ND 1709 Objective 2

GENETIC AND ENVIRONMENTAL STRATEGIES TO IMPROVE THE EFFICIENCY

OF LEAN TISSUE ACCRETION IN LAMBS: 2001 UPDATE: LEAN LAMB

PRODUCTION

P.T.Berg1 and T.C.Faller2

1Animal and Range Sciences Department, NDSU, Fargo, ND 58105

2Hettinger Research Extension Center, Hettinger, ND 58639

The primary focus of 2001 was to continue to accumulate data on offspring of the seven sires identified through Bioelectical Impedance Analysis (BIA) in 1999. These rams were selected based on estimated lean tissue accretion per day of age and the ratio of lean per day of age to estimated fat per day of age. The procedure by which the rams were selected has been described in previous Western Dakota Sheep Day Reports. Based on BIA data, rams were assigned as "lean" or "fat" sires.

A group of Western White-faced ewes was acquired as mates for the selected rams. The flock was managed as a typical commercial ewe flock and the resulting offspring fed to acceptable slaughter weights under typical feedlot conditions. Lambs were shipped to Iowa Lamb Company at Hawarden, Iowa, for slaughter and carcass evaluation. End-point weight was a minimum of 125 pounds (at Hettinger) as Iowa Lamb does not allow "breaking" of carcasses which weigh less than 56 pounds. Because of the distance to the slaughter facility and the cost of transportation, some lambs less than the desired weight were shipped to fill out a load.

 

As of the end of this second group of offspring slaughter (October, 2001), 227 lambs have been slaughtered. Because of light weights or tags lost during transportation, full carcass data is available on 197 head. This data is summarized in Table 1.

Table 1. Carcass data of feedlot lambs slaughtered in 2000 and 2001 by treatment group.

Group

N

Age in

Days

Carc

Wt

REA

Fat

Body

Wall

Th

Lbs

Lean

Lbs

Fat

#

Lean/

Day

#

Fat/

Day

FAT

107

224

62.7

2.24

.22

.88

37.8

15.6

.169

.070

LEAN

78

222

61.7

2.16

.21

.87

37.3

15.4

.168

.069

CONTROL

12

225

65.8

2.36

.20

.79

40.3

15.1

.172

.067


Table 2 summarizes the same data set by sire.

Table 2. Carcass data averages by sire for 2000 and 2001.

Sire

N

Age in

Days

Carc

Wt

REA

Fat

Body

Wall

Th

Lbs

Lean

 

Lbs

Fat

 

#

Lean/

Day

#

Fat/

Day

FAT 1

34

240

63.3

2.20

.21

.87

38.3

15.9

.160

.066

FAT 2

35

227

63.2

2.29

.20

.84

38.4

15.4

.169

.068

FAT 3

21

202

60.0

2.24

.24

.89

35.9

14.9

.177

.073

FAT 4

17

214

64.0

2.24

.27

.97

37.4

16.4

.175

.077

LEAN 1

21

229

62.4

2.21

.23

.90

37.7

15.8

.164

.069

LEAN 2

18

202

58.9

2.20

.19

.72

36.6

13.2

.181

.065

LEAN 3

38

227

62.7

2.11

.21

.93

37.2

16.4

.164

.072

CONTROL 1

5

230

72.3

2.44

.23

.82

43.8

17.3

.190

.075

CONTROL 2

7

212

62.7

2.33

.19

.79

38.3

14.4

.181

.068


Much of the differences between the F and L sired lambs which were demonstrated in the 2000 data for fat at the 12th rib and body wall has disappeared. Among the non-control sires, LEAN 2 had the highest lean per day and lowest fat per day averages for his offspring, however, he became unsound and was culled prior to the 2000 breeding season. Most of the differences in the averages in the 2000 data was due the offspring of LEAN 2. Furthermore, in an effort to increase the number of offspring born to each of the BIA selected rams, we culled two rams from each of the FAT and LEAN lines and, further, chose not to mate any ewes to the CONTROL rams in the fall of 2000. Lambs slaughtered in 2000 were slightly younger at slaughter, had slightly lighter carcasses, slightly larger REA, and slightly less body wall thickness than did the 2001 lambs (215 days vs 236; 61.9 pounds vs 63.5 pounds; 2.27 square inches vs 2.15 square inches; .84 inches vs .92 inches for 2000 vs 2001 respectively). Because only four rams had offspring represented in both years (FAT 1 and 2 and LEAN 1 and 3), year by ram interactions may have played a role in comparisons. The tradeoff is that more accurate evaluation of the four rams should result.

Within flock EPDs calculated for lean and fat tissue accretion per day of age based on offspring data were very similar for each of the four selected rams. These EDPs, when compared to the EPDs calculated from each ram's individual BIA data taken at six months of age, are summarized in Table 3.

 

Table 3.  Within flock EPD’s for lean and fat tissue accretion per day of age compared to individual ram BIAs.

Sire

Lean/Day

Ind BIA

Fat/Day

Ind BIA

Lean/Day

Offspring

Fat/Day

Offspring

LEAN 1

+0.0066

+0.0042

-0.00069

+0.00161

LEAN 3

+0.0128

-0.0065

-0.00494

+0.00505

 

 

 

 

 

FAT 1

+0.0094

+0.0069

-0.00496

-0.00057

FAT 2

+0.0117

+0.0079

+0.00368

+0.00071


The individual BIA based wfEPDs for LEAN 3 are what we were looking for: a PLUS value for lean tissue and a NEGATIVE value for fat tissue accretion. Unfortunately, the offspring calculated EPDs were the reverse of the desired. Comparison of pounds of retail product among the four rams revealed a range of just over a pound in offspring average. Since EPDs are calculated from the population average, if there is minimal difference within the population, there can be no great difference in the EPDs.

As a further analysis of the efficacy of BIA as a predictor of lean tissue for selecting replacement sires, we did a statistical procedure known as regression, regressing the offspring's carcass calculated pounds of retail product on the sire's BIA predicted pounds of retail product. Based on this data set, the correlation between the six-month BIA predicted pounds of retail product and the calculated pounds of retail product of their offspring carcasses was essentially zero. Again, in order to have statistical significance, there must be differences demonstrated somewhere in the data. The selected rams show little differences in tissue differentiation when the BIA analysis is done at six months of age. This lack of differences within the population is apparently what is frustrating our efforts at improvement.