wilson, D.

Digital Repository @ Iowa State University (ISU)

2001 Beef Research Report — Iowa State University100Body Composition Changes of Angus Females fromInitial Breeding through Second Parturition andWeaning Determined by Real-time UltrasoundA.S. Leaflet R1757G. H. Rouse, professor,D. E. Wilson, professor,and Abebe Hassen, assistant scientistIntroductionA new Iowa State University beef cattle breedingproject was initiated in 1996 and is being conducted at theRhodes and McNay Research and Demonstration Farms.The project will use the field data of the American AngusAssociation (AAA) along with the research resource cattleat the farms to study questions that will enhance geneticrelationships between reproduction, production and carcasstraits.Initially Angus heifer calves were purchased fromseedstock ranches in South Dakota and Nebraska.  Theseheifers were developed and became part of the foundationherd of Quality and Retail Product lines.  The objective ofthis study was to scan the heifers with real-time ultrasoundas they developed from breeding time through secondparturition and weaning to evaluate body compositionchanges.Materials and Methods• 255 spring-born Angus females were developed frominitial breeding time through second parturition.  Real-time ultrasound scans and weights were collectedserially 5 times on the females:Scan times1. Before initial breeding (13-14 months of age)2. Before first calving (2 years of age)3. Weaning 1st calf4. Before 2nd calving (3 years of age)5. Weaning 2nd calf• Ultrasound images were collected with a 500VALOKA real-time ultrasound machine and an attached3.5 MHZ, 17 cm linear array transducer.  The imageswere stored digitally on a black box and interpreted at alater date in the Centralized Ultrasound ProcessingLaboratory• Ultrasound measurements collected at the 12th - 13thrib included subcutaneous fat cover thickness, ribeyemuscle area, and percent intramuscular fat.  Table 1compares percent intramuscular fat and marbling scoresto put values into perspective relative to quality grade.Table 1.  Intramuscular fat, quality grade, degree of marbling and marbling score relationships.Percentintramuscular fat Quality grade Marbling degree Marbling score2.3 - 3.0 Select - Slight 0 - 40 4.0 - 4.43.1 - 3.9 Select + Slight 50 - 90 4.5 - 4.94.0 - 5.7 Choice - Small 0 - 90 5.0 - 5.95.8 - 7.6 Choice ° Modest 0 - 90 6.0 - 6.97.7 - 9.7 Choice + Moderate 0 - 90 7.0 - 7.99.9 - 12.1 Prime - Slightly Ab 0 - 90 8.0 - 8.912.3 - Prime ° Moderately Ab 0 - 9.0 -2001 Beef Research Report — Iowa State University101Results and Discussion• Least squares means and standard errors for liveweight, and live animal ultrasound measures includingfat cover, percent intramuscular fat and ribeye area foreach of the five serial scans are shown in Table 2.• Figures 1-6 indicate the growth and body compositionchanges during the five serial scans.• Heifers weighed 907 pounds initially at breeding time.Live weight (Figure 1) increased 102 lbs. from breedinguntil first calving.  First calf heifers lost 84 lbs. during a183 day lactation in a drier than normal season. Thesefemales then continued to gain weight linearly untiltheir second calf was weaned when the cows were1,331 days of age and weighed 1,263 lbs.Table 2.  Live weight and ultrasound measurements determined serially on the heifers.Fat Cover, in. % Intramuscular fat Weight, lbs. Wt. Ribeye area, in2Measurement taken:Before Breeding 0.08 ± .08a,b 4.95 ± .91a,b 907 ± 68a,c 6.69 ± 1.03aBefore 1st Calving 0.16 ± .03a,b 5.13 ± .34a,b      1009 ± 20b 8.02 ± .38bWeaning 1st Calf 0.14 ± .01a 4.53 ± .11a,b 925 ± 24a 9.20 ± .13cBefore 2nd Calving 0.24 ± .03b 4.11 ± .35a       1103 ± 48b,c 9.91 ± .40dWeaning 2nd Calf 0.29 ± .07b 5.11 ± .81b       1263 ± 100d      11.95 ± .92cLeast squares means within a column with a different superscript are statistically significant (P<.05).• Ultrasound subcutaneous fat measurements (Figure 2)increased from .08 to .29 from Scan 1 to Scan 5 in apattern very similar to live weight.• Percent intramuscular fat (Figure 3) changed onepercent during the scanning period; however, thepattern of fat deposition was unique when comparedwith subcutaneous fat.  Values continued to declineuntil females had their second calf.• The intramuscular fat deposition pattern was examinedin more detail in Figures 4 & 5.  Figure 4 reflects 72 ofthe heifers that demonstrate a pattern similar to themeans for all heifers except shifts in percentintramuscular fat are more pronounced, more than twopercent.  Figure 5 reflects 41 females that have a similarfat deposition pattern; however, the shifts in percentintramuscular fat are very small - less than one percent.• Figure  6 relates linear growth of ribeye area, growthduring the 905 day scanning period, suggesting thatweight loss or energy repartitioning was never severeenough to restrict muscle growth.• To help understand the relationship betweensubcutaneous fat and percent intramuscular fatdeposition, heifers were divided into three framecategories based on adjusted yearling hip height (lessthan 5, 5-6 and greater than 6).• Figure 7 relates the weights of the three framecategories.  At first scan, the tallest heifers were 130lbs. heavier than the shortest heifers and 92 lbs. heavierat the last scan when the second calf was weaned.• Smaller framed heifers had less subcutaneous fatinitially (however, differences were not-significant),and significantly (P<.01) more fat cover when theheifers calved the second time at three years of age (seeFigure 8).• Figure 9 indicates the small framed heifers had less(P<.05) intramuscular fat than large framed heifersinitially, and this percent intramuscular fat differencestill existed (P<.10) when the second calf was weaned.Implications• Real-time ultrasound can be used as a tool to evaluatebody composition changes of live beef cattle as theygrow and develop.• The fat deposition pattern for subcutaneous and percentintramuscular fat were not the same.  It took longer forpercent intramuscular fat levels to recover from thestresses of first calving and lactation than it did forsubcutaneous fat.• A large percentage of the heifers demonstrated a verysimilar percent intramuscular fat deposition pattern;2001 Beef Research Report — Iowa State University102however, the rate of change during the five serial scansvaried markedly.• Ribeye area growth during the scanning period suggeststhat weight loss or energy repartitioning was neversevere enough to restrict muscle growth.SummaryGrowth and body composition changes on 255 spring-born Augus heifers was measured five times with real-time ultrasound from initial breeding through secondparturition and weaning.  Heifers weighed 907 poundsinitially, lost 84 pounds during their first calving andlactation, then continued to gain weight and weighed1,263 pounds when their second calf was weaned.Ribeye area and measure of growth continued to grow ina linear pattern during the total time frame suggestingthat weight loss or energy repartitioning was neversevere enough to restrict muscle growth.  The fatdeposition pattern for subcutaneous and intramuscularfat were not the same.  Fat cover followed a pattern verysimilar to changes in weight, although it took longer forintramuscular fat levels to recover from the stresses offirst calving and lactation.60070080090010001100120013001 2 3 4 5scan timewt, lbswtFigure 1.  Heifer weights.00.050.10.150.20.250.30.351 2 3 4 5scan timeftk, inFTKFigure 2.  Subcutaneous fat measurements.01.534.561 2 3 4 5scan t imepfat,%pfatFigure 3.  % intramuscular fat measurements.2.533.544.555.566.571 2 3 4 5scan timepfat,%Figure 4.  % intramuscular fat measurements of72 heifers.2001 Beef Research Report — Iowa State University1032.533.544.555.561 2 3 4 5scan timepfat, %Figure 5.  % intramuscular fat measurements of 41heifers.456789101112131 2 3 4 5scan timerea, sq. inreaFigure 6.  Ribeye area measurements.6008001000120014001 2 3 4 5scan timeWT, lbs< than Frame 5Frame 5-6> than Frame 6Figure 7.  Heifer weights for three frame sizes of heifers.00.050.10.150.20.250.30.351 2 3 4 5scan timeftk. in.< than Frame 5Frame 5-6> Frame 633 . 544 . 555 . 561 2 3 4 5s c a n  t i m epfat %<  t h a n  F r a m e  5F r a m e  5 - 6>  t h a n  F r a m e  6Figure 8.  Subcutaneous fat measurements for threeframe sizes of heifers.Figure 9.  % Intramuscular fat measurements for threeframe sizes of heifers.

Body Composition Changes of Angus Females from Initial Breeding through Second Parturition and Weaning Determined by Real-time Ultrasound

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Body Composition Changes of Angus Females from Initial Breeding through Second Parturition and Weaning Determined by Real-time Ultrasound

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